The presence of a critical point in the QCD phase diagram can deform the trajectories describing the evolution of the expanding fireball in the $μ_B-T$ phase diagram. If the average emission time of hadrons is a function of transverse velocity, as microscopic simulations of the hadronic freeze-out dynamics suggest, the deformation of the hydrodynamic trajectories will change the transverse velocity ($β_{\rm T}$) dependence of the proton-antiproton ratio when the fireball passes in the vicinity of the critical point. An unusual $β_{\rm T}$-dependence of the $\bar{p}/p$ ratio in a narrow beam energy window would thus signal the presence of the critical point.
We formulate the QCD critical point focusing effect on transverse velocity ($β_{t}$) dependence of antiproton to proton ($\bar{p}/p$) ratio, which was recently proposed by Asakawa {\it et al.} as an experimental signature of QCD critical point in high energy heavy ion collisions (HICs). For quantitative analysis, Ultra-relativistic Quantum Molecular Dynamics (UrQMD) transport model and THERMal heavy-IoN generATOR (THERMINATOR) are applied to calculate the corresponding $β_{t}$ dependence of $\bar{p}/p$ ratio for three gedanken focused isentropic trajectories with different focusing degree on Q…
Coalescence of minijet partons with the partons from the quark-gluon plasma formed in relativistic heavy ion collisions is suggested as the mechanism for production of hadrons with intermediate transverse momentum. The resulting enhanced antiproton and pion yields at intermediate transverse momentum gives a plausible explanation for the observed large antiproton to pion ratio. With further increasing momentum, the ratio is predicted to decrease and approach the small value given by independent fragmentations of minijet partons after their energy loss in the quark-gluon plasma.
The momentum or transverse momentum spectra of antiprotons produced at mid-rapidity in proton-helium ($p$+He), gold-gold (Au+Au), deuton-gold ($d$+Au), and lead-lead (Pb+Pb) collisions over an energy range from a few GeV to a few TeV are analyzed by the Erlang distribution, the inverse power-law (the Hagedorn function), and the blast-wave fit, or the superposition of two-component step function. The excitation functions of parameters such as the mean transverse momentum, initial state temperature, kinetic freeze-out temperature, and transverse flow velocity increase (slightly) from a few GeV t…
We show that the polarized proton-antiproton Drell-Yan process is ideal to probe the pretzelosity distribution ($h_{1T}^\perp$), which is one of the new transverse-momentum-dependent parton distributions of the nucleon. We present predictions of the $\cos(2ϕ+ ϕ_a - ϕ_b)$ asymmetry in the transversely polarized proton-antiproton Drell-Yan process at PAX kinematics and find that the results are significantly larger compared with those of the $\sin(3ϕ_h - ϕ_S)$ asymmetry in the semi-inclusive deep inelastic scattering process at HERMES, COMPASS, and JLab kinematics. We conclude that the $\cos(2ϕ+…
The rapidity dependent directed flow of particles produced in a relativistic heavy ion collision can be generated in the hydrodynamic expansion of a tilted source. The asymmetry of the pressure leads to a build up of a directed flow of matter with respect to the collision axis. The experimentally observed ordering of the directed flow of baryons, pions and antibaryons can be described as resulting from the expansion of a baryon inhomogeneous fireball. An uneven distribution of baryons in the transverse plane leads to an asymmetry in the collective push for protons and antiprotons. Precise meas…
We present predictions of the unweighted and weighted double spin asymmetries related to the transversal helicity distribution $g_{1T}$ and the longitudinal transversity distribution $h_{1L}^\perp$, two of eight leading-twist transverse momentum dependent parton distributions (TMDs) or three-dimensional parton distribution functions (3dPDFs), in the polarized proton-antiproton Drell-Yan process at typical kinematics on the Facility for Antiproton and Ion Research (FAIR). We conclude that FAIR is ideal to access the new 3dPDFs towards a detailed picture of the nucleon structure.
Using a covariant coalescence model, we study hadron production in relativistic heavy ion collisions from both soft partons in the quark-gluon plasma and hard partons in minijets. Including transverse flow of soft partons and independent fragmentation of minijet partons, the model is able to describe available experimental data on pion, kaon, and antiproton spectra. The resulting antiproton to pion ratio is seen to increase at low transverse momenta and reaches a value of about one at intermediate transverse momenta, as observed in experimental data at RHIC. A similar dependence of the antikao…
We investigate the polarization parameters in low-energy antiproton-proton elastic ($\bar{p}p\rightarrow\bar{p}p$) and charge-exchange ($\bar{p}p\rightarrow\bar{n}n$) scattering. The predictions for unmeasured observables are based on our new energy-dependent partial-wave analysis of all antiproton-proton scattering data below 925 MeV/$c$ antiproton laboratory momentum, which gives an optimal description of the existing database. Sizable and remarkable spin effects are observed, in particular for charge-exchange scattering. These result from the spin dependence of the long- and medium-range on…
On the basis of the generalized eikonal approximation we study the exclusive reactions $\bar p d \to J/ψ\, n$ and $\bar p d \to ψ^\prime\, n$ in vicinity of the thresholds for charmonium production on a free proton target. It is shown that the rescattering of the incoming antiproton and outgoing charmonium on the spectator neutron leads to a depletion of the charmonium production at low- and to an enhancement at high transverse momenta. This is in qualitative agreement with previous studies of hard proton knockout in proton-deuteron collisions. We analyze different physical sources of uncertai…
We deduce approximate equations of state from experimental measurements in proton-proton and proton-antiproton collisions. Thermodynamic quantities are estimated combining the measure of average transverse momentum <pt> vs pseudorapidity density dN/deta with the estimation of the interaction region size from measures of Bose Einstein correlation, or from a theoretical model which relates dN/deta to the impact parameter. The results are very similar to theory predictions in case of crossover from hadron gas to quark gluon plasma. According to our analysis, the possible crossover should start at…
An enhanced antiLambda/antiproton ratio in heavy-ion relative to p+p collisions has been proposed as one of the signatures for the Quark-Gluon Plasma (QGP) formation. A significantly large (antiLambda+antiSigma0+1.1*antiSigma-)/antiproton ratio of 3.5 has been observed in the mid-rapidity and low transverse momentum region in central Au+Au collisions at the nucleon-nucleon center-of-mass energy of 4.9 GeV at the Alternating Gradient Synchrotron (AGS). This is an order of magnitude larger than the values in peripheral Au+Au collisions and p+p collisions at the corresponding energy. By using the…
Transverse momentum (mass) spectra of positively and negatively charged pions, positively and negatively charged kaons, protons and antiprotons produced at mid-(pseudo)rapidity in various collisions at high energies are analyzed in this work. The experimental data measured in central gold-gold, central lead-lead, and inelastic proton-proton collisions by several international collaborations are studied. The (two-component) standard distribution is used to fit the data and extract the excitation function of effective temperature. Then, the excitation functions of kinetic freeze-out temperature,…
High-p_T pion and kaon production is studied in relativistic proton-proton, proton-nucleus, and nucleus-nucleus collisions in a wide energy range. Cross sections are calculated based on perturbative QCD, augmented by a phenomenological transverse momentum distribution of partons (``intrinsic k_T''). An energy dependent width of the transverse momentum distribution is extracted from pion and charged hadron production data in proton-proton/proton-antiproton collisions. Effects of multiscattering and shadowing in the strongly interacting medium are taken into account. Enhancement of the transvers…
We present calculations of dilepton and photon spectra for the energy range $E_{\text{lab}}=2-35$ $A$GeV which will be available for the Compressed Baryonic Matter (CBM) experiment at the future Facility for Anti-Proton and Ion Research (FAIR). The same energy regime will also be covered by phase II of the Beam Energy Scan at the Relativistic Heavy-Ion Collider (RHIC-BES). Coarse-grained dynamics from microscopic transport calculations of the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model is used to determine temperature and chemical potentials, which allows for the use of dilepto…
An energy dependence of the mean transverse mass $\langle m_T\rangle$ at mid-rapidity in proton-proton ($p+p$) reactions is studied within the ultra-relativistic quantum molecular dynamics (UrQMD). The UrQMD model predicts a nonmonotonous dependence of $\langle m_T\rangle$ on collision energy for several hadron species: for $π^+$, $p$, $K^+$, and $Λ$ the mean transverse mass has a maximum at the center of mass energy region $5\le \sqrt{s}\le 8$ GeV. These results are a consequence of an interplay of two contributions: 1) excitations and decays of the baryonic resonances $N^*$ and $Δ$; 2) excit…
Transverse momentum spectra of pions, protons and antiprotons in Au+Au collisions at intermediate RHIC energy of $\sqrt{s_{NN}}=62$ GeV are studied in a model that includes both quark coalescence from the dense partonic matter and fragmentation of the quenched perturbative minijet partons. The resulting baryon to meson ratio at intermediate transverse momenta is predicted to be larger than that seen in experiments at higher center of mass energies.
We aggregate the transverse momentum spectra of $J/ψ$ mesons produced in high energy gold-gold (Au-Au), deuteron-gold ($d$-Au), lead-lead (Pb-Pb), proton-lead ($p$-Pb), and proton-(anti)proton ($p$-$p(\overline{p})$) collisions measured by several collaborations at the Relativistic Heavy Ion collider (RHIC), the Tevatron Proton-Antiproton Collider, and the Large Hadron Collider (LHC). The collision energy (the center-of-mass energy) gets involved in a large range from dozens of GeV to 13 TeV (the top LHC energy). We consider two participant or contributor partons, a charm quark and an anti-cha…
The transverse momentum spectra of $J/ψ$, $ψ(2S)$, and $Υ(nS, n=1,2,3)$ produced in proton-proton ($p$+$p$), proton-antiproton ($p$+$\bar{p}$), proton-lead ($p$+Pb), gold-gold (Au+Au), and lead-lead (Pb+Pb) collisions over a wide energy range are analyzed by the (two-component) Erlang distribution, the Hagedorn function (the inverse power-law), and the Tsallis-Levy function. The initial temperature is obtained from the color string percolation model due to the fit by the (two-component) Erlang distribution in the framework of multisource thermal model. The excitation functions of some paramete…
The presence of a critical point in the QCD phase diagram can deform the trajectories describing the evolution of the expanding fireball in the QCD phase diagram. The deformation of the hydrodynamic trajectories will change the transverse velocity dependence of the proton-antiproton ratio when the fireball passes in the vicinity of the critical point. An unusual transverse velocity dependence of the anti-proton/proton ratio in a narrow beam energy window would thus signal the presence of the critical point.
The single-freeze-out model with parametrized hypersurface and flow geometry is employed to analyze the transverse-momentum spectra of hadrons produced in the Pb+Pb collisions at the collision energy of {$\sqrt{s_{\rm NN}}=2.76$ TeV} at the CERN Large Hadron Collider (LHC). With the notable exception for protons and antiprotons, we find a very good agreement between the model results and the data for the measured hadron species. The additional analysis of the HBT radii of pions helps us to select, from several different types of freeze-out studied in this work, the most realistic form of the f…
We present a single-freeze-out model with thermal and geometric parameters dependent on the position within the fireball and use it to describe the rapidity and transverse-momentum spectra of pions, kaons, protons, and antiprotons measured at RHIC at 200 GeV} by BRAHMS. THERMINATOR is used to perform the necessary simulation, which includes all resonance decays. The result of the fit to the data is the expected growth of the baryon and strange chemical potentials with the spatial rapidityα_\parallel. The value of the baryon chemical potential at α_\parallel ~ 3 is about 200 MeV, i.e. lies in t…
We study the scaling regime of nucleon-anti-nucleon annihilation into a deeply virtual photon and a photon or meson, \bar p N -> gamma ^* pi, \bar p N -> gamma ^* gamma, in the forward direction. The leading twist amplitude factorizes into an antiproton distribution amplitude, a short-distance matrix element and a long-distance dominated transition distribution amplitude (TDA) which describes the nucleon to meson or photon transition. The impact representation of this TDA maps out the transverse locations of the small size core and the meson or photon cloud inside the proton.
