Muon Alignment at CMS

Transcription

1 Muon Alignment at CMS for CMS Collaboration 1

2 The CMS Detector Compact Muon Solenoid 8[7] TeV in Run 1 > 13 TeV for Run 2 4 main components Tracker Electromagnetic Calorimeter Hadron Calorimeter Superconducting Solenoid Muon Detector 2

3 The CMS Muon System 250 Drift Tubes (DT) Chambers in the central barrel region. 612 Cathode Strip Chambers (CSC) in the endcap region (72 new in Run 2) Resistive Parallel Plate Chambers (RPC) in both the barrel and endcaps used for triggering Measurement Error error Muon system only Inner tracker only Full system

4 Importance of Muon Detectors and Alignment Searches for Z rely on high mass dilepton resonances. Here a hypothetical Z decays into 2 muons. The muon detectors are further from the IP, allowing for greater precision in determining the momentum of high momentum muons and sign determination Both Ideal Both Misaligned Misaligned Muon System Misaligned Tracker 4

5 Track Based Alignment The tracker tells us about the muons kinematics Simulate where the muons should be heading based on interaction tion with magnetic field and materials propagate the muon Compare actual hit location with expected hit location residual Need to average over many muon s residuals due to multiple scattering 5

6 Weak Modes Some shifts can be hard to detect with track based alignment A shift along local z and y away or towards the interaction point is hard to distinguish 6

7 Upgrade to Run 2 Collision energy: Peak luminosity: 8TeV 13Tev cm 2 s cm 2 s 1 50ns to 25ns bunch spacings ~30 collision per bunch crossing in run 1 ~25 for 25ns bunch spacing in run 2 and up to 75 for 50ns easier to operate at 50ns and more collisions, but also more pileup 7

8 Shifts in Local Y Run 2 Surprises Run 2 Software Run 1 Software Wheel -2, Station 1 8

9 Degenerate Hits 2 potential hit locations as only distance from center is measured 9

10 Degenerate Hits 10

11 Degenerate Hits 11

12 Results 73comb v 73 Mean Timer with chi2 chi2 cut: (dt2->chi2() / double(dt2->ndof())) < 2.0) New Software combinatorics: New Software Mean timer with chi2: Wheel -2, Station 1 12

13 Future improvements Potentially align all 6 Degrees of Freedom Layer based Alignment of detectors Finding and eliminating known and unknown systematic errors

14 Goals for Run micron accuracy with track based alignment reduction of systematic uncertainties using track based alignment to align layers for run 2 We are looking forward to new exotica searches soon 14

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16 Software upgrades A big change for us was the change from combinatorial pattern recognition to Mean-Timer Mean-Timer gives better spacial and time measurement resolution-better for physics, but a bit messy for alignment without our chi^2 cut

17 Multiple Scattering Multiple scattering of the muon (and uncertainties in muon kinematics? other factors?) mean that the muons don t travel in straight lines need to average over many muons to find center 17

18 Why Tails are Bad

19 Why Muon Detector and Tracker? Muon system only Inner tracker only Full system 19

20 Alignable Elements and Degrees of Freedom The DT and CSC detectors are alignable elements of the CMS muon system. CMS global coordinates

21 Alignment Algorithm Propagate muons to detector Select high quality muon tracks in tracker Calculate residuals visual here and align detector 21

22 Alignment algorithm 1. Select high quality muon tracks (based on tracking information e.g. number of hits, chisquared of fit, etc.) 1. muons should have a transvers momentum greater than 30 GeV to reduce multiple scattering 2. muons should have a transfers momentum less than 200 Gev to avoid muon showering 2. Fit the muon tracks with tracker information 3. Equalize positively and negatively charged muons to avoid bias from magnetic field positive and negative muons pull alignment in opposite directions 4. Propagate muon tracks from tracker to muon detector 5. Calculate muon residuals from hit locations and propagated tracks 6. Align chambers one by one with residuals cutting muons with very large residuals 7. Save alignment results to an SQL database for easy reference

23 Results 73comb v 73 Comb v Mean-Timer 73 Comb: 73 Mean-Timer: 23

24 Alignment Matrix 24

25 Design of the CMS Muon System CMS detector: Total weight : 12,500 ton Overall diameter : 15 m Overall length : 21.6 m Magnetic field : 4 Tesla CMS use three types of gaseous particle detectors for muon identification: 250 Drift Tubes (DT) Chambers Each DT chamber, on average 2m x 2.5m in size, consists of 12 aluminium layers, arranged in three groups of four, each up with up to 60 tubes: the middle group measures the coordinate along the direction parallel to the beam and the two outside groups measure the perpendicular coordinate 540 Cathode Strip Chambers (CSC) Each CSC module contains six layers making it able to accurately identify muons and match their tracks to those in the tracker. CSC