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Physics at the LHC: Hardware commissioning, Pilot Physics, and Provisional Running

This paper discusses the physics roadmap for the LHC, including the commissioning of the hardware, pilot physics, and provisional running. It also emphasizes the importance of understanding and calibrating the detector and trigger, measuring cross-sections, and looking for new physics.

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Physics at the LHC: Hardware commissioning, Pilot Physics, and Provisional Running

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  1. First Physics at the LHC Thanks to: G. Polesello F. Giannotti R. Chierici R. Tenchini P. Bartalini M. Cobal (1), E. Migliore (2) (1) University of Udine and INFN Trieste (2) University of Torino and INFN Torino IV Workshop Italia ATLAS-CMS Bologna, 23-25 November 2006

  2. 2008 should look something like… Hardware commissioning to 7 TeV Machine Checkout 1 month Commissioning with beam 2 months Pilot Physics 1 month Reach 1031 Provisional Running at 75 ns L~ 1032 cm-2s-1 ~ 3 months of running +some optimism ~ 1 fb-1 IV Workshop Italiano ATLAS-CMS

  3. LHC: physics roadmap Understand/calibrate detector and trigger in situ using “candles” samples e.g. - Z  ee,  tracker, ECAL, muon chamber calibration and alignment, etc. - tt  bl bjj jet scale from Wjj, b-tag performance, etc. Understand basic SM physics at s = 14 TeV • measure cross-sections for e.g. minimum bias, W, Z, tt, QCD jets (to ~20 %), • start to tune Monte Carlo • measure top mass  give feedback on detector performance Note : statistical error negligible with O(10 pb-1) Prepare the road to discovery: • measure backgrounds to New Physics : e.g. tt and W/Z+ jets • look at specific “control samples” for the individual channels: e.g. ttjj with j  b “calibrates” ttbb irreducible background to ttH  ttbb Look for New Physics potentially accessible in first year(s) e.g. Z’, SUSY, Higgs ? IV Workshop Italiano ATLAS-CMS

  4. How many events at the beginning ? Assumed selection efficiency: W l, Z ll : 20% tt  l+X :1.5% (no b-tag, inside mass bin) similar statistics to CDF, D0 today + lots of minimum-bias and jets (107 events in 2 weeks of data taking if 20% of trigger bandwidth allocated) 10 pb-1 1 month at 1030 and < 2 weeks at 1031,=50% 1 fb-1 100 pb-1 few days at 1032 , =50% IV Workshop Italiano ATLAS-CMS

  5. Which detector performance on day one ? Based on detector construction quality, test-beam results, cosmics, simulation Expected performance day 1Physics samples to improve ECAL uniformity ~ 1% Minimum-bias, Z ee e/ scale ~ 2 % Z  ee HCAL uniformity ~ 3 % Single pions, QCD jets Jet scale < 10% Z ( ll) +1j, W  jj in tt events Tracking alignment 20(100)-200 m in R? Generic tracks, isolated m , Z mm Ultimate statistical precision achievable after few weeks of operation. Then face systematics…. E.g. : tracker alignment : 100 mm (1 month)  20mm (4 months)  5 mm (1 year) ? IV Workshop Italiano ATLAS-CMS

  6. What we will know @ LHC start? W, Z cross-sections: to 3-4% (NNLO calculation  dominated by PDF) tt cross-section to ~7% (NLO+PDF) Lot of progress with NLO matrix element MC interfaced to parton shower MC (MC@ NLO, AlpGen,.. ) LHC <Nch> at  =0 for generic pp collisions (minimum bias) PYTHIA6.214 - tuned PHOJET1.12 Transverse < Nchg > x 3 LHC ? x1.5 — AlpGen Candidate to very early measurement:  tuning of MC models  understand basics of pp collisions, occupancy, pile-up, … IV Workshop Italiano ATLAS-CMS

  7. Minimum Bias • Non-single diffractive evts, s≈ 60-70 mb • Soft interactions • Low PT, low Multiplicity. • Soft tracks: pTpeak~250MeV • Approx flat distribution in h to |h|~3 and in f • Nch~30; |h|<2.5 • Rate: R~700kHz @ L=1031cm-2s-1, For dN/dh require ~10k • What we would observe with a fully inclusive detector/trigger. • Several MB interactions can take place in a single beam crossing. • MB seen if “interesting” triggered interaction also produced. • Pile-up effect. • Tracking detectors help to separate the different primary vertices. • Possible overlap of clusters in calorimeters. Need energy flow. IV Workshop Italiano ATLAS-CMS

  8. Initial Tracking & Alignment • Very first alignment will be based on: • Mechanical precision • Detailed survey data • Cosmic data • Minimum bias events and inclusive bb • Studies indicate good efficiencies after initial alignment • ~ 80% down to PT = 500 MeV • Precision will need Zs and resonances to fix energy scales, constrain twists, etc. pT (MeV) • Even lower PT accessible with reduced tracking ? • PT = 400 MeV - tracks reach end of TRT • PT = 150 MeV - tracks reach last SCT layer • PT = 50 MeV - tracks reach all Pixel layers 150MeV IV Workshop Italiano ATLAS-CMS

  9. High PT scatter Beam remnants ISR Underlying Event • All the activity from a single particle-particle interaction on top of the “interesting” process. • Initial State Radiation (ISR). • Final State Radiation (FSR). • Spectators. • … Multiple Interactions ? (These models are certainly very successful!). • The UE is correlated to its “interesting” process. • Share the same primary vertex. • Events with high PT jets or heavy particles have more underlying activity Pedestal effect. • UE ≠ MB but some aspects & concepts are similar. • Phenomenological study of Multiplicity & PT of charged tracks. IV Workshop Italiano ATLAS-CMS

  10. UE: measurement plan at the LHC From charged jet usingMB and jet triggers) Topological structure of p-p collision from charged tracks The leading Ch_jet1 defines a direction in the f plane The transverse region is particularly sensitive to the UE Main observables: + dN/dhdf, charged density + d(PTsum)/dhdf, energy density From D-Y muon pair production (using muon triggers) observables are the same but defined in all the fplane (after removing the m pairs everything else is UE) IV Workshop Italiano ATLAS-CMS

  11. MC MB JET60 JET120 PT>0.9, |h|<1 Main observables: - dN/dhdf, charged density - d(PTsum)/dhdf, energy density UE with charged jets dNch/dhdf VS PT_ch_jet1 Njets > 1, |ηjet| < 2.5, ETjet >10 GeV, PT_ch_jet1 Good RECO/MC agreement in shape Differences compatible with the expected corrections from charged jet PT calibration, charged tracks innefficiencies and fake rate RECO/MC Differences absorb in the ratio, no need to apply corrections! Emphasis on the reconstruction of soft tracks… IV Workshop Italiano ATLAS-CMS

  12. UE with Drell-Yan dPTsum/dhdf dN/dhdf M(m,m) M(m,m) Ratio PT>0.9GeV/PT>0.5GeV (PT tracks threshold) Ratio observables are sensitive to differences between models !!! IV Workshop Italiano ATLAS-CMS

  13. Production of W and Z boson • Large W (Z) cross section: 10 nb (1 nb) and clean leptonic signatures • Compare to theo. prediction or assume prediction and use to measure luminosity • Example : uncertainties with 1 fb-1 in the muon channel in detector fiducial volume IV Workshop Italiano ATLAS-CMS

  14. PDFs:LHC Kinematic regime Kinematic regime for LHC much broader than currently explored Test of QCD: • Test DGLAP evolution at small x: • Is NLO DGLAP evolution sufficient at so small x ? • Are higher orders important? • Improve information of high x gluon distribution At TeV scale New Physics s’s predictions are dominated by high-x gluon uncertainty (not sufficiently well constrained by PDF fits) At the EW scale theoretical predictions for LHC are dominated by low-x gluon uncertainty (i.e. W and Z masses) => see later slides How can we constrain PDF’s at LHC? IV Workshop Italiano ATLAS-CMS

  15. CTEQ61 CTEQ61 MRST02 MRST02 ZEUS-S ZEUS-S Generator Level Error boxes are the Full PDF Uncertainties ATLAS Detector Level with sel. cuts GOAL: syst. exp. error ~4% Wen rapidity distributions • W production over |y|<2.5 at LHC involves 10-4 < x1,2 < 0.1  region dominated by g  qq HERWIG MC Simulations with NLO Corrections e-rapidity e+ rapidity At y=0 the total PDF uncertainty is ~ ±5.2% from ZEUS-S ~ ±3.6% from MRST01E ~ ±8.7% from CTEQ6.1M ZEUS-S to MRST01E central value difference ~5% ZEUS-S to CTEQ6.1 central value difference ~3.5% IV Workshop Italiano ATLAS-CMS

  16. low-x gluon shape parameter λ,xg(x) ~ x –λ BEFOREλ = -0.199 ± 0.046 AFTER λ = -0.181 ± 0.030 40% error reduction Including ATLAS data on PDF fits Generate 1M “data” sample with CTEQ6.1 PDF through ATLFAST detector simulation and then include this pseudo-data (with imposed 4% error) in the global ZEUS PDF fit (with Det.->Gen. level correction). Central value of ZEUS-PDF prediction shifts and uncertainty is reduced: ZEUS-PDFBEFORE including W data ZEUS-PDFAFTER including W data e+CTEQ6.1 pseudo-data e+CTEQ6.1 pseudo-data |h| |h| In few day stat. of LHC at low Luminosity Systematics (e.g. e acceptance vs ) can be controlled to few % with Z  ee (~ 30000 events for 100 pb-1) IV Workshop Italiano ATLAS-CMS

  17. Top physics in the early phase The LHC will be a top-factory !  NLO~830 pb : 2 tt events per second !  more than 10 million tt /year • Measure total ttbar cross section: • test of pQCD calculations (predicted at ~ 10%) • sensitive to top mass • Measure differential cross sections • sensitive to new physics • Make initial direct measurement of top mass • Measure single top production (t-channel) IV Workshop Italiano ATLAS-CMS

  18. Top physics during commissioning • Several months to achieve pixel alignment • Study separation of top from background without b-tagging • Use high multiplicity in final states • High Pt cuts to clean sample • Use kinematical features • Even with a 5% efficiency 10evts/hour at 1033 Hadronic top: Three jets with highest PT W boson: Two jets in hadronic top with highest PT in reconstructed jjj C.M. frame W CANDIDATE TOP CANDIDATE IV Workshop Italiano ATLAS-CMS

  19. m(Wjj) m (topjjj) m (topjjj) L=300 pb-1 S S/B = 1.77 B S/B = 0.45 Top physics during commissioning |mjj-mW| < 10 GeV S : MC @ NLO B : AlpGen x 2 to account for W+3,5 partons (pessimistic) Expect ~ 100 events inside mass peak with only 300 pb-1 • top signal observable in early days with no b-tagging and simple analysis • W+jets background can be understood with MC+data (Z+jets) IV Workshop Italiano ATLAS-CMS

  20. W+jets x 2 W+jets x 4 W+jets x 8 Nominal W+jets Siginficance (s) Luminosity (pb-1) Top signal significance vs luminosity Siginficance (s) Fitted #signal events Luminosity (pb-1) Luminosity (pb-1) IV Workshop Italiano ATLAS-CMS

  21. Miscalibrated detector or escaping ‘new’ particle Events Perfect detector What can you do with early tops?  Calibrate light jet energy scale - impose PDG value of the W mass (precision < 1%)  Estimate/calibration b-tagging e - From data (precision ~ 5%) - Study b-tag (performance) in complex events  Study lepton trigger  Calibrate missing transverse energy - use W mass constraint in the event - range 50 GeV < p T < 200 GeV  Estimate (accuracy ~20%) of mt and tt. Use W boson mass to enhance purity Missing ET (GeV) IV Workshop Italiano ATLAS-CMS

  22. Systematic effects for top physics • Almost all SM measurements at LHC dominated by systematic errors. • Can be divided into instrumental and from theory/modeling • Dominant instrumental uncertainties for top physics: Luminosity:  Reasonable goal is 3-5%  measure number of interactions/bunch crossing (HF) and (pp) (TOTEM) Reconstruction related:  Jet energy scale need calibrated calorimetry (beam tests, MB, single particles, Z, W…) need jet energy calibration to a few % (with Z()+jet) need excellent energy flow (association tracker+calo+muon system)  b-tagging efficiency+fake rate use tt for calibration: to 4-5% with 10/fb  Lepton identification and energy scale use Z, other mesons. Less crucial than for the W mass measurement Theory related systematics are as important as instrumental ones ! IV Workshop Italiano ATLAS-CMS

  23. UE, MPI MEs PS fragmentation Learning from data We model most of our description of reality at the LHC:  Need to quote a confidence on the description of our simulations  Need to avoid non realistic scenarios (ex: FSR OFF)  Need to avoid to double count errors • pdfs constrain using LHC data • hard scattered partons process description (signal AND backgrounds) scale dependency • final state radiation vary QCD and Q2max consistently ? • hadronization b+light jets: is LEP good enough? • initial state radiation vary QCD and Q2max consistently ? • minimum bias and underlying event energy dependent. Do our own tuning ! PDFs Jets UE PDF tuning  UE tuning  radiation tuning  fragmentation tuning LHC must learn the best way to use its own data to constrain models IV Workshop Italiano ATLAS-CMS

  24. X-section of tt semileptonics at 1 fb-1 Single lepton selection  Lepton with cuts on ET and   Missing ET>40 GeV  Hadronic activity (4 jets)  b-tagging of 2 jets IV Workshop Italiano ATLAS-CMS

  25. Top mass measurement at fb-1 ttbar semileptonics • Should be able to measure top mass at ~ 1% in both dileptonic and semileptonic channel • Need control of the jet energy scale ! • Larger error ~2-3% in the hadronic channel IV Workshop Italiano ATLAS-CMS

  26. Conclusions • LHC startup will require a long period of development and understanding • With first data measure • detector performance in situ  physics • particle multiplicity in minimum bias • top signal with ~ 30 pb-1 • s(tt) to 20% and Mtop to 7-10 GeV with 100 pb-1 ? • PDF (low-x gluons !) with W/Z (O(100) pb-1 ?) • first tuning of MC (MB, UE, tt, W/Z+jets, QCD jets,…) • Goal is to arrive @ high statistics (few fb-1) data-taking ready to go for early discovery physics • BUT….as soon as interactions @ 14 TeV happen interesting and new physics will appear in the data. Surprises? ….see discussion of Ernesto! IV Workshop Italiano ATLAS-CMS

  27. IDEE PER LA DISCUSSIONE capacità di fare misure accurate/difficili possibilità di fare scoperte … con 100-1000 pb-1

  28. Cross-sections and rates At luminosity 1032 cm-2 s-1 • Inelastic: 107 Hz • bb production: 104 Hz • W ℓ: 1 Hz • Z  ℓℓ: 0.1 Hz • tt production: 0.1 Hz IV Workshop Italiano ATLAS-CMS

  29. b-physics with 100 pb-1: control channels • Sensitive tests of understanding of detector properties • learn how to do b-physics in exclusive channels w/o particle-ID • test of tracking: alignment, material budget, B field • test of trigger: L1+HLT ATLAS • Need to be measured at low luminosity to fully exploit the high luminosity LHC run IV Workshop Italiano ATLAS-CMS

  30. BsJ/  CMS • Sensitivity to s/s (SM10%) in the “no-tag” mode • BsJ/  +-K+K- (SM: σ75 pb) • Trigger selection: • L1: di-μ (pT>3 GeV) • HLT: J/ and  reconstruction using only 5 Tracker hits and w/o μ-ID • |M(J/) |<150 MeV (L2) Mass resolution: σ(J/) 50 MeV • Transverse decay length (Lxy/s>3) • |M () |<20 MeV, |M(Bs )|<190 MeV (L3) Mass resolution: σ() 5 MeV,σ(Bs) 60 MeV • sig20% bgd=10-5 • HLT rate(sig+bgd): 0.1 Hz @ 1033 cm-2s-1, 15000 evts at 1 fb-1 • Offline selection: • μ-ID+Full Tracker reconstruction • Kinematic fit • sig75% (Offline/HLT) • Mass resolution: σ(Bs) 15 MeV IV Workshop Italiano ATLAS-CMS

  31. BsJ/  Plots for 30 fb-1 CMS • Likelihood for s/s • diff. decay rate as a function of (cos,,cos;t) [PLB 369(1996) 144] + K+ • Accurate knowledge of (t) “c distorsion” (ie. track seeds at HLT level) • determine (t) from B0J/ K0* +-K+- • K/ mis-id: narrow MBs range (±36 MeV) low stat. included in the likelihood with higher stat. • 20% accuracy at 1.5 fb-1 Offline HLT IV Workshop Italiano ATLAS-CMS

  32. Bsμ+μ- ATLAS • Sensitivity to new physics MSSM: BR ~ (tan) 6 • Selection: • Trigger • L1: 1-μ (di-μ) 1031(1033) pT>6 GeV • L2: di-μ (pT>6 GeV) μ/tracker matching mass cut • Offline • pT> 6 GeV, ||<2.5, Rμμ<0.9 • m(μμ)=MBs+140-70 MeV • Isolation • Transverse decay length (Lxy/s>11) + pointing (<1°) flight direction • Affected by bgd • Bsμ+-(BR10-4)with / mis-id  x10 larger than SM predictions for Bsμ+μ- 8 10-8 SM: 3.5 10-9 90% upper limit S.Sivoklokov ICHEP06 IV Workshop Italiano ATLAS-CMS

  33. MW with “Scaled Observables Method” CMS • Exploit large Z→ℓℓ statistics available at LHC (104-105 evts with 100 pb-1) • measurement of MW from the lepton pT spectrum (no MT No MET) • R(x) different detector acceptance to leptons from W and Z PRD 57 (1998) 4433 Scaled lepton pT “template” MT IV Workshop Italiano ATLAS-CMS

  34. Double Pomeron exchange: Single diffraction: 2 gluon exchange with vacuum quantum numbers “Pomeron” X X Diffractive physics • SD~ 15 mb DPE ~ 1 mb • 1032 cm-2s-1→ no/low pile-up → selection of events based on Large Rapidity Gap between scattered proton and X • Measurement of SD and DPE cross-sections in presence of hard scale (dijets, vector bosons, heavy quarks) • Test of the scale where the factorization is violated • Handle for understanding parton-parton interactions (UE) IV Workshop Italiano ATLAS-CMS

  35. Di-lepton resonances CMS • Z’→ μ+μ- • single-μ OR di-μ trigger • opposite charge • μ brems. accounted 100 pb-1 Z’: M=1 TeV σ*BR=150 fb (σ*BR=370 fb with /Z/Z’ interf.) initial alignment RMS±30%120 GeV ±1σ MC truth DY • Unbinned max likelihood for bgd and sig+bgd • Improve alignment: ie. CMS long term alignment (1fb-1) RMS±30%60 GeV IV Workshop Italiano ATLAS-CMS

  36. Z’ discovery reach (5) ATLAS CMS IV Workshop Italiano ATLAS-CMS

  37. Di-jet resonances CMS • Physics interest in the high mass tail • W’, Z’ • excited quarks • RS gravitons • Limits from CDF and DØup to 1 TeV • Narrow resonances • ie. Z’: /M1-3% • Crucial knowledge of the physics of jets • absolute jet energy scale • modeling of jets |jet |<1 dσ/dM (pb/GeV)=exp (- M/486 GeV) Luminosity for 10 evts above threshold 1 10 100 pb-1 IV Workshop Italiano ATLAS-CMS

  38. Dfdijet= p 2p/3Dfdijetp Di-jet azimuthal decorrelation ATLAS p/2Dfdijet2p/3 Dfdijet~2p/3 dijet sensitive to higher orders QCD radiation w/o measuring the 3rd or the 4th jet IV Workshop Italiano ATLAS-CMS

  39. Di-jet azimuthal decorrelation • Di-jet event selection: • Cone jet algorithm (R=0.7) • Njets = 2 • |ηjet| < 0.5 • ETjet #2 > 80 GeV ATLAS 300 < ETMAX < 600 GeV 600 < ETMAX < 1200 GeV IV Workshop Italiano ATLAS-CMS

  40. The Higgs Boson F.Gianotti ICHEP06 IV Workshop Italiano ATLAS-CMS

  41. H WW(*)ℓℓ MH=165 GeV CMS • σ2.4 pb • No narrow m(WW) peak • exploit the spin-0 of SM Higgs • Counting exp. in (ℓℓ) distribution • It requires low and well known background (ggtt (tt and qqWW) • Selection: • 2 isolated opposite charge ℓ • Jet veto (ET>15 GeV and ||<2.5) • MET>50 GeV • ℓ kinem.*: ||<2, 12 <m(ℓℓ)<40 GeV, (ℓℓ)<45˚ 30< pTmax< 55 GeV, 25< pTmin< 55 GeV W+ W- + m- S/B=1.66 σ/σ bgd=20% (syst) * Optimized for 1fb-1 IV Workshop Italiano ATLAS-CMS

  42. SUSY with 100-1000 pb-1 ATLAS • If s-particles have the same couplings as SM particles the production is dominated by s-quark and gluinos (if light enough) Dominant signatures:Jets andMET Hard at the beginning! DØ (V.Shary CALOR04) IV Workshop Italiano ATLAS-CMS

  43. Low Mass SUSY MET m(ll) High pT jets • “Early discovery” selection • 2 isolated leptons pT>10 GeV • 24 jets: pTjet1>100 GeV, …, pTjetN>50 GeV • MET>200 GeV SM bgd: tt (10-4), W/Z+jets (10-5), WW/ZZ+jets • SameFlavourOppositeSign (ie. μ+μ-+ e+e- from °2 chain) • Bgd subtraction with DifferentFlavourOppositeSign (ie. eμ) • SameFlavourSameSign (ie. μ±μ±+ e±e± from two ±) • No tt and DY bgd IV Workshop Italiano ATLAS-CMS

  44. Low Mass SUSY: di-lepton endpoint CMS ATLAS 1 fb-1 Prelim. ATLAS “SU3” mSUGRA point m(~g)= 720 GeV  = 19 pb CMS “LM1” mSUGRA point m(~g)= 600 GeV  = 50 pb IV Workshop Italiano ATLAS-CMS

  45. Outlook • Se siamo “bravi”… • Possibilità di fare misure preciseMtop, MW, canali esclusivi del b • … ed anche “fortunati” • Canali dileptonici (ma dopo avere capito tt !): • Z’ • Low Mass SUSY • Higgs (ma solo per MH=165 GeV) • Credits: M.Arneodo, P.Bartalini, U.De Sanctis, F.Gianotti, T.Lari, G.Polesello, R.Tenchini IV Workshop Italiano ATLAS-CMS

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