Alessandro Tricoli W production at LHC By In collaboration with Monika Wielers Rutherford-Appleton Laboratory ATLAS UK Physics Meeting at Durham, 18th September 2006

Alessandro Tricoli, RAL Overview Introduction W production mechanism Importance of W production as standard candle process Reconstruction of W->en events and background rejection Standard ATLAS W Selection as in the TDR Trigger-aware selection of W->en events against background MWT and electron rapidity, ET distributions Alternative approach for W selection: CMS-like Jet Multiplicity with Cone and KT algorithms in W->en events effect of jet-finder choice on W selection Distortion on W-Asymmetry due to W selection cuts Conclusions and Outlook ATLAS UK Physics Meeting- Durham, 18th Sept. 2006 Alessandro Tricoli, RAL

Alessandro Tricoli, RAL W± Production at LHC LHC pp -> W± + … W p p Cabibbo Suppressed Valence-Sea and mainly Sea-Sea : largest contribution Sea-Sea: next largest contribution (Cabibbo dominating), whereas ~5% at Tevatron (17%) (23%) Cabibbo Suppressed Contribution 1-3% at LHC ATLAS UK Physics Meeting- Durham, 18th Sept. 2006 Alessandro Tricoli, RAL

Why accurate W reconstruction is important W production is a standard candle process: theoretically and experimentally well known large statistics: ~21 W->ln events per sec. at 1033 cm-2 s-1 lumi. (10 times larger than Z production) Together with Z it is a control-process for detector calibrations/performances: trigger selection efficiencies particle ID efficiency: calorimeter and tracker performances missing ET calibration (i.e. W->ln) jet reconstruction (i.e. in situ JES calib. with W->jj in tt events) luminosity monitor Control-process for physics performances: Theory cross check: electro-weak corrections, LO-NLO-NNLO approximations etc. PDF constraining (see Mandy’s talk): low-x gluon using W+ and W- rapidity distributions low-x valence quarks using W± asymmetry W+jets process is background to new physics important to accurately determine its kinematics parameters and quantify uncertainties See: ATLAS Calorimeter Calibration Workshop 5-8 Sept. 2006 ATLAS UK Physics Meeting- Durham, 18th Sept. 2006 Alessandro Tricoli, RAL

Alessandro Tricoli, RAL Analysis scope W reconstruction linked to various performance and physics groups: egamma, muon, jet/Etmiss/tau SM, Higgs, SUSY, Exotics This work focuses on the electron channel W->en Immediate aim is to contribute to CSC papers: W/Z inclusive, W/Z+jets and PDF ATLAS UK Physics Meeting- Durham, 18th Sept. 2006 Alessandro Tricoli, RAL

Alessandro Tricoli, RAL Data Sets Signal (W->en) and Backgrounds generated/simulated with PYTHIA Athena 11.0.41(2) Reconstruction ATHENA v11.0.5 Offline Analysis: AOD/AAN-tuples Sample Dataset Sim rel N. Gen. Events  (filt.) (pb) We 5104 11.0.42 15,000 11270 W 5106 4,608 3462 Zee 5144 1,889 1419 Z 5146 109 82 Di-jet (QCD) 5802 11.0.41 144,456 2.05·108 Top background negligible ATLAS UK Physics Meeting- Durham, 18th Sept. 2006 Alessandro Tricoli, RAL

Alessandro Tricoli, RAL W Event Selection Standard (ATLAS-TDR) W Selection : Trigger menu e25i applied: one isolated e±, tuned for efficiently select e± with ET> 25 GeV L1, L2 and EF only exception QCD, due to poor stat.: no trigger sel. Standard Electron Identification: isEM and cluster-track matching requirement cracks removal h=1.37-1.52 and |h|<2.4 Electron ET>25 GeV Missing-ET >25 GeV Jet Veto Cuts: Jets PT<30 GeV, Event Recoil PT< 20 GeV 60 GeV < MWT <100 GeV pnT in MWT is not estimated by Missing-ET (from cells), but by the vector sum of hard objects. Alternative (CMS-TDR-like) ATLAS UK Physics Meeting- Durham, 18th Sept. 2006 Alessandro Tricoli, RAL

Efficiencies for We From Monika Wielers Use W events generated with Pythia, Herwig and MC@NLO Generated/simulated with 11.0.41(2), reconstructed with 11.0.5 Select events with ET(e)>25GeV, ||<1.37 or 1.52< ||<2.47 at generator level Efficiencies very comparable between Pythia and Herwig MC@NLO gives slightly higher efficiencies, but still consistent within errors, e.g. small differences in L1 isolation Pythia Eff % Herwig MC@NLO L1 98.3 98.5 98.7 +L2 90.2 91.1 91.7 +EF 83.3  0.9 83.0  1.1 84.0  1.1 +offline 80.6  0.9 80.7  1.1 81.6  1.1 Offline only 90.2  1.0 89.6  1.1 90.4  1.2 CERN ATLAS SM Group, 6th Sept. 2006 Alessandro Tricoli, RAL

Missing ET in W->en events missETTruth – missETFinal: Compare: Missing ET Truth (MET_Truth) Standard ATLAS reconstructed Missing ET (MET_Final) from cells CMS-like pnT reconstructed from hard objects (ele&jets) electrons selected by isEM jets selected if there is no electron within DR<0.4 and PTJet>20 GeV Fit differences missETTruth – missETFinal and missETTruth - pTn missETTruth - missETFinal missETTruth - pTn MET_Truth MET_Final pnT Fit missETTruth – missETFinal: Mean= -2.08 ± 0.07 GeV s = 5.46 ± 0.07 GeV 2/NDF = 225.8 / 22 missETTruth – pTn: Mean= -1.36 ± 0.15GeV s = 11.38 ± 0.16GeV 2/NDF = 419.5/62 Asymmetric, Large tails CERN ATLAS SM Group, 6th Sept. 2006 Alessandro Tricoli, RAL

W Transverse Mass ATLAS-like vs CMS-like W -> tn Z -> e-e+ Z -> t+t- QCD W -> en Cumulative Bkg W Transverse Mass ATLAS-like vs CMS-like ATLAS-like ATLAS-like after e-ID only After Miss ET >25GeV CMS-like after e-ID only 60< MWT< 100 GeV CMS-like analysis: larger QCD and Z->e+e- background (no Miss ET cut) ATLAS-like analysis: electron ET and missing ET cuts efficiently reject backgrounds CERN ATLAS SM Group, 6th Sept. 2006 Alessandro Tricoli, RAL

MWT, and electron h, PT ATLAS Jet Veto Cuts ATLAS-like After Jet Veto Cuts W -> tn Z -> e-e+ Z -> t+t- QCD W -> en Cumulative Bkg After Jet Veto Cuts ATLAS-like ATLAS-like After Jet Veto Cuts (GeV) Electron Jet veto cuts efficiently reject fake electron background CERN ATLAS SM Group, 6th Sept. 2006 Alessandro Tricoli, RAL

Event Selection and Bkg Rejection Selection cuts We Nevnts (Cut Reduction) W Nevnts (Signal Contamination) Zee Z Di-jets Trigger, e-selection, crack removal 7390 365 (4.9%) 1784 (24.1%) 18 (0.2%) 52,760 + Electron ET>25 GeV Full Sim 6531 (-11.6%) 253 (3.8%) 1557 (23.8%) 14 4,686 (71.8%) + 60 GeV < MWT < 100 GeV Full Sim (CMS-like) 4567 (-30.1%) 86 (1.9%) 913 (20%) 6 (0.1%) 660 (14.5%) + ET(miss) > 25 GeV Full Sim Previous ATLFAST study 5678 (-17.0%) (-15%) 167 (2.9%) (1.6%) 19 (0.3%) 8 426 (7.8%) + no jet with ET > 30GeV Full Sim 4710 (-11.8) 115 (2.4%) (1.2%) 2 (0.0%) 7 36 (0.8%) + pT(recoil) < 20 GeV Full Sim 3712 (-21.2%) 90 1 (0.02%) 28 QCD background difficult to estimate: rate and shape very sensitive to selection cuts Good agreement between Full Simulation and previous ATLFAST estimates on Bkg contamination CMS-like has larger Bkg contamination than the standard (ATLAS-TDR) selection CERN ATLAS SM Group, 6th Sept. 2006 Alessandro Tricoli, RAL

Accompanying Jets in W->en events Jet Multiplicity Before Jet Veto Cuts (after Missing ET cut) CONE R=0.4 KT D=1.0 After Jet Veto Cuts e n jet p Large discrepancy between Cone and KT algorithms KT D=1.0 has larger jet multiplicity than Cone with R=0.4 Cone has more events with no jet in the event CERN ATLAS SM Group, 6th Sept. 2006 Alessandro Tricoli, RAL

Impact of Jet Algorithms on Jet Veto Cuts Using KT instead of Cone for the Jet Veto cuts ATLAS-like Selection cuts We W Zee Z Di-jets + no jet with ET > 30GeV CONE R=0.4 KT D=1.0 Difference (KT-CONE) 4710 3934 (-16%) 115 105 (-9%) 2 1 7 36 + pT(recoil) < 20 GeV 3712 3384 90 87 (-3%) 28 The choice of Jet Algorithm has impact on the W selection efficiency CERN ATLAS SM Group, 6th Sept. 2006 Alessandro Tricoli, RAL

Impact of selection cuts on W-Asymmetry Look at the e± Asymmetry From W± decay Rome Full Sim. Data: 67K W->en events, Herwig+Jimmy, CTEQ5L, Athena 10.0.1 e-Asym. Ae Ae(h) Before W sel cuts (only ele-ID) Ae(h) After W sel cuts Shape of asymmetry distribution in h is crucial to constrain PDF W Selection cuts deform Ae shape: ele-ET cut mainly responsible for this distortion effect reproducible with analytic calculations (Mandy) CERN ATLAS SM Group, 6th Sept. 2006 Alessandro Tricoli, RAL

Impact of selection cuts on W-Asymmetry Rome Full Sim. Data Difference between Ae(h) at Gen. (no cuts) and Det (all cuts) levels Difference between Ae(h) at Gen. (all cuts) and Det (all cuts) levels Mean = -0.271 ± 0.034 Mean = -0.018 ± 0.052 electron reconstruction and W sel. cut distortions ~27% on average (h-dependency) distortion seems to be reproducible at generator level (higher stat needed) if true with higher stat and if same cuts applied on analytic calc. => data unfolding can be small CERN ATLAS SM Group, 6th Sept. 2006 Alessandro Tricoli, RAL

Conclusions and Outlook W->en trigger/offline selection comparable between Pythia, Herwig. Only slightly higher with MC@NLO Background contamination is small ~3% QCD background difficult to estimate due to large cross section QCD events are very sensitive to the chosen cuts higher stat and/or better tools needed CMS-like selection can be used as a cross-check for data commissioning Missing ET from hard objects can be used to cross check MET_Final at detector start up. but CMS-like selection leaves larger background contamination it can be improved (i.e. removal of 2 electron events, see Z->e+e-) Jet Multiplicity and ET are very much algorithm dependent The efficiency of Jet Veto cuts strongly depends on the Jet Algorithm W-Asymmetry for PDF constraining: Distortions in h due to selection cuts can be under control if reproducible on calculations as it is at MC-generator level CERN ATLAS SM Group, 6th Sept. 2006 Alessandro Tricoli, RAL

Alessandro Tricoli, RAL EXTRAS ATLAS UK Physics Meeting- Durham, 18th Sept. 2006 Alessandro Tricoli, RAL

Alessandro Tricoli, Oxford University Reconstruction Reconstruction done using 11.0.5 Run trigger and offline reconstruction Select events triggered by e25i L1, L2 (IDscan as L2 track algo), offline as prototype for EF Use EF optimisations as prototype for offline e-identification Eff* % e± with ET=25 GeV We with ET>25 GeV Rate L1 96.2 97.7 6.5 KHz L2 Calo 95.1 95.4 1.1 KHz L2 ID 92.9 93.7 510 Hz L2 Match 90.6 90.2 160 Hz EF Calo 87.6 87.7 80±11 Hz EF ID 82.2 83.9 46±8 Hz EF Match 80.0 82.4 42±8 Hz (*) eff given with barrel/endcap crack excluded, ||<2.47 Alessandro Tricoli, Oxford University

Accompanying Jets in W->en events Jet ET All jets in the event Highest-ET jet in the event Before Jet Veto Cuts (after Missing ET cut) Before Jet Veto Cuts (after Missing ET cut) ? <ET>=31.9 <ET>=31.0 <ET>=20.1 <ET>=26.6 After Jet Veto Cuts ? After Jet Veto Cuts <ET>=14.7 <ET>=16.0 <ET>=17.4 <ET>=16.5 If all jets are considered: KT R=1.0 jets are softer than Cone R=0.4 If the highest-ET jet in the event is considered: KT jets are harder than Cone (?) CERN ATLAS SM Group, 6th Sept. 2006 Alessandro Tricoli, RAL

Electron ET and h (ATLAS-like) After Missing ET > 25 GeV After Missing ET > 25 GeV ATLAS-like ATLAS-like (GeV) After Jet Veto Cuts After Jet Veto Cuts ATLAS-like ATLAS-like (GeV) Jet veto cuts efficiently reject background especially QCD CERN ATLAS SM Group, 6th Sept. 2006 Alessandro Tricoli, RAL