Speaker
Description
The measurement of direct photons at forward rapidity in high-energy proton-nucleus collisions is a key to investigate the high-density parton distribution functions and to understand the initial state of nuclear collisions. Gluon distributions at very small x (below 10$^{-4}$) may reach saturation of the phase space. The Color Glass Condensate is a theoretical framework that describes the coherent dynamics of this saturated regime of QCD.
In order to enable the separation of direct photons from the decay photons, a high-granularity-readout electromagnetic calorimeter (FoCal-E) in the forward rapidity region (3.5 $<$ $\eta$ $<$ 5.3) has been proposed in the ALICE experiment at LHC. FoCal-E consists of 20 layers of tungsten absorber plates, interleaved with two types of active silicon layers, low granularity readout layers (LGL) with silicon pads and high-granularity readout layers (HGL) with Monolithic Active Pixel Sensors.
We have constructed a prototype calorimeter consisting of 20 alternating layers of tungsten and LGL pads. The performance of this prototype was evaluated with positron and hadron beams at CERN PS and SPS in 2018. The results of these testbeam measurements will be reported. This performance evaluation is crucial to determine the final design of FoCal-E.
