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First attempt of an analytical theory of rate effects in timming RPCs

First attempt of an analytical theory of rate effects in timming RPCs. D. González-Díaz, A. Mangiarotti and P. Fonte. [A. Mangiarotti, P. Fonte, A. Gobbi NIM A 533(2004)16]. Ineff [%]. σ τ (n 0 ’) [1/s units]. n 0 ’. Primary statistics. Multiplication process. σ τ (n 0 ’) [1/s units].

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First attempt of an analytical theory of rate effects in timming RPCs

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  1. First attempt of an analytical theory of rate effects in timming RPCs D. González-Díaz, A. Mangiarotti and P. Fonte

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

  3. στ(n0’) [1/s units] rmsE /E Intrinsic time resolution Fluctuations in the field Drop in the field [ A. Blanco et al. NIM A 535 (2004) 272 ]

  4. DATA SET H. Alvarez-Pol et al, NIM A 533(2004)79 and 535(2004)277 • 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/gap • Rates: 0.1-1.5 kHz/cm2

  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 and to the drop in the field: Drop in the field As the gas mixture was slightly different from the standard one, it will help that S=α Vdcan 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!! ] Accurate description of the efficiency trend with HV for this kind of detector Time delay Linear increase with voltage [A. Blanco et al. IEEE Trans. Nucl. Sci. 48(2001)1249 and C. Lippmann (Thesis)] Field in the gap Ohmic drop in the glass [G.Aielli, NIMA 456(2000)82] Behavior in strong space-charge regime [P.Fonte, V.Peskov, NIMA 477(2002)17 G. Carboni et al. , NIMA 498(2003)135]

  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 FITTED NOT FITTED! Data [re-scaled ‘prompt charge’]

  10. HV = 3.2 kV/gap HV = 3.3 kV/gap 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.

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