Status of muon simulations at GSI

1

Status of muon simulations at GSI

Status of muon simulations at GSI

Anna Kiseleva

2

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

3

•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

4

ToF measurements for muon identificationToF measurements for muon identification

5

Reconstructed backgroundReconstructed background

Masse of particles:

μ – 106 MeV

π – 140 MeV

Κ – 498 MeV

p – 938 MeV

6

Background rejection via mass determinationBackground rejection via mass determination

m2 =

β =

γ =

m2 = P2 ( - 1)

Lc × t

√1 – β2

1

(β × γ)2

P2

β2

1

(L, t) → β

Muon ToF

7

Mass distribution for different time resolutionsMass distribution for different time resolutions

30 psec

50 psec

80 psec

time resolution μω background

8

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

9

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

10

LMVM trigger with muon ToFLMVM trigger with muon ToF

11

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

12

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)

13

— 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

14

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

15

J/ψ pT reconstruction*J/ψ pT reconstruction*

Au+Au collisions at 25 AGeV

* see presentation in the Simulation section

16

DetectorsDetectors

• STS: – sts_standard.geo – sts_standard.digi.par

• MuCh– modular design

• TRD– as last MuCh station behind last

muon absorber

• ToF – standard

17

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

18

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



Invariant mass spectra for different PtJ/ψInvariant mass spectra for different PtJ/ψ

19

Spectra of the like sign pairs for different PtJ/ψSpectra of the like sign pairs for different PtJ/ψ




— like sign pairs

20

Spectra of extracted J/ψ for different PtJ/ψSpectra of extracted J/ψ for different PtJ/ψ




21

Fit of the background spectra for different PtJ/ψFit of the background spectra for different PtJ/ψ




— exponential fit

22

Spectra of extracted J/ψ for different PtJ/ψSpectra of extracted J/ψ for different PtJ/ψ




23

Pt spectraPt spectra

Losses in the signal efficiency:tracking efficiency – ~90%+ selection cuts – ~80 %

Pt distribution Efficiency

24

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

25

Reducing of the detector acceptanceReducing of the detector acceptance

26

μJ/ψ μω mbias

PLUTO PLUTO UrQMD


standard beam pipe

increased pipe hole

1. Pair angle distribution: + vs. -1. Pair angle distribution: + vs. -

27

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]


28

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

29

= 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

30

reduced CBM setupfull CBM setup

Acceptance for reconstructed J/ψAcceptance for reconstructed J/ψ

31

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).

32

Thank you for your attention!Thank you for your attention!

Status of muon simulations at GSI

Documents

Transcript of Status of muon simulations at GSI