W/Z Production Cross Sections and Asymmetries at ECM = 2TeV Dr. Angela Bellavance (University of Nebraska for the CDF and DØ collaborations ) Motivation Experiments and Detectors Z and W Cross Sections Z and W Asymmetries Summary March 15, 2005 - page 1
Fermilab CDF and DØ experiments are at Proton-antiproton collider at ECM = 1.96 TeV ( Tevatron ) Measurements rely on sheer numbers of W s and Z s 146 pb-1 ~800 pb-1 for RunII! March 15, 2005 - page 2
Detectors CDF detector DØ detector March 15, 2005 - page 3
Event Topology Use lepton decay channels because they are clean W Z ± 0 energetic lepton 2 energetic leptons missing ET ( ET ) (leptons w/ opposite signs) March 15, 2005 - page 4
Analysis Methods CDF and DØ use similar analysis strategies Measure backgrounds with QCD dijet events Selection criteria Common limiting systematic uncertainties: lepton + ET Þ W 2 (opp. sign) leptons Þ Z Measure ID efficiencies with Zs luminosity (~6%) PDF (1-2%) March 15, 2005 - page 5
Analysis Methods cont. Electron requirements EM-type, isolated calorimeter cluster track pointing to cluster Muon requirements track matched to calorimeter MIP or muon system track appropriate timing coincidence and impact parameter track and calorimeter isolation Tau requirements 1 or 3 tracks plus reconstructible p 0s narrow jet in calorimeter and isolated track(s) hadronic products recontruct to t mass March 15, 2005 - page 6
Z Results - Z ee cross section Largest background: QCD dijet (~2%, calculated from data) PRL 94, 091803 (2005) 2 EM objects with ET > 25 GeV 4242 cands. 177 pb-1 4625 cands. h range: CDF: central + plug cal. ( h <2.8) DØ: central cal. only ( h <1.05) Largest systematic uncertainties: PDF & e ID (~1.5% each) DØ: s x BR(Z ee)= 264.9 ±3.9stat ±9.9sys ±17.2lum pb CDF: s x BR(Z ee)= 255.8 ±3.9stat ±5.5sys ±15lum pb NLO(vanNeerven): s x BR(Z ℓℓ)= 251.3±5.0 pb March 15, 2005 - page 7
Z Results - Z mm cross section CDF DØ 2 objects with pt > 15-20 GeV/c Small backgrounds: ~1% (QCD, Z tt,...) 14352 cands. 148 pb-1 h <2. CDF RunII Preliminary 3568 cands. 194 pb-1 h <1. Largest systematic uncertainties: (both) PDF & Drell-Yann corrections (~1.5% each) (DØ only) DØ: s x BR(Z mm)= 291.3 ±3.0stat ±6.9sys ±18.9lum pb CDF: s x BR(Z mm)= 253.1 ±4.2stat +(+8.3 ) ±15.2lum pb -6.4 sys NLO(vanNeerven): s x BR(Z ℓℓ)= 251.3±5.0 pb March 15, 2005 - page 8
Z Results - Z tt cross section Z 0 tt (e or m)n n p ±n + N p 0 FERMILAB-PUB-04/381-E submitted to PRL Look for one t to decay hadronically, the other leptonically 39 cands. 2008 cands. 226 pb-1 OS stands for opposite sign for the leptons Largest backgrounds: QCD (dijet ~10%, Z ℓℓ ~6%) DØ: s x BR(Z tt )= 237 ±15stat ±18sys ±15lum pb CDF: s x BR(pp g* / Z tt)= 242 ±48stat ±26sys ±15lum pb NLO(vanNeerven): s x BR(Z ℓℓ)= 251.3±5.0 pb March 15, 2005 - page 9
W Results - W en cross section Require forward central 177 pb-1 h <1.05 116,569 cands. ET (e) > 20-25 GeV, track match PRL 94, 091803 (2005) ET > 25 GeV 72 pb-1 h <1 37,584 cands. Largest backgrounds: QCD dijet (~2%, calculated from data), Z ee (~2%) Largest uncertainties: PDF & e ID (~1.5% each) CDF (central): s x BR(W en )= 2780 ±14stat ±60sys ±166lum pb DØ: s x BR(W en )= 2865 ±8.3stat ±76sys ±186lum pb NLO(vanNeerven): s x BR(W ℓn )= 2687±54 pb March 15, 2005 - page 10
W Results - W mn cross section Require h <2. 96 pb-1 62,285 cands. pt(m ) > 20 GeV ET > 20 GeV CDF RunII Preliminary h <0.6 194 pb-1 57,109 cands. Largest backgrounds: Z mm + W tn (~6%), QCD b-jets (~1%, calculated from data) Largest uncertainties: efficiencies (~1.5%), PDF (~1%) CDF: s x BR(W mn )= 2786 ±12stat +(+65 ) ±166lum pb -55 sys DØ: s x BR(W mn )= 2989 ±15stat ±81sys ±194lum pb NLO(vanNeerven): s x BR(W ℓn )= 2687±54 pb March 15, 2005 - page 11
W Results - W tn cross section Require ET (t) > 25 GeV ET > 25 GeV no other jets above 5 GeV Largest backgrounds: QCD dijet (~15%), W en (~4%) Largest uncertainties: t ID (~5.5%) CDF: s x BR(W tn )= 2620 ±70stat ±21sys ±160lum pb NLO(vanNeerven): s x BR(W ℓn )= 2687±54 pb March 15, 2005 - page 12
Cross Sections Summary SM curve: C.R. Hamberg, W.L van Neerven and T. Matsuura, Nucl. Phys.B359, 343 (1991) March 15, 2005 - page 13
Asymmetries : Drell-Yann+Z forward/backward CDF 5,211 cands. 5,259 cands. arxiv:hep-ex/0411059 Data agrees with SM predictions across Mee shown March 15, 2005 - page 14
Asymmetries : W charge Require E(e) > 25 GeV ET > 25 GeV W charge asymmetry factors into u and d PDF u quarks carry higher fraction of momentum Þ W+ boosted in proton direction arxiv:hep-ex/0501023 (10 Jan 2005) Assume SM W en coupling; measure e s Largest background: QCD dijet March 15, 2005 - page 15
Summary Results are consistent with Standard Model Tevatron is making good progress in refining electroweak parameter values - laying the groundwork necessary for other important analyses to follow March 15, 2005 - page 16
Additional Plots March 15, 2005 - page 17
Z ee Differential Cross Section March 15, 2005 - page 18
Indirect W Width Measurement σ p p W l ν R σ p p Z l l Γ W l σ p p W Γ Z = σ p p Z Γ Z l l Γ W Using a ratio of cross sections, can indirectly measure W width D0(177pb-1): R(e) = 10.82 ± 0.16stat ± 0.28sys CDF(72pb-1): R(e+m) = 10.92 ± 0.15stat ± 0.14sys CDF (W m ): G(W ) = 2056 ± 44 MeV CDF (W m + W e ): G(W ) = 2079 ± 41 MeV World Average: G(W ) = 2118 ± 41 MeV March 15, 2005 - page 19