a r X i v :0805.3720v 1 [h e p -p h ] 23 M a y 2008SMU-HEP-08-01,ANL-HEP-PR-08-21,NSF-KITP-08-56
Trilepton Production at the LHC —Standard Model Sources and
Beyond
Zack Sullivan
Southern Methodist University,Dallas,Texas 75275-0175,USA and
High Energy Physics Division,Argonne National Laboratory,Argonne,Illinois 60439,USA Edmond L.Berger High Energy Physics Division,Argonne National Laboratory,Argonne,Illinois 60439,USA (Dated:May 27,2008)Abstract Events with three or more isolated leptons in the ?nal state are known to be signatures of new physics phenomena at high energy collider physics facilities.Standard model sources of isolated trilepton ?nal states include gauge boson pair production such as W Z and W γ?,and t ˉt production.We demonstrate that leptons from heavy ?avor decays,such as b →lX and c →lX ,provide sources of trileptons that can be orders-of-magnitude larger after cuts than other standard model backgrounds to new physics processes.We explain the physical reason heavy ?avor backgrounds survive isolation cuts.We propose new cuts to control the backgrounds in the speci?c case of chargino plus neutralino pair production in supersymmetric models.After these cuts are imposed,we show that it should be possible to ?nd at least a 4σexcess for supersymmetry parameter space point LM9with 30fb ?1of integrated luminosity.PACS numbers:13.85.Qk,13.85.Rm,12.60.Jv
I.INTRODUCTION
Events with three or more isolated leptons in the?nal state have attracted signi?cant attention as possible signatures of new physics phenomena produced at high energy collider physics facilities such as the Fermilab Tevatron and the CERN Large Hadron Collider(LHC). To the extent that new physics at the scale of100GeV or more is related to electroweak symmetry breaking,new states predicted in beyond the standard model(BSM)schemes typically couple to the W±or Z0gauge bosons which,in turn,decay to leptons.
Supersymmetry(SUSY)is a well studied potential realization of physics beyond the standard model[1].Trilepton events have long been mentioned as potential golden discovery modes for SUSY processes in which a chargino χ+i and a neutralino χ0j are jointly produced. Isolated three lepton signatures arise from the decay modes χ+i→W?+ χ01→ˉlν χ01,along with χ0j→Z? χ01→lˉl χ01.In this example,the χ01is the lowest mass SUSY particle assumed to be e?ectively stable and therefore a source of missing energy;W?+and Z?stand for on-shell or virtual gauge bosons.This SUSY example provides a relatively clean source of isolated trilepton events[2,3].Within SUSY,one can also pair-produce heavy sparticles that carry color quantum number,such as gluinos and squarks.The cascade decays of these states,while parameter dependent,will generally result in trilepton?nal states along with hadronic jets[4].
Other BSM constructs,such as Higgsless models,extra-dimensional models,and models with extended gauge groups,predict states at high mass,such as Kaluza-Klein towers and extra gauge bosons,that decay to the more familiar W and Z electroweak gauge bosons.In one example of a Higgsless model,a massive W′is predicted with dominant decays into pairs of gauge bosons,such as W±Z,which is a source of isolated three lepton?nal states[5,6,7]. Our intent here is not to present a survey of BSM sources of multi-lepton events.We cite the cases mentioned as indicative of a range of possibilities.
In this paper we are concerned with obtaining as good an estimate as possible of the production of isolated three lepton?nal states that arise entirely from sources within the standard model(SM)itself.An obvious and important example is the associated production of a pair of gauge bosons,such as W Z,along with its generalizations Wγ?,whereγ?is a virtual photon that decays asγ?→lˉl.We?nd that the Wγ?contribution is much more signi?cant than is widely appreciated.Unlike W Z,the Wγ?contribution cannot be reduced
by an anti-selection of events in which the invariant mass of the lˉl system is in the vicinity of the Z0peak.
In this work,we use MadEvent[8]to compute the full matrix elements for partonic subprocesses that result in a lllν?nal state.For the W Z/γ?process,this method allows us to retain important angular correlations among the?nal leptons.Here Z/γ?stands for the full range of lˉl pairs resulting from a Z,a Drell-Yan virtual photon,and photon-Z interference.Our estimates are larger for this process than those one would obtain from a modeling of W Z alone from within PYTHIA[9],and we describe these di?erences.Inclusion of theγ?contribution accounts for part of these di?erences.Since W Z/γ?is an important standard model background in many searches for new physics,we suggest that events be generated by a matrix element program and be fed into the PYTHIA showering routines, rather than use of the W Z routine built into PYTHIA.
A major new contribution in this paper is the demonstration that isolated leptons from bottom and charm decays are a potent source of standard model backgrounds to new physics signatures in the three lepton?nal state.This study is an extension of our prior investi-gation[10]of SM heavy?avor backgrounds to the isolated two-lepton?nal state that is important in searches for the Higgs boson.In this new paper we compute contributions from a wide range of SM heavy?avor processes including bZ/γ?,cZ/γ?,bˉbZ/γ?,cˉc Z/γ?. We also include contributions from tˉt production,and from processes in which a W is pro-duced in association one of more heavy?avors such as tW,bˉbW,cˉc W.In all these cases, one or more of the?nal observed isolated leptons comes from a heavy?avor decay.The bˉbW and cˉc W contributions have not been examined previously.
To examine signal discrimination(and to compute signal to background ratios),we choose the speci?c case of chargino and neutralino pair production as the signal process.We focus on the SUSY parameter space points LM1,LM7,and LM9considered by the CMS Collaboration[11,12]and on the SU2point studied by the ATLAS Collaboration[13].These points are expected to have favorable SUSY cross sections at the LHC.The dominant nature of some of the SM backgrounds motivates the investigation of new selections(cuts)on the ?nal state kinematic distributions that would be e?ective in reducing the backgrounds.One of these cuts involves selections on the opening angles among the three charged leptons in the?nal state.The cuts are de?ned and their e?ectiveness is discussed in Secs.IV and V.
We begin in Sec.II with an explanation of the source and magnitude of isolated leptons
from heavy?avor production and decay.Issues important in our simulation of?nal states are discussed in Sec.III.We generate events using MadEvent,pass them through a PYTHIA showering Monte Carlo code,and?nally through a heavily modi?ed PGS detector simulation program.Our overall results and comparisons with studies done by the CMS and ATLAS groups are presented in Secs.IV and V.Our conclusions are summarized in Sec.VI.We show that it should be possible to?nd at least a4σexcess in30fb?1for SUSY point LM9.
II.ISOLATED LEPTONS FROM BOTTOM AND CHARM DECAYS
The use of leptons inside jets to tag bottom and charm jets has led to the recognition that strong isolation criteria are required to distinguish leptons from primary interactions from those caused by secondary decays.In Ref.[10]we demonstrate that the rate for secondary leptons to pass isolation cuts is surprisingly large—about1part in200.In this section we explain the reasons these leptons pass the isolation cuts at such a large rate.
The simplest case to understand is the production of muons from b quark decay.The branching fraction of various B hadrons(B d,B s,Λb,etc.)to muons is roughly9–14%. Observation of these leptons requires,however,that their charged tracks generally be above some transverse momentum threshold(see the Appendix for details of isolated lepton re-construction).In the dotted line of Fig.1we show the shape of the probability to produce a muon with p Tμ>10GeV versus the transverse momentum of an initial b quark.This curve is determined predominantly from the V?A matrix element decay of the B hadron into Dlν[9]and kinematics imposed by the muon momentum threshold.1The probability of producing a10GeV muon is small at low b transverse momentum,and it grows toward the branching fraction limit as the transverse energy of the b moves farther above threshold. This curve leads to the false impression that low-p T b quarks are unimportant.
There are two ways in which a muon can pass isolation cuts applied to detector data.The ?rst is if the other decay products of the B hadron are physically separated in pseudorapidity ηand/or radial angleφ.This separation accounts for no more than1/2of the isolated
GeV
GeV
(GeV)N o r m a l i z e d P r o b a b i l i t y 504540353025
201510FIG.1:Normalized probability for an existing b quark to produce an isolated muon with p T μ>10GeV (solid)vs.the b transverse momentum.This curve is a multiplicative combination of the probability of producing a muon with p T μ>10GeV (dotted)and the probability the muon will be isolated (dashed).The b production spectrum is not included.Muon isolation criteria are described in the Appendix.
rate.One could imagine rejecting secondary muons by increasing the area examined for accompanying radiation,but this technique reduces acceptance of primary muons and is of limited utility.Of more importance is the isolation energy cut.When muons come from low-p T b quarks,they must have taken most of the transverse momentum of the B hadron.This means there is not enough energy left in the other B decay products to fail the energy cuts for isolation.The net isolated muon probability is the multiplication of the probability for production and for passing isolation cuts.This probability is shown as the solid line of Fig.1,and it peaks fairly close to threshold.
There is little freedom to change the picture in Fig.1.An attempt could be made to lower the energy threshold beyond which events are rejected,but this cut is already nearly optimized for the acceptance of real muons.Hence,one might expect to reduce the rate of muons from higher-p T b decays,but there will not be much gain.One other handle might be to look for secondary vertices,but our tests indicate that virtually all muons that pass isolation point back at the primary vertex.A preliminary examination of CDF data [15]appears to con?rm this ?nding.
The physics behind ?nding an isolated electron from b quark decay is similar to that for ?nding a muon.Figure 2demonstrates the same probability for production of an electron.The probability of satisfying the isolation cuts is ?atter with respect to p T b than for the muon,because noise in the electromagnetic calorimeter requires less stringent cuts to maintain electron acceptance.It is possible to achieve some purity with a loss of acceptance,but we ?nd little di?erence in the net rate of leptons from heavy ?avors between the ATLAS reconstruction algorithm that we use [13]and less sophisticated algorithms.
GeV
GeV
(GeV)N o r m a l i z e d P r o b a b i l i t y 55
504540353025201510FIG.2:Normalized probability for an existing b quark to produce an isolated electron with p T e >10GeV (solid)vs.the b transverse momentum.This curve is a multiplicative combination of the probability of producing an electron with p T e >10GeV (dotted)and the probability the electron will be isolated (dashed).The b production spectrum is not included.Electron isolation criteria are described in the Appendix.
While physical limitations of the experimental apparatus control the acceptance of a lepton produced from a b decay,the overall rate of reconstructed leptons includes the e?ect the p T b production spectrum.With the exception of top-quark decay,the p T b spectrum tends to fall steeply.In Fig.3we display the net isolated lepton cross section as a function of p T b for b ˉb production.Despite the larger acceptance for isolated muons around p T b ～25GeV and isolated electrons with p T b ～30–50GeV,the peak production comes from b quarks around 20GeV.The position of this peak has a profound e?ect on the simulation of isolated leptons,because fully 1/2of the reconstructed muon rate comes from b quarks with
p T b <20GeV.A natural tendency is to ignore these lower energy b quarks based on the low probability of lepton production shown in the dotted lines of Figs.1and 2.The complete picture,however,demonstrates that these events are important and most di?cult to reject.
GeV
(GeV)(p b /G e V )50
45403530252015106
5
43
2
1
0FIG.3:Cross section for production of a muon or electron from b ˉb production and decay (solid),an isolated muon (dashed),or an isolated electron (dotted).
An examination of charm decay into isolated muons and electrons leads to essentially identical conclusions as bottom decay with one minor addition.In Fig.4we show the cross section for production of a muon or electron vs.p T c ,and their isolated rates.In practice,because of “fakes”(charged hadrons mistaken for electrons),the reconstructed rate for electrons is larger than expected from the decay of c to e times an isolation acceptance.A large number of charged pions can be produced in decays of D mesons.A reasonable fraction of these pions are reconstructed as electrons,and so the net rate for “isolated electrons”shown as the dot-dashed line is about 50%larger than expected.Electron reconstruction algorithms are constructed in order to balance this contamination of charged pions versus acceptance.The goal across detectors is typically a fake rate for pions from jets of 10?4(compared to the rate of leptons we ?nd of a few times 10?3from b and c decays)[11,13].Depending of the physics study,it may be worth including the decays from heavy quarks as a part of the design of electron isolation algorithms.For the case of trileptons we examine here,the leptons from heavy quarks dominate the backgrounds.
We conclude this section by noting that Figs.3and 4indicate the expected rate of isolated
Tot.“”GeV
(GeV)(
p b /G e V )50
454035302520151010
8
64
2
0FIG.4:Cross section for production of a muon or electron from c ˉc production and decay (solid),an isolated muon (dashed),an electron which is then isolated (dotted),or “isolated electron”including fakes (dash-dot).
electrons from processes containing b and c quarks can be signi?cantly larger than the rate for isolated muons.Consequently,new physics processes with muons should have a higher purity than those with electrons.One general strategy would be to look for signals with an excess that is more apparent in muon channels than electron channels.A second observation is that looser cuts cause the typical transverse momentum of surviving isolated electrons to be slightly higher than that for muons.This recognition suggests that electron events will be more suppressed than muon events by cuts on maximum lepton energy,e.g.,the Z -peak cut used below.This lepton ?avor dependence may allow an additional handle on in-situ calibration of background sources.
III.SIMULATION
The backgrounds we discuss tend to arise from the tails or end points of physical pro-cesses and challenge detector capabilities.To achieve a believable and detailed simulation of reconstructed events,we follow the methods developed and validated in Ref.[10],with some modi?cations for e?cient production and analysis of the results.
We generate events with a customized2version of MadEvent3.0[8]and run them through the PYTHIA6.327[9]showering Monte Carlo.Both programs use the CTEQ6L1parton distribution functions[16]evaluated via an e?cient evolution code[17].The showered events are fed through a version of the PGS3.2[18]fast detector simulation,modi?ed to match ATLAS geometries,e?ciencies,and detailed reconstruction procedures[13].We con?rm that our results agree with full ATLAS detector simulations at both the reconstructed object (leptons,jets,/E T)and analysis levels to better than10%(and in some cases better than 1%).
For this paper we use the ATLAS muon and electron reconstruction procedure(described in the Appendix)and detector e?ciencies to produce initial candidate leptons for both CMS and ATLAS studies.We then apply the CMS or ATLAS geometric acceptance,transverse momentum threshold,and analysis cuts in order to compare to their to their respective studies.We reproduce the results of the published CMS analysis to better than1%in most cases.As we expect from Sec.II,and as observed in Ref.[10],we?nd that since the detectors have been optimized for the same lepton acceptance and lepton fake rate from jets,the lepton rate from heavy-?avor decays is insensitive to details of the detector reconstruction.
In Sec.II we explain the physics reasons for simulating low-p T b and c quarks.In Ref.
[10]we determined that at least1000samples of phase space are required to reproduce the interesting angular correlations in phase space for these types of events.As missing energy plays an important role in these signals,we cannot just multiply the spectrum of produced quarks by an average lepton isolation acceptance.Instead,we iterate over each point in phase space between104and5×105times,ensuring we produce at least10events that pass a minimal set of cuts.This number is su?cient if there are two b or c quarks that are needed to produce leptons.
Simulating any cross section that requires3or more heavy quarks to produce leptons (bbbb,cccc,bbcc)would require at least1000times the number of events we simulate.Hence, we can provide only an order-of-magnitude estimate of the e?ect of these four-heavy-?avor processes in Sec.IV.
Several technical hurdles have to be overcome to achieve the statistically signi?cant and systematically controlled results shown in Secs.IV and V.We have already described our
method of iterating multiple times over the same phase space points to give showering an opportunity to generate isolated leptons.Even though the detector simulation is techni-cally a“fast”detector simulation,over10billion events were required to produce su?cient statistics to describe the heavy?avor decays to isolated leptons throughout their available phase space.This computation was carried out with2CPU years of time on the Argonne Laboratory Computing Resource Center JAZZ cluster,a Pentium Xeon Linux cluster with 350compute nodes.The large number of events raises a practical issue regarding the total amount of data generated.Because of the time involved in generation,and our desire to an-alyze both angular correlations and di?erent cuts for CMS and ATLAS,we must store event information.Standard PYTHIA,STDHEP,or compressed data structures for this analysis would require more than100TB of storage,a simply impractical requirement.Therefore, we write only events that produce at least3isolated leptons(see the Appendix for the def-inition of isolation),and store the four-vectors of the leptons,leading jet(for vetoes),and missing transverse energy.This is the minimal necessary information to analyze the data presented below.
https://www.doczj.com/doc/bc3483532.html,PARISON TO CMS
In their technical design report(TDR)[12],the CMS Collaboration de?nes several several sets of minimal supergravity(mSUGRA)parameters that have sensitivity to di?erent aspects of SUSY.The points LM1,LM7,and LM9are the only subset of the9points examined that exhibit a large trilepton signature from χ02 χ±1decay.These points assume A0=0,μ>0, and(m0,m1/2,tanβ)are(60,250,10),(3000,230,10),and(1450,175,50)for LM1,LM7, and LM9,respectively.The reach for discovery of χ02 χ±1decays to trileptons is summarized in the TDR,but we follow the more detailed account from Ref.[19]below.
The basic CMS analysis looks for3isolated leptons,with p Tμ>10GeV,p T e>17GeV, and|ηl|<2.4(see the Appendix for the method of isolation).Events that contain jets with E T j>30GeV are vetoed in order to reduce the contribution from processes such as tˉt production and more complex SUSY processes involving cascade decays of massive SUSY states.Since real Z decays dominate the usual standard model backgrounds,events are removed in which the invariant mass of the opposite-sign same-?avor(OSSF)leptons is more than75GeV.CMS then performs a neural net analysis with7variables to suppress the
backgrounds from SM production of Z+jets and virtual photon+jets(called Drell Yan in their terminology)to achieve a signal to background ratio S/B of1/3.There are not enough details or referenced notes regarding the neural net for us to reproduce the results,but we can con?rm agreement for the backgrounds considered.However,the new backgrounds calculated here far outweigh the ones studied by CMS.As all of our estimated backgrounds are larger than those determined by CMS,we explain in detail where our simulations agree and where and why they di?er.
There are three overriding observations to keep in mind.First,each signi?cant back-ground involving leptons from heavy?avor decays,not estimated by CMS,is more than10 times larger than the largest background considered by CMS.Second,as explained below, our?rst benchmark process,W Z includes additional physics that enhances this background. Third,the ISASUGRA7.69evolution code used by CMS for the supersymmetric spectrum gives mass di?erences and branching fractions incompatible with the more recent version employed in our work.Nevertheless,we?nd good agreement with the CMS results when we consider only their backgrounds and use their assumptions.Therefore,we are con?dent that the simulation improvements discussed below are valid and will be useful for future studies.
A.W Z,tˉt,and W t?nal states
In order to maintain consistency across processes considered,we elect to present results using leading-order cross sections rather than introducing next-to-leading order(NLO)K factors.While NLO calculations exist for most of these processes[21],there is considerable overlap at NLO between?nal states,e.g.,bZ and bˉbZ.Furthermore,the jet veto will reject some of the higher order radiation that enhances the cross sections.Proper matching between orders is beyond the scope of this paper.
Since our goal is to establish a direct connection with the CMS analysis,we?rst con?rm that our detector simulation reproduces the CMS detector simulation for reconstructed leptons.Performing a PYTHIA-based calculation of W Z,minus decays to taus,and using the CMS K-factor of2,we predict171events after cuts in30fb?1vs.173events in Table6 of the CMS analysis[19].Any di?erences in lepton reconstruction enter3times;hence, this comparison shows that our detector simulation agrees exceedingly well with the CMS detector simulation.
The PYTHIA code used by CMS for W Z production omits virtual photon γ?production and interference with the Z .Given that the Z peak will be removed by cuts,we ?nd that the additional contribution from W plus a virtual photon is at least as important.This result agrees with other work [3,20]in which the importance of the virtual photons is emphasized.In all of our simulations we include the virtual photon continuum and photon-Z interference along with the Z .In the case of the SM W Z contribution,we denote the full contribution from W Z ,W γ?,and W +Z,γ?interference by W Z/γ.In Figs.5–7we show the transverse momentum distribution of the p T -ordered leptons from W Z/γcompared with the distributions from W Z alone.The peak at 20GeV in Fig.5is produced by the minimum p T cuts on the individual leptons that make up the virtual photon contribution.Essentially all of the leptons from o?-shell photons combine survive the Z -peak mass cut.When there are 3muons or 3electrons,both OSSF pairings pass the cuts.Hence,about 1/2of the virtual photon events appear twice when counting events.
(GeV)(f b /G e V )120
1008060402000.45
0.40
0.35
0.300.25
0.20
0.15
0.10
0.05
0.00FIG.5:Transverse momentum (p T )distribution of the leading-p T lepton in W Z/γcompared with W Z .
Table I compares the LO W Z/γcross section with a virtual photon included to a CMS-like NLO W Z estimate using PYTHIA.Given that a K -factor of 2is used in the CMS estimate,there is a full factor of 6di?erence between W Z built into PYTHIA,and W Z/γgenerated by MadEvent and showered by PYTHIA.Nearly 1/2of the excess is attributable to the virtual photon that is not included in PYTHIA.Some of the excess comes from
(GeV)(f b /G e V )80
7060504030201000.60
0.55
0.50
0.45
0.400.350.30
0.25
0.20
0.15
0.10
0.05
0.00FIG.6:Transverse momentum (p T )distribution of the second leading-p T lepton in W Z/γcom-pared with W Z .
(GeV)
(f b /G e V )504540353025201510501.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0FIG.7:Transverse momentum (p T )distribution of the lowest-p T lepton in W Z/γcompared with W Z .
correlations captured by the full matrix element that are sensitive to the cuts.In particular,angular correlations among the ?nal-state leptons are missing from the CMS study.In order to study these correlations,and to quote a more realistic background,we use the full matrix element for W Z/γ→lllνfrom MadEvent showered through PYTHIA in our results below.
TABLE I:Comparison of two backgrounds calculated by CMS and by this study.W Z/γand tˉt are our estimates.W Z PYT is calculated from PYTHIA and normalized to the CMS NLO total cross section.tˉt CMS j uses the CMS acceptance for the jet veto,based on a matched calculation that produces signi?cantly more radiation than a leading order calculation.The second column shows the number of events expected with30fb?1of integrated luminosity after the requirements that there be3leptons and no jets with E T j>30GeV.In the third column an additional requirement is imposed that the invariant mass of any pair of OSSF leptons be no greater than75GeV.
N l=3,
Channel no jets M OSSF
<75GeV
ll
661171
W Z NLO
PYT
tˉt CMS j394208
The remaining increase in the normalization of the cross section is connected with the requirement that there be no jets with E T>30GeV.We compare W Z→lllνevents generated with MadEvent and showered with PYTHIA to W Z events which are generated, decayed,and showered all within PYTHIA.In the process we observe that the initial-state QCD radiation spectrum is harder in the all-PYTHIA events.The jet veto rejects a larger fraction of this pure electroweak process assuming PYTHIA generation,and hence leads to a smaller normalization of the cross section after cuts.This e?ect is consistent across all processes we calculate,and hence leads to an overall uncertainty in the absolute cross section.Our main concern in this paper is to understand the relative importance of the various backgrounds,and their shapes.When data are in hand,we expect the total background to be normalized to data.Because most of the processes we evaluate are not in PYTHIA,we perform and demonstrate the cross sections for MadEvent generated events, and discuss the e?ect of normalization on a discovery signal at the end.
CMS also quotes their estimated background from tˉt production.It is important to compare with their result because this background requires one lepton from a b decay.The CMS analysis uses a matched[22]tˉt cross section which produces more jets in the?nal state than our LO calculation.Hence,CMS has a higher rejection rate based on their jet veto.If
we rescale our result using the e?ciency of their jet veto instead of ours,we?nd208events in 30fb?1vs.239events in the CMS paper.We?nd excellent agreement between our estimate of a background with a lepton from a b and the CMS estimate.A similar rescaling for W t would give us37events vs.45in the CMS paper.Our systematic10%underestimate of the e?ect of isolated leptons from b decay in the tˉt sample suggests our other results involving leptons from heavy?avor decays are conservative.The comparison between our calculation of tˉt and the jet-acceptance reduced version are summarized in Table I.
B.Heavy?avor?nal states
Before addressing the importance of leptons from heavy-?avor decays,we comment on one subtlety in the supersymmetric models studied.The243events we?nd for SUSY point LM9are similar to the238events expected by CMS.However,we predict123events vs. 91for point LM7,and44events vs.70events for LM1.The di?erences are attributable to the use of ISASUGRA7.75in our study vs.ISASUGRA7.69by CMS3.There was a small bug in the evolution codes in ISASUGRA7.69that,when corrected,leads to10GeV shifts in the neutralino mass spectrum.The Z mass peak cut is sensitive to the endpoint of the lepton spectrum,M max
=
ll
3We are unable to use ISASUGRA7.69due to a change in data format.
TABLE II:Leading order signal and background statistics for several?nal states in a CMS-like analysis,and with two additional cuts.The second column shows the number of events expected with30fb?1of integrated luminosity after the requirements that there be3isolated leptons and no jets with E T j>30GeV.In the third column an additional requirement is imposed that the invariant mass of any pair of OSSF leptons be no greater than75GeV.The virtual photon components are large after cuts.
N l=3Angular
Channel no jets M OSSF
<75GeV/E T>30GeV cuts
ll
W Z/γ1880538325302
tˉt1540814696672
tW273146123121
tˉb1.11.00.770.73
bZ/γ140006870270177
cZ/γ345014004535
bˉbZ/γ89902220119103
cˉc Z/γ468018306935
bˉbW9.17.65.65.3
cˉc W0.190.150.120.11 Addressing the contributions of Z/γplus heavy?avors and W plus heavy?avors,we see in Table II that,before the Z peak cut,Z/γplus heavy?avors produces trileptons16 times more often than W Z/γ.After the Z peak cut,the ratio rises to23times W Z/γ.In particular,bˉbZ/γ,which includes a virtual photon,is over30times the CMS estimate of the cross section that does not have a photon.In Figs.8–10,we see the opposite-sign same ?avor(OSSF)dilepton invariant mass for the signals,W Z/γbackground,and(bZ/γ)/5. Cutting out the Z mass peak reduces the backgrounds,but the remaining tail for Z/γplus heavy?avors overwhelms the signal.
The number of handles available to reject the huge background from Z/γ+heavy?avors
()/5(SUSY LM1)
cut
peak (GeV)(f b /G e V )120
1008060402000.8
0.6
0.4
0.20.0FIG.8:Invariant mass of the opposite-sign same-?avor (OSSF)lepton pairs for the SUSY LM1signal (×10,dotted),the W Z/γbackground (dashed),and the bZ/γbackground (divided by 5,solid).Other Z/γ+heavy ?avor backgrounds (not shown)have the same shape as bZ/γ.is limited.In Ref.[10]we recommend raising the minimum lepton p T threshold since the lepton p T spectrum from b and c decays tends to fall rapidly.In typical trilepton studies,however,the leptons are very soft.Hence,any increase in the cut on the lepton p T tends to reject too much of the signal.
Missing transverse energy /E T is a partial discriminator.The SUSY signals contain invis-ible neutralinos which leave a broad range of /E T in the detector.In Fig.11we show the /E T spectrum for the SUSY LM9signal and for the W Z/γand bZ/γbackgrounds.Trilepton
signatures from t ˉt
production generally have two neutrinos which lead to large missing en-ergy.The contribution from Z/γ+heavy ?avor processes peaks at over 400times the size of the LM9signal at low /E T ,but it falls rapidly to below the signal by /E T >50GeV.These di?erences present both opportunities and challenges,especially since the precision of /E T measurements is not as great as one might prefer.
In the fourth column of Table II,we show that the requirement /E T >30GeV removes most of the Z/γ+heavy ?avor backgrounds 4for a modest loss of signal.A cut below 20
()/5(SUSY LM7)
cut
peak (GeV)(f b /G e V )120
1008060402000.8
0.6
0.4
0.20.0FIG.9:Invariant mass of the opposite-sign same-?avor (OSSF)lepton pairs for the SUSY LM7signal (×2,dotted),the W Z/γbackground (dashed),and the bZ/γbackground (divided by 5,solid).Other Z/γ+heavy ?avor backgrounds (not shown)have the same shape as bZ/γ.
GeV is not as useful and is likely not achievable at the LHC.A cut above 40GeV removes most of the Z/γ+X backgrounds,but it begins to signi?cantly reduce the signal and is of
little additional help with W Z/γand t ˉt backgrounds.The sharply falling /E T spectrum in
Z/γ+X is extremely sensitive to uncertainties in the measurement of /E T .This uncertainty makes it di?cult to predict absolute cross sections after cuts.On the other hand,this sensitivity could provide an excellent opportunity to measure the background in situ and reduce concerns regarding modeling details.The background can be ?t in the data and the /E T cut adjusted to optimize the purity of the sample.
Since the accuracy of /E T measurements is limited,we examine instead the utility of angular cuts without a /E T cut.There are signi?cant angular correlations in the Z/γ+heavy ?avor backgrounds that are di?erent from those in the SUSY trilepton signals or the W Z/γ
and t ˉt
backgrounds.In Figs.12–14we plot the angular distribution between pairs of p T -ordered leptons in the trilepton center-of-momentum (CM)frame without a /E T cut.The Z/γ+heavy ?avor backgrounds have signi?cant peaks at both small and large angles.The
signal and other backgrounds either peak only at large angles (θCM 12,θCM 13),or are fairly
central (θCM 23).
We examine the impact of these angular correlations by themselves by imposing three
()/5SUSY LM9
cut
peak (GeV)(f b /G e V )120
1008060402000.8
0.6
0.4
0.20.0FIG.10:Invariant mass of the opposite-sign same-?avor (OSSF)lepton pairs for the SUSY LM9signal (dotted),the W Z/γbackground (dashed),and the bZ/γbackground (divided by 5,solid).Other Z/γ+heavy ?avor backgrounds (not shown)have the same shape as bZ/γ.
angular cuts in the trilepton center-of-momentum frame:θCM 12>45?,θCM 13>40?,and
θCM 23<160?.These angle cuts reduce the heavy ?avor backgrounds and W Z/γby ～30%,with only a 5%reduction of the signal.These cuts could be further optimized,but in general they are more useful for increasing purity than for increasing signi?cance.
Figures 15–17show the angular distributions between pairs of p T -ordered leptons in the trilepton CM frame after the missing transverse energy cut.The last column of Table II demonstrates the e?ect of adding the three angular cuts after the /E T cut.There is almost no correlation between the e?ects of the angle cuts and the missing transverse energy cut except in bZ/γ,where the cut is slightly more e?ective after the /E T cut (acceptance is 0.32vs.0.37).The real advantage of angular cuts over a /E T cut is that the angles are well measured.Whether or not missing transverse energy can be well-measured,the use of the angular cuts will improve any ?nal analysis.
One class of backgrounds not treated so far is one in which all three leptons come from heavy ?avor production (b ˉbb ˉb ,c ˉc c ˉc ,b ˉbc ˉc ).As mentioned in Sec.III,practical limitations prevent us from simulating this background directly.Instead we provide a rough estimates for the trilepton signature from three sources of b ˉbb ˉb production.First,using W b ˉb production,we obtain an estimate for the probability of ?nding an isolated lepton at the LHC of 7.5×10?3
SUSY LM9
(GeV)(f b /G e V )100
8060402000.8
0.6
0.4
0.2
0.0FIG.11:Missing transverse energy spectrum /E T of the opposite-sign same-?avor (OSSF)lepton
pairs for the SUSY LM9signal (dotted),the W Z/γbackground (dashed),t ˉt
(dot-dashed),and bZ/γ(solid).Other Z +heavy ?avor backgrounds (not shown)have the same shape as bZ/γ.
per b .The cross section for direct production of b ˉbb ˉb from MadEvent multiplied by (7.5×
10?3)3gives about 500trilepton events in 30fb ?1of data.Second,multiple interactions per beam crossing,where more than one b ˉb pair is produced,can lead to a trilepton signature.For a total inelastic cross section of about 80mb [12],the rate for two scatters to give three isolated leptons is about 60events per interaction per 30fb ?1.5At 10interactions per crossing,this method leads to about 600events,though the jet veto will likely reduce this ?gure somewhat.
Multiple scattering in a given interaction (e.g.,double parton scattering),or even show-ering of heavy quarks,is a third source,arising from successive production of b ˉb pairs.The rate may be comparable to direct 4-b production after cuts on transverse momentum [23],and it can double the backgrounds listed so far.These rough estimates are the same order of magnitude as the number of events from Z/γ+heavy ?avor processes,and they are a po-tentially serious problem with the default analysis.A sum over all production processes and decays to both muons and electrons would increase these numbers by an order of magnitude.On the other hand,in Ref.[10]we observe that a missing energy cut serves to signi?cantly
小学三年级英语:知识点归纳知识归纳是一个不错的学习计划，把知识归纳总结可以帮助自己更方便学习提高效率，减少许多不必要的时间。下面就一起来看看归纳的知识点吧！希望同学们可以学习一下！ 一、单词 Unit1学习文具：pen（钢笔）pencil（铅笔）pencil-case（铅笔盒）ruler （尺子）eraser（橡皮）crayon（蜡笔）book（书）bag（书包）sharpener （卷笔刀）school（学校） Unit2身体部位：head（头）face（脸）nose（鼻子）mouth（嘴）eye （眼睛）leg（腿）ear（耳朵）arm（胳膊）finger（手指）leg（腿）foot（脚）body（身体） Unit3颜色：red（红色的）yellow（黄色的）green（绿色的）blue （蓝色的）purple（紫色的）white（白色的）black（黑色的）orange （橙色的）pink（粉色的）brown（棕色的） Unit4动物：cat（猫）dog（狗）monkey（猴子）panda（熊猫）rabbit（兔子）duck（鸭子）pig（猪）bird（鸟）bear（熊）elephant （大象）mouse（老鼠）squirrel（松鼠） Unit5食物：cake（蛋糕）bread（面包）hotdog（热狗）hamburger （汉堡包）chicken（鸡肉）Frenchfries（炸薯条）coke（可乐）juice（果汁）milk（牛奶）water（水）tea（茶）coffee（咖啡）
Unit6数字：one（一）two（二）three（三）four（四）five（五）six（六）seven（七）eight（八）nine（九）ten（十）doll（玩具娃娃）boat（小船）ball（球）kite（风筝）balloon（气球）car （小汽车）plane（飞机） 二。对话、 1、向别人问好应该说——A：Hello！（你好！） B：Hi！（你好！） 2、问别人的名字应该说-——A：What‘syourname？你的名字是什么？ B：Myname‘sChenJie.我的名字是陈洁。 3、跟别人分手应该说——A：Bye.\Goodbye！（再见） B：Seeyou.（再见）\Goodbye.（再见） 4、A：Ihaveapencil\bag\ruler我有一只铅笔\书包\尺子。 B：Metoo.我也有。 5、早上相见应该说-——A：Goodmorning.早上好！ B：Goodmorning！早上好！ 6、下午相见应该说——A：Goodafternoon！下午好！ B：Goodafternoon！下午好！ 7、跟新朋友第一次见面——A：Nicetomeetyou！见到你很高兴。 B：Nicetomeetyou，too！见到你也很高兴！ 8、A：Let‘sgotoschool！让我们一起去上学！ B：OK！好的。
小学语文阅读理解专项练习题 1、种辣椒 常识课上，老师对植物的讲解，把我带到植物世界里。听完课，我动了心，决心种点什么，仔细观察它的生长过程。 回到家，我找到了两个花盆，满心欢喜地种下了辣椒籽。下种后，我每天都要给它浇些水，盼望种子早些发芽。一天中午，弟弟告诉我花盆里出小苗了，我飞一样地跑到窗台前，只见一棵小嫩芽拱出土，又过了两天，好几棵小芽出来了。小芽越来越多，我给小辣椒间苗，把太密的小苗小心翼翼地拔掉了一些。 到了盛夏，每株辣椒已有半尺多高了，它们的茎上都缀满了欲放的花苞，几天后，一朵朵雪白的小花，先后开放了。大约又过了四五天，辣椒就开始结果了，出现了青绿的椭圆形的小辣椒，一个个缀在茎上，真惹人喜爱。 秋风吹进窗来，带进一股香气，辣椒开始由青变红，看上去更让人喜爱。一个个两寸多长的小辣椒挂在枝头对我微笑，感谢我对它们的辛勤培育。收获的时节到了，我满怀欣喜地把成熟的辣椒一个一个摘下，竟收了小半筐。 我看着筐里的辣椒，心想：这多有意思呀！知识来源于实践，而实践又必须付出辛勤的劳动，这难道不是真理吗？ 1．找出文章中点明中心的句子，在下面画横线。 2．把文章分成三段，在段尾用“‖”表示，并写出段意。 3．读下面句子，在括号里写出各运用了什么修辞手法。 ①小辣椒挂在枝头对我微笑，感谢我对它们的辛勤培育。（） ②我飞一样地跑到窗台前。（） 2、蒙蒙的小雨 蒙蒙的小雨正落着，陈红骑着自行车悠然于柏油路上。她没有穿雨衣，因为她觉得在这样细雨中骑车很浪漫。她望着路两边来去匆匆的行人，心想：这些人真是的，干嘛要东躲西藏的。 忽然迎面一辆的士飞驰而来她猛地拐向路边但车把挂在树干上她摔倒了小妹妹没事吧一个小伙子站在她身边问道陈红白了他一眼，没有理他。心想：谁是你的小妹妹？她一翻身想站起来，可左腿的剧痛却使她不得不重新坐在地上，她接连两次试图站起来，都没成功。最后，只好放弃了努力。小伙子一笑，“别逞强了，还是送你上医院吧。”接着，拉起陈红的车子，又扶陈红坐到车架上，推起车子向医院走去。温柔如丝的春雨淅淅沥沥地落着。陈红已不再潇洒，只感到沉重。她坐在车上，望着前面推车的小伙子，不知该说些什么。 她发现小伙子走路不太自然，仔细观察，只见小伙子左腿的袜端与裤腿之间不时地露出一段刺目的棕色。那是什么？啊，他装着一只假腿。陈红想问问他的腿，却不愿张嘴。这时，只听到小伙子自言自语地说：“三年前，我也喜欢在细雨中骑车，那的确很潇洒，可是我却重重地跌倒了，像你一样。不，还不如你。”“噢，你的左腿——？”停了一会儿，小伙子说：“就在那次跌倒时被后面的汽车轧断了。”听了这话，陈红陷入了沉思?? 医院到了，小伙子搀着陈红进了急诊室。“我去通知你父母，你知道他们的电话吗？”陈红把号码告诉了他。不一会儿，陈红的父母风风火火地赶来了。见到女儿腿上雪白的绷带，忙问这问那。陈红把经过告诉了他们，又说，“要不是那位大哥哥，我真不知该怎么办好，哎，他呢？”这时，只听护土小姐说：“那个小伙子，看见你爸妈来后，他就离开医院了。”陈红怔住了：“我还不知他叫什么呢！” 父亲背起陈红，母亲在旁边扶着，一家人走出医院的时候，他们多么希望在人流中再次寻到那小伙子的身影。 1．给第二自然段中没有标点的地方加上标点。 2．联系上下文解释加粗词的意思。
三年级上册英语知识点归纳 一、26个字母手写体： 二、英语中有五个元音字母，分别是：Aa、Ee、Ii、Oo、Uu.其它21个都是辅音字母。以元音开头的名词，表示有一个的时候，在前面加an,例如：an eye一只眼睛,an ear一只耳朵。 以辅音开头的名词，表示有一个的时候，在前面加a, 例如：a dog一只狗，a hand一只手。 三、通常情况下，单个的单词书写时要小写，例如：good 好的。也有部分单词书写时第一个字母要大写，比如人名、地点等单词书写时，第一个字母要大写。例如：Ms 女士,Aki阿基,Beijing北京等。也有单词不管什么时候都要大写，例如：OK好的，里面的2个字母都要大写。
四、我们要知道下面的词的原形及缩写形式： 1）I’m=I am 我是2）name’s=name is 名字是3）what’s=what is 是什么4)let’s=let us让我们 5)that’s=that is 那是6)he’s=he is他是 7)she’s=she is 她是8)who’s=who is是谁 9)don’t=do not不10)isn’t=is not不是 五、单词归类： 1）时间：morning早上,afternoon下午,evening傍晚,night晚上2）家庭成员：mum妈妈,dad爸爸,grandma奶奶, grandpa爷爷,father父亲,mother母亲, sister姐妹,brother兄弟,aunt阿姨,uncle叔叔3）身体部位：face脸,eye眼睛（单数）,eyes眼睛（复数）, hand手,hands手（复数）,hair头发, nose鼻子,ear耳朵,ears耳朵（复数）,foot脚, feet脚（复数）,head头,mouth嘴巴,leg腿, legs腿（复数）,tooth牙齿,teeth牙齿（复数）4）形容词：good好的,fine好的,nice好的,new新的, pretty漂亮的,old老的,cute可爱的,thin瘦的, strong强壮的,young年轻的,tall高的,tidy正确的5）学习用品：ruler尺子,pencil铅笔,bag书包、袋子, pen钢笔,book书,rubber橡皮，box盒子
阅读理解练习题大全 飞人——刘翔 小时候的刘翔是个顽皮的男孩，“胆子大”是很多人对他的评价。正是因为看到他比别的孩子更顽皮，家长才把他送到少年体校。体校的道路走得并不很顺利，他几乎决定放弃，但一件事情改变了年少的刘翔的决定。 他七八岁的时候，他的爷爷已经70岁了，此前老人家是不会骑自行车的，但70岁那年突然就想学，而且学会了，老人说自己学会了去哪儿都方便。刘翔就想，爷爷70岁都能学会骑自行车，自己为什么要放弃呢？现在回想起来，刘翔还在感叹，如果没有爷爷这个行动的刺激，也许就没有现在的他了。 开始的时候，刘翔练的是跳高，他很自信地说：“如果我的身高能够达到两米，我在跳高项目上将会很有作为。”他当时已经拿过上海市少年跳高冠军了，的确是一个很不错的跳高人才。但是就是那一年，他现在的跨栏教练孙海平看上他了。用孙海平的话说，跨栏选手需要胆量，很多人看到1米多高的栏横在眼前就不敢过，而刘翔有这样的胆量，再就是从他练跳高看，他的速度和爆发力很好。 2000年11月，法国里昂的一次室内田径大奖赛，6名选手进入60米栏的决赛，刘翔站在第五道，其中有3个美国选手，他旁边的第六道也是一名美国选手。发令枪响过了，没想到第六道的那个美国选手在跨第二个栏的时候就摔倒了，刘翔则是第三个冲过终点，这样的兴奋仅保存了2秒钟，裁判和大屏幕宣布：第五道中国刘翔没有成绩。怎么会这样呢？刘翔和他的教练感到很气愤，就去找裁判理论。原来裁判误将那个摔倒的美国选手当成刘翔了，因为在他们看来，中国人是不会在这个项目上跑出好成绩的。那是一次没有电视转播的比赛，幸好刘翔的教练用自己的微型摄像机将全部过程拍下来，这是孙海平的习惯，刘翔的每一次比赛他都会用摄像机拍下来，而这成了那次证明刘翔没有摔倒的唯一证据，录像十分清楚地显示，中国刘翔第三。终于还了刘翔一个清白，也给国际田径界的裁判提了个醒：中国人是可以在短距离的项目上有所作为的。 正是这样的一次偶然事故，给了刘翔师徒很大的刺激，也让他们的训练更加有了动力。真正让世界知道刘翔是2002年7月份瑞士洛桑的一次国际田联大奖赛。19岁的他跑出了13秒12的个人最好成绩，并打破了美国人保持了24年之久的世界青年纪录和中国人李彤保持了8年的亚洲纪录。 真正让世界瞩目刘翔的是2004年雅典奥运会他一举夺得奥运金牌并打破奥运会纪录、
英语（三年级上册）重要知识点归纳总结 一. 26个英文字母的正确认读和正确规范占格书写。 字母Gg 和Jj 的发音、Ii 和Rr 的发音易混淆。 Bb 和Dd 、Pp 和Qq Ii 和LI 的外形容易混淆，尤其是它们的小写。Cc 的 发音容易读错。 能准确认读并书写五个元音字母：Aa , Ee , Ii , Oo ,Uu 的大小写。 二. Miss, Mr , Mrs 这三个词的准确认读及听辨。 Mr （先生），指男性Miss （小姐）、Mrs （夫人、太太）指女性 这要涉及到“人称代词”的选择及图片的选择。 例如：选择题 （）This is Mr Li. _____ is tall and thi n. B. He C. She 因为Mr Li 是男的，所以，下文的代词应该用 he （他）,又因为这个代词在句首, 所以要大写首字母。因此，这道题应该选择 B. 三. be 动词在一般现在时中的三种形式 am, is ,are 2. He / She is my frie nd. He /She is tall a nd thn.连着 he/she/it 1.1 am Peter 」 ama boy. J I 用 am, you 用 are My mother is beautiful. 不可数用is This is my is cool. （可数）单数is,复数are Sally is my sister. She is lovely. 3. You are a girl .You are beautiful . 变疑问，be 提前 肯定回答不缩写
Kitty and Alice are good friends. 否定be后加not 4. My eyes are big. My hair is long.
专项练习一Name： 选出每组中不同类的那个单词 （）1. A: I B: you C: are （）2. A: no B: not C: yes （）3. A: is B: are C: me （）4. A: he B:my C: she （）5.A: family B: father C: mother （）6.A: Miss Li B: Mr Wang C: Mrs Fang （）7. A: afternoon B: evening C: good （）8. A: Helen B: Yang Ling C: Su Hai （）9. A: nice B:good C:this （）10.A: Hi. B: Hello. C: Goodbye （）11.A: an B: a C:this （）12.A: friend B: father C: mother （）13.A: yellow B:colour C: green （）14. A: he B:me C: I （）15. A: I B:my C:you （）16. A: Helen B: Mike C: Tim （）17.A: look B: are C:is （）18.A: this B:that C:what （）19.A: nice B: new C: too （）20.A: doll B: toy C:robot （）21.A: happy B: new C: what （）22.A: skirt B: pie C:sweet （）23.A: doll B: ball C: brown （）24 .A: uncle B:grandpa C: family （）25. A: she B:you C: my （）26. A: Miss B: Mrs C: Mr （）27.A:it B: he C:is （）28.A: green B:great C:brown （）29.A: Miss Li B: Mike C: Yang Ling （）30.A: egg B: orange C:hot dog
小学语文阅读理解专项练习题、种辣椒1常识课上，老师对植物的讲解，把我带到植物世界里。听完课，我动了心，决心种点什么，仔细观察 它的生长过程。回到家，我找到了两个花盆，满心欢喜地种下了辣椒籽。下种后，我每天都要给它浇些水，盼望种子 早些发芽。一天中午，弟弟告诉我花盆里出小苗了，我飞一样地跑到窗台前，只见一棵小嫩芽拱出土，又过了两天，好几棵小芽出来了。小芽越来越多，我给小辣椒间苗，把太密的小苗小心翼翼地拔掉了一些。一朵朵雪白的小花，几天后，每株辣椒已有半尺多高了，它们的茎上都缀满了欲放的花苞，到了盛夏，先后开放了。大约又过了四五天，辣椒就开始结果了，出现了青绿的椭圆形的小辣椒，一个个缀在茎上，真惹人喜爱。秋风吹进窗来，带进一股香气，辣椒开始由青变红，看上去更让人喜爱。一个个两寸多长的小辣椒挂 我满怀欣喜地把成熟的辣椒一个一个摘下，收获的时节到了，在枝头对我微笑，感谢我对它们的辛勤培育。竟收了小半筐。我看着筐里的辣椒，心想：这多有意思呀！知识来源于实践，而实践又必须付出辛勤的劳动，这难道 不是真理吗？．找出文章中点明中心的句子，在下面画横线。1 2．把文章分成三段，在段尾用“‖”表示，并写出段意。 3．读下面句子，在括号里写出各运用了什么修辞手法。 ）①小辣椒挂在枝头对我微笑，感谢我对它们的辛勤培育。（ ）我飞一样地跑到窗台前。（② 、蒙蒙的小雨2蒙蒙的小雨正落着，陈红骑着自行车悠然于柏油路上。她没有穿雨衣，因为她觉得在这样细雨中骑车 很浪漫。她望着路两边来去匆匆的行人，心想：这些人真是的，干嘛要东躲西藏的。一个没事吧小妹妹她摔倒了飞驰而来忽然迎面一辆的士她猛地拐向路边但车把挂在树干上 陈红白了他一眼，没有理他。心想：谁是你的小妹妹？她一翻身想站起来，可左小伙子站在她身边问道 腿的剧痛却使她不得不重新坐在地上，她接连两次试图站起来，都没成功。最后，只好放弃了努力。小伙”接着，拉起陈红的车子，又扶陈红坐到车架上，推起车子向医子一笑，“别逞强了，还是送你上医院吧。院走去。温柔如丝的春雨淅淅沥沥地落着。陈红已不再潇洒，只感到沉重。她坐在车上，望着前面推车的小伙子，不知该说些什么。她发现小伙子走路不太自然，仔细观察，只见小伙子左腿的袜端与裤腿之间不时地露出一段刺目的棕 色。那是什么？啊，他装着一只假腿。陈红想问问他的腿，却不愿张嘴。这时，只听到小伙子自言自语地“三年前，我也喜欢在细雨中骑车，那的确很潇洒，可是我却重重地跌倒了，像你一样。不，还不如说：”听了这话，“就在那次跌倒时被后面的汽车轧断了。你。”“噢，你的左腿——？”停了一会儿，小伙子说：?? 陈红陷入了沉思“我去通知你父母，你知道他们的电话吗？”陈红把号码告医院到了，小伙子搀着陈红进了急诊室。 诉了他。不一会儿，陈红的父母风风火火地赶来了。见到女儿腿上雪白的绷带，忙问这问那。陈红把经过“那这时，只听护土小姐说：“要不是那位大哥哥，我真不知该怎么办好，哎，他呢？”告诉了他们，又说，”个小伙子，看见你爸妈来后，他就离开医院了。”陈红怔住了：“我还不知他叫什么呢！父亲背起陈红，母亲在旁边扶着，一家人走出医院的时候，他们多么希望在人流中再次寻到那小伙子
回家的敲门声 一、现代文阅读（本大题共1小题，共30.0分） 1.回家的敲门声 ①每一个夜晚的来临，一听到我下班回家叩打门环的声音，父母便像赛跑一样一 前一后争着为我开门，总怕被对方抢了先。 ②母亲的脚步细碎而轻柔，父隶的脚步则如重锤般有力，踩得地面“咚咚”直响。 因此尽管母亲非常的努力，但总是比父亲慢半拍，为我开门的似乎永远都是父亲！ 有时候母亲也会站在父亲身后大声的嗔怪：“平时让你干点事，你磨磨蹭蹭慢慢腾腾的，一听到儿子回来你跑的比兔子都快！”父亲此时总是呵呵的憨笑两声，但并不驳斥母亲的话。 ③门在开启的瞬间，我照例能听到两声一高一低苍老而亲切的问候。随后老两口 就像勤务员似的一人给我推自行车，一人帮我拿包，让我尽享“领导”般的待遇。就这样，父母一前一后紧紧相随的身影，或重或轻的脚步声，或高或低的问候声一直伴随我走过了一年又一年… ④后来为我开门的只有父亲一个人了，因为母亲病了，她已经彻底失去了与父亲 竞争的能力，腿脚已不太灵便的她大多数时间里只能坐在床头迎接我的归来，目送我的离去，而我也很难听到母亲那风风火火细碎而轻柔的脚步声了。 ⑤母亲久治不愈的病带走了父亲很大一部分活力，他的脚步声不再像重锤般的有 力而变得有些迟缓了。除了他亲切的问候，温和的眼神未变，父亲脸上的皱纹已增加了很多，头上的白发也增加了很多…… ⑥随着年纪越来越大，父母对我的依恋似乎更浓更深了。有时晚上加班回家迟一 些，父亲便携着孱弱的母亲在街口翘首以盼、望眼欲穿的看着儿子来时的路……大老远我就能看到昏黄的路灯下站着两个互相搀扶着的老人雕塑般静静的、久久的凝视着远方，他们灰白的头发不时被风吹起。来回飞舞……我知道那是父母在等我回家。 ⑦虽然我不知道他们究竟等了我多久，但我肯定想像得出从家到街口，他们已经 进进出出很多遍了。很可惜，那时候我并没有任何的感恩之心，丝毫也没有，我只是觉得做父母的都是这样。 ⑧不知从什么时候起，一进大门我发现门口忽然多了一把椅子，起初我很奇怪， 不知道椅子放在这里究竟有何用？后来我知道了椅子是父亲放在这里的，是他专门坐在这里等着为我开门的。父母亲年纪都大了，耳朵都有些发沉，母亲怕我敲门时他们听不到，便建议父亲在门口放一把椅子，快到我回来的时间，父亲便坐在这儿等着我的敲门声…… ⑨再后来，我结婚了，回家的次数浙渐少了起来。但是发在门口的那把椅子却始 终未动。 ⑩他喝光了瓢里的水，接着说为了抄近路，他蹚着水过的十里河，可过河的时候把脚给崴了，一拐一拐地又走了十里路，拐回了家。
Unit 1.Hello again！ 一．单词 人称 1.she 她 2.he 他 3. my 我的 4.her 她的 5. his 他的 6.your 你的 物品 1.blackboard 黑板 2.chalk 粉笔 3. chair椅子 4.pencil 铅笔 5.markers 水彩笔 6. glue 胶水 7. pen 钢笔 8. eraser 橡皮 9. paper 纸 10. pencil-case铅笔盒11. scissors 剪刀 12. desk 桌子 地点 1. classroom 教室 2. library 图书馆 3. school 学校 4. gym 体育馆 方位 1. on 在…..上 2. in 在….里 3. under 在….下边 4. above 在….的上方 5. below 在….下方 6. beside 在…旁边 7. behind 在….后边 8. in front of 在…前边 数字 1.one 一 2. two 二 3.three 三 4.four 四 5. five 五 6.six 六 7.seven 七 8.eight 八 9.nine 九10.ten 十11.eleven十一12.twelve 十二13.thirteen十三 14.fourteen 十四 15.fifteen 十五 16.sixteen 十六17.seventeen 十七18.eighteen 十八 19.nineteen 十九 20.twenty 二十 21.twenty-one二十一22.twenty-two 二十二23.thirty 三十24.forty 四十25.fifty 五十26.sixty 六十 27.seventy 七十 28.eighty 八十29.ninety 九十 30.one hundred 一百 动词短语 1.put in 放在…里 2.read a book 读一本 3.draw on the paper 在纸上画画 4.play ping-pong 玩乒乓球 5.write on the blackboard 写在黑板上 二．重点句子： 1. How are you ? 你好吗？ Fine , thanks . 我很好，谢谢 2. Are you ready for school ?你准备好上学了吗？Yes . 是的。 3. ①What’s your name ? 你叫什么名字？My name is Danny . 我叫Danny 。 ②What’s her name ?她叫什么名字？Her name is Jenny . 她叫Jenny 。 ③What’s his name ?他叫什么名字？ His name is Steven . 他叫Steven 。 4. This is chalk/glue . 这是粉笔/胶水.（单数/不可数）These are pencils . 这些是铅笔。（复数）
三年级英语上册专项训练（基础1） 一、写出下面单词的中文： pen eraser school bag book pencil crayon ruler sharpener pencil-case head eye finger face ear leg mouth nose arm foot body hand blue brown purple yellow green red white pink orange 二、写出下面Let’s do的中文，并读一读，做一做。 Snap your fingers. Clab your hands. Wave your arms. Cross your legs. Stamp your foot. Shake your body. Touch your head. Show me you red crayon. Black,black.Stand up. White,white.Turn around. Pink,pink.Sit down. Brown,brown.Touch the ground. Orange,orange.Touch your head.
三、为下列句子选择合适的搭配，把字母编号填入括号里，再读一读。（）1．Good morning！A：Hi!/ Hello! （）2．Hello! B：I am Mike./ My name is Mike. （）3．See you! C: Me too! （）4．Good afternoon! D: Nice to meet you. （）5．What’s your name?- E: Good afternoon!- （）6．This is John. F: OK!/Great. （）7．Nice to meet you. G: Thank you. （）8．Let’s paint. H: Nice to meet you，too! （）9. I have a pencil. I: Good morning! （）10．Happy teachers’ Day! J: Goodbye! ( )11.Where is your book? K:Here it is. ( )12.How are you? L:Fine,thanks. /I’m fine,thank you./ Very well,thanks.
【部编语文】阅读理解练习题(含答案)经典 一、二年级语文下册阅读理解练习 1．阅读下文，回答问题 拔萝卜 一天，小兔子来拔萝卜，它拔啊拔，就剩下一个大大的萝卜没有拔完，它就去拔那根大 萝卜。可是它怎么拔也拔不上来，它急得转圈跑。小狗看见了，对它说：“我来帮你拔萝卜吧。”它们俩一起拔呀拔，还是拔不上来，这时候小熊来了，它们俩一起说：“小熊的力气大，你来帮我们拔萝卜吧。”小熊说：“好吧。”它们又一起拔啊拔，还是拔不出来，，最后 小象来了，对它们说：“我来帮你们拔萝卜吧”。于是，小象就用长鼻子把一些萝卜叶子卷 上，使劲拔。终于把大萝卜拔上来了。小兔高兴地说：“小狗，小熊，小象，谢谢你们帮我 拔萝卜，我们晚上一起吃蜜汁大萝卜吧！” 到了晚上，小狗，小象，还有小熊都来了，小象先把大萝卜用鼻子卷到了桌子上，小狗 负责把皮刮掉，小兔把大萝卜切开，小熊往上边抹了很多很多的蜜汁。这下，大萝卜成了 又香又脆的蜜汁大萝卜。它们每人都咬一口，呀！这个蜜汁大萝卜实在是太甜了！ （1）这篇短文共________个自然段。 （2）小兔子在拔萝卜，最后一个大萝卜拔不动，________、________、________来帮小兔子拔萝卜。 （3）这个故事告诉我们什么道理？________ A. 团结的力量大。 B. 小象的力气最大了。 C. 蜜汁大萝卜真好吃。 【答案】（1）2 （2）小狗 ；熊 ；小象 （3）A 【解析】 2．读短文，完成练习。 两只小鸟 雨，哗哗哗地下着，树叶、树干全被淋湿了。飞禽走兽都在寻找避雨的地方。 有两只聪明的小鸟，飞到草地上，躲进蘑菇伞下。蘑菇伞摇晃晃地支撑着。 一只小鸟说：“我的左边淋雨了，你往右边靠一靠！” 另一只小鸟说：“我的右边淋湿了，你往左边靠一靠！” 你争我吵，你拥我挤，谁也不往外边靠一靠。挤着，挤着，“咔嚓”一声，蘑菇伞断了……两只小鸟红着脸蛋儿，你看看我，我看看你，不知说什么好！ 雨，仍在哗哗哗地下着…… （1）这篇短文共有________个自然段。 （2）在文中找出下列词语的近义词或反义词。 ①近义词：争——________
等你回家 (1)我曾陪一个父亲，去800里外的戒毒所，探视他在那里戒毒的儿子。 (2)戒毒所坐落在荒郊野外，我们的车，在乡间土路上颠簸着。路边，野葵和蒲公英开得正盛，一些鸟在草地间飞起又落下，天空很蓝，显得很高远。父亲的心，却低落得如一棵衰败的草，他恨恨地说：“真不想来啊。” (3)一路之上，他不停地痛骂着儿子，历数着儿子种种的不是，说他毁了一个家，毁了他。他含辛茹苦养大他，为他在城里买了房，买了车，帮他娶了媳妇.那个不肖子，却被一帮狐朋狗友拖下水，去吸食毒品。房子吸没了，媳妇吸跑了……他一辈子积攒的家业，几乎被他掏空了。 (4)“我真想跟他同归与尽！”这位父亲说到激愤处，双眼通红地睁着，抛出这样一句狠话来。若儿子在跟前，他是要把他撕成碎片才甘心的。 (5)我坐在一边，听他痛骂，隐隐地担心：这样的父亲去见儿子，会有怎样的结果？ (6)车子一路向前，野葵和蒲公英一路跟着。终于，远远望见了几幢房子，青砖青瓦，连在一起，坐落在一块开阔地。开车的师傅说：“到了。”父亲像突然被谁猛击了一掌似的，愣愣地，不相信地问：“到了？”一看表，快上午10点了。他急了，说：“也不知能不能见着。”因为这家戒毒所的规定，上午10点之后，一律不允许探视。 (7)他一口气跑到大门口，还好，还有15分钟的时间。办完相关手续，这个父亲一秒也不曾停留，急急火火地往探视室跑。很快，他儿子被管教干部带进来。这个个子高高的年轻人，脸上既无欢喜也无悲伤。看到父亲，他嘴角稍稍撇了撇，有嘲讽的意味。一层玻璃隔着，他在里面，父亲在外头。从他进来起。父亲就一直盯着他，话筒拿在手上，却不说话。 (8)旁边，亦有来探视的人。一个长相甜美的女孩子，在玻璃窗外头，不停地用手指头在举起的另一个手掌上画着什么。里头是个清秀的男孩子。他眼睛跟着女孩的手指转动，频频点头，含着泪笑。他读懂了她爱的密码--从此，都改了吧。还有几个人，男男女女，大概是一家子，围在一起争着跟里面的一个中年人说话。里面的中年人，一张脸憔悴无比，却一直笑着，一直笑着。这时，他们中的一个，突然到探视室外面叫了一个男孩进去。孩子不过十一二岁，白净的面容，文文弱弱的。孩子怯怯地打量了一下四周，然后拿过话筒，隔着玻璃窗，才说了一句什么，里面笑着的中年人立即不笑了，他愣愣地看着孩子，眼泪流了下来。 (9)“哭什么呢？你会改好的！”我听到那些人里的一个大声说。 (10)探视的时间快要过去了，管教干部已进来提醒。一直跟儿子对峙着的父亲这才掉过头来。我发现他与刚才的强悍判若两人，竟是一脸的戚容。低声说:“里面的日子不好过，看他黑了，也瘦了。” (11)他转身问我“你有纸笔吗？” (12)“当然有。”我掏出来给他，正疑惑着他要做什么，只见他低头在纸上迅速写下几个字，贴到玻璃窗上给儿子看。里面的年轻人，看着看着，神情变了，两行泪缓缓地从腮边滚落下来。 (13)探视结束后，我看到这位父亲在纸上留下的字，那几个字是：儿子，等你回家。 19.第（4）段划线句中有一个错别字是______，它的正确写法是_______。（2分） 20.第（2）段划线句是______描写，作用是____________ _____ 。（3分） 21.根据文章内容，完成下表。（6分）人物地点情境父亲的表现父亲去戒毒所的路上想起儿子的吸毒经历情绪激愤，痛骂儿子戒毒所大门（1）（2）探视室（3）拿着话筒，却盯着儿子不说话听到管教干部的时间提醒后（4） 22．第（12）段中年轻人“两行泪缓缓地从腮边滚落下来的原因是_____________（4分） 23.对文中父亲形象的理解错误的一项是_________。（2分A．这是一个严厉、不近人情的父亲。 B．这是一个有着宽大胸怀、无私的父亲。 C．这是一个对爱表现含蓄、又能给儿子精神力量的父亲。 D．这是一个望子成龙又恨铁不成钢的父亲。 24.本文题目是“等你回家”的含义是：（1）___________ __; （2）_____ ________。（4分）等你回家答案 19．与（1分）于(1分) 20．自然环境（景物）（1分）通过写花革的茂盛、飞鸟的活跃和天空的高远，反衬出父亲心情的低落。（2努） 21．(1)发现快过探视时间了（1分） (2) 一口气跑到大门口，并急急火火地往探视室跑（2分） (3)看到儿子被管教干部带进来后（1分） (4) 一脸悲戚，为儿子写下“儿子，等你回家”的纸
（一）猫 猫是捉老鼠的能手。它的耳朵很灵敏，能转来转去，哪怕是极小的声音，它也能及时辨出。猫有一双明亮的眼睛，狡猾的老鼠逃不过它的眼睛。猫的胡须像把尺，能测出各个洞的大小。猫的脚趾上有锋利的爪子，能爬树、跳墙、追捕老鼠。 1、短文有＿＿＿＿＿＿句话。 2、短文写了猫的＿＿＿＿＿＿、＿＿＿＿＿＿、＿＿＿＿＿＿和＿＿＿＿＿＿。 3、用“＿＿”划出描写猫的耳朵的句子。 4、这篇文章主要写：（选择正确的“√”） ①猫的耳朵很灵敏。……………………………………（） ②猫有一双明亮的眼睛。………………………………（） ③猫的脚趾上有锋利的爪子。…………………………（） （二）蚂蚁 蚂蚁整天辛勤的劳动，没有一个偷懒的。它们很团结，见了面就相互摇着触角打招呼。我很喜欢它们，有时候捉虫子给它们吃。 1．这段话中的“它们”指的是_____________ 。 2．“我”喜欢它们的原因：一是它们_______ ；二是它们__________ 。3．“我”喜欢它们表现在：___________________________________ 。
我有一支心爱的铅笔，是爸爸妈妈给我买的。 这支铅笔花花绿绿，很美丽。铅笔上画着一支大白鹅，红嘴巴，高额头，浑身雪白。它在池塘里快活地游来游去，可爱极了。水面上有一片片的荷叶，好像漂着一顶顶帽子。水早缓缓地流着，好像在说：“小朋友，你要好好学习呀！” 1、这篇短文＿＿＿＿＿＿节。 2、第二节有＿＿＿＿＿＿句话。 3、用“＿＿＿＿”划出描写铅笔头上大白鹅的句子。 4、这篇短文主要写了：（用“√”） ①这支铅笔是爸爸妈妈给我买的。………………（） ②水要小朋友好好学习。…………………………（） ③这支铅笔很美丽。………………………………（） （二）春天的田野 春天的田野真美啊！柳树发芽了。桃树开了花。青青的小草悄悄地从泥土里钻出来，地上像插遍了密密的松针。金黄的油菜花，引得蜜蜂来回地飞舞。 1、这段话主要写了（）的景色。 2、这段话中表示颜色的词有（） 3、把这段话中比喻的句子画出来。
《回家》现代文阅读及答案 阅读下面的文字，完成题目。 回家 （美）皮特·哈米尔 三个小伙子和三个姑娘乘坐公共汽车去佛罗里达，在车上，他们开始注意到文戈。 文戈坐在他们前面，衣着简朴，但不很合身。他坐在那里，一直没有动一下，满是灰尘的脸上看不出他的实际年龄。他一直咬着嘴唇，一语不发。 过了一会儿，他们还是知道了文戈辛酸的经历。 他在纽约监狱里关了四年，现在是回家去。他的妻子是一个极好的女人，他在坐牢时曾写信劝她再找个丈夫，还告诉她不必给他写信。果真如此，三年半里她没有给他写过一封信。 “你现在回家，对家里的情况什么都不知道?”有一个姑娘问。 “是的，”他羞怯地说，“不过，上一周，当我确信假释就要批准时，我又给她写了信。我告诉她，如果她没有改嫁，愿意等我回家，那就在镇口的橡树上系一条黄手帕。我看见黄手帕就会下车回家。如果她不想要我，就不系手帕，这样我就继续坐在车上走过去。” 他们都关注着布伦斯威克镇的到来，并相互传看着文戈拿出来的几张照片。照片上是他妻子和三个孩子——妻子透露出一种淳朴之美，孩子们尚未发育成熟。可以看得出来，照片不知被文戈抚摩多少次了。
现在他们离布伦斯威克镇还有二十英里，几个年轻人都坐在右边靠窗的座位上，等待着那棵大橡树的出现。文戈不再向车窗外张望，脸上的肌肉绷得紧紧的，好像他在给自己鼓劲，决心战胜另一次失望。 这时离布伦斯威克镇只有十英里，五英里……突然，所有年轻人都从座位上站了起来，他们叫呀，喊呀，高兴得手舞足蹈——镇口那棵橡树上挂满了黄手帕，二十条，三十条，也许有几百条。那棵树，真像一面欢迎的旗帜，在迎风招展。 只有文戈坐在那儿，呆呆地望着那棵橡树。 （原文有删改） (1)简要概括文戈妻子的主要形象特点。 答： ___________________________________________________________ _____ ___________________________________________________________ _________ (2)简析这篇小说中文戈的心理变化。 答： ___________________________________________________________ _____
小学三年级英语的主要知识点整理1名词单复数： 英语中名词分可数与不可数名词： ①能用数目来计算的叫可数名词，有单、复数两种形式，复数形式多数是在词尾加“s”如：pens,books; ②不可数名词是无法用数目来计算的名词，如：milk,juice. 2用情态动词can的用法 ①“can’t”是“cannot”的缩写。 Shecan’tsing.Hecan’tdance.（她不会唱歌。他不会跳舞。） ②can等情态动词后，用动词原形 Shecandance.Hecanswim. 1打招呼 Hi!Hello!（你好!你好!） Howdoyoudo?（你好？） Goodmorning/afternoon/evening!（早上好/中午好/晚上好） Howareyou?—I'mOK./I'mfine.（你好吗？我很好/我很好。） Andyou?—I'mfine,too.（你呢？我也很好。） Nicetomeetyou.—Nicetomeetyou,too.（很高兴理解你.-也很高兴理解你。） Gladtomeetyou.—Gladtomeetyou,too.（很高兴见到你。我也很高兴见到你。）
Goodbye!Bye-bye!（再见!再见!） 2介绍自己 Mynameis….（我的名字叫） Whatisyourname?（你的名字叫什么？） I'm…./Mynameis…（我是…/我的名字叫） 3询问年龄 Howoldareyou?—I'mnine/ten。/Sorry,Idon'tknow.（你多大了？我 是九/十/对不起，我不知道。） Areyounine,too?—Yes,Iam./No,I'mten.（你也是九岁吗？是的，我是。/不，我十岁。） 一般疑问句： Areyouboy?—Yes,Iam./No,Iamagirl.（你是男孩吗？是的，我是/不，我是一个女孩。） Areyounew?—Yes,Iam./No,I'mnot.（你是新来的吗？是的，我是/不，我不是。） Isthis…?—Yes,itis./No,itisn't.（这是...？— 是的，它是。/不，它不是。） Isthat…?—Yes,itis./No,itisn't.(那是...？是的，它是。/不，它 不是。） It's…Isthisbig/fat?—Yes,itis./No,itisn't. （这是大的/胖的吗？--是的，它是。/不，它不是。) 【篇二】 特殊疑问句：
部编版三年级下册语文课内外阅读理解专项练习题含答案1．阅读下文，回答问题。 最痛苦的是，老师傅习惯用一把老掉牙的推剪，它常常会咬住一绺头发不放，让小沙吃尽苦头。这还不算，老师傅眼神差了点儿，总把碎头发掉在小沙的脖子里，痒得小沙哧哧笑。你想想，这一会儿痛一会儿痒的，跟受刑一样。 最让小沙耿耿于怀的是，每次剃完头，姑父还要付双倍的钱给“害人精”。 （1）查字典填空。 “惯”用音序查字法，应查字母________，再查音节________。它在字典中的意思有：①纵容（子女等）养成不良习惯或作风；②习以为常，积久成性。“惯”在“习惯”一词中的意思是________，我能用它的另外一个意思组词：________。 （2）老师傅剃头时________让小沙吃尽苦头，小沙因为________而痛，又因________而痒。小沙剃头时的感受我们可以用“________”这个成语来概括。 （3）用画线的词语写一句话。 （4）文中“害人精”指的是谁？为什么这样称呼他？ 【答案】（1）G；guan；②；娇惯 （2）推剪；常常咬住一绺头发不放；碎头发掉在脖子里；如坐针毡 （3）小弟弟喜怒无常，一会儿哇哇大哭，一会儿哈哈大笑。 （4）文中“害人精”指的是老剃头师傅。这样称呼他是因为老剃头师傅剃头时让小沙感到很痛苦，还收取双倍的钱。 【解析】【分析】（1）此题考查汉语拼音、音序、字义等方面的知识。因此，应全面扎实地掌握各方面的知识，同时在运用知识时，注意把握其不同的特点和要求。惯，音节 guàn ，音序为G，应先查字母G，再查音节guan。习惯的惯，应该是习以为常的意思。可以用纵容这个义项，组词为惯坏、娇惯等。 （2）本题主要考查对课文内容的理解记忆能力。解答本题，需要回顾课文的内容，然后结合前后句(题目提供的信息)进行补充填空即可。小沙的头发被推剪夹住，所以剃头让他吃尽了苦头，碎发落进脖子里，又让他感觉很痒，根据头发像针一样刺，可以用“如坐针毡”来形容小沙的剃头感受。 （3）一会儿……一会儿……，这个关联词表示并列关系，用于描述不定时地先后发生的两件事。可以写：小弟弟喜怒无常，一会儿哇哇大哭，一会儿哈哈大笑。 （4）考查对课文内容的理解能力。解答时要带着问题读课文整体感知文章内容，再用简洁的语言概括出来即可。 故答案为：（1）G、guan、②、娇惯（2）推剪、常常咬住一绺头发不放、碎头发掉在脖子里、如坐针毡（3）小弟弟喜怒无常，一会儿哇哇大哭，一会儿哈哈大笑。（4）文中“害人精”指的是老剃头师傅。这样称呼他是因为老剃头师傅剃头时让小沙感到很痛苦，还收取双倍的钱。 【点评】（1）本题考查用音序法查字典的能力。先根据所查字的音节的第一个大写字母，找到所在的音序，然后找到汉字的音节所在的页码，即可找到所查的字。根据字典正文对汉字的解释，可以得到字义、组词等帮助信息。 （2）这道题是按课文内容填空，一定要熟悉课文，边读边思考，才能填
回家的路 朱道能 ①那年年三十，我和妻子回老家看一年多未见面的儿子，由于耽误了最后一趟班车，只能去公路上拦车，可年三十的公路上，哪还有往日的车水龙马？ ②当时，我看到路边有一家三口人，也在焦急地张望着。一问，也是拦车回家的，还是河南老乡。一直等到下午4点多，我们终于看到一辆“豫L”牌号的空货车，轰隆隆驶了过来。不知是谁喊了一声“上”，几个人便冲上公路……随着一阵刺耳的刹车声，一个黑黑胖胖的司机跳了下来，吼道：大过年的，你们找死啊？ ③许是听到一声声熟悉的乡音，司机的脸色缓和下来了。他说：前面没座位了，只能坐车厢了。一个人30元，要上就快。当我们手忙脚乱地爬上车厢，一股腥臭味扑鼻而来，原来这是一辆拉猪的货车。坐下后，我们都长长地舒了一口气，然后轻松地聊起家常来。林姓老乡谈他卖菜起早摸黑的劳累，我谈摆地摊日晒雨淋的辛苦，然后就是一阵唏嘘。而两个女人谈论的，则是家里的孩子。林大嫂说，儿子叫虎子，两岁。老家还有一个七岁的女儿，叫大妮，跟着爷爷奶奶过，一年了，都想不起大妮的模样了。说到这里，她哽咽起来。妻子咬着嘴唇，别过脸去。 ④虎子很乖，躺在妈妈的怀里，一声不吭。我掏出买给儿子的玩具手枪，递了过去。虎子一见，喜欢得不得了，睡着了，还紧紧抱在怀里。 ⑤走到半路，下雪了，雨夹雪。风一刮，透心地凉。我跟妻子一对眼，就挪动身子，围挡在母子俩面前。无声中，四人相视，轻轻一笑。 ⑥雪越下越大，风也一阵紧似一阵。跟见就要进入河南境内了，突然，车停了下来。过了一会儿，司机敲着车，喊：下来活动一下，车走不了了。 ⑦原来公路结冰打滑，前面出车祸了。司机听说孩子睡着后，大着嗓门嚷，咋不早说哩？赶快抱到驾驶室去，感冒了咋办？我们心头一热，就跟司机聊了起来。他说因为货款到不了位，所以拖到过年才往回赶。这时，离公路不远处的村子里，传来了一阵阵的鞭炮声。我轻叹一声：出门在外，都不容易啊！ ⑧不知过了多久，车子终于蠕动起来了。这时，林大嫂一个人爬上了车厢。她说虎子还在睡觉，另外一个换班司机抱着。车子虽然开动了，却是单边放行，不但蜗牛般缓慢，且走走停停…… ⑨昏昏沉沉中，我听到司机喊了一声：信阳的老乡，到家了！和老乡挥手告别后，我跑到驾驶室边，刚把手伸进口袋，司机说了一声：快回家吧。然后一加油门，轰的一声，开走了。等我回过神来，只看到两个红色的尾灯，一闪一闪…… ⑩又跌跌撞撞地走了十几里山路，我们终于推开了家门。 11妻子把提包一放，伸手抱过儿子，一声声地喊：骏儿，妈妈回来了……娘说：别喊了，睡实了。早上就拉着爷爷的手，到村口去接你们，一直等到11点才睡着…… 12妻子把头埋在儿子胸前，紧紧地抱着。这时，我才想起买给儿子的玩具手枪来──呵呵，就算送给虎子的新年礼物吧。 13这时爹开腔了，对娘说：“你别光顾着说话了，赶快热饭热菜，一起吃团圆饭！”我一愣：你们还没吃饭？爹拿出一挂鞭炮，憨憨一笑：________我鼻子一酸，连忙接过爹手中的鞭炮，快步走到院中。 14噼噼啪啪，在欢快的鞭炮声中，我们家也过年了！ (选自2015年1月14日《河南日报》，有改动) 13．文章主要写了两件事，请用简洁的语言分别概括出来。(3分)