Thibault Guillemin LAPP, Annecy, France W and Z total cross sections measurements ATLAS-LAPP & LAPTH Japan meeting, 21/01/08 Outline Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/20081/18 ATLAS-LAPP SM group Example: We e analysis Acceptance study in the CSC note Perspectives ATLAS-LAPP SM group 2 main subjects (now): measurement of the Zee and We e total cross sections strategies/tools for early data analysis (~100 pb -1 ) use of these processes for the understanding/calibration of the detector (physics candles): EM energy scale, efficiencies from data, alignment, MET scale, precision measurements (~1 fb -1 ) precise measurements of the electroweak parameters: W, M W, l eff, lepton universality, pdfs constraints ultimately: use of Ws and Zs bosons as luminosity monitors Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/20082/18 Analysis example: W e e with: N mes : number of W events N bckgd : number of background events A: acceptance (includes kinematic and geometric cuts) trigger : trigger efficiency offline : offline electron reconstruction efficiency Int(Ldt): integrated luminosity Experimentally: Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/20083/18 Analysis strategy Event selection: cut-based method 1) Online: trigger EF_e25i 2) Offline: good electron candidate such that E T > 25 GeV, outside the cracks MET > 25 GeV Backgrounds determined from data Acceptance computed from MC error ~3% (pdfs = main contribution) Trigger and offline electron reconstruction efficiencies measured from Zee events Luminosity given by machine parameters at t 0 and then measured by very forward dedicated detectors The precision of the measurement depends on the systematical error on each term estimation (and reduction when possible) of all the systematics Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/20084/18 Trigger selection Trigger signature: EF_e25i: 1 isolated electron / E T > 25 GeV + identification criteria L1 RoIs (=0.1*0.1) L2 access to all the cells in the RoIs subdetectors combination EF access to all the cells of the detector offline algorithms = f(E T ) L1_EM25 L2_e25i EF_e25i ATLAS TDR Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/20085/18 Signal and backgrounds SamplesCuts at generator level Filter efficiency N events Integrated luminosity (pb -1 ) W e e 1 e: p T e > 10 GeV, | e | < QCDp T (hard process) > 17 GeV W 1 e/: p T l > 5 GeV, | l | < Z ee1 e: p T e > 10 GeV, | e | 60 GeV Signal charaterized by the presence of an electron with high E T and a high transverse missing energy possible backgrounds: irreductible: W e e Zee: one electron escapes the detection QCD (multijets): one electron in a jet or a jet is identified as an electron t-tbar: neglictible Datasets used in the analysis fake MET due to the bad reconstruction of objects Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/20086/18 Electron selection Electron reconstruction performed in several steps: EM cluster identification (sliding window, topoclusters) matching with a track of the inner tracker criteria on the shower shape criteria on the track quality 3 levels of identification: isEM loose, isEM medium, isEM tight Distributions for the main EM estimators Hadronic leakage Total width (strips) Shower shape (middle) r incident particle Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/20087/18 Efficiencies determination from data Tag-and-probe method on Zee events selection of 1 electron passing all the cuts tag selection of 1 electron passing all the cuts except one probe + constraint to the Z mass possibility of measuring the trigger efficiency with double trigger signatures (EF_2e25i) e - (probe) e - (tight) Z EM calorimeter Comparison of electron for the W and Z events sample eff Zee: 2 electronsWenu isEM medium76.5 0.2 Correction needed: = f(E T, ) global factor Dot: W Triangle: Z 2 electrons Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/20088/18 Transverse missing energy reconstruction Method based on the calorimeter cells: MET = MET Calo + MET Cryo + MET Muon 1) selection of cells from signal/noise topoclusters 4/2/0 2) calibration of the cells in function of the object they belong to (non compensating calorimeter) map cells-objects weights to each cell MET distributions for signal and backgrounds MET = very efficient criterion for QCD and Zee backgrounds reduction Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/20089/18 Backgrounds estimation (1/2) Electroweak backgrounds are (will be?) estimated from MC W e e : f = 2.40.2% Zee: f = 0.20.02% QCD (data) extract the number of QCD events in the signal region Method: 1) define an anti-W cut (uncorrelated with MET) to get a QCD reference sample Ex: photons sample, non-isolated electrons sample,.. 2) from the reference sample, normalize in the W sample the low (10 20 GeV) and high MET (>25 GeV) regions Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/200810/18 Backgrounds estimation (2/2) Example of anti-W cut: on-isolated electron (isolation = E cone /E) AB CD signal region In this study: anti-W cut electron candidate failing isEM loose QCD10-20 GeV25-60 GeV failing loose medium531 67, N extr = 87, N/N 0 = +30% Assuming the MET distribution for QCD is the same in the W and in the anti-W sample: Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/200811/18 Comparison of the systematics for 1 fb -1 QuantityAssumption (nb) NWNW statistical error0.01 NBNB f~10%, f~2% 0.4 electron ~0.5% 0.1 trigger ~0.5% 0.1 IntL IntL/IntL~10% 1.7 A A/A~3% fb -1 : N W ~ events = 17.3 nb (LO) NB: a lot of systematical effects are not taken into account: EM energy scale, MET biases, correlations Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/200812/18 Acceptance study in the W&Z CSC note In the CSC note: study on the systematics of We e /Zee acceptances study done by M.Goulette Goal: to estimate the systematic uncertainty on A W and A Z with standard cuts applied to the decay leptons Principle of the study; comparison of generators Pythia 6.4 Herwig Jimmy Pdfs: LO CTEQ6L, NLO CTEQ6M Estimate the impact of different sources: turn on/off ISR, intrinsic kT, UE, Photos, ME pdfs impact These three generators are interfaced with Athena Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/200813/18 Comparison at LO Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/200814/18 EW corrections with Photos Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/200815/18 Systematics at LO Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/200816/18 NLO correction Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/200817/18 Perspectives estimate the theoretical uncertainty on the acceptance for We e and Zee processes: not the key parameter for the start, but solid/official numbers are required need to estimate the impact of mixed EW-QCD NLO corrections study the effect of varying phase-space cuts: differential distributions of main observables are needed for generators interfaced with ATLAS: possibility of precise studies at generator level and at detector level real phase-space, MET with very forward particles, the most precise computation of the total cross section is really required for the use of W and Z processes as luminosity monitors several fb -1 ATLAS-SM-LAPP wants to start to work on the acceptances of the We e and Zee processes: open to collaborations, ideas, tools Thibault Guillemin ATLAS LAPP & LAPTH Japan meeting, 21/01/200818/18 BACK-UP protons beam cylindrical detector length: 44 m diameter: 22 m weight: 7000 tons mirror symmetry coordinates system: Z Y X use of the pseudo-rapidy = - ln (tan(/2)) Aim of the detector: to identify photons, electrons, muons and jets to measure their energy and direction to measure the transverse missing energy (hermicity of the detector) The ATLAS detector 4/ 27 beam axis =