Abstract
The production of low-mass dielectrons and dimuons is a powerful tool for the understanding of the properties of the quark–gluon plasma (QGP) created in ultra-relativistic heavy-ion collisions. Since such pairs do not interact strongly and are emitted during all stages of the collisions, they provide information about the full time evolution and dynamics of the medium created. Measurements in pp and p–Pb collisions are the necessary reference for heavyion studies. In addition, they can be used to extract charm and beauty cross sections.In this contribution, we present the latest measurements of e + e − and µ + µ − pair production in pp, p–Pb and Pb–Pb collisions performed by ALICE at different energies.
Highlights
Photons and lepton pairs are penetrating probes that allow us to investigate the full time evolution and dynamics of the dense and hot medium created in ultra-relativistic heavy-ion collisions, since they don’t undergo strong interactions in the final state
Dileptons can be emitted during all the stages of the collision and a differential study as a function of the invariant mass ml+l− and transverse momentum pT,l+l− allow one to disentangle the various sources
While at high pT it is dominated by hard QCD processes, such as partonic scattering, which can be described by perturbative calculations, at low pT is dominated by soft non-perturbative processes, described by phenomenological models
Summary
Photons and lepton pairs (electrons or muons) are penetrating probes that allow us to investigate the full time evolution and dynamics of the dense and hot medium created in ultra-relativistic heavy-ion collisions, since they don’t undergo strong interactions in the final state. Dileptons can be emitted during all the stages of the collision and a differential study as a function of the invariant mass ml+l− and transverse momentum pT,l+l− (with l = e, μ) allow one to disentangle the various sources. Measurements of φ mesons, due to their ss quark content, are useful to study the strangeness production, which is one of the key observables for the QGP. The ρ meson is potentially sensitive to chiral symmetry restoration, which is expected to happen close to the phase transition to the QGP in heavy-ion collisions [1]. This meson has a shorter lifetime than that of the medium.
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