Abstract
The Zero Degree Calorimeters (ZDCs) of the ALICE experiment were designed with the twofold purpose of both estimating the centrality in heavy ion collisions by measuring the energy carried away by the spectator nucleons and of measuring the luminosity delivered to the experiment exploiting the high cross sections for neutron emission from electromagnetic dissociation processes. The measurement of centrality has been successfully extended to p–A collisions with the detection of nucleons ejected from the nucleus by the collisions with the projectile proton (“gray” nucleons) and those resulting from de-excitation processes (“black” nucleons). The applications of the detector in triggering and analysis have expanded during the years of operation in the LHC RUN1 and RUN2. These now include both the reaction plane and the longitudinal asymmetry measurements in heavy ion collisions. Moreover the ZDCs are used to reject the parasitic interactions of main bunches with satellite bunches in A–A and p–A collisions and to tag diffractive events in pp collisions. The foreseen operation in RUN3 with the tenfold increase in the luminosity delivered by LHC in heavy ion collisions, together with the continuous acquisition strategy that is being adopted by ALICE, will be challenging for the ZDC readout system. The readout upgrade will be based on FMC digitizers with trigger, timing and charge integration functionality performed through FPGA.
Highlights
IntroductionALICE [1] is the LHC experiment dedicated to the study of the properties of Quark-Gluon Plasma (QGP), a state of nuclear matter where quarks and gluons are deconfined, that can be created in relativistic heavy ion collisions
The Zero Degree Calorimeters (ZDCs) of the ALICE experiment were designed with the twofold purpose of both estimating the centrality in heavy ion collisions by measuring the energy carried away by the spectator nucleons and of measuring the luminosity delivered to the experiment exploiting the high cross sections for neutron emission from electromagnetic dissociation processes
The foreseen operation in RUN3 with the tenfold increase in the luminosity delivered by LHC in heavy ion collisions, together with the continuous acquisition strategy that is being adopted by ALICE, will be challenging for the ZDC readout system
Summary
ALICE [1] is the LHC experiment dedicated to the study of the properties of Quark-Gluon Plasma (QGP), a state of nuclear matter where quarks and gluons are deconfined, that can be created in relativistic heavy ion collisions. ALICE is composed of several detector systems providing excellent tracking and particle identification capabilities [2] to study the different signals emerging from the QGP: hadronic particles, photons, dielectrons and dimuons It is complemented by several detectors (mainly at forward rapidities) that allow the characterization of the global properties of the heavy-ion collisions in terms of time, vertex position, impact parameter (centrality) and collision plane. At LHC energies, in the operation with heavy ions, the minimum bias rate on the ZDCs is dominated by electromagnetic dissociation processes [3] These can occur even when the impact parameter of the two colliding ions is larger than the sum of the nuclear radii and hadronic interactions are not possible. It has been observed that the ZN information, thanks to different underlying physics process, is free from biases due to multiplicity fluctuations that affect centrality estimators based on particle production around mid-rapidity in p–A
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