We present recent results from CDF and D0 on W and Z production cross
sections, the width of the W boson, tau-e universality in W decays, trilinear
gauge boson couplings, and on the observation of Z -> b bbar.Comment: Paper presented at the International Europhysics Conference on High
  Energy Physics, Tampere, Finland, 15-21 July, 199

Ellison, John

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The authors present recent results from CDF and D0 on W and Z production cross sections, the width of the W boson, {tau}-e universality in W decays, trilinear gauge boson couplings, and on the observation of Z {r{underscore}arrow} b{anti b}

Ellison, J.

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F Fermi National Accelerator LaboratoryFERMILAB-Conf-99/309-ECDF and D0W and Z Properties at the TevatronJohn EllisonFor the CDF and D0 CollaborationsUniversity of CaliforniaRiverside, California 92521Fermi National Accelerator LaboratoryP.O. Box 500, Batavia, Illinois 60510January 2000Published Proceedings of the International Europhysics Conference on High Energy Physics,Tampere, Finland, July 15-21, 1999Operated by Universities Research Association Inc. under Contract No. DE-AC02-76CH03000 with the United States Department of EnergyDisclaimerThis report was prepared as an account of work sponsored by an agency of the United StatesGovernment. Neither the United States Government nor any agency thereof, nor any oftheir employees, makes any warranty, expressed or implied, or assumes any legal liability orresponsibility for the accuracy, completeness, or usefulness of any information, apparatus,product, or process disclosed, or represents that its use would not infringe privately ownedrights. Reference herein to any specic commercial product, process, or service by tradename, trademark, manufacturer, or otherwise, does not necessarily constitute or imply itsendorsement, recommendation, or favoring by the United States Government or any agencythereof. The views and opinions of authors expressed herein do not necessarily state or reectthose of the United States Government or any agency thereof.DistributionApproved for public release; further dissemination unlimited.Copyright NoticationThis manuscript has been authored by Universities Research Association, Inc. under con-tract No. DE-AC02-76CH03000 with the U.S. Department of Energy. The United StatesGovernment and the publisher, by accepting the article for publication, acknowledges thatthe United States Government retains a nonexclusive, paid-up, irrevocable, worldwide licenseto publish or reproduce the published form of this manuscript, or allow others to do so, forUnited States Government Purposes.arXiv:hep-ex/9910037   18 Oct 1999UCR/D/99-22FERMILAB-CONF-99/309-EW and Z Properties at the TevatronyJohn Ellison(for the CDF and D Collaborations)Department of Physics, University of California, Riverside, CA 92521E-mail: john.ellison@ucr.eduAbstractWe present recent results from CDF and D onW and Z production cross sections,the width of the W boson,    e universality in W decays, trilinear gauge bosoncouplings, and on the observation of Z ! bb.1. IntroductionIn this paper we review some recent results onW and Z properties obtained by the CDF andD collaborations at the Fermilab Tevatron. Theresults are based on data sets collected duringthe 1994-95 run (\Run 1b"), with total integratedluminosities of 85 90 pb 1 per experiment. CDF(D) observed 41,666 (67,078) W ! e candidateevents and 5,152 (5,397) Z ! e+e  candidates.2. Measurement of the Ratio ofW ! e andZ ! e+e  Cross SectionsNew results on the W and Z production crosssections times electronic branching ratios fromCDFand D are shown in Fig. 1. D measure [1]W B(W ! e) = 2310  10 (stat)  50 (syst) 100 (lum) pb and Z  B(Z ! e+e ) = 221 3 (stat)  4 (syst)  10 (lum) pb, where \lum" isdue to the uncertainty on the integrated luminosity.CDF obtain Z  B(Z ! e+e ) = 249 5 (stat  syst)  10 (lum) pb and Z  B(Z !+ ) = 237  9 (stat lum)  9 (lum) pb [2].The errors are dominated by the uncertainty inthe integrated luminosity of the data samples. TheD and CDF results must be compared with care,since the experiments use dierent total pp crosssections to determine their integrated luminosities.CDF use their own measurement, while D take theaverage of the CDF, E710 and E811 measurements.As a result there is a scale factor which must bey Paper presented at the International Europhysics Confer-ence on High Energy Physics, Tampere, Finland, 15-21 July,1999.22.53√s = 1800 GeVσ W · B (nb)O(αs2) Theory(van Neerven et al.)DØW → lνData set: 92/93 94/96eµe µτCDF92/93 94/96e0.150.20.250.3σ Z · B (nb)eµeµeµeµZ → l+l-Figure 1. Measurements of the W ! e and Z !e+e  cross sections from D and CDF.applied to the measured cross sections: e.g. ifusing the CDF normalization, the D Run 1b crosssections must be multiplied by 1.062. Note that theresults in Fig. 1 have not been rescaled.The integrated luminosity uncertainty andmany of the other systematic errors cancel in theratio of cross sections R = W  B(W ! e)=Z B(Z ! e+e ). This allows indirect, precisemeasurements of the W ! e branching fractionand the width of the W boson. This follows usingW B(W ! e)Z B(Z ! e+e )=WZ1B(Z ! e+e ) (W ! e) (W )together with the theoretical calculation of29 10 11 12B(W → eν) (%)SMPreliminary:CDF+DØ 10.43 +- 0.25OPALL3DELPHIALEPH10.52 +- 0.4510.31 +- 0.4710.11 +- 0.6011.34 +- 0.49Figure 2. Measurements of B(W ! e).W=Z [3], the measured Z ! e+e  branchingratio from LEP [4], and the SM value of  (W !e) [5].The measured values of R are R = 10:49 0:14 (stat)  0:21 (syst) for D and R = 10:380:14 (stat)0:17 (syst) for CDF, using the combinedelectron data from Runs 1a and 1b. The mainsources of systematic errors are due to uncertaintiesin backgrounds, eciencies, and electron energyscale. A 1% error due to NLO electroweakradiative corrections is also included. The two Rmeasurements have been combined, yielding R =10:42  0:18. Using this combined value of R,the resulting branching fraction is B(W ! e) =(10:43  0:25)% and the width of the W bosonis determined to be  (W ) = 2:171  0:052 GeV.The results agree with the SM predictions when theerrors are taken into account, as shown in Figs. 2and 3. A signicant source of systematic error(1.5%) arises from the theoretical uncertainty onW=Z due to the choice of renormalization schemeand electroweak radiative corrections. Note that atpresent the errors due to theoretical uncertaintieson B(W ! e) and  (W ) are larger than thestatistical uncertainty.A direct measurement of the W boson widthis possible using a t to transverse mass (MT )spectrum inW events. TheW width directly aectsthe shape of the distribution, most prominently athigh values of MT , where the Breit-Wigner lineshape dominates over detector resolution eects.CDF have new preliminary results for Run 1bW ! e and W !  events, using a binnedlikelihood t in the region MT > 100 GeV=c2. The1.5 1.75 2 2.25 2.5Γ  (GeV)SMDirect:CDF+DØ 2.171 +- 0.052CDF 2.055 +- 0.125(Preliminary)Indirect:(Preliminary)DELPHI 2.48 +- 0.41OPAL 1.84 +- 0.38L3 2.12 +- 0.25Figure 3. Direct and indirect measurements of the Wboson width.W events are modeled using a similar simulationto that used in the W mass analyses [6]. Thismethod is less model-dependent than the indirectmeasurement discussed above, but with the currentdata sets it is statistically limited. The transversemass ts are shown in Figs. 4 and 5. The resultsare  (W ) = 2:17 0:125 (stat)  0:105 (syst) GeVfrom the electron data and  (W ) = 1:78 0:195 (stat)  0:135 (syst) GeV from the muondata. These results are combined with the Run1a electron measurement, yielding  (W ) = 2:0550:100 (stat)  0:075 (syst) GeV. This result isconsistent with the SM prediction, as shown inFig. 3.3.    e universality in W decaysD have updated their preliminary measurementof the W cross section times W !  branchingratio using Run 1b data and the new luminositynormalization, and obtain W  B(W ! ) =2220  90 (stat)  100 (syst)  100 (lum) pb.The ratio of this quantity to the correspondingelectron-channel quantity measures the ratio ofthe electroweak charged current couplings, gW =gWe .D measure gW =gWe = 0:980:03, to be comparedwith the earlier CDF result of gW =gWe = 0:970:07using Run 1a data, and the preliminary CDF resultgW =gWe = 1:01 0:19 which uses Run 1b data, butis obtained from an analysis based on the dierencein electron impact parameter distributions in W ! ! e and W ! e events. These results areshown in Fig. 6.3MT(e,ν) (GeV)events / GeV CDF(1B) PreliminaryΓW = 2.175 ± 0.165 GeV(stat+syst)MT(e,ν) (GeV)events / 2GeV 49844 events shown(1490 ± 170 bkg)438 with 100<MT<200 GeV211 with 110<MT<200 GeV7 with MT>200 GeV01000200040 60 80 100 120 140 160 180 20011010 210 340 60 80 100 120 140 160 180 200-2 log(L) vs ΓW3253303353403453503553601.6 1.8 2 2.2 2.4 2.6 2.8Figure 4. CDF direct measurement of the W bosonwidth using a t to the e transverse mass.MT(µ,ν) (GeV)# EventsCDF(1B) PreliminaryΓW = 1.78 +- 0.240 GeVΤW-2 log(L)MT(µ,ν) (GeV)# EventsBackgrounds196 ev. in fit region(100 < MT < 200)21791 ev. in normalisation region(50 < MT < 200)0250500750100050 100 150 2002462482502521 1.5 2 2.5 310-111010 210 350 100 150 200Figure 5. CDF direct measurement of the W widthusing a t to the  transverse mass.4. Updated D results on trilinear gaugeboson couplingsD have recently published limits on the trilineargauge boson couplings from pp ! WW=WZ ! jj events [7]. They use a likelihood t to thepT () spectrum, which is sensitive to non-SMcouplings. Anomalous couplings would result inan enhancement of events at high pT (). Nosuch enhancement is seen and D obtain 95%condence level limits, assuming equal WW andWWZ couplings (i.e.  = Z and  = Z)using a dipole form factor with form factor scaleUA1UA2CDF 1aCDF 1bDØ 1bAverageFigure 6. Measurements of gW =gWe .FF = 2 TeV:  0:52 <  < 0:54 and  0:62 < < 0:88.D have also searched for WZ events in thee ee and  ee channels [7]. One event passesthe selection criteria, an e ee candidate, shownin Fig. 7. For both channels combined, theSM prediction is 0:245  0:0154 events, with anestimated background of 0:50  0:15 events. Inthe absence of an excess of events, which wouldbe an indication of non-SM WWZ couplings, Dset limits on anomalous couplings. This analysis ismost sensitive to the couplings  and gZ1 , withresulting limits jj < 1:42 andgZ1 < 1:63 atthe 95% CL, using a form factor scale of 1 TeV.Because WZ production is sensitive only to theWWZ coupling, these results are independent ofany assumptions about the WW coupling.The new results on the trilinear gauge bosoncouplings have been combined with previous resultsfrom D to yield new global limits from Dutilizing all diboson production analyses. Figure 8shows the results for the couplings  and . TheD results use a form factor scale of 2 TeV, andtherefore, the LEP errors should be scaled by afactor of (1 + s=FF)2 when comparing with D.Here, s is the LEP c.m. energy. This is not donein Fig. 8, since the eect only amounts to a fewpercent increase. As can be seen, the D resultsare comparable to those from the LEP experiments,and because of the dierent production mechanismsand eects of anomalous couplings, the results arecomplementary.4CAL+TKS END VIEW 15-MAY-1997 13:27 Run   89912 Event   23020     26-MAR-1995 22:54................................... ..................................... .. ................................... .................................... .....MUON           ELEC           TAUS           VEES           OTHER           EM             ICD+MG         HAD            MISS ET        Max ET =   51.6 GeV           MISS ET(3)=   40.8 GeV        ETA(MIN:-25-MAX: 25)         EM2EM3EM1Miss. EtMT(2)=74.7 GeV M13=93.6 GeVFigure 7. End view of the D calorimeter and trackingsystems showing a candidate WZ ! e ee decay.ALEPH −0.05 +0.07−0.06DELPHI 0.02 +0.08−0.08L3 0.00 +0.07−0.07OPAL −0.11 +0.08−0.07LEP −0.03 +0.04−0.04D0 0.00 +0.10−0.10LEP+D0 −0.03 +0.03−0.03preliminaryχ2/Ndof =1.48/4λγ-0.2 -0.1 0 0.1 0.2ALEPH 0.09 +0.18−0.14DELPHI 0.25 +0.21−0.17L3 −0.12 +0.16−0.14OPAL 0.00 +0.27−0.19LEP 0.06 +0.09−0.09D0 −0.05 +0.30−0.30LEP+D0 0.05 +0.09−0.08preliminaryχ2/Ndof =2.08/4∆κγ-0.5 0 0.5Figure 8. Measurements of the trilinear gauge bosoncoupling parameters  and  from D and LEP.-20-10010203040500 20 40 60 80 100 120 140 160 180 200CDF PRELIMINARYDijet Invariant Mass (GeV/c2)Events per 10 GeV/c2Excess over background— Expected MC shape (PYTHIA)Predicted bgr.Observed eventsDijet Mass (GeV/c2)Events per 10 GeV/c20204060801000 50 100 150 200Figure 9. CDF Z ! bb invariant mass plot. The gureshows the dijet invariant mass for events containing acentral muon and two SVX-tagged jets.5. CDF observation of Z ! bbThe Z ! bb decay channel, copious at LEP andSLC, is challenging to observe at the Tevatron dueto the large QCD dijet background. However, it isan important benchmark signal for future physicsat the Tevatron { it can be used to improve the jetresolution in Higgs searches involving the H ! bbdecay, and it will be an important calibration toolfor the top quark mass measurement.In the CDF analysis, semi-leptonic decaysof the b-quark are utilized by selecting eventsfrom a sample collected with a central muontrigger. Oine, a good muon candidate withpT > 7:5 GeV is required, together with twojets containing charged tracks forming a well-identied, displaced secondary vertex in the SiliconVertex Detector. Topological cuts are appliedto reject QCD background, based on the amountand topology of the radiation surrounding the twoleading jets. Figure 9 shows the background-subtracted dijet invariant mass distribution. Thepeak and width of the distribution are as expectedfrom Monte Carlo Z ! bb signal. Accountingfor the systematic uncertainty on the backgroundprediction (4%), the signicance of the excess overbackground is 3.2 standard deviations.References5[1] B. Abbott et al., (The D Collaboration), submittedto Phys. Rev. D, FERMILAB PUB-99/171-E (1999),hep-ex/9906025.[2] (CDF Collaboration), Phys. Rev. D, 59, 052002 (1999);(CDF Collaboration), submitted to Phys. Rev. Lett.[3] R. Hamburg, W.L. van Neerven, T. Matsuura, Nucl.Phys. B 359, 343 (1991); W.L. van Neerven,E.B. Zijlstra, Nucl. Phys. B 382, 11 (1992).[4] L. Montanet et al., (Particle Data Group), Phys. Rev.D 54, 1 (1996).[5] J.L. Rosner, M.P. Worah, T. Takeushi, Phys. Rev. D49, 1363 (1994).[6] W. Carithers, these proceedings.[7] B. Abbott et al., (The D Collaboration), Phys. Rev.D 60, 072002 (1999).

W and Z properties at the Tevatron

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W and Z Properties at the Tevatron

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