Download - Status of muon simulations at GSI
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Status of muon simulations at GSI
Status of muon simulations at GSI
Anna Kiseleva
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OutlineOutline
• 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
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•release CBMROOT Jun09
•realistic MuCh segmentation (pads: min 0.280.28, max 4.484.48 cm2)
•L1 STS tracking
•LIT global tracking
CBM setup with muon detectorCBM setup with muon detector
Muonsystem
TRD
ToF
STS track, vertex and momentum reconstruction
Muon system muon identification
TRD global tracking
RPC-ToF time-of-flight measurement
STS
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ToF measurements for muon identificationToF measurements for muon identification
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Reconstructed backgroundReconstructed background
Masse of particles:
μ – 106 MeV
π – 140 MeV
Κ – 498 MeV
p – 938 MeV
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Background rejection via mass determinationBackground rejection via mass determination
m2 =
β =
γ =
m2 = P2 ( - 1)
Lc × t
√1 – β2
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(β × γ)2
P2
β2
1
(L, t) → β
Muon ToF
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Mass distribution for different time resolutionsMass distribution for different time resolutions
30 psec
50 psec
80 psec
time resolution μω background
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Full reconstructionFull reconstruction
ω→μ+μ- + central Au+Au collisions at 25 AGeV
time
informationwithout with
time
resolution30
psec50
psec80
psec
S/B ratio 0.099 0.201 0.175 0.155
ε, % 1.85 1.57 1.56 1.56
time information:— without with time resolution: — 80 psec— 50 psec— 30 psec
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Reconstructed backgroundReconstructed background
tracks
eventall μ π K p ghost
without time information
0.233 0.134 0.013 0.057 0.008 0.021
with time information
80 psec 0.166 0.118 0.012 0.019 0.001 0.016
50 psec 0.155 0.116 0.011 0.012 0.001 0.014
30 psec 0.145 0.114 0.011 0.006 0.001 0.013
central Au+Au collisions at 25 AGeV
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LMVM trigger with muon ToFLMVM trigger with muon ToF
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Trigger strategyTrigger strategy
zz targettarget
xtarget,ytarget
∆x,∆y1. Find events with min. 12
hits in 6 detector layers, which might correspond to two tracks (hit selection in muon ToF: velocity value)
2. Straight line fit
3. Track selection: fit criteria
Remark: if track passes cuts, its hits will not used for second track searching
Muon ToF
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VelocityVelocity
cut: β [0.96; 1.02]
β =
Lc × t
ToF measurements:
L – distance from target to the ToF
t – particle time of flight
(time resolution 80 psec)
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— x = a0 + a1 z — y = b0 + b1 z
2fit x and y (ztarget) z (xtarget or ytarget)
Parameters of straight line fit (μω)Parameters of straight line fit (μω)
Optimization of the cuts taking into account signal efficiency and background suppression factor
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TriggerTrigger
1000 central events (Au+Au collisions at 25 AGeV)
min. 12 hits in 6 detector layers +
β [0.96; 1.02]
(β cut)
β cut
+
χ2, XZ=0, YZ=0 cuts
β cut
+
χ2, XZ=0, YZ=0 cuts
+
ZX=Y=0 cut
676 211 114
ω→μ+μ- + central Au+Au collisions at 25 AGeV
εall trigger cuts/εwithout trigger cuts
40%
background suppression factor for mbias events ~35
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J/ψ pT reconstruction*J/ψ pT reconstruction*
Au+Au collisions at 25 AGeV
* see presentation in the Simulation section
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DetectorsDetectors
• STS: – sts_standard.geo – sts_standard.digi.par
• MuCh– modular design
• TRD– as last MuCh station behind last
muon absorber
• ToF – standard
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Reconstruction resultsReconstruction results
S/B ratio 3 7*
εJ/ψ (%) 14 16*
* 10th CBM Collaboration Meeting: different setup (only ideal STS+MuCh), different geometries and segmentations, cuts: χ2
prim.vertex < 2, NSTS ≥ 4, NMuCh = 18, χ2MuCh*ndf < 55
J/ψ multiplicity: counts in region mJ/ψ 2
accepted J/ψ: MC muon tracks have
≥ 4 STS MC points≥ 12 MuCh MC points≥ 3 TRD MC points≥ 1 ToF MC point
reconstructed J/ψ: reconstructed muon tracks after the cuts
≥ 4 STS hits + χ2prim. vertex
≥ 12 MuCh hits ≥ 3 TRD hitsβToF ≥ 0.99
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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
Invariant mass spectra for different PtJ/ψInvariant mass spectra for different PtJ/ψ
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Spectra of the like sign pairs for different PtJ/ψSpectra 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
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Spectra of extracted J/ψ for different PtJ/ψSpectra 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
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Fit of the background spectra for different PtJ/ψFit 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
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Spectra of extracted J/ψ for different PtJ/ψSpectra 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
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Pt spectraPt spectra
Losses in the signal efficiency:tracking efficiency – ~90%+ selection cuts – ~80 %
Pt distribution Efficiency
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Measurement timeMeasurement time
• Used J/ψ statistics• 1.99105 J/ψ
• multiplicity 1.9210-5, branching ratio 0.06
• needed central events 1.99105 / (1.9210-50.06) 1.71011
• needed minimum bias events 6.81011
• reaction rate 107 events/sec: 6.8104 sec 19 h
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Reducing of the detector acceptanceReducing of the detector acceptance
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μJ/ψ μω mbias
PLUTO PLUTO UrQMD
Au+Au collisions at 25 AGeV
standard beam pipe
increased pipe hole
1. Pair angle distribution: + vs. -1. Pair angle distribution: + vs. -
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3.0
5.7
J/ψ
3.0
5.7
ω
2. Muon system2. Muon system
Feasibility study shown:1. acceptance of the vector mesons doesn't change2. the reconstruction efficiency is slightly smaller3. the S/B ratio is the same
2006-2007
acceptance [z0.1, z0.5]
Au+Au collisions at 25 AGeV
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J/ψ measurements with reduced detector acceptanceJ/ψ measurements with reduced detector acceptance
"dead" area in the detectors: R = Zdetector tg tg = 0.1
First STS (example):• MC points• hits
hits
/(ev
ent
cm2)
hit density
The hits only from these regions in TRD and ToF were used in the reconstruction
TRD ToFhit density
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= 32 MeV/c2
= 26 MeV/c2
acceptance full reduced STS, TRD, ToF
S/B ratio 3.4 5.1
εJ/ψ (%) 17.5 16.8
Cuts• STS:
2prim.vertex
– N of STS hits
• MuCh:– N of MuCh hits
• TRD: – N of TRD hits
• TOF:– hit in ToF cut
acceptance:
full
reduced
Reconstruction resultsReconstruction results
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reduced CBM setupfull CBM setup
Acceptance for reconstructed J/ψAcceptance for reconstructed J/ψ
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ConclusionsConclusions
• 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).
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Thank you for your attention!Thank you for your attention!