1. 1 c. mills (Harvard U.) 20 September, 2010 W and Z Physics at ATLAS Corrinne Mills Harvard DOE Site Visit 20 September 2010

2. 2 c. mills (Harvard U.) 20 September, 2010 W and Z at the LHC 5 months of 7 TeV collisions 5 months of coherent effort by Harvard group on muon-focused analysis Results presented at PLHC, ICHEP, HCP/SUSY conferences Work shown here to be submitted for publication event selection lepton charge asymmetry cross section calculations muon definition & efficiency muon definition & efficiency data quality QCD background Kashif Mills Belloni Smith Kagan Martinez-Outschoorn Prasad Zevi della Porta Jeanty

3. 3 c. mills (Harvard U.) 20 September, 2010 Combined muon: matched inner detector (ID) and muon spectrometer (MS) track Selection:  p T (combined) > 15 GeV  p T (MS) > 10 GeV  |p T (MS) – p T (ID)| < 15 GeV Muons in ATLAS  |  | < 2.4 (trigger geometry) Trigger: L1 (hardware)  p T > 6 GeV reject decays in flight

4. 4 c. mills (Harvard U.) 20 September, 2010 Muon Quality Criteria Leverage knowledge from studies of cosmic ray data Consistency requirement for combined muon kinematics: |p T (MS) – p T (ID)| < 15 GeV

5. 5 c. mills (Harvard U.) 20 September, 2010 Refine muon selection: p T > 20 GeV and relative track isolation < 0.2  Sum  p T of tracks in cone around muon of  R < 0.4, divided by the muon p T Reduce backgrounds by requiring E T miss > 25 GeV Selecting the W signal (I) electron channel muon channel

6. 6 c. mills (Harvard U.) 20 September, 2010 Selecting the W signal (II) Clean up sample with M T > 40 GeV Transverse mass electron channel muon channel

7. 7 c. mills (Harvard U.) 20 September, 2010 W Cross Section Measure cross section times branching ratio BR(W→ l ) Theoretical prediction:  10.46 ± 0.02 nb Luminosity uncertainty is 11% channelint. lumi.N cand N background acceptance x efficiency electron315 nb -1 106959.9 ± 10.80.304 ± 0.048 muon310 nb -1 1181100.4 ± 11.20.364 ± 0.034 channelcross section (nb) electron 10.52 ± 0.34 (stat) ± 0.81 (sys) ± 1.16 (lum) muon9.58 ± 0.30 (stat) ± 0.50 (sys) ± 1.05 (lum) combined 9.96 ± 0.23 (stat) ± 0.50 (sys) ± 1.10 (lum) S. Prasad thesis: graduation ~ May 2011

8. 8 c. mills (Harvard U.) 20 September, 2010 W Cross Section in Context

9. 9 c. mills (Harvard U.) 20 September, 2010 Charge Asymmetry W + favored in proton-proton collisions Sensitive to valence quark PDFs electron muon integral result0.200 ± 0.022 (stat) ± 0.006 (sys) theory prediction0.20 V. Martinez-Outschoorn thesis: graduation ~ May 2011

10. 10 c. mills (Harvard U.) 20 September, 2010 Oppositely-charged muon candidates p T > 20 GeV,  range, quality requirements as with W analysis, including track isolation 66 GeV < M ll < 116 GeV Selecting the Z →  signal muon channel muon

11. 11 c. mills (Harvard U.) 20 September, 2010 Z Cross Section Measure cross section times branching ratio BR(W→ l ) Theoretical prediction:  0.964 ± 0.039 nb Luminosity uncertainty is 11% channelint. lumi.N cand N background acceptance x efficiency electron316 nb -1 701.18 ± 0.430.290 ± 0.066 muon331 nb -1 1090.25 ± 0.040.376 ± 0.045 channelcross section (nb) electron 0.75 ± 0.09 (stat) ± 0.08 (sys) ± 0.08 (lum) muon0.87 ± 0.08 (stat) ± 0.05 (sys) ± 0.10 (lum) combined 0.83 ± 0.06 (stat) ± 0.04 (sys) ± 0.09 (lum) L. Kashif thesis: graduation ~ Dec. 2010

12. 12 c. mills (Harvard U.) 20 September, 2010 Z Cross Section in Context

13. 13 c. mills (Harvard U.) 20 September, 2010 More Data in the Pipeline muon channel

14. 14 c. mills (Harvard U.) 20 September, 2010Conclusion Establishing the W and Z samples at ATLAS Rapidly increasing dataset  Better precision  W/Z properties, differential cross sections  W p T (next talk) W and Z data at the LHC will illuminate the Standard Model in a new momentum regime And pave the way to find what may lie beyond it  key to validation of high-p T leptons and E T miss Harvard role  Developing baseline muon selection for high-p T muon analysis  Driving W and Z cross section analyses, W lepton charge asymmetry in muon channel  Major contributor to 310 nb -1 paper, to be submitted soon

15. 15 c. mills (Harvard U.) 20 September, 2010 Backup

16. 16 c. mills (Harvard U.) 20 September, 2010 W   event selection good run list, filled bunch crossing, jet cleaning (data only) vertex with ≥ 3 matched tracks and |z| < 150 mmexists passed trigger (via p T cut on matched L1 trigger object)L1_MU6 at least one combined muon with p T > 15, |  | < 2.4 exists muon spectrometer p T > 10 GeV/c | p T (spectrometer) – p T (ID) |< 15 GeV/c combined muon |z0 - z(pv)|< 10 mm muon combined p T > 20 GeV/c muon |  | < 2.4 (track iso (cone 0.4))/p T (  ) < 0.2 MET> 25 GeV transverse mass> 40 GeV P RESELECTION W SELECTION

17. 17 c. mills (Harvard U.) 20 September, 2010 Backgrounds to W →  Z → , W → , Z → , ttbar: 77.6 ± 5.4 (stat+sys) events  From simulation QCD: 21.1 ± 9.8 (stat+sys) events  “Matrix Method”  Solve for N QCD using number of candidates with and without isolation req. (N loose = 1272, N isol = 1181)  Measure  non-QCD = 0.984 ± 0.01 from Z’s  Measure  QCD in data with 15 < p T  < 20 GeV (get 0.292 ± 0.004)  extrapolate to p T  > 20 GeV by scaling based on simulated dijet events (get 0.227) Cosmics: 1.7 ± 0.8 event  Consideration of empty and unpaired bunch crossings

18. 18 c. mills (Harvard U.) 20 September, 2010 QCD BG: Matrix Method (1) Solve for N QCD in isolated candidate sample N isol (1181) and N loose (1272) are number of W candidates with and without isolation cut  QCD and  non-QCD are efficiency of isolation cut for QCD and prompt muons  Measure  non-QCD = 0.984 ± 0.01 in tag-and-probe with Z’s  Measure  QCD in QCD-dominated data: candidate events with 15 < p T  < 20 GeV  extrapolate to p T  > 20 GeV by scaling by  (p T  > 20 GeV)/  (15 < p T  < 20 GeV) as measured in the MC (more on next slide)

19. 19 c. mills (Harvard U.) 20 September, 2010 QCD BG: Matrix Method (2) Measure  QCD in QCD-dominated data: candidate events with 15 < p T  < 20 GeV (get 0.292 ± 0.004)  extrapolate to p T  > 20 GeV by scaling by  (p T  > 20 GeV)/  (15 < p T  < 20 GeV) as measured in the MC  (0.238 ± 0.005)/(0.307 ± 0.003) = 0.776 ± 0.017 Uncertainties  systematic from 100% uncertainty on extrapolation  stat. uncert. from  non-QCD also significant Bottom line 21.1 ± 4.5 (stat) ± 8.7 (sys)

20. 20 c. mills (Harvard U.) 20 September, 2010 Backgrounds to Z Predicted total backgrounds:  electron: 1.18 ± 0.11 (stat) ± 0.41 (syst)  muon: 0.25 ± 0.01 (stat) ± 0.04 (syst)  compare to 3 (0) same-sign events in electron (muon) channel  2.8 same-sign events from Z → ee signal are expected Magnitude is small (<1% relative to expected signal) ttbar Z →  W → e /  QCD (muon channel) QCD (electron channel)  Sideband subtraction for loose-loose electron-positron pairs  Apply loose  medium “rejection factor” measured in data from simulation

21. 21 c. mills (Harvard U.) 20 September, 2010 Electrons in ATLAS EM calorimeter cluster matched to inner detector (ID) track E T > 20 GeV, |  | < 2.47  exclude gap between barrel and endcap 1.37 < |  | < 1.52 “Loose” selection  shower shape in middle layer of calorimeter “Medium” selection  add fine-granularity shower shape and track match  “Tight” selection  add E/p, more track quality, high-threshold TRT hits, conversion veto Trigger: Level 1 (hardware) requires coarse-granularity cluster with |  | 5 GeV

22. 22 c. mills (Harvard U.) 20 September, 2010 More on Electrons Trigger: sliding-window algorithm using reduced-granularity clusters  x  = 0.1 x 0.1 Offline reconstruction: sliding window of 3x5 cells or 0.075 x 0.125 in  x   Electron = cluster with E T > 2.5 GeV and matched track with p T > 0.5 GeV Reconstruction: exact requirements vary with E T and |  |, but three categories: Loose electrons  Fiducial: |  | < 2.37 and exclude 1.37 < |  | < 1.52  Shower shape in middle (largest) layer of calorimeter: cluster width in   Hadronic leakage: E T (innermost later of HCAL) / cluster E T Medium electrons: loose +=  Shower shape in innermost (finely segemented in  ) layer of calorimeter  Track match (  )  Track quality (pixel, SCT hits and impact parameter) Tight electrons: medium +=  High-threshold hits in transition-radiation tracker (TRT); hit in innermost pixel layer  E/p http://cdsweb.cern.ch/record/1273197/files/ATLAS-CONF-2010-005.pdf