Particle Yield Ratios Research Articles

Probing configuration of α clusters with spectator particles in relativistic heavy-ion collisions

We propose to use spectator particle yield ratios to probe the configuration of α clusters in 12C and 16O by their ultracentral collisions at RHIC and LHC energies. The idea is illustrated based on initial density distributions with various α-cluster configurations generated by a microscopic cluster model, and without α clusters from mean-field calculations. The multifragmentation of the spectator matter produces more spectator light nuclei including α clusters in collisions of nuclei with chain structure of α clusters, compared to those of nuclei with a more compact structure. The yield ratio of free spectator neutrons to spectator particles with mass-to-charge ratio A/Z=2 scaled by their masses can be practically measured by the zero-degree calorimeter (ZDC) at RHIC and LHC, serving as a clean probe free from modeling the complicated dynamics at midrapidities.

Observation of abnormal suppression of f0(980) production in p–Pb collisions at [formula omitted] = 5.02 TeV

The dependence of f0(980) production on the final-state charged-particle multiplicity in p–Pb collisions at sNN=5.02 TeV is reported. The production of f0(980) is measured with the ALICE detector via the f0(980)→π+π− decay channel in a midrapidity region of −0.5<y<0. Particle yield ratios of f0(980) to π and K⁎(892)0 are found to be decreasing with increasing charged-particle multiplicity. The magnitude of the suppression of the f0(980)/π and f0(980)/K⁎(892)0 yield ratios is found to be dependent on the transverse momentum pT, suggesting different mechanisms responsible for the measured effects. Furthermore, the nuclear modification factor QpPb of f0(980) is measured in various multiplicity ranges. The QpPb shows a strong suppression of the f0(980) production in the pT region up to about 4 GeV/c. The results on the particle yield ratios and QpPb for f0(980) may help to understand the late hadronic phase in p–Pb collisions and the nature of the internal structure of f0(980) particle.

Evolution of midrapidity average transverse momentum of pions, kaons, protons and antiprotons in Au+Au collisions in (snn)1∕2= 7–39-GeV energy range from the beam energy scan program

The [Formula: see text] dependencies of the experimental average transverse momentum, [Formula: see text], of the charged pions, charged kaons, protons and antiprotons produced at midrapidity ([Formula: see text]) in [Formula: see text] collisions from the Beam Energy Scan (BES) program at the RHIC (Relativistic Heavy Ion Collider), measured by STAR Collaboration in the [Formula: see text]–39-GeV energy range, have been described quite well with the power-law model function. We have obtained [Formula: see text] inequality at all BES energies, indicating the clear mass ordering (dependence) of the power parameter [Formula: see text]. On the whole, the exponent parameter [Formula: see text] for the charged kaons as well as (anti)protons decreases noticeably with increasing [Formula: see text] collision energy from [Formula: see text][Formula: see text]GeV to [Formula: see text][Formula: see text]GeV. Drastic change observed in the energy ([Formula: see text]) dependence of the parameter [Formula: see text] for the charged kaons at [Formula: see text][Formula: see text]GeV could possibly indicate a significant change in the mechanism(s) of the charged kaon production in [Formula: see text] collisions at around [Formula: see text][Formula: see text]GeV. Significant change in the [Formula: see text] dependence of the parameter [Formula: see text] for the charged pions observed at around [Formula: see text][Formula: see text]GeV is consistent with a possible change in the mechanism(s) of the particle production in [Formula: see text] collisions at around [Formula: see text][Formula: see text]GeV, reported earlier by STAR Collaboration. Significant gaps between [Formula: see text] (protons) and [Formula: see text] (antiprotons) as well as between ([Formula: see text]) and [Formula: see text] have been seen in the region [Formula: see text]–20[Formula: see text]GeV. These gaps diminish and practically disappear with [Formula: see text] and [Formula: see text] (protons) [Formula: see text] (antiprotons) in the region [Formula: see text][Formula: see text]GeV. Altogether, the findings, regarding collision energy dependencies of the parameter [Formula: see text] for the studied particle species, could indicate the probable phase transition of a nuclear matter to the mixed phase of QGP and hadrons taking place in [Formula: see text] collisions at around [Formula: see text][Formula: see text]GeV. The differences found between parameter [Formula: see text] versus [Formula: see text] dependencies of the particles and antiparticles have been connected with the ratios of antiparticle and particle yields and differences in the mechanisms of production of particles and antiparticles. It is deduced that the exponent parameter [Formula: see text] should be sensitive to the degree of particle (system) thermalization and particle production mechanisms, and its drastic change could be related to the change in the mechanisms of particle production or/and phase transitions in the nuclear/hadronic matter.

Production of strange hadrons in jets and underlying events in pp and p–Pb collisions with ALICE

The production of strange (, Λ) and multi-strange (Ξ± and Ω±) hadrons in jets and underlying events in pp and p–Pb collisions is studied with ALICE at the LHC. Transverse momentum (p T) differential density distribution of particles produced in a jet is compared to that of inclusive particle production and that in underlying events. The particle yield ratios of and as a function of p T are also investigated in jets and underlying events. The production of the multi-strange hadrons, Ξ± and Ω±, and the corresponding ratio in jets and underlying events are measured for the first time. The p T-differential density distribution of hadrons associated with hard scattering decreases slower than that for inclusive production. The baryon-to-meson and baryon-to-baryon ratios measured in jets exhibit clear differences from values obtained from the inclusive spectra in the intermediate p T range. The p T distribution of strange hadrons produced in jets is also studied in pp collisions at and and in p–Pb collisions at . The p T spectra of particle produced in jets are independent of collision systems and collision energies. No apparent collision energy and collision system dependence is observed for the particle yield ratios of and associated with energetic jets. These new results are compared to PYTHIA 8 event generator. The ratio are generally reproduced by the model, but large discrepancies between data and PYTHIA simulations are observed for .

Studying light flavour hadrons produced in the collision of different nuclei at the LHC

The study of identified particle production as a function of event multiplicity is a key tool for understanding the similarities and differences among different colliding systems. Now for the first time, we can investigate how particle production is affected by the collision geometry in heavy-ion collisions at the LHC. In these proceedings, we report newly obtained ALICE results on charged and identified particle production in Pb–Pb and Xe–Xe collision at √SNN = 5.02 and √SNN = 5.44 TeV, respectively, as a function of transverse momentum (pT) and collision centrality. Particle spectra and ratios are compared between two different colliding systems at similar charged-particle multiplicity densities (〈dNch/dη〉), and different initial eccentricities. We find that in central collisions, spectral shapes of different particles are driven by their masses. The pT-integrated particle yield ratios follow the same trends with 〈dNch=dη〉 as previously observed in other systems, further suggesting that at the LHC energies, event hadrochemistry is dominantly driven by the charged-particle multiplicity density and not the collision system, geometry or center-of-mass energy.

Production of light-flavor hadrons in pp collisions at sqrt{s}~=~7text { and }sqrt{s} = 13 , text { TeV}

The production of pi ^{pm }, mathrm{K}^{pm }, mathrm{K}^{0}_{S}, mathrm{K}^{*}(892)^{0}, mathrm{p}, phi (1020), Lambda , Xi ^{-}, Omega ^{-}, and their antiparticles was measured in inelastic proton–proton (pp) collisions at a center-of-mass energy of sqrt{s} = 13 TeV at midrapidity (|y|<0.5) as a function of transverse momentum (p_{mathrm{T}}) using the ALICE detector at the CERN LHC. Furthermore, the single-particle p_{mathrm{T}} distributions of mathrm{K}^{0}_{S}, Lambda , and overline{Lambda } in inelastic pp collisions at sqrt{s} = 7 TeV are reported here for the first time. The p_{mathrm{T}} distributions are studied at midrapidity within the transverse momentum range 0le p_{mathrm{T}}le 20 GeV/c, depending on the particle species. The p_{mathrm{T}} spectra, integrated yields, and particle yield ratios are discussed as a function of collision energy and compared with measurements at lower sqrt{s} and with results from various general-purpose QCD-inspired Monte Carlo models. A hardening of the spectra at high p_{mathrm{T}} with increasing collision energy is observed, which is similar for all particle species under study. The transverse mass and x_{mathrm{T}}equiv 2p_{mathrm{T}}/sqrt{s} scaling properties of hadron production are also studied. As the collision energy increases from sqrt{s} = 7–13 TeV, the yields of non- and single-strange hadrons normalized to the pion yields remain approximately constant as a function of sqrt{s}, while ratios for multi-strange hadrons indicate enhancements. The p_mathrm{{T}}-differential cross sections of pi ^{pm }, mathrm {K}^{pm } and mathrm {p} (overline{mathrm{p}}) are compared with next-to-leading order perturbative QCD calculations, which are found to overestimate the cross sections for pi ^{pm } and mathrm{p} (overline{mathrm{p}}) at high p_mathrm{{T}}.

QCD Critical Point and High Baryon Density Matter

We report the latest results on the search for the QCD critical point in the QCD phase diagram through high energy heavy-ion collisions. The measurements discussed are based on the higher moments of the net-proton multiplicity distributions in heavy-ion collisions. A non-monotonic variation in the product of kurtosis times the variance of the net-proton distribution is observed as a function of the collision energy with 3$\sigma$ significance. We also discuss the results of the thermal model in explaining the measured particle yield ratios in heavy-ion collisions and comparison of the different variants of hardon resonance gas model calculation to the data on higher moments of net-proton distributions. We end with a note that the upcoming programs in high baryon density regime at various experimental facilities will complete the search for the QCD critical point through heavy-ion collisions.

Unified description from small to large colliding systems within dynamical core–corona initialisation

We build the dynamical core–corona initialisation model to perform gradual and multiplicity-dependent generation of quark-gluon plasma (QGP) fluids in high energy nuclear collisions. This model reasonably describes the multiplicity dependence of particle yield ratios measured by ALICE Collaboration. We also find that non-zero fraction of energy in non-single diffractive p+p collision events is converted to the QGP fluid even at the average multiplicity.

Light Particle and Quark Chemical Potentials from Negatively to Positively Charged Particle Yield Ratios Corrected by Removing Strong and Weak Decays

The yield ratios of negatively to positively charged pions (π−/π+), negatively to positively charged kaons (K−/K+), and anti-protons to protons (p¯/p) produced in mid-rapidity interval in central gold-gold (Au-Au) collisions, central lead-lead (Pb-Pb) collisions, and inelastic (INEL) or non-single-diffractive (NSD) proton-proton (pp) collisions, as well as in forward rapidity region in INEL pp collisions are analyzed in the present work. Over an energy range from a few GeV to above 10 TeV, the chemical potentials of light flavor particles (pion, kaon, and proton) and quarks (up, down, and strange quarks) are extracted from the mentioned yield ratios in which the contributions of strong decay from high-mass resonance and weak decay from heavy flavor hadrons are removed. Most energy dependent chemical potentials show the maximum at about 4 GeV, while the energy dependent yield ratios do not show such an extremum.

Hadronization using the Wigner function approach for a multiphase transport model

In the string melting version of a multiphase transport model, the hadronization algorithm has been improved by favoring parton combinations close in not only coordinate space but also momentum space. Formation probabilities of mesons, baryons, and antibaryons during hadronization are determined by their corresponding Wigner functions for the valence parton combinations with no free parameters, and the net baryon, electric, and strangeness charges are conserved during quark coalescence. Effects of the hadronization on anisotropic flows, collision energy dependence of the proton directed flow, relative particle yield ratios, as well as di-hadron correlations in relativistic heavy-ion collisions at the energies ranging from RHIC beam energy scan to LHC have been extensively discussed.

Transverse Momentum Distributions of Pions, Kaons and Protons in p − p Interactions at 2.76 TeV

The spectra and particle yield ratios of π±, K± meson, protons and anti-protons in proton-proton (p − p) interactions at $$ \sqrt{s}=2.76 $$ TeV are presented. CRMC generators: EPOS-LHC, EPOS1.99 and QGSJETII-04, are used for simulations and the results are compared with LHC-CMS experimental data. The particles are identified in the transverse momentum range of pT ≈ 0.1 − 1.7 GeV/c and absolute rapidity, ∣y∣ < 1. In simulation, same cuts in pT and y are used as in the experiment. The EPOS1.99 model predicts the data well as compared to the other two models, which predict in some of the pT regions only. The different models used could not effectively describe the experimental data in all pT range.

Particle decay from statistical thermal model in high-energy nucleus-nucleus collisions

In high energy nucleus-nucleus collisions, it is difficult to measure the contributions of resonance strong decay and weak decay to the final measured hadrons as well as the corresponding effects on some physical observables. To provide a reference from statistical thermal model, we performed a systematic analysis for the energy dependence of particle yield and yield ratios in Au + Au collisions. We found that the primary fraction of final hadrons decreases with increasing collision energy and somehow saturates around $\sqrt{s_\textrm{NN}}$ = 10 GeV, indicating a limiting temperature in hadronic interactions. The fraction of strong or weak decay for final hadrons show a different energy dependence behavior comparing to the primarily produced hadrons. These energy dependences of various particle yield and yield ratios from strong or weak decay can provide us with baselines for many hadronic observables in high energy nucleus-nucleus collisions.

Energy dependence of ϕ(1020) production at mid-rapidity in pp collisions with ALICE at the LHC

Hadronic resonances are unique tools to investigate the interplay of re-scattering and regeneration effects during the hadronization phase in heavy-ion collisions. Measurements in small collision systems provide a necessary baseline for heavy-ion data, help to tune pQCD inspired event generators and give insight into the search for the onset of collective effects. As the ϕ meson has a longer lifetime compared to other resonances, it is expected that its production would be much less affected by regeneration and re-scattering processes. We report on measurements of ϕ meson production in minimum bias pp collisions at different beam energies and as a function of charged particle multiplicity with the ALICE detector at the LHC. The results include the transverse momentum (pT) distributions of ϕ as well as the particle yield ratios. Finally, we have also studied the ϕ effective strangeness content by comparing our results to theoretical calculations.

Chemical Potentials of Light Flavor Quarks from Yield Ratios of Negative to Positive Particles in Au+Au Collisions at RHIC

The transverse momentum spectra of π-, π+, K-, K+, p¯, and p produced in Au+Au collisions at center-of-mass energy sNN=7.7, 11.5, 19.6, 27, 39, 62.4, 130, and 200 GeV are analyzed in the framework of a multisource thermal model. The experimental data measured at midrapidity by the STAR Collaboration are fitted by the (two-component) standard distribution. The effective temperature of emission source increases obviously with the increase of the particle mass and the collision energy. At different collision energies, the chemical potentials of up, down, and strange quarks are obtained from the antiparticle to particle yield ratios in given transverse momentum ranges available in experiments. With the increase of logarithmic collision energy, the chemical potentials of light flavor quarks decrease exponentially.

News from the NA61/SHINE experiment

The main goals of the NA61/SHINE experiment at the CERN SPS are the search for the critical point of strongly interacting matter and the study of the properties of the onset of deconfinement. These aims are pursued by performing a two-dimensional scan of the phase diagram of strongly interacting matter by varying the momentum and size of the colliding nuclei. This contribution summarises the latest results from the NA61/SHINE experiment, in particular, new results on spectra and yields of ϕ meson in p+p interactions at 40, 80 and 158 GeV/c and K+ and K- production in central Be+Be collisions at mid-rapidity. In addition, results on system size dependence of particle yield ratios and fluctuations are presented.

Sensitivity of multiplicity fluctuations to freeze-out conditions in heavy ion collisions

We study the sensitivity of the higher-order moments of produced particle multiplicity distributions to the chemical freeze-out parameters in relativistic heavy ion collisions using the Hadron Resonance Gas (HRG) model. We compare the obtained sensitivity level to the one extracted from the ratios of particle yields. We find that, for certain final state hadrons, the fluctuation measurements add significant information to the determination of the hadro-chemical freeze-out properties of the deconfined phase of matter obtained at RHIC and the LHC.

Higher order fluctuations of strangeness and flavour hierarchy

We present a preliminary analysis on the sensitivity to the chemical freeze-out temperature of higher order moments of strange particle multiplicity distributions in heavy ion collisions. Within the Hadron Resonance Gas (HRG) model we evaluate ratios of cumulants for kaons (K±) and hyperons (Λ, Σ±, Ξ−,0, Ω−) as a function of the temperature and compare them to the sensitivity profiles obtained from ratios of particle yields. We show that ratios of higher order fluctuations of strange baryons could provide a useful tool to extract the range of freeze-out temperature, once experimental data are available. Finally, a connection to lattice data through the fourth to second cumulant ratio is made. The deconfinement transition on the lattice seems to indicate the possibility of a flavour hierarchy, namely strange quarks seem to deconfine at a higher temperature. We would like to test the possibility for the same scenario to occur at the chemical freeze-out and we show how the inclusion of multi-strange baryons in the evaluation of higher order cumulants might provide a sensitive observable to extract the freeze-out temperature.

Role of model ingredients in the production of light particles and entropy

We study the role of different entrance channels and model ingredients on the composite particle yield ratios and entropy production. We find that the composite particle yield ratios show some sensitivity towards equation of state. The Gaussian width of the nucleons affects the production of light charged particles significantly.

Phase-space dependence of particle-ratio fluctuations in Pb + Pb collisions from 20Ato 158A GeV beam energy

A novel approach, the identity method, was used for particle identification and the study of fluctuations of particle yield ratios in Pb+Pb collisions at the CERN Super Proton Synchrotron (SPS). This procedure allows to unfold the moments of the unknown multiplicity distributions of protons (p), kaons (K), pions ($\pi$) and electrons (e). Using these moments the excitation function of the fluctuation measure $\nu_{\text{\text{dyn}}}$[A,B] was measured, with A and B denoting different particle types. The obtained energy dependence of $\nu_{\text{dyn}}$ agrees with previously published NA49 results on the related measure $\sigma_{\text{dyn}}$. Moreover, $\nu_{\text{dyn}}$ was found to depend on the phase space coverage for [K,p] and [K,$\pi$] pairs. This feature most likely explains the reported differences between measurements of NA49 and those of STAR in central Au+Au collisions.

Chemical Potentials of Quarks Extracted from Particle Transverse Momentum Distributions in Heavy Ion Collisions at RHIC Energies

In the framework of a multisource thermal model, the transverse momentum distributions of charged particles produced in nucleus-nucleus (A-A) and deuteron-nucleus (d-A) collisions at relativistic heavy ion collider (RHIC) energies are investigated by a two-component revised Boltzmann distribution. The calculated results are in agreement with the PHENIX experimental data. It is found that the source temperature increases obviously with increase of the particle mass and incident energy, but it does not show an obvious change with the collision centrality. Then, the values of chemical potentials for up, down, and strange quarks can be obtained from the antiparticle to particle yield ratios in a wide transverse momentum range. The relationship between the chemical potentials of quarks and the transverse momentum with different centralities is investigated, too.