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First one-two years Physics at LHC

First one-two years Physics at LHC. Workshop on LHC Physics TIFR, September4-8,2006. Monoranjan Guchait TIFR. Compilation…. CMS,ATLAS notes, talks from ICHEP06, Many papers, review articles, presentations, Home pages…. The LHC Experiment. Proton Proton Collsion

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First one-two years Physics at LHC

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  1. First one-two years Physics at LHC Workshop on LHC Physics TIFR, September4-8,2006 Monoranjan Guchait TIFR

  2. Compilation… CMS,ATLAS notes, talks from ICHEP06, Many papers, review articles, presentations, Home pages….

  3. The LHCExperiment Proton Proton Collsion Center of Mass energy :14 TeV Luminosity 1034cm-2s-1 New energy domain( ~8 times) New luminosity domain(~100 times)

  4. The LHC Experiment • Physics Goals: - Testing Standard Model at 14 TeV Complete with Higgs discovery - New Discovery? SUSY, Quantum Gravity… - Anything else?

  5. LHCSchedule Machine and Experiments closed : 31 st August, 2007 First collisions at cm: 900 GeV with L ~ 1029cm-2s-1, November 2007. - Static run, mainly to debug machine and detectors - Commissioning run at Injection energy until end 2007, then shutdown. First Collision at cm =14 TeV : Spring 2008 2808 X 2808 bunches, 25 ns bunch crossing, Expected to achieve few fb-1 by the end of 2008 Interesting Physics….

  6. Experimental Challenges • The total p-p cross section ~100 mb • At design luminosity about 109 inelastic events/second • Trigger should reduce this event no more than about 100 events/s for storage and analysis within an interval 25ns, needs a very efficient design of the readout and trigger systems. Needs a good synchronization among different channels.. …………..many more Computation.. And Computation 15petabyte(PB) per year, professing them and making the information available to thousands of Physicists all round the world. For Comparison: ALEPH: Total data 3.5 TB D0 1992-’96 stored 30 TB( “Farm” came up) LHC 15PB/year ( 1PB = 103TB) Model: Tiered structures, 100,000 processors multi-PB disk, tape capacity(co-processors estimation 2004)

  7. Pre-Collision Phase First detector understanding before commisioning with real collision Detector Alignment and Calibration Both ATLAS and CMS has developed simulation studies in order to better understand how to use data. On going Study.. In CMS this month there will be a Workshop to decide the strategy for 2007 run.

  8. CMSDetector

  9. Initial Detectors • CMS will start without muon RPC in the region 1.6 <  < 2.1 • Fourth layer of the end cap muon chambers will be absent during the pilot run • NO EE and pixel detector, but will be installed during the shut down after the 2007 run ----thinking the psossibility to install all these for new two months delay. • ATLAS will start with two pixel layers (instead three) and without Transition Radiation Tracker in the region 2 <eta<2.4. What about Trigger and DAQ: Initial L1 rate 50kHz(instead of 100) and 35 kHz(instead of 75) in ATLAS.

  10. Performances Good muon identification and momentum Resolution over a wide range of momenta in the region || < 2.5 ( about 1% at 100 GeV/C2). Good charged particle momentum resolution (~ 1% at 100 GeV/c2) and rec. eff. in the inner tracker. Eff. b/tau tagging and triggering on taus Good electromagnetic energy resolution,good diphoton,dielectron resolution(<1 %) wide geometric coverage(eta <2.5), measurement of the direction of photons and/or correct localization of the promary interaction vetext, pi0 rejection. Good missing ET and dijet mass resolution with fine lateral segmentaion ( X φ < 0.1 X 0.1) in HCAL.

  11. First Data • 1 fb-1(100 pb-1)=6 months(few days) at L=1032cm-2sec-1 with 50% data taking efficiency a few 1/fb per experiment at the end of 2008 W,Z events will be used for calibration Top events also will be used to for JES,..

  12. Calculations and tools • For many of the interesting physics processes, higher order calculation exist, still there is a wish list.. Event Generators: PYTHIA, HERWIG,ISAJET Physics process; ALPGEN,MC@NLO,MCFM,NLOJET++, Madgraph,Comphep….

  13. Outline SM at 14 TeV - UE events studies - Jet Studies - W/Z studies - PDF - Early Top Physics New Physics - Zprime - Higgs - SUSY..

  14. Cross sections

  15. “Hard Scattering” Component Min Bias and UE events • MB events: Events collected with a trigger that is not very restrictive are referred as MB events. • UE is everything else accompanying the hard scattering component, consists of “beam-beam remnants” and from particles arising from soft or semi-soft multiple interactions(MPI). UE receives contribution from ISR and FSR “Underlying Event” TheTH The UE is an unavoidable background to most collider observables, requires good understanding

  16. MB andUEmodeling The Multiple parton interaction model extending pQCD to the soft regime, describe the physics of MB and UE • MPI models are implemented in the general purpose simulation program lik General purpose simulation programs PYTHIA, JIMMY, SHERPA, HERWIG are modeled for MB and UE. Tunned with data from UA5 and Tevatron Hard scattering events are having different topological structures in the -φ regions. Regions sensitive to UE components of the interaction.

  17. UE event studies :Jet Production Charged Particle Df Correlations PT > 0.5 GeV/c |h| < 1 • Look at charged particle correlations in the azimuthal angle Df relative to the leading charged particle jet. • Define |Df| < 60o as “Toward”, 60o < |Df| < 120o as “Transverse”, and |Df| > 120o as “Away”. • All 3 regions have the same size in h-f space, DhxDf = 2x120o = 4p/3.

  18. UE at CDF

  19. Extrapolation to LHC

  20. Example: top physics Different UE models shift top mass by about ~ 5 GeV Needs very good tunning!

  21. Inclusive Jets • The measurement of jet production cross section at LHC will provide a stringent test of pQCD at a regime which was not probed before so far. • The first data will be used to provide systematics connected to measurements. QCD is a background to almost all New physics scenarios. A high pT tails to inclusive jets are sensitive to new physics A bad estimations of errors may lead to fake as a new physics Computed using NLOJET,CTEQ6.1

  22. Different Sub processes

  23. Jets at Tevatron Uncertainties:JES ~10% for low pT and ~60% at High pT Energy resolution below 10%, UE: -22% to 4% Hadronisation:13% to 4%

  24. LHC:Statistical Errors • Statistics is not a problem.. e.g for pT ~ 1 TeV, about 1% for large pseudorapidty region it is ~10% for L = 1fb-1 Assuming one month luminosity @1032cm-2sec-1 and 40% trigger efficiency

  25. Theoretical Errors ~10% for pT ~ 1 TeV Main Sources µR and µF Parton distribution Function(PDF) For PDF, mainly g(x), at low x, e.g. ~15% for pT =1 teV

  26. Experimental Errors • Main Source - Jet Energy Scale(JES) - Luminosity Measurements - resolution, triggering efficiency UE subtraction…. Detector effects:Jet Reconstruction - R and ET threshold - Calo Jet to Particle level jet, jet Calibration 1% uncert. In JES→10% on σ(Jet) 5% uncert. In JES→30% on σ(Jet)

  27. Gamma+jet Calibration Different available processes for calibration (/Z+jet, Wjj (from top decay)) Example:make use of the PT balance in +jets Event selection: selection of events with isolated photons, no high-PT secondary jet, photon and jet well separated in the transverse plane (Etisol < 5 GeV, ETjet2 < 20 GeV, φγ,jet > 172°) Trigger efficiencies included in the analysis,stat error smal (well below 1%) after 10 fb-1 The main systematics is due to non leading radiation effects, QCD backgrounds, gluon-light jet difference, etc.

  28. W/Z at LHC • LHC is a W and Z factory • For L=1/fb σ(W→lν)~ 15 nb, ~107 events σ(Z→ll) ~1.5nb, ~106 events Theory cross section 2-4% accuracy Mass, width, W/Z+jets PDF constraining. Detector Performances ECAL calibration using Z→ee Alignment using Z→µµ Lepton identification Luminosity measurements

  29. W/Z at Tevatron Very good agreement with theory Luminosity error dominates ~5-6%

  30. W/Z at LHC σ(W→µν+X)=14700±7(stat)±485(syst) Systematic ~3.3% (dominated by theory) σ(Z→µµ+X)=1160±2(stat)±27(syst.)heory) Systematic 2.3%( dominated by theory) Theoretical prediction ~4% Luminosity measurement~6-7% expected

  31. Theory accuracy about 2-3% Strategy: I. Count the number of events within some sets of cuts Compare against a theoretical simulation subject to same cuts OR Take a MC and evaluate the acceptance (A) of the cuts, to get the cross section σ = 1/A N/Lum Accuracy of the calculation dependence of accuracy of calculation A. 6-7% accuracy expected.. Luminosity measurement

  32. PDF

  33. Parton Distribution Function Proton Structure Need to understand for testing SM and BSM PDFs are determined by global analyses of data From DIS,DY and jet production Two major groups regularly update whenever new data available:MRS,CTEQ ALL the above groups provide a way to estimate the error on the central PDF LHAPDF : calculates the PDF uncertainties for any observables

  34. Parton Distribution Function(PDF) Proton Structure Need to understand For testing SM and BSM very low x X1,2=(M/14TeV)exp(±y) y:rapidity Q=M, mass of the final state

  35. Parton Distribution:HERA HERA PDF: fair agreement

  36. e-rapidity e+ rapidity CTEQ61 CTEQ61 MRST02 MRST02 ZEUS02 ZEUS02 ds(We)/dy Generated Generated y ds(We)/dy Reconstructed Reconstructed y PDF: W/Z process W±→e±ν rapidity distributions The experimental uncertainty small to Distinguish the PDF sets. PDF errors are sensitive to e rapidity Distributions ATLAS studies shows it is possible to distinguish different PDF if Exp. Uncertainty ~3-5%

  37. ZEUS-PDFBEFORE including W data e+CTEQ6.1 pseudo-data Constraining PDF : ATLAS W rapidity events, CTEQ6.1, ATLFAST, 4% syst err(by hand),100/pb Uncertainties is reduced, error low x gluon by 50% are reduced ZEUS-PDFAFTER including W data |h| |h|

  38. Top Physics

  39. Early top Physics • Top cross section ~840pb(1±5%(scale)+3%(pdf)) • gg fusion : 90% • qq annhilation:10% For low L=1033cm-2sec-1, every 4 second one “lepton+jet” event, and one second one top pair. ~ 0.1 m top events for L=1fb-1 Top mass and cross section Top production is one of main SM background for most of the new physics signal. Top events can be used for estimating JES, b-tagging, One lepton mode Dilepton mode Hadronic mode J/psi mode

  40. Top Physics: Dilepton mode • Two OS lepton with pt>20GeV, at least two b-tagged jets with pt>30GeV,Etmiss>30GeV • Upper cuts on the number of high pt jets. • Backgrounds: Z+jets,

  41. Top Physics: Single lepton mode tt→ bWbW →bbqqµν • Single muon trigger, at least one muon with pt > 20 GeV, • Four non-overlapping jets with Et>30, • Two of them b –jets • And the other two non b-tagged jets • Etmiss>40GeV • Upper cuts on the multiplicity of jets mt(semi-leptonic,1fb-1)=±0.7(stat.)±1.9(syst.)GeV/C2

  42. Top Physics: Hadronic Final states • Four Partonic jets, two b-jets, huge QCD backgrounds challenging • Selection inclusive jet trigger, b-jet trigger, • Events shape variables like centrality,aplanarity • Used to supres the QCD backgrounds. tt→ bWbW →bbqqqq mt(semi-leptonic,1fb-1)=±0.6(stat.)±4.2(syst.)GeV/C2

  43. Top Physics: J/psi meson • J/psi arises mainly from B quark fragmentation • Reconstruction of J/psi gives significant information about b flight direction. • Top reconstruction is done taking lepton from W decays and leptons from J/psi • Rate is too low, Br ~ 10-5 • => 4500 events for 10/fb • Systematic uncert. contributes: mt=1.47 GeV/c2

  44. Single top production • Direct measurement of vtb2 • V-A structures,polarised top, Spin of top,good candidate • Background for new physics • Coupling structures tWb, can indicate some new physics • Results: t-channel • Bg W+jets, • Signal events survived 7000 for L=30/fb, S/B=3 • Result s-channel: • Signal events 2050, S/B=0.15 tw channel:Bg top pair Signal events 4700 events,S/B~1/7

  45. Top Physics: summaryCMS • A combined top mass accuracy ~ 1GeV/C2 for 10-20/fb data will be feasible

  46. Z’

  47. Zprime:Very Easy to Discover • Additional Z’ boson predicted by Superstring inspired, GUT, Dynamical Symmetry breaking model, little Higgs.. Current limit >0.6-0.7 TeV Tevatron reach ~ 1 TeV pp →Z’ →µ+ µ-, Main Dominant SM: DY

  48. Z prime(contd.) Large enough to find up tp ~1 TeV, for 0.1 /fb, signal as a mass peak, DY is very easily managable

  49. New Discovery: SUSY SUSY at TeV Scale, m~ 1 TeV Large cross section ~10 events/day Decision for ILC!!

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