Speaker
Summary
The ALICE detector has been designed to study the strongly interacting matter
created in nucleus-nucleus collisions at the Large Hadron Collider~(LHC).
Measurement of direct photons is probing the initial state of the interactions.
In the heavy ion collisions program at LHC, it is very critical to measure thermal
radiated photons, which is known to carry the temperature information of
created hot medium, with very fine energy and position resolution.
The ALICE PHOton Spectrometer~(PHOS) consists of 17920 PWO crystals to
each having size of $22\times22\times180mm$ and Avalanche Photo Diode~
(APD) for readout of scintillation light. First PHOS module consisting of 3584
crystals was constructed and tested by utilizing 2GeV/{\it c} electron beam in
the summer of 2006 and cosmic rays in 2007. The HV bias for APDs were
calibrated in order to obtain equal gain for better trigger performance. Second
PHOS module is under construction and installed for the first p+p collisions at
LHC. Further research and development program for improved performance of
PHOS as a electro-magnetic calorimeter are under studying.
In this paper, we will present the construction and installation status of the
PHOS modules and performance results. In addition, physics potential with the
PHOS module during the first physics run of LHC will be discussed.
