Leader-to-leader collision events in the Alice detector. **cern
After a five-year pause, on the evening of September 26, lead ions were delivered at the Large Hadron Collider (LHC) at 5 per pair of nucleons (protons or neutrons).An unprecedented high-energy collision of 36 TEV with a collision rate six times higher than before.
In the early morning of October 30, after the forced magnet "quenched", the last lead ion beam of this latest heavy ion run was dumped to better understand the energy deposited when the LHC's superconducting magnet lost its superconducting state. This knowledge of the Large Hadron Collider will help further increase the rate of heavy ion collisions in the near future.
In addition to the improved beam parameters, the LHC's heavy ion specialist Alice experiment utilized its significantly upgraded detector and continuous readout electronics in this highly anticipated heavy ion run. This means that every collision can now be recorded, which can be used for physics analysis, whereas in the past, only a small percentage of collisions could be selected for recording.
This continuous reading was achieved by improving the experiment's Time Projection Chamber (TPC) detectors and upgrading the readout electronics of all detectors. In addition, the new Internal Tracking System (ITS) detector based on high-particle silicon pixel technology provides clear collision images with a length of 10 meters2 of active silicon area and a 3D detector volume of nearly 13 billion pixels.
The deployment of a new computing infrastructure for data processing has led to a significant increase in data rates. The infrastructure includes a new data processing farm that sends the data generated by the experiment directly to the CERN data center, about 5 kilometers from Alice, via a dedicated high-speed fiber optic connection, which must be established to cope with the increased data rates.
The number of lead-lead collisions collected by Alice in 2023, expressed as cumulative collisions (right vertical axis) and a correlated number called integrated photometry (left vertical axis). **cern
During the five-week run, Alice recorded approximately 12 billion lead-to-lead collisions, 40 times the total number of collisions recorded by Alice during heavy ion data acquisition between 2010 and 2018. The new data processing farm consists of 2,800 graphics processing units (GPUs) and 50,000 processing units (CPUs) cores, typically digesting conflicting data at a rate of 770 gigabits per second. It then compresses the data to about 170 gigabits per second, ships it to a data center for storage on disk, and then stores it on tape at a limited speed of 20 gigabits per second for long-term preservation.
This new dataset - equivalent to 47The 7 petabytes of disk space, which is currently being analyzed, will advance physicists' understanding of quark-gluon plasmas, a state of matter in which quarks and gluons roam freely for a very short period of time before forming a composite particle called a hadron detected by Alice.
The increase in the number of recorded collisions will allow ALICE researchers to determine the temperature of the plasma using precise measurements of thermal radiation in the form of photon, electron, and positron pairs. It will also allow for more precise measurement of other properties of near-perfect fluids, in particular the use of hadrons containing heavy charisma and beautiful quarks.