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Status of muon simulations at GSI

Status of muon simulations at GSI. Anna Kiseleva. Outline. CBM setup and simulation environment ToF measurements for muon identification LMVM trigger with muon ToF J/ ψ p T reconstruction Muon measurements with r educed of the detector acceptance Conclusions.

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Status of muon simulations at GSI

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  1. Status of muon simulations at GSI Anna Kiseleva

  2. Outline • CBM setup and simulation environment • ToF measurements for muon identification • LMVM trigger with muon ToF • J/ψ pT reconstruction • Muon measurements with reduced of the detector acceptance • Conclusions

  3. CBM setup with muon detector STS track, vertex and momentum reconstruction Muon system muon identification TRD global tracking RPC-ToF time-of-flight measurement ToF TRD Muon system • release CBMROOT Jun09 • realistic MuCh segmentation (pads: min 0.280.28, max 4.484.48 cm2) • L1 STS tracking • LIT global tracking STS

  4. ToF measurements for muon identification

  5. Reconstructed background Masse of particles: μ – 106 MeV π – 140 MeV Κ – 498 MeV p – 938 MeV

  6. Background rejection via mass determination m2 = β = γ = m2 = P2 ( - 1) 1 P2 β2 (β × γ)2 L 1 c × t √1 – β2 (L, t) → β Muon ToF

  7. Mass distribution for different time resolutions time resolution μω background 30 psec 50 psec 80 psec

  8. Full reconstruction ω→μ+μ- + central Au+Au collisions at 25 AGeV time information: — without with time resolution: — 80 psec — 50 psec — 30 psec

  9. Reconstructed background central Au+Au collisions at 25 AGeV

  10. LMVM trigger with muon ToF

  11. Trigger strategy ∆x,∆y • Find events with min. 12 hits in 6 detector layers, which might correspond to two tracks (hit selection in muon ToF: velocity value) • Straight line fit • Track selection: fit criteria • Remark: if track passes cuts, its hits will not used for second track searching Muon ToF xtarget,ytarget ztarget

  12. Velocity β = L c × t ToF measurements: L – distance from target to the ToF t – particle time of flight (time resolution 80 psec) cut: β [0.96; 1.02]

  13. Parameters of straight line fit (μω) — x = a0 + a1 z —y = b0 + b1 z 2fitx and y (ztarget) z (xtarget or ytarget) Optimization of the cuts taking into account signal efficiency and background suppression factor

  14. Trigger 1000 central events (Au+Au collisions at 25 AGeV) background suppression factor for mbias events ~35

  15. J/ψ pT reconstruction* Au+Au collisions at 25 AGeV * see presentation in the Simulation section

  16. Detectors • STS: • sts_standard.geo • sts_standard.digi.par • MuCh • modular design • TRD • as last MuCh station behind last muon absorber • ToF • standard

  17. Reconstruction results reconstructed J/ψ: reconstructed muon tracks after the cuts ≥ 4 STS hits + χ2prim. vertex ≥ 12 MuCh hits ≥ 3 TRD hits βToF≥ 0.99 * 10th CBM Collaboration Meeting: different setup (only ideal STS+MuCh), different geometries and segmentations, cuts: χ2prim.vertex < 2, NSTS ≥ 4, NMuCh = 18, χ2MuCh*ndf < 55 accepted J/ψ: MC muon tracks have ≥ 4 STS MC points ≥ 12 MuCh MC points ≥ 3 TRD MC points ≥ 1 ToF MC point J/ψ multiplicity:counts in region mJ/ψ 2

  18. Invariant mass spectra for different PtJ/ψ Pt [0.0, 0.2] GeV/c Pt [0.2, 0.4] GeV/c Pt [0.4, 0.6] GeV/c Pt [0.6, 0.8] GeV/c Pt [0.8, 1.0] GeV/c Pt [1.0, 1.2] GeV/c Pt [1.2, 1.4] GeV/c Pt [1.4, 1.6] GeV/c Pt [1.6, 1.8] GeV/c Pt [1.8, 2.0] GeV/c Pt [2.0, 2.2] GeV/c Pt [2.2, 2.4] GeV/c

  19. Spectra of the like sign pairs for different PtJ/ψ Pt [0.0, 0.2] GeV/c Pt [0.2, 0.4] GeV/c Pt [0.4, 0.6] GeV/c Pt [0.6, 0.8] GeV/c Pt [0.8, 1.0] GeV/c Pt [1.0, 1.2] GeV/c Pt [1.2, 1.4] GeV/c Pt [1.4, 1.6] GeV/c Pt [1.6, 1.8] GeV/c Pt [1.8, 2.0] GeV/c Pt [2.0, 2.2] GeV/c Pt [2.2, 2.4] GeV/c — like sign pairs

  20. Spectra of extracted J/ψ for different PtJ/ψ Pt [0.0, 0.2] GeV/c Pt [0.2, 0.4] GeV/c Pt [0.4, 0.6] GeV/c Pt [0.6, 0.8] GeV/c Pt [0.8, 1.0] GeV/c Pt [1.0, 1.2] GeV/c Pt [1.2, 1.4] GeV/c Pt [1.4, 1.6] GeV/c Pt [1.6, 1.8] GeV/c Pt [1.8, 2.0] GeV/c Pt [2.0, 2.2] GeV/c Pt [2.2, 2.4] GeV/c

  21. Fit of the background spectra for different PtJ/ψ Pt [0.0, 0.2] GeV/c Pt [0.2, 0.4] GeV/c Pt [0.4, 0.6] GeV/c Pt [0.6, 0.8] GeV/c Pt [0.8, 1.0] GeV/c Pt [1.0, 1.2] GeV/c Pt [1.2, 1.4] GeV/c Pt [1.4, 1.6] GeV/c Pt [1.6, 1.8] GeV/c Pt [1.8, 2.0] GeV/c Pt [2.0, 2.2] GeV/c Pt [2.2, 2.4] GeV/c —exponential fit

  22. Spectra of extracted J/ψ for different PtJ/ψ Pt [0.0, 0.2] GeV/c Pt [0.2, 0.4] GeV/c Pt [0.4, 0.6] GeV/c Pt [0.6, 0.8] GeV/c Pt [0.8, 1.0] GeV/c Pt [1.0, 1.2] GeV/c Pt [1.2, 1.4] GeV/c Pt [1.4, 1.6] GeV/c Pt [1.6, 1.8] GeV/c Pt [1.8, 2.0] GeV/c Pt [2.0, 2.2] GeV/c Pt [2.2, 2.4] GeV/c

  23. Pt spectra Pt distribution Efficiency Losses in the signal efficiency: tracking efficiency – ~90% + selection cuts – ~80 %

  24. Measurement time • Used J/ψ statistics • 1.99105 J/ψ • multiplicity 1.9210-5, branching ratio 0.06 • needed central events 1.99105/ (1.9210-50.06)  1.71011 • needed minimum bias events  6.81011 • reaction rate 107 events/sec: 6.8104 sec  19 h

  25. Reducing of the detector acceptance

  26. 1. Pair angle distribution: + vs. - Au+Au collisions at 25 AGeV PLUTO PLUTO UrQMD μJ/ψ μω mbias standard beam pipe increased pipe hole

  27. 2. Muon system 2006-2007 3.0 5.7 J/ψ Au+Au collisions at 25 AGeV 3.0 5.7 ω acceptance  [z0.1, z0.5] • Feasibility study shown: • acceptance of the vector mesons doesn't change • the reconstruction efficiency is slightly smaller • the S/B ratio is the same

  28. J/ψ measurements with reduced detector acceptance First STS (example): • MC points • hits hit density hits/(eventcm2) The hits only from these regions in TRD and ToF were used in the reconstruction TRD ToF hit density  "dead" area in the detectors: R = Zdetector tg tg = 0.1

  29. Reconstruction results Cuts • STS: • 2prim.vertex • N of STS hits • MuCh: • N of MuCh hits • TRD: • N of TRD hits • TOF: • hit in ToF •  cut • = 32 MeV/c2 •  = 26 MeV/c2 acceptance:  full reduced

  30. Acceptance for reconstructed J/ψ full CBM setup reduced CBM setup

  31. Conclusions • LMVM: • background reduction by factor of 2 using ToF inside muon system • trigger reduction factor of 35 • J/ψ mesons: • different procedures for the background subtraction possible • 200.000 J/ψ measured in 19 h at 10 MHz • improved S/B ratio and mass resolution for J/ψ when increasing min emission angle from 3 to 6 degrees (reducing mismatches).

  32. Thank you for your attention!

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