Hadronization Mechanism Research Articles

Recent results on heavy flavours and quarkonia from ALICE

Heavy-flavour hadrons, containing at least one charm or beauty quark, are excellent probes of the deconfined medium created in ultrarelativistic heavy-ion collisions, known as quark–gluon plasma. Results in smaller collision systems, such as proton–proton and p–Pb collisions, besides representing an important baseline for interpreting heavy-ion measurements, are crucial to test perturbative QCD calculations and hadronisation mechanisms in the absence of hot medium effects, as well as to search for commonalities with heavy-ion systems. Recently, measurements in proton–proton and p–Pb collisions have revealed unforeseen features with respect to the expectations based on previous results from e+e− and ep collisions, showing that fragmentation fractions of heavy quarks are not universal. In this contribution, an overview of the most recent ALICE heavy-flavour measurements, along with the comparison to available calculations, will be discussed.

Charm and Bottom hadron production with a coalescence plus fragmentation hadronization approach: AA system size scan down to pp collisions

Heavy baryon production in pp, pA, and AA collisions at RHIC and LHC energies provides new challenges to the theoretical understanding of heavy-quark hadronization. In recent years, a hybrid coalescence-plusfragmentation model has successfully predicted the large baryon/meson ratio observed in AA and pp collisions. This approach also predicts an enhancement of Ξc and Ωc production in pp collisions that is in agreement with the recent ALICE data. In this paper, we provide predictions for bottom hadrons in PbPb and pp collisions at LHC energies. The comparison between charm and bottom hadron production offers new insights into both the hadronization mechanisms. Finally, the extension of the model to multi-charmed baryons like Ξcc and Ωccc has shown that multi-charmed baryon yields, especially Ωccc, are sensitive to the thermalization of charm quarks, offering insights into hadronization and quark equilibration dynamics across different systems.

Investigation of charm-quark hadronization into baryons in hadronic collisions with ALICE

A comprehensive investigation into charm-baryon production provides insight into understanding charm-quark hadronization process. In this contribution, the charm-quark hadronization mechanism is discussed in terms of the production yield ratio between charm hadron species measured by ALICE Collaboration. Measurements of Λc+, ∑c0,+ +, Ξc0,+ and Ωc0 in pp collisions, Λc+ and Ξc0 in p–Pb collisions are presented, together with the Λc+ measurement in larger collision systems, Pb–Pb collisions. Furthermore, the charm-quark hadronization mechanism is discussed based on the fragmentation fractions computed for pp and p–Pb collisions. A preliminary result on ∑c0,+ + measurement with Run 3 data is also presented.

Experimental overview on light (anti)(hyper)nuclei production at the LHC

For many years, significant efforts at the LHC have been put towards the measurements of the production of (anti)(hyper)nuclei in high-energy hadronic collisions. The ALICE experiment has contributed with measurements in pp, p–Pb, Xe–Xe, and Pb–Pb collisions, at various center-of-mass energies. Recently, also the LHCb experiment has measured the production of nuclei in both collider and fixed-target modes. The highlights of recent experimental measurements are discussed in the context of the production models used to describe the hadronization mechanism.

PHENOMENOLOGY OF HIGH MULTIPLICITY IN LEPTON INTERACTIONS

Interest to processes of multiparticle production in lepton and hadron interactions is not decreased. Development of strong interaction theory, quantum chromodynamics, allowes describing of these interactions at the quark-gluon level. Transit from partons to observable hadrons at the hadronization stage is extremely difficult. This paper presents the gluon dominance model that describes multiparticle production of secondary particles including the hadronization stage. This model is applied to the description of 𝑒+𝑒−- annihilation. It confirms the active role of the gluon component at the secondary particle formation, evidences about fragmentation mechanism of hadronization, which is realized in vacuum, describes multiplicity distribution data.

Measurement of beauty production via non-prompt charm hadrons in p–Pb collisions at sNN = 5.02 TeV

The production cross sections of D0, D+, and Λc+ hadrons originating from beauty-hadron decays (i.e. non-prompt) were measured for the first time at midrapidity in proton–lead (p–Pb) collisions at the center-of-mass energy per nucleon pair of sNN = 5.02 TeV. Nuclear modification factors (RpPb) of non-prompt D0, D+, and Λc+ are calculated as a function of the transverse momentum (pT) to investigate the modification of the momentum spectra measured in p–Pb collisions with respect to those measured in proton–proton (pp) collisions at the same energy. The RpPb measurements are compatible with unity and with the measurements in the prompt charm sector, and do not show a significant pT dependence. The pT-integrated cross sections and pT-integrated RpPb of non-prompt D0 and D+ mesons are also computed by extrapolating the visible cross sections down to pT = 0. The non-prompt D-meson RpPb integrated over pT is compatible with unity and with model calculations implementing modification of the parton distribution functions of nucleons bound in nuclei with respect to free nucleons. The non-prompt Λc+/D0 and D+/D0 production ratios are computed to investigate hadronisation mechanisms of beauty quarks into mesons and baryons. The measured ratios as a function of pT display a similar trend to that measured for charm hadrons in the same collision system.

Study of multiplicity dependence of heavy flavor production in pp collisions using rope hadronization mechanism

The multiplicity dependence of the production of the charm mesons in pp collisions at [Formula: see text][Formula: see text]TeV and 13[Formula: see text]TeV as measured by ALICE experiment has been investigated using Pythia 8 event generator by studying the effect of various processes at partonic level such as the effect of different modes of color reconnections and rope hadronization. The relative yields ([Formula: see text]) of D-mesons and [Formula: see text] as a function of relative charged particle multiplicity for various transverse momentum ([Formula: see text]) ranges as measured by the ALICE experiment are in reasonable agreement with the estimations of Pythia 8 model within the framework of microscopic processes. The relative yields of B mesons for various [Formula: see text] intervals ([Formula: see text][Formula: see text]GeV/c) have also been predicted in pp collisions at [Formula: see text][Formula: see text]TeV and [Formula: see text][Formula: see text]TeV.

Revealing the Production Mechanism of High-energy Neutrinos from NGC 1068

The detection of high-energy neutrino signals from the nearby Seyfert galaxy NGC 1068 provides us with an opportunity to study nonthermal processes near the center of supermassive black holes. Using the IceCube and latest Fermi-LAT data, we present general multimessenger constraints on the energetics of cosmic rays and the size of neutrino emission regions. In the photohadronic scenario, the required cosmic-ray luminosity should be larger than ∼1%−10% of the Eddington luminosity and the emission radius should be ≲15R S in low-β plasma and ≲3R S in high-β plasma. The leptonic scenario overshoots the NuSTAR or Fermi-LAT data for any emission radii we consider, and the required gamma-ray luminosity is much larger than the Eddington luminosity. The beta-decay scenario also violates not only the energetics requirement but also gamma-ray constraints, especially when the Bethe–Heitler and photomeson production processes are consistently considered. Our results rule out the leptonic and beta-decay scenarios in a nearly model-independent manner and support hadronic mechanisms in magnetically powered coronae if NGC 1068 is a source of high-energy neutrinos.

Observation of strangeness enhancement with charmed mesons in high-multiplicity pPb collisions at sNN=8.16 TeV

The production of prompt Ds+ and D+ mesons is measured by the LHCb experiment in proton-lead (pPb) collisions in both the forward (1.5<y*<4.0) and backward (−5.0<y*<−2.5) rapidity regions at a nucleon-nucleon center-of-mass energy of sNN=8.16 TeV. The nuclear modification factors of both Ds+ and D+ mesons are determined as a function of transverse momentum, pT, and rapidity. In addition, the Ds+ to D+ cross section ratio is measured as a function of the primary charged particle multiplicity in the event. An enhanced Ds+ to D+ production in high-multiplicity events is observed for the whole measured pT range, in particular at low pT and backward rapidity, where the significance exceeds six standard deviations. This constitutes the first observation of strangeness enhancement in charm quark hadronization in high-multiplicity pPb collisions. The results are also qualitatively consistent with the presence of quark coalescence as an additional charm quark hadronization mechanism in high-multiplicity proton-lead collisions. © 2024 CERN, for the LHCb Collaboration 2024 CERN

How higher charmonia shape the puzzling data of the e+e−→ηJ/ψ cross section

Recently, the BESIII collaboration performed a precise measurement of the e+e−→ηJ/ψ cross section. It is puzzling that the resonance parameters of the reported Y(4230) show a substantial divergence from the previously measured results in both the open-charmed and hidden-charmed decay channels, and the line shape asymmetry of the data approaching 4.2 GeV also suggests that it might be difficult to characterize the details of the structure around 4.2 GeV by a single resonance. This has motivated our great curiosity about how the charmonium states are distributed in the measured energy range and how they shape the puzzling data of the e+e−→ηJ/ψ cross section. In this work, we use five theoretically constructed charmonia in the range of 4.0–4.5 GeV, i.e., ψ(4040), ψ(4160), ψ(4220), ψ(4380), and ψ(4415), to apply a combined fit to the data, in which their calculated decay ratios into ηJ/ψ via hadronic loop mechanism are taken as input. The fit results can reproduce the measured cross section data well, especially for the subtle line shape around 4.2 GeV, showing that the structure around 4.2 GeV is possible from the contribution of both ψ(4160) and ψ(4220). Published by the American Physical Society 2024

Hadronization of heavy quarks

Heavy-flavor hadrons produced in ultrarelativistic heavy-ion collisions are a sensitive probe for studying hadronization mechanisms of the quark-gluon-plasma. In this paper, we survey how different transport models for the simulation of heavy-quark diffusion through a quark-gluon plasma in heavy-ion collisions implement hadronization and how this affects final state observables. Utilizing the same input charm-quark distribution in all models at the hadronization transition, we find that the transverse-momentum dependence of the nuclear modification factor of various charm hadron species has significant sensitivity to the hadronization scheme. In addition, the charm-hadron elliptic flow exhibits a nontrivial dependence on the elliptic flow of the hadronizing partonic medium. Published by the American Physical Society 2024

Heavy-flavor transport and hadronization in pp collisions

Recent experimental results on the Λc+/D0 ratio in proton-proton (pp) collisions have revealed a significant enhancement compared to expectations based on universal fragmentation fractions/functions across different colliding systems, from e+e− to pp. This unexpected enhancement has sparked speculation about the potential effects of a deconfined medium impacting hadronization, previously considered exclusive to heavy-ion collisions. In this study, we propose a novel approach that assumes the formation of a small, deconfined, and expanding fireball even in pp collisions, where charm quarks can undergo rescattering and hadronization. We make use of the same in-medium hadronization mechanism developed for heavy-ion collisions, which involves local color-neutralization through recombination of charm quarks with nearby opposite color charges from the background fireball. Our model incorporates the presence of diquark excitations in the hot medium, which promotes the formation of charmed baryons. Moreover, the recombination process, involving closely aligned partons from the same fluid cell, effectively transfers the collective flow of the system to the final charmed hadrons. We show that this framework can qualitatively reproduce the observed experimental findings in heavy-flavor particle-yield ratios, pT-spectra and elliptic-flow coefficients. Our results provide new, complementary supporting evidence that the collective phenomena observed in small systems naturally have the same origin as those observed in heavy-ion collisions. Published by the American Physical Society 2024

Latest ALICE results on charm and beauty hadronisation in hadronic collisions

The study of heavy-flavour mesons and baryons in hadronic collisions provides unique access to the properties of heavy-quark hadronisation in the presence of large partonic densities, where new mechanisms of hadron formation beyond in-vacuum fragmentation can emerge. Performing these measurements in intervals of charged-particle multiplicities across different collision systems provides sensitivity to understand whether different hadronisation mechanisms are at play in small and large hadronic colliding systems. In this contribution, a selection of the latest charm and beauty production measurements in proton–proton (pp) collisions is presented, which can shed light on the modification of the heavy-quark hadronisation mechanisms with respect to leptonic collisions. New published results of the production of all prompt charm ground states in pp collisions at √S = 13 TeV, which allowed us to measure the charm fragmentation fractions and the total cc production cross section at midrapidity, will be shown. The new final measurement of non-prompt (i.e. originating from beauty-hadron decays) Λc+ baryons in the same collisions system will be discussed to provide a quantitative comparison between the hadronisation properties of beauty and charm hadrons. New measurements of Ξc0 production as a function of charged-particle multiplicity in pp collisions at √S = 13, and of Ξc0 production in p–Pb collisions at √SNN = 5.02 TeV, will be also presented, shedding further light on the hadronisation of charm-strange baryons in different colliding systems.

Modification of heavy quark hadronization in high-multiplicity collisions at LHCb

The ratio of heavy flavor hadrons is very sensitive to the hadronization mechanism. This proceeding will present recent LHCb results on the crosssection ratios of Ds+/D+, Ξc+/ Λc+ and Λb0 / B0 in different collision systems. The significantly enhanced production ratios Ds+/D+ and Λb0 / B0 with the increase of multiplicity may imply that hadronization mechanisms are modified in highmultiplicity events.

Experimental overview on open-heavy flavours

Heavy flavours, i.e. charm and beauty quarks, are recognised as excellent probes of the colour-deconfined medium created in ultrarelativistic heavy–ion collisions, the quark–gluon plasma (QGP). In this document, the most recent measurements of heavy-flavour hadrons in heavy-ion collisions are summarised. Measurements of nuclear modification factors and angular anisotropies of open charm and beauty hadrons are reported to investigate the properties of the heavy-quark interactions in the QGP. A particular focus is given to the measurement of heavy-flavour baryons and hadrons with strangequark content for the study of the hadronisation mechanisms in both heavy–ion and proton–proton collisions. Finally, the polarisation of the charm vector mesons D*+ and J/ψ in heavy–ion collisions is presented.

Overview of hadronization of quarks in proton-proton and e+e− collisions

The so-called hadronization is a non-perturbative QCD phenomenon corresponding to the formation of colourless hadrons from coloured quark con stituents. The hadron formation in point-like e+e− collisions can be described by string models. According to the Lund model, the qq¯ pair production in the scattering is followed by a shower of light partons produced via multiple colour-string breaking, which produce colour singlets in the final states. The probability to obtain a hadron of a given species carrying a certain momentum fraction of the original quark is quantified by the fragmentation functions. They are assumed universal and usually constrained from e+ e− and e−p collisions, and they successfully describe the production of mesons in e+e− and pp colli sions at the colliders. However, recent measurements of pp collision data from the LHC showed a surprising relative enhancement of baryon production com pared to mesons, and model predictions based on string fragmentation do not describe the data. In this talk, an overview of the most recent experimental re sults of hadron production cross section in pp collisions at the LHC compared with e+e− results will be provided. A comparison with novel theoretical models implementing hadronization mechanisms different from the Lund string frag mentation will be also discussed, as well as experimental results obtained in larger systems, like p–Pb and Pb–Pb collisions.

Heavy-flavor transport and hadronization in a small fireball

We study heavy-flavor hadron production in high-energy pp collisions, assuming the formation of a small, deconfined and expanding fireball where charm quarks can undergo rescattering and hadronization. We adopt the same in-medium hadronization mechanism developed for heavy-ion collisions, which involves Local Color-Neutralization (LCN) through recombination of charm quarks with nearby opposite color charges from the background fireball. Diquark excitations in the hot medium favor the formation of charmed baryons. The recombination process, involving closely aligned partons from the same fluid cell, effectively transfers the collective flow of the system to the final charmed hadrons. This framework can qualitatively reproduce the observed experimental findings in heavy-flavor particle-yield ratios, pT -spectra and ellipticflow coefficients. Our results provide new, complementary support to the idea that the collective phenomena observed in small systems have the same origin as those observed in heavy-ion collisions.

Baryon correlations in Pythia

We present the results from our investigation of angular correlations between baryons pairs in the Pythia8 event generator. We show how colour reconnection models and hadronization mechanisms influence such angular correlations and in particular address the effect of gluons on the baryon production mechanism in the Lund string fragmentation model. We conclude by discussing the new theoretical ideas in comparison with the ALICE pp\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{pp} $$\\end{document} collision results for the baryon angular correlations. We propose a hypothesis for suppressing baryons produced in gluon jets and show how that may influence the angular correlations.

Measurement of the non-prompt D-meson fraction as a function of multiplicity in proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV

The fractions of non-prompt (i.e. originating from beauty-hadron decays) D0 and D+ mesons with respect to the inclusive yield are measured as a function of the charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy of s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV with the ALICE detector at the LHC. The results are reported in intervals of transverse momentum (pT) and integrated in the range 1 < pT< 24 GeV/c. The fraction of non-prompt D0 and D+ mesons is found to increase slightly as a function of pT in all the measured multiplicity intervals, while no significant dependence on the charged-particle multiplicity is observed. In order to investigate the production and hadronisation mechanisms of charm and beauty quarks, the results are compared to PYTHIA 8 as well as EPOS 3 and EPOS 4 Monte Carlo simulations, and to calculations based on the colour glass condensate including three-pomeron fusion.

First measurement of [formula omitted] production in pp collisions at [formula omitted] TeV

The inclusive production of the charm–strange baryon Ωc0 is measured for the first time via its hadronic decay into Ω−π+ at midrapidity (|y|<0.5) in proton–proton (pp) collisions at the centre-of-mass energy s=13 TeV with the ALICE detector at the LHC. The transverse momentum (pT) differential cross section multiplied by the branching ratio is presented in the interval 2<pT<12GeV/c. The pT dependence of the Ωc0-baryon production relative to the prompt D0-meson and to the prompt Ξc0-baryon production is compared to various models that take different hadronisation mechanisms into consideration. In the measured pT interval, the ratio of the pT-integrated cross sections of Ωc0 and prompt Λc+ baryons multiplied by the Ω−π+ branching ratio is found to be larger by a factor of about 20 with a significance of about 4σ when compared to e+e− collisions.