D. González-Díaz, A. Mangiarotti and P. Fonte

)'2('1

')( )(

01)(0

)exp()(

'0

0

th

th

thth

enIen

e

e

nn

))1(log('0 effn

driftvS

Primary statistics

Multiplication process

[A. Mangiarotti, P. Fonte, A. Gobbi NIM A 533(2004)16]σ τ(

n 0’)

[1/s

uni

ts]

n0’

Ineff [%]

tS

gapE

Et rmsdE

dS

SdE

d

Srms

Srms

2

2

22

22 11

Intrinsic time resolution Fluctuations in the field Drop in the field

[ A. Blanco et al. NIM A 535 (2004) 272 ]

rmsE /E

σ τ(n 0’

) [1

/s u

nits

]

DATA SET

•Date: April-2003.•Place: HADES, GSI•Physical conditions: Ionizing particles from CC collisions at 1 GeV A.•Detector:

0.3 mm 4-gap RPC (Al-Glass-Al-Glass-Al)Mixture: Freon/Iso-butan/SF6 (98.5/0.5/1)HV: 3.1-3.4 kV/gapRates: 0.1-1.5 kHz/cm2

H. Alvarez-Pol et al, NIM A 533(2004)79 and 535(2004)277

OBSERVABLES NEEDED:

Mainly the total charge and the rms of the total charge. They are directly

related to the fluctuations of the field:

)](,[2 QrmsQE

rRAQVVgap

Fluctuations in the field

Drop in the field

and to the drop in the field:

As the gas mixture was slightly different from the standard one, it will

help that S=α Vd can also be obtained independently from data.

HV = 3.1 kV/gapHV = 3.2 kV/gapHV = 3.3 kV/gapHV = 3.4 kV/gap

OBSERVABLES AVAILABLE:

How to go from the available to the needed?: [ the usual problem!! ]

)(

)'/log()( 0

0gap

tgap VS

nmVt

glassgap VVV

)( Tgap VVcq

gapbVSS 0

Time delay

Field in the gap

Behavior in strong space-charge regime

Linear increase with voltage

)exp(1

995.0)(

K

VVVeff

refgapgap

Accurate description of the efficiency trend

with HV for this kind of detector

[P.Fonte, V.Peskov, NIMA 477(2002)17 G. Carboni et al. , NIMA 498(2003)135]

[G.Aielli, NIMA 456(2000)82]

[A. Blanco et al. IEEE Trans. Nucl. Sci.48(2001)1249 and C. Lippmann (Thesis)]

rRAqIRVglass Ohmic drop in the glass

OBSERVABLES AVAILABLE->OBSERVABLES NEEDED [result]

HV = 3.1 kV/gapHV = 3.2 kV/gapHV = 3.3 kV/gapHV = 3.4 kV/gap

NOT FITTED!

FITTED

Data [re-scaled ‘prompt charge’]

CONCLUSIONS:

- A first (indirect) confirmation of the validity of the proposed modelfor describing rate effects on the time resolution of an RPC is shown.

- Better comparison requires:* Direct measurement of the total charge as a function of the rate together with its rms. * At least a factor 4 larger files. [The expected improvementof sigma with voltage is 5ps/100V-> Hard to see!].* Independent MC cross-check.

HV = 3.2 kV/gapHV = 3.3 kV/gap