Epsilon'Epsilon in the Standard Model Theoretical Update

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a r X i v :h e p -p h /0410215v 1 14 O c t 2004ε′/εIN THE STANDARD MODEL:THEORETICAL UPDATEA.PICHDepartament de F´ısica Te`o rica,IFIC,Universitat de Val`e ncia–CSIC,E-46071Val`e ncia,Spain.E-mail:Antonio.Pich@ific.uv.esA complete analysis of isospin breaking in K →2πamplitudes,including both strong (m u =m d )andelectromagnetic corrections at next-to-leading order in chiral perturbation theory,has been achieved recently.1We discuss the implication of these effects,together with the previously knownchiral loop corrections,2on the direct CP-violating ratio ε′/ε.One finds Re (ε′/ε)= 19+11−9·10−4.1IntroductionThe CP–violating ratio ε′/εconstitutes afundamental test for our understanding of flavour–changing phenomena.The exper-imental status has been clarified by the KTEV,3Re (ε′/ε)=(20.7±2.8)·10−4,and NA48,4Re (ε′/ε)=(14.7±2.2)·10−4,mea-surements.The present world average,3,4,5,6Re (ε′/ε)=(16.7±1.6)·10−4,(1)demonstrates the existence of direct CP vio-lation in K decays.The CP violating signal is generated through the interference of two different K 0→ππdecay amplitudes,ε′√Re A 2−Im A 0√Below the resonance region one can use symmetry considerations to define another effectivefield theory in terms of the QCDGoldstone bosons.Chiral perturbation the-ory(χPT)describes13,14the pseudoscalar–octet dynamics,through a perturbative ex-pansion in powers of momenta and quarkmasses over the chiral symmetry breakingscaleΛχ∼1GeV.Chiral symmetryfixes the allowed operators.At lowest order,the mostgeneral effective bosonic Lagrangian with thesame SU(3)L⊗SU(3)R transformation prop-erties as L∆S=1effcontains three terms:L∆S=12=G8L8+G27L27+G ew L ew.(4) L ew gives the low–energy realization of Q8, while Q6is included in the octet term.L∆S=12determines the K→ππampli-tudes at O(p2).The calculation of the chi-ral couplings G i from the short–distance La-grangian(3)requires to perform the match-ing between the two effective theories.This can be done in the limit of an infinite num-ber of quark colours,because the four–quark operators factorize into currents which have well–known chiral realizations.This is equiv-alent to the standard large–N C evaluations of Q i .Therefore,up to minor variations on some input parameters,the correspond-ingε′/εprediction,obtained at lowest order in both the1/N C andχPT expansions,repro-duces the published results of the Munich11 and Rome12groups.3Chiral CorrectionsThe large–N C limit is only applied to the matching between the3–flavour quark the-ory andχPT.The evolution from the elec-troweak scale down toµ<m c has to be done without any unnecessary expansion in powers of1/N C;otherwise,one would miss large corrections of the form1M WW,Z,γ,gτ,µ,e,νit,b,c,s,d,uStandardModel<∼m cγ,g;µ,e,νis,d,u Ln f=3QCD,L∆S=1,2effM Kγ;µ,e,νiπ,K,ηχPT?OPEN C→∞Figure1.Evolution from M W to M K.16mic corrections,through chiral loops which are of higher order in both the momen-tum and1/N C expansions.2These next-to-leading contributions,which give rise to the large S–wave strong phasesδI(δI=0at N C→∞),were overlooked in thefirst large–N C predictions11,12giving a too smallε′/ε. Larger values ofε′/εwere in fact obtained within models containing some kind of pion rescattering.17TheχPT framework allows us to incorporate rigorously these corrections in a model independent way.The one–loopχPT analyses1,2,18of K→2πshow indeed that pion loops provide an important enhancement of the A0amplitude, associated with large infrared logarithms in-volving the light pion mass,and a sizeable reduction of A2.These chiral corrections de-stroy the numerical cancellation between the Q6and Q8contributions,generating a large enhancement of theε′/εprediction.2A complete one–loop calculation,includ-ing electromagnetic and isospin violation cor-rections,has been achieved recently.1The loop contributions are fully determined by chiral symmetry.The local corrections gen-erated by the different higher-order chiral la-grangians have been computed at leading or-der in the1/N C expansion.To account for isospin breaking,we can writeε′√Re A(0)0(1−Ωeff)−Im A emp200311(EURIDICE),MCYT(FPA-2001-3031)and Generalitat Valenciana(GRU-POS03/013and GV04B-594).References1.V.Cirigliano,G.Ecker,H.Neufeld andA.Pich,Eur.Phys.J.C33(2004)369;Phys.Rev.Lett.91(2003)162001.2.E.Pallante, A.Pich and I.Scimemi,Nucl.Phys.B617(2001)441;E.Pal-lante and A.Pich,Phys.Rev.Lett.84(2000)2568;Nucl.Phys.B592(2000)294.3.KTeV collab.,Phys.Rev.D67(2003)012005;Phys.Rev.Lett.83(1999)22.4.NA48collab.,Phys.Lett.B544(2002)97;Eur.Phys.J.C22(2001)231;Phys.Lett.B465(1999)335.5.NA31collab.,Phys.Lett.B206(1988)169;Phys.Lett.B317(1993)233.6.E731collab.,Phys.Rev.Lett.70(1993)1203.7.F.J.Gilman and M.B.Wise,Phys.Rev.D20(1979)2392;D21(1980)3150.8.A.J.Buras,hep-ph/9806471.9.A.J.Buras,M.Jamin and ut-enbacher,Nucl.Phys.B408(1993)209;Phys.Lett.B389(1996)749.10.M.Ciuchini et al.,Phys.Lett.B301(1993)263;Z.Phys.C68(1995)239. 11.S.Bosch et al.,Nucl.Phys.B565(2000)3;A.J.Buras et al.,Nucl.Phys.B592(2001)55; A.J.Buras and M.Jamin,JHEP01(2004)048.12.M.Ciuchini et al.,hep-ph/9910237.13.S.Weinberg,Physica96A(1979)327.14.J.Gasser and H.Leutwyler,Nucl.Phys.B250(1985)456;517;539.15.W.A.Bardeen, A.J.Buras and J.-M.G´e rard,Nucl.Phys.B293(1987)787;Phys.Lett.B192(1987)138,B180(1986)133.16.A.Pich,hep-ph/9806303.17.S.Bertolini et al.,Rev.Mod.Phys.72(2000)65;T.Hambye et al.,Nucl.Phys.B564(2000)391.18.J.Kambor et al.,Nucl.Phys.B346(1990)17;Phys.Lett.B261(1991) 496;Phys.Rev.Lett.68(1992)1818;J.Bijnens,E.Pallante and J.Prades, Nucl.Phys.B521(1998)305;E.Pal-lante,JHEP01(1999)012.19.V.Cirigliano,J.F.Donoghue,and E.Golowich,Eur.Phys.J.C18(2000)83.20.G.Ecker,G.M¨u ller,H.Neufeld andA.Pich,Phys.Lett.B477(2000)88.21.E.G´a miz et al.,JHEP01(2003)060;hep-ph/0408044;M.Jamin,J.A.Oller and A.Pich,Eur.Phys.J.C24(2002) 237;K.Maltman and J.Kambor,Phys.Rev.D65(2002)074013;S.M.Chen et al.,Eur.Phys.J.C22(2001)31;H.Wittig,hep-lat/0210025; C.Aubinet al.,Phys.Rev.D70(2004)031504;M.G¨o ckeler et al.,hep-lat/0409312. 22.V.Cirigliano et al.,Phys.Lett.B555(2003)71,B522(2001)245,B475 (2000)351;Phys.Rev.D65(2002) 054014;J.F.Donoghue and E.Golowich, Phys.Lett.B478(2000)172.23.M.Knecht,S.Peris and E.de Rafael,Phys.Lett.B508(2001)117,B457 (1999)227;S.Peris and E.de Rafael, Phys.Lett.B490(2000)213.24.S.Narison,Nucl.Phys.B593(2001)3.25.J.Bijnens et al.,hep-ph/0309216;JHEP10(2001)009,06(2000)035,01(1999) 023.26.J.I.Noaki et al.,Phys.Rev.D68(2003)014501;T.Blum et al.,Phys.Rev.D68 (2003)114506;D.Be´c irevi´c et al.,Nucl.Phys.B(Proc.Suppl.)119(2003)619.27.S.Peris,hep-ph/0310063;T.Hambye,S.Peris and E.de Rafael,JHEP05 (2003)027.28.M.Golterman and E.Pallante,Phys.Rev.D69(2004)074503;JHEP10 (2001)037,08(2001)023.29.T.Bhattacharya et al.,hep-lat/0409046;D.Pekurovsky and G.Kilcup,Phys.Rev.D64(2001)074502.。