Central Rapidity Region Research Articles

Centrality definition in e+A collisions at the Electron-Ion Collider

Abstract In this work, we investigate the feasibility of defining centrality in electron-ion collisions at the Electron-Ion Collider (EIC) by examining the correlation between the impact parameter and several observables, including total energy, total transverse momentum, and total number of particles. Using the BeAGLE Monte Carlo generator, we simulate e+Au and e+Ru collisions at different energies and analyze the correlation between the impact parameter and these observables across different kinematic regions. Our findings indicate that the correlation is weak in the central rapidity region but becomes stronger in the forward and far-forward rapidity regions. However, the correlation is not sufficiently robust to allow for precise centrality determination. We conclude that defining centrality in electron-ion collisions is more challenging than in ion-ion collisions, necessitating further studies to develop a robust centrality definition for the EIC.

Multiplicity distributions in the eikonal and the U -matrix unitarization schemes

The multiplicity distribution of charged particles produced in the central rapidity (|η|<2.5) region is calculated for the eikonal and the U-matrix unitarization schemes using the Abramovsky-Gribov-Kancheli (AGK) cutting rules and compared with the ATLAS 13 TeV data. The data favors the eikonal approach. Published by the American Physical Society 2024

Measurement of inclusive charged-particle jet production in pp and p-Pb collisions at sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s_{\ extrm{NN}}} $$\\end{document} = 5.02 TeV

Measurements of inclusive charged-particle jet production in pp and p-Pb collisions at center-of-mass energy per nucleon-nucleon collision sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s_{\ extrm{NN}}} $$\\end{document} = 5.02 TeV and the corresponding nuclear modification factor RpPbchjet\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {R}_{\ extrm{pPb}}^{\ extrm{ch}\\ \ extrm{jet}} $$\\end{document} are presented, using data collected with the ALICE detector at the LHC. Jets are reconstructed in the central rapidity region |ηjet| < 0.5 from charged particles using the anti-kT algorithm with resolution parameters R = 0.2, 0.3, and 0.4. The pT-differential inclusive production cross section of charged-particle jets, as well as the corresponding cross section ratios, are reported for pp and p-Pb collisions in the transverse momentum range 10 <pT,jetch\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {p}_{\ extrm{T},\ extrm{jet}}^{\ extrm{ch}} $$\\end{document}< 140 GeV/c and 10 <pT,jetch\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {p}_{\ extrm{T},\ extrm{jet}}^{\ extrm{ch}} $$\\end{document}< 160 GeV/c, respectively, together with the nuclear modification factor RpPbchjet\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {R}_{\ extrm{pPb}}^{\ extrm{ch}\\ \ extrm{jet}} $$\\end{document} in the range 10 <pT,jetch\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {p}_{\ extrm{T},\ extrm{jet}}^{\ extrm{ch}} $$\\end{document}< 140 GeV/c. The analysis extends the pT range of the previously-reported charged-particle jet measurements by the ALICE Collaboration. The nuclear modification factor is found to be consistent with one and independent of the jet resolution parameter with the improved precision of this study, indicating that the possible influence of cold nuclear matter effects on the production cross section of charged-particle jets in p-Pb collisions at sNN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s_{\ extrm{NN}}} $$\\end{document} = 5.02 TeV is smaller than the current precision. The obtained results are in agreement with other minimum bias jet measurements available for RHIC and LHC energies, and are well reproduced by the NLO perturbative QCD Powheg calculations with parton shower provided by Pythia8 as well as by Jetscape simulations.

Correlation of the hyperon potential stiffness with hyperon constituents in neutron stars and heavy-ion collisions

The breaking of SU(6) symmetry to a more general flavor SU(3) symmetry could serve as a potential explanation for the “hyperon puzzle” of neutron stars by adjusting the hyperon potentials. Specifically, when the soft relativistic mean-field (RMF) Λ hyperon potentials fall within the domains of chiral SU(3) interactions NLO13 with two-body forces, the maximum mass of neutron stars is expected to be lower than 2.0 M⊙, whereas it can exceed 2.0M⊙ if the RMF Λ hyperon potentials are sufficiently stiff to be consistent with those from chiral SU(3) interactions NLO13 with three-body forces. In our investigation involving these two types of Λ hyperon potentials, we explore how the hyperon yields and flows are affected in heavy-ion collisions. We find that the inclusion of hyperon potentials results in better agreement of the Λ directed flows with data but without clear differentiation in the stiffness of the hyperon potentials. Similarly negligent is the disparity in the rapidity distributions of the Λ collective flows predicted by the stiff and soft hyperon potentials. In contrast, the Λ collective flows beyond the central rapidity region turn out to be sensitive to the stiffness of the RMF equation of state (EOS) with the preference of a soft RMF EOS to a stiff one. Notably, the transverse momentum distributions of Λ hyperon production are sensitive to both the stiffness of the RMF EOS and Λ hyperon potential at high transverse momenta.

The Yield Ratio of Anti-Nuclei and Nuclei in Relativistic Nuclear Collisions in the Central Rapidity Region

This article describes calculations of the yield ratio of anti-particles to the yield of particles ($\bar{p}/p$, $\bar{d}/d$,$\overline{^{3}\mathrm{He}}$/$^{3}$He) in proton-proton and nuclear-nuclear interactions using the self-similarity parameter in the central rapidity region. The used approach is based on the study of relativistic nuclear interactions in the four-velocity space. The results of the calculations are compared with the existing experimental data in a wide center-of-mass energy range ($SPS$, $RHIC$, $LHC$). Within this approach the inclusive spectra of pions and kaons and ratios of their yields in $pp$ collisions have been successfully described earlier.

Measurement of inclusive charged-particle b-jet production in pp and p-Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV

A measurement of the inclusive b-jet production cross section is presented in pp and p-Pb collisions at sqrt{s_{mathrm{NN}}} = 5.02 TeV, using data collected with the ALICE detector at the LHC. The jets were reconstructed in the central rapidity region |η| < 0.5 from charged particles using the anti-kT algorithm with resolution parameter R = 0.4. Identification of b jets exploits the long lifetime of b hadrons, using the properties of secondary vertices and impact parameter distributions. The pT-differential inclusive production cross section of b jets, as well as the corresponding inclusive b-jet fraction, are reported for pp and p-Pb collisions in the jet transverse momentum range 10 ≤ pT,ch jet≤ 100 GeV/c, together with the nuclear modification factor, {R}_{mathrm{pPb}}^{mathrm{b}-mathrm{jet}} . The analysis thus extends the lower pT limit of b-jet measurements at the LHC. The nuclear modification factor is found to be consistent with unity, indicating that the production of b jets in p-Pb at sqrt{s_{mathrm{NN}}} = 5.02 TeV is not affected by cold nuclear matter effects within the current precision. The measurements are well reproduced by POWHEG NLO pQCD calculations with PYTHIA fragmentation.

Continuous evolution of electromagnetic field in heavy-ion collisions

In relativistic heavy-ion collisions the electromagnetic field exists before the hot nuclear matter emergence. Requiring the field continuity we compute it in the central rapidity region by taking into account the electromagnetic response of the Quark Gluon Plasma. We show that the electromagnetic field is nearly time-independent from about 1 fm/c after the collision until the freezeout. In particular, its value is about 10% of the initial magnitude of the magnetic field. Our result provides a theoretical basis for the common assumption that the electromagnetic field produced in relativistic heavy-ion collisions varies slowly with time.

Coherent mathrm{J}/psi \xa0and {uppsi '}\xa0photoproduction at midrapidity in ultra-peripheral Pb\u2013Pb \xa0collisions at sqrt{s_{mathrm {NN}}}~=~5.02\xa0TeV

The coherent photoproduction of mathrm{J}/psi and {uppsi '} mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy sqrt{s_{mathrm {NN}}}~=~5.02 TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The mathrm{J}/psi is reconstructed using the dilepton (l^{+} l^{-}) and proton–antiproton decay channels, while for the {uppsi '} the dilepton and the l^{+} l^{-} pi ^{+} pi ^{-} decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 mu {mathrm{b}}^{-1}. The results are compared with theoretical models for coherent mathrm{J}/psi and {uppsi '} photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken-x of around 6times 10^{-4}, such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent mathrm{J}/psi cross section including ALICE measurements at forward rapidity. The ratio of {uppsi '} to mathrm{J}/psi coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.

Cosmological particle creation in the little bang

Particle production by expanding in the future light cone scalar quantum field is studied by assuming that the initial state is associated with the quasiequilibrium statistical operator corresponding to fluid dynamics. We calculate particle production from a longitudinally boost-invariant expanding quantum field designed as a simple but reliable model for the central rapidity region of a relativistic collision. Exact diagonalization of the model is performed by introducing a notion of quasiparticles.

First measurement of the |t|-dependence of coherent J/ψ photonuclear production

The first measurement of the cross section for coherent J/ψ photoproduction as a function of |t|, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02TeV with the J/ψ produced in the central rapidity region |y|<0.8, which corresponds to the small Bjorken-x range (0.3−1.4)×10−3.The measured |t|-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky–Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken-x.

Study of K*(892)0 and ϕ (1020) meson production in proton–proton and Pb–Pb collisions at = 2.76 TeV

In this paper, we describe a study of charged particle yield as a function of p T for K *(892)0 and ϕ (1020) mesons in proton–proton (pp) and Pb–Pb collisions at = 2.76 TeV in the central rapidity region of ∣y∣ < 0.5, in a p T range of 0 < p T < 15 GeV c −1 in pp collisions and in a p T range of 0 < p T < 20 GeV c −1 in Pb-Pb collisions. We also investigated a very important ratio, the nuclear modification factor, to study the effects of the medium in the most central region, i.e. 0%–5% centrality. For data simulation, we used the EPOS-LHC and EPOS-1.99 models. To check the validity of these models’ simulations, we compared the data obtained from these Monte Carlo simulation programs with ALICE experimental data for = 2.76 TeV. It was concluded that the models’ predictions for the ϕ-meson in pp and for the most central Pb-Pb collisions disagreed with the ALICE data, and that the difference increased with p T . This may be connected with the essential role of collective parton behaviors which could not have been taken into account by the models. For K *0 mesons, both programs gave almost the same predictions, and with p T in the interval p T > 3 GeV c −1, the predictions were very close to the experimental data. Both models gave higher predictions for the soft p T interval and lower predictions for the hard interactions. The values of the R AA distributions were lower than unity and both models were very close to the ALICE data. It is very interesting that the models were not able to describe the p T distributions, but they gave good predictions for their ratios. This may possibly be due to parton collective behaviors. We observed some additional suppression of K ∗0 at low values of p T with respect to ϕ-mesons, which may be related to the role of the masses of the particles in soft interactions. The rising trend for R AA in the region from p T = 10 GeV c −1 to 20 GeV c −1 observed by the ALICE experiment was absent for the ϕ-mesons.

Influence of electromagnetic fields in proton-nucleus collisions at relativistic energy

We study proton-gold collisions at RHIC energy $\sqrt{s_{NN}}=200$ GeV within the Parton-Hadron-String Dynamics (PHSD) off-shell transport approach, investigating the influence of the intense electromagnetic fields generated in these small systems. We show the space-time evolution of the magnetic and electric components, emphasizing the huge values of the latter one, in particular the electric field $E_x$ along the impact parameter direction whose magnitude is comparable to the magnetic field $B_y$ perpendicular to the reaction plane. We find a fair agreement of the charged particle pseudorapidity density of the high-multiplicity events with respect to the experimental result of the PHENIX Collaboration. Focusing on the most central collision, we show rapidity distributions and spectra as well as the flow coefficients $v_1$ and $v_2$ and we discuss the impact of the electromagnetic fields on identified particle observables. We compute the directed flow $v_1$ of $\pi^+$, $\pi^-$, $K^+$, $K^-$ for collisions at fixed impact parameter and predict that an electromagnetically-induced splitting in the $v_1$ of positively and negatively charged particles is generated in the Au-going side of p+Au reaction mainly driven by the huge $E_x$ component. We find that this effect is stronger for the strange mesons and increases for increasing impact parameter. Furthermore, we highlight the amount of directed flow generated in the deconfined phase, finding that it constitutes the main contribution in the central rapidity region, especially for kaons. Thus, we support the idea that the directed flow is a promising probe for the electromagnetic fields generated in relativistic nuclear collisions and show that in proton-induced reactions the electric component along the impact parameter axis is the primary origin of a charge-odd $v_1$ of pions and kaons.

Femtoscopy of stopped protons

The longitudinal proton-proton femtoscopy (HBT) correlation function, based on the idea that in a heavy ion collision at $\sqrt{s} \lesssim 20$ GeV stopped protons are likely to be separated in configuration space, is evaluated. It shows a characteristic oscillation which appears sufficiently pronounced to be accessible in experiment. The proposed measurement is essential for estimating the baryon density in the central rapidity region, and can be also viewed as an (almost) direct verification of the Lorentz contraction of the fast-moving nucleus.

Large baryon densities achievable in high-energy heavy-ion collisions outside the central rapidity region

Nuclei are nearly transparent to each other when they collide at high energy, but the collisions do produce high energy density matter in the central rapidity region where most experimental measurements are made. What happens to the receding nuclear fireballs? We calculate the energy loss of the nuclei using the color glass condensate model. We then use a simple space-time picture of the collision to calculate the baryon and energy densities of the receding fireballs. For central collisions of large nuclei at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider we find baryon densities more than ten times that of normal nuclear matter. These results provide initial conditions for subsequent hydrodynamic evolution and could test the equation of state at very high baryon densities.

High Baryon Densities Achieveable at RHIC and LHC

In high energy collisions nuclei are practically transparent to each other but produce very hot, nearly baryon-free, matter in the central rapidity region. Where do the baryons go? We calculate the energy loss of the nuclei using the color glass condensate model. Using a space-time picture of the collision we calculate the baryon and energy densities of the receding baryonic fireballs. For central collisions of large nuclei at RHIC and LHC we find baryon densities more than ten times that of atomic nuclei over a large volume which appear at high rapidities. These results can and are being used as initial conditions for subsequent hydrodynamic evolution and could test the equation of state of matter at very high baryon densities.

Analytical description of hadron production in hadron-hadron and nuclear-nuclear collisions in the mid-rapidity region

It is shown that the inclusive spectra of the produced hadrons in hadron-hadron and nuclear-nuclear collisions can be presented as the universal function dependent of the self-similarity parameter in the analytical form. The article gives a description of the self-similarity parameter depending on the rapidity in the mid-rapidity region. The experimental data are in good agreement with the results of our calculations in a wide energy range from a few GeV to a few TeV in the central rapidity region.

Longitudinal dynamics of high baryon density matter in high-energy heavy-ion collisions

In high energy heavy-ion collisions, the two colliding nuclei pass through each other leaving behind an almost baryon free central rapidity region. Most of the baryons are carried away by the nuclear remnants and are located in the so-called fragmentation regions. In previous papers \cite{Li:2016wzh,Li:2018ini}, it has been argued that very high baryon densities, more than ten times larger than the normal nuclear density, can be achieved in these fragmentation regions. In this paper, we assume the high baryon density matter is thermalized at the same time as the baryon-free quark-gluon plasma in the central rapidity region. We perform a 1+1D (temporal + longitudinal) hydrodynamic simulation covering both the fragmentation regions and the central rapidity region with the baryon diffusion equation included. Baryons are found to diffuse from the fragmentation regions to the central rapidity region driven by fugacity gradients. The baryon chemical potential at freezeout monotonically increases from the central rapidity region to the fragmentation regions, suggesting a rapidity scan in high energy heavy-ion collisions might be helpful in searching for the critical point of the QCD phase diagram.

Description of ϕ-meson production in hadronic and nuclear collisions at very high energies

We expose the current experimental and theoretical situation of the interesting case of the production of [Formula: see text] mesons in up to very high energy collisions of hadrons on both nucleon and nuclear targets, and we present a quantitatively good theoretical description of the corresponding experimental data, based on the formalism of the well established Quark–Gluon String Model, that has proved to be valid for a wide energy range. All the available experimental data for [Formula: see text]-meson production in hadron–nucleon collisions on the spectra of secondary [Formula: see text], and on the ratios of [Formula: see text] and [Formula: see text] production cross-sections, as well the corresponding ones for [Formula: see text]-meson production on nuclear targets, are considered. In particular, it is seen that the production of [Formula: see text]-mesons on nuclear targets presents unusually small shadow corrections for the inclusive density in the central rapidity region.

Production of single-charm hadrons by the quark-combination mechanism in p -Pb collisions at sNN=5.02 TeV

If QGP-like medium is created in $p$-Pb collisions at extremely high collision energies, charm quarks that move in the medium can hadronize by capturing the co-moving light quark(s) or anti-quark(s) to form the charm hadrons. Using light quark $p_{T}$ spectra extracted from the experimental data of light-flavor hadrons and a charm quark $p_{T}$ spectrum that is consistent with perturbative QCD calculations, the central-rapidity data of $p_{T}$ spectra and the spectrum ratios for $D$ mesons in the low $p_{T}$ range ($p_{T}\lesssim7$ GeV/$c$) in minimum-bias $p$-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV are well described by quark combination mechanism in equal-velocity combination approximation. The $\Lambda_{c}^{+}/D^{0}$ ratio in quark combination mechanism exhibits the typical increase-peak-decrease behavior as the function of $p_{T}$, and the shape of the ratio for $p_{T}\gtrsim3$ GeV/$c$ is in agreement with the data of ALICE collaboration in central rapidity region $-0.96<y<0.04$ and the preliminary data of LHCb collaboration in forward rapidity region $1.5<y<4.0$. The global production of single-charm baryons is quantified using the data and the possible enhancement (relative to light flavor baryons) is discussed. The $p_{T}$ spectra of $\Xi_{c}^{0}$, $\Omega_{c}^{0}$ in minimum-bias events and those of single-charm hadrons in high-multiplicity event classes are predicted, which serves as the further test of the possible change of the hadronization characteristic for low $p_{T}$ charm quarks in the small system created in $p$-Pb collisions at LHC energies.

N3LO corrections to jet production in deep inelastic scattering using the Projection-to-Born method

Computations of higher-order QCD corrections for processes with exclusive final states require a subtraction method for real-radiation contributions. We present the first-ever generalisation of a subtraction method for third-order (N3LO) QCD corrections. The Projection-to-Born method is used to combine inclusive N3LO coefficient functions with an exclusive second-order (NNLO) calculation for a final state with an extra jet. The input requirements, advantages, and potential applications of the method are discussed, and validations at lower orders are performed. As a test case, we compute the N3LO corrections to kinematical distributions and production rates for single-jet production in deep inelastic scattering in the laboratory frame, and compare them with data from the ZEUS experiment at HERA. The corrections are small in the central rapidity region, where they stabilize the predictions to sub per-cent level. The corrections increase substantially towards forward rapidity where large logarithmic effects are expected, thereby yielding an improved description of the data in this region.