The most recent Electroweak results from the Tevatron are presented. The importance of precise Standard Model measurements in the Higgs sector, quantum chromodynamics and searches for new physics is emphasized. Analyzed data correspond to 1–7 fb−1 of integrated luminosity recorded by the CDF and DØ detectors at the Tevatron Collider at √s = 1.96TeV during the period between 2002 and 2010

Sekaric, J.

English

The most recent Electroweak results from the Tevatron are presented. The importance of precise Standard Model measurements in the Higgs sector, quantum chromodynamics and searches for new physics is emphasized. Analyzed data correspond to 1-7 fb{sup -1} of integrated luminosity recorded by the CDF and D0 detectors at the Tevatron Collider at {radical}s = 1.96 TeV during the period between 2002-2010. The main goal of the Electroweak (EW) physics is to probe the mechanism of the EW symmetry breaking. An important aspect of these studies is related to precise measurements of the Standard Model (SM) parameters and tests of the SU(2) x U(1) gauge symmetry. Deviations from the SM may be indicative of new physics. Thus, the interplay between the tests of the 'standard' physics and searches for a 'nonstandard' physics is an important aspect of the EW measurements. The observables commonly used in these measurements are cross sections, gauge boson couplings, differential distributions, asymmetries, etc. Besides, many EW processes represent a non-negligible background in a Higgs boson and top quark production, and production of supersymmetric particles. Therefore, the complete and detailed understanding of EW processes is a mandatory precondition for early discoveries of very small new physics signals. Furthermore, several EW analyses represent a proving ground for analysis techniques and statistical treatments used in the Tevatron Higgs searches

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ELECTROWEAK PHYSICS AT THE TEVATRONJ. Sekaric for the CDF and DØ CollaborationsDepartment of Physics and Astronomy, University of Kansas,Lawrence, Kansas 66045, USAAbstractThe most recent Electroweak results from the Tevatron are presented. The im-portance of precise Standard Model measurements in the Higgs sector, quantumchromodynamics and searches for new physics is emphasized. Analyzed data corre-spond to 1 - 7 fb−1 of integrated luminosity recorded by the CDF and DØ detectorsat the Tevatron Collider at√s = 1.96 TeV during the period between 2002 - 2010.FERMILAB-CONF-11-253-EOperated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. 1 IntroductionThe main goal of the Electroweak (EW) physics is to probe the mechanism of theEW symmetry breaking. An important aspect of these studies is related to precisemeasurements of the Standard Model (SM) parameters and tests of the SU(2)×U(1)gauge symmetry. Deviations from the SM may be indicative of new physics. Thus,the interplay between the tests of the “standard” physics and searches for a “non-standard” physics is an important aspect of the EW measurements. The observablescommonly used in these measurements are cross sections, gauge boson couplings,differential distributions, asymmetries, etc. Besides, many EW processes representa non-negligible background in a Higgs boson and top quark production, and pro-duction of supersymmetric particles. Therefore, the complete and detailed under-standing of EW processes is a mandatory precondition for early discoveries of verysmall new physics signals. Furthermore, several EW analyses represent a provingground for analysis techniques and statistical treatments used in the Tevatron Higgssearches.2 Single Boson ProductionMeasurements of gauge boson properties such as mass, differential distributionsand production asymmetries represent an important input to theoretical predictionswhich will provide a better description of Tevatron data and increase sensitivity tonew physics signals.Precise measurements of the W boson mass are important, because theyrestrict the phase space of the so far unseen SM Higgs and set indirect constraintson new physics via EW radiative corrections. At the Tevatron, the W bosonmass is measured using three kinematic variables: lepton transverse momentum,plT (where l = e, µ), imbalace in transverse energy arising from the neutrino, pνT(offten refered as to missing ET ), and the W boson transverse mass defined as MT =√2plTpνT (1 − cos∆φ), where ∆φ is the opening angle between the electron (muon)and neutrino momenta in the plane transverse to the beam. Correct modeling of thehadronic recoil from the QCD radiation is highly important for W mass measure-ment as it balances the boson’s pT . CDF selects events with plT > 18 (30) GeV/c inthe electron (muon) channel, missing ET > 30 GeV and |~u| < 15 GeV/c in 0.2 fb−1of integrated luminosity using both the electon and muon channel. DØ selects eventswith plT > 25 GeV/c, missing ET > 25 GeV and |~u| < 15 GeV/c in 1.0 fb−1 of in-tegrated luminosity using only the electon channel. Both experiments use all threereconstructed variables to measure the W boson mass. CDF measures q W mass of80.413 ± 0.034 (stat) ± 0.034 (syst) GeV/c2 1). DØ measures the W mass to be80.401 ± 0.021 (stat) ± 0.038 (syst) GeV/c2 2) which represents the most precisesingle W mass measurement to date. Using the same data DØ extracts the widthof the W boson to be ΓW = 2.028 ± 0.039 (stat) ± 0.061 (syst) GeV using MTdistribution 3).The production of single W bosons in pp̄ collisions also provides informa-tion on the momentum fraction dependence of the u and d quark parton distributionfunctions (PDF) within the proton. The boost along the z-axis in the direction ofmore energetic parton causes an asymmetry in the W boson and charged leptonproduction. After data has been corrected for detector effects, efficiencies, chargemis-identification, etc, the asymmetry A is measured as a function of rapidity yWof the W boson or pseudorapidity ηl of charged lepton, and transverse momentum.Current results on lepton charge asymmetry from 1 fb−1 of CDF integrated luminos-ity, electron charge asymmetry from 0.75 fb−1 of DØ integrated luminosity 4) andmuon charge asymmetry from 5 fb−1 of DØ integrated luminosity 5), show mutualdisagreement when split in different lepton pT bins. In addition, both CDF and DØlepton charge asymmetries do not agree with CTEQ6.6 PDF prediction when splitinto pT bins while W boson aymmetry measured by CDF agrees well with higherorder predictions 6).The study of Z boson kinematic distributions is yet another test that con-tributes to the tuning of theoretical QCD predictions. Distibutions such as trans-verse momentum, rapidity and φ∗η of dilepton pairs are studied at the Tevatron.The differential cross section as a function of the dimuon pT distributionhas been studied with 1 fb−1 of integrated luminosity recorded at DØ. Unfoldeddata normalized to the pythia Perugia 6 prediction is compared to other generatorsas shown in Fig. 1. In the low pT region (Z pT < 30 GeV) the resummation describesdata well while the high Z pT > 30 GeV region shows the best shape agreementwith higher order pertubative QCD but with an offset in normalization. Since the pTdistribution is sensitive to resolution effects, the φ∗η distribution based exclusivelyon angular resolution is an excelent place to probe QCD predictions with higherprecision. It is defined as φ∗η = tan(φacop/2)sin(θ)∗η where φacop is the acoplanarityangle φacop = π − ∆φll and ∆φll is the difference in azimuthal angle φ between thetwo leptons. The variable (θ)∗η is defined as (θ)∗η = acos[tanh(η− − η+)/2] whereη− and η+ are the pseudorapidities of the negatively and positively charged lepton,respectively. As presented in Fig. 2 where the ratio of the corrected distribution(1/σ)×(dσ/dφ∗η) to resbos is shown for three different rapydity regions, predictions1 10 210 (1/GeV)   T/dpZσ d× Zσ1/-610-510-410-310-210-110-1, L=0.97 fb∅DNLO pQCD + corr.PYTHIA Perugia 6< 115 GeVµµ65 < M > 15 GeVT| < 1.7, muon pηmuon | ∅D (1/GeV)   T/dpZσ d× Zσ1/1 10 210Ratio to PYTHIA Perugia 6  1-1, L=0.97 fb∅DPYTHIA 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 fb∅DNLO 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 fb∅DSHERPAPYTHIA scale unc.ALP+HERWIGALP+PY Tune D6ALP+PY Perugia 620.70.5Ratio to PYTHIA Perugia 6  Figure 1: The normalized differential cross section and its ratio relative to pythiaPerugia 6 in bins of Z pt for Z/γ∗(→ µµ)+X events. The data are shown withstatistical and systematic uncertainties. The distribution is compared to differentgenerators and NLO predictions.from resbos fail to describe the detailed shape of the data, and a prediction thatincludes the effect of small-x broadening is disfavored.The CDF experiment performs a measurement of dσ/dy selecting Z/γ∗ →e+e− events in the mass range of 66 to 116 GeV/c2 using data of 2.1 fb−1 of integratedluminosity. The comparison of unfolded data to different QCD predictions shows agood agreement as presented in Fig. 3. The measured cross section for Z productionof σZ × BR(Z → e+e−) = 256.6 ± 15.5 (stat+syst) pb is in good agreement withhigher order QCD predictions. In addition, the selected data is used to extract pTdependent angular coefficients, A0, A2, A3 and A4. The pT dependence of A0 and A2is found to be in agreement with the predictions of perturbative QCD, confirmingthe Lam-Tung relation which implies that the spin of the gluon is 1 if A0 = A2. Thevalues of A3 and A4 are in agreement with the predictions of all QCD models7).The measured A4 is used to extract sin2θW = 0.2329±0.0008+0.0010−0.0009 (QCD) as shownin Fig. 3.0.911.10.811.20.911.10.911.1 -1DØ 7.3 fb dataµµee dataResBos)2ResBos (tuned gResBos (small-x) scale uncertainty⊕PDF (a) |y| < 1 (b) 1 < |y| < 2(c) |y| > 2 = 25/24)µµ(ee,2χ  = 27/24)µµ(ee,2χη*φ η*φRatio to ResBos-210 -110 1 -210 -110 1Figure 2: Ratio of (1/σ)×(dσ/dφ∗η) to resbos in different Z rapidity bins. The yel-low band around the resbos prediction represents the quadrature sum of uncertaintydue to CTEQ6.6 PDFs and the uncertainty due to the QCD scale. Comparisons tothe resbos predictions when g2 is set to 0.66 GeV2 (dotted blue line) and to thesmall-x broadening (solid black line) are shown as well.3 Diboson ProductionAs an important production mechanism for understanding the EW symmetry break-ing, diboson physics focuses on precise measurements of the cross section and thetrilinear gauge boson couplings (TGCs) 8). Besides, the most precise knowledgeof these processes and their proper modeling is highly valuable in many searchesfor new physics which may exist at some energy scale Λ. The quantity Λ is physi-cally interpreted as the mass scale where the new phenomenon responsible for theanomalous couplings is directly observable.The Zγ → l+l−γ (l = e, µ) and Zγ → νν̄γ events selected from theCDF data of 5 fb−1 of integrated luminosity have a photon with transverse energyET > 50 GeV which is spatially separated from a lepton by ∆Rlγ > 0.7. Chargedleptons are required to have pT > 20 GeV/c (ET > 20 GeV) for one muon (electron)candidate and pT > 10 GeV/c (ET > 10 GeV) for the other. The three-body masscut of 100 GeV is applied to separate events which originate from the final stateradiation. Photon ET spectra from l+l−γ and νν̄γ candidate events are combinedand used to set the limits on Zγγ/ZZγ TGCs. The one-dimensional 95% C.L. limitson hγ,Z3,4 at Λ = 1.5 TeV are −0.017 < hZ,γ3 < 0.016, −0.0006 < hZ4 < 0.0005 and|hγ4 | < 0.0006. They are the most restrictive limits on these couplings to date 9).Figure 3: Left: Ratio of data to theory prediction for (1/σ)×(dσ/dy). The predictionuses pythia MC with NLO CTEQ6.1M and CTEQ6.6M PDFs. Right: The valueof sin2θW as a function of A4. Measured values of sin2θW and A4 are shown inred, and the blue band corresponds to different QCD predictions. The green linesrepresent the total uncertainty from measurement of A4.The φdecay distribution of ten ZZ → ll̄l′ l̄′ (l, l′ = e, µ) candidate eventsobserved in DØ data of 6.4 fb−1 of integrated luminosity with a significance of 6standard deviations are shown in Fig. 4. The φdecay distribution is sensitive todifferent scalar models arising from new physics 10). The measured cross sectionis σZZ = 1.24+0.47−0.37 (stat) ± 0.11 (syst) ± 0.08 (lumi) pb and it represents themost precise σZZ measurement at a hadron collider to date11). The ZZ → ll̄νν̄(l = e, µ) events selected from data of 5.9 fb−1 of integrated luminosity at CDFwere used to measure the cross section of σZZ = 1.45+0.60−0.51 (stat+syst) pb12). TheNeural Network output shown in Fig. 4 is used in analysis to separate ZZ eventsform the most dominant Drell-Yan background. The measured ZZ cross sectionsare in agreement with the SM prediction.The most precise measurement of the WZ → lνll cross section has beenrecently performed by the CDF Collaboration. The analysis selects events withmissing ET > 25 GeV and leptons of pT > 15 GeV/c where two leptons are of thesame flavour, opposite charge and lie in the mass window (mll −MZ) < 15 GeV/c2.After the final selection 50 candidate events are selected with expected backgroundof 11.2 ± 1.63 events. The WZ cross section, measured relative to the Z crosssection is σWZ/σZ = [5.5 ± 0.8 (stat) ± 0.5 (syst)]·10−4. Using a next-to-NLOcalculation of the σZ ·BR(Z → ll) = (251.3 ± 5) pb gives the cross section ofσWZ = 4.1 ± 0.6 (stat) ± 0.4 (syst) pb 13). The DØ Collaboration measuresthe σWZ cross section selecting events in the same final states, requiring leptoncandidates with pT > 15 GeV/c and missing ET > 20 GeV. The selection yields 34 (radians)decayφ0 1 2 3 4 5 6/4 rad)πEvents/(0123456/4 rad)πEvents/(DataSignalBackground-1DØ, 6.4 fb-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1020406080100120140160180200220 DYW+jetsγW+tt WWWZZZNN OutputEvents/0.05CDF Run II Preliminary-1 L dt = 5.9 fb∫FIT RESULTFigure 4: Left: The azimuthal angle decay distribution of the Z/γ∗ candidates se-lected in the ZZ → ll̄l′ l̄′ analysis, compared to the expected signal and background.Right: The Neural Network output used in the fit to the data to measure the ZZcross section.WZ candidate events with an estimated 23.3 ± 1.5 signal, and 6.0 ± 0.6 backgroundevents. The measured cross section of σWZ = 3.90+1.01−0.85 (stat+syst) ± 0.31 (lumi)pb. Inaddition, Z pT spectrum shown in Fig. 5 is used to set the limits on WWZTGCs. The one-dimensional 95% C.L. limits on ∆κZ , λZ and ∆gZ1 at Λ = 2.0 TeVare -0.376 < ∆κZ < 0.686, -0.075 < λZ < 0.093 and -0.053 < ∆gZ1 < 0.156.They are the best limits on these couplings to date as measured from direct WZproduction 14).4 SummaryThe most recent EW results from CDF and DØ Collaborations using Tevatrondata of 1-7 fb−1 of integrated luminosity have been presented. The W mass, crosssections and TGCs are measured with the best precision to date at a hadron collider.Observations are in agreement with the SM predictions though some descrepancieswith theoretical predictions have been observed.References1. T. Aaltonen et al (CDF Collaboration), Phys. Rev. Lett. 99, 151801 (2007).2. V. Abazov et al (D0 Collaboration), Phys. Rev. Lett. 103, 141801 (2009).3. V. Abazov et al (D0 Collaboration), Phys. Rev. Lett. 103, 231802 (2009).TW m0 20 40 60 80 100 120 140 160 180 200Events/10.0024681012dataWZ + jetsµ µ →Z ee + jets→Zγ + µ µ →Zγ ee + →ZZZ-1 L dt = 6 fb∫CDF Run II Preliminary  (GeV)TZ p0 20 40 60 80 100 120 140Events/30 GeV0510152025DataBackgroundSM WZ + Background =  0.2κ∆ = -0.1, λ = -0.2κ∆ = -0.1, λEvents/30 GeVFigure 5: Left: Transverse mass of W bosons in WZ candidates. Right: Comparisonof the Z boson pT spectrum from data, total background, the SM WZ signal+totalbackground and two TGC models.4. V. Abazov et al (D0 Collaboration), Phys. Rev. Lett. 101, 211801 (2008).5. V. Abazov et al (D0 Collaboration), D0 Note 5976-CONF (2009).6. T. Aaltonen et al (CDF Collaboration), Phys. Rev. Lett. 102, 181801 (2009).7. T. Aaltonen et al (CDF Collaboration), arXiv:1103.5699v3 [hep-ex] (2011).8. K. Hagiwara, J. Woodside, and D. Zeppenfeld, Phys. Rev. D 41, 2113 (1990).9. T. Aaltonen et al (CDF Collaboration), arXiv:1103.2990v1 [hep-ex] (2011).10. Q. Cao et al, Phys. Rev. D 81, 015010 (2010).11. V. Abazov et al (D0 Collaboration), arXiv:1104.3078v1 [hep-ex] (2011).12. T. Aaltonen et al (CDF Collaboration), CDF Note 10358 (2010).13. T. Aaltonen et al (CDF Collaboration), CDF Note 10238 (2010).14. V. Abazov et al (D0 Collaboration), Phys. Lett. B 695, 67 (2011).

Electroweak Physics at the Tevatron

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2012-11113-1Colloquia: LaThuile11IL NUOVO CIMENTO Vol. 35 C, N. 1 Gennaio-Febbraio 2012Electroweak physics at the TevatronJ. Sekaric for the CDF and DØ CollaborationsDepartment of Physics and Astronomy, University of Kansas - Lawrence, KS 66045, USA(ricevuto il 29 Settembre 2011; pubblicato online il 17 Gennaio 2012)Summary. — The most recent Electroweak results from the Tevatron are pre-sented. The importance of precise Standard Model measurements in the Higgssector, quantum chromodynamics and searches for new physics is emphasized. An-alyzed data correspond to 1–7 fb−1 of integrated luminosity recorded by the CDFand DØ detectors at the Tevatron Collider at√s = 1.96TeV during the periodbetween 2002 and 2010.PACS 12.15.Ji – Applications of electroweak models to specific processes.PACS 13.85.Qk – Inclusive production with identified leptons, photons, or othernonhadronic particles.PACS 14.70.Fm – W bosons.PACS 14.70.Hp – Z bosons.1. – IntroductionThe main goal of the Electroweak (EW) physics is to probe the mechanism of theEW symmetry breaking. An important aspect of these studies is related to precise mea-surements of the Standard Model (SM) parameters and tests of the SU(2)×U(1) gaugesymmetry. Deviations from the SM may be indicative of new physics. Thus, the interplaybetween the tests of the “standard” physics and searches for a “non-standard” physicsis an important aspect of the EW measurements. The observables commonly used inthese measurements are cross sections, gauge boson couplings, differential distributions,asymmetries, etc. Besides, many EW processes represent a non-negligible background ina Higgs boson and top quark production, and production of supersymmetric particles.Therefore, the complete and detailed understanding of EW processes is a mandatoryprecondition for early discoveries of very small new physics signals. Furthermore, severalEW analyses represent a proving ground for analysis techniques and statistical treatmentsused in the Tevatron Higgs searches.2. – Single-boson productionMeasurements of gauge boson properties such as mass, differential distributions andproduction asymmetries represent an important input to theoretical predictions whichwill provide a better description of Tevatron data and increase sensitivity to new physicssignals.c© Societa` Italiana di Fisica 293294 J. SEKARIC for the CDF and DØ COLLABORATIONSPrecise measurements of the W boson mass are important, because they restrict thephase space of the so far unseen SM Higgs and set indirect constraints on new physicsvia EW radiative corrections. At the Tevatron, the W boson mass is measured usingthree kinematic variables: lepton transverse momentum, plT (where l = e, μ), imbalacein transverse energy arising from the neutrino, pνT (offten refered as to missing ET ),and the W boson transverse mass defined as MT =√2plT pνT (1− cosΔφ), where Δφis the opening angle between the electron (muon) and neutrino momenta in the planetransverse to the beam. Correct modeling of the hadronic recoil from the QCD radiationis highly important for W mass measurement as it balances the boson’s pT . CDF selectsevents with plT > 18 (30)GeV/c in the electron (muon) channel, missing ET > 30GeVand |u| < 15GeV/c in 0.2 fb−1 of integrated luminosity using both the electon andmuon channel. DØ selects events with plT > 25GeV/c, missing ET > 25GeV and|u| < 15GeV/c in 1.0 fb−1 of integrated luminosity using only the electon channel. Bothexperiments use all three reconstructed variables to measure the W boson mass. CDFmeasures q W mass of 80.413 ± 0.034 (stat) ± 0.034 (syst)GeV/c2 [1]. DØ measuresthe W mass to be 80.401 ± 0.021 (stat) ± 0.038 (syst)GeV/c2 [2] which represents themost precise single W mass measurement to date. Using the same data DØ extracts thewidth of the W boson to be ΓW = 2.028 ± 0.039 (stat) ± 0.061 (syst)GeV using MTdistribution [3].The production of single W bosons in pp¯ collisions also provides information on themomentum fraction dependence of the u and d quark parton distribution functions (PDF)within the proton. The boost along the z-axis in the direction of more energetic partoncauses an asymmetry in the W boson and charged lepton production. After data has beencorrected for detector effects, efficiencies, charge mis-identification, etc, the asymmetryA is measured as a function of rapidity yW of the W boson or pseudorapidity ηl ofcharged lepton, and transverse momentum. Current results on lepton charge asymmetryfrom 1 fb−1 of CDF integrated luminosity, electron charge asymmetry from 0.75 fb−1 ofDØ integrated luminosity [4] and muon charge asymmetry from 5 fb−1 of DØ integratedluminosity [5], show mutual disagreement when split in different lepton pT bins. Inaddition, both CDF and DØ lepton charge asymmetries do not agree with CTEQ6.6PDF prediction when split into pT bins while W boson aymmetry measured by CDFagrees well with higher-order predictions [6].The study of Z boson kinematic distributions is yet another test that contributes tothe tuning of theoretical QCD predictions. Distibutions such as transverse momentum,rapidity and φ∗η of dilepton pairs are studied at the Tevatron.The differential cross section as a function of the dimuon pT distribution has beenstudied with 1 fb−1 of integrated luminosity recorded at DØ. Unfolded data normalizedto the pythia Perugia 6 prediction is compared to other generators as shown in fig. 1. Inthe low pT region (Z pT < 30GeV) the resummation describes data well while the high ZpT > 30GeV region shows the best shape agreement with higher-order pertubative QCDbut with an offset in normalization. Since the pT distribution is sensitive to resolutioneffects, the φ∗η distribution based exclusively on angular resolution is an excelent place toprobe QCD predictions with higher precision. It is defined as φ∗η = tan(φacop/2) sin(θ)∗ηwhere φacop is the acoplanarity angle φacop = π − Δφll and Δφll is the difference inazimuthal angle φ between the two leptons. The variable (θ)∗η is defined as (θ)∗η =a cos[tanh(η− − η+)/2] where η− and η+ are the pseudorapidities of the negatively andpositively charged lepton, respectively. As presented in fig. 2 where the ratio of thecorrected distribution (1/σ)× (dσ/dφ∗η) to resbos is shown for three different rapydityELECTROWEAK PHYSICS AT THE TEVATRON 295 (1/GeV)   T/dpZσ d× Zσ1/-610-510-410-310-210-110-1, L=0.97 fb∅DNLO pQCD + corr.PYTHIA Perugia 6< 115 GeVμμ65 < M > 15 GeVT| < 1.7, muon pηmuon | ∅D (1/GeV)   T/dpZσ d× Zσ1/Ratio to PYTHIA Perugia 6  1-1, L=0.97 fb∅DPYTHIA scale unc.HERWIG+JIMMYPYTHIA Tune D620.70.5Ratio to PYTHIA Perugia 6   (GeV)ZTp1 10210Ratio to PYTHIA Perugia 6  1-1, L=0.97 fb∅DNLO pQCDScale & PDF unc.RESBOSLO pQCDScale & PDF unc.PYTHIA scale unc.20.70.5Ratio to PYTHIA Perugia 6   (GeV)ZTp1 10210Ratio to PYTHIA Perugia 6  1-1, L=0.97 fb∅DSHERPAPYTHIA scale unc.ALP+HERWIGALP+PY Tune D6ALP+PY Perugia 620.70.5Ratio to PYTHIA Perugia 6  Fig. 1. – The normalized differential cross section and its ratio relative to pythia Perugia 6 inbins of Z pt for Z/γ∗(→ μμ) + X events. The data are shown with statistical and systematicuncertainties. The distribution is compared to different generators and NLO predictions.regions, predictions from resbos fail to describe the detailed shape of the data, and aprediction that includes the effect of small-x broadening is disfavored.The CDF experiment performs a measurement of dσ/dy selecting Z/γ∗ → e+e−events in the mass range of 66 to 116GeV/c2 using data of 2.1 fb−1 of integrated lumi-nosity. The comparison of unfolded data to different QCD predictions shows a goodagreement as presented in fig. 3. The measured cross section for Z production ofσZ × BR(Z → e+e−) = 256.6 ± 15.5 (stat + syst) pb is in good agreement with higherorder QCD predictions. In addition, the selected data is used to extract pT dependentangular coefficients, A0, A2, A3 and A4. The pT dependence of A0 and A2 is found tobe in agreement with the predictions of perturbative QCD, confirming the Lam-Tungrelation which implies that the spin of the gluon is 1 if A0 = A2. The values of A3 andA4 are in agreement with the predictions of all QCD models [7]. The measured A4 isused to extract sin2 θW = 0.2329± 0.0008+0.0010−0.0009 (QCD) as shown in fig. 3.3. – Diboson productionAs an important production mechanism for understanding the EW symmetry break-ing, diboson physics focuses on precise measurements of the cross section and the trilineargauge boson couplings (TGCs) [8]. Besides, the most precise knowledge of these pro-cesses and their proper modeling is highly valuable in many searches for new physicswhich may exist at some energy scale Λ. The quantity Λ is physically interpreted asthe mass scale where the new phenomenon responsible for the anomalous couplings isdirectly observable.296 J. SEKARIC for the CDF and DØ COLLABORATIONS0.911.10.811.2  -1D∅ 7.3 fb dataμμee dataResBos)2ResBos (tuned gResBos (small-x) scale uncertainty⊕PDF (a) |y| < 1 (b) 1 < |y| < 2(c) |y| > 2 = 25/24)μμ(ee,2χ  = 27/24)μμ(ee,2χη*φ η*φRatio to ResBos-210 -110 1 -210 -110 1Fig. 2. – Ratio of (1/σ) × (dσ/dφ∗η) to resbos in different Z rapidity bins. The yellow bandaround the resbos prediction represents the quadrature sum of uncertainty due to CTEQ6.6PDFs and the uncertainty due to the QCD scale. Comparisons to the resbos predictions wheng2 is set to 0.66GeV2 (dotted blue line) and to the small-x broadening (solid black line) areshown as well.The Zγ → l+l−γ (l = e, μ) and Zγ → νν¯γ events selected from the CDF data of5 fb−1 of integrated luminosity have a photon with transverse energy ET > 50GeV whichis spatially separated from a lepton by ΔRlγ > 0.7. Charged leptons are required to havepT > 20GeV/c (ET > 20GeV) for one muon (electron) candidate and pT > 10GeV/c(ET > 10GeV) for the other. The three-body mass cut of 100GeV is applied to separateFig. 3. – (Colour on-line) Left: Ratio of data to theory prediction for (1/σ) × (dσ/dy). Theprediction uses pythia MC with NLO CTEQ6.1M and CTEQ6.6M PDFs. Right: The value ofsin2 θW as a function of A4. Measured values of sin2 θW and A4 are shown in red, and the blueband corresponds to different QCD predictions. The green lines represent the total uncertaintyfrom measurement of A4.ELECTROWEAK PHYSICS AT THE TEVATRON 297 (radians)decayφ0 1 2 3 4 5 6/4 rad)πEvents/(0123456/4 rad)πEvents/(DataSignalBackground-1D∅, 6.4 fb-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1020406080100120140160180200220 DYW+jetsγW+tt WWWZZZNN OutputEvents/0.05CDF Run II Preliminary -1 L dt = 5.9 fb∫FIT RESULTFig. 4. – Left: The azimuthal angle decay distribution of the Z/γ∗ candidates selected in theZZ → ll¯l′ l¯′ analysis, compared to the expected signal and background. Right: The NeuralNetwork output used in the fit to the data to measure the ZZ cross section.events which originate from the final-state radiation. Photon ET spectra from l+l−γand νν¯γ candidate events are combined and used to set the limits on Zγγ/ZZγ TGCs.The one-dimensional 95% CL limits on hγ,Z3,4 at Λ = 1.5TeV are −0.017 < hZ,γ3 < 0.016,−0.0006 < hZ4 < 0.0005 and |hγ4 | < 0.0006. They are the most restrictive limits on thesecouplings to date [9].The φdecay distribution of ten ZZ → ll¯l′ l¯′ (l, l′ = e, μ) candidate events ob-served in DØ data of 6.4 fb−1 of integrated luminosity with a significance of 6 stan-dard deviations are shown in fig. 4. The φdecay distribution is sensitive to differentFig. 5. – Left: Transverse mass of W bosons in WZ candidates. Right: Comparison of the Zboson pT spectrum from data, total background, the SM WZ signal+total background and twoTGC models.298 J. SEKARIC for the CDF and DØ COLLABORATIONSscalar models arising from new physics [10]. The measured cross section is σZZ =1.24+0.47−0.37 (stat) ± 0.11 (syst) ± 0.08 (lumi) pb and it represents the most precise σZZmeasurement at a hadron collider to date [11]. The ZZ → ll¯νν¯ (l = e, μ) events se-lected from data of 5.9 fb−1 of integrated luminosity at CDF were used to measure thecross section of σZZ = 1.45+0.60−0.51 (stat + syst) pb [12]. The Neural Network output shownin fig. 4 is used in analysis to separate ZZ events form the most dominant Drell-Yanbackground. The measured ZZ cross sections are in agreement with the SM prediction.The most precise measurement of the WZ → lνll cross section has been recentlyperformed by the CDF Collaboration. The analysis selects events with missing ET >25GeV and leptons of pT > 15GeV/c where two leptons are of the same flavour, oppositecharge and lie in the mass window (mll −MZ) < 15GeV/c2. After the final selection 50candidate events are selected with expected background of 11.2± 1.63 events. The WZcross section, measured relative to the Z cross section is σWZ/σZ = [5.5 ± 0.8 (stat) ±0.5 (syst)]·10−4. Using a next-to-NLO calculation of the σZ ·BR(Z → ll) = (251.3±5) pbgives the cross section of σWZ = 4.1±0.6 (stat)±0.4 (syst) pb [13]. The DØ Collaborationmeasures the σWZ cross section selecting events in the same final states, requiring leptoncandidates with pT > 15GeV/c and missing ET > 20GeV. The selection yields 34 WZcandidate events with an estimated 23.3 ± 1.5 signal, and 6.0 ± 0.6 background events.The measured cross section of σWZ = 3.90+1.01−0.85 (stat + syst)± 0.31 (lumi) pb.In addition, Z pT spectrum shown in fig. 5 is used to set the limits on WWZ TGCs.The one-dimensional 95% CL limits on ΔκZ , λZ and ΔgZ1 at Λ = 2.0TeV are −0.376 <ΔκZ < 0.686, −0.075 < λZ < 0.093 and −0.053 < ΔgZ1 < 0.156. They are the bestlimits on these couplings to date as measured from direct WZ production [14].4. – SummaryThe most recent EW results from CDF and DØ Collaborations using Tevatron data of1–7 fb−1 of integrated luminosity have been presented. The W mass, cross sections andTGCs are measured with the best precision to date at a hadron collider. Observationsare in agreement with the SM predictions though some descrepancies with theoreticalpredictions have been observed.REFERENCES[1] Aaltonen T. et al. (CDF Collaboration), Phys. Rev. Lett., 99 (2007) 151801.[2] Abazov V. et al. (D0 Collaboration), Phys. Rev. Lett., 103 (2009) 141801.[3] Abazov V. et al. (D0 Collaboration), Phys. Rev. Lett., 103 (2009) 231802.[4] Abazov V. et al. (D0 Collaboration), Phys. Rev. Lett., 101 (2008) 211801.[5] Abazov V. et al. (D0 Collaboration), D0 Note 5976-CONF (2009).[6] Aaltonen T. et al. (CDF Collaboration), Phys. Rev. Lett., 102 (2009) 181801.[7] Aaltonen T. et al. (CDF Collaboration), Phys. Rev. Lett., 106 (2011) 241801,arXiv:1103.5699v3 [hep-ex] (2011).[8] Hagiwara K., Woodside J. and Zeppenfeld D., Phys. Rev. D, 41 (1990) 2113.[9] Aaltonen T. et al. (CDF Collaboration), Phys. Rev. Lett., 107 (2011) 051802,arXiv:1103.2990v1 [hep-ex] (2011).[10] Cao Q. et al., Phys. Rev. D, 81 (2010) 015010.[11] Abazov V. et al. (D0 Collaboration), Phys. Rev. D, 84 (2011) 011103,arXiv:1104.3078v1 [hep-ex] (2011).[12] Aaltonen T. et al. (CDF Collaboration), CDF Note 10358 (2010).[13] Aaltonen T. et al. (CDF Collaboration), CDF Note 10238 (2010).[14] Abazov V. et al. (D0 Collaboration), Phys. Lett. B, 695 (2011) 67.

Electroweak physics at the Tevatron

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Electroweak physics at the Tevatron

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