Offline Data Processing of MRPC End cap

Transcription

1 Offline Data Processing of MRPC End cap SUN Shengsen EPD Seminar Dec. 27 th,

2 Outline Particle Identification (PID) Time-of-Flight Detector (TOF) Multi-gap Resistive Plate Chamber (MRPC) BESIII Endcap TOF system Detector and Electronics Multi-peak of Time-Over-Threshold (TOT) Alignment of detector Reconstruction and Calibration Summary 2

3 A traditional particle physics experiment Conceptual design of a traditional particle physics experiment Tracking system EM calorimeter Hadron calorimeter Muon system Particle identification is a crucial aspect. r, e, μ, π, K, p p, E 3

4 WHY PID is crucial? Invariant mass M 2 = m m (E 1 E 2 p 1 p 2 cccθ) Improvement in the signal-to-background ratio with PID without PID φ K + K 4

5 Particle Identification (PID) Measurement of the energy deposit by ionization Time-of-flight measurements Detection of Cherenkov radiation Detection of transition radiation β v c = p c E 1 γ 1 β = E 2 mc 2 p = γmm m = p cββ 5

6 Particle identification capability p = γmm m = p cββ dd m 2 = dp p 2 + γ 2 dβ β 2 Separation power n σ = R A R B <σ AA > 6

7 Time-of-Flight detector 飞行时间探测器是通过测量带电粒子的飞行时间, 结合径迹探测器测量的粒子的动量和飞行径迹长度, 得到粒子的质量, 实现粒子鉴别 L c t = v p c = β = c E = 1 m c 2 p +1 m = p c c t L 2 1 p,v c, β 1 σ(m) m = σ(p) p + σ t γ2 ( t + σ(l) L ) 7

8 TOF PID Comparison between measured and expected time: t i ppppppp = L,β c β i = p c,e i E i = m 2 i + p 2 i χ = Δt = t i mmmmmmm t ppppppp σ n TTT = t A t B σ TTT = σ Normal distribution LL 2p 2 σ TTT m A 2 m B 2 Particle separation power of TOF depends on: The flight time difference between different species particles with same momentum. Time resolution 8

9 Scintillation TOF Scintillator bar coupled with PMT Good time resolution PMT under strong magnetic field Increase of granularity 9

10 Multi-gap Resistive Plate Chamber MRPC-TOF Charged particle Primary ionization Avalanche Induced signal Readout of scintillator is expensive, RPC is much cheaper. The RPC design was improved by Multi-gap RPC: Reducing gap sizes restrict fluctuation of drift time improve time resolution Increasing the electric field sum of the induced signals good detection efficiency 10

11 Scintillator End cap BESIII The designed target is ps The time res for pions is 138ps. Multiple scattering has worsen the performance Intrinsic time resolution: 80 ps Uncertainty of bunch time: 20 ps Uncertainty of bunch length: 8-15mm 20 35ps Extrapolation of track: 10mm 50ps Electronics: 25 ps Expected time: 30 ps Time slewing: 10ps Overall time resolution: ps 11

12 MRPC End cap TOF Intrinsic time resolution < 55 ps OLD NEW Detector Scintillator MRPC Modules Electronics =1728 Time Res 138ps < 80~100ps 12

13 Structure of the MRPC 9.1cm 3mm 2.4cm 14.1cm Readout strip: Width: 2.4 cm Length: cm Gas gap: 2 x 6 Gap size: 0.22 mm Resistive plate: floating glass Total thickness: ~20 mm 13

14 Electronics Time precision contributed by electronics (RMS) < 25ps 14

15 Trigger / Slow Control / Gas Trigger conditions: NETOF>=1, NETOF>=2, Back to Back 15

16 MRPC Installation Oct. 2015, new MRPC End cap TOF take place of scintillator endcap TOF The total last about 60 days. 16

17 Procedure of MRPC Installation leakage Ratio check electronics check location guarantee installation gas pipes & HV wires test with HV 17

18 MRPC Endcap TOF Reconstruction Event Start Time t 0 MDC Reconstruction Extrapolated track Momentum, path length expected time Hit position TOF Raw Data Leading time t lllllll Time-over-threshold (TOT) 18

19 Event Start Time n 1 n t i rrr i=1 i t cccc t eee 19

20 Signal of MRPC TOF t ccc = t ppp sssss (z) + t tttt wwww (q) + t ddddd t = t mmm t eee TTT = t 0 + t mmm + t ccc t 1 Q 20

21 Transmission time on the strip Dependence of measured time on the hit position 4-order polynomial function 21

22 Multi-peak TOT Distribution Reflection of the signal in strip t lllllll = l/2 z v t tttttttt = l/2 z v fff t tttttttt = l/2+z v + t ddddd + ttt + t ddddd + ttt + n t sssss + t ddddd t tttttttt t lllllll = ttt ttt fff = ttt + 2 z v + n t sssss ttt nnnn = ttt + 2n t sssss nnnn t tttttttt = l/2 z v + ttt + 2n t sssss + t ddddd 22

23 Multi-peak TOT Distribution Reflection of the signal in strip Length of strip: 13 cm Length of foot: 2.8 cm Velocity of signal: 55ps/cm Transmission time for total strip (13+2.8)*55=869ps 869ps*2=1.738ns Time interval (19.65ns-11.2ns)/5=1.69ns Time interval 23 (18.0ns-12.8ns)/3=1.73ns;

24 Time Walk (Time Slewing) Measured raw time depend on hit position Multi-peak TOT partly depend on hit position Hit position correction 24

25 MRPC TOF Calibration Bhabha events are used for calibration sample Empirical calibration function for single end of strip t cccc = p 0 + p 1+p 2 z Q + p 3+p 4 z Q + p 5 + p 6 z Q + p 7 Q 2 + p 8 Q 3 + p 9 Q 4 + p 10 z + p 11 z 2 +p 12 z 3 Empirical calibration function for strip t cccc = p 0 + p 1 Q + p 2 Q + p 3 Q + p 4 Q 2 + p 5 Q 3 + p 6 Q 4 t ccccccc cccc = 1 2 (t llll rrrrr cccc + t cccc ) 25

26 MRPC TOF Reconstruction Extrapolated strip as center, search signals in the range of strips Multi-signals: Match hit position Compare TOT 26

27 Alignment of MRPC TOF Detector t 1 = l/2 z v t 2 = l/2 z v 1 + t ddddd 2 + t ddddd True Geometry t 2 t 1 2 Ideal Geometry = z v + c Assumption no misalignment along the beam direction 27

28 Alignment of MRPC TOF Detector East Endcap 7mm West Endcap 0.45 degree 28

29 Time Resolution and Efficiency of Bhabha left end: 69ps right end: 69ps combine: 57ps Time Resolution Efficiency Module number Strip number Hit Position 29 29

30 Time Resolution for π Scintillator ETOF: 138 ps Designed Target of MRPC ETOF: 80~100 ps BESIII: 65ps pion 0.8GeV/c 65ps Accelator Detector Time Resolution(π) RHIC STAR 80ps LHC ALICE 86ps (Without t0) BEPCII BESIII 65ps 30

31 χ Calculation in PID Algorithm Time difference is not observed to depend on species of particle (?) Time difference depends on the momentum and polar angle. χ i = t mmm t eee i σ(sssss, p) 31

32 STAR Experiment --- Spline Fit 96ps 32

33 ALICE Experiment 33

34 Summary and Discussion Particle identification is crucial MRPC TOF: good time resolution, high efficiency and low cost Offline data processing of MRPC BESIII Analysis of multi-peak TOT Alignment of detector Empirical calibration function. The time resolution of 0.8 GeV/c pion achieved 65 ps. Thank you & Happy New Year! 34