Tests of the Standard Model with Electroweak Physics have been performed over
many decades. In these proceedings, we present several analyses from the
Tevatron involving single $W$ or $Z$ bosons.Comment: XIX International Workshop on Deep-Inelastic Scattering and Related
  Subjects (DIS 2011

Lyon, Adam L.

English

arXiv

Tests of the Standard Model with Electroweak Physics have been performed over many decades. In these proceedings, we present several analyses from the Tevatron involving single W or Z bosons. Electroweak (EW) physics has been crucial for discovering and confirming many aspects of the Standard Model (SM). Furthermore, through radiative corrections EW physics allows for indirect views of heavy particles. Indeed the relationship between W boson, top quark, and Higgs boson masses is instrumental in predicting at what mass the Higgs boson may finally be found. In these proceedings, we present several recent analyses from the Tevatron involving single W or Z bosons to test the SM. The Tevatron is a p {bar p} collider at {radical}s = 1.96 TeV located at the Fermi National Accelerator Laboratory. CDF and D0 are its two multi-purpose detectors concentrating on high P{sub T} physics. Both detectors are described in detail elsewhere

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FERMILAB-CONF-11-381-EStudies of Single Electroweak Bosons at theTevatronAdam L. Lyon(For the CDF and D0 Collaborations)Fermi National Accelerator Laboratory, Batavia, IL 60510, USAAbstract. Tests of the Standard Model with Electroweak Physics have been performed over mnaydecades. In these proceedings, we present several analyses from the Tevatron involving single W orZ bosons.Keywords: Electroweak Physics, TevatronPACS: 12.15.-y,12.15.Ji, 14.70.Fm, 14.70.HpElectroweak (EW) physics has been crucial for discovering and confirming manyaspects of the Standard Model (SM). Furthermore, through radiative corrections EWphysics allows for indirect views of heavy particles. Indeed the relationship between Wboson, top quark, and Higgs boson masses is instrumental in predicting at what massthe Higgs boson may finally be found. In these proceedings, we present several recentanalyses from the Tevatron involving single W or Z bosons to test the SM.The Tevatron is a pp̄ collider at√s = 1.96 TeV located at the Fermi National Ac-celerator Laboratory. CDF and D0 are its two multi-purpose detectors concentrating onhigh PT physics. Both detectors are described in detail elsewhere[1, 2].W boson mass and widthHere, we merely summarize the Tevatron W boson mass and width results. D0 (CDF)has analyzed data corresponding to 1 (0.2) fb−1 of luminosity. Figure 1 shows thecombined Tevatron results in comparison with other measurements for both the Wboson mass[3] and width[4]. Both experiments are aiming for future mass results with∼ 25 MeV/c2 precision.W-Boson Mass  [GeV]mW  [GeV]80 80.2 80.4 80.6!2/DoF: 0.9 / 1TEVATRON 80.420 ± 0.031LEP2 80.376 ± 0.033Average 80.399 ± 0.023NuTeV 80.136 ± 0.084LEP1/SLD 80.363 ± 0.032LEP1/SLD/mt 80.365 ± 0.020July 2010W-Boson Width [GeV]!W [GeV]2 2.2 2.4"2/DoF: 2.4 / 1 640.2NORTAVET ± 0.049 691.22PEL ± 0.083 580.2egarevA ± 0.042pp# 141.2tceridni ± 0.057 190.2DLS/1PEL ± 0.003LEP1/SLD/mt 2.091 ± 0.002July 2010FIGURE 1. Combined Tevatron results for the W boson mass and width compared to other experiments.Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of EnergyCDFFIGURE 2. Measurement of Z/γ∗ dσ/dy from CDF and comparisons to PDFs.Z boson rapidityThe remaining sections of these proceedings involve properties of Z boson production.Note that Z includes not only on shell Z bosons, but also Drell-Yan events from a pro-duced γ∗. The first such analysis we consider is a measurement of the Z boson rapiditydσ/dy from decays to ee pairs (daughters of Z/γ∗ are always oppositely charged pairs)by CDF[5]. Events at large rapidity are produced in collisions where the momentumfraction x of the quarks in either the proton or antiproton is large. Therefore, such eventsprovide tests of parton distribution functions (PDFs) at large x. Data corresponding to2.1 fb−1 were utilized.Figure 2 displays the measured unfolded distribution and then comparisons to severalPDFs. One notices that the next-to-leading order (NLO) CTEQ6 PDFs agree quite wellwith the data and that the next-to-next-to-leading order (NNLO) MSTW2008 agreesbetter than the NLO version. Determining the inclusive cross section gives 256.6±0.7stat±2.0sys±15.4lum pb, the most precise measurement of this quantity to date.Tests of resummation and pQCD with Drell-Yan PµµTLeading order (LO) QCD corrections to the Drell-Yan production diagram involveproduction of a Z/γ∗ with an additional gluon via qq̄ annihilation and production of Z/γ∗with an additional quark via qg compton scattering. By measuring the PT of the Z/γ∗one studies these corrections and tests predictions from fixed order perturbative QCD(pQCD) at large PT and gluon resummation at low PT . D0 analyzed data correspondingto 0.97 fb−1 and measured the Z/γ∗ PT with µµ pairs[6]. Figure 3 displays the measuredspectrum corrected for resolutions and efficiency only along with comparisons to variousevent generators. One notes decent agreement except for generators using tune D6.RESBOS includes gluon resummation and nicely matches the low PT data. Nearly all ofthe generators have a normalization problem when matching the data in the range 30 -100 GeV/c.T/dpZ! d" Z!1/-610-510-410-310-210-110-1, L=0.97 fbNLO pQCD + corr.PYTHIA Perugia 6< 115 GeVµµ65 < M > 15 GeVT| < 1.7, muon p#muon | T/dpZ dZ1/Ratio to PYTHIA Perugia 6  1-1, L=0.97 fbDPYTHIA scale unc.HERWIG+JIMMYPYTHIA Tune D620.70.5Ratio to PYTHIA Perugia 6   (GeV)ZTp1 10 210Ratio to PYTHIA Perugia 6  1-1, L=0.97 fbNLO pQCDScale & PDF unc.RESBOSLO pQCDScale & PDF unc.PYTHIA scale unc.20.70.5Ratio to PYTHIA Perugia 6   (GeV)ZTp1 10 210Ratio to PYTHIA Perugia 6  1-1, L=0.97 fbSHERPAPYTHIA scale unc.ALP+HERWIGALP+PY Tune D6ALP+PY Perugia 620.70.5Ratio to PYTHIA Perugia 6  DØØDØDØDØGluon resummationbetterNLO pQCDbetterParton shower generatorsMatrix element +parton shower generatorsFIGURE 3. Measurement of Z/γ∗ PT from D0 and comparisons to various generators.Improving Z/γ∗ PZT with anglesMeasuring the Z/γ∗ PT leads to several limitations. For low PT , the correction of theresolution and efficiencies dominates the uncertainty. Furthermore, the bin widths of thedistribution are governed by resolution and not statistics.Decomposing PT with respect to a thrust axis will lead to a variable aT which is lesssusceptible to the problems mentioned above[7], but further improvement may be gainedby measuring angles instead of momentum. An angle φ∗η is constructed[8] withφ∗η = tan(φacop/2)sin(θ∗η)where φacop is an acoplanarity angle and cosθ ∗η = tanh((η−− η+)/2). φ∗η is highlycorrelated with aT /m`` (where the denominator is the dilepton invariant mass) and hassignificantly improved resolution due to the excellent angular resolution of the D0 track-ing detectors. In nearly all bins of angle, the total systematic uncertainty is substantiallysmaller than the statistical uncertainty. Figure 4 shows a comparison of the φ∗η distri-bution in both the electron and muon channels with RESBOS. Data corresponding to7.3 fb−1 were utilized. One notes the deficit at large angle, corresponding to the similardeficit in the PT distributions, is evident. Furthermore, RESBOS with small-x broaden-ing is disfavored.Tests of pQCD with Angular Coefficients of Drell-Yan ee pairs and PeeTThis topic is covered in detail elsewhere in these proceedings[9]. The differentialcross section dσ/ d cosθdφ is expanded into terms involving angles in the Collins-Soper center of mass frame. The coefficients are measured by CDF[10] with datacorresponding to 2.1 fb−1 and compared to pQCD predictions from various generators.Two interesting by-products of this procedure are an indirect measurement of sin2 θWand the “Lam-Tung relation” which is sensitive to the spin of the gluon. sin2 θW is related051015-210 -110 1-310-210-110110(a)0 0.1 0.2 0.3051015-210 -110 1-310-210-110110(c)-210 -110 1-410-310-210-110110(b)0 0.1 0.2 0.3-210 -110 1-410-310-210-110110(d) -1DØ 7.3 fb    (966K events) dataµµee dataResBosResBos (small-x)0.1 0.2 0.3-210 -110 1-410-310-210-110110(e)2 < |y| < 11 < |y|2 > |y|2 < |y| < 11 < |y|η*φ η*φ η*φ)η* φ/dσ) (dσ(1/FIGURE 4. Measurement of Z/γ∗ φ ∗η from D0 and comparisons to RESBOS.to the A4 coefficient. CDF thus measures sin2 θW = 0.2329± 0.0008+0.0010−0.0009 where thefirst uncertainty is from the measurement of A4 and the second is a systematic from QCDtheory and PDFs. The “Lam-Tung relation” stipulates that coefficients A0 = A2 when thegluon has spin 1. CDF measures this difference in coefficients across a range of PZT bins.The average difference is 0.02±0.02, consistent with a spin 1 gluon.ConclusionSeveral analyses involving single electroweak bosons have been presented here, andall are important tests of the Standard Model. All of these results are generally in goodagreement with SM predictions, and many of the comparisons will be used to fine-tunePDFs and generators.REFERENCES1. D. Acosta et al., Phys. Rev. D71, 032001 (2005).2. V. Abazov et al., Nucl. Instrum. Methods Phys. Res., Sect. A565, 463 (2006); M. Abolins et al., Nucl.Instrum. Methods Phys. Res., Sect. A584, 75 (2008); R. Angstadt et al., Nucl. Instrum. Methods Phys.Res., Sect. A622, 298 (2010).3. Tevatron Electroweak Working Group, FERMILAB-TM-2439-E, arxiv:0908.1374 (2009).4. Tevatron Electroweak Working Group, FERMILAB-TM-2460-E, arxiv:1003.2826 (2010).5. T. Aaltonen et al., Phys. Lett. B 692, 232 (2010).6. V.M. Abazov et al., Phys. Lett. B 693, 522 (2010).7. M. Vesterinen and T.R. Wyatt, Nucl. Instrum. Methods Phys. Res., Sect. A602, 432 (2009).8. A. Banfi et al., Eur. Phys. J. C 71, 1600 (2011) and V.M. Abazov et al., Phys. Rev. Lett. 106, 122001(2011).9. See A. Bodek in these proceedings.10. T. Aaltonen et al., Phys. Rev. Lett. 106, 241801 (2011).

Studies of Single Electroweak Bosons at the Tevatron

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