Physics via Photons at ALICE

Kenta Shigaki （ ）for the

ALICE Group at Hiroshima Universityat

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 pt essential– penetrating probes never easy to measure

photons: worth a challenge at LHC

13.10.2008 Physics via Photons at ALICE - K.Shigaki 2/5

PHOS: new and improved tool

13.10.2008 Physics via Photons at ALICE - K.Shigaki

high resolution, high granularity EM calorimeter– s/E ~ 3 %/E up to 100 GeV – PbWO4 of 22 (1.0 RMoliere)×22×180 (20 X0) mm3

– APD + charge sensitive preamplifier readout– temperature controlled at -250.1 ˚C

|h| < 0.12, Df = 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 studies3/5

13.10.2008 Physics via Photons at ALICE - K.Shigaki

#1: thermal photons

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RHIC/PHENIX ： indirect measurement via g*

– 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

13.10.2008 Physics via Photons at ALICE - K.Shigaki

interesting behavior of meson RAA 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 pt

photon separation pt limit extended due to PHOS granularity

– another path after obvious starting point (p0)– feasibility studies underway

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members/supporters at Hiroshima

13.10.2008 Physics via Photons at ALICE - K.Shigaki

photonsPHOS

PHENIX

ALICE

6/5