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MVD Simulations with Digitizer. Christian Trageser 1 , Michael Deveaux 1,3 , Christina Dritsa 1,2,3 IKF Frankfurt 1 , GSI Darmstadt 2 , IPHC Strasbourg 3. CBM Collab. Split Croatia, Oct 05- 09.10.2009. Outline Motivation Simulation Setup Results Summary and Conclusion. - PowerPoint PPT Presentation
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MVD Simulations with Digitizer
Christian Trageser1, Michael Deveaux1,3, Christina Dritsa1,2,3
IKF Frankfurt1, GSI Darmstadt2, IPHC Strasbourg3
Outline• Motivation• Simulation Setup• Results• Summary and Conclusion
CBM Collab. Split Croatia, Oct 05- 09.10.2009
Motivation: Running conditions of the MVD
Mean hit density from nuclear collisions (@ 10cm)
Incl. delta electrons from the target
~700 hits / evt
Hot spots up to 1 hit / evt / mm2
Hits
/mm
²/co
ll. x
100
0
100 kHz => 0.7k (1/mm²) 1 MHz => 7k (10/mm²) 10 MHz => 70k (100/mm²)
Adapt beam to abilitiesof the detector!
Rate Hits (Max.)
Even more difficult for first station at 5 cm
Motivation
Efficient STS – MVD Track matching is essential for good open charm reconstruction!
Can the MVD, STS and L1-Tracking provide a sufficient tracking efficiency?
Approach:
• Use the newly available MVD-Digitizer• Study tracking quality including delta-electrons and pile-up• Benchmark different geometries according to:
• Tracking efficiency• p-resolution• Impact parameter resolution• Number of tracks passing the single track selection cuts
Simulation Setup
Global simulation setup:
CbmRoot JUN 09MVD (with Digitizer), STS (with Digitizer), other detectors absent
Simulated geometries:
STS => Standard geometry JUN 09
MVD => Two options simulated:
2 Stations (z= 10, 20 cm; Thick: 500 µm)Inner radius: 5.5 mm (z=10 cm), 10.5 mm (z=20 cm)
3 Stations (z= 5,10,15cm; Thick: 300, 500, 600 µmInner radius: 5.5 mm (z=5,10 cm), 10.5 mm (z=15 cm)
Collision system:
Au-Au @25 AGeV
Simulation Setup
MVD-Digitizer Settings:
Pixel pitch = 18.4 µmADC = 12 bit Threshold = 1 ElectronNoise = 15 ElectronsFake hit generator = Off
Cuts:
Ideal readout
Pixels with signal charge receive noiseBUT: No fake hits are created due to noise
Long tracks More than 7 hits in MVD + STSp > 1 GeV
Cluster merging as function of pile-up
Up to 20% of all clusters are merged> 80% of all merged clusters are in the delta electron region
0 2 4 6 8 10
0,96
0,98
1,00
1,02
1,04
1,06
1,08
1,10M
omen
tum
res
olut
ion
[%]
Pile-up
2 Stations 3 Stations
Momentum resolution (only “long” tracks)
Momentum resolution gets moderately worse for higher pile upThe results indicate no difference between the two geometries
preliminary
0 2 4 6 8 10
0,86
0,88
0,90
0,92
0,94
0,96
0,98
1,00M
VD
-Tra
ckin
g E
ffici
ency
Pile-up
2 Stations 3 Stations
Only long tracks. Only tracks in acceptance. Assume tracking successful if no wrong hit or merged cluster is associated in the MVD
MVD Tracking Efficiency
MVD Tracking Efficiency decreases for high pile upThe results indicate no difference between the two geometries
preliminary
Factor 5 in inefficiency
IP Resolution as function of pile-up
0 2 4 6 8 10
100
1000IP
-Res
olut
ion
(RM
S)
[µm
]
Pile-up
Accepted & Good Accepted & Bad Not Accepted All tracks
2 Stations
Good tracks: IP Resolution < 80 µm (RMS) „Bad“ tracks: IP Resolution ~ 600 µm (RMS), would be better without MVD
prelimínary
Response for “bad tracks” not Gaussian => RMS shown50
IP Resolution (RMS) for all and only good tracks
0 2 4 6 8 1050
60
70
80
90
100
IP-r
esol
utio
n (R
MS
) go
od tr
acks
[µs]
Pile-up
2 Stations 3 Stations
0 2 4 6 8 10200
220
240
260
280
300
320
340
360
380
IP-r
esol
utio
n (R
MS
) al
l tra
cks
[µs]
Pile-up
2 Stations 3 Stations
IP-resolution of all tracks gets worse with increasing pile-up
The Comparison of the two geometries show no clear trend (yet)
preliminary
preliminary
Good tracks All tracks
Mind the scale!
Efficiency drop of the PV-cut
0 1 2 3 4 5 6 7 8 9 10 110
5
10
15
Acc
epte
d B
G-t
rack
s [%
]
Pile-up
2 Stations 3 Stations
Fraction of tracks passing the PV-cut(Only primary BG tracks are included, reject Strange particles)
Number of accepted background tracks increases by a factor fourMostly, “bad” tracks are accepted
preliminary x 4
Summary and conclusion
The impact of pile-up on the MVD-tracking was studied
We observe:
• Few impact on momentum resolution• A substantial impact on tracking efficiency:
97 % => 87 % (> 1GeV “long” tracks)• A decreased eff. of the PVChi-cut:
97% rejection => 88% rejection (> 1GeV “long” tracks)
Our results show few preferences for a specific detector design (yet)
Conclusion: Shrinking MVD tracking efficiency is an issue.Substantial room for optimization, needs interaction with tracking experts
Next steps:• Repeat study with higher statistics• Study detector layouts in a systematic way• Estimate SvZ-Resolution• Start a study on open charm reconstruction• Optimize hit finding
Thank you for your attention!
Cluster merging as function of pile-up
> 80% of all merged clusters are in the delta electron region
Digitizer: Simulated vs. measured resolution
18.4 µm pitch1 bit readoutThreshold = threshold N
3,5 4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,50
1
2
3
4
5
Res
olut
ion
[µm
]
Threshold [S/N]
Simulation - X Simulation - Y Experiment
IP Resolution as a function of Pile-up
3 Stations
preliminary
Same trend for
Running conditions of the MVD
The occupancy is dominated by delta electrons generated in the target.Handling them needs detector with very high granularity
Hits
/eve
nt
distance between station and target[cm]
Motivation
Good track finding is essential for open charm reconstruction.
• To find a optimized Geometry for the MVD– Check Tracking Efficiency– Check Efficiency of the cuts– Different pile up scenarios