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Direct Photon + Jet Events at CMS with Ö s = 14 TeV

Direct Photon + Jet Events at CMS with Ö s = 14 TeV. Michael Anderson University of Wisconsin Preliminary Exam. Outline. Standard Model g + jet Events Large Hadron Collider Compact Muon Solenoid Detector Computing Reconstructed Jets and Photons Future Steps. Computing @Wisconsin.

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Direct Photon + Jet Events at CMS with Ö s = 14 TeV

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  1. Direct Photon + Jet Events at CMS with Ös = 14 TeV Michael Anderson University of Wisconsin Preliminary Exam

  2. Outline • Standard Model • g + jet Events • Large Hadron Collider • Compact Muon Solenoid Detector • Computing • Reconstructed Jets and Photons • Future Steps Computing @Wisconsin

  3. Standard Model Higgs Quarks (Fermions) Force Carriers (Bosons) • 12 elementary matter particles • 4 force-carrying particles • 1 so far undetected particle: Higgs Leptons (Fermions)

  4. Direct Photons  + Jet • Why Photons? • Photons don’t fragment • Energy & position can be measured accurately • Provide good probe of hard-scattering process • Provides direct measure of pdf for gluons • g+Jet has high cross-section,s ~ 2*108 mb • Photons also can be used in new physics searches • Gauge Mediated SUSY Breaking • Prompt photon & extra dimension models Compton-like Annihilation Signals involve’s + missing energy

  5. Photon + Jet • Good for Calibration! • High resolution on prompt  energy ~1% • Jet &  balance in  • Can use data to make jet energy corrections • Photon energy calibrated from 0 decays • Can then be used to calibrate all jet algorithms g p p

  6. Calibrating Jets • The jet energy losses can be divided into categories: • response of the calorimeter to different particles, • non-linearity response of the calorimeter to the particle energies, • un-instrumented regions of the detector, • energy radiated outside the jet clustering algorithm, • multiple interactions and underlying event • +jet calibration used by D0 for better than 3% accuracy for jets with 20 GeV < Et < GeV B. Abbot et al. “Determination of the Absolute Jet Energy Scale in the D0 Calorimeter.” Nucl Instr and Meth. A424 (1999)

  7. Large Hadron Collider • 14 TeV proton-proton collider • Circumference of 27 km • Luminosity up to 1034 cm-2s-1 • 8T Magnets

  8. General-Purpose Detectors • ATLAS • Weight: 7,000 T • Diameter: 25 m • Length: 46 m • CMS • Weight: 12,500 T • Diameter: 15.0 m • Length: 21.5 m

  9. Proton interactions at LHC @start-up 1028 - 1031 cm-2s-1 Luminosity L = particle flux/time Interaction rate Cross section  = “effective” area of interacting particles

  10. CMS 4T solenoid Muon chambers Forward calorimeter Silicon Strip & Pixel Tracker Electromagnetic Calorimeter PbWO4 Crystals Hadronic calorimeterBrass/Scintillator

  11. Current CMS Underground Surface

  12. Particle Detection in CMS • Photons: • “Super Cluster” of Energy in ECAL • No nearby track • Jets • Energy deposit in ECAL & HCAL • With tracks • Detailed Reconstruction discussed on later slide

  13. Silicon Tracker • Measures pt & path of charged particles within |h| < 2.5 • Strip Tracker • 200 m2 coverage • 10m precision measurements • 11M electronic channels • Inner Pixel tracking system • 66M channels • Used for rejecting electrons in this analysis

  14. Electromagnetic Calorimeter • Measures energy & position of electrons and photons within |h| < 3 • PbWO4 crystals • 61K in the barrel, 22 x 22 mm2 • 15K in the endcaps, 28 x 28 mm2 • Ultimate precision of energy resolution: 0.5% • Preshower detector for endcaps • Silicon sensors, 4300 modules, 137K channels

  15. Hadron Calorimeter • HB and HE: brass & scintillator with WLS fiber readout • Coverage to  < 3,  x  =0.087x0.087 (coarser for  >1.8) • Hadron Outer calorimeter (tail catcher) outside solenoid • Hadron Forward: steel & quartz fiber: coverage 3 <  < 5 Approx. 10K channels,Hybrid PhotoDiode readout for all but HF (PMT) HB HE

  16. Trigger • Level 1: Hardware trigger operating at beam crossing rate • Level 2: • Reconstruction done using High-Level Trigger (HLT) -- computer farm • Reduces rate from Level-1 value of up to 100 kHz to final value of ~100 Hz • Slower, but determines energies and track momenta to high precision

  17. Level-1 Trigger Calorimeter Trigger Muon Trigger • Every event is ~1MB each • Identifies potential photons, jets… • Hardware implemented • Reduces rate from 40 MHz -> 100 kHz • Processes each event in 3 s RPC CSC DT HF HCAL ECAL Local CSC Trigger Local DT Trigger RegionalCalorimeterTrigger PatternComparator Trigger CSC TrackFinder DT TrackFinder GlobalCalorimeterTrigger 40 MHz pipeline, latency < 3.2 ms Global Muon Trigger e, J, ET, HT, ETmiss 4 m Global Trigger max. 100 kHz L1 Accept

  18. Computing • Tier 0 at CERN • Record raw data and Data Summary Tapes (DST) • Distribute these to T1’s • Tier 1 centers • Pull data from T0 to T1 and store • Make data available to T2 UW Madison RAL Oxford T1 FNAL Chicago T1 T2 FZK Karlsruhe T1 T0 • Tier 2 centers • DST analysis…. • Local data distribution • Wisconsin is a T2 site T1 T1 CNAF Bologna T1 IN2P3 Lyon CMS data sizes and computing needs require a worldwide approach to Physics analysis. FNAL is US CMS national computing center. PIC Barcelona

  19. Simulation Workflow ALPGEN Hard scattering • g+jets simulated with Alpgen v2.1 • Fixed order matrix element simulated event generator • Generates multi-parton and boson + multi-parton processes in hadronic collisions. • Jet simulation with Pythia v6.409 • Generates event hadronization, parton shower, and I/FSR, underlying event • Detector simulated using GEANT4 • Toolkit for the simulation of the passage of particles through matter • Reconstruction with CMS software PYTHIA Underlying event GEANT4 Detector simulation CMSSW Reconstruction of event

  20. Photon Reconstruction • Photons are built from ECAL SuperClusters • Hybrid clustering algorithm in barrel • Island algorithm in endcaps • All SuperClusters are candidate Photons • “Photon object” contains: • energy in 5x5 crystals • Ratio of energy in 3x3 crystal to SuperCluster energy (R9) • ratio of the energy in center crystal to 3x3 crystals (R19) • presence or not of a matched pixel seed R9 R19

  21. Reducing Fake Photons • Jet can fake photon • Leading neutral mesons in jet (like 0-> and ->) can make narrow deposit of electromagnetic energy • Charged mesons and electrons rejected by tracking system • Strategies to minimize this fake  background: • Reconstruct multiple  energy deposits - see if are decay products of a neutral meson • Shower is often wider for meson decay • Reject ->e+e- conversions (multiple ’s from meson decay more likely to have conversions) • Isolation: require no high energy particles near it

  22. Reducing Fake Photons

  23. Cuts Starting with: 481,910 +jeteventswhere gen not in ECAL  gap, and Et > 15 GeV Photon  < 1.479 Select barrel photons 325,268 events ( 67%)‏ R Nearest Track > 0.1(track pt > 10 GeV) Isolation 311,609 events (65%)‏ Photon R9 > 0.9 Narrow Energy Deposit(Shower shape & rejects conversions) Final Count: 235,594 events (49%)‏

  24. Gen & Reco Photon: h, f • Relatively flat in h and f • Crack in ECAL h : 1.479 - 1.653 • Photons near this h harder to find/reconstruct h f

  25. Gen & Rec Photon: Et • Et of the generated & reconstructed photon match well • Difference in Et ~< 10% • Used default vertex (0,0,0) GeV Etgen – Etrec Etgen Longer tail on positive side

  26. Reco Photon: R9 E (3x3 crystals) E (SuperCluster) • R9 = • Photon shower is narrow • Photons that convert to e+e- pair in Tracker have lower R9 • ~73% of all photons have R9 > 0.94 • R9 used to select well measured photons R9

  27. Reco Photon: Nearest Track • Nearest Track where • Track pt > 10 GeV • R = Ö()2 + ()2 • Want isolated photons Nearest Track R R Nearest Track pt GeV

  28. Gen & Rec Photon: DEt/Etgen • (Etgen–Etrec)/ Etgen • After cuts, fewer events in positive tail • ~24% loss in # of events after R9 cut Before R9 cut After R9 cut

  29. Jet Reconstruction • Jet algorithms: • Iterative Cone • Seed Et > 1 GeV • DR = 0.5 or 0.7 • Good for new physics searches and photon+Jet balancing • Other algorithms useful also • Midpoint Cone • Merges jets based on overlap Threshold: 0.75 • Kt …

  30. Gen & Rec Jet: h, f • Jet alg: Iterative Cone • R = 0.5 • (Will try out others) • Highest-pt Jet with • pt > 10 GeV • 0.8p < |fjet-fg | < 1.2p • ~93% of events have reco jet that meet this criteria

  31. Gen & Rec Jet • Et of reco photon matches well with gen jet pt • But reco jet pt lower by ~ 22 GeV • Even the MC must be calibrated GeV (ptgen  – ptrec g) ptgen  (ptgenJet – ptrecJet) ptgenJet

  32. Conclusions • Photon + Jet events have high cross section • can get 1 fb-1 data in 1 year • Measure Photon+Jet Cross section • Probe hard scattering processes • Measure gluon pdf • Tune MC generators • Calibration of Jet energies is possible and effective using prompt photons • Does not require dependence on monte-carlo jet simulations

  33. Next Steps • Use L1 Trigger selection • Use HLT selected objects (photons, jets…) • Validate using RECO objects • Create a sample of good direct photon + jet events • Calibrate jet algorithms • Do physics with photons!

  34. Extras

  35. LHC Commissioning • Establish colliding beams as quickly & safely as possible • Planned turn on in 2008 • L = 1031 -> ~1 fb-1 in year

  36. Muon System • 3 technologies, all self-triggering • drift-tubes(DT), cathode strip chambers(CSC), resistive plate chambers (RPC) • 25000 m2 of active detection planes • 100m position precision in DT and CSC • About 1M electronic channels DT CSC RPC

  37. Problem h Regions • Just events whereDEt/Etgen > 0.1 • Spikes at module boundaries • biggest at h = 1.479 • Cuts over 50% of these events Before R9 cut h After R9 cut h

  38. Higgs -> g g • Inclusive Search for the Higgs Boson in the H → γγ Channel, M. Pieri, S. Bhattacharya, I. Fisk, J. Letts, V. Litvin, J.G. Branson CMS Note 2006/112 • Studied 6 types of background and used various higgs masses Note multiplication • Tried to optimize signal 2 different ways: with cuts and with neural nets • Here are their results with cuts:

  39. LHC Details In the LEP tunnel • pp s =14 TeV L=1034 cm-2 s-1=10 mb-1MHz • crossing rate 40 MHz • Heavy ions (1 month/year)

  40. Computing M.I.T. Wisconsin* Purdue Nebraska Caltech* UC San Diego* Florida* T0 at CERN, T1 at Fermilab as US CMS national center (“super” Tier 1 with twice the resources of other Tier1s). Keep many of the trigger streams at FNAL. T2 at UCSD, Caltech, UFlorida, Wisconsin, MIT, Nebraska and Purdue as regional US CMS centers. ( + Brazil + ?) Not every country has a T1. There are strong “T3” institutions springing up also.

  41. Production of Higgs Gluon Fusion Bremsstrahlung Top Fusion Vector Boson Fusion

  42. Higgs Decay to Photons • Branching Fraction of ~10-3 in range 120-150 GeV

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