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A. Andronic

Publications and source records attributed to A. Andronic.

At least 19 recordsLinked to original sources
arXiv2026

Experimental exploration of the QCD phase diagram

The different phases of strongly interacting matter are governed by Quantum Chromodynamics (QCD). At high temperature and/or density a deconfined, chirally symmetric phase of quarks and gluons is expected to govern the nature of strongly interacting matter, the so-called quark-gluon plasma. Here we review what is known about the existence of this exotic form of matter from an experimental point of view and confront the results with QCD predictions based on 'Lattice QCD', where QCD is discretized on a space-time lattice and solved numerically in a Monte Carlo approach. The form of the presentation is explicitly pedagogical but the results include even very recent developments. Our research is based on the interpretation of hadron production data from relativistic nucleus--nucleus collisions over a wide energy range, with the aim to make progress in the understanding of the QCD phase, and of phenomena like deconfinement and hadronization.

nucl-ex↗
arXiv2026

Demonstrating CBM Capabilities by $\Lambda$ Baryon Reconstruction in Ni+Ni Collisions with the mCBM Experiment at SIS18 of GSI/FAIR

The Compressed Baryonic Matter (CBM) experiment at the upcoming Facility for Antiproton and Ion Research (FAIR) is a high-rate fixed-target experiment designed to investigate nuclear matter at extreme baryon densities in relativistic nucleus-nucleus collisions. To enable high-statistics measurements of rare probes, CBM is designed to operate at event rates up to 10 MHz. This necessitates the development of fast and radiation-tolerant detectors, self-triggered front-end electronics, a free-streaming data acquisition architecture, and real-time event reconstruction capabilities. Prototype versions and pre-series productions of the CBM detector systems have been deployed in the mini-CBM demonstrator setup mCBM - an experimental precursor comprising sub-components of all major CBM systems, installed at the SIS18 facility of GSI/FAIR within the FAIR Phase-0 program. In 2024, Ni+Ni collisions at a kinetic beam energy of 1.93 AGeV and an average interaction rate of about 250 kHz were successfully recorded. This dataset enables a detailed evaluation of the operational performance of the detector systems as well as the complete CBM data chain, while the reconstruction of rare $\Lambda$ baryons serves as a natural benchmark. This paper presents the first results on $\Lambda$ signal reconstruction with the mCBM experiment, demonstrating the readiness of the detector technologies and the data chain for the upcoming full-scale CBM experiment.

physics.ins-det↗
arXiv2026

Statistical hadronization: successes and some open issues

Hadron production in relativistic nuclear collisions is well described in the framework of the statistical hadronization model, over a broad range of collision energies. We outline this for hadrons composed of light (u, d, s) and heavy (charm and beauty) quarks, discuss recent findings relevant for understanding the phase structure of QCD and formulate some open issues.

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arXiv2025

Quarkonia and Deconfined Quark-Gluon Matter in Heavy-Ion Collisions

In this report, we present an experimental overview of quarkonium results obtained in nucleus-nucleus collisions, with a focus on the data collected at the LHC. We discuss the current understanding of charmonium and bottomonium behavior in the deconfined medium produced in such collisions, comparing the various observables now accessible to state-of-the-art theoretical models. We also discuss the open points and how future heavy-ion experiments aim to clarify these aspects.

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arXiv2024

The $v^{1/3}_{3}/v^{1/2}_{2}$ ratio in PbAu collisions at $\sqrt{s_{\mathrm{NN}}} = $ 17.3 GeV: a hint of a hydrodynamic behavior

The Fourier harmonics, $v_2$ and $v_3$ of negative pions are measured at center-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}}$= 17.3 GeV around midrapidity by the CERES/NA45 experiment at the CERN SPS in 0--30\% central PbAu collisions with a mean centrality of 5.5\%. The analysis is performed in two centrality bins as a function of the transverse momentum $\mathrm{p_{\mathrm{T}}}$ from 0.05 GeV/$c$ to more than 2 GeV/$c$. This is the first measurement of the $v^{1/3}_{3}/v^{1/2}_{2}$ ratio as a function of transverse momentum at SPS energies, that reveals, independently of the hydrodynamic models, hydrodynamic behavior of the formed system. For $\mathrm{p_{\mathrm{T}}}$ above 0.5 GeV/$c$, the ratio is nearly flat in accordance with the hydrodynamic prediction and as previously observed by the ATLAS and ALICE experiments at the much higher LHC energies. The results are also compared with the SMASH-vHLLE hybrid model predictions, as well as with the SMASH model applied alone.

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arXiv2024

Comparative Study of Quarkonium Transport in Hot QCD Matter

This document summarizes the efforts of the EMMI Rapid Reaction Task Force on "Suppression and (re)generation of quarkonium in heavy-ion collisions at the LHC", centered around their 2019 and 2022 meetings. It provides a review of existing experimental results and theoretical approaches, including lattice QCD calculations and semiclassical and quantum approaches for the dynamical evolution of quarkonia in the quark-gluon plasma as probed in high-energy heavy-ion collisions. The key ingredients of the transport models are itemized to facilitate comparisons of calculated quantities such as reaction rates, binding energies, and nuclear modification factors. A diagnostic assessment of the various results is attempted and coupled with an outlook for the future.

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arXiv2020

Impact of scale, nuclear PDF and temperature variations on the interpretation of medium-modified jet production data from the LHC

In this paper we present a study of in-medium jet modifications performed with JEWEL and PYTHIA 6.4, focusing on the uncertainties related to variations of the perturbative scales and nuclear parton distribution functions (PDFs) and on the impact of the initial and crossover temperature variations of the medium. The simulations are compared to LHC data for the jet spectrum and the nuclear modification factor. We assess the interplay between the choice of nuclear PDFs and different medium parameters and study the impact of nuclear PDFs and the medium on the jet structure via the Lund plane.

hep-ph↗
arXiv2020

Influence of modified light-flavor hadron spectra on particle yields in the statistical hadronization model

Hadron production in relativistic nuclear collisions is well described in the framework of the Statistical Hadronization Model (SHM). We investigate the influence on SHM predictions of hadron mass spectra for light-flavor baryons and mesons modified by the addition of about 500 new states as predicted by lattice QCD and a relativistic quark model. The deterioration of the resulting thermodynamic fit quality obtained for PbPb collision data at sqrt(s_nn) = 2.76 TeV suggests that the additional states are not suited to be naively used since also interactions among the states as well as non-resonant contributions need to be considered in the SHM approach. Incorporating these effects via the pion nucleon interaction determined from measured phase shifts leads again to excellent reproduction of the experimental data. This is a strong indication that at least the additional nucleon excited states cannot be understood and used as independent resonances.

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arXiv2020

QCD Challenges from pp to A-A Collisions

This paper is a write-up of the ideas that were presented, developed and discussed at the third International Workshop on QCD Challenges from pp to A-A, which took place in August 2019 in Lund, Sweden. The goal of the workshop was to focus on some of the open questions in the field and try to come up with concrete suggestions for how to make progress on both the experimental and theoretical sides. The paper gives a brief introduction to each topic and then summarizes the primary results.

hep-ph↗
arXiv2019

A next-generation LHC heavy-ion experiment

The present document discusses plans for a compact, next-generation multi-purpose detector at the LHC as a follow-up to the present ALICE experiment. The aim is to build a nearly massless barrel detector consisting of truly cylindrical layers based on curved wafer-scale ultra-thin silicon sensors with MAPS technology, featuring an unprecedented low material budget of 0.05% X$_0$ per layer, with the innermost layers possibly positioned inside the beam pipe. In addition to superior tracking and vertexing capabilities over a wide momentum range down to a few tens of MeV/$c$, the detector will provide particle identification via time-of-flight determination with about 20~ps resolution. In addition, electron and photon identification will be performed in a separate shower detector. The proposed detector is conceived for studies of pp, pA and AA collisions at luminosities a factor of 20 to 50 times higher than possible with the upgraded ALICE detector, enabling a rich physics program ranging from measurements with electromagnetic probes at ultra-low transverse momenta to precision physics in the charm and beauty sector.

physics.ins-det↗
arXiv2019

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

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.

hep-ph↗
arXiv2019

Wide acceptance measurement of the K$^-$/K$^+$ ratio from Ni+Ni collisions at 1.91A GeV

The FOPI Collaboration at the GSI SIS-18 synchrotron measured charged kaons from central and semi-central collisions of Ni+Ni at a beam energy of 1.91A GeV. We present the distribution of the K$^-$\K$^+$ ratio on the energy vs polar angle plane in the nucleon-nucleon center-of-mass frame, with and without subtraction of the contribution of $ϕ$(1020) meson decays to the K$^-$ yield. The acceptance of the current experiment is substantially wider compared to the previous measurement of the same colliding system. The ratio of K$^-$ to K$^+$ energy spectra is expected to be sensitive to the in-medium modifications of basic kaon properties like mass. Recent results obtained by the HADES Collaboration at 1.23A and 1.76A GeV indicate that after inclusion of the $ϕ$ meson decay contribution to the K$^-$ production no difference between the slopes of the K$^-$ and K$^+$ energy spectra is observed within uncertainties. For our data a linear fit to this ratio obtained after subtraction of the $ϕ$ meson contribution still shows a decrease with kinetic energy, although a constant value cannot be rejected. The contribution of $Λ(1520) \rightarrow p\text{K}^-$ decays estimated from fitting the thermal model to the experimental yields appears to be another factor of moderate relevance.

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arXiv2019

Elucidating the multiplicity dependence of J/$ψ$ production in proton-proton collisions with PYTHIA8

A study of prompt and non-prompt J/$ψ$ production as a function of charged-particle multiplicity in inelastic proton--proton (pp) collisions at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV based on calculations using the PYTHIA8 Monte Carlo is reported. Recent experimental data shows an intriguing stronger-than-linear increase of the self-normalized J/$ψ$ yield with multiplicity; several models, based on initial or final state effects, have been able to describe the observed behaviour. In this paper, the microscopic reasons for this behaviour, like the role of multiple parton interactions, colour reconnections and auto-correlations are investigated. It is observed that the stronger-than-linear increase and the transverse momentum ($p_{\rm T}$) dependence, contrary to what is predicted by the other available models, can be attributed to auto-correlation effects only. In absence of auto-correlation effects, the increase of the yield of J/$ψ$ with multiplicity -- and in general for all hard processes -- is weaker than linear for multiplicities exceeding about three times the mean multiplicity. The possibility of disentangling auto-correlation effects from other physical phenomena by measuring the charged-particle multiplicity in different pseudo-rapidity and azimuthal regions relative to the J/$ψ$ direction is investigated. In this regard, it is suggested to extend the experimental measurements of J/$ψ$ production as a function of the charged-particle multiplicity by determining the multiplicity in several azimuthal regions and in particular in the Transverse region with respect to the direction of the J/$ψ$ meson.

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arXiv2018

Extraction of Heavy-Flavor Transport Coefficients in QCD Matter

We report on broadly based systematic investigations of the modeling components for open heavy-flavor diffusion and energy loss in strongly interacting matter in their application to heavy-flavor observables in high-energy heavy-ion collisions, conducted within an EMMI Rapid Reaction Task Force framework. Initial spectra including cold-nuclear-matter effects, a wide variety of space-time evolution models, heavy-flavor transport coefficients, and hadronization mechanisms are scrutinized in an effort to quantify pertinent uncertainties in the calculations of nuclear modification factors and elliptic flow of open heavy-flavor particles in nuclear collisions. We develop procedures for error assessments and criteria for common model components to improve quantitative estimates for the (low-momentum) heavy-flavor diffusion coefficient as a long-wavelength characteristic of QCD matter as a function of temperature, and for energy loss coefficients of high-momentum heavy-flavor particles.

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arXiv2018

Testing charm quark thermalisation within the Statistical Hadronisation Model

A wealth of data on charmonium production in Pb-Pb collisions from the LHC experiments has provided strong evidence for (re-)generation as a dominant production mechanism at low transverse momentum. We present an important extension of the statistical hadronisation model to describe $\rm{J}/ψ$ transverse momentum distributions based on input parameters from hydrodynamical simulations. Comparison to the data allows the testing of the degree of thermalisation of charm quarks in the quark-gluon plasma. To this end we will report analyses of the $\rm{J}/ψ$ transverse momentum spectra in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ and $5.02$ TeV.

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arXiv2018

Decoding the phase structure of QCD via particle production at high energy

Recent studies based on non-perturbative lattice Monte-Carlo solutions of Quantum Chromodynamics, the theory of strong interactions, demonstrated that at high temperature there is a phase change from confined hadronic matter to a deconfined quark-gluon plasma where quarks and gluons can travel distances largely exceeding the size of hadrons. The phase structure of such strongly interacting matter can be decoded via analysis of particle abundances in high energy nuclear collisions within the framework of the statistical hadronization approach. The results imply quark-hadron duality at and experimental delineation of the location of the phase boundary of strongly interacting matter.

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