Future physics opportunities for high-density QCD at the LHC with heavy-ion and proton beams

Abstract

The future opportunities for high-density QCD studies with ion and proton beams at the LHC are presented. Four major scientific goals are identified: the characterisation of the macroscopic long wavelength Quark-Gluon Plasma (QGP) properties with unprecedented precision, the investigation of the microscopic parton dynamics underlying QGP properties, the development of a unified picture of particle production and QCD dynamics from small (pp) to large (nucleus-nucleus) systems, the exploration of parton densities in nuclei in a broad (x, Q 2 ) kinematic range and the search for the possible onset of parton saturation. In order to address these scientific goals, high-luminosity Pb-Pb and p-Pb programmes are considered as priorities for Runs 3 and 4, complemented by high-multiplicity studies in pp collisions and a short run with oxygen ions. High-luminosity runs with intermediate-mass nuclei, for example Ar or Kr, are considered as an appealing case for extending the heavy-ion programme at the LHC beyond Run 4. The potential of the High-Energy LHC to probe QCD matter with newly-available observables, at twice larger center-of-mass energies than the LHC, is investigated.

ALICE Highlights

“…In parallel, the online and offline systems will be completely renewed [43] to allow us to manage the new features of the DAQ model. To improve during Run-3 and Run-4 the physics program related to charm and beauty probes [44], a Muon Forward Tracker [46] will be installed and the ITS detector will be replaced with a new one [45] with a higher capability for secondary vertex reconstruction and a much lower material budget. The lower material budget will allow also to extend the ALICE sensitivity at lower momenta, especially when running in a lower magnetic field configuration (B = 0.2T).…”

Scaling behaviors of heavy flavor meson suppression and flow in different nuclear collision systems at the LHC

“…This has triggered hot debates on whether the collectivity observed in small systems originates from final-state QGP effects or from initial-state gluon saturation effects [36][37][38][39][40][41][42][43]. One possible way of disentangling the initial-state and finalstate contributions to jet observables is to scan the jet quenching effect across various sizes of nuclear collision systems [44,45]. This would bridge the gap between large and small systems and may hopefully help identify the boundary across which QGP disappears.…”

The sixth order cumulant of net-proton number in Binomial distribution at $\sqrt{s_{NN}} = $ 200 GeV

“…4 GeV, unlike the QCD predicted negative behavior. In the future, with the sufficient statistics accumulated, the anal-ysis of the net-proton C 6 /C 2 is possible by the ALICE collaboration at LHC [15]. Before illustrating the physics of measured C 6 /C 2 , the contributions of non-phase transition related influences should be subtracted, such as the conservation of the total baryon number, experimental acceptances in terms of kinematic variables, efficiency corrections, the difference of C 6 /C 2 in net-proton and net-baryon and so on [16][17][18][19].…”