Weak Radiative Hyperon Decays and Vector Meson Dominance

a rXiv:h ep-ph/9212266v116Dec1992SLAC–PUB–6017WIS–92/99/Dec–PH December 1992T/E The Subleading Isgur-Wise Form Factor χ3(v ·v ′)to Order αs in QCD Sum Rules Matthias Neubert Stanford Linear Accelerator Center Stanford University,Stanford,California 94309Zoltan Ligeti and Yosef Nir Weizmann Institute of Science Physics Department,Rehovot 76100,Israel We calculate the contributions arising at order αs in the QCD sum rule for the spin-symmetry violating universal function χ3(v ·v ′),which appears at order 1/m Q in the heavy quark expansion of meson form factors.In particular,we derive the two-loop perturbative contribution to the sum rule.Over the kinematic range accessible in B →D (∗)ℓνdecays,we find that χ3(v ·v ′)does not exceed the level of ∼1%,indicating that power corrections induced by the chromo-magnetic operator in the heavy quark expansion are small.(submitted to Physical Review D)I.INTRODUCTIONIn the heavy quark effective theory(HQET),the hadronic matrix elements describing the semileptonic decays M(v)→M′(v′)ℓν,where M and M′are pseudoscalar or vector mesons containing a heavy quark,can be systematically expanded in inverse powers of the heavy quark masses[1–5].The coefficients in this expansion are m Q-independent,universal functions of the kinematic variable y=v·v′.These so-called Isgur-Wise form factors characterize the properties of the cloud of light quarks and gluons surrounding the heavy quarks,which act as static color sources.At leading order,a single functionξ(y)suffices to parameterize all matrix elements[6].This is expressed in the compact trace formula[5,7] M′(v′)|J(0)|M(v) =−ξ(y)tr{(2)m M P+ −γ5;pseudoscalar meson/ǫ;vector mesonis a spin wave function that describes correctly the transformation properties(under boosts and heavy quark spin rotations)of the meson states in the effective theory.P+=1g s2m Q O mag,O mag=M′(v′)ΓP+iσαβM(v) .(4)The mass parameter¯Λsets the canonical scale for power corrections in HQET.In the m Q→∞limit,it measures thefinite mass difference between a heavy meson and the heavy quark that it contains[11].By factoring out this parameter,χαβ(v,v′)becomes dimensionless.The most general decomposition of this form factor involves two real,scalar functionsχ2(y)andχ3(y)defined by[10]χαβ(v,v′)=(v′αγβ−v′βγα)χ2(y)−2iσαβχ3(y).(5)Irrespective of the structure of the current J ,the form factor χ3(y )appears always in the following combination with ξ(y ):ξ(y )+2Z ¯Λ d M m Q ′ χ3(y ),(6)where d P =3for a pseudoscalar and d V =−1for a vector meson.It thus effectively renormalizes the leading Isgur-Wise function,preserving its normalization at y =1since χ3(1)=0according to Luke’s theorem [10].Eq.(6)shows that knowledge of χ3(y )is needed if one wants to relate processes which are connected by the spin symmetry,such as B →D ℓνand B →D ∗ℓν.Being hadronic form factors,the universal functions in HQET can only be investigated using nonperturbative methods.QCD sum rules have become very popular for this purpose.They have been reformulated in the context of the effective theory and have been applied to the study of meson decay constants and the Isgur-Wise functions both in leading and next-to-leading order in the 1/m Q expansion [12–21].In particular,it has been shown that very simple predictions for the spin-symmetry violating form factors are obtained when terms of order αs are neglected,namely [17]χ2(y )=0,χ3(y )∝ ¯q g s σαβG αβq [1−ξ(y )].(7)In this approach χ3(y )is proportional to the mixed quark-gluon condensate,and it was estimated that χ3(y )∼1%for large recoil (y ∼1.5).In a recent work we have refined the prediction for χ2(y )by including contributions of order αs in the sum rule analysis [20].We found that these are as important as the contribution of the mixed condensate in (7).It is,therefore,worthwhile to include such effects also in the analysis of χ3(y ).This is the purpose of this article.II.DERIV ATION OF THE SUM RULEThe QCD sum rule analysis of the functions χ2(y )and χ3(y )is very similar.We shall,therefore,only briefly sketch the general procedure and refer for details to Refs.[17,20].Our starting point is the correlatord x d x ′d ze i (k ′·x ′−k ·x ) 0|T[¯q ΓM ′P ′+ΓP +iσαβP +ΓM+Ξ3(ω,ω′,y )tr 2σαβ2(1+/v ′),and we omit the velocity labels in h and h ′for simplicity.The heavy-light currents interpolate pseudoscalar or vector mesons,depending on the choice ΓM =−γ5or ΓM =γµ−v µ,respectively.The external momenta k and k ′in (8)are the “residual”off-shell momenta of the heavy quarks.Due to the phase redefinition of the effective heavy quark fields in HQET,they are related to the total momenta P and P ′by k =P −m Q v and k ′=P ′−m Q ′v ′[3].The coefficient functions Ξi are analytic in ω=2v ·k and ω′=2v ′·k ′,with discontinuities for positive values of these variables.They can be saturated by intermediate states which couple to the heavy-light currents.In particular,there is a double-pole contribution from the ground-state mesons M and M ′.To leading order in the 1/m Q expansion the pole position is at ω=ω′=2¯Λ.In the case of Ξ2,the residue of the pole is proportional to the universal function χ2(y ).For Ξ3the situation is more complicated,however,since insertions of the chromo-magnetic operator not only renormalize the leading Isgur-Wise function,but also the coupling of the heavy mesons to the interpolating heavy-light currents (i.e.,the meson decay constants)and the physical meson masses,which define the position of the pole.1The correct expression for the pole contribution to Ξ3is [17]Ξpole 3(ω,ω′,y )=F 2(ω−2¯Λ+iǫ) .(9)Here F is the analog of the meson decay constant in the effective theory (F ∼f M√m QδΛ2+... , 0|j (0)|M (v ) =iF2G 2tr 2σαβΓP +σαβM (v ) ,where the ellipses represent spin-symmetry conserving or higher order power corrections,and j =¯q Γh (v ).In terms of the vector–pseudoscalar mass splitting,the parameter δΛ2isgiven by m 2V −m 2P =−8¯ΛδΛ2.For not too small,negative values of ωand ω′,the coefficient function Ξ3can be approx-imated as a perturbative series in αs ,supplemented by the leading power corrections in 1/ωand 1/ω′,which are proportional to vacuum expectation values of local quark-gluon opera-tors,the so-called condensates [22].This is how nonperturbative corrections are incorporated in this approach.The idea of QCD sum rules is to match this theoretical representation of Ξ3to the phenomenological pole contribution given in (9).To this end,one first writes the theoretical expression in terms of a double dispersion integral,Ξth 3(ω,ω′,y )= d νd ν′ρth 3(ν,ν′,y )1Thereare no such additional terms for Ξ2because of the peculiar trace structure associated with this coefficient function.possible subtraction terms.Because of theflavor symmetry it is natural to set the Borel parameters associated withωandω′equal:τ=τ′=2T.One then introduces new variables ω±=12T ξ(y) F2e−2¯Λ/T=ω0dω+e−ω+/T ρth3(ω+,y)≡K(T,ω0,y).(12)The effective spectral density ρth3arises after integration of the double spectral density over ω−.Note that for each contribution to it the dependence onω+is known on dimensionalgrounds.It thus suffices to calculate directly the Borel transform of the individual con-tributions toΞth3,corresponding to the limitω0→∞in(12).Theω0-dependence can be recovered at the end of the calculation.When terms of orderαs are neglected,contributions to the sum rule forΞ3can only be proportional to condensates involving the gluonfield,since there is no way to contract the gluon contained in O mag.The leading power correction of this type is represented by the diagram shown in Fig.1(d).It is proportional to the mixed quark-gluon condensate and,as shown in Ref.[17],leads to(7).Here we are interested in the additional contributions arising at orderαs.They are shown in Fig.1(a)-(c).Besides a two-loop perturbative contribution, one encounters further nonperturbative corrections proportional to the quark and the gluon condensate.Let usfirst present the result for the nonperturbative power corrections.WefindK cond(T,ω0,y)=αs ¯q q TT + αs GG y+1− ¯q g sσαβGαβq√y2−1),δn(x)=1(4π)D×1dλλ1−D∞λd u1∞1/λd u2(u1u2−1)D/2−2where C F=(N2c−1)/2N c,and D is the dimension of space-time.For D=4,the integrand diverges asλ→0.To regulate the integral,we assume D<2and use a triple integration by parts inλto obtain an expression which can be analytically continued to the vicinity of D=4.Next we set D=4+2ǫ,expand inǫ,write the result as an integral overω+,and introduce back the continuum threshold.This givesK pert(T,ω0,y)=−αsy+1 2ω0dω+ω3+e−ω+/T(16)× 12−23∂µ+3αs9π¯Λ,(17)which shows that divergences arise at orderαs.At this order,the renormalization of the sum rule is thus accomplished by a renormalization of the“bare”parameter G2in(12).In the9π¯Λ 1µ2 +O(g3s).(18)Hence a counterterm proportional to¯Λξ(y)has to be added to the bracket on the left-hand side of the sum rule(12).To evaluate its effect on the right-hand side,we note that in D dimensions[17]¯Λξ(y)F2e−2¯Λ/T=3y+1 2ω0dω+ω3+e−ω+/T(19)× 1+ǫ γE−ln4π+2lnω+−ln y+12T ξ(y) F2e−2¯Λ/T=αsy+1 2ω0dω+ω3+e−ω+/T 2lnµ6+ y r(y)−1+ln y+1According to Luke’stheorem,theuniversalfunction χ3(y )vanishes at zero recoil [10].Evaluating (20)for y =1,we thus obtain a sum rule for G 2(µ)and δΛ2.It reads G 2(µ)−¯ΛδΛ224π3ω00d ω+ω3+e −ω+/T ln µ12 +K cond (T,ω0,1),(21)where we have used that r (1)=1.Precisely this sum rule has been derived previously,starting from a two-current correlator,in Ref.[16].This provides a nontrivial check of our ing the fact that ξ(y )=[2/(y +1)]2+O (g s )according to (19),we find that the µ-dependent terms cancel out when we eliminate G 2(µ)and δΛ2from the sum rule for χ3(y ).Before we present our final result,there is one more effect which has to be taken into account,namely a spin-symmetry violating correction to the continuum threshold ω0.Since the chromo-magnetic interaction changes the masses of the ground-state mesons [cf.(10)],it also changes the masses of higher resonance states.Expanding the physical threshold asωphys =ω0 1+d M8π3 22 δ3 ω032π2ω30e −ω0/T 26π2−r (y )−ξ(y ) δ0 ω096π 248T 1−ξ(y ).It explicitly exhibits the fact that χ3(1)=0.III.NUMERICAL ANALYSISLet us now turn to the evaluation of the sum rule (23).For the QCD parameters we take the standard values¯q q =−(0.23GeV)3,αs GG =0.04GeV4,¯q g sσαβGαβq =m20 ¯q q ,m20=0.8GeV2.(24) Furthermore,we useδω2=−0.1GeV from above,andαs/π=0.1corresponding to the scale µ=2¯Λ≃1GeV,which is appropriate for evaluating radiative corrections in the effective theory[15].The sensitivity of our results to changes in these parameters will be discussed below.The dependence of the left-hand side of(23)on¯Λand F can be eliminated by using a QCD sum rule for these parameters,too.It reads[16]¯ΛF2e−2¯Λ/T=9T4T − ¯q g sσαβGαβq4π2 2T − ¯q q +(2y+1)4T2.(26) Combining(23),(25)and(26),we obtainχ3(y)as a function ofω0and T.These parameters can be determined from the analysis of a QCD sum rule for the correlator of two heavy-light currents in the effective theory[16,18].Onefinds good stability forω0=2.0±0.3GeV,and the consistency of the theoretical calculation requires that the Borel parameter be in the range0.6<T<1.0GeV.It supports the self-consistency of the approach that,as shown in Fig.2,wefind stability of the sum rule(23)in the same region of parameter space.Note that it is in fact theδω2-term that stabilizes the sum rule.Without it there were no plateau.Over the kinematic range accessible in semileptonic B→D(∗)ℓνdecays,we show in Fig.3(a)the range of predictions forχ3(y)obtained for1.7<ω0<2.3GeV and0.7<T< 1.2GeV.From this we estimate a relative uncertainty of∼±25%,which is mainly due to the uncertainty in the continuum threshold.It is apparent that the form factor is small,not exceeding the level of1%.2Finally,we show in Fig.3(b)the contributions of the individual terms in the sum rule (23).Due to the large negative contribution proportional to the quark condensate,the terms of orderαs,which we have calculated in this paper,cancel each other to a large extent.As a consequence,ourfinal result forχ3(y)is not very different from that obtained neglecting these terms[17].This is,however,an accident.For instance,the order-αs corrections would enhance the sum rule prediction by a factor of two if the ¯q q -term had the opposite sign. From thisfigure one can also deduce how changes in the values of the vacuum condensates would affect the numerical results.As long as one stays within the standard limits,the sensitivity to such changes is in fact rather small.For instance,working with the larger value ¯q q =−(0.26GeV)3,or varying m20between0.6and1.0GeV2,changesχ3(y)by no more than±0.15%.In conclusion,we have presented the complete order-αs QCD sum rule analysis of the subleading Isgur-Wise functionχ3(y),including in particular the two-loop perturbative con-tribution.Wefind that over the kinematic region accessible in semileptonic B decays this form factor is small,typically of the order of1%.When combined with our previous analysis [20],which predicted similarly small values for the universal functionχ2(y),these results strongly indicate that power corrections in the heavy quark expansion which are induced by the chromo-magnetic interaction between the gluonfield and the heavy quark spin are small.ACKNOWLEDGMENTSIt is a pleasure to thank Michael Peskin for helpful discussions.M.N.gratefully acknowl-edgesfinancial support from the BASF Aktiengesellschaft and from the German National Scholarship Foundation.Y.N.is an incumbent of the Ruth E.Recu Career Development chair,and is supported in part by the Israel Commission for Basic Research and by the Minerva Foundation.This work was also supported by the Department of Energy,contract DE-AC03-76SF00515.REFERENCES[1]E.Eichten and B.Hill,Phys.Lett.B234,511(1990);243,427(1990).[2]B.Grinstein,Nucl.Phys.B339,253(1990).[3]H.Georgi,Phys.Lett.B240,447(1990).[4]T.Mannel,W.Roberts and Z.Ryzak,Nucl.Phys.B368,204(1992).[5]A.F.Falk,H.Georgi,B.Grinstein,and M.B.Wise,Nucl.Phys.B343,1(1990).[6]N.Isgur and M.B.Wise,Phys.Lett.B232,113(1989);237,527(1990).[7]J.D.Bjorken,Proceedings of the18th SLAC Summer Institute on Particle Physics,pp.167,Stanford,California,July1990,edited by J.F.Hawthorne(SLAC,Stanford,1991).[8]M.B.Voloshin and M.A.Shifman,Yad.Fiz.45,463(1987)[Sov.J.Nucl.Phys.45,292(1987)];47,801(1988)[47,511(1988)].[9]A.F.Falk,B.Grinstein,and M.E.Luke,Nucl.Phys.B357,185(1991).[10]M.E.Luke,Phys.Lett.B252,447(1990).[11]A.F.Falk,M.Neubert,and M.E.Luke,SLAC preprint SLAC–PUB–5771(1992),toappear in Nucl.Phys.B.[12]M.Neubert,V.Rieckert,B.Stech,and Q.P.Xu,in Heavy Flavours,edited by A.J.Buras and M.Lindner,Advanced Series on Directions in High Energy Physics(World Scientific,Singapore,1992).[13]A.V.Radyushkin,Phys.Lett.B271,218(1991).[14]D.J.Broadhurst and A.G.Grozin,Phys.Lett.B274,421(1992).[15]M.Neubert,Phys.Rev.D45,2451(1992).[16]M.Neubert,Phys.Rev.D46,1076(1992).[17]M.Neubert,Phys.Rev.D46,3914(1992).[18]E.Bagan,P.Ball,V.M.Braun,and H.G.Dosch,Phys.Lett.B278,457(1992);E.Bagan,P.Ball,and P.Gosdzinsky,Heidelberg preprint HD–THEP–92–40(1992).[19]B.Blok and M.Shifman,Santa Barbara preprint NSF–ITP–92–100(1992).[20]M.Neubert,Z.Ligeti,and Y.Nir,SLAC preprint SLAC–PUB–5915(1992).[21]M.Neubert,SLAC preprint SLAC–PUB–5992(1992).[22]M.A.Shifman,A.I.Vainshtein,and V.I.Zakharov,Nucl.Phys.B147,385(1979);B147,448(1979).FIGURESFIG.1.Diagrams contributing to the sum rule for the universal form factorχ3(v·v′):two-loop perturbative contribution(a),and nonperturbative contributions proportional to the quark con-densate(b),the gluon condensate(c),and the mixed condensate(d).Heavy quark propagators are drawn as double lines.The square represents the chromo-magnetic operator.FIG.2.Analysis of the stability region for the sum rule(23):The form factorχ3(y)is shown for y=1.5as a function of the Borel parameter.From top to bottom,the solid curves refer toω0=1.7,2.0,and2.3GeV.The dashes lines are obtained by neglecting the contribution proportional toδω2.FIG.3.(a)Prediction for the form factorχ3(v·v′)in the stability region1.7<ω0<2.3 GeV and0.7<T<1.2GeV.(b)Individual contributions toχ3(v·v′)for T=0.8GeV and ω0=2.0GeV:total(solid),mixed condensate(dashed-dotted),gluon condensate(wide dots), quark condensate(dashes).The perturbative contribution and theδω2-term are indistinguishable in thisfigure and are both represented by the narrow dots.11。

故有此名，其作用范围
精细结构常数小103倍。

这个比例反映了两种作用在低能下强度的差别。

弱作用流的具体形式，总结建立了普适费密型弱相互作用理论。

但是费密作用的场论是不可重正化的，无法计算微扰论的高阶效应。

把费密作用的形式用于高能量还有其他原则性的困难，因此费密作用不能作为弱相互作用的基本理论。

另一方面人们注意到弱相互作用与电磁相互作用虽然很不相同，却又有相似之处。

弱作用流与电流一样是守恒的，它们之间还有以对称性相联系的关系。

因此在60年代末提出了弱作用和电磁作用统一的规范理论（见电弱统一理论）。

这种理论描述轻子和组成强子的夸克以及一些称为黑格斯粒子（见黑格斯机制）的自旋为零的粒子与统一的电-弱规范场的相互作用。

这是一种规范对称性自发破缺的理论。

理论中有一个规范粒子无质量，它是传递电磁作用的光子,其余的规范粒子得到质量,它们是传递弱作用的粒子，称为中间玻色子。

这种理论把似乎没有关系的自然界的两种基本相互作用联系起来，而且是可重正化的。

标准的电弱统一规范模型与所有低能的弱作用实验结果一致。

理论中预言的中间玻色子也已于1983年发现。

因此电弱统一规范理论正确地描述了弱相互作用。

Quantity量speed of light in vacuum光在真空中的速度magn. constant MAGN。

不变electric constant电热恒温characteristic impedance of vacuum特性阻抗的真空Newtonian constant of gravitation万有引力常数Newtonian constant of gravitation overh-bar c牛顿万有引力常数H-巴C Planck constant普朗克常数Planck constant in eV s普朗克常数EV小号Planck constant over 2 pi times c in MeV fm 普朗克常数超过2次c MeV的FM PIPlanck constant over 2 pi普朗克常数超过2 PIPlanck constant over 2 pi in eV s普朗克常数超过2π的EV小号Planck mass普朗克质量Planck temperature普朗克温度Planck length普朗克长度Planck time普朗克时间elementary charge基本电荷elementary charge over h基本电荷较Hmagn. flux quantum MAGN。

磁通量子conductance quantum电导量子inverse of conductance quantum逆的量子电导Josephson constant约瑟夫森常数von Klitzing constant冯Klitzing不变Bohr magneton玻尔磁子Bohr magneton in eV/T"EV / T单位下的玻尔磁子"Bohr magneton in Hz/T"Hz / T单位下的玻尔磁子"Bohr magneton in inverse meters pertesla玻尔磁子的逆米，每颗TeslaBohr magneton in K/T"K / T单位下的玻尔磁子"nuclear magneton核磁nuclear magneton in eV/T核磁EV / Tnuclear magneton in MHz/T核磁以MHz / Tnuclear magneton in inverse meters pertesla在逆米，每颗Tesla核磁nuclear magneton in K/T在K / T核磁fine-structure constant精细结构常数inverse fine-structure constant逆精细结构常数Rydberg constant里德伯常数Rydberg constant times c in Hz里德伯常数次c，单位为HzRydberg constant times hc in J里德伯常数次HC在JRydberg constant times hc in eV里德伯常数倍EV在HCBohr radius玻尔半径Hartree energy哈特里能源Hartree energy in eV哈特里能在EVquantum of circulation量子流通quantum of circulation times 2量子循环时间2Fermi coupling constant费米耦合常数Fundamental Physicalweak mixing angle弱混合角electron mass电子质量electron mass in u电子质量在uelectron mass energy equivalent电子质量的能量相当于electron mass energy equivalent in MeV电子质量在兆电子伏的能量相electron-muon mass ratio电子，μ介子的质量比electron-tau mass ratio电子tau蛋白的质量比electron-proton mass ratio电子，质子的质量比electron-neutron mass ratio电子，中子的质量比electron-deuteron mass ratio电子氘核的质量比electron to alpha particle mass ratioα粒子的质量比电子electron charge to mass quotient电子电荷量的商electron molar mass电子摩尔质量Compton wavelength康普顿波长Compton wavelength over 2 pi康普顿波长超过2 PI classical electron radius经典电子半径Thomson cross section汤姆森横截面electron magn. moment电子MAGN。

什么是“重⼦声学震荡”重⼦声学震荡（英⽂：Baryon Acoustic Oscillations，简称BAO）是宇宙学中⼀个⾮常重要的概念。

这个名字看起来有点复杂且吓⼈，但其实概念上并不是太难理解。

这⾥我试着⽤最简单的语⾔来解释⼀下BAO的基本概念。

⼤量的现代天⽂学观测显⽰，早期宇宙中充满着⾼温⾼密度的等离⼦体，我们这⾥所说的“重⼦”指的就是等离⼦体中的离⼦（包含了质⼦和中⼦）。

总体上来说，早期宇宙中的等离⼦体的分布是均匀的；但是从局部来看，有些地⽅的密度会略⾼⼀点，⽽另⼀些地⽅的密度则会略低，这称之为“密度涨落”。

密度涨落会在等离⼦体中以波的形式传播，产⽣“重⼦声学震荡”。

之所以称其为“声学震荡”，是因为这种波和声波⾮常类似，都是依靠介质密度的变化来传播的纵波。

随着宇宙不断膨胀并冷却下来，这种震荡很快变得⽆法继续传播，但是早先的震荡会在很多地⽅留下其痕迹。

如今，我们即可以从宇宙微波背景辐射中观测到早期BAO信号，也可以通过研究当前宇宙中星系的分布来从统计学上找到BAO信号。

这些观测可以互相补充和印证，从⽽为我们研究宇宙的结构和演化提供了⼀个极其重要的⼯具。

我们也可以⽤⼀个不太严格的简单类⽐来描述这个过程。

想象早期宇宙就像流动的湖⾯，总体上看很平整，但是到处都有着波动的涟漪。

当湖⾯冷却结冰以后，湖⾯虽然不再波动，但是固定的冰⾯上依然可以看到各种起伏，这些起伏就是早先波动的涟漪所留下的痕迹。

通过观测当前冰⾯的起伏，我们可以从统计学上来推断之前波动的湖⾯到底是什么模样。

探测BAO信号是很多星系红移巡天项⽬的主要动机之⼀，因为想要从星系分布中探测到BAO信号，我们需要⼀份⼤规模的星系三维地图。

斯隆数字化巡天（SDSS）和2度视场星系红移巡天（2dFGRS）是最早探测到BAO信号的巡天项⽬，随后的⼀系列巡天项⽬都先后探测到了BAO信号，包括WiggleZ暗能量巡天、6度视场星系红移巡天（6dFGRS）、以及SDSS第三期项⽬中的重⼦震荡光谱巡天（BOSS）等等。

原子核物理专业词汇中英文对照表absorption cross-section 吸收截面activity radioactivity 放射性活度activity 活度adiabatic approximation 浸渐近似allowed transition 容许跃迁angular correlation 角关联angular distribution 角分布angular-momentum conservation 角动量守恒anisotropy 各项异性度annihilation radiation 湮没辐射anomalous magnetic moment 反常极矩anti neutrino 反中微子antiparticle 反粒子artificial radioactivity 人工放射性atomic mass unit 原子质量单位atomic mass 原子质量atomic nucleus 原子核Auger electron 俄歇电子backbending 回弯bag model 口袋模型baryon number 重子数baryon 重子binary fission 二分裂变binging energy 结合能black hole 黑洞bombarding particle 轰击粒子bottom quark 底夸克branching ration 分支比bremsstrahlung 轫致辐射cascade radiation 级联辐射cascade transition 级联跃迁centrifugal barrier 离心势垒chain reaction 链式反应characteristic X-ray 特征X 射线Cherenkov counter 切连科夫计数器coincidence measurement 符合剂量collective model 集体模型collective rotation 集体转动collective vibration 集体震动color charge 色荷complete fusion reaction 全熔合反应complex potential 复势compound-nucleus decay 复合核衰变compound-nucleus model 复合核模型compound nucleus 复合核Compton effect 康普顿效应Compton electron 康普顿电子Compton scattering 康普顿散射cone effect 圆锥效应conservation law 守恒定律controlled thermonuclear fusion 受控热核聚变cosmic ray 宇宙射线Coulomb barrier 库仑势垒Coulomb energy 库伦能Coulomb excitation 库仑激发CPT theorem CPT定理critical angular momentum 临界角动量critical distance 临界距离critical mass 临界质量critical volume 临界体积daily fuel consumption 燃料日消耗量dalitz pair 达立兹对damage criteria 危害判断准则damage 损伤damped oscillations 阻尼震荡damped vibration 阻尼震荡damped wave 阻尼波damper 减震器damping factor 衰减系数damping 衰减的damp proof 防潮的damp 湿气danger coefficient 危险系数danger dose 危险剂量danger range 危险距离danger signal 危险信号dark current pulse 暗电瘤冲dark current 暗电流data acquisition and processing system 数据获得和处理系统data base 数据库data communication 数据通信data processing 数据处理data reduction equipment 数据简化设备data 数据dating 测定年代daughter atom 子体原子daughter element 子体元素daughter nuclear 子核daughter nucleus 子体核daughter nuclide 子体核素daughter 蜕变产物dd reaction dd反应dd reactor dd反应器deactivation 去活化dead ash 死灰尘dead band 不灵敏区dead space 死区dead time correction 死时间校正dead time 失灵时间deaerate 除气deaeration 除气deaerator 除气器空气分离器deaquation 脱水debris activity 碎片放射性debris 碎片de broglie equation 德布罗意方程de broglie frequency 德布罗意频率de broglie relation 德布罗意方程de broglie wavelength 德布罗意波长de broglie wave 德布罗意波debuncher 散束器debye radius 德拜半径debye scherrer method 德拜谢乐法debye temperature 德拜温度decade counter tube 十进计数管decade counting circuit 十进制计数电路decade counting tube 十进管decade scaler 十进位定标器decagram 十克decalescence 相变吸热decalescent point 金属突然吸热温度decanning plant 去包壳装置decanning 去包壳decantation 倾析decanter 倾析器decanting vessel 倾析器decan 去掉外壳decarburization 脱碳decascaler 十进制定标器decatron 十进计数管decay chain 衰变链decay coefficient 衰变常数decay constant 衰变常数decay constant 衰变常量decay energy 衰变能decay factor 衰变常数decay fraction 衰变分支比decay heat removal system 衰变热去除系统decay heat 衰变热decay kinematics 衰变运动学decay out 完全衰变decay period 冷却周期decay power 衰减功率decay rate 衰变速度decay scheme 衰变纲图decay series 放射系decay storage 衰变贮存decay table 衰变表decay time 衰变时间decay 衰减decelerate 减速deceleration 减速decigram 分克decimeter wave 分米波decladding plant 去包壳装置decladding 去包壳decommissioning 退役decompose 分解decomposition temperature 分解温度decomposition 化学分解decontaminability 可去污性decontamination area 去污区decontamination factor 去污因子decontamination index 去污指数decontamination plant 去污装置decontamination reagent 去污试剂decontamination room 去污室decontamination 净化decoupled band 分离带decoupling 去耦解开decrease 衰减decrement 减少率deep dose equivalent index 深部剂量当量指标deep inelastic reaction 深度非弹性反应deep irradiation 深部辐照deep therapy 深部疗deep underwater nuclear counter 深水放射性计数器deep water isotopic current analyzer 深海水连位素分析器de excitation 去激发de exemption 去免除defecation 澄清defective fuel canning 破损燃料封装defective fuel element 破损元件defect level 缺陷程度defectoscope 探伤仪defect 缺陷defence 防护deficiency 不足define 定义definite 确定的definition 分辨deflagration 爆燃deflecting coil 偏转线圈deflecting electrode 偏转电极deflecting field 偏转场deflecting plate 偏转板deflecting system 偏转系统deflecting voltage 偏转电压deflection angle 偏转角deflection plate 偏转板deflection system 偏转系统deflection 负载弯曲deflector coil 偏转线圈deflector field 致偏场deflector plate 偏转板deflector 偏转装置deflocculation 解凝defoamer 去沫剂defoaming agent 去沫剂defocusing 散焦deformation bands 变形带deformation energy 变形能deformation of irradiated graphite 辐照过石墨变形deformation parameter 形变参量deformation 变形deformed nucleus 变形核deformed region 变形区域deform 变形degassing 脱气degas 除气degeneracy 简并degenerate configuration 退化位形degenerate gas 简并气体degenerate level 简并能级degenerate state 简并态degeneration 简并degradation of energy 能量散逸degradation 软化degraded spectrum 软化谱degree of acidity 酸度degree of anisotropic reflectance 蛤异性反射率degree of burn up 燃耗度degree of cross linking 交联度degree of crystallinity 结晶度degree of degeneration 退化度degree of dispersion 分散度degree of dissociation 离解度degree of enrichment 浓缩度degree of freedom 自由度degree of hardness 硬度degree of ionization 电离度degree of moderation 慢化度degree of polymerization 聚合度degree of purity 纯度dehumidify 减湿dehydrating agent 脱水剂dehydration 脱水deionization rate 消电离率deionization time 消电离时间deionization 消电离dejacketing 去包壳delay circuit 延迟电路delayed alpha particles 缓发粒子delayed automatic gain control 延迟自动增益控制delayed coincidence circuit 延迟符合电路delayed coincidence counting 延迟符合计数delayed coincidence method 延迟符合法delayed coincidence unit 延迟符合单元delayed coincidence 延迟符合delayed criticality 缓发临界delayed critical 缓发临界的delayed fallout 延迟沉降物delayed fission neutron 缓发中子delayed gamma 延迟性射线delayed neutron detector 缓发中子探测器delayed neutron emitter 缓发中子发射体delayed neutron failed element monitor 缓发中子破损燃料元件监测器delayed neutron fraction 缓发中子份额delayed neutron method 缓发中子法delayed neutron monitor 缓发中子监测器delayed neutron precursor 缓发中子发射体delayed neutron 缓发中子delayed proton 缓发质子delayed reactivity 缓发反应性delay line storage 延迟线存储器delay line 延迟线delay system 延迟系统delay tank 滞留槽delay time 延迟时间delay unit 延迟单元delay 延迟delineation of fall out contours 放射性沉降物轮廓图deliquescence 潮解deliquescent 潮解的delivery dosedose 引出端delta electron 电子delta metal 合金delta plutonium 钚delta ray 电子demagnetization 去磁demagnetize 去磁dematerialization 湮没demineralization of water 水软化demineralization 脱盐demonstration reactor 示范反应堆demonstration 示范dempster mass spectrograph 登普斯特质谱仪denaturalization 变性denaturant 变性剂denaturation of nuclear fuel 核燃料变性denaturation 变性denature 变性denaturize 变性denitration 脱硝dense plasma focus 稠密等离子体聚焦dense 稠密的densimeter 光密度计densimetry 密度测定densitometer 光密度计densitometry 密度计量学density analog method 密度模拟法density bottle 密度瓶density effect 密度效应density gradient instability 密度梯度不稳定性density of electrons 电子密度deoxidation 脱氧deoxidization 脱氧departure from nucleate boiling ratio 偏离泡核沸腾比departure from nucleate boiling 偏离泡核沸腾dependability 可靠性dependence 相依dependency 相依dephlegmation 分凝酌dephlegmator 分馏塔depilation dose 脱毛剂量depilation 脱毛depleted fraction 贫化馏分depleted fuel 贫化燃料depleted material 贫化材料depleted uranium shielding 贫铀屏蔽depleted uranium 贫化铀depleted water 贫化水depleted zone 贫化区域deplete uranium tail storage 贫化铀尾料储存depletion layer 耗尽层depletion 贫化;消耗depolarization 去极化depolymerization 解聚合deposit dose 地面沉降物剂量deposited activity 沉积的放射性deposition 沉积deposit 沉淀depression 减压depressurization accident 失压事故depressurizing system 降压系统depth dose 深部剂量depth gauge 测深计depth of focus 焦点深度depthometer 测深计derby 粗锭derivant 衍生物derivate 衍生物derivative 衍生物derived estimate 导出估价值derived unit 导出单位derived working limit 导出工撰限desalinization 脱盐desalting 脱盐descendant 后代desensitization 脱敏desensitizer 脱敏剂desiccation 干燥desiccator 干燥器防潮器design basis accident 设计依据事故design basis depressurization accident 设计依据卸压事故design basis earthquake 设计依据地震design dose rate 设计剂量率design of the safeguards approach 保障监督方法设计design power 设计功率design pressure 设计压力design safety limit 设计安全限design temperature rise 设计温度上升design transition temperature 设计转变温度design 设计desmotropism 稳变异构desmotropy 稳变异构desorption 解吸desquamation 脱皮destruction test 破坏性试验destructive distillation 干馏detailed balance principle 细致平衡原理detailed decontamination 细部去污detectable activity 可探测的放射性detectable 可检测的detection efficiency 探测效率detection efficiency 探测效率detection limit 探测限detection of neutrons from spontaneous fission 自发裂变中子探测detection of radiation 辐射线的探测detection probability 探测概率detection time 探测时间detection 探测detector 1/v 1/v探测器detector efficiency 探测僻率detector foil 探测骗detector noise 探测齐声detector shield 探测屏蔽detector tube 检波管detector with internal gas source 内气源探测器detector 探测器敏感元件detect 探测;检波detergent 洗涤剂determination 确定deterrence of diversion 转用制止detonating gas 爆鸣气detonation altitude 爆炸高度detonation point 爆炸点detonation yield 核爆炸威力detonation 爆炸detoxifying 净化detriment 损害detted line 点线deuteride 氘化物deuterium alpha reaction 氘反应deuterium critical assembly 重水临界装置deuterium leak detector 重水检漏器deuterium moderated pile low energy 低功率重水慢化反应堆deuterium oxide moderated reactor 重水慢化反应堆deuterium oxide 重水deuterium pile 重水反应堆deuterium sodium reactor 重水钠反应堆deuterium target 氘靶deuterium tritium fuel 氘氚燃料deuterium tritium reaction 氘氚反应deuterium 重氢deuteron alpha reaction 氘核反应deuteron binding energy 氘核结合能deuteron induced fission 氘核诱发裂变deuteron neutron reaction 氘核中子反应deuteron proton reaction 氘核质子反应deuteron stripping 氘核涎deuterum moderated pile 重水反应堆deuton 氘核development of uranium mine 铀矿开发development 发展deviation from the desired value 期望值偏差deviation from the index value 给定值偏差deviation 偏差dewatering 脱水dewindtite 水磷铅铀矿dew point 露点dextro rotatory 右旋的diagnostic radiology 诊断放射学diagnostics 诊断diagram 线图dialkyl phosphoric acid process 磷酸二烷基酯萃取法dialysis 渗析dial 度盘diamagnetic effect 抗磁效应diamagnetic loop 抗磁圈diamagnetic substance 抗磁体diamagnetic susceptibility 抗磁化率diamagnetism of the plasma particles 等离子体粒子反磁性diamagnetism 反磁性diamagnet 抗磁体diameter 直径diamond 稳定区;金刚石diaphragm gauge 膜式压力计diaphragm type pressure gauge 膜式压力计diaphragm 薄膜diapositive 透谬片diascope 投影放影器投影仪diathermance 透热性diathermancy 透热性diatomic gas 双原子气体diatomic molecule 二原子分子dibaryon 双重子diderichite 水菱铀矿dido type heavy water research reactor 迪多型重水研究用反应堆dido 重水慢化反应堆dielectric after effect 电介质后效dielectric constant 介电常数dielectric hysteresis 电介质滞后dielectric polarization 电介质极化dielectric strain 电介质变形dielectric strength 绝缘强度dielectric 电介质diesel engine 柴油机diesel oil 柴油difference ionization chamber 差分电离室difference linear ratemeter 差分线性计数率计difference number 中子过剩difference of potential 电压difference scaler 差分定标器differential absorption coefficient 微分吸收系数differential absorption ratio 微分吸收系数differential albedo 微分反照率differential control rod worth 控制棒微分价值differential cross section 微分截面differential cross-section微分截面differential discriminator 单道脉冲幅度分析器differential dose albedo 微分剂量反照率differential energy flux density 微分能通量密度differential particle flux density 粒子微分通量密度differential pressure 压差differential range spectrum 射程微分谱differential reactivity 微分反应性differential recovery rate 微分恢复率differential scattering cross section 微分散射截面differentiator 微分器diffraction absorption 衍射吸收diffraction analysis 衍射分析diffraction angle 衍射角diffraction grating 衍射光栅diffraction instrument 衍射仪diffraction pattern 衍射图diffraction peak 衍射峰值diffraction scattering 衍射散射diffraction spectrometer 衍射谱仪diffraction spectrum 衍射光谱diffraction 衍射diffractometer 衍射仪diffusate 扩散物diffuse band 扩散带diffused junction semiconductor detector 扩散结半导体探测器diffused 散射的diffuseness parameter 扩散性参数diffuse reflection 漫反射diffuser 扩散器diffuse scattering 漫散射diffuse 扩散diffusion approximation 扩散近似diffusion area 扩散面积diffusion barrier 扩散膜diffusion cascade 扩散级联diffusion chamber 扩散云室diffusion coefficient for neutron flux density 中子通量密度扩散系数diffusion coefficient for neutron number density 中子数密度扩散系数diffusion coefficient 扩散系数diffusion column 扩散塔diffusion constant 扩散常数diffusion cooling effect 扩散冷却效应diffusion cooling 扩散冷却diffusion cross section 扩散截面diffusion current density 扩散淋度diffusion current 扩散电流diffusion energy 扩散能diffusion equation 扩散方程diffusion factory 扩散工厂diffusion kernel 扩散核diffusion layer 扩散层diffusion length 扩散长度diffusion length 扩散长度diffusion mean free path 扩散平均自由程diffusion plant 扩散工厂diffusion pump 扩散泵diffusion rate 扩散速率diffusion stack 务马堆diffusion theory 扩散理论diffusion time 扩散时间diffusion 扩散diffusivity 扩散系数digital analog converter 数模转换器digital computer 数字计算机digital data acquisition and processing system 数字数据获取与处理系统digital data handling and display system 数字数据处理和显示系统digital recorder 数字记录器digital time converter 数字时间变换器dilation 扩胀dilatometer 膨胀计diluent 稀释剂dilute solution 稀溶液dilute 冲淡dilution analysis 稀释分析dilution effect 稀释效应dilution method 稀释法dilution ratio 稀释比dilution 稀释dimensional change 尺寸变化dimension 尺寸diminishing 衰减dimorphism 双晶现象di neutron 双中子dineutron 双中子dingot 直接铸锭dip counter tube 浸入式计数管dipelt 双重线dipole dipole interaction 偶极子与偶极子相互酌dipole layer 偶极子层dipole momentum 偶极矩dipole moment 偶极矩dipole radiation 偶极辐射dipole transition 偶极跃迁dipole 偶极子di proton 双质子dirac electron 狄拉克电子dirac equation 狄拉克方程dirac quantization 狄拉克量子化dirac theory of electron 狄拉克电子论direct and indirect energy conversion 直接和间接能量转换direct contact heat exchanger 直接接触式换热器direct conversion reactor study 直接转换反应堆研究direct conversion reactor 直接转换反应堆direct current 直流direct cycle integral boiling reactor 直接循环一体化沸水堆direct cycle reactor 直接循环反应堆direct cycle 直接循环direct digital control 直接数字控制direct energy conversion 能量直接转换direct exchange interaction 直接交换相互酌direct exposure 直接辐照direct fission yield 原始裂变产额direct interaction 直接相互酌directional correlation of successive gamma rays 连续射线方向相关directional counter 定向计数器directional distribution 方向分布directional focusing 方向聚焦directional 定向的direction 方向direct isotopic dilution analysis 直接同位素稀释分析directly ionizing particles 直接电离粒子directly ionizing radiation 直接电离辐射direct measurement 直接测量direct radiant energy 直接辐射能direct radiation proximity indicator 直接辐射接近指示器direct radiation 直接辐射direct reaction 直接反应direct reaction 直接反应direct use material 直接利用物质direct voltage 直羚压direct x ray analysis 直接x射线分析dirft tube 飞行管道dirt column 尘土柱dirty bomb 脏炸弹disadvantage factor 不利因子disagreement 不一致disappearence 消失discharge chamber 放电室discharge current 放电电流discharge in vacuo 真空放电discharge potential 放电电压discharge tube 放电管discharge voltage 放电电压discharge 放电discomposition 原子位移discontinuity 非连续性discontinuous 不连续的disc operating system 磁盘操椎统discrepancy 差异discrete energy level 不连续能级discrete spectrum 不连续光谱discrete state 不连续态discrete 离散的discrimination coefficient 甄别系数discriminator 鉴别器disinfectant 杀菌剂disintegrate 蜕衰disintegration chain 放射系disintegration constant 衰变常数disintegration curve 衰变曲线disintegration energy 衰变能disintegration heat 衰变热disintegration of elementary particles 基本粒子衰变disintegration particle 衰变粒子disintegration probability 衰变概率disintegration product 蜕变产物disintegration rate 衰变速度disintegration scheme 蜕变图disintegration series 蜕变系disintegrations per minute 衰变/分disintegrations per second 衰变/秒disintegration 蜕变disk source 圆盘放射源dislocation edge 位错边缘dislocation line 位错线dislocation 位错dismantling 解体disorder scattering 无序散射disorder 无序dispersal effect 分散效应dispersal 分散disperser 分散剂dispersing agent 分散剂dispersion fuel element 弥散体燃料元件dispersion fuel 弥散体燃料dispersion 分散dispersive medium 色散媒质displacement current 位移电流displacement kernel 位移核displacement law of radionuclide 放射性核素位移定律displacement law 位移定律displacement spike 离位峰displacement 替换displace 位移;代替disposal of radioactive effluents 放射性瘤液处置disposition 配置disproportionation 不均disruption 破坏disruptive instability 破裂不稳定性disruptive voltage 哗电压dissipation of energy 能消散dissipation 耗散dissociation constant 离解常数dissociation energy 离解能dissociation pressure 离解压dissociation 离解dissociative ionization 离解电离dissolution 溶解dissolver gas 溶解气体dissolver heel 溶解泣滓dissolver 溶解器distance control 遥控distant collision 远距离碰撞distillate 蒸馏液distillation column 蒸馏塔distillation method 蒸馏法distillation tower 蒸馏塔distillation 蒸馏distilled water 蒸馏水distiller 蒸馏器distilling apparatus 蒸馏器distilling flask 蒸馏瓶distorted wave Born approximation,DWBA 扭曲波波恩近似distorted wave impulse approximation 畸变波冲动近似distorted wave theory 畸变波理论distorted wave 畸变波distortionless 不失真的distortion 畸变distributed ion pump 分布式离子泵distributed processing 分布式处理distributed source 分布源distribution coefficient 分配系数distribution factor 分布因子distribution function 分布函数distribution law 分配定律distribution of dose 剂量分布distribution of radionuclides 放射性核素分布distribution of residence time 停留时间分布distribution ratio 分配系数distribution 分布distrubited constant 分布常数disturbance 扰动disturbation 扰动diuranium pentoxide 五氧化二铀divergence of ion beam 离子束发散divergence problem 发散问题divergence 发散divergent lens 发射透镜divergent reaction 发散反应diversing lens 发射透镜diversion assumption 转用假定diversion box 转换箱diversion hypothesis 转用假设diversion path 转用路径diversion strategy 转用战略diversion 转向divertor 收集器divider 分配器division of operating reactors 反应堆运行部division 刻度djalmaite 钽钛铀矿document information system 文献情报体系doerner hoskins distribution law 德尔纳霍斯金斯分配定律dollar 元domain 磁畴dome 圆顶水柱dominant mutation 显性突变donut 环形室doping control of semiconductors 半导体掺杂物第Dopper effect 多普勒效应doppler averaged cross section 多普勒平均截面doppler broadening 多普勒展宽doppler coefficient 多普勒系数doppler effect 多普勒效应doppler free laser spectroscopy 无多普勒激光光谱学doppler shift method 多普勒频移法doppler width 多普勒宽度dosage measurement 剂量测定dosage meter 剂量计dosage 剂量dose albedo 剂量反照率dose build up factor 剂量积累因子dose commitment 剂量负担dose effect curve 剂量效应曲线dose effect relationship 剂量效应关系dose equivalent commitment 剂量当量负担dose equivalent index 剂量当量指标dose equivalent limit 剂量当量极限dose equivalent rate 剂量当量率dose equivalent 剂量当量dose equivalent 剂量当量dose fractionation 剂量分割dose limit 剂量极限dose measurement 剂量测量dose meter 剂量计dose modifying factor 剂量改变系数dose of an isotope 同位素用量dose prediction technique 剂量预报技术dose protraction 剂量迁延dose rate meter 剂量率测量计dose ratemeter 剂量率表dose rate 剂量率dose reduction factor 剂量减低系数dose response correlation 剂量响应相关dose unit 剂量单位dose 剂量dosifilm 胶片剂量计dosimeter charger 剂量计充电器dosimeter 剂量计dosimetry applications research facility 剂量测定法应用研究设施dosimetry 剂量测定法dotted line 点线double beam 双射束double beta decay 双衰变double bond 双键double charged 双电荷的double clad vessel 双层覆盖容器double compton scattering 双康普顿散射double container 双层容器double contingency principle 双偶然性原理double decomposition 复分解double differential cross section 二重微分截面double focusing mass spectrometer 双聚焦质谱仪double focusing 双聚焦double-humped barrier 双峰势垒double ionization chamber 双电离室double precision 双倍精度double probe 双探针double pulse 双脉冲double resonance spectroscopy 双共振光谱学double resonance 双共振double scattering method 双散射法doublet splitting 双重线分裂doublet 电子对double walled heat exchanger 双层壁换热器doubling dose 加倍剂量doubling time meter 倍增时间测量计doubling time 燃料倍增时间doubly charged 双电荷的doubly closed shell nuclei 双闭合壳层核doughnut 环形室downcomer 下降管down quark 下夸克down time 停机时间downwards coolant flow 下行冷却剂流downwind fall out 下风放射性沉降物draft 通风drain tank 排水槽draught 通风drell ratio 多列尔比dressing of uranium ore 铀矿石选矿dressing 选矿drier 干燥器drift instability 漂移不稳定性drift mobility 漂移率drift speed 漂移速度drift transistor 漂移晶体管drift velocity 漂移速度driven magnetic fusion reactor 从动磁核聚变反应堆driver fuel 驱动燃料drive voltage 控制电压drop reaction 点滴反应drop 点滴dry active waste 干放射性废物dry analysis 干法分析dry box 干箱dry criticality 干临界dry distillation 干馏dryer 干燥器dry friction 干摩擦dry ice 干冰drying oil 干性油drying oven 烘干炉drying 干燥dry out 烧干dry reprocessing 干法再处理dry way process 干法过程dry well 干井dt fuel cycle dt燃料循环dt reactor dt反应堆dual cycle boiling water reactor system 双循环沸水反应堆系统dual cycle reactor 双循环反应堆dual decay 双重放射性衰变dual energy use system 能量双重利用系统duality 二重性dual purpose nuclear power station 两用核电站dual purpose reactor 两用反应堆dual temperature exchange separation process 双温度交换分离法dual temperature exchange 双温度交换duant d形盒ductile brittle transition temperature 延性脆性转变温度ductility 延伸性duct 管dummy load 仿真负载dumontite 水磷铀铅矿dump condenser 事故凝汽器dump tank 接受槽dump valve 事故排放阀dump 烧毁元件存放处dunkometer 燃料元件包壳破损探测器duplet 电子对duration of a scintillation 闪烁持续时间duration 持续时间dust chamber 集尘室dust cloud 尘埃云dust collector 集尘器dust cooled reactor 粉尘冷却反应堆dust monitor 灰尘监测器dust sampler 灰尘取样器dust trap 集尘器dye laser 染料激光器dynamical friction 动摩擦dynamic behaviour 动态dynamic characteristic 动特性dynamic equilibrium ratio 动态平衡比dynamic equilibrium 动态平衡dynamic pressure 动压dynamic process inventory determination 动态过程投料量测定dynamic stabilization 动力稳定dynamic viscosity 动力粘滞系数dynamitron 地那米加速器并激式高频高压加速器dynamometer 测力计dynamo 发电机dyne 达因dynode 倍增电极dysprosium 镝dystectic mixture 高熔点混合物elastic scattering cross-section 弹性散射截面elastic scattering 弹性散射electronic stopping 电子阻止elementary particle 基本粒子EMC effect EMC效应endothermic reaction 吸能反应energy conservation 能量守恒energy loss 能量损失energy resolution 能量分辨率evaporation model 蒸发模型even-even nucleus 偶偶核exchange force 交换力excitation curve 激发曲线excitation function 激发函数excited state 激发态exothermic reaction 放能反应experimental Q-wave 实验Q值exposure 照射量fabrication 制造facility attachment 设施附属文件facility practice 设施实行facility safeguards approach 设施的保障监督方法facility 设施factor of porosity 孔隙率factor of stress concentration 应力集中因数factor 系数fading 阻尼failed can detection 破损燃料探测failed element indicator 破损元件指示器failed element monitor 破损元件监测器failed element 破损元件failed fuel detection and location 破损燃料探测和定位failed fuel detection 破损燃料探测failed fuel detector 破损燃料探测器fail safe instrument 故障时安全运行的仪器fail safe operation 安全运行failsafe 故障自动保险的failure checking 故障检查failure free operation 无故障运行failure mode 故障种类failure of parity conservation 宇称守恒的破坏failure prediction 故障预测fall back 回落falling stream method 降哩fallout density 放射性沉降物密度fallout monitoring 沉降物监测fallout particle 沉降粒子fallout pattern 沉降物分布型式fallout radioactive material 放射性沉降物fallout sampling network 沉降物取样网fallout shelter 沉降物掩蔽所fall out 放射性沉降fall time 下降时间false alarm probability 假报警几率false curvature 假曲率false scram 错误信号紧急停堆family 系fano's theorem 法诺定理faraday cage 法拉第笼faraday constant 法拉第常数faraday cup 法拉第笼farad 法拉far field 远场far infra red radiation 远红外辐射far ultraviolet radiation 远紫外辐射farvitron 线振质谱仪fast acting control rod 快动棕制棒fast advantage factor 快中子有利因子fast amplifier 宽频带放大器fast and thermal reactor burnup computer code 快和热反应堆燃耗计算机代码fast breeder reactor 快中子增殖反应堆fast breeder 快中子增殖反应堆fast burst reactor facility 快中子脉冲反应堆装置fast burst reactor 快中子脉冲反应堆fast ceramic reactor 陶瓷燃料快堆fast chamber 快速电离室fast chopper 快中子选择器fast coincidence unit 快符合单元fast coincidence 快符合fast compression cloud chamber 快压缩云室fast conversion 快中子转换fast cosmic ray neutron 宇宙射线的快中子fast critical assembly 快中子临界装置fast cross section 快中子截面fast detector 快速探测器fast effect 快中子倍增效应fast electron 快电子fast exponential experiment 快中子指数实验装置fast fissionability 快中子致裂变性fast fission effect factor 快中子裂变效应系数fast fission region 快中子裂变区fast fission 快中子裂变fast flux test facility 快中子通量试验装置fast flux 快中子通量fast fragment 快碎片fast killing dose 快速杀伤剂量fast leakage factor 快中子泄漏因子fast mean free path 快中子平均自由程fast medium 快中子介质fast multiplication effect 快中子倍增效应fast multiplication factor 快中子倍增因子fast neutron activation method 快中子活化法fast neutron breeder reactor 快中子增殖反应堆fast neutron breeding 快中子增殖fast neutron calibration 快中子刻度fast neutron collimator 快中子准直器fast neutron counter tube 快中子计数管fast neutron cycle 快中子增殖循环fast neutron detector 快中子探测器fast neutron diffusion length 快中子扩散长度fast neutron dose equivalent 快中子剂量当量fast neutron dosimeter 快中子剂量计fast neutron fission cross section 快中子裂变截面fast neutron fission increase rate 快中子裂变增加率fast neutron fluence 快中子积分通量fast neutron generator 快中子发生器fast neutron non leakage probability 快中子不泄漏几率fast neutron range 快中子区fast neutron reaction 快中子反应fast neutron reactor 快中子裂变反应堆fast neutron selector 快中子选择器fast neutron spectrometer 快中子谱仪fast neutron 快中子fast plutonium reactor 快中子钚反应堆fast radiochemistry 快速放射化学fast reaction 快速核反应fast reactor core test facility 快堆堆芯试验装置fast reactor physics 快速反应堆物理学fast reactor test assembly 快堆试验装置fast reactor thermal engineering facility 快堆热工程研究设施fast reactor 快中子裂变反应堆fast region 快中子区fast setback 迅速下降fast slow coincidence circuit 快慢符合电路fast sub critical assembly 快中子次临界装置fast test reactor 快中子试验反应堆fast thermal coupled reactor 快热耦合反应堆fast zero power reactor 快中子零功率反应堆fatal dose 致命剂量fatalities 死亡事故fatigue fracture 疲劳断裂fatigue limit 疲劳极限fatigue test 疲劳试验fatigue 疲劳faulted condition 损伤状态faulty fuel assembly 破损燃料组件fault 故障favorable geometry 有利几何条件fb 快中子增殖反应堆fcc 核燃料循环成本fcf 核燃料循环设施feather analysis 费塞分析feather's empirical formula 费瑟经验公式feather's rule 费瑟规则feed adjustment tank 进料蝶槽feedback circuit 反馈回路feedback control 反馈控制feedback loop 反馈回路feedback ratio 反馈比feedback signal 反馈信号feedback 反馈feed end 加料端feed material 给料物质feed plant 核燃料生产工厂feed pump 给水泵feed stage 给料段feed water control system 给水控制系统feedwater equipment 给水设备feedwater flow control 给水量控制feed water 给水feed 供给ferganite 水钒铀矿fermat's principle 费马原理fermi acceleration 费米加速fermi age equation 费米年龄方程fermi age theory 费米年龄理论fermi age 费米年龄fermi beta decay theory 费米衰变理论fermi characteristic energy level 费米能级fermi constant 费米常数fermi dirac gas 费米狄拉克气体fermi dirac statistics 费米狄拉克统计学fermi distribution function 费米狄拉克分布函数fermi distribution 费米分布fermi energy 费米能级fermi function 费米函数Fermi function 费米函数fermi gas model 费米气体模型fermi gas 费米气体Fermi interaction F相互作用fermi interaction 费米相互酌fermi intercept 散射长度fermi level 费米能级fermi limit 费米能级fermion 费米子fermi particle 费米子fermi perturbation 费米微扰fermi plot 费米线图fermi potential 费米势fermi reactor 费米中子反应堆fermi resonance 费米共振fermi selection rules 费米选择定则fermi's golden rule 费米黄金法则fermi spectrum 费米谱。

a r X i v :h e p -p h /9812285v 1 8 D e c 1998The Standard Model of Particle PhysicsMary K.Gaillard 1,Paul D.Grannis 2,and Frank J.Sciulli 31University of California,Berkeley,2State University of New York,Stony Brook,3Columbia UniversityParticle physics has evolved a coherent model that characterizes forces and particles at the mostelementary level.This Standard Model,built from many theoretical and experimental studies,isin excellent accord with almost all current data.However,there are many hints that it is but anapproximation to a yet more fundamental theory.We trace the development of the Standard Modeland indicate the reasons for believing that it is incomplete.Nov.20,1998(To be published in Reviews of Modern Physics)I.INTRODUCTION:A BIRD’S EYE VIEW OF THE STANDARD MODEL Over the past three decades a compelling case has emerged for the now widely accepted Standard Model of elementary particles and forces.A ‘Standard Model’is a theoretical framework built from observation that predicts and correlates new data.The Mendeleev table of elements was an early example in chemistry;from the periodic table one could predict the properties of many hitherto unstudied elements and compounds.Nonrelativistic quantum theory is another Standard Model that has correlated the results of countless experiments.Like its precursors in other fields,the Standard Model (SM)of particle physics has been enormously successful in predicting a wide range of phenomena.And,just as ordinary quantum mechanics fails in the relativistic limit,we do not expect the SM to be valid at arbitrarily short distances.However its remarkable success strongly suggests that the SM will remain an excellent approximation to nature at distance scales as small as 10−18m.In the early 1960’s particle physicists described nature in terms of four distinct forces,characterized by widely different ranges and strengths as measured at a typical energy scale of 1GeV.The strong nuclear force has a range of about a fermi or 10−15m.The weak force responsible for radioactive decay,with a range of 10−17m,is about 10−5times weaker at low energy.The electromagnetic force that governs much of macroscopic physics has infinite range and strength determined by the finestructure constant,α≈10−2.The fourth force,gravity,also has infinite range and a low energy coupling (about 10−38)too weak to be observable in laboratory experiments.The achievement of the SM was the elaboration of a unified description of the strong,weak and electromagnetic forces in the language of quantum gauge field theories.Moreover,the SM combines the weak and electromagnetic forces in a single electroweak gauge theory,reminiscent of Maxwell’s unification of the seemingly distinct forces of electricity and magnetism.By mid-century,the electromagnetic force was well understood as a renormalizable quantum field theory (QFT)known as quantum electrodynamics or QED,described in the preceeding article.‘Renormalizable’means that once a few parameters are determined by a limited set of measurements,the quantitative features of interactions among charged particles and photons can be calculated to arbitrary accuracy as a perturbative expansion in the fine structure constant.QED has been tested over an energy range from 10−16eV to tens of GeV,i.e.distances ranging from 108km to 10−2fm.In contrast,the nuclear force was characterized by a coupling strength that precluded a perturbativeexpansion.Moreover,couplings involving higher spin states(resonances),that appeared to be onthe same footing as nucleons and pions,could not be described by a renormalizable theory,nor couldthe weak interactions that were attributed to the direct coupling of four fermions to one another.In the ensuing years the search for renormalizable theories of strong and weak interactions,coupledwith experimental discoveries and attempts to interpret available data,led to the formulation ofthe SM,which has been experimentally verified to a high degree of accuracy over a broad range ofenergy and processes.The SM is characterized in part by the spectrum of elementaryfields shown in Table I.The matterfields are fermions and their anti-particles,with half a unit of intrinsic angular momentum,or spin.There are three families of fermionfields that are identical in every attribute except their masses.Thefirst family includes the up(u)and down(d)quarks that are the constituents of nucleons aswell as pions and other mesons responsible for nuclear binding.It also contains the electron and theneutrino emitted with a positron in nuclearβ-decay.The quarks of the other families are constituentsof heavier short-lived particles;they and their companion charged leptons rapidly decay via the weakforce to the quarks and leptons of thefirst family.The spin-1gauge bosons mediate interactions among fermions.In QED,interactions among elec-trically charged particles are due to the exchange of quanta of the electromagneticfield called photons(γ).The fact that theγis massless accounts for the long range of the electromagnetic force.Thestrong force,quantum chromodynamics or QCD,is mediated by the exchange of massless gluons(g)between quarks that carry a quantum number called color.In contrast to the electrically neutralphoton,gluons(the quanta of the‘chromo-magnetic’field)possess color charge and hence couple toone another.As a consequence,the color force between two colored particles increases in strengthwith increasing distance.Thus quarks and gluons cannot appear as free particles,but exist onlyinside composite particles,called hadrons,with no net color charge.Nucleons are composed ofthree quarks of different colors,resulting in‘white’color-neutral states.Mesons contain quark andanti-quark pairs whose color charges cancel.Since a gluon inside a nucleon cannot escape its bound-aries,the nuclear force is mediated by color-neutral bound states,accounting for its short range,characterized by the Compton wavelength of the lightest of these:theπ-meson.The even shorter range of the weak force is associated with the Compton wave-lengths of thecharged W and neutral Z bosons that mediate it.Their couplings to the‘weak charges’of quarksand leptons are comparable in strength to the electromagnetic coupling.When the weak interactionis measured over distances much larger than its range,its effects are averaged over the measurementarea and hence suppressed in amplitude by a factor(E/M W,Z)2≈(E/100GeV)2,where E is the characteristic energy transfer in the measurement.Because the W particles carry electric charge theymust couple to theγ,implying a gauge theory that unites the weak and electromagnetic interactions,similar to QCD in that the gauge particles are self-coupled.In distinction toγ’s and gluons,W’scouple only to left-handed fermions(with spin oriented opposite to the direction of motion).The SM is further characterized by a high degree of symmetry.For example,one cannot performan experiment that would distinguish the color of the quarks involved.If the symmetries of theSM couplings were fully respected in nature,we would not distinguish an electron from a neutrinoor a proton from a neutron;their detectable differences are attributed to‘spontaneous’breakingof the symmetry.Just as the spherical symmetry of the earth is broken to a cylindrical symmetry by the earth’s magneticfield,afield permeating all space,called the Higgsfield,is invoked to explain the observation that the symmetries of the electroweak theory are broken to the residual gauge symmetry of QED.Particles that interact with the Higgsfield cannot propagate at the speed of light,and acquire masses,in analogy to the index of refraction that slows a photon traversing matter.Particles that do not interact with the Higgsfield—the photon,gluons and possibly neutrinos–remain massless.Fermion couplings to the Higgsfield not only determine their masses; they induce a misalignment of quark mass eigenstates with respect to the eigenstates of the weak charges,thereby allowing all fermions of heavy families to decay to lighter ones.These couplings provide the only mechanism within the SM that can account for the observed violation of CP,that is,invariance of the laws of nature under mirror reflection(parity P)and the interchange of particles with their anti-particles(charge conjugation C).The origin of the Higgsfield has not yet been determined.However our very understanding of the SM implies that physics associated with electroweak symmetry breaking(ESB)must become manifest at energies of present colliders or at the LHC under construction.There is strong reason, stemming from the quantum instability of scalar masses,to believe that this physics will point to modifications of the theory.One shortcoming of the SM is its failure to accommodate gravity,for which there is no renormalizable QFT because the quantum of the gravitationalfield has two units of spin.Recent theoretical progress suggests that quantum gravity can be formulated only in terms of extended objects like strings and membranes,with dimensions of order of the Planck length10−35m. Experiments probing higher energies and shorter distances may reveal clues connecting SM physics to gravity,and may shed light on other questions that it leaves unanswered.In the following we trace the steps that led to the formulation of the SM,describe the experiments that have confirmed it,and discuss some outstanding unresolved issues that suggest a more fundamental theory underlies the SM.II.THE PATH TO QCDThe invention of the bubble chamber permitted the observation of a rich spectroscopy of hadron states.Attempts at their classification using group theory,analogous to the introduction of isotopic spin as a classification scheme for nuclear states,culminated in the‘Eightfold Way’based on the group SU(3),in which particles are ordered by their‘flavor’quantum numbers:isotopic spin and strangeness.This scheme was spectacularly confirmed by the discovery at Brookhaven Laboratory (BNL)of theΩ−particle,with three units of strangeness,at the predicted mass.It was subsequently realized that the spectrum of the Eightfold Way could be understood if hadrons were composed of three types of quarks:u,d,and the strange quark s.However the quark model presented a dilemma: each quark was attributed one half unit of spin,but Fermi statistics precluded the existence of a state like theΩ−composed of three strange quarks with total spin3A combination of experimental observations and theoretical analyses in the1960’s led to anotherimportant conclusion:pions behave like the Goldstone bosons of a spontaneously broken symmetry,called chiral symmetry.Massless fermions have a conserved quantum number called chirality,equalto their helicity:+1(−1)for right(left)-handed fermions.The analysis of pion scattering lengths andweak decays into pions strongly suggested that chiral symmetry is explicitly broken only by quarkmasses,which in turn implied that the underlying theory describing strong interactions among quarksmust conserve quark helicity–just as QED conserves electron helicity.This further implied thatinteractions among quarks must be mediated by the exchange of spin-1particles.In the early1970’s,experimenters at the Stanford Linear Accelerator Center(SLAC)analyzed thedistributions in energy and angle of electrons scattered from nuclear targets in inelastic collisionswith momentum transfer Q2≈1GeV/c from the electron to the struck nucleon.The distributions they observed suggested that electrons interact via photon exchange with point-like objects calledpartons–electrically charged particles much smaller than nucleons.If the electrons were scatteredby an extended object,e.g.a strongly interacting nucleon with its electric charge spread out by acloud of pions,the cross section would drop rapidly for values of momentum transfer greater than theinverse radius of the charge distribution.Instead,the data showed a‘scale invariant’distribution:across section equal to the QED cross section up to a dimensionless function of kinematic variables,independent of the energy of the incident electron.Neutrino scattering experiments at CERN andFermilab(FNAL)yielded similar parison of electron and neutrino data allowed adetermination of the average squared electric charge of the partons in the nucleon,and the result wasconsistent with the interpretation that they are fractionally charged quarks.Subsequent experimentsat SLAC showed that,at center-of-mass energies above about two GeV,thefinal states in e+e−annihilation into hadrons have a two-jet configuration.The angular distribution of the jets withrespect to the beam,which depends on the spin of thefinal state particles,is similar to that of themuons in anµ+µ−final state,providing direct evidence for spin-1√where G F is the Fermi coupling constant,γµis a Dirac matrix and12fermions via the exchange of spinless particles.Both the chiral symmetry of thestrong interactions and the V−A nature of the weak interactions suggested that all forces except gravity are mediated by spin-1particles,like the photon.QED is renormalizable because gauge invariance,which gives conservation of electric charge,also ensures the cancellation of quantum corrections that would otherwise result in infinitely large amplitudes.Gauge invariance implies a massless gauge particle and hence a long-range force.Moreover the mediator of weak interactions must carry electric charge and thus couple to the photon,requiring its description within a Yang-Mills theory that is characterized by self-coupled gauge bosons.The important theoretical breakthrough of the early1970’s was the proof that Yang-Mills theories are renormalizable,and that renormalizability remains intact if gauge symmetry is spontaneously broken,that is,if the Lagrangian is gauge invariant,but the vacuum state and spectrum of particles are not.An example is a ferromagnet for which the lowest energy configuration has electron spins aligned;the direction of alignment spontaneously breaks the rotational invariance of the laws ofphysics.In QFT,the simplest way to induce spontaneous symmetry breaking is the Higgs mech-anism.A set of elementary scalarsφis introduced with a potential energy density function V(φ) that is minimized at a value<φ>=0and the vacuum energy is degenerate.For example,the gauge invariant potential for an electrically charged scalarfieldφ=|φ|e iθ,V(|φ|2)=−µ2|φ|2+λ|φ|4,(3)√λ=v,but is independent of the phaseθ.Nature’s choice forθhas its minimum atspontaneously breaks the gauge symmetry.Quantum excitations of|φ|about its vacuum value are massive Higgs scalars:m2H=2µ2=2λv2.Quantum excitations around the vacuum value ofθcost no energy and are massless,spinless particles called Goldstone bosons.They appear in the physical spectrum as the longitudinally polarized spin states of gauge bosons that acquire masses through their couplings to the Higgsfield.A gauge boson mass m is determined by its coupling g to theHiggsfield and the vacuum value v.Since gauge couplings are universal this also determines the√Fermi constant G for this toy model:m=gv/2,G/2|φ|=212F=246GeV,leaving three Goldstone bosons that are eaten by three massive vector bosons:W±and Z=cosθw W0−sinθw B0,while the photonγ=cosθw B0+sinθw W0remains massless.This theory predicted neutrino-induced neutral current(NC)interactions of the typeν+atom→ν+anything,mediated by Z exchange.The weak mixing angleθw governs the dependence of NC couplings on fermion helicity and electric charge, and their interaction rates are determined by the Fermi constant G Z F.The ratioρ=G Z F/G F= m2W/m2Z cos2θw,predicted to be1,is the only measured parameter of the SM that probes thesymmetry breaking mechanism.Once the value ofθw was determined in neutrino experiments,the√W and Z masses could be predicted:m2W=m2Z cos2θw=sin2θwπα/QUARKS:S=1LEPTONS:S=13m3m Q=0m quanta mu1u2u3(2–8)10−3e 5.11×10−4c1c2c3 1.0–1.6µ0.10566t1t2t3173.8±5.0τ 1.77705/3g′,where g1isfixed by requiring the same normalization for all fermion currents.Their measured values at low energy satisfy g3>g2>g1.Like g3,the coupling g2decreases with increasing energy,but more slowly because there are fewer gauge bosons contributing.As in QED,the U(1)coupling increases with energy.Vacuum polarization effects calculated using the particle content of the SM show that the three coupling constants are very nearly equal at an energy scale around1016GeV,providing a tantalizing hint of a more highly symmetric theory,embedding the SM interactions into a single force.Particle masses also depend on energy;the b andτmasses become equal at a similar scale,suggesting a possibility of quark and lepton unification as different charge states of a singlefield.V.BRIEF SUMMARY OF THE STANDARD MODEL ELEMENTSThe SM contains the set of elementary particles shown in Table I.The forces operative in the particle domain are the strong(QCD)interaction responsive to particles carrying color,and the two pieces of the electroweak interaction responsive to particles carrying weak isospin and hypercharge. The quarks come in three experimentally indistinguishable colors and there are eight colored gluons. All quarks and leptons,and theγ,W and Z bosons,carry weak isospin.In the strict view of the SM,there are no right-handed neutrinos or left-handed anti-neutrinos.As a consequence the simple Higgs mechanism described in section IV cannot generate neutrino masses,which are posited to be zero.In addition,the SM provides the quark mixing matrix which gives the transformation from the basis of the strong interaction charge−1Finding the constituents of the SM spanned thefirst century of the APS,starting with the discovery by Thomson of the electron in1897.Pauli in1930postulated the existence of the neutrino as the agent of missing energy and angular momentum inβ-decay;only in1953was the neutrino found in experiments at reactors.The muon was unexpectedly added from cosmic ray searches for the Yukawa particle in1936;in1962its companion neutrino was found in the decays of the pion.The Eightfold Way classification of the hadrons in1961suggested the possible existence of the three lightest quarks(u,d and s),though their physical reality was then regarded as doubtful.The observation of substructure of the proton,and the1974observation of the J/ψmeson interpreted as a cp collider in1983was a dramatic confirmation of this theory.The gluon which mediates the color force QCD wasfirst demonstrated in the e+e−collider at DESY in Hamburg.The minimal version of the SM,with no right-handed neutrinos and the simplest possible ESB mechanism,has19arbitrary parameters:9fermion masses;3angles and one phase that specify the quark mixing matrix;3gauge coupling constants;2parameters to specify the Higgs potential; and an additional phaseθthat characterizes the QCD vacuum state.The number of parameters is larger if the ESB mechanism is more complicated or if there are right-handed neutrinos.Aside from constraints imposed by renormalizability,the spectrum of elementary particles is also arbitrary.As discussed in Section VII,this high degree of arbitrariness suggests that a more fundamental theory underlies the SM.VI.EXPERIMENTAL ESTABLISHMENT OF THE STANDARD MODELThe current picture of particles and interactions has been shaped and tested by three decades of experimental studies at laboratories around the world.We briefly summarize here some typical and landmark results.FIG.1.The proton structure function(F2)versus Q2atfixed x,measured with incident electrons or muons,showing scale invariance at larger x and substantial dependence on Q2as x becomes small.The data are taken from the HERA ep collider experiments H1and ZEUS,as well as the muon scattering experiments BCDMS and NMC at CERN and E665at FNAL.A.Establishing QCD1.Deep inelastic scatteringPioneering experiments at SLAC in the late1960’s directed high energy electrons on proton and nuclear targets.The deep inelastic scattering(DIS)process results in a deflected electron and a hadronic recoil system from the initial baryon.The scattering occurs through the exchange of a photon coupled to the electric charges of the participants.DIS experiments were the spiritual descendents of Rutherford’s scattering ofαparticles by gold atoms and,as with the earlier experi-ment,showed the existence of the target’s substructure.Lorentz and gauge invariance restrict the matrix element representing the hadronic part of the interaction to two terms,each multiplied by phenomenological form factors or structure functions.These in principle depend on the two inde-pendent kinematic variables;the momentum transfer carried by the photon(Q2)and energy loss by the electron(ν).The experiments showed that the structure functions were,to good approximation, independent of Q2forfixed values of x=Q2/2Mν.This‘scaling’result was interpreted as evi-dence that the proton contains sub-elements,originally called partons.The DIS scattering occurs as the elastic scatter of the beam electron with one of the partons.The original and subsequent experiments established that the struck partons carry the fractional electric charges and half-integer spins dictated by the quark model.Furthermore,the experiments demonstrated that three such partons(valence quarks)provide the nucleon with its quantum numbers.The variable x represents the fraction of the target nucleon’s momentum carried by the struck parton,viewed in a Lorentz frame where the proton is relativistic.The DIS experiments further showed that the charged partons (quarks)carry only about half of the proton momentum,giving indirect evidence for an electrically neutral partonic gluon.1011010101010FIG.2.The quark and gluon momentum densities in the proton versus x for Q 2=20GeV 2.The integrated values of each component density gives the fraction of the proton momentum carried by that component.The valence u and d quarks carry the quantum numbers of the proton.The large number of quarks at small x arise from a ‘sea’of quark-antiquark pairs.The quark densities are from a phenomenological fit (the CTEQ collaboration)to data from many sources;the gluon density bands are the one standard deviation bounds to QCD fits to ZEUS data (low x )and muon scattering data (higher x ).Further DIS investigations using electrons,muons,and neutrinos and a variety of targets refined this picture and demonstrated small but systematic nonscaling behavior.The structure functions were shown to vary more rapidly with Q 2as x decreases,in accord with the nascent QCD prediction that the fundamental strong coupling constant αS varies with Q 2,and that at short distance scales (high Q 2)the number of observable partons increases due to increasingly resolved quantum fluc-tuations.Figure 1shows sample modern results for the Q 2dependence of the dominant structure function,in excellent accord with QCD predictions.The structure function values at all x depend on the quark content;the increases at larger Q 2depend on both quark and gluon content.The data permit the mapping of the proton’s quark and gluon content exemplified in Fig.2.2.Quark and gluon jetsThe gluon was firmly predicted as the carrier of the color force.Though its presence had been inferred because only about half the proton momentum was found in charged constituents,direct observation of the gluon was essential.This came from experiments at the DESY e +e −collider (PETRA)in 1979.The collision forms an intermediate virtual photon state,which may subsequently decay into a pair of leptons or pair of quarks.The colored quarks cannot emerge intact from the collision region;instead they create many quark-antiquark pairs from the vacuum that arrange themselves into a set of colorless hadrons moving approximately in the directions of the original quarks.These sprays of roughly collinear particles,called jets,reflect the directions of the progenitor quarks.However,the quarks may radiate quanta of QCD (a gluon)prior to formation of the jets,just as electrons radiate photons.If at sufficiently large angle to be distinguished,the gluon radiation evolves into a separate jet.Evidence was found in the event energy-flow patterns for the ‘three-pronged’jet topologies expected for events containing a gluon.Experiments at higher energy e +e −colliders illustrate this gluon radiation even better,as shown in Fig.3.Studies in e +e −and hadron collisions have verified the expected QCD structure of the quark-gluon couplings,and their interference patterns.FIG.3.A three jet event from the OPAL experiment at LEP.The curving tracks from the three jets may be associated with the energy deposits in the surrounding calorimeter,shown here as histograms on the middle two circles,whose bin heights are proportional to energy.Jets1and2contain muons as indicated,suggesting that these are both quark jets(likely from b quarks).The lowest energy jet3is attributed to a radiated gluon.3.Strong coupling constantThe fundamental characteristic of QCD is asymptotic freedom,dictating that the coupling constant for color interactions decreases logarithmically as Q2increases.The couplingαS can be measured in a variety of strong interaction reactions at different Q2scales.At low Q2,processes like DIS,tau decays to hadrons,and the annihilation rate for e+e−into multi-hadronfinal states give accurate determinations ofαS.The decays of theΥinto three jets primarily involve gluons,and the rate for this decay givesαS(M2Υ).At higher Q2,studies of the W and Z bosons(for example,the decay width of the Z,or the fraction of W bosons associated with jets)measureαS at the100GeV scale. These and many other determinations have now solidified the experimental evidence thatαS does indeed‘run’with Q2as expected in QCD.Predictions forαS(Q2),relative to its value at some reference scale,can be made within perturbative QCD.The current information from many sources are compared with calculated values in Fig.4.4.Strong interaction scattering of partonsAt sufficiently large Q2whereαS is small,the QCD perturbation series converges sufficiently rapidly to permit accurate predictions.An important process probing the highest accessible Q2 scales is the scattering of two constituent partons(quarks or gluons)within colliding protons and antiprotons.Figure5shows the impressive data for the inclusive production of jets due to scattered partons in pp collisions reveals the structure of the scattering matrix element.These amplitudes are dominated by the exchange of the spin1gluon.If this scattering were identical to Rutherford scattering,the angular variable0.10.20.30.40.511010FIG.4.The dependence of the strong coupling constant,αS ,versus Q using data from DIS structure functions from e ,µ,and νbeam experiments as well as ep collider experiments,production rates of jets,heavy quark flavors,photons,and weak vector bosons in ep ,e +e −,and pt ,is sensitive not only to to perturbative processes,but reflectsadditional effects due to multiple gluon radiation from the scattering quarks.Within the limited statistics of current data samples,the top quark production cross section is also in good agreement with QCD.FIG.6.The dijet angular distribution from the DØexperiment plotted as a function ofχ(see text)for which Rutherford scattering would give dσ/dχ=constant.The predictions of NLO QCD(at scaleµ=E T/2)are shown by the curves.Λis the compositeness scale for quark/gluon substructure,withΛ=∞for no compositness(solid curve);the data rule out values of Λ<2TeV.5.Nonperturbative QCDMany physicists believe that QCD is a theory‘solved in principle’.The basic validity of QCD at large Q2where the coupling is small has been verified in many experimental studies,but the large coupling at low Q2makes calculation exceedingly difficult.This low Q2region of QCD is relevant to the wealth of experimental data on the static properties of nucleons,most hadronic interactions, hadronic weak decays,nucleon and nucleus structure,proton and neutron spin structure,and systems of hadronic matter with very high temperature and energy densities.The ability of theory to predict such phenomena has yet to match the experimental progress.Several techniques for dealing with nonperturbative QCD have been developed.The most suc-cessful address processes in which some energy or mass in the problem is large.An example is the confrontation of data on the rates of mesons containing heavy quarks(c or b)decaying into lighter hadrons,where the heavy quark can be treated nonrelativistically and its contribution to the matrix element is taken from experiment.With this phenomenological input,the ratios of calculated par-tial decay rates agree well with experiment.Calculations based on evaluation at discrete space-time points on a lattice and extrapolated to zero spacing have also had some success.With computing advances and new calculational algorithms,the lattice calculations are now advanced to the stage of calculating hadronic masses,the strong coupling constant,and decay widths to within roughly10–20%of the experimental values.The quark and gluon content of protons are consequences of QCD,much as the wave functions of electrons in atoms are consequences of electromagnetism.Such calculations require nonperturbative techniques.Measurements of the small-x proton structure functions at the HERA ep collider show a much larger increase of parton density with decreasing x than were extrapolated from larger x measurements.It was also found that a large fraction(∼10%)of such events contained afinal。

第二章夸克与轻子Quarks and leptons2.1 粒子园The particle zoo学习目标Learning objectives：我们怎样发现新粒子？能否预言新粒子？什么是奇异粒子？大纲参考：3.1.1￣太空入侵者宇宙射线是由包括太阳在内的恒星发射而在宇宙空间传播的高能粒子。

如果宇宙射线粒子进入地球大气层，就会产生寿命短暂的新粒子和反粒子以及光子。

所以，就有“太空入侵者”这种戏称。

发现宇宙射线之初，大多数物理学家都认为这种射线不是来自太空，而是来自地球本身的放射性物质。

当时物理学家兼业余气球旅行者维克托·赫斯（Victor Hess）就发现，在5000m高空处宇宙射线的离子效应要比地面显著得多，从而证明这种理论无法成立。

经过进一步研究，表明大多数宇宙射线都是高速运动的质子或较小原子核。

这类粒子与大气中气体原子发生碰撞，产生粒子和反粒子簇射，数量之大在地面都能探测到。

通过云室和其他探测仪，人类发现了寿命短暂的新粒子与其反粒子。

μ介子（muon）或“重电子”（符号μ）。

这是一种带负电的粒子，静止质量是电子的200多倍。

π介子（pion）。

这可以是一种带正电的粒子（π＋）、带负电的粒子（π－）或中性不带电粒子（π0），静止质量大于μ介子但小于质子。

K介子（kaon）。

这可以是一种带正电的粒子（K＋）、带负电的粒子（K－）或中性不带电粒子（K0），静止质量大于π介子但小于质子。

科学探索How Science Works不同寻常的预言An unusual prediction在发现上述三种粒子之前，日本物理学家汤川秀树（Hideki Yukawa）就预言，核子间的强核力存在交换粒子。

他认为交换粒子的作用范围不超过10－15m，并推断其质量在电子与质子之间。

由于这种离子的质量介于电子与质子之间，所以汤川就将这种粒子称为“介子”（mesons）。

一年后，卡尔·安德森拍摄的云室照片显示一条异常轨迹可能就是这类粒子所产生。