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

November Aerogel threshold detector for ALICE2 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)

November Aerogel threshold detector for ALICE3 ALICE LAYOUT: PID TOF PID (K,p,  ) -0.9<  <0.9 HMPID: High Momentum Particle Identification ( , K, p) RICH Hard Probes

November Aerogel threshold detector for ALICE4 ALICE hadron PID today , K, p identified in large acceptance (2  * 1.8 units  ) via a combination of dE/dx in Si and TPC and TOF from ~100 MeV to 2 (p/K) (K/p) GeV/c In small acceptance HMPID extends PID to ~5 GeV p (GeV/c) TPC + ITS (dE/dx)  /K K/p e /  HMPID (RICH) TOF ? The new results from RHIC point out for a serious need to extend the PID range especially for protons

November Aerogel threshold detector for ALICE5 Reasons to increase the momentum range of the PID The present RHIC has strongly increased the need for 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 GeV for protons

November Aerogel threshold detector for ALICE6 where does the large proton over pion ratio at high p t come from? why do protons not exhibit the same suppression as pions?  fragmentation yields N p /N π <<1  fragmentation starts with a single fast parton: energy loss affects pions and protons in the same way! The baryon puzzle at RHIC

November Aerogel threshold detector for ALICE7 Jet-Quenching: Primer partons can lose energy and/or fragment differently than in the vacuum hadrons q q leading particle leading particle fragmentation of hard scattered partons into collimated “jets” of hadrons What is a jet? What happens if partons traverse a high energy density colored medium? hadrons q q leading particle suppressed leading particle suppressed

November Aerogel threshold detector for ALICE8 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

November Aerogel threshold detector for ALICE9 Belle type –Collect scattered photons Non-directional lights Area of photocathode/cell size

November Aerogel threshold detector for ALICE10 Simulation of the “Belle” design Ingredients of the simulation: –Treatment of the Raileigh scattering –98% reflection from the walls

November Aerogel threshold detector for ALICE11 One photon Full event

November Aerogel threshold detector for ALICE12 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

November Aerogel threshold detector for ALICE13 integrating box design Integration Sphere Aerogel Advantage – possibility to use only one PM – not dependent on the coordinate of the impact

November Aerogel threshold detector for ALICE14 N=1.008 Results for the integrating box design

November Aerogel threshold detector for ALICE15 Summary I The Belle type with two PMTs gives ~ 50% light more compared to the integrating box

November Aerogel threshold detector for ALICE16 Study of the aerogel thickness & variation with n With one PMT operation at still possible

November Aerogel threshold detector for ALICE17 WLS readout of the aerogel Alternative design A. Onuchin, A. Shamov, Yu. Skovpen and A. VorobiovA. Danilyuk, T. Gorodetskaya and V. Kuznetsov NIM 315, 1992, 517 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

November Aerogel threshold detector for ALICE18 Preliminary results 7 GeV negative beam at CERN PS Possibility to trigger out of the WLS Efficiency n = % n= Number of photoelectrons n= = 1-2 photoelectrons = 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.

November Aerogel threshold detector for ALICE19

November Aerogel threshold detector for ALICE20

November Aerogel threshold detector for ALICE21 Summary II Possibilities of light output increase. – The ratio of signals from 1.05 and 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 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 % quantum efficiency (MCP PMTs we use have multialcali photocathode with mean QE=22%)

November Aerogel threshold detector for ALICE22 Charged particles multiplicity: ~ 80 m-2 Interaction rate: 10 4 (3% central events) Interaction rate: 10 4 (3% central events) PID: PID: 1 < p < 3 GeV/c p K 1 < p < 3 GeV/c p K 2 < p < 5 GeV/c p 2 < p < 5 GeV/c p ALICE HMPID Where to place the VHMPID

November Aerogel threshold detector for ALICE23 summary The aerogel threshold detectors are well suited for heavy ion collisions to identify protons up to 12 GeV Integrating box and WLS have possibilities to be used if the WLS background ids understood