Simulation of J/ψ detection via electron-positron decay

Transcription

1 1 Simulation of J/ψ detection via electron-positron decay Goran Kružić Faculty of Science, University of Zagreb, Croatia 6 th Austrian Croatian Hungarian meeting Summer workshop for theoretical physics Nonabelian Gauge Theories and Quark Matter Rab, Croatia, 30 August 04 September 2013

2 2 This presentation is based on calculations made for Compressed Baryonic Matter experiment at GSI Darmstadt, Germany, 2005 available in Technical Status Report. Presentation serves for information sharing purposes only and neither represents current CBM status nor progress which has been made since 2005.

3 3 Theoretical models and software packages used in simulation

4 4 STS Silicon Tracking System RICH- Ring Imaging Cherenkov detector TRD Transition Radiation detector TOF Time of Flight ECAL - Electromagnetic Calorimeter PSD Projectile Spectator detector

5 Available at 5

6 6

7 Available at: 7

8 Available at : 8

9 CBM Analysis and Simulation framework 9

10 Example of simple simulation macro 10

11 11

12 12 Hits in STS Silicon Tracking System for UrQMD event, Au-Au, at 25 AGeV. Geometrical layout of STS detector. p t = p x2 + p y 2 p = p t2 + p z 2 y = 1 2 ln p 0 +p z p 0 p z η = 1 2 ln p+p z p p z = - ln(tg θ 2 ) p μ = (p 0, p)

13 J/ψ ->e + e - reconstruction 13

14 14 UrQMD (Background Au-Au 25AGeV) PLUTO J/ψ ->e + e - (Signal, thermal model) GEANT4 Transport (Geometrical Acceptance) Track finding/fitting (Momentum resolution σ p p = 1%) HSD (J/ψ, ρ, ω, φ multiplicities) Branching Ratios taken from Particle Physics Booklet Electron poin misidentification 0.01% Cuts (P t 1 GeV) Event Mixing (Background only) Invariant mass

15 15 HSD Hadron String Dynamics ( Au+Au, E = 25 AGeV ) Particle Mass [MeV/c 2 ] Multiplicity per event π η ρ ω φ J/ψ * 10-5

16 Distribution of rapidity for J/ψ ->e + e - decayed pairs. PLUTO J/ψ ->e + e - (Thermal model) black all e + e - pairs red - e + e - accepted in detector blue - e + e - after p t 1 GeV/c T = 170 MeV Branching Ratio taken from Particle Physics Booklet (6%) 16 Distribution of transverse momentum for J/ψ ->e + e - decayed pairs.

17 17 Cut P t 1 GeV/c Multiplicity per event * Branching ratio

18 Track finding/fitting (Momentum resolution σ p p = 1%) 18 Track fitting algorithm shows 90% efficiency for high particles with high momentum, meaning that 90% particles tracks (trajectories) which have entered STS can be reconstructed. Remark: Track fitting state vector R(x, y, t x, t y, q/p) t x = p x /p z, t y = p y /p z, p is momentuma and q charge of particle. Software based test case shows a bit different result for track finding and fitting algorithm.

19 19 M J/ψ = E e + E 2 p p e + p 2 p Event mixing applied for background Gaussian fit applied for S/B and ε-efficiency calculations Bremsstrahlung is switched ON Electron-Pion missidentification assumed to be 0,01% S signal, Gaussian fit integrated arround mean value [ M - 3σ M ; M + 3σ M ] S/B ε(p) B background, polynomial fit integrated arround mean value [ M - 3σ M ; M + 3σ M ] Geom. Acc Geom. Acc. + Tracking ε(p) = S S+B

20 RICH added in reconstruction chain 20

21 21 Mirror Photodetector plate Track RICH hits (blue) Found rings (red) Track projections (green) Cherenkov radiation Schematic figure of RICH Ring Imagine Cherenkov Detector. RICH ring radius versus particle momentum.

22 22 Input: 5000 J/ψ ->e + e - d min - distance between track projection and closest ring centre. Photo-detector plane x d min Track projection RICH+STS acceptance for e -. RICH mirror Particle Track z Number of L1 STS events with at least 2 tracks: 2372 y Photo-detector plane RICH mirror

23 23 Number of events with at least 2 track projections at photo-plane: 2267 Number of events with at least 2 rings found at photo-plane: 101 & d min < 2cm Just 89 out of 5000 J/ψ ->e + e - are reconstructed!! Potential reasons could be: a) STS and RICH detectors missallignment. b) RICH mirrors are not properly set up, cherenkov radiation is reflected out of photodetector plane. c) RICH ring find algorithm should be improved.

24 Summmary and further strategy Since Track reconstruction through whole detector setup: ECAL, TOF, TRD,RICH, STS was not available in 2005, following assumptions (requirements on detector design) are made: Combined RICH and TRD gives an electron identification efficiency of 90%. A electron-pion (charged pions) missidentification 0.01% Momentum resolution σ p p = 1% J/ψ selection procedure: 1. Tracking in TRD. 2. Electron positron selection and roughly estimation of their momentum from deflection angle in magnetic field. 3. Propagate these candidates to STS and connect them with found tracks in STS. 24 Secondary particles created by interaction with detector can be recognised by STS tracking routine. (J/ψ decays within 250μm thick target additional vertex cut V z < 1 cm can be applied.) 4. Improve track parameters in target region. 5. Calculate invariant mass. Under mentioned conditions J/ψ can be detected on proposed detector setup.

25 Thank you for your attention! 25

26 26 References.Technical Status Report, Compressed Baryonic Matter Experiment,

27 Backup slides 27

28 Hadron String Dynamics model 28

29 29

30 30

31 31

32 32

33 UrQMD multiplicities 33

34 34

35 J/ψ Reconstruction 35

36 36

37 37

38 Test Case 38

39 39

40 40