RPC simulations for CBM

D. Gonzalez-Diaz (GSI-Darmstadt)

for the CBM-TOF working group

26-02-2008

1. Engineering design

2. Simulation design

3. Detector response

4. Physics results

1. Engineering design

The CBM spectrometer (di-electron/hadron setup).The CBM spectrometer (di-muon setup).

10 m

15 m

Dwall = 10 m

σT = 80 ps (gaussian)

The CBM-ToF wall. Column and super-module layout.

Θ[ 2.5-25 deg]

Asuper-module = 1.5 m x 1 m

column

The CBM-ToF wall. Generic super-module inner

structure.

honeycomb

stesalit

screws for rollingnylon spacers

module

2. Simulation design

Simulation. Module inner structure.

module strip

Regions of different strip length (constant width), to keep the occupancy uniform

Simulation. Wall layout.

5 different regions were defined, with 5 different cell sizes:

Pad region (1): 2.0 x 2.0 cm2 ( 27072 channels, A=11 m2 ).Strip region (2): 2.0 x 12.5 cm2 ( 3840 x 2 channels, A=10 m2 ).Strip region (3): 2.0 x 25.0 cm2 ( 5568 x 2 channels, A=28 m2 ).Strip region (4): 2.0 x 50.0 cm2 ( 6150 x 2 channels, A=62 m2 ).Strip region (5): 2.0 x 100.0 cm2 ( 2900 x 2 channels, A=58 m2 ).

TOTAL ( 63988 channels, A=170 m2 ).

Simulation. Number of electronic channels.

3. Detector response

V=HV

V=0

V=0

no

clusters e--I

active region xd

gap size g

gxnn doo /'

log(i)

1, t1

log(ithres)

1. Separate fluctuations in avalanche multiplication, primary ionization and cluster size from deterministic multiplication in exponential regime.

2. Assume that only multiplication inside the active region is relevant.

3. Back-extrapolate the corresponding probability distributions for avalanche multiplication and primary ionization to t=0.

4. Obtain from the back-extrapolated distribution of the current io, the distribution of times at threshold (time response) assuming operation in exponential regime.

2, t2

3, t3

i1, t1 i2, t2 i3, t3t

A.Blanco, P. Fonte et al.NIM A, 513 (2003) 8-12

Model from:

space-charge regime

exponentialregime

i = i1+ i2 + i3

Hit generation (I). Private version. Under development.

Structure of the current TOFHitProducer! (version 1.0)

Vo

t1 t2 t3 t4

1. Add gaussian fluctuations due to detector response (same for left and right)

For simplicity, in this version the gaps are treated as if they were independent

2. Add gaussian fluctuations in theelectronic response(independent for left and right)

Efficiency per gap is assumed to be 75%

Prescription: the fastest hit in the left and right is stored !

...tn

particles produced locally(4 cm) are disregarded8 gaps

Hit generation (II). Operative version

NOTE: This algorithm results in a slightly non-Gaussian response (~1-2% tails towards delayed times), and is tuned to provide for particles crossing 8 gaps:

σT=80 ps, σx=5 mm

4. Physics results

Kaon identification. D. Kresan

t

σ

β=σ T

m 2

2

2

2p

Dynamical Fluctuations (I).

Idea: Measure the fluctuations in the particle

production, e.g.: (number of k)/(number of π), with

σ= rms/mean:

data2 = fin

2 + exp2 + dyn

2

background

Event mixing: two tracks coming from different events

mixed-events

Experimentally:

dyn2 = data

2 mixed-events2

D. Kresan

Dynamical Fluctuations (II).

dyn2 = data

2 mixed-events2

generic study (ideal tracking, no ToF segmentation, Gaussian time response)

Full reconstruction

D. Kresan

Muon identification.A. Kiseleva(20/06/07)

suppression of K's and fake matches

1.40.005

0.20.095

0.80.008

3.50.11

1.60.3

Efficiency %

S/B ratio

1.60.001

0.20.014

0.90.002

3.80.05

1.80.13

Efficiency %

S/B ratio

ω

φ

η

[0.2, 0.3] ηD

[0.2, 0.9] ρ

without ToF wall with ToF wall

C. Hoehne / S. Das(29/08/07)Electron identification.

suppression of π's

this is where ToF works!

The CBM-ToF wall. Design requirements (by now).

Overall time resolution σT ~ 80 ps.

Occupancy < 5 % for Au-Au central collisions at E=25

GeV/A.

Space resolution ~ 5 mm x 5 mm.

Efficiency > 95 %.

Pile-up < 5%.

Rate capability > 20 kHz/cm2.

Reduced cross-talk and charge-sharing.

Compact and low consuming electronics (~65.000

electronic channels).

The CBM-ToF wall. Summary.

1. Studies on fluctuations are very sensitive to the tails and

to the presence of double-hits. The maximum tolerable tails

and occupancy could be extracted from this observable.

2. A better estimate of the required σT could come from a) the

use of PiD in Do (or strange resonances) reconstruction, b)

di-electron spectroscopy (an improvement of a factor

~2/3 will nicely overlap ToF and TRD PiD capabilities (the

later very bad [a priori] below 1 GeV)) and c) K

identification for flow studies, etc.

3. Position resolution is not likely to have any constraint from

physics point of view.

The CBM-ToF wall. Outlook.

1. A detailed detector response depending on energy loss,

angle, etc will be made available for physics studies in a

period of 3-4 months. Debugging and comparison with

data must be done first.

2. A detailed implementation of the module inner structure

requires of a concept for the electrode read-out (?) and

an evaluation of the charge sharing and cross-talk in the

resulting configuration. Once these studies are available the

simulation design can proceed further.

3. More physics studies are needed. CBM-ToF requirements

are yet poorly constrained by physics.