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The ALICE experiment operates at CERN-LHC accelerator complex and was designed having as main goal the study of relativist heavy ion collisions, and in particular the properties of the quark gluon plasma (QGP) nuclear matter status. The detector layout is characterized by a good coverage in the mid-rapidity ($| \eta| < 1$), especially optimized to allow measuring up to quite soft part (p$\approx$150 MeV) of particle spectrum. In the forward regions the ALICE detector is characterised by an asymmetric layout, with a muon spectrometer in the $-4.5 < \eta < -2.5$ region, while the positive side is presently lightly instrumented.
After many years of preliminary technological development and better characterization of the physics case, in 2020 a Letter of Intent for a Forward Calorimeter (FoCal) was presented, and the project was approved both by the ALICE collaboration and by the LHC Experiment Committee.
The main goal of Focal is to measure with a high-precision the inclusive production of direct photons and $\gamma$-jet and jet-jet coincidences in the high rapidity region, for both proton-proton and proton-Pb collisions, providing, in such a way, the possibility to investigate the Parton Distribution Function in the small Bijorken-x region, which is still quite experimentally unexplored.
The FoCal consists of a high-granularity electromagnetic calorimeter (FoCal-E) followed by a conventional (Cu or Pb scintillating fibre spaghetti design) hadron calorimeter (FoCal-H). The FoCal-E is sampling calorimeter which uses tungsten (small Molière radius) as converter, and silicon to detect and track the shower. The current proposal foresees 18 layers formed by tungsten and silicon pads (pad size ${\rm \approx 1 \: cm^2} $) and two (or three) layers of tungsten and silicon pixels providing high granularity readout ($\approx 30 \times 30 \: {\rm \mu m ^2}$ ). The pad layers will allow the measurement of the shower energy and profile, and the pixel layers will provide two-photon separation with high spatial precision in order to separate between isolated photons and merged showers of decay photon pairs from neutral pions.
The Brazilian groups in ALICE (USP, UNICAMP, UFABC and UFRGS) aimed contribution to this project is the characterization of the FoCal silicon pad layers readout system. Given the extensive experience of the groups obtained during the development of the SAMPA chip, that instruments the ALICE TPC and MCH detectors, it is natural to expect that a significant contribution to this part of the project can be achieved. Combined to this, given the interest of the groups in the development of a research infrastructure for silicon detectors, the contribution to the readout of the silicon pad detectors naturally matches such endeavour.
| Key Words | ALICE, Forward Calorimeter, Read-out eletronics |
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