Physics via Photons at ALICE Kenta Shigaki （ ） for the ALICE Group at Hiroshima University at ATHIC2008 on 13 October 2008 in Tsukuba

vital probe of initial hot dense phase –thermal photons… temperature –thermal photon HBT… space-time evolution –direct photons… pQCD processes + jet tagging –neutral mesons… quark energy loss even more powerful at LHC than ever –# prompt photons ~ # decay photons at > 60 GeV –large rates up to ~ 100 GeV high quality measurement at low/mid p t essential –penetrating probes never easy to measure photons: worth a challenge at LHC Physics via Photons at ALICE - K.Shigaki1/5

PHOS: new and improved tool Physics via Photons at ALICE - K.Shigaki high resolution, high granularity EM calorimeter –  /E ~ 3 %/  E up to 100 GeV –PbWO 4 of 22 (1.0 R Moliere )×22×180 (20 X 0 ) mm 3 –APD + charge sensitive preamplifier readout –temperature controlled at  25  0.1 ˚C |  | < 0.12,  = 100 degrees –56×64×5 modules = 17,920 crystals (12.5 t) 1 “warm” module installed; 3 cold ones in 2009 –many final stage efforts ongoing commissioning; calibration; feasibility studies 2/5

Physics via Photons at ALICE - K.Shigaki #1: thermal photons 3/5 RHIC/PHENIX ： indirect measurement via  * –thermal component at 300 – 600 MeV suggested –models not strongly constrained LHC/ALICE ： high precision direct measurement –longer life of equilibrated hot phase –background photons suppressed due to quenching –high performance PHOS detector feasible above 3 – 4 GeV –expected S/N ~ 3 – 9 % at 3 GeV/c –systematic error ~ 9 % at 2 GeV/c

#2: quark energy loss systematics Physics via Photons at ALICE - K.Shigaki interesting behavior of meson R AA at RHIC –a key: systematic study of flavor/spin/… dependences –ref. M.Ouchida, 2D2, tomorrow various nuetral mesons via photon decay modes –experimental virtues: photon identification up to very high p t photon separation p t limit extended due to PHOS granularity –another path after obvious starting point (   ) –feasibility studies underway 4/5

members/supporters at Hiroshima Physics via Photons at ALICE - K.Shigaki photons PHOS PHENIX ALICE 5/5