R&D ON A DETECTOR FOR VERY HIGH MOMENTUM CHARGED HADRON IDENTIFICATION IN ALICE

1. HMPID Available space Photon detector: 2 m photosensitive CsI layer (300 nm) Cherenkov photon CF4 Townsend avalanche International Conference on Advanced Technology and Particle Physics R&D ON A DETECTOR FOR VERY HIGH MOMENTUM CHARGED HADRON IDENTIFICATION IN ALICE Abraham Gallas INFN, Sez. Bari On behalf of the ALICE/HMPID group. CENTRO DI CULTURA SCIENTIFICA A.VOLTA, VILLA OLMO (COMO-ITALY) ALICE EXPERIMENT • The problem: • The latest theoretical and experimental results suggest investigating a physics domain for pt higher than the actual one covered by the HMPID detector in the ALICE experiment (1 - 5 GeV/c) [1]. • Goals of the new Cherenkov detector: • ID of charged hadrons with pt 10 GeV/c. • Inclusive measurement, particle yields, (anti)protons play a very important role in HI Physics. • Weak identification, i.e. ,  - protons can be enough, since observables like anti-p / p, mesons/baryons are very sensitive to QGP Physics. • Requirements: • Compactness, it must fit in the present ALICE layout. Space constrains are the most strict requirement. The fact of use a gas radiator (high pt) and the barrel geometry makes the use of a classical RICH difficult. • Operation in a B-field up to 0.5T. • Environment: • High charged particle multiplicity, up to dNCH / dy= 8000 (100/m2 (CC), Alice design parameters) . • Low interaction rates: from 8kHz (Pb-Pb) up to 300 kHz (p-p). • A possible solution: • A Threshold imaging Cherenkov TIC as already used in NA44 [2]: • Two gas radiators (CF4, C4F10) (UV region), to match the momentum range, separated by a CaF2 window. • Two photon detectors on the sides of the gas vessel measure the UV Cherenkov photons reflected by the central mirrors. • A third tracking detector placed after the mirrors could improve the positioning of the track of the charged particle. NA44 TIC Layout: Radiator: CF4 and C4F10[8]: A MWPC with segmented cathodes coated with CsI, like the one used in the HMPID detector @ ALICE [3]. This time operated in pure CF4 at atmospheric pressure. Although a rapid aging of proportio- nal counters operated with CF4 has been observed [4], owing to this geo metry, wire material and collected charge ( ~ 0.8 mC/m, ~ 30 ALICE years) we do not expect aging e-ffects [5]. Still, stable operation of the chamber has to be proven. CF4transparent to 110 nm ~ 1 m PID PERFORMANCE Since the maximum Cherenkov angles for C4F10 and CF4 are very similar, the Cherenkov photons produced in both Radiators will be close in the photon detector. A third de- tector after the mirrors could improve the positioning of the particle track, helping in identifying the origin of the Cherenkov photons. Another possibility is to use a GEM (Gas Electron Multiplier) with a CsI photocathode deposited in the first GEM in a cascade [6]. It can be ope- rated in a stable mode in pure CF4 [7], so we can get rid of the window. Acceptable degradation of the CsI layer was observed for a total ion-back flow charge of ~ 7 mC/cm2 [7]. ~ 25 < Nphe > for C4F10 , ~ 30 < Nphe > for CF4 (50 cm). In order to achieve a good transparency of CF4 and C4F10 to UV photons we need a clean gas system, H2O and O2 less than few ppm. This is critical for the CF4 since this gas is in contact with the CsI, that has a large hygroscopicity. We could replace one of the gas radiators by an aerogel or add it. In this case we would use solid state photon detectors in the visible, getting rid of the scintillation problem in the CF4 gas radiator. We are as well considering the possibility of using a solid state photon detector. In this case we could move from the UV range to the visible. Some R&D needs to be done in order to operate those photon detectors inside the magnetic field (0.5 T) of the ALICE experiment. • Conclusions & Outlook • The PID capability of ALICE can be extended up to 30 GeV/c making use of available technologies at reasonable cost and time. • Simulation studies are underway in order to optimize the detector layout. • Laboratory tests are being scheduled to investigate the ageing of the MWPC and the CsI in presence of CF4 • Scintillation in CF4 is being simulated, to clarify if the setup with the MWPC / GEM coated with CsI is feasible. • Other options, like solid state photon detectors and aerogel as one of the radiators are being studied as a backup for the presented layout. References: [1] See for instance C. A. Salgado, I. Tserruya, B. Mueller talks in Quark Matter 2005, Budapest. [2] A. Braem et al., Nuclear Instruments and Methods A 409, 426-431 (1998). [3] Alice Collaboration, HMPID TDR, CERN/LHCC 98-19. F. Piuz et al., Nuclear Instruments and Methods A 433, 222 (1999) [4] M. Danilov et al., Nuclear Instruments and Methods A 515 202-219 (2003). [5] J.Wise et al., J. Appl. Phys. 74 No 9 5327-5340 (1993). [6] Thomas Meinschad et al., Nuclear Instruments and Methods A 535, 324-329 (2004). [7] A. Kozlov et al., Nuclear Instruments and Methods A 523 345-354 (2004). [8] Data from K. Zeitelhack et al., Nuclear Instruments and Methods A 433 201-206 (1999).