Study of hard and electromagnetic processes at CERN-SPS energies: an investigation of the high-$\mu_{\mathbf{B}}$ region of the QCD phase diagram with NA60+

TL;DR

NA60+ aims to explore the QCD phase diagram at CERN SPS energies by studying thermal dimuons, chiral symmetry restoration, and quarkonium production, providing insights into the phase transition and properties of the quark-gluon plasma.

Contribution

The paper proposes a new experiment, NA60+, with a detailed setup and physics program to investigate the high baryochemical potential region of the QCD phase diagram at SPS energies.

Findings

Design of the NA60+ experimental setup with advanced detectors.

Feasibility studies showing significant physics potential.

Expected to improve understanding of the QCD phase transition.

Abstract

The exploration of the phase diagram of Quantum ChromoDynamics (QCD) is carried out by studying ultrarelativistic heavy-ion collisions. The energy range covered by the CERN SPS ($\sqrt{s_{\rm \scriptscriptstyle{NN}}} \sim$ 6-17 GeV) is ideal for the investigation of the region of the phase diagram corresponding to finite baryochemical potential ($\mu_{\rm B}$), and has been little explored up to now. We propose in this document a new experiment, NA60+, that would address several observables which are fundamental for the understanding of the phase transition from hadronic matter towards a Quark-Gluon Plasma (QGP) at SPS energies. In particular, we propose to study, as a function of the collision energy, the production of thermal dimuons from the created system, from which one would obtain a caloric curve of the QCD phase diagram that is sensitive to the order of the phase transition. In addition, the measurement of a $\rho$-a$_1$ mixing contribution would provide conclusive insights into the restoration of the chiral symmetry of QCD. In parallel, studies of heavy quark and quarkonium production would also be carried out, addressing the measurement of transport properties of the QGP and the investigation of the onset of the deconfinement transition. The document also defines an experimental set-up which couples a vertex telescope based on monolithic active pixel sensors (MAPS) to a muon spectrometer with tracking (GEM) and triggering (RPC) detectors within a large acceptance toroidal magnet. Results of physics performance studies for most observables accessible to NA60+ are discussed, showing that the results of the experiment would lead to a significant advance of our understanding of strong interaction physics. The document has been submitted as an input to the European Particle Physics Strategy Update 2018-2020 (http://europeanstrategyupdate.web.cern.ch/).