physics via photons at alice kenta shigaki ( ) for the alice group at hiroshima university at...
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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
4/5
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
5/5
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