Tevatron Results on W and Z Boson Production

Transcription

1 Les Arcs, Moriond QCD, March -9, 3 Tevatron Results on W and Z Boson Production Tommaso Dorigo (Università di Padova) Introduction to Run II New W/Z cross section results Cross section ratios and Γ W Dielectron asymmetry WW production Concluding remarks

2 Les Arcs, Moriond QCD, March -9, 3 Introduction to Run II at the Tevatron The Tevatron runs at s = 1.96 TeV since 1. So far L max = cm s 1. Total delivered luminosity: 18 pb 1. Expect to collect pb 1 in 3. The recycler will be integrated in data taking this summer. It will bring luminosity up by a factor. Other improvements are in progress. Tommaso Dorigo, Padova University

3 Les Arcs, Moriond QCD, March -9, 3 Tommaso Dorigo, Padova University 3

4 Les Arcs, Moriond QCD, March -9, 3 The new D and CDF II Since Run I both detectors have undergone massive improvements: CDF upgraded its silicon tracking (now 1+5+ layers), extended muon coverage to η < 1.5, and built a brand new plug calorimeter ( e ID up to η < ). D inserted an inner silicon tracker and a fiber tracker into a T axial field magnet. New mini-drift tubes for forward muons have been added; a new preshower improves electron triggering at low P T. Tommaso Dorigo, Padova University 4

5 Les Arcs, Moriond QCD, March -9, 3 W and Z production at the Tevatron W and Z bosons are produced at the Tevatron through q q ( ) annihilation. The cleanest signatures involve high-p T electrons and muons: W eν or µν, Z e + e or µ + µ ; the W τν decay can also be observed with clarity although backgrounds are larger. Other decays are hard to use for precise EW measurements ET Electron P T W W eν Muon Z P T P T P T U Hadronic recoil Underlying event Neutrino E T Z µ + µ U Hadronic recoil Underlying event Muon P T Tommaso Dorigo, Padova University 5

6 Les Arcs, Moriond QCD, March -9, 3 New σw measurements - 1: electrons W! e Cross Se 8 tion Analysis Blessing, EWK Meeting, 13 Feb 3 D and CDF presented 1.96 T ev cross sections last summer (ICHEP ). Ba kground FOR BLESSING: CDF updated its result adding data collected till Jan 3 (L = 7. ± 4.3 pb 1 ). Background sources: Sour es of the ba number out of ± (syst.); andidate events NQCD = 1344±8 (stat.) QCD pro esses stat 67sy st events W! (! e ) 768 ZN! (MC); We τ + e ν = 768 ± NZ e+ e = 344 ± 17 (MC); (from MC study) (from MC study) Number of the QCD ba from Start with central electron trigger (ET > 18 GeV ); 1.8 > 1 GeV /c; quality cuts on EHAD /EEM, Eiso, strip χ, E/P. 38, 68 W candidates; A = 4.6 ±.4(MC)±.69(syst)%. Tommaso Dorigo, Padova University vs. MET kground events was estimated plot, assuming that isolation and The QCD contamination is obtained NC E NB =N / by extrapolation Ninbg = the T vs A Ie plot: Isolation Fraction Iso MET are un /T > 5 GeV ; ET > 5 GeV, E PTe kground orrelated. Isolation vs. Missing Transverse Energy A C 1.6 CDF Run II Preliminary L ~ 7 pb 1.4 QCD Background C 1. 1 = B A.8.6 W e ν Candidates.4. B E T (GeV) 6

7 Les Arcs, Moriond QCD, March -9, 3 Acceptance systematics are dominated by: PDFs (.58%) Material (.9%) Total:.69%. Other factors: ǫ ID = 84. ±.7 ±.%; ǫ Zv = 95.1 ±.1 ±.5%; ǫ trig = 96.6 ±.1%. Events per GeV E T CDF Run II Preliminary, 7pb Cut Entries 9387 DATA Sum W eν MC Z ee MC W τν MC QCD E T, GeV Events per GeV/c CDF Run II Preliminary, 7pb Entries 3868 DATA Sum W eν MC Z ee MC W τν MC QCD M T, GeV/c Result: σ W B(W eν) =.64 ±.1 (stat.) ±.9 (syst.) ±.16(lum.) nb. ICHEP :.6 ±.7 ±.11 ±.6 nb (CDF),.67 ±.6 ±.33 ±.7 nb (D); Prediction by W.J.Stirling et al. (NNLO):.73 pb. Tommaso Dorigo, Padova University 7

8 Les Arcs, Moriond QCD, March -9, 3 New σ W measurements - : muons CDF updated its result for σ W B(W µν) with L = 7. ± 4.3 pb 1. CDF Run II Preliminary, 7pb Use central ( η <.6) muon triggers P T > GeV/c; E Iso ( R <.4) <.1 P T ; other fiduciality and matching cuts; remove cosmics, Z µµ; E/ T > GeV, 3 < M T < 1 GeV ; 1,599 W µν candidates Events per 3GeV/c DATA Entries 1599 Sum W µν MC 18 Z µµ MC W τν MC 16 QCD 14 Cosmic M T, GeV/c Tommaso Dorigo, Padova University 8

9 Les Arcs, Moriond QCD, March -9, 3 Tommaso Dorigo, Padova University 9

10 Les Arcs, Moriond QCD, March -9, 3 Backgrounds: Source Method Amount Cosmics Rev. z cut 1.8 ±.8 ±.9% QCD E/ T vs E Iso 1.3 ±.6 ±.6% Z µµ MC 5.31 ±.4 ±.% W τν MC 3. ±.14 ±.% Total 1.8 ±.18 ±.96% Events per 3GeV Data W µν MC CDF Run II Preliminary, 7pb Entries 1599 Acceptance: A = 14.8 ± 5 (stat) ±.51 (syst.)%; systematics mainly due to PDF (.41%), recoil scale (.3%); PDF contribution obtained by varying them to span ±1σ of dσ Z /dy measured in Run I; Recoil scale effect studied by shifting scale to get better agreement with MC and recomputing A. Result: σ W B(µν) =.64 ±. (stat.) ±.1 (syst.) ±.16 (lum) nb (CDF ICHEP :.7 ±.4 ±.19 ±.7 nb; D ICHEP :.67 ±.6 ±.33 ±.7 nb). Events per 3GeV Recoil E, GeV 5 CDF Run II Preliminary, 7pb Entries 6768 DATA Sum W µν MC Z µµ MC W τν MC QCD Cosmic E T, GeV Tommaso Dorigo, Padova University 1

11 Les Arcs, Moriond QCD, March -9, 3 σ W using τ leptons (CDF) Collect W τν signal with E/ T > 5 GeV L1 trigger, τ ID at L3. 1. Monojet events: E j T > 5 GeV, with one P T > 4.5 GeV track in 1 cone, no tracks in 1 3 ;. No other jet with E T > 5 GeV ; 3. E/ T > 5 GeV ; 4. tight electrons removed; 341 evts (611 ± 56 from bgr sources). Result: σ W B(τν) =.6 ±.7 ±.1 ±.16 nb. Using W eν signal removed at step (4), extract: R = B(τν)/B(eν) =.99 ±.3 (stat.) ±.4 (syst). 14 W τ ν : number of tracks, associated with the τ candidate CDF Run II Preliminary, 345 events number of tracks L = 7 pb Data W τ ν W µ ν W e ν Z τ τ QCD Tommaso Dorigo, Padova University 11

12 Les Arcs, Moriond QCD, March -9, 3 Z cross section: 1 - electrons (CDF) Data selection: Two central electrons E T > 5 GeV, P T > 1 GeV ; at least one must pass tight cuts; 66 < M ee < 116 GeV, opposite charge. 183 evts / 1 ± 5 from backgrounds. Other ingredients: Acceptance: 11.49±.6% (syst. mainly from material & PDF uncertainties); Z efficiency: 87. ±.9%, ǫ Zv = 95.1 ±.5%; Result: σ Z B(Z ee) = 67. ± 6.3 ± 15. ± 16. pb. (theory: 5.5 pb (Stirling, NNLO)). ÓÖ Ð Ò CDF Run II Preliminary L dt = 7.7 pb Ø Ï Ø ÓÖÖ Ø ÓÒ Z ee DATA Z ee MC Å ½½ λ ¾ Æ Ò ÇË Ë˵ ½ ¼ ¾¾µ Ø Øº µ Evts/ GeV/c E corr / P corr (GeV/c ) M ee Opposite Sign Z ee DATA Z ee MC CDF Run II Preliminary L dt = 7.7 pb Tommaso Dorigo, Padova University 1

13 Les Arcs, Moriond QCD, March -9, 3 Tommaso Dorigo, Padova University 13

14 Les Arcs, Moriond QCD, March -9, 3 Z cross section: - muons Both CDF and D have updated σ Z B(Z µµ). D: L = 31.8 pb 1 (Sept. to Jan. 3). two good muons, 1 isolated; P T > 15 GeV/c, R µµ >., E Iso(.5) <.5 GeV ; 1585 candidates, 1.5 ± 1.% backgrounds; Total acceptance:.163 ±.11. Result: σ Z B(µµ) = 63.8 ± 6.8 ± 17.3 ± 6.4 pb (ICHEP, electrons: 66 ± ± ± 1 pb) CDF: central µ, P T > GeV/c; 163 candidates N Z = 1618 ± 11. Result: σ Z B(µµ) = 46 ± 6 ± 1 ± 15 pb Events / 3 GeV Events per 1GeV/c D Run II Preliminary Data MC M µ+µ- (GeV) Entries 1631 Data Z µµ MC CDF Run II Preliminary, 7pb M µµ, GeV/c Tommaso Dorigo, Padova University 14

15 Les Arcs, Moriond QCD, March -9, 3 A global view of W/Z cross sections What do we expect to learn from these measurements? W/Z cross section measurements require critical understanding of detector and DAQ. Good to do it right from the start! Can use W yields to monitor acquired luminosity during the run and normalize other measurements involving electrons Ratios of cross sections tell us more σ W, Z B (pb) DØ and CDF Run Preliminary pp _ W+X lν+x pp _ Z+X ll+x DØ(e) Run DØ(µ) Run CDF(e) Run CDF(µ) Run DØ(e) DØ(µ) CDF(e) CDF(µ) UA1 UA 1 Center of Mass Energy (TeV) Tommaso Dorigo, Padova University 15

16 Les Arcs, Moriond QCD, March -9, 3 σ W /σ Z ratio and W width (CDF) Using the new W and Z cross section measurements CDF finds: R e = σ W B(W eν)/σ Z B(Z ee) = 9.88 ±.4 (stat.)±.47 (syst.), R µ = 1.69 ±.7 (stat.) ±.33 (syst.). (NNLO, Stirling: R th = 1.9). From WA values of W/Z widths and σ W /σ Z = ±.4 (Stirling, p.c.) we can then extract Γ W = σ W Γ W e Γ Z Γ e W Γ µ W σ Z Γ Z ee R : =.9 ±.6 (stat.)±.1 (syst.) GeV, =.11 ±.5 (stat.)±.7 (syst.) GeV (PDG:.118 ±.4 GeV ). The combined result is: Γ W =.146 ±.78 GeV Year World Average CDF II (e+µ) D I (e+µ) Standard Model CDF I (e) UA(e) UA1(e+µ) Γ(W) CDF Run II Preliminary L dt = 7. pb Tommaso Dorigo, Padova University 16

17 Mee_CCs_MC Mee_CCs_DT Entries Mean RMS Mee_CCs_DT Entries Mean 68.5 RMS Les Arcs, Moriond QCD, March -9, 3 A FB of electron pairs CDF used the new Run II data (5438 events) to measure A FB of e + e pairs from p p Z(γ )X e + e X, with 4 < M ee < 6 GeV. A FB (QCD) CDF Run II Preliminary (GeV) M ee χ /ndf = 18.4/15 Electron scale/resolution calibrated in data and MC in central and plug regions QCD bgr for CP combs is obtained from high-e iso electrons CDF Run II Preliminary CC Invariant Mass (GeV) CDF Run II Preliminary CP Invariant Mass (GeV) Points: data Yellow: Simulation CC Invariant Mass (M ee ) Same Sign CC Invariant Mass (M ee ) Same Sign (MC subtracted) For CC pairs, same-sign electrons N QCD = 1.5 ± 5.9 events; CP: N QCD = 18 ±65. Tommaso Dorigo, Padova University 17

18 Les Arcs, Moriond QCD, March -9, 3 Events/ GeV The new A FB measurement is corrected for acceptance, efficiency, resolution, and QED radiation. Results agree with Pythia predictions (GeV) M ee Points: Data Yellow:Simulation Green: Backgrounds CDF Run II Preliminary L=7pb A FB A FB CDF Run II Preliminary L=7pb - Z/γ* e e MC band includes several theoretical calculations -.4 Statistical Total M ee (GeV) CDF Run II Preliminary L=7pb - Z/γ* e e MC band includes several theoretical calculations Statistical Total M ee (GeV) + + Tommaso Dorigo, Padova University 18

19 Les Arcs, Moriond QCD, March -9, 3 Blessing Plots Searches for WW production φ(et,closest l,jet) In Run I CDF used 5 events (Nb = 1. ±.3) to measure σw W = ± 1.6 pb. A similar search for dilepton candidates is going on.5 in the sample used to look for dilepton tt production, 1.5 requiring Nj =. Total backgrounds amount to 1.5 ±.6 events, the 1 expected W W signal yield is.7 ±.6 events..5 Global likelihood So far events have been observed in L = 56 pb 1. 4 W + ud sample MC WW Data ee Data e µ Data µµ distribution( ont'd) ET (GeV) { CDF PRELIMINARY { WW! dilepton BG RUNI WW EVENTS MEAN RMS RUN I data WW BG Global Likelihood Tommaso Dorigo, Padova University 39 S/BG 5 1 S/ BG Number of events In the Run I sample an optimized search has been carried out for pp W W + X lνjj. Limits have been set at σw W < 61 pb. The search has established new methods to search for hadronic W jj decays, useful for Run II searches. Dave Waters Global likelihood cut -4-4 Global likelihood cut We set the G.L threshold at 1.5 to minimize the expe ted upper 19 limit of W +W produ tion.

20 Les Arcs, Moriond QCD, March -9, 3 Concluding remarks W and Z cross sections rise with s agrees well with NNLO; Z asymmetry probed up to s = 6 GeV ; other searches have started. Run II is starting to deliver - xs results already reached accuracy levels similar to Run I Next steps in EW physics are W mass, W asymmetry! We expect first results soon. Detectors largely understood with small caveats; not yet exploited to fullest potential Expect to collect at least pb 1 in 3; 3 pb 1 is stretch goal Tommaso Dorigo, Padova University