CBM-ToF vs

RPC workshop

D. Gonzalez-Diaz and A. Schüttauffor the CBM-TOF working group

26-02-2008

1. Fundamentals

2. Systems

3. Ageing

4. Gas System

5. Detector Control System

6. Electronics

1. Fundamentals

C2H2F4/C4H10/SF6 (94.7/5/0.3)

2 mm RPCs

G. ChiodiniGas properties

resolution better than 20 μm!

(interesting alternative to studies based on UV illumination)

W. RieglerTiming (I)

Power law cluster size distribution

1/n2 cluster size distribution

HEED

Semi-analytical generalization of FGM model (Fonte, Gobbi Mangiarotti) including cluster size distribution.

A. SchüttaufTiming (II)

Systematic study on the effect of SF6 in the mixture

N. MajumdarElectrostatics

Calculations based on the nearly exact Boundary Element Method (neBEM) were described. For regions where the field has singularities it is much better than conventional FEM.

ALSO: A new approach for simulating 3D avalanche dynamics (PARSUE: Particles on Surface) was introduced and further work will follow.

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D. Gonzalez-DiazM. Morales

Glass response

cellcell

N

isi

s

is

s

A RCttC

tqCC

C

tqACti )/)(exp(

)()(

)()(

MC reproducing the RPC transient behaviour at high rates, before reaching the DC (stationary) situation.

C. Lippmann

Response to annihilation photons

Annihilation photons from a Na source are often used for a first test of timing performances, yielding resolutions at the level of 90 ps.

The simulated time resolution of ~37ps (at 100kV/cm) does not confirm the measured results, which are much worse (~90ps), and highly independent from the field.

But there is still some work going on... maybe this apparent puzzle is solved in time for the proceedings??

Sorry, the uploaded talk is incomplete

2. Systems

The famous HARP '500 ps' effect has a 'real' contribution from the energy loss and a 'fake' contribution from the momentum reconstruction

HARP J. Wotschack

FOPI A. Schüttauf

v [cm/ns]

p [

Ge

V/c

]

pdt

+

-

K+

K-

Preliminary: interesting correlation with energy loss (factor 4 increase in dEdx yields 16% increase in <Q>) --> practical use?

HADES P. Fonte, P. Cabanelas

10 15 20 25 301

1.05

1.1

1.15

1.2

Row

Mea

n C

lust

er S

ize

1.023

1.023

1.0694Fully shielded region

cross-talk performances

Further shielding betweenfeedthrougs. Cross-talk is a delicate issue!

3. Ageing

Cathode ONLY

structural modification

A plausible alternative to the intuitive picture based on HF corrosion was proposed -> increased sputtering of positive ions due to adsorbed fluorine:

No change in dark current for ageing tests.

Here, showed an example of the detailed studies performed by inducing fast ageing in the chambers through operation in sustained discharge

[Chemical sputtering of fluorinated silicon, Yung-Yi Tu, Physical Review B, vol. 23, n.2, 1982]

Glass L. Lopes

4. Gas system

Open loop with recovery system Joshi

(~1/10 times cheaper than ATLAS closed loop mode according to the speaker [?])

Closed loop R. Guida

Fresh mixture

A zoom of the same region for the mixture before and after the purifiers:

Not all extra peaks can be filtered, with any combination of the tested filters (signals 2, 4 remain)It seems that the Ni filter produce or enhance one extra signal (number 8)

Purifiers: - better configuration (?) - effectiveness - lifetime - regeneration process

Recirculation: which fraction (?)

Purifiers: - better configuration (?) - effectiveness - lifetime - regeneration process

Recirculation: which fraction (?)

CMS

Gas contamination Ferroni

BaBar

Second chamber in a series gets sick

5. Detector control system

Gas gap health parameters

Gas mixture composition fluoride production and entrapment Gas flow (1 change/h with radiation) and line tightness Relative humidity both in the atmosphere and in the gas

mixture (30%<RH<50%) Temperature (possibly 21 °C max 24 for a few unlucky

cases) ohmic and exponential currents plate resistivity

F.E. and readout stability

LV current absorption stable and within the foreseen levels, channel by channel (any variation points out a problem)

Current pull down stability Periodic monitoring of the softest workable thresholds

ATLAS

G. AielliWhat to monitor?

6. Electronics

A. GilPseudo-random pulse generator for RPC-FEE testing of jitter, cross-talk, stability (RYGEL)

AND

Systems

ALICE 33 ps 15-20 ps 25 ps 15 ps 40 mW/ch

HADES 40 ps 15 ps 37 ps 0 ps 0.4 W/ch

FOPI 25 ps 15 ps 12 ps 15 ps 0.51 W/ch

FEE Digitizer Misc. W/chFull chain

D. Belver, G. Scioli, A. Schüttauf

ALICE system performance

Global time resolution < 100

ps

σ2TOT = σ2

MRPC + σ2T0 + σ2

CLK + σ2CLK-TRM + σ2

CAL

MRPC+

ELEC.(50 ps)

Clockfrom LHCto crates(15 ps)

(50 ps)For Pb-Pbby TOF for2000-3000chargedparticles (5 – 10 ps)

(10 ps)

Different time delay of different channels(cable lengths and timeslewing) (30 ps)

G. Scioli

Conclusions.

Current ToF systems (HARP, FOPI, HADES) show routinely resolutions at the level of 100 ps or better.

Response to annihilation photons not yet understood. Pseudo-Random test pulser available for FEE stability tests. Difficulties of cross-talk elimination illustrated (and overcame). Open loop is not possible in view of high cost and environment

contamination. Separation of gases at the end of the circuit and re-injection, or a re-circulating system seem to be valid options.

Role of F in ageing poorly understood. In CBM, due to the x100 higher rates than normal tRPCs, the effects are likely to be much more dramatic.

Poisoning of second chamber in a series clearly observed. Effect of SF6 in time resolution systematically studied. Some dEdx PiD capabilities preliminary shown. HARP '500 ps' effect vanished. Laser method for fundamental studies seems to be an useful tool!. Existing electronics chains can do the job, but ASIC is always much

better in terms of power dissipation.