5.9 KiB
| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| ALICE experiment | 5/7 | https://en.wikipedia.org/wiki/ALICE_experiment | reference | science, encyclopedia | 2026-05-05T13:02:56.303258+00:00 | kb-cron |
Muons may be identified by using the fact that that they are the only penetrating charged particle. This is because muons with less than several hundred GeV/c of momentum do not produce electromagnetic showers, and because they are leptons, and so do not interact via the strong force with atomic nuclei they pass through or near. This allows muons to be identified simply by placing muon detectors behind calorimeters or thick absorbers. Muons are thus the only charged particle capable of reaching these detectors. The muon spectrometer is located in the forward region of ALICE. It includes an iron wall 1.2 m thick as a muon filter, as well as a complex absorber. A dedicated set of detectors precisely measures muon candidates that penetrate the absorbers.
=== Characterization of the collision === It is necessary for ALICE to be able to determine the strength of particle collisions. This is done by measuring the remnants of the colliding nuclei in detectors made of high density materials, which are located about 110 metres on both sides of ALICE (the Zero Degree Calorimeters) and by measuring with the FMD, V0 detector, and T0 detector the number of particles produced in the collision and their spatial distribution. The T0 detector also measures with high precision the time when the event takes place.
==== Zero degree calorimeter ====
The zero degree calorimeters (ZDCs) are calorimeters that detect the energy of the spectator nucleons in order to determine the overlap region of the two colliding nuclei. It is composed of four calorimeters, two to detect protons (ZP) and two to detect neutrons (ZN). They are located 115 meters away from the interaction point on both sides, exactly along the beam line. The ZN is placed at zero degrees with respect to the LHC beam axis, between the two beam pipes. That is why they are called zero degree calorimeters. The ZP is positioned externally to the outgoing beam pipe. The spectator protons are separated from the ion beams by means of the dipole magnet D1. The ZDCs are "spaghetti calorimeters", made by a stack of heavy metal plates grooved to allocate a matrix of quartz fibers. Their principle of operation is based on the detection of the Cherenkov light produced as the charged particles produced in the fibers as the result of a particle shower.
==== V0 detector ==== The V0 detector is made of two arrays of scintillator counters set on either side of the ALICE interaction point, called V0-A and V0-C. The V0-C counter is located upstream of the dimuon arm absorber and cover the spectrometer acceptance, while the V0-A counter is located around 3.5 m away from the collision vertex, on the other side. It is used to estimate the centrality of the collision by summing up the energy deposited in the two disks of V0. This value scales directly with the number of primary particles generated in the collision and therefore to the centrality. V0 is also used as reference in Van Der Meer scans that give the size and shape of colliding beams and therefore the luminosity delivered to the experiment.
==== T0 detector ====
ALICE's T0 detector serves as a start, trigger and luminosity detector for ALICE. The accurate interaction time (start) serves as the reference signal for the Time-of-Flight detector that is used for particle identification. T0 supplies five different trigger signals to the Central Trigger Processor. The most important of these is the T0 vertex, providing prompt and accurate confirmation of the location of the primary interaction point along the beam axis within the set boundaries. The detector is also used for online luminosity monitoring, providing fast feedback to the accelerator team. The T0 detector consists of two arrays of Cherenkov counters (T0-C and T0-A) positioned at the opposite sides of the interaction point (IP). Each array has 12 cylindrical counters, equipped with a quartz radiator and a photomultiplier tube.
=== ALICE Cosmic Rays Detector (ACORDE) === The ALICE cavern provides an ideal place for the detection of high energy atmospheric muons coming from cosmic ray showers. The ALICE Cosmic Rays detector (ACORDE) detects cosmic ray showers by detecting the arrival of muons to the top of the ALICE magnet. The ALICE cosmic ray trigger is made of 60 scintillator modules distributed on the three upper faces of the ALICE magnet yoke. The array can be configured to trigger on single or multi-muon events, from 2-fold coincidences up to the whole array if desired. ACORDE's high luminosity allows the recording of cosmic events with very high numbers of parallel muon tracks, the so-called muon bundles. With ACORDE, the ALICE Experiment has been able to detect muon bundles with the highest multiplicity ever registered as well as to indirectly measure very high energy primary cosmic rays.
== Data acquisition == ALICE requires a data acquisition system that can function both during the very frequent small events of proton-proton operation and the relatively infrequent but large events of Pb-Pb operation. ALICE therefore needs to be able to both manage the constant stream of data from central collisions and to distinguish and record rare cross-section processes. It therefore has an event building bandwidth of up 2.5 GB/s and the ability to store data at up to 1.25 GB/s. The physical hardware of the DAQ system is fairly standard. The event building network is composed of PCs running Linux and standard Ethernet switches. These PCs are then connected in a DAQ fabric to achieve the necessary performances. The Mass Storage System consists of two parts: Global Data Storage, doing temporary data storage in the experimental area; and Permanent Data Storage, doing long-term data archiving.
== Results ==
The physics program of ALICE includes the following main topics: