Aerogel Cherenkov Counters for the ALICE Detector

1. Aerogel Cherenkov Counters for the ALICE Detector G. Paić Instituto de Ciencias Nucleares UNAM For the ALICE VHMPID group

2. Layout • PID in ALICE in the current design • Physics needs • Current studies • Simulations of the Belle design • Simulations of the integrating box design (Phenix) • Preliminary test beam results for the WLS readout of aerogel type (Novosibirsk) Aerogel threshold detector for ALICE

3. ALICE LAYOUT: PID • HMPID: High Momentum Particle Identification (, K, p) • RICH • Hard Probes TOF PID (K,p,) -0.9<<0.9 Aerogel threshold detector for ALICE

4. p/K TPC + ITS (dE/dx) K/p e /p p/K TOF e /p K/p HMPID (RICH) p/K K/p 0 1 2 3 4 5 p (GeV/c) ALICE hadron PID today • p, K, p identified in large acceptance (2p * 1.8 units h) via a combination of dE/dx in Si and TPC and TOF from ~100 MeV to 2 (p/K) - 3.5 (K/p) GeV/c • In small acceptance HMPID extends PID to ~5 GeV ? The new results from RHIC point out for a serious need to extend the PID range especially for protons Aerogel threshold detector for ALICE

5. Reasons to increase the momentum range of the PID • The present situations @ RHIC has strongly increased the need for PID @large momenta • The jet quenching has not resulted in an adequate increase of the low momentum multiplicities • The interesting range for protons is well above 5 GeV/c • At LHC one may estimate that the interesting range will up to 10-12 GeV for protons Aerogel threshold detector for ALICE

6. The baryon puzzle at RHIC • where does the large proton over pion ratio at high pt come from? • why do protons not exhibit the same suppression as pions? • fragmentation yields Np/Nπ<<1 • fragmentation starts with a single fast parton: energy loss affects pions and protons in the same way! Aerogel threshold detector for ALICE

7. leading particle hadrons q q hadrons leading particle leading particle suppressed hadrons q q hadrons leading particle suppressed Jet-Quenching: Primer What happens if partons traverse a high energy density colored medium? What is a jet? • partons can lose energy and/or fragment differently than in the vacuum fragmentation of hard scattered partons into collimated “jets” of hadrons Aerogel threshold detector for ALICE

8. The case for aerogel threshold detectors • Due to the space constraints in ALICE the only conceivable extension of the PID is the use of threshold Cherenkov detectors with aerogel. • Currently studying three basic designs • The “Belle” design • The integrating box design • The WLS Aerogel threshold detector for ALICE

9. Belle type • Collect scattered photons • Non-directional lights • Area of photocathode/cell size http://utkhii.px.tsukuba.ac.jp/~highpt/ Aerogel threshold detector for ALICE

10. Simulation of the “Belle” design • Ingredients of the simulation: • Treatment of the Raileigh scattering • 98% reflection from the walls Aerogel threshold detector for ALICE

11. One photon Full event Aerogel threshold detector for ALICE

12. Number of photoelectrons in function of impact for the Belle configuration Good agreement with exp results at n=1.017 With 2 PMT we can reach ~15 p.e/event Aerogel threshold detector for ALICE

13. integrating box design Integration Sphere Aerogel Advantage – possibility to use only one PM – not dependent on the coordinate of the impact Aerogel threshold detector for ALICE

14. Results for the integrating box design N=1.008 Aerogel threshold detector for ALICE

15. Summary I • The Belle type with two PMTs gives ~ 50% light more compared to the integrating box Aerogel threshold detector for ALICE

16. Study of the aerogel thickness & variation with n With one PMT operation at 1.005 still possible Aerogel threshold detector for ALICE

17. Alternative design A. Onuchin, A. Shamov, Yu. Skovpen and A. VorobiovA. Danilyuk, T. Gorodetskaya and V. Kuznetsov NIM 315, 1992, 517 WLS readout of the aerogel Test made in October 2004 at the CERN PS • Al container with sizes of 56 x 56 x 310 mm, • total volume of Aerogel ~ 0.5 liters • multi-layer Tetratex PTFE UV-film reflector, • WLS - Plexiglas plates ( 3 x 10 x 250 mm ) doped with BBQ • plastic light-guide • micro-channel plates (MCP) PMT with multi-alkali photocathode of 18 mm dia Aerogel threshold detector for ALICE

18. Preliminary results • 7 GeV negative beam at CERN PS • Possibility to trigger out of the WLS • Efficiency • n = 1.008 -- 65-70% • n= 1.05 -- 99 • Number of photoelectrons • n= 1.008 --<N>= 1-2 photoelectrons = 1.008 • n= 1.008 --<N>= 1-2 photoelectrons • Comparison with the simulations of the integrating box. The number of photoelctrons is much smaller but: • Smaller photo detector by a factor 4 • To be investigated the contribution to contamination by WLS. Aerogel threshold detector for ALICE

19. Aerogel threshold detector for ALICE

20. Aerogel threshold detector for ALICE

21. Summary II • Possibilities of light output increase. • The ratio of signals from 1.05 and 1.008 are in agreement with the ratio of intensities of Cherenkov light from radiators of given indices. • the KEDR detector use the same aerogel (n=1.05) as was tested in our experiment. • Having the same quality of WLS and better MCP PMTs we could increase light output from proposed counters by a factor of 203/69=2.94. • The length of WLS used in our prototype is 250 mm, KEDR ASHIPH counter – 500 mm. • We expect the light attenuation in our shifters could be smaller by a factor of 1.3-1.4. • The design of our counter gives the possibility to increase thickness of aerogel from 200 mm to 250 mm and more (additional factor of 1.25) • Using the existing technology the light output could be increased by a factor of 5. • The further possibilities are: • PMT with AsGa photocathode of 30-40 % quantum efficiency (MCP PMTs we use have multialcali photocathode with mean QE=22%) Aerogel threshold detector for ALICE

22. Where to place the VHMPID ALICE HMPID • Charged particles multiplicity: ~ 80 m-2 • Interaction rate: 104 (3% central events) • PID: • 1 < p < 3 GeV/c p K • 2 < p < 5 GeV/c p Aerogel threshold detector for ALICE