A lead-lead collision occasion within the ALICE detector. (Picture: CERN)
After a five-year pause, on the night of 26 September, lead ions collided on the Massive Hadron Collider (LHC) at an unprecedented excessive power of 5.36 TeV per pair of nucleons (protons or neutrons) and a collision charge six occasions larger than earlier than. The ultimate lead-ion beam of this newest heavy-ion run was dumped early within the morning of 30 October, after a compelled magnet ‘quench’, carried out to higher perceive the quantity of deposited power at which the LHC superconducting magnets lose their superconducting state. This improved understanding of the LHC machine will assist to additional improve the heavy-ion collision charge within the close to future.
For this much-anticipated heavy-ion run, alongside improved beam parameters, the ALICE experiment – the LHC’s heavy-ion specialist – made use of its considerably upgraded detector with steady readout electronics. Because of this every collision can now be recorded and is thus accessible for physics evaluation, whereas, up to now, solely a fraction of collisions might be chosen for recording. This steady readout was achieved by revamping the experiment’s time projection chamber (TPC) detector and upgrading the readout electronics of all the detectors. As well as, the brand new inside monitoring system (ITS) detector, which relies on extremely granular silicon pixel expertise, gives sharp photos of the collisions with its 10 m2 of energetic silicon space and almost 13 billion pixels throughout the three-dimensional detector quantity.
The ensuing dramatic improve within the information charge was facilitated by the deployment of a brand new computing infrastructure for on-line information processing. This infrastructure features a new information processing farm that sends the info produced by the experiment on to CERN’s Knowledge Centre, situated about 5 kilometres from ALICE, by means of a devoted high-speed optical-fibre connection that needed to be established to deal with the elevated information charge.
Throughout the five-week run, ALICE recorded about 12 billion lead-lead collisions – 40 occasions extra collisions than the full recorded by ALICE within the earlier intervals of heavy-ion information taking, from 2010 to 2018. The brand new information processing farm, consisting of 2800 graphics processing items (GPUs) and 50 000 central processing unit (CPU) cores, routinely digested collision information at a charge of as much as 770 gigabytes per second. It then compressed the info to about 170 gigabytes per second earlier than transport it to the Knowledge Centre for storage on disk and later, at a restricted velocity of 20 gigabytes per second, for storage on tape for long-term preservation.
The recent information set – which quantities to 47.7 petabytes of disk house and is now being analysed – will advance physicists’ understanding of quark-gluon plasma, a state of matter by which quarks and gluons roam round freely for a really brief time earlier than forming the composite particles referred to as hadrons that ALICE detects. The elevated variety of recorded collisions will permit the ALICE researchers to find out the temperature of the plasma utilizing exact measurements of thermal radiation within the type of photons and pairs of electrons and positrons. It’s going to additionally permit different properties of the nearly-perfect fluid to be measured with larger precision, particularly utilizing hadrons containing heavy appeal and sweetness quarks.
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