Top Ilya

1. Top Ilya • Outline • Top Physics • Top Working Group • Group convener • Group resources • List of mayor institutions in the group • Overview of the main analyses • List of ongoing analyses & 2005 ATL notes • Jet calibration • Top mass measurement • Top WG studies during the detector commissioning with the first collisions • Group goals for 2006 • Summary

2. Top WG • http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/TPHYSICS/tphysics.html • 1-2 WG meetings per month • ~ 20-30 people currently involved in the analyses, • the number grows up rapidly • Conveners: • Dominique PallinUniversite Blaise Pascal de Clermond FerrondCERN office: 40-R-C06, tel: 71128 • Stan BentvelsenNIKHEF, Kruislaan 409, 1098 SJ, AmsterdamCERN office: 40-2-D06, tel: 71157 • List of main institutions in the group: • NIKHEF (Amsterdam), SACLAY • Centre de Physique des Particules de Marseille • Universite Blaise Pascal de Clermond Ferrand • U.of Alberta, DAPNIA, U.Udine, LIP

3. Top quark exists and will be produced abundantly. • Top production cross section approximately 100x Tevatron • In SM: top- and W-mass constrain Higgs mass • Sensitivity through radiative corrections • Scrutinize SM by precise determination top mass • Beyond SM: New Physics? • Many heavy particles decay in tt Handle on new physics by detailed properties of top • Experiment: Top quark useful to calibrate the detector • Beyond Top: Top quarks will be a major source of background for almost every search for physics beyond the SM • Top mass determination • Commissioning phase • Top properties • Single top production Top Physics at ATLAS

4. Top WG analysis list Ongoing Analyses • Jet Calibration and Top mass reconstruction(Clermont+Alberta) • Top mass reconstruction (DAPNIA) • Commissioning with tt and single top events(NIKHEF) • Single top (s-channel and t-channel) (Grenoble) • Single top trigger studies (MSU) • Single top (Wt channel) and tt cross section (Udine+Tufts+Pisa) • Single top (Wg channel) (Carleton) • Top spin polarization and W polarization (CPPM+Prague) • FCNC in top decays (tt and single top), Asymmetries (LIP+RHUL) Analyses done in 2005 (ATL notes) • Top quark mass measurement in the lepton plus jets channel using full simulationATL-COM-PHYS-2005-059 • Top studies for the Atlas detector commissioningATL-COM-PHYS-2005-039 • ATLAS sensitivity to top quark and W boson polarization in ttbar eventsSN-ATLAS-2005-052 • Study of ATLAS sensitivity to FCNC top decays ATL-COM-PHYS-2005-023 • Top quark mass measurement in the lepton plus jets channel using full simulation ATL-COM-PHYS-2005-020 • Measurement of the W polarization in top decays with semileptonic ttbar events ATL-COM-PHYS-2005-015

5. j1 n W1 W2 l(e,m) j2 t1 t2 b1 b2 Light jet energy scale determination with Top events Motivation • The absolute energie scale will be known at the level of few percent at LHC start • The calibration function varies with E and  • => Get the light jet energy scale such that E jet  E parton AOD Cone 04 Calibration function  (Ejet) = Eparton / Ejet An example: Rome AOD  (Ejet) = 1. to 1.1, ‘cone 04’ Method • Use the well defined W mass to rescale the jet energies from the W decay Wj1 j2 such that MW=MWPDG • Dont use any hypothesis for the calibration function • Dont rely on MC • Select an enriched W sample from ttbar sample

6. Preliminary result with 1000 W +bkg evts • Calibration marginaly sensible to BKG (purity=85%) EPart / E preliminary To reach the 1% precision on the E scale, 10000 Ws should be enough = 1month data taking Studies of systematic errors do take place after the Rome workshop. E • Three methods were investigated to get in-situ light jet calibration for Top mass measurement • Preliminary results from AOD • AOD and ATLFAST comparable for top studies • 1% precision on the jet scale seems achievable in 1-2 month of data taking at 1033 • Top in-situ Light jet scale seems usable for all jets (if calibration is done for jets with same selection, checked on gamma+jet sample) • Future • Run on all AOD files + physical BKG • Detailed look into jet algorithms

7. Lepton side Hadron side Golden-plated: MTop from lepton+jet • Golden channel • Clean trigger from isolated lepton • The reconstruction starts with the W mass: • different ways to pair the right jets to form the W • jet energies calibrated using mW • Important to tag the b-jets: • enormously reduces background (physics and combinatorial) • clean up the reconstruction Br(ttbbjjl)=30%for electron + muon • Typical selection efficiency: ~5-10%: • Isolated lepton PT>20 GeV • ETmiss>20 GeV • 4 jets with ET>40 GeV • >1 b-jet (b40%, uds10-3, c10-2) Background: <2% W/Z+jets, WW/ZZ/WZ

8. j2 j1 b-jet t Lepton + jet: reconstruct top • Hadronic side • W from jet pair with closest invariant mass to MW • Require |MW-Mjj|<20 GeV • Assign a b-jet to the W to reconstruct Mtop • Kinematic fit • Using remaining l+b-jet, the leptonic part is reconstructed • |mlb -<mjjb>| < 35 GeV • Kinematic fit to the tt hypothesis, using MW constraints • Selection efficiency 5-10% • Method works: • Linear with input Mtop • Largely independent on Top PT • Biggest uncertainties: • Jet energy calibration • FSR: ‘out of cone’ give large variations in mass • B-fragmentation • Verified with detailed detector simulation and realistic calibration Challenge: determine the mass of the top with around 1 GeV accuracy on 10 fb^-1

9. Consequences from Mtop Thanks to M.Grunewald • Assuming total uncertainty on W-mass of 15 MeV • Combined LHC prospect • Very challenging measurement! • Repeat the Electro-Weak fit changing the uncertainties: • Mtop=1 GeV • MW =15 MeV • Same central values • SM constraints on MHiggs: • Summer 2003 values: direct EXCLUDED (mH/mH  32%) (mH/mH  53%) Chances to rule out SM

10. Top while Commissioning the detectors • Determination MTop in initial phase • Use ‘Golden plated’ lepton+jet • Selection: • Isolated lepton with PT>20 GeV • Exactly 4 jets (R=0.4) with PT>40 GeV • Reconstruction: • Select 3 jets with maximal resulting PT Calibrating detector in comissioning phase Assume pessimistic scenario: -) No b-tagging -) No jet calibration -) But: Good lepton identification No background included • Signal can be improved by kinematic constrained fit • Assuming MW1=MW2 and MT1=MT2

11. While Commissioning the detectors • Most important background for top: W+4 jets • Leptonic decay of W, with 4 extra ‘light’ jets • Alpgen, Monte Carlo has ‘hard’ matrix element for 4 extra jets(not available in Pythia/Herwig) ALPGEN: W+4 extra light jets Jet: PT>10, ||<2.5, R>0.4 No lepton cuts Effective : ~2400 pb L = 150 pb-1 With extreme simple selection and reconstruction the top-peak should be visible at LHC measure top mass (to 5-7 GeV) give feedback on detector performance

12. What we can provide • Top enriched samples • Estimate of a light jet energy scale • Estimate of the b-tagging efficiency • Estimate of missing energy • using Tevatron top mass • Determine of Mtop and σtop • Any hope for single top? Inputs • Single lepton trigger efficiency • Lepton identification efficiency • Integrated luminosity • At startup around 10-20%. • Ultimate precision < 5% • Eventually: • B-tagging efficiency • Jet scales ToDo list (among others): - Complete background - Full trigger information - Apply JES corrections - Influence jet algorithms - Repeat study with realistic alignment and condition simulation (DC3) Summary: Understand the interplay between using the top signal as tool to improve the understanding of the detector (b-tagging, jet E scale, ID, etc..) and top precision measurements

13. Top topics vs. more data • Top mass while commissioning the detectors -> feedback on the performance • Light jet absolute scale calibration With ttbar sample of w->jj • Sample of 10 fb-1 and more: • Top properties precision measurements • Top cross section and mass • Top spin correlations • Top charge determination • Decay modes, … • Single top measurements • Cross sections • Vtb matrix element • Exotics involving top • Ttbar resonances • SuSy in top vertex • FCNC, …

14. Top WG 2006 • Produce a paper on top physics with 100pb-1 and 10fb-1 • Estimates of luminosity in 2007/2008 • Time schedule: end of 2006 • Draft for one of first ATLAS publications with “real” data • Topics to settle • Trigger • What calibration samples and tools are required? • Analysis tools • Background checks using data • Simulate with as built (realistic) detector • An estimate of top cross section is candidate for “top three of first papers” of Atlas • Ratio of cross sections? For example: σ(tt)/σ(W-production)?

15. Summary • Top WG studies were very well organized last few years. • The WG has, at the moment, ~30 active members and this number grows. • The Top physics topics are not many but are certain. • The strategy to follow the luminosity build-up is defined. • W->jj calibration is nicely advanced to the systematic studies. • Top mass measurement was studied under different assumptions on the detector readiness. • The group has rather well defined plan for the next two years: • Concentrate on the analyses that require 10 inv fb or less • Study triggers • Define calibration samples and tools. • Background checks using data • Simulate with as built (realistic) detector • The group aims to make one out of “top three of first papers” of Atlas