MVD Simulations with Digitizer

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