Speaker
Description
We will present the design and physics performance of a high-granularity Forward Calorimeter (FoCal) upgrade for ALICE. The main goal of the FoCal detector is to measure isolated direct photon production to constrain the low-x gluon density in the proton and nuclei and to look for deviations from linear QCD evolution in the high gluon-density regime. In addition, correlation measurements using forward hadrons and photons will be used to explore possible CGC effects as well as long-range flow-like phenomena.
The detector will cover the pseudorapidity range from 3.4 to 5.8 with a Si-W electromagnetic calorimeter (ECal) with pad and pixel readout and a hadronic calorimeter with conventional metal-scintillator technology with optical readout.
The high granularity of the ECal will allow us to separate decay photons from neutral pions with unprecedented spatial resolution, providing a reconstruction efficiency for neutral pions above 80% over a large range in transverse momentum.
The impact of the direct photon measurements with the FoCal on the gluon density is evaluated by reweighting the nNNPDF 2.0 nuclear PDFs with pseudo data. It is shown that the FoCal accesses a unique small-x range down to $x \approx 10^{-5}$.
