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Preliminary Oral Exam

Preliminary Oral Exam. Aram Avetisyan Brown University February 25, 2009. Outline. Part 1 : Validation of HCAL Software CMS in general and its hadronic calorimeter in particular Software used in CMS Details of hadronic calorimeter validation Part 2: The T 5/3 Top Partner model

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Preliminary Oral Exam

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  1. Preliminary Oral Exam Aram Avetisyan Brown University February 25, 2009

  2. Outline • Part 1: Validation of HCAL Software • CMS in general and its hadronic calorimeter in particular • Software used in CMS • Details of hadronic calorimeter validation • Part 2: The T5/3 Top Partner model • Description of model • Fast Simulation and the Physics Analysis Toolkit in CMS • Event selection • Charge misidentification study • Reconstruction of T5/3 invariant mass

  3. ECAL Magnet HCAL Tracker Muon chambers The CMS Experiment • Compact Muon Solenoid (CMS) Experiment • One of two general purpose experiments at the Large Hadron Collider (LHC) • Compact: 15m in diameter, 21.5m long, weighs 12500T

  4. The CMS Hadronic Calorimeter (HCAL) • HCAL is designed to measure the kinematics of jets and missing transverse energy • Brass absorber plates interspersed with plastic scintillator • The section closest to beam pipe is made of steel embedded with quartz fibers • Steel on inside and outside to provide support

  5. HCAL Subdetectors • Four subdetectors covering pseudorapidity ( ) up to |η| = 5: • Barrel (HB): |η| < 1.4 • Endcap (HE): 1.3 < |η| < 3.0 • Forward (HF): 2.9 < |η| < 5.2 • Outer (HO): |η| < 1.26 • HO is outside the magnet Inside the magnet η = 1 η = 0.5 η = 1.4 η = 2.1 η = 3 η = 2.4

  6. Beam Splash Event • Splash from 2E9 protons impacting a collimator about 150m upstream of CMS • HCAL is blue

  7. HCAL Software Objects SimHits • Simulation is done with GEANT4 • SimHit: Sum of scintillator energies for each cell • Also stores time of hit, subdetector and location of cell • Simulation only • Digi: Signal from one readout channel • Stores cell identification info and up to 10 integers corresponding to charge deposited in a 25 ns time bin • RecHit: Stores energy in GeV, time of hit and cell identification info • CaloTower: 1 HCAL cell + 5x5 ECAL crystals • Used for High Level Trigger which doesn’t have time to process all ECAL and HCAL cells Digis RecHits CaloTowers ECAL

  8. HCAL Software Validation • CMS Software Framework (CMSSW): the entire collection of software used for simulation, calibration, reconstruction, analysis, etc. • Used for both processing both Monte Carlo and real data • Constantly in development • Pre-release about once every 2 weeks • Release about once every 2 months • Validation for HCAL: compare all software objects to last good CMSSW version • Quick validation: TTbar and QCD • Full validation for known major changes, new production release or unexpected results from quick validation

  9. Monte Carlo Samples for Validation • TTbar and QCD • 50 GeV π+ shot at 3 pairs of η, φ towers • Corresponding to HB, HE and HF • 500 GeV π+ randomly distributed in |η|<1.3 and all φ • Energetic particles needed to reach HO • Neutrinos for noise validation • Generation software needs some particle to run • Simulation runs quickly • 50 GeV photons (for HF) in 3<|η|<5 and all φ • 20 and 50 GeV pions randomly distributed in |η|<5 and all φ

  10. Single Pion Events Pion first decaying in ECAL Pion decaying entirely in HCAL

  11. TTbar Events TTbar event in CMS Same event in HCAL only

  12. Full Validation Processing • Most processing is done using full chains: • SimHits, Digis, RecHits and CaloTowers produced in one instance of running CMSSW • No magnetic field for full validation • Validation is of HCAL software • Easier to hit the same tower each time • ECAL+HCAL geometry except for 500 GeV pions, photons and randomly distributed 50 GeV pions which are HCAL only • ECAL needed for CaloTowers

  13. Validation Output • Running these chains results in a large number of histograms • More than 1000 altogether • Only about 100 are ordinarily used • Histograms are analyzed using ROOT macros • Histograms are produced for all software objects and are thus quite different • Variety of dimensions, range, scaling of axis, etc. • Difficult to treat them in a unified manner

  14. Histograms: Energy Fraction vs. iEta-iPhi 50 GeV Single π full scan of CMS

  15. Histograms: Number of CaloTowers Number of CaloTowers in HB from TTbar events

  16. Histograms: HE Signal Amplitude vs. SimHits

  17. Steering File • Solution: steering file for macros that includes all of these parameters: HcalRecHitTask_energy_ecal_plus_hcal_HE 0 HcalRecHitTask_energy_ecal_plus_hcal_in_cone_HE 1 HcalRecHitTask_energy_ecal_plus_hcal_in_cone_HE.gif 100. -1 1D Statrv Chi2 NoLog 41 43 HE ecal+hcal energy in cone (GeV) HcalRecHitTask_energy_hcal_vs_ecal_HE 1 HcalRecHitTask_energy_hcal_vs_ecal_HE.gif 100. 100. 2D noStat noChi2 NoLog 41 42 HE banana plot Colors File Title x-axis range y-axis range x-axis title

  18. Automation & Web Publication • 3 separate macros: CaloTowers, Digis and RecHits • Each with its own steering file in the format from the previous slide • Shell script: • Takes CMSSW versions to be compared as arguments and passes them on to macros • Runs all three and distributes resulting histograms into the proper directories, creates index.html files for each directory • Directories are then published on the web • Static HTML formatting • Example: http://cmsdoc.cern.ch/cms/cpt/Software/html/General/Validation/SVSuite/ HCAL/2_1_0_pre9_vs_2_1_0_pre6/RecHits/Global/index.html

  19. T5/3 Top Partner Model Heavy Top Partner Heavy Bottom Partner -- Signature: -- Look for tW invariant mass peak (T5/3)

  20. Cross Sections (at 14 TeV) • Almost two orders of magnitude difference between the two mass points

  21. Fast Simulation • Monte Carlo events are generated with MadGraph • Full simulation is accurate, but slow – particularly for events with a lot of particles and jets • Fast simulation uses a simplified model of CMS and algorithms optimized for speed • No GEANT4 • 10-100 times faster for samples used in this study • Output has the same format as full simulation • Validated against full simulation at each release • It has some limitations • No charge misidentification for leptons

  22. Event Selection: Isolation • Jets: • Remove those overlapping with electrons • Leptons: • Remove duplicate electrons (same track or ECAL supercluster) • Isolation parameters for leptons: • trackIso: sum of energies of tracks within ΔR < 0.3 of lepton • caloIso: sum of energy deposits in ECAL and HCAL within ΔR < 0.3 for muons and ΔR < 0.4 for electrons • Define • relIso > 0.8

  23. Event Selection: Cuts • Cuts on electrons, muons, jets and missing transverse energy (MET) used to separate signal from background • Transverse momentum: • Due to different cross sections and masses some cuts for 1 TeV sample differ from the 500 GeV ones • Common cuts on leptons (electrons or muons): • |η| < 2.4 • First lepton with pT > 50 GeV • Second lepton with pT > 25 GeV • Lepton charges must have same sign

  24. Lepton pT Distributions Normalized to 1

  25. JetMET Cuts • Different cuts on JetMET: • M = 500 GeV • |η| < 5 • Leading jet with pT > 100 GeV • Second jet with pT > 80 GeV • 5 jets with pT > 30 GeV • M = 1 TeV • |η| < 5 • Leading jet with pT > 200 GeV • Sum of Leading and Second Jets > 300 GeV • Second jet with pT > 80 GeV • 5 jets with pT > 30 GeV • ET > 20 GeV

  26. Jet pT Distributions Normalized to 1

  27. Charge MisID • Most significant selection criterion: presence of same signed leptons • If lepton charge is misidentified, backgrounds with much larger cross-sections (e.g. ttbar) become relevant • Data-driven approach: Tag & Probe • Look at Z->l+l- events • Select pair of leptons with invariant mass near MZ at least one of which is well-measured (“tag”) • Look how often charge of the other lepton (“probe”) is the same as that of the tag • Used large, centrally produced full simulation samples

  28. Charge MisID • Muons: • Tag: Muon with ET > 20 GeV • MisID rate is slightly less than 5E-4 • Not enough events to make plots even after running over more than 1 million events • Defined as a constant 5E-4 in analysis • Electrons: • Tag: Isolated electron passing High Level Trigger with |η| < 2.5 • About 2.2% of electron pairs have the same charge so average mis-ID rate is ~1.1% • Implemented as an array in (Pt, Eta) in analysis • Tag & Probe consistent with generator level information

  29. Electron Charge MisID Plots • No relIso-based Isolation applied • MisID rate grows with |η|, but remains fairly low

  30. M = 500 GeV Results # of Events assumes 300pb-1 of integrated luminosity 289 pb-1 integrated luminosity needed to get

  31. M = 1 TeV Results # of Events assumes 70fb-1 of integrated luminosity 71 fb-1 integrated luminosity needed to get

  32. T5/3 Invariant Mass • The T5/3 can be reconstructed from the hadronic fraction branch of the decay • Require all cuts from above and that two jets be tagged as b-jets • High efficiency track counting algorithm, loose working point • b-jet closest to the lepton with the second highest pT is assumed to come from leptonic branch of decay • The remaining jets are then used to reconstruct the two W’s, the top and the T5/3

  33. T5/3 Invariant Mass • Reconstruct First W: • Pair of jets with invariant mass closest to W ( must be within 20 GeV) • Jets must have ΔR < 1.5 and are discarded if used • W must have pT > 50 GeV • Reconstruct Second W: • Pair of jets with invariant mass closest to W (must be within 25 GeV) • Jets must have ΔR < 2.0 and are also discarded if used • W must have pT > 30 GeV • Reconstruct top quark: • Consider (W, b-jet) pairs and take combination with invariant mass closest to top quark (must be within 40 GeV) • Reconstruct T5/3 from top quark and the unused W

  34. Invariant Mass W Plots

  35. Invariant Mass Plots

  36. Summary • HCAL software validation is ongoing • Validation is now close to fully automated • Changes are easy to configure via steering files • T5/3 Top Partner study at 14 TeV • Accounted for possibility of charge misidentification • Effects are small • In the case of M = 500 GeV, early discovery is feasible (300 pb-1) • M = 1 TeV needs 71 fb-1 • Reconstructed T5/3 invariant mass from hadronic decay chain • Only minor adjustments needed for 10 TeV run

  37. Acknowledgements & References • HCAL software validation: • Salavat Abdullin • https://twiki.cern.ch/twiki/bin/view/CMS/HcalValidation • T5/3 study • Tulika Bose and Meenakshi Narain • CERN-CMS-CR-2008-005

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