Hadron Production Research Articles

Non-Extensive Aspects of Gluon Distribution and the Implications for QCD Phenomenology

This study presents new insights into gluon transverse momentum distributions through non-extensive statistical mechanics, addressing their implications for QCD phenomenology. The saturation physics and scaling laws present in high-energy collision data are investigated as a consequence of gluon distribution modification in a high-density regime. This analysis explores how these modifications influence observables across different collision systems, such as proton–proton, proton–nucleus, and relativistic heavy-ion collisions. Both particle high- and low-transverse-momentum regions are successfully described in hadron production.

The impact of data from future lepton colliders on light hadrons fragmentation functions

In this work, we study the constraining power of future lepton colliders on fragmentation functions (FFs) to light charged hadrons from quarks and gluon in the framework of QCD collinear factorization. We perform analyses of FFs at NLO by including a wide range of pseudo-data from future lepton colliders, such as measurements on hadron multiplicities in the production of two jets and W boson pairs, at various center of mass energies, and from hadronic decays of the Higgs boson, including both to heavy quarks and to gluons. The high luminosity and high energies of future lepton colliders allow for quark flavor separations and ensure a precise determination of FFs based solely on data from electron-positron collisions. We find that either the CEPC, FCC-ee or ILC can significantly reduce the uncertainties of FFs in a wide kinematic range, compared to the NPC23 set obtained with a global analysis to current world data. We also discuss the impact of higher-order QCD corrections, and the potential constraints from measurements of three-jet production. Furthermore, we describe an update of the FMNLO program allowing for calculating hadron production cross sections at next-to-next-to-leading order in QCD, which is used in this study.

PHENIX results on identified hadron production in small and large collision systems

Identified charged hadron ([Formula: see text], [Formula: see text], p and [Formula: see text]) nuclear modification factors and ratios of [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] measured by the PHENIX experiment in p[Formula: see text]Al, 3He[Formula: see text]Au, Cu+Au collisions at [Formula: see text] = 200[Formula: see text]GeV and in U+U collisions at [Formula: see text] = 193 GeV are presented. The interpretation of experimental results has been carried out by comparison to theoretical predictions involving recombination and fragmentation models, implemented in the string melting version of AMPT package and in PYTHIA/ANGANTYR package, respectively. It is shown that in low [Formula: see text] range ([Formula: see text] [Formula: see text]GeV/c) fragmentation processes seem to dominate over recombination processes in collisions, characterized by small numbers of participant nucleons ([Formula: see text]). The contribution of recombination processes increases with increase of [Formula: see text] values and becomes dominant in collisions with [Formula: see text] which correspond to central collisions of large systems (Cu+Au and U+U).

Transverse momentum spectra and angular correlations in $$Z/\gamma$$-hadron production in relativistic heavy-ion collisions

Transverse momentum spectra and angular correlations in $$Z/\gamma$$-hadron production in relativistic heavy-ion collisions

Hadron production through Higgs boson decay at next-to-leading order in the zero-mass variable-flavor-number scheme

Hadron production through Higgs boson decay at next-to-leading order in the zero-mass variable-flavor-number scheme

Multiplicity and Rapidity Dependent Study of (Multi)-strange Hadrons in d+Au collisions using the STAR detector

Strangeness enhancement has long been considered as a signature of the quark-gluon plasma formation in heavy-ion collisions. Strangeness enhancement has also been observed in small systems at the Large Hadron Collider (LHC), but the underlying physics still needs to be fully understood. This motivates us to study the strange hadron production in small systems at RHIC. We present new measurements of (multi-)strange hadrons (KS0, Λ, Ξ and Ω), Λ, Ξ and Ω) in d+Au collisions at √sNN = 200 GeV, collected by STAR in 2016. We report the multiplicity and rapidity dependence of strange hadron transverse momentum (pT) spectra, pT-integrated yields dN/dy, average transverse momentum (<pT>), yield ratios of these strange hadrons to pions, nuclear modification factors and rapidity asymmetry for these particles in d +Au collisions.

Recent results from NA61/SHINE

The NA61/SHINE experiment at the CERN SPS is a multipurpose fixed-target spectrometer for charged and neutral hadron measurements. Its research program includes studies of strong interactions as well as reference measurements for neutrino and cosmic-ray physics. A significant advantage of NA61/SHINE over collider experiments is its extended coverage of phase space available for hadron production. This includes the nearly entire forward hemisphere for charged hadrons and additionally, a large part of the backward hemisphere for specific neutrals. This paper summarizes a selected set of new results, obtained by NA61/SHINE since the last SQM conference (Busan, 2022). Particular attention is devoted to (1) the first-ever direct measurement of open charm production in nucleus-nucleus collisions at SPS energies (2) the difference observed between charged and neutral meson production in Ar+Sc reactions, up to now not understood by existing models, and (3) the importance of baseline effects in the search for the critical point of strongly interacting matter.

PHENIX highlights: Recent results from PHENIX

The Relativistic Heavy Ion Collider (RHIC) PHENIX experiment has provided new insights into the behavior of quark-gluon plasma (QGP) under extreme conditions. While PHENIX concluded data collection in 2016, the collaboration remains actively engaged in analyzing the rich dataset yielding the following three important results recently. (1) Heavy flavor (HF) with charm and bottom quark separation indicates a clear mass dependence observed in central collisions. Additionally, forward rapidity J/ψ and v2 measurements show a result consistent with zero, in contrast to LHC findings. (2) Precise direct photon yields obtained via large statistical datasets, spanning a wide range of transverse momentum (pT) and centrality bins have the scaling behavior across various large systems, and non-prompt direct photon results reveal temperature (Teff) dependence on pT. (3) Charged hadron production was examined in collision systems of varying sizes, revealing that RAA is primarily dependent on the overlap volume (Npart). Moreover, RdAu obtained by experimental Ncoll suggests the clear yield suppression in central collisions.

Strange hadron production at high baryon density

Strange hadrons have been suggested as sensitive probes of the properties of the nuclear matter created in heavy-ion collisions. At few-GeV collision energies, the formed medium is baryon-rich due to baryon stopping effect. In these proceedings, the recent results on strange hadron production in Au+Au collisions at √sNN = 3.2, 3.5, 3.9 and 4.5 GeV with the fixed-target mode from the STAR Beam Energy Scan phase-II program are presented. The transverse momentum spectra, rapidity density distributions, excitation function and centrality dependence of strange hadrons (KS0, Λ, Ξ−) are shown. These results are compared with those from higher collision energies and physics implications are discussed by comparing to the transport model calculations.

Scaling Properties of ∅-Meson and Light Charged Hadron Production in Small and Large Systems at PHENIX

Recent results on the identified charged-hadron (π±, K±, p, p¯) production vat midrapidity region (|η| < 0.35) have been measured by the PHENIX experiment in p + Al, 3He + Au, Cu + Au collisions at √SNN = 200 GeV and U + U collisions at √SNN = 193 GeV. These measurements are presented through the invariant transverse-momentum (pT ) and transverse-mass (mT) spectra for different collision centralities. The averaged freeze-out temperature value for different systems was found to be 166.1 ± 2.2 MeV, and do not exhibit any dependence on the collision centrality and 〈Nparti〉 values. The particle ratios of K/π and p/π have been measured in different centrality ranges of large and small collision systems. The values of K/π ratios measured in all considered collision systems were found to be consistent with those measured in p+p collisions. Furthermore, the identified charged-hadron nuclear-modification factors (RAB) are also presented. Enhancement of proton RAB values over meson RAB values was observed in central 3He+Au, Cu+Au, and U+U collisions. The proton RAB values measured in p+Al collision system were found to be consistent with RAB values of ∅, π±, K±, and π0 mesons, suggesting that the size of the system produced in p+Al collisions is too small for recombination to cause a noticeable increase in proton production.

New insights into strange-quark hadronization measuring multiple (multi-)strange hadron production in small collision systems with ALICE

Among the most important results from the Run-1 and Run-2 of the LHC is the observation of an enhanced production of (multi-)strange to non-strange hadron yields, gradually rising from low-multiplicity to highmultiplicity pp and p–Pb collisions, reaching values close to those measured in peripheral Pb–Pb collisions [1]. The observed behaviour cannot be quantitatively reproduced by any of the available QCD-inspired MC generators. In this contribution an extension of this study is presented: the measurement of the Ks0, Λ, Ξ− and Ω− (together with antiparticles) multiplicity distributions in pp collisions at √s = 5.02 TeV as a function of the charged-particle multiplicity, together with the average probability for the multiplets production, extending the study of strangeness production beyond its average. This novel method, based on counting the number of strange particles event-by-event, represents a new test bench for production mechanisms, probing events with a large imbalance between strange and non-strange content.

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.

Isospin-symmetry breaking in kaon production: The role of charge-symmetry

An excess of charged versus neutral kaons has been recently reported by the NA61/SHINE collaboration. Similar excesses were also present in previous experiments, even if with larger errors. Models for hadron productions in heavy ion collisions systematically underestimate the measured charge-toneutral kaon ratio. In this report, we comment on the role of charge-symmetry as a specific isospin transformation. In particular, we show that the ensemble of the initial colliding nuclei being charge-symmetric is sufficient for producing an equal number of charged and neutral kaons in the isospin-symmetry exact limit.

Strangeness production in pp and pPb collisions at LHCb

Strange hadron production provides information about the hadronisation process in high-energy hadron collisions. Strangeness enhancement has been interpreted as a signature of quark-gluon plasma formation in heavy-ion collisions, and recent observations of strangeness enhancement in small collision systems have challenged conventional hadronisation models. With its forward geometry and excellent particle identification capabilities, the LHCb detector is well-suited to study strangeness production in a unique kinematic region. Recent studies of strangeness production with the LHCb detector are presented, including measurements of strangeness enhancement in the charmand beauty-hadron systems.

Simulation of dark scalar particle sensitivity in $\eta$ rare decay channels at HIAF

Abstract Searching dark portal particle is a hot topic in particle physics frontier. We present a simulation study of an experiment targeted for searching the scalar portal particle at Huizhou $\eta$ factory. The HIAF high-intensity proton beam and a high event-rate spectrometer are suggested for the experiment aimed for the discovery of new physics. Under the conservative estimation, $5.9\times 10^{11}$ $\eta$ events could be produced in one month running of the experiment. The hadronic production of $\eta$ meson ($p + ^7\text{Li} \rightarrow \eta X$) is simulated at beam energy of 1.8 GeV using GiBUU event generator. We tend to search for the light dark scalar particle in the rare decay channels $\eta \rightarrow S \pi^0 \rightarrow \pi^+ \pi^- \pi^0$ and $\eta \rightarrow S \pi^0 \rightarrow e^+ e^- \pi^0$. The detection efficiencies of the channels and the spectrometer resolutions are studied in the simulation. We also present the projected upper limits of the decay branching ratios of the dark scalar particle and the projected sensitivities to the model parameters.

Multiplicity, transverse momentum and pseudorapidity dependence of open-heavy flavored hadron production in proton+proton collisions at s = 13TeV using PYTHIA8

Recently, with the upgradation of LHC, it is realized that study of heavy-flavored hadrons, namely [Formula: see text] and [Formula: see text] in hadronic collisions, could reveal the possibility of thermalization of charm quarks. With this motivation, we study the production dynamics of these hadrons using a pQCD-inspired Monte Carlo event generator called PYTHIA8 in proton+proton collisions at [Formula: see text][Formula: see text]TeV. The production dynamics of these hadrons are analyzed through charged-particle multiplicity, transverse momentum and pseudorapidity. With the help of the established PYTHIA8 tunes to mimic the behavior of flow-like features, we investigated the variation of effective temperature and degree of nonextensivity using thermodynamically consistent nonextensive Tsallis statistics. We further attempted to establish a connection between the initial state and final state by estimating the correlation between the number of multi-partonic interactions ([Formula: see text]) with the Knudsen number.

QCD evolution of entanglement entropy

Entanglement entropy has emerged as a novel tool for probing nonperturbative quantum chromodynamics (QCD) phenomena, such as color confinement in protons. While recent studies have demonstrated its significant capability in describing hadron production in deep inelastic scatterings, the QCD evolution of entanglement entropy remains unexplored. In this work, we investigate the differential rapidity-dependent entanglement entropy within the proton and its connection to final-state hadrons, aiming to elucidate its QCD evolution. Our analysis reveals a strong agreement between the rapidity dependence of von Neumann entropy, obtained from QCD evolution equations, and the corresponding experimental data on hadron entropy. These findings provide compelling evidence for the emergence of a maximally entangled state, offering new insights into the nonperturbative structure of protons.

Sudakov double logs in single-inclusive hadron production in DIS at small x from the color glass condensate formalism

We investigate the high Q2 (photon virtuality) limit of single-inclusive hadron production in deep inelastic scattering at small x, using the color glass condensate formalism at next-to-leading order. We focus on the ΛQCD2≪ph2≪Q2 kinematic regime, where ph is the produced hadron transverse momentum, and extract the Sudakov double logarithms. We further argue that compatibility between the color glass condensate calculation and transverse momentum dependent distribution factorization at one-loop order can only be achieved if the small-x evolution is kinematically constrained. Published by the American Physical Society 2024

Polarized Semi-Inclusive Deep-Inelastic Scattering at Next-to-Next-to-Leading Order in QCD.

Semi-inclusive hadron production in longitudinally polarized deep-inelastic lepton-nucleon scattering is a powerful tool for resolving the quark flavor decomposition of the proton's spin structure. We present the full next-to-next-to-leading order QCD corrections to the coefficient functions of polarized semi-inclusive deep-inelastic scattering (SIDIS) in analytical form, enabling the use of SIDIS measurements in precision studies of the proton spin structure. The numerical impact of these corrections is illustrated by a comparison with data of polarized single-inclusive hadron spectra from the DESY HERMES and CERN COMPASS experiments.

Exploring the photoproduction of ρ and ϕ in hadronic heavy-ion collisions

Significant enhancements of J/ψ production have been observed by various experiments at RHIC and LHC for very low transverse momenta in peripheral heavy-ion collisions, which has ignited a surge of investigations into photon-induced processes in hadronic heavy-ion collisions (HHICs). Within this wave of research enthusiasm, the search for more photon induced products in HHICs becomes paramount. In this paper, we perform the calculation of the ρ and ϕ production resulting from photon-nucleus interactions in HHICs, which are crucial probes for studying the properties of quark-gluon plasma (QGP) in HHICs. Our study reveals that, in comparison to hadronic production, the photon-induced production of ρ and ϕ does not reach the same level of significance as that observed in J/ψ production. Nevertheless, it remains substantial, especially in peripheral collisions, holding great promise for experimental verification in the imminent future.