First Lead-Ion Collisions at Record Energy at LHC

First Lead Ion Collisions at Record Energy at LHC
Ion Collisions of First Course at Record Energy at LHC - ALICE Event image and geometry rendering: Pb-Pb 18 TeV on 2022 November 5,36

In preparation for next year's lead-lead physics study, a test involving lead ions was conducted at the LHC on Friday, November 18. In this way, experiments had a chance to validate new detectors and new data processing systems.

After the successful launch of Run 13,6, involving proton-proton collisions at a record energy of 3 TeV, in July of this year, interaction with lead nuclei followed. This interaction took place at the Large Hadron Collider (LHC) last year after a four-year hiatus.

Quark-gluon plasma (QGP), a state of matter in which fundamental components, quarks and gluons are not constrained within nucleons but can move and interact in a much larger volume, is studied using lead nuclei with 208 nucleons (protons and neutrons).

During the test carried out last Friday, the lead cores were accelerated and collided at a record energy of 5.36 TeV. This marks an important milestone in the development of lead-lead collision physics studies planned for 2023 and the following Run 3 and Run 4 years.

For the High Luminance LHC, the CERN ion injector complex has undergone a series of refinements to allow the total density of the lead-ion beams to double.

To do this, the Super Proton Synchrotron (SPS) is used in a process known as "momentum shift stacking".

Two batches of four lead-ion beams separated by 100 nanoseconds are processed to produce a single batch of 50 lead beams separated by 8 nanoseconds.

In this way it will be possible to increase the total number of beams injected into the LHC from 2 in Run 648 to 3 in Run 1248 and later. The LHC will deliver 10 times more heavy ion collisions compared to previous work after all enhancements are complete.

This test also marked an important milestone for ALICE, the LHC experiment focused on lead-ion collision research. During the last shutdown of the LHC, several completely new or significantly better detectors were added to the ALICE instrument, as well as new hardware and software for data processing.

In reconstructing the trajectories and properties of particles formed in collisions, the new detectors offer better spatial resolution. The improved equipment and processing chain can also save all collision information twice as fast.

Other experiments benefited from test work to commission the upgraded and newly installed subsystems in the new heavy ion environment with higher energy and 50ns beam spacing.

In Study 3, ATLAS evaluated changes in selection (trigger) software aimed at improving data collection for heavy ion physics. A new particle trail trigger that can detect a wider variety of "ultra-environmental collisions" has been specifically tested by physicists. CMS developed a series of reads, data acquisition, triggering and reconstruction chains to take full advantage of high-energy lead-lead collisions.

Thanks to the lead-lead fillers supplied by the LHC, CMS was able to arm the entire system with the beam and identify areas where it could be further optimized for 2023 heavy-ion studies.

When lead-lead collisions with extremely high particle abundances occurred, the LHCb began commissioning its brand new detector. The new SMOG2 instrument, specific to the experiment and aimed at injecting noble gases into the LHCb collision area, was used by the LHCb to collect lead-argon collisions in fixed target mode in addition to lead-lead collisions.

Despite its short duration, the 2022 lead-lead program can be seen as a success for the LHC accelerator, experiments and CERN's heavy-ion injector complex. For the first time, lead-lead collisions at a new record energy have been observed and recorded by four large LHC detectors. Now scientists await the heavy ion physics campaign in 2023 and the years that follow.


Günceleme: 28/11/2022 12:06

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