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Summary of the 2005 Rome ATLAS Physics Workshop

Summary of the 2005 Rome ATLAS Physics Workshop. M. Cobal, University of Udine Physics Plenary, ATLAS Week, June05. Rome physics workshop. 91 entries (out of about 100 talks), 21 F plus 70 M. Some numbers : ~450 participants 100 talks ~ 35 hours of presentations and discussions.

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Summary of the 2005 Rome ATLAS Physics Workshop

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  1. Summary of the 2005 Rome ATLAS Physics Workshop M. Cobal, University of Udine Physics Plenary, ATLAS Week, June05

  2. Rome physics workshop 91 entries (out of about 100 talks), 21 F plus 70 M Some numbers: • ~450 participants • 100 talks • ~ 35 hours of presentations and discussions June 05 ATLAS Week - M. Cobal

  3. Sessions for physics groups • B-physics • Top • Higgs • Standard Model • SUSY • Exotics • Heavy Ions • HUGE amount of work/results • Cannot do justice to everything presented!! • Give general flavour of the workshop highlights • Focus as requested in talk title on early physics For all groups bulk of analyses performed on fully simulated “Rome” samples Concentrate on analyses possible with few fb-1 Displace center of interest from exploration of ATLAS parametrised potential to: • Control of detector systematics affecting measurements and discovery • Study of dependency of discovery potential from achieved level of alignment calibration • Development of strategies for estimate of systematics on background evaluation June 05 ATLAS Week - M. Cobal

  4. A new point of view: Commissioning! The game to play: Understand detector /Minimize MC dependency • Knowing the detector • Redundancy between detectors • Straight tracks, etc. • Physics: available ‘candle’ signals in physics • Presence and mass of the W±, Z0, top-quark • Presence of b-jets • Balance in transverse plane, PT • Prepair with detector pessimistic scenarios • Non-perfect alignment at startup, e.g. in b-tagging • Dead regions in the calorimeter / noise • Unknown precise jet energy scale • Assess trigger dependencies Only after full understanding of these the road to discovery starts… June 05 ATLAS Week - M. Cobal

  5. Top physics Standard Model • Minimum bias/Underlying event • Before Rome: comparing existing models with SPS/Tevatron and extrapolating to LHC • Now: based on the full ATLAS software chain, explore how well we can measure typical quantities: • Studies on W • Large statistics • Basic benchmark process • Aim at constraining proton PDFs • Emphasis on understanding systematic detector effects

  6. Minimum bias events (~20/beam cross) Example of “very early” physics: only need a few thousands interactions “Soft” part of pp interactions not described by PQCD Constitutes unavoidable background for all physics Measure typical quantities using full ATLAS chain: dNch/d dNch/dpT Large uncertainty track densities! Charged particle density at  = 0 LHC? Multiple interaction model in PHOJET predicts a ln(s) rise in energy dependence. PYTHIA suggests a rise dominated by the ln2(s) term. June 05 ATLAS Week - M. Cobal

  7. Generated vs reconstructed tracks Explore special runs without solenoid magnetic field? Charged particle densities dNch/d 1000 events dNch/d B=0 dNch/dPT Black = Generated charged tracks Blue = Reconstructed: NO TRT, NO solenoid Red = Reconstructed: NO TRT, WITH solenoid limited rapidity coverage Can only reconstruct track down to ~500 MeV PT MeV June 05 ATLAS Week - M. Cobal

  8. Uncertainty in pdf transferred to sizeable variation in rapidity distribution electrons Limited by systematic uncertainties To discriminate between conventional PDF sets we need to achieve an accuracy ~3% on rapidity distributions. Error boxes: The full PDF Uncertainties CTEQ61 (MC@NLO) MRST02 (MC@NLO) e- e+ ZEUS02 (MC@NLO) MRST03 (Herwig+k-Factors) Stat ~6 hours at low Lumi. h h Pdf determination using W bosons W+ and W- Rapidity June 05 ATLAS Week - M. Cobal

  9. Full simulation Pdf determination using W bosons • Generator level for Ws e+ e- Pseudo-Rapidity W+ and W- Rapidity e- e+ W+ Selection Cuts applied W- W- /W+ Ratio e- /e+ Ratio Selection Cuts applied June 05 ATLAS Week - M. Cobal

  10. Charge Misidentification dilutes Asymmetry Correction: Charge Asimmetry W Asymmetry e+e- Asymmetry Selection Cuts applied ARAW = Measured Asymmetry ATRUE = Corrected Asymmetry F-= rate of true e- misidentified as e+ F+ = rate of true e+ misidentified as e- June 05 ATLAS Week - M. Cobal

  11. Systematics using Full Simulation Charge misidentification F- ARAW = Measured Asymmetry ATRUE = Corrected Asymmetry F-= rate of true e- misidentified as e+ F+ = rate of true e+ misidentified as e- h Detector Level F+ • Use Z -> e+e- sample from • Full Simulation Rome production • ~98K events, Herwig+CTEQ5L • data-like analysis (No MC-Truth) • Mis-ID rate negligible? h June 05 ATLAS Week - M. Cobal

  12. Ratio <NTrackReco>/<NTrackMC> Underlying event UE is defined as the Transverse Region Transverse <nch> Df = f - fljet • Soft component in hard scattering event • On fully simulated jet sample compare reconstructed and generated multiplicity. Njets > 1, |ηjet| < 2.5, ETjet >10 GeV, |ηtrack | < 2.5, pTtrack > 1.0 GeV/c Good agreement reconstructed/generated Can use to tune MonteCarlo Pt leading jet (GeV) June 05 ATLAS Week - M. Cobal

  13. Aim to determine M(W) with precision of 15 MeV Highest precision expected in Wν Observables Transverse mass MT Missing PTmiss PT lepton W-mass June 05 ATLAS Week - M. Cobal

  14. Top physics Top physics • Top production: basic calibration tool for early physics 1500 tt->bW(ln)bW(jj) requiring 4 jets above 40 GeV/day at low L. • Need to select clean top sample from the beginning • Past work: show in fast simulation that top signal observable with no b-tagging • Rome work: perform signal and background analysis in full simulation stt(tot) = 759 pb stt(semi-lept: e,m)~ 30% Nevents ~ 700 per hour

  15. TOP CANDIDATE Reconstruct top w/o b-tag Observe top quarks after ~1 week? When no b-tag is yet present? Hadronic top: Three jets with highest vector-sum pT as the decay products of the top W boson: Two jets with highest momentum in reconstructed jjj C.M. frame. Selection cuts: Missing ET > 20 GeV 1 lepton Pt > 20 GeV Selection efficiency = 5.3% 4 jets PT > 40 GeV Trigger efficiency not taken into account yet June 05 ATLAS Week - M. Cobal

  16. Analysis including W+4jets background Observe both top and hadronic W peaks! W+jets bckg is large (and has large uncertainty) m(t) m(W) S/B = 0.45 S/B = 0.27 S 300 pb-1 Number of events / 5.1 GeV Number of events / 5.1 GeV B W+jets and MC@NLO signal W+jets and MC@NLO signal W mass (GeV) Top mass (GeV) Use peak position M(W) for light jet energy calibration June 05 ATLAS Week - M. Cobal

  17. Various cuts to improve purity Ask for: 70 < M(jj) < 90 GeV m(t) Top peak clearly visible after 1 week of LHC data m(t) Top mass (GeV) B-JET CANDIDATE Ask for: b signal probability> 0.90 on 4th jet Top mass (GeV) June 05 ATLAS Week - M. Cobal

  18. R EPart / E E E Use W in top events for jet calibration Effect of a mis-calibration of jet energy dominant systematics Several methods to calibrate. Simplest one: • compute R for k bins in E • apply kfactors on R and recompute R n times => June 05 ATLAS Week - M. Cobal

  19. Results after recalibration • Use Top sample to correct jet energies of Z+jet sample • TOP 12000 jets, Z+jet 8000 jets • Apply same cuts on jets energies • => Top light jet scale seems to work for all light jets • In progress: repeat exercise with backgrounds Top Z+jets EPart / E EPart / E After calib ‘Top’ E E June 05 ATLAS Week - M. Cobal

  20. Single top production • Three production mechanism • Some could be seen at Tevatron • At LHC ‘precise’ determination of all of them • Main backgrounds • Non top events • Z+jets, W+jets • Top-pair production • B-tagging essential in this case! Detailed simulation of single top only just started. No realistic backgrounds yet. NLO generator MC@NLO expected! June 05 ATLAS Week - M. Cobal

  21. Finding the Higgs particle • We have two options: • We find the Higgs at the LHC • Gain deep knowledge on the Standard Model • We do not find the Higgs at the LHC • Something serious wrong with our understanding of the Standard Model and it is observable at LHC • In the absence of Higgs, the WW scattering amplitude violates unitarity

  22. H is very sensitive to detector performance Study impact of new layout (initial/Rome) is underway Energy reconstruction of converted photons is critical issue Inclusive H to NLO • Energy reconstruction of converted and non-converted photons E()/E(true) Non-converted E()/E(true) converted E() June 05 ATLAS Week - M. Cobal

  23. NLO QCD corrections Higgs production via MC@NLO generator Higgs decay via HDecay program Used QCD NLO corrections to background pp+X Signal significance possibly further enhanced by 40%. H may be a discovery channel on its own for 10 fb-1 Inclusive H to NLO H+0j TDR-like analysis with NLO σ H+1j June 05 ATLAS Week - M. Cobal

  24. H 4 leptons • The HZZ*4leptons channel is the golden channel for SM Higgs search in the mass range 120 GeV < MH<~800 GeV • TDR studies on both e and m channels • Main backgrounds are: • ZZ*/g* (irreducible) • Zbb, tt (reducible) • Background rejection based on cuts on leptons pT, reconstructed Z and Higgs masses, lepton isolation based on calorimeter energies, impact parameter significance • Current studies aim mainly at assessing the reconstruction and selection performance • 4-muons channel • 4-leptons channel June 05 ATLAS Week - M. Cobal

  25. Preselection cuts as in TDR First two leptons pT>20 and |h|<2.5, second pair pT>7 and |h|<2.5 Likelihood for reducible background (Zbb and ttbar) rejection 2 largest IP, 2 largest pT, 2 largest transverse energies in a DR=0.2 cone Likelihood for irreducible background (ZZ) rejection Z invariant masses, angles between two Z’s decay planes, m angles in Z’s frame Normalized to 30 fb-1 H 4 muons June 05 ATLAS Week - M. Cobal

  26. H4m - different group Signal QCD ZZ Zbb ttbar NLO, Normalized to 30fb-1 June 05 ATLAS Week - M. Cobal

  27. Significances Significances using LO cross sections, 10 fb-1: Significances using LO and NLO for 10 fb-1: ● NLO ◦ LO • For large range of Higgs masses discovery after 10 fb-1 (one year?) • Combining electron and muon channels essential June 05 ATLAS Week - M. Cobal

  28. Counting experiment No Higgs mass peak! Discriminant variable is e.g. angle φbetween leptons Background top-pair productionand di-boson production: Event topology A nasty one: HW+W-l+νl-ν Require forward jets Two opposite leptons Reject central jets Missing energy • This decay mode significant in region 150 < MH < 180 GeV • At MH=170 BR 100 times HZZ • Understanding of bckgr’s critical! • Develop clever methods to assess backgrounds from data • Statistically can claim discovery with ~5fb-1 of data June 05 ATLAS Week - M. Cobal

  29. Backgrounds: Top-pair production with extra jets Rely heavily on ID tracking and b-tagging capabilities Very interesting alternative to Higgs discovery using photons Determination largest Yukawa coupling from production cross section: (ttHttbb,tttt,ttWW) g2ttHBR(Hbb,Htt,HWW) Challenging channel: 4 b-jets 2 light jets Missing energy Isolated lepton Another one: ttH signal • Detailed knowledge detector needed • Not done with realistic simulation and backgrouond treatment yet… Low Luminosity: 30/fb June 05 ATLAS Week - M. Cobal

  30. Search for SUperSYmmetry Search for SuperSymmetry Elegant extension to the ‘Standard Model’ that… stabilizes the Higgs mass; predict light Higgs mass. unifies the coupling constants of the three interaction provides a candidate for dark matter is consistent with all electroweak precision data Complex signatures: e, µ, t, jets, b-jets, Etmiss Good test for detector performance and reconstruction. Analyses divided by signature

  31. Various ways to create some order in the chaos of multi-parameter space Unified boson and fermion masses at GUT scale as in mSUGRA models: Only 4 free parameters remain: m0, m½, tanβ, A0, sign =± Select several mSUGRA points Consistent with WMAP data for cold dark matter Don’t believe mSUGRA, but use it to suggest interesting possible particle spectra Typically σ>1 pb, so early discovery physics Analyze each of these points E.g. point SU1: SuSy parameter space SU1 SU6 SU2 SU3 June 05 ATLAS Week - M. Cobal

  32. Susy characterized by decays: Decay to jets, perhaps leptons, and escaping LSP (missing ET) Events characterized by large Meff = ETmiss+Σ|pT, jet| All hadronic decay Backgrounds given by SM processes: Z and W-production, top production, multi QCD jets At TDR this background was estimated Convincing SuSy signal obtained using parton shower MC’s Hadronic SuSy topologies SU2 June 05 ATLAS Week - M. Cobal

  33. However, it is well known that parton showers underestimate the high PT region So complete background estimation is redone Using ME approach where possible Susy signal effectively disappeared in this channel Use the right MC generators! Hadronic SuSy June 05 ATLAS Week - M. Cobal

  34. SUSY:Background Main difference from PT jet For ETmiss> 700 GeV : clear excess ETmiss vital for SUSY searches High PT jets are emitted by background as well: not clear separation June 05 ATLAS Week - M. Cobal

  35. SUSY: s-transverse mass for SU1 In all possible ways and compute: June 05 ATLAS Week - M. Cobal

  36. Signal reduced by factor 5 Background reduced by factor 20-30 Dominant background are semi-leptonic top-quark pairs Largest uncertainty in Meff originates from estimation of ETmiss ETmiss distribution sensitive to detector imperfections One-lepton SuSy Simulation of 3-4% calo dead channels June 05 ATLAS Week - M. Cobal

  37. Add SuSy Repeat procedure with SuSy signal included ETmiss distribution from data Clear excess from SuSy at high ETmiss observed: method works! Obtain the ETmiss distribution from data using top events By fixing the top mass in the leptonic channel, predict ETmiss Select top without b-tagging ETmiss for top signal minus sideband Reduce combinatorical background Normalise at low ETmiss, where SuSy signals are small One-lepton SuSy: ETmiss estimate Estimate background from data Example of reducing MC dependency on ETmiss distribution June 05 ATLAS Week - M. Cobal

  38. In most scenarios the first SUSY decay reconstructed is leptonic decay of neutralinos. “Smoking gun”: excess of opposite-sign lepton pairs with an edge structure in invariant mass No mass peak themselves can be reconstructed Muon reconstruction efficiency is essential Example at point SU3: p p ~ c01 ~ ~ ~ q ~ c02 l g q q l l Di-lepton SuSy 4.37 fb-1 No cuts Muons opposite sign same sign June 05 ATLAS Week - M. Cobal

  39. SUSY: SU1 Leptonic Signatures D. Costanzo, F.Paige 20.6 fb-1, No cuts Coannihilation point MC Truth, lL Soft lepton MC Truth, lR Hard lepton MC Data Two edges from: Each s-lepton close in mass to one of the neutralinos – one of the leptons is soft June 05 ATLAS Week - M. Cobal

  40. SUSY: SU-2 Dileptons Focus-Point Heavy scalars: no scalar lepton in  decay 1° edge T.L. 6.9 fb-1 No cuts Direct 3-body decays: The two edges measure the two mass differences Δm = m(n0) -m(10) 2° edge Z 6.9 fb-1 No cuts Two edges expected at 57.0 and 76.4 GeV June 05 ATLAS Week - M. Cobal

  41. SUSY: SU-2 Dileptons • SU2 SUSY production is: •  (direct) (4.5 pb) • Do not pass cuts to reject SM • (little jets & ETmiss) • gg →+jets(0.5 pb) • This can be separated • efficiently from SM • After cuts (from fast sim), • only few events remain. • Edge reconstruction in SU2 needs higher integrated luminosity. 6.9 fb-1 2j100+4j50+xE100 2.6s excess SU2 dilepton invariant mass, after cuts to reject SM June 05 ATLAS Week - M. Cobal

  42. Tau signatures in SuSy • Tau signatures (mostly hadronic decays) are important in much of the mSUGRA parameter space, particularly at high tan • At some points in the parameter space (e.g. funnel) can only observe kinematic endpoints in  invariant mass distributions • Can often see endpoints in m, mq, etc, but: •  triangular shape distorted due to ETmiss from ν •  statistics much lower due to t-reconstruction efficiency (expecially for soft-taus, coannihilation point) • typically achieve /jet  100 for a t-reconstruction ε of 50% June 05 ATLAS Week - M. Cobal

  43. Typical distortion due to escaping neutrino’s in tau decay However, can still fit this distorted distribution to obtain edge point Black points: MC truth  note the triangular shape Red line: distribution from non-leptonic decay products  (distorted shape) SuSy: Tau signatures (98.3 GeV) 4.9 fb-1 4.9 fb-1 a strong di-t edge has been identified in the bulk region and it looks Possible to extract a useful measurement in the coannihilation region June 05 ATLAS Week - M. Cobal

  44. SUSY: b-tagging June 05 ATLAS Week - M. Cobal

  45. Exotics Among the most popular: - Alternatives to EW symmetry breaking - Extended gauge symmetries - Extra dimensions besides our 4D space time

  46. Signal: High pT bosons Few/no jets in central region (no colour exchange) Forward tag jets No light Higgs at the LHC? • Scenario without ‘light Higgs’ particle: VL VL → VL VL violates unitarity at scales ~TeV, reachable by LHC! • Increase in cross section damped e.g. by strong symmetry breaking mechanism • VL VL → VL VL described at low energy by an effective theory • General parameterisation of the “new physics”.Can lead to resonances in WW / WZ scattering Important backgrounds : • W+jets, Z+jets • ttbar • qq→WZqq , WWqq June 05 ATLAS Week - M. Cobal

  47. Separation of signal from background difficult Again ttbar background is essential ; need better undertanding Example resonances in Wlν, Wjj no resonance Scalar Vector 30 fb-1 of data - Signal - ttbar June 05 ATLAS Week - M. Cobal

  48. Exotics: H++ L-R symmetric model would be a natural extension of the SM • SU(2)L x SU(2)R x U(1)B-L • predicts new fermions: heavy Majorana neutrino • predicts new gauge bosons: WR • predicts new Higgs sector June 05 ATLAS Week - M. Cobal

  49. q q q W- q W+ 150 GeV Exotics: H++ ee mm WW+jets Example ee mm H++ - Signal:150, 200, 500 GeV(~5K) - Backgrounds: WW+jets (~5K) - Fake rate: jet/e Mass Mean Sigma Expected Selected (GeV) GeV GeV 150149.2 ± 0.089.9 ± 0.06 148.9 ± 0.09 11.9 ± 0.06 ee+mm 240 20 ± 1. WW+jets 0 June 05 ATLAS Week - M. Cobal

  50. Exotics: Narrow Resonance Z’ ee June 05 ATLAS Week - M. Cobal

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