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

2. Primary statistics Multiplication process [A. Mangiarotti, P. Fonte, A. Gobbi NIM A 533(2004)16] σ τ (n 0 ’) [1/s units] n0’n0’ Ineff [%]

3. Intrinsic time resolutionFluctuations in the fieldDrop in the field [ A. Blanco et al. NIM A 535 (2004) 272 ] rms E /E σ τ (n 0 ’) [1/s units]

4. 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/SF 6 (98.5/0.5/1) HV: 3.1-3.4 kV/gap Rates: 0.1-1.5 kHz/cm 2 H. Alvarez-Pol et al, NIM A 533(2004)79 and 535(2004)277

5. OBSERVABLES NEEDED: Mainly the total charge and the rms of the total charge. They are directly related to the fluctuations of the field: 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 V d can also be obtained independently from data.

6. HV = 3.1 kV/gap HV = 3.2 kV/gap HV = 3.3 kV/gap HV = 3.4 kV/gap OBSERVABLES AVAILABLE:

7. How to go from the available to the needed?: [ the usual problem!! ] Time delay Field in the gap Behavior in strong space-charge regime Linear increase with voltage 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)] Ohmic drop in the glass

8. OBSERVABLES AVAILABLE->OBSERVABLES NEEDED [result]

9. HV = 3.1 kV/gap HV = 3.2 kV/gap HV = 3.3 kV/gap HV = 3.4 kV/gap NOT FITTED! FITTED Data [re-scaled ‘prompt charge’]

10. CONCLUSIONS: - A first (indirect) confirmation of the validity of the proposed model for 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 improvement of sigma with voltage is 5ps/100V-> Hard to see!]. * Independent MC cross-check. HV = 3.2 kV/gap HV = 3.3 kV/gap