Robustness Studies of the CMS Tracker for the LHC Upgrade Phase I

Transcription

1 Robustness Studies of the CMS Tracker for the LHC Upgrade Phase I Juan Carlos Cuevas Advisor: Héctor Méndez, Ph.D University of Puerto Rico Mayagϋez May 2,

2 OUTLINE Objectives Motivation CMS pixel upgrade Current Tracker Geometry Methods Tracking Reconstruction Robustness studies Conclusions 2

3 General Objective Study and simulate the CMS tracker performance with and without pile-up as luminosity increases. Instantaneous Luminosity LHC (2012) SLHC~(2015) 3

4 Specific Objectives Compare the tracking efficiency performance with different tracker system geometries. Describe the impact on the tracker performance from turning off the outer tracker modules in special regions of CMS detector (Efficiency plots). Implement code in the CMS Software to simulate the reduction of collected charge by the ROC through an empirical and simple method. 4

5 MOTIVATION WHAT IS THE PURPOSE? 5

6 LHC and Standard Model Overview Experiments LHC Quark-Gluon Plasma Higgs Bosson Dark Matter Matter-AntiMatter Higgs Bosson Dark Matter»» 0.99c 6

7 Key Concepts Luminosity (L): Number of particles traversing an unit area every second. Cross Section (σ): refers to the probability of interactions in a two particle initial state. Decay rate: The probability per unit time that a particle will decay (Γ). Pseudorapidity (η): angle relative to the beam line (Lorentz boost (z)) 7

8 The Compact Muon Solenoid (CMS) y φ HCAL x ECAL z 4T Solenoid Tracking Sub-detectors on CMS 8

9 CMS Collaboration CMS Collaboration>3000 scientist, 172 institutes in 40 countries. UPRM 3PhD, 1 Post-doc and 8 students. Only in the Caribbean! 9

10 Current Tracker Geometry CMS tracker consists of various concentric cylinders High Instantaneous Luminosity: Increase Luminosity major # events η r z 10

11 What is the Upgrade? Prepare the CMS detector for higher radiation and a big amount of data due to increase in the Luminosity. Old New Detailed view Diode Detector element Increase the measurement points. (e.g efficiency, isolation, occupancy,etc) 11

12 METHODS HOW DO WE DO THESE STUDIES? 12

13 Track Reconstruction in CMS Longitudinal view Tracker(y-z) Local Reconstruction Triplet Hits Seed Finding Trajectory building 13

14 Trajectory building Track Candidates Compatibility Split (candidates) Propagated track? invalid Hit Fitting and Filtering Cuts: loose,tight, High purity 14

15 Iterative Tracking Initial Hit Collection Hit Removal (Second Hit Collection) First Track Collection (Hight Pt) Second Track Collection (Lower Pt) SO ON... 15

16 ROBUSTNESS STUDIES 16

17 Tracking Performance ttbar Sample 10k events Iterative steps 428 release : Reconstructed Tracks : Simulated Tracks (Truth) Є= f= efficiency fake rate 17

18 Tracking Concepts Primary vertex P-P Collision (4 pileup) Particle's track Secondary vertex Decay of unstable particles Beam Spot Interaction vertex Material-Detector 18

19 Tracking Degradation produced by dead modules CMS Tracker Map CMS Tracker Hit Plots Dead Regions 19

20 Tracking Degradation produced by dead modules up to 16% pixel ROC data loss for <PU>=50. 20

21 Tracking Degradation produced By dead modules Tracking Efficiency Mainly due to TIB dead modules Efficiency drop ~15% current ~5% upgrade 21

22 Tracking Degradation produced By dead modules Ratio Plots Ratio= dead >> efficiency loss for high pile up Relative efficiency loss 20% current 8% upgrade 22

23 Tracking Degradation produced By dead modules Fake Rate Increase fake rake in the η central region 23

24 Tracking Degradation produced By dead modules Ratio Plots Ratio= dead modules fr Not conclusive Gain fake rate 24% current 8% upgrade 24

25 TIB Degradation produced by uniform Inefficiency Current Geometry Tracker 20% loss of the tracking hit finding efficiency Near to the pixel detector up to 16% pixel ROC data loss for <PU>=50. 25

26 TIB Degradation produced by uniform Inefficiency Tracking Efficiency TIB central degradation Efficiency drop ~18% current ~3% upgrade 26

27 TIB Degradation produced by uniform Inefficiency Fake Rate Increase fake rake in the η central region and the ends ~negligible 27

28 Radiation Damage Simulation Previous Studies CMS NOTE-2007/033 (M. Swartz, D. Fehling, G. Giurgiu, P. Maksimovic, V. Chiochia) Charge Collection How it works Charge Profile What we want to do 28

29 A brief description of exponential method FIRST APPROXIMATION J. Cuevas, H. Mendez, C. Pollack, E. Brownson Simulated the reduction of collected charge by ROC through an exponential function. Exit point N0 N =N0e k L depth L L depth=0 Max Attenuation depth= L N = N 0 L Entry point Ylocal (Zglobal) ROC ROC Ylocal (Zglobal) FLIPPED SENSOR Zlocal & E depth=exit point-entry point depth Zlocal & E UNFLIPPED SENSOR N0 k N =N0e depth L depth=0 N =N 0 depth= L Max Attenuation L 29

30 Transversal and Longitudinal Pixel Hit Resolution Exponential Method vs Pixelav Simulation CMS NOTE-2007/033(M. Swartz) Resolution (sigma) as function of η. Three cases: Simple way to simulate the lost charge. Reproduce similar degradation Juan Carlos Cuevas -Bautista 30

31 Primary vertex PU0 Transverse Resolution Longitudinal Resolution Dependence on the number of tracks is showed. Resolution loss by radiation damage Juan Carlos Cuevas -Bautista 31

32 Conclusions Outer Tracker Inefficiencies Radiation Damage Method RecoHit Resolution Primary Vertex resolution Tracking efficiency and fake rate Shows small changes between an irradiated (k=1.0,1.5) and non irradiated sensor 32

33 Conclusions Tracker Upgrade Simulation Meeting, CERN, April 23th (2013) CMS Internal Note In progress (2013) 33

34 Thanks for your Attention! 34

35 BACKUP 35

36 References CMS Collaboration. Compact muon solenoid experiment. CMS Collaboration. Detector performance and software, Technical Design Report. Technical report, CMS Collaboration. Technical proposal for the upgrade of the CMS detector through 2020, Technical Design Report. Technical report, CMS Collaboration. Performance of the CMS tracker. Technical report, he_week_archives 36

37 References W. Adam. Vertex and Track Reconstruction in CMS. Presentation from cms collaboration K. Burkett. Details of Tracking at CMS. Presentation LHC physics Workshop, Mumbay, India (October 27,2009) Pollack, C. A. Performance Study with Irradiated Pixel Sensors. University of Puerto Rico, Mayaguez PR, USA (August 20, 2012). It is possible to simulate the loss of charge collection from the pixel detector pixel in CMS due to radiation damage with a simple function such as an exponential 37

38 TIB Degradation produced by uniform Inefficiency Ratio Plots 38

39 TIB Degradation produced by uniform Inefficiency Ratio Plots 39

40 Collection Charge Φeq = n/cm2 n+side Φeq = n/cm2 p-side 2 years LHC low luminosity AGEING 2 years LHC high luminosity P = point = ionization point where point is the coordinate of the middle point of each segment -de/dx =eloss/distance X0 = exit point X1 = entry point 40

41 Exponential Approximation Current Geometry: - CMSSW_4_2_8_SLHCstd2_patch1 (ttbar, 10k evts) /RelValTTbar_Tauola/CMSSW_4_2_3_patch3-DESIGN42_V11_110612_special-v1/GEN-SIM Use empirical attenuation function to produce the radiation damage in the detector ROC sensor Track UNFLIPPED Interaction Point FLIPPED sensor ROC R1 Entry point (distance to ROC) R2 Exit point (distance to sensor) 41

42 Exponential Approximation Identifying the orientation of sensor (we take advantage of coordinates of the primary ionization method). Convert local coordinates to global: r1global = toglobal(entry_point) r2global = toglobal(exit_point) Condition used in the code: if r1global > r2global Flipped sensor. if r1global < r2global Non-Flipped sensor. 42

43 Transversal Pixel Hit Resolution Exponential Method vs Pixelav Simulation CMS NOTE-2007/033(M. Swartz) We plotted the SimHit-RecHit values for different bins of pseudorapidity η for BPix Layer1. Then we did the Gaussian fit and plotted the sigmas (Resolution) as function of η. Only layer 1! Juan Carlos Cuevas -Bautista 43

44 Primary vertex PU0 Reference Studies Transverse Resolution Longitudinal Resolution Juan Carlos Cuevas -Bautista 44

45 B-tagging PU0- ndloss Radiation damage K=1.0 K=1.5 Current pixel detector Juan Carlos Cuevas -Bautista 45

46 Rapidity transformation Cuts Dxy<0.2mm Intersect beam spot Juan Carlos Cuevas -Bautista 46

47 Tracker and Pixel Geometry Current Juan Carlos Cuevas -Bautista Upgrade 47