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![The Transverse Mass
Definition
For the lack of longitudinal information of nu
2
MT = (ET;` + ET;º )2 ¡ (~T;` + ~T;º )2
p
p
= 2jpT;` jjpT;º j[1 ¡ cos(¢Á`;º )]
MissET is the key here
Relies on robust calorimeter detectors
Usually poorer than direct measurements
52](https://image.slidesharecdn.com/ychao20130123-140117061814-phpapp01/75/Detector-Simulation-for-HEP-52-2048.jpg)
Uploaded byYuan CHAO
Detector Simulation for HEP
The document provides an overview of detector simulation. It introduces the goals of tracking systems, calorimeters, and muon detectors. It discusses full simulation with GEANT and fast simulation tools like PGS and Delphes. Events are generated, passed through the detector simulation, and then reconstructed. Visualization tools can display tracks and energy deposits. Exercises are provided to give hands-on experience with simulation and analysis concepts.
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Detector Simulation for HEP
- 1. Detector Simulation Yuan CHAO( 趙元 ) (National Taiwan University, Taipei, Taiwan) Numerical Simulation in HEP 2013/01/23
- 2. Outlines Introduction High Energy Detectors Coordinationsystem Four-vector conversion Detector Simulation Tracking System Energy Calorimeter Muon Detector Fast Simulation PGS Delphes Event Display Exercises 2
- 3. Goal of HighEnergy Physics LHC was built for the following purposes: To find the origin of mass... the Higgs boson. Looking for the unification.. Supersymmetry as well as other candidates of Dark Mater & Dark energy Investigate the mystery of anti-matter disappearance Physics at the early stage of the universe: Heavy Ion collisions and QGP 3
- 4. The Large HadronCollider Four major experiments at LHC Atlas, Alice, CMS, LHCb LHC first beam in Sep. 2008 A technical trouble occurred 10 days after the start Physics restarted in Nov. 2009 CERN Energy starts at 0.9 TeV Pushed up to 2.36 TeV in Dec. New energy record in 2010 Collision at 7 TeV on Mar. 30 Delivered data ~36/pb in 2010 Reached ~5.7/fb in 2011 Increased to 8 TeV in 2012 LHC ~20/fb data recorded 4
- 5. The Large HadronCollider Four major experiments at LHC Atlas, Alice, CMS, LHCb LHC first beam in Sep. 2008 A technical trouble occurred 10 days after the start Physics restarted in Nov. 2009 Energy starts at 0.9 TeV Pushed up to 2.36 TeV in Dec. New energy record in 2010 Collision at 7 TeV on Mar. 30 Delivered data ~36/pb in 2010 Reached ~5.7/fb in 2011 Increased to 8 TeV in 2012 ~20/fb data recorded 5
- 6. Atlas Detector A ToroidalLHC Apparatus A general purposed detector 6
- 7. CMS Detector Compact MuonSolenoid A general purposed detector 3.8 7
- 8. CMS Detector Compact MuonSolenoid A general purposed detector 3.8 8
- 9. Long Lived Particles Mostproduct of a collision decays before they reach the detectors Check the life-time on PDG handbook or web site: http://pdglive.lbl.gov/ Look for the value of cτ What we see in the detectors: e±, μ±, γ, π±,K±, KL, n, p± 9
- 10. Long Lived Particles Mostproduct of a collision decays before they reach the detectors Check the life-time on PDG handbook or web site: http://pdglive.lbl.gov/ Look for the value of cτ What we see in the detectors: e±, μ±, γ, π±,K±, KL, n, p± Others can be found through resonances search Resonance mass is like the finger print of particles: unique Similar to line spectra analysis of lights 10
- 11. Coordination System Most colliderdetectors built in barrel shape Detector build along the beam line Interesting particles have higher transverse momenta Symmetric shape to have uniform acceptance Special purpose detectors have different shapes LHCb 11
- 12. Coordination System Most colliderdetectors built in barrel shape Detector build along the beam line Interesting particles have higher transverse momenta Symmetric shape to have uniform acceptance Special purpose detectors have different shapes Coordination convention: Use cylindrical coordinate (r, θ, φ) Beam direction 12
- 13. Coordination System (cont.) Mostcollider detectors built in barrel shape Detector build along the beam line Interesting particles have higher transverse momenta Symmetric shape to have uniform acceptance Special purpose detectors have different shapes Coordination convention: Use cylindrical coordinate (r, θ, φ) Adopt Lorentz invariant variable: rapidity 1 y = ln 2 µ E + pL E ¡ pL ¶ jpj + pL jpj ¡ pL ¶ Pseudo-rapidity (approximation for m ≈ 0) 1 ´ = ln 2 µ · µ ¶¸ µ = ¡ ln tan 2 13
- 14. Four Vectors The keyvariables: 4-vectors Motion of particles can be described with (px, py, pz, E) in Cartesian More common used: (pT, η, Φ, m0) or (pT, η, Φ, E) q Conversions: px = pT cos Á py = pT sin Á pz = pT = tan µ = pT sinh ´ jpj = pT cosh ´ pT = p2 + p2 x y tan Á = py =px Implemented in ROOT, CLHEP, ... Will use through out the exercises One can use TLorentzVector with helper functions to simply the calculations needed 14
- 15. From Theory toDetectors To know the possible behaviors of some theoretical predictions: Development of a new model Super-symmetry Extra dimensions Lepton quarks ... Implementation and generation of hard interactions MadGraph/MadEvent (MG/ME) CalHEP ... Simulation of hadronization and parton showers Pythia Herwig 15
- 16. Detector Simulation The considerations: Geometryof the system Materials used Particles of interest Generation of test events of particles Interactions of particles with matter and EM fields Response to detectors Records of events and tracks Visualization of the detector system and tracks Analysis of the full simulation at whatever detail you like 16
- 17. Workflow of Simulation EventGen GEANT Sim Geometry info Digitization Fast Simulation Reconstruct Analyzer / Visualization 17
- 18. GEANT (Full) Simulation Standsfor "Geometry and Tracking" Build a detector and fire initial particles → simulation the particles "step-by-step" Define volumes Define step sizes Define cut-offs Physics in Geant4 EM processes Hadronic processes Photon/lepton-hadron processes Optical photon processes Decay processes Shower parameterization Event biasing techniques User plug-in processes 18
- 19. Interact Particles withMatters "Passage of particles through matter" in PDG booklet Energy deposition (dE/dx) Radiation length Molière radius K. Nakamura et al., JPG 37, 075021 (2010) http://pdg.lbl.gov/2010/reviews/rpp2010rev-passage-particles-matter.pdf 19
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- 21. Fast Simulation Geant simulatesdetailedly and extremely SLOWLY For LHC detector simulation, a single event can take 10-20 minutes, depending on the process Theorists need a quick way to validate some model and does not need detailed detector description and reconstruction algorithm A "Fast Simulation" will do the job One can use a simplified GEANT simulation by parameterizing the slowest part One can parameterize the whole response of the detector and reconstruction effects Major choices on the market: PGS (Pretty Good Simulation) Delphes 21
- 22. Fast Simulation ToolI PGS Started in 1998 by John Conway (UC Davis) Can parameterize any generic cylindrical detector Written in Fortran Latest version: PGS4 - 090401 LHC Olympics (theorists' favorite) Fine for most signal efficiencies: within factor of 2, can be as good as ~20% for many cases Not as good for fakes (especially for tau) Pretty slow (slow jet algorithm) http://www.physics.ucdavis.edu/~conway/research/software/pgs/pgs4-general.htm 22
- 23. Fast Simulation ToolI PGS is not good enough simulation Ideally to have something closer to full simulation At least for physics processes interested Physics could be added to PGS Magnetic B-field Jet energy correction Pile-up and multi-parton interactions Z-vertex Realistic muon reconstruction Charged hadron track reconstruction Realistic calorimeter and track isolation … 23
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- 25. What does PGSdo Main detector effects: PT smearing EEM, EHAD smearing Energy deposition in towers (granularity of HCAL) Tagging efficiencies, (muon ID, tau-tag, b/c tag) Detector parameters Partly from input cards, partly hard-coded Not included B-field effect on charged tracks (jet broadness) Pile-up (for high luminosity runs of LHC) Underlying events Background processes ... 25
- 26. LHCO Format Event startswith a row labeled "0" The second column indicates the type of object 0 = photon 1 = electron 2 = muon 3 = hadronically-decaying tau 4 = jet 6 = missing transverse energy 26
- 27. Fast Simulation ToolII Delphes a new generic fast simulation package in C++ Written by CMS experimentalists, S. Ovyn, X. Rouby, V. Lemaitre (UC Louvain) Considerably more realistic than PGS (ex. B field) Separate treatment of barrel, endcap and forward Cal. Considerably faster than PGS (using FastJet package) with SISCone, C/A, Anti-kT jet algorithms Smart tau reconstruction model Detector and trigger settings in separate input cards Well tested against expected response of Atlas and CMS http://arxiv.org/abs/0903.2225v3 27
- 28. Tracks Charged particles canbe detected as “tracks" So called "tracking system" Silicon, wired chamber, gas tubes... Magnetic filed for the momentum Curving direction for charge sign Parameterization Helix parameters 28
- 29. Tracking System Detecting chargedparticles Pixel detector Silicon Vertex detector Drift (wire) chambers / tubes Measures the momentum of particles Detection of trail gives trajectory Obtain the particles in/out positions and directions Bending direction gives the charge sign Amount of ionization depends on momentum Can also be used for particle identification Needs magnets Strength and uniformity Used for electron, muon... charged particle detection Energy derived from the mass of the particle Very good spatial resolution Worse for very energetic particles (curvature) 29
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- 31. Simulate Tracks Tracker isembedded in a magnetic field Energy loss: dE/dX Position of charged particles is modified Length and radius of the tracker are important 31
- 32. Simulation of solenoidalB field Exact calculation of the movement of a charged particle: Assuming Bx = By = 0 Homogeneous Constant inside a cylinder Time of flight to exit the cylinder t max = min ( tT, tz) tT: time to hit the R tz: time to hit the +/-Z For complex field => iterative method Step by step Slower method 32
- 33. Calorimeters Calorimeter for energymeasurement ElectroMagnetic Calorimeter Hadron Calorimeter To fully absorb the particle Heavy material Showers Convert into counts or light Granularity Used for electron & neutral particle detection Better energy resolution at very high pT Usually worse spatial resolution 33
- 34. Calorimeters EM Calorimeter ElectroMagnetic interactions Detectinge±, γ Showering Bremsstrahlung (low E: compton) Pair production Pair annihilation Shower size Moliere radius RM = 0:0265X0(Z + 1:2) Radiation length Shower length ln(E0 =Ec ) X = X0 ln 2 34
- 35. Calorimetric Cells Segmentation inη / φ Energy deposition Radiation length Ecal vs. Hcal ratios 35
- 36. Jets Jets are productsof out-going partons Including quarks and gluons Hadronization as strong interaction Particles pulled out of vacuum for colorless Detecting Jets Bunches of particles Including kaons, pions, leptons... Usually detected with "calorimeters" Various types and clustering algorithms 36
- 37. Jets in HadronMachines TrackJet Charged Tracks are used for clustering Good for early data study CaloJet Uses ECal/HCal towers for clustering JPT (Jet Plus Tracks) Replace the avg. calo response with individual charged hadrons measured in tracker system Zero Supp. offset correction Correction for in-calo-cone tracks Adding out-of-calo-cone tracks Correction for track eff. & muons PFJet (Particle Flow Jet) New approach in CMS JME-09-002 37
- 38. Jets at LHC Severaljet clustering algorithm available in CMS: Jet is the energy sum of a cluster p Cone algorithm: R = ¢´2 + ¢Á2 ' 0:5 Iterative cone, midpoint cone, SISCone 2p 2p Pairing distance: dij = min kT i ; kT j ´¢ ij D Kt: p=1, CA: p=0, Anti-Kt: p=-1 CMS uses FastJet package http://fastjet.fr Algorithm consideration Infrared & colinear safe Good performance (Energy, position ...) Robust to Piled-ups & UE CPU efficient: O( N2 ln(N) ) : O( N ln(N) ) G. Salam, “Jetography" Sequential recombination: ³ Priority needed on various jet algorithms Good to have many for cross checking The default jet algorithm is Anti-Kt 38
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- 41. Summary Introduced the experiments Motivation& goals Accelerators & detectors Basics on HEP data The four-vector Mass reconstruction Missing ET Fast Detector Simulation PGS Delphes Visualization Q&A 41
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- 50. 以上 Thank YOU! 謝謝 Remercie deVotre Attention
- 51. Introduction Accelerators & detectors KEK-B,BELLE (lepton machine) Tsukuba, Japan Lpeak=2.1 x 1034 /cm2/s2 Aerogel Cherenkov counter SC solenoid 1.5T CsI(Tl) 16X0 TOF counter n=1.015~1.030 3.5 GeV e+ 8 GeV e− EFC (online Lum.) Si vtx. det. 3/4 lyr. DSSD 3.5 GeV e+ on 8 GeV eWCM = M( Υ(4s) ) 3km circumference ~11mrad crossing angle BELLE Detector Central Drift Chamber small cell +He/C2H6 µ/ KL detection 14/15 lyr. RPC+Fe 51
- 52. The Transverse Mass Definition Forthe lack of longitudinal information of nu 2 MT = (ET;` + ET;º )2 ¡ (~T;` + ~T;º )2 p p = 2jpT;` jjpT;º j[1 ¡ cos(¢Á`;º )] MissET is the key here Relies on robust calorimeter detectors Usually poorer than direct measurements 52