Central diffraction and ultra-peripheral collisions in ALICE in Run 3 and 4

TL;DR

This paper discusses the ALICE experiment's upgrades and the challenges in detecting central diffractive and ultra-peripheral collisions during Runs 3 and 4 at the LHC, focusing on new detector technology and data processing.

Contribution

It presents the motivation and feasibility studies for selecting central diffractive and ultra-peripheral events with upgraded ALICE detectors in upcoming runs.

Findings

Feasibility of selecting rare collision events with new detector technology

Enhanced data acquisition rates enable large sample collection

Event selection strategies for rapidity gap events are outlined

Abstract

The ALICE experiment at the LHC is undergoing a major upgrade during the Long Shutdown 2 (2019-2021). In particular, the Time Projection Chamber (TPC) is being equipped with new GEM-based readout chambers and the readout electronics of several detectors are being replaced with faster and more flexible technology. This will allow ALICE to read out most of the detectors in the continuous mode and record minimum bias Pb-Pb events at rates of about 50 kHz in Run 3 (2021-2024) and Run 4 (2027-2030). The ALICE Collaboration is also considering the possibility to collect a large sample of proton-proton collisions at interaction rates of about 1 MHz using online and offline preselection of rare events. These goals require a completely new online computing system that will be used to perform fast reconstruction and compression of the data stream. The event selection strategy becomes especially challenging for the case of central diffractive events and ultra-peripheral Pb-Pb collisions characterized by rapidity gaps at forward and backward directions with only few tracks at central rapidity. In this contribution, the motivation for studying central diffractive and ultra-peripheral events is presented, and feasibility studies for their selection in Run 3 and 4 will be given.