Quark Matter 2025, the XXXI International Conference on Ultra-relativistic Nucleus-Nucleus Collisions, is being held this week (6–12 April 2025) at Goethe University Frankfurt, Germany. This time, the conference welcomes a record number of more than 1000 participants, bringing together theorists and experimentalists from around the world to discuss new developments in high-energy heavy-ion physics.
The ALICE collaboration is presenting a series of new results in 1 plenary overview tallk, 33 parallel session talks and 105 posters, featuring 77 new preliminaries from LHC Run 3 and 12 from Run 2! The ALICE overview talk by Alexander Schmah highlighted new results from LHC Run 3, updates from Run 2, ongoing upgrade projects (ITS3 and FoCal) and the proposal for a completely new detector, ALICE 3 as a follow-up to the current ALICE experiment. Here are some of the key new results presented at the conference inlcuing the two presentations on new results highlighted by the European Physical Journal (EPJ).
B-meson production in proton-proton collisions:
ALICE has delivered the first measurement of fully reconstructed B⁰-meson pT-differential production cross sections in proton-proton collisions at midrapidity, extending down to pT = 1 GeV/c – lower than ever before. These results impose stringent constraints on perturbative QCD predictions and enrich ALICE’s previous insights in the heavy-flavour sector. These exciting results were enabled by major upgrades to the ALICE detector for LHC Run 3 and an innovative software trigger that selects the most significant events from the vast amount of data, ensuring efficient and precise analysis.
First measurement of Λc+ flow in Pb-Pb collisions:
ALICE has achieved the first measurement of elliptic flow (v2) coefficients for Λc+ baryons in semicentral heavy-ion collisions, using the largest Pb-Pb dataset ever collected at √sNN = 5.36 TeV. Thanks to the outstanding performance of the upgraded ALICE detector, both prompt and non-prompt Λc+ baryon v2 coefficients were measured. Results revealed a clear hierarchy between charm baryon and meson v2 values, mirroring patterns already observed in the light-flavor sector. This breakthrough measurement provides crucial insight into charm and beauty quark thermalization and their participation in collective motion of the quark-gluon plasma.
First measurement of anti-alpha production in proton-proton collisions:
The first measurement of (anti)alpha production in proton-proton collisions at a center-of-mass energy of 13.6 TeV is presented, including the measurement of an antialpha transverse-momentum spectrum. The production yields and transverse-momentum spectra of nuclei are of particular interest since they provide a stringent test of particle production models.
EPJ Featured Talk on Evidence for J/ψ suppression in incoherent photonuclear production:
According to quantum chromodynamics, at high energy, hadrons exhibit a dynamic equilibrium between gluon splitting and recombination, reflecting the non-Abelian nature of gluons, known as gluon saturation. Photonuclear production of J/ψ vector mesons in the electromagetic field of two colliding nuclei, provides unique insights into the gluon distribution inside hadrons. The Mandelstam- 𝑡 variable, representing the four-momentum transfer, probes hadron structure within the impact-parameter plane, with different 𝑡 ranges sensitive to gluon field dynamics at various spatial scales. ALICE presents new results on the energy dependence of incoherent photonuclear production of J/𝜓 mesons off lead ions, at √𝑠NN=5.02 TeV, for three different Mandelstam-𝑡 intervals. The energy dependence of the photonuclear cross section at the highest |𝑡| range measured, (0.81< |𝑡|< 1.44) GeV2, is sensitive to subnucleonic structures of the Pb target. The observed energy evolution pattern in the data is similar to that of gluon saturation models, while the shadowing model is disfavored. (Refer to: https://arxiv.org/abs/2503.18708 for details).
EPJ Featured Talk on First direct measurement of radial flow in heavy-ion collisions with ALICE:
The measurements of long-range transverse-momentum correlations has been obtained using a newly defined observable, 𝑣0(𝑝T), which measures long-range correlations of transverse momentum in a 𝑝T-differential way. Results are reported for inclusive charged particles, pions, kaons, and protons across various centrality intervals in Pb−Pb collisions at √𝑠NN=5.02 TeV, recorded by the ALICE detector. A pseudorapidity-gap technique, similar to that used in anisotropic-flow studies, is employed to suppress short-range correlations. At low 𝑝T, a characteristic mass ordering consistent with collective flow is observed. These results are sensitive to the bulk viscosity and the equation of state of the QCD medium formed in heavy-ion collisions. (Refer to: https://arxiv.org/abs/2504.04796 for details).
