Talk at USTRO?'09, XXXIII International Conference of Theoretical Physics MATTER TO THE DEEPEST: Recent Developments in Physics of Fundamental Interactions

Cristinziani, M

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ATL-PHYS-SLIDE-2009-26214September2009Tests of the Standard Model with Early LHC DataMarkus CristinzianiUniversität BonnXXXIII International Conference of Theoretical PhysicsMATTER TO THE DEEPEST: Recent Developments in Physics of Fundamental Interactions, USTROŃ'09 OutlineStatus of LHCATLAS and CMSQCD physicsB physicsW and Z physicsTop quarksUstron September 2009 M. Cristinziani (Bonn) 2/41CERN accelerator complexUstron September 2009 M. Cristinziani (Bonn) 3/41The LHC machineo 1232 high-tech superconducting dipole magnets Magnetic field: 8.33 T Operation temperature: 1.9 K (pressurized superfluid helium) Dipole current: 11.85 kA, stored energy: 7 MJ Dipole weight: 34 tons 7600 km of Nb-Ti superconducting cable27km tunnel, 100m undergroundCERN, GenevaCollides protons up to √s = 14TeVUstron September 2009 M. Cristinziani (Bonn) 4/41First beams on September 10th 2008 o Spectacular start of the LHC At 1030 beam 1 around the ring, makes 3 turns At 1500 beam 2 around the ring, 3-4 turns At 2200 beam 2 circulates for hundreds of turnso Both detectors ready Record beam-splash events, beams collide with collimatorsUstron September 2009 M. Cristinziani (Bonn) 5/41The 19th September accidento During powering tests in Sector 3-4, LHC down time Electrical fault producing electrical arc Significant mechanical and electrical damage over 700m Release of He from magnet cold mass Contamination of vacuumo At 8.7 kA (~ 5.1 TeV), a resistive zone appeared in the superconducting busbar between quadrupole Q24 and the neighboring dipole Specified <0.6 nΩ, average <0.2 nΩ In cell 24R3-25R3 ~ 220 nΩ measured (post-mortem) bad welding ‘splice’Ustron September 2009 M. Cristinziani (Bonn) 6/41Interconnection of magnetsCable Junction Box Cross-sectionUpper Tin/Silver Soldering alloy LayerInter-Cable Tin/Silver Soldering Alloy LayerSuperconducting Cable in Copper StabilizerUpper Copper ProfileLower Copper U ProfileLower Tin/Silver Soldering Alloy LayerCompleted JunctionUstron September 2009 M. Cristinziani (Bonn) 7/41Collateral damageo Electric arc between dipole C24 and quadrupole Q24 > 4MW dissipated after one second Helium enclosure punctured Fast discharge of helium into insulation vacuum (2 tons) Large pressure resulted in longitudinal displacement up to tens of cmSupporting jacksHeat of electrical arcs melted 375kg of Copper (equivalent)Ustron September 2009 M. Cristinziani (Bonn) 8/41The LHC repairs in detailUstron September 2009 M. Cristinziani (Bonn) 9/41Ustron September 2009 M. Cristinziani (Bonn) 10/41LHC scheduleo Information updated on  http://lhc-commissioning.web.cern.ch/lhc-commissioning/o Current best guess (M. Lamont, Aug 2009) 2009• Start collisions at 900GeV in November 2009• Ramp up to 7TeV before 12days Christmas shutdown 2010• Possibly run three months at 7TeV• Run 5 months at 8-10TeV• One month heavy ionso Most recent simulation studies performed at 10TeVUstron September 2009 M. Cristinziani (Bonn) 11/41What is discussed in this talko NOT discussed initial LHC “engineering” runs at √s = 900 GeV (injection energy) very low luminosities ( < 1030 cm-2 s-1 ) pre-calibrations, cosmic runso Instead I will present physics at √s = 10-14 TeV for instantaneous luminosities in the range 1030-1032 cm-2 s-1 for integrated luminosities << 1 fb-1 in the two general purpose detectors ATLAS and CMSIn summary:  EARLY MEASUREMENTS AT THE LHCUstron September 2009 M. Cristinziani (Bonn) 12/41Cross-sections and events at LHCChannel 7 TeV 10 TeV 14 TeVJ/ψ→μμ 400k 600k 1100kW→μν 110k 150k 200kZ→ee 13k 18k 25ktt→l+jets 400 700 1500o Interesting physics is hidden beneath a large total cross-sectiono Trigger strategies need careful thinkingo Expected selected events per 50 pb-1Ustron September 2009 M. Cristinziani (Bonn) 13/41A general purpose detector24m45m7000tUstron September 2009 M. Cristinziani (Bonn) 14/41Performance OverviewATLAS CMSINNER TRACKER• Silicon pixels + strips• TRT with particle identification• B = 2T• (pT) ~ 3.8% (at 100 GeV,  = 0)• Silicon pixels + strips• No dedicated particle identification• B = 3.8T  • (pT) ~ 1.5% (at 100 GeV,  = 0)MAGNETS• Solenoid + Air-core muon toroids• Calorimeters outside field • 4 magnets• Solenoid• Calorimeters inside field• 1 magnet EM CALORIMETER• Pb / Liquid argon accordion• (E) ~ 10–12% / E  0.2–0.35%• Uniform longitudinal segmentation • Saturation at ~ 3 TeV• PbWO4 scintillation crystals • (E) ~ 3–5.5% / E   0.5%• No longitudinal segmentation• Saturation at 1.7 TeVHAD CALORIMETER• Fe / Scint. & Cu-liquid argon• (E) ~ 45% / E   1.3% (Barrel)• Brass / scintillator• (E) ~ 100% / E  8% (Barrel)MUON • Monitored drift tubes + CSC (fwd)• (pT) ~ 10.5 / 10.4% (1 TeV,  = 0)(standalone / combined with tracker)• Drift tubes + CSC (fwd)• (pT) ~ 13 / 4.5% (1 TeV,  = 0)(standalone / combined with tracker)Source: Froidevaux-Sphicas, Ann Rev 56, 375 (2006) Ustron September 2009 M. Cristinziani (Bonn) 15/41Object reconstructionUstron September 2009 M. Cristinziani (Bonn) 16/41e/γ reconstructiono combine information from calorimeters and tracking  narrow clusters in EM calorimeter, all energy deposited e (γ) clusters must (not) match with incoming track e can be separated from pionsusing transition radiation in TRT (ATLAS) e’s and γ’s are typically isolated from other particles However, not so for• e’s from charm and beauty decays• γ’s from π0 decays Backgrounds stem mostly from misidentified jetsUstron September 2009 M. Cristinziani (Bonn) 17/41μ identificationo identified using muonchambers at outer detector (other particles are absorbed) µ momentum and charge can be determined from track bending in B field of muon chambers Backgrounds stem mostly from charged π/K decays in flightUstron September 2009 M. Cristinziani (Bonn) 18/41Understand dimuon eventso Thousands of di-muons from J/ψ and Υ for 1 pb-1, hundreds from Z.o First opportunity to understand tracking and muonresolutions as a function of pT multiple scattering, alignment distortions, magnetic field uncertainties, …Ustron September 2009 M. Cristinziani (Bonn) 19/41Jet reconstructiono # high pT jets/pb-1 at LHC much larger than Tevatron At 10TeV there are O(105) jets/pb-1 with pT>200 GeV• 320jets/pb-1 with pT>0.5TeV• 50dijets/pb-1 with mjj>1.4TeVo Jet reconstruction Cone (seeded, seedless, iterative), (Anti)kT algorithmso Jet energy calibration, e.g.  at CMS Factorized approach: offset, relative and absolute correction Data driven: dijet, γ+jet, Z+jet balancing Systematic uncertainty expect ~10% at startupUstron September 2009 M. Cristinziani (Bonn) 20/41Physics menu with very 1st collisionso Goal: prepare for high-pT physics and discoveries calibrate detector tune software to LHC physics understand physics of soft hadron interactions o Minimum bias (MB) events σNSD (14 TeV) ~ 70 mb (~70% of the total cross section) ~25 MB events superimposed (pile-up)  nominal LHC running (1034 cm-2 s-1)o Underlying event (UE) Everything that is not the hard scatteringo Hadronic event shapeso B physicsUstron September 2009 M. Cristinziani (Bonn) 21/41Minimum Bias Eventso η and pT differential distribution of Nch Learn about soft part of underlying event Important to do it early ⟶ avoid pile-up Energy dependence not well constrainedo Backgrounds Beam-gas, beam-haloo Trigger strategies MB trigger scintillators or random Min # of spacepoints in ID Two tracks (and vertex) SD and DD events selectedUstron September 2009 M. Cristinziani (Bonn) 22/41σnsd = σtot - σelas - σsd = σdd + σndMB differential distributionsPythia vs Phojet predictiono Stable charged particles onlyo Need to correct for Track-to-particle Vertex reconstruction Trigger biaso Reconstruction of low-pT tracks challengingo Systematics Misalignment NSD xsection Composition Trk selectionUstron September 2009 M. Cristinziani (Bonn) 23/41Understand the underlying evento Density of tracks and pT in transverse region Extracted distributions well matched with input simulation Model sensitivityCMS PAS QCD-07-003o Underlying activity mainly affects the transverse region of the eventUstron September 2009 M. Cristinziani (Bonn) 24/41Hadronic event shapeso Defined in terms of 4-momenta of final state objectso Infrared and collinear safe ⟶ calculable in pQCD e.g. directly global transverse thrusto Normalized to total transverse momentum/energy Energy scale dependence should cancel out (resulting 5%) Useful to understand early QCD events and tune MCo Can distinguish e.g. Pythia vs Alpgen Three jet ET bins, 10pb-1 integrated luminosity CMS PAS QCD-08-003Ustron September 2009 M. Cristinziani (Bonn) 25/41√s = 14TeV√s = 14TeV√s = 14TeVB physics with early datao Require low-pT muon trigger Select J/ψ⟶μμ and discard background from K and πo Study inclusive J/ψ and Υ productiono Cross-section and lifetime with 10pb-1 @ 10TeV B+⟶J/ψ K+, B0⟶J/ψ K*0 dσ/dpT(B) and proper lifetime• Max. likelihood fit in several bins of pT(B)• Expect τ(B+)/τ(B0) to 5%(stat) + 1%(syst) • Expect diff. cross section ratio to <10%(stat) o σbb and dσ/dΔφ in 50pb-1 @ 10TeV Opening angle between J/ψ and μ• Test QCD, tune Monte-Carloo Further early data topics Radiative χc decays,  B0s⟶J/ψ φ,  J/ψ and Υ polarisationUstron September 2009 26/41M. Cristinziani (Bonn)CMS PAS BPH-08-004CMS PAS BPH-09-001CERN-OPEN-2008-020Electroweak measurementso “Known” physics from previous colliders Unique tool to calibrate the detectors Understand backgrounds for new physics signals Understand detector details and develop tools• B-tagging, missing transverse energy, …muon momentum scaleZ⟶ eeECAL intercalibrationUstron September 2009 M. Cristinziani (Bonn) 27/41Electroweak measurementso “Known” physics from previous colliders Unique tool to calibrate the detectors Understand backgrounds for new physics signals Understand detector details and develop tools• B-tagging, missing transverse energy, …o Not so well known after all ! higher cm energy, PDF uncertainties (gluons dominate)o physics channels involving Z, W, γ*,top production are easily distorted any new physics sources at new energy scales opened up, even with low luminosity!Ustron September 2009 M. Cristinziani (Bonn) 28/41W and Z cross-sectiono Theoretical uncertainty of higher order corrections <1% W and Z production stringent test of QCD• Differential distributions constrain resummation of initial partonemissions and PDFs of the protono Detector calibration with Z Energy scale, resolution, lepton id efficiencyo Electroweak parameters MW (from W boson decay distribution) sin2θW (NC AFB) Lepton universalityo Backgrounds:  W/Z decaying to τ’s, top-pair production,  inclusive jet events with fake leptons,  low-mass Drell-Yan, diboson eventsUstron September 2009 M. Cristinziani (Bonn) 29/41W and Z cross-section with electronso Assume 1031 cm-2s-1 trigger menu and 50pb-1o W⟶eν and  Z⟶ee Expect 200k and 25k events High ET electron, MET, MT (l, ν) or isolation+M(ll)o Jet events important bckg Normalization uncertainty Data-driven background subtraction before MET cut Select photons instead of electronsZ⟶eeselectionUstron September 2009 M. Cristinziani (Bonn) 30/41√s = 14TeV√s = 14TeVW and Z cross-section with muonso Analysis with muons in final state ttbar major background Jet events less serious• contribution from semi-leptonic b decayso Systematic uncertainties (excl. luminosity) Efficiency ~2% Acceptance (ISR, PDF, UE, …) ⟶ differential distributionsΔσ/σ (W⟶lν) =  0.2% (stat) + 3-5% (syst)          Δσ/σ (Z⟶ll) =  0.8% + 4%Ustron September 2009 M. Cristinziani (Bonn) 31/41√s = 14TeV50pb-1√s = 14TeV50pb-1Tag and probeo Extract trigger and lepton reconstruction efficiency Purely data driven E.g. Z ll decaysUstron September 2009 M. Cristinziani (Bonn) 32/41√s = 14TeV50pb-1Diboson production and TGCo Important background for new process E.g. H->WWo Test Standard Model constraining anomalous TGCo WZ production observable early on 5σ discovery possible at √s = 14TeV  with 350pb-1 (CMS) With BDT ATLAS expects >5σ with 100pb-1Ustron September 2009 M. Cristinziani (Bonn) 33/4114TeV300pb-1CMS PAS EWK-08-003√s = 14TeV√s = 14TeVSelected events in 1fb-1CERN-OPEN-2008-020Top physicso Abundant in 14 TeV collisions: ~1 pair/sec at 1033 cm-2 s-1 Reduced at 10TeV or 7 TeV, still significantStrong: ~ 900 pb electroweak: ~ 320 pbttSingle tops-channelt-channelWt-channelUstron September 2009 M. Cristinziani (Bonn) 34/41Top reconstructionHadronic (BR ≈ ⅔)+ can fully reconstruct W and top momenta- faked by QCD multi-jets (esp. heavy flavor)Leptonic (BR ≈ ⅓)+ Lepton indicates W’scharge, helicity+ Reject QCD via leptonand missing ET- Kinematic info (partly) losto σ(tt) will validate Lepton identification Jets/missing ET B-taggingUstron September 2009 M. Cristinziani (Bonn) 35/41o Dilepton channel, 10pb-1 (eμ S/B ~ 9) 2 OS leptons, MET>30GeV, ≥2jets Combined Δσ/σ = 15%(stat)+10%(syst)+lumiTop rediscovery in tt at 10TeVo Lepton+jets 20pb-1 Muon+jets S/B = 1.8• Template fit to M3 or η(μ)• Δσ/σ = 12%(stat)+19%(syst)+lumi Electron+jets, S/B=1.6• Δσ/σ = 23%(stat)+2o%(syst)+lumieμCMS PAS TOP-09-002, -003, -004μ+jets e+jetsMET(GeV)M3(GeV)Ustron September 2009 M. Cristinziani (Bonn) 36/41Top quark dileptonATL-PHYS-PUB-2009-086o ATLAS study for 10TeV at 200pb-11200 selected evtsCombination ofsystematicsUstron September 2009 M. Cristinziani (Bonn) 37/41Top quark lepton+jetso Standard object selection, no b-tago Cut-and-count or likelihood fit S/B ~ 2 for e and μ channelo Exercised in different flavors Δσ/σ = 3%(stat)+<15%(syst)+lumi Δσ/σ = 3-6%(stat)+15-20%(syst)+lumi (w/o MET)W mass constraintATL-PHYS-PUB-2009-087Ustron September 2009 M. Cristinziani (Bonn) 38/4110 TeV200pb-1Single topo Evidence in t-channel expected with 200pb-1@10TeVo Select  single-top events against QCD, tt and W+jetso Top is 100% polarized ⟶ further discriminationo Measure σ(single-top) with uncertainties 35%(stat) +14%(syst) +10%(lumi) o Possible improvement: charge asymmetry in pp collisionsCMS PAS TOP-09-005Ustron September 2009 M. Cristinziani (Bonn) 39/41Z’ searcho Search for heavy resonance decaying to a lepton pair With 100 pb-1 large enough signal for discovery up to m > 1 TeV Signal is (narrow) mass peak on top of small  Drell-Yan background Ultimate calorimeter performance not neededo … decaying toa top pair Kinematic fitin events w/ μ Up to ~2TeVCMS PAS TOP-09-0091fb-1Ustron September 2009 M. Cristinziani (Bonn) 40/41√s = 10TeV√s = 10TeVCERN-OPEN-2008-020√s = 14TeVATLAS-PHYS-PUB-2009-087What changes at lower √s ?o Plan to run at 14TeV, 10TeV, 7TeV,…o Reduced cross-sections e.g.  ttbar from ~900pb-1 to ~400pb-1 to ~150pb-1 W/Z ~65% (14TeV⟶ 10TeV)o Strong reduction of energy reach for high masses and energy scales Z’ resonance (m=2TeV) 20% One order of magnitude less reach for new physics effects at scales ≥ 4 TeVo More subtle effects Less gluon-gluon relative to qqbar hard interactionsUstron September 2009 M. Cristinziani (Bonn) 41/41Summaryo QCD and EW processes at start-up extremely important Understand detector and validate algorithms Not so well known: PDF uncertainties and new regime Main background for searcheso Sizeable samples with low luminosity 1pb-1 ⟶ jets, W/Z, J/ψ, Υ 20pb-1⟶ top, B 100pb-1 ⟶W/Z + 4jets 150pb-1 ⟶ dibosonso LHC experiments are developing strategies and organizing efforts to understand as soon as possible the detectors and the basic QCD/EW processeso This is critical for the success of the LHC programUstron September 2009 M. Cristinziani (Bonn)Referenceso Baseline studies (14TeV) The ATLAS Experiment at the CERN Large Hadron Collider, JINST 3 S08003, 2008 Expected Performance of the ATLAS Experiment Detector, Trigger and Physics, CERN-OPEN-2008-020; arxiv/0901.0512 Physics Performance TDR, CMS Collaboration, CERN/LHCC 2006-021, J. Phys. G: Nucl. Part. Phys. 34 (2007)o Most recent public studies (incl. Summer’09,  10TeV)  ATLAS: https://atlas-physco.web.cern.ch/atlas-physco/ATLASPubNotes.html CMS: https://twiki.cern.ch/twiki/bin/view/CMS/PhysicsResultsUstron September 2009 M. Cristinziani (Bonn)

Tests of the Standard Model with Early LHC Data

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