Potential performance for Pb-Pb, p-Pb and p-p collisions in a future circular collider

The hadron collider studied in the Future Circular Collider (FCC) project could operate with protons and lead ions in similar operation modes as the LHC. In this paper the potential performances in lead-lead, proton-lead and proton-proton collisions are investigated. Based on average lattice parameters, the strengths of intra-beam scattering and radiation damping are evaluated and their effect on the beam and luminosity evolution is presented. Estimates for the integrated luminosity per fill and per run are given, depending on the turnaround time. Moreover, the beam-beam tune shift and bound free pair production losses in heavy-ion operation are addressed.Comment: Submitted to PRSTA

Bound-free pair production from nuclear collisions and the steady-state quench limit of the main dipole magnets of the CERN Large Hadron Collider

During its Run 2 (2015-2018), the Large Hadron Collider (LHC) operated at almost twice higher energy, and provided Pb-Pb collisions with an order of magnitude higher luminosity, than in the previous Run 1. In consequence, the power of the secondary beams emitted from the interaction points by the bound-free pair production (BFPP) process increased by a factor ~20, while the propensity of the bending magnets to quench increased with the higher magnetic field. This beam power is about 35 times greater than that contained in the luminosity debris from hadronic interactions and is focused on specific locations that fall naturally inside superconducting magnets. The risk of quenching these magnets has long been recognized as severe and there are operational limitations due to the dynamic heat load that must be evacuated by the cryogenic system. High-luminosity operation was nevertheless possible thanks to orbit bumps that were introduced in the dispersion suppressors around the ATLAS and CMS experiments to prevent quenches by displacing and spreading out these beam losses. Further, in 2015, the BFPP beams were manipulated to induce a controlled quench, thus providing the first direct measurement of the steady-state quench level of an LHC dipole magnet. The same experiment demonstrated the need for new collimators that are being installed around the ALICE experiment to intercept the secondary beams in the future. This paper discusses the experience with BFPP at luminosities very close to the future High Luminosity LHC (HL-LHC) target, gives results on the risk reduction by orbit bumps and presents a detailed analysis of the controlled quench experiment.Comment: 16 pages, 11 figure

New physics searches with heavy-ion collisions at the CERN Large Hadron Collider

This document summarises proposed searches for new physics accessible in the heavy-ion mode at the CERN Large Hadron Collider (LHC), both through hadronic and ultraperipheral gamma gamma interactions, and that have a competitive or, even, unique discovery potential compared to standard proton-proton collision studies. Illustrative examples include searches for new particles-such as axion-like pseudoscalars, radions, magnetic monopoles, new long-lived particles, dark photons, and sexaquarks as dark matter candidates-as well as new interactions, such as nonlinear or non-commutative QED extensions. We argue that such interesting possibilities constitute a well-justified scientific motivation, complementing standard quark-gluon-plasma physics studies, to continue running with ions at the LHC after the Run-4, i.e. beyond 2030, including light and intermediate-mass ion species, accumulating nucleon-nucleon integrated luminosities in the accessible fb(-1) range per month.Peer reviewe

Heavy-ion performance of the LHC and future colliders

In 2008 the Large Hadron Collider (LHC) and its experiments started operation at the European Centre of Nuclear Research (CERN) in Geneva with the main aim of finding or excluding the Higgs boson. Only four years later, on the 4th of July 2012, the discovery of a Higgs-like particle was proven and first published by the two main experiments ATLAS and CMS. Even though proton–proton collisions are the main operation mode of the LHC, it also acts as an heavy-ion collider. Here, the term “heavy-ion collisions” refers to the collision between fully stripped nuclei. While the major hardware system of the LHC is compatible with heavy-ion operation, the beam dynamics and performance limits of ion beams are quite different from those of protons. Because of the higher mass and charge of the ions, beam dynamic effects like intra-beam scattering and radiation damping are stronger. Also the electromagnetic cross-sections in the collisions are larger, leading to significantly faster intensity decay and thus shorter luminosity lifetimes. As the production cross-sections for various physics processes under study of the experiments are still small at energies reachable with the LHC and because the heavy-ion run time is limited to a few days per year, it is essential to obtain the highest possible collision rate, i.e. maximise the instantaneous luminosity, in order to obtain enough events and therefore low statistical errors. Within this thesis, the past performance of the LHC in lead-lead (Pb-Pb) collisions, at a centre-of-mass energy of 2.76 TeV per colliding nucleon pair, is analysed and potential luminosity limitations are identified. Tools are developed to predict future performance and techniques are presented to further increase the luminosity. Finally, a perspective on the future of high energy heavy-ion colliders is given

Beam-Beam Interaction Studies at LHC

The beam-beam force is one of the most important limiting factors in the performance of a collider, mainly in the delivered luminosity. Therefore, it is essential to measure the effects in LHC. Moreover, adequate understanding of LHC beam-beam interaction is of crucial importance in the design phases of the LHC luminosity upgrade. Due to the complexity of this topic the work presented in this thesis concentrates on the beam-beam tune shift and orbit effects. The study of the Linear Coherent Beam-Beam Parameter at the LHC has been determined with head-on collisions with small number of bunches at injection energy (450 GeV). For high bunch intensities the beam-beam force is strong enough to expect orbit effects if the two beams do not collide head-on but with a crossing angle or with a given offset. As a consequence the closed orbit changes. The closed orbit of an unperturbed machine with respect to a machine where the beam-beam force becomes more and more important has been studied and the results are as well presented