The vector $U$-bosons, or so called 'dark photons', are one of the possible candidates for the dark matter mediators. We present a procedure to derive theoretical constraints on the upper limit of kinetic mixing parameter $ε^2(M_U)$ from heavy-ion as well as $p+p$ and $p+A$ dilepton data from SIS to LHC energies. Our study is based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which reproduces the measured dilepton spectra in $p+p$, $p+A$ and $A+A$ collisions well. In addition to the different dilepton channels originating from interactions and decays of ordinary Standard Model matter particles (mesons and baryons), we incorporate in the PHSD the decay of hypothetical $U$-bosons to dileptons, $U \to e^+ e^-$, where the $U$-bosons themselves are produced by the Dalitz decay of pions, $η$-mesons, Delta resonances as well as by vector meson and $K^+$ decays. This analysis provides the upper limit on the $ε^2(M_U)$ and can also help to estimate the requested accuracy for future experimental searches of 'light' dark photons by dilepton experiments.
The estimate based on the parton model is made on the rate of production of Super Heavy Particle ( SHP ) in subthreshold collision of heavy ions at LHC. For the one month run of lead-lead collision the yield of 16 TeV particle is of the order of 70 per year.
We present a model for radiative energy loss of heavy quarks in quark gluon plasma which incorporates coherence effects. We then study its consequences on the radiation spectra as well as on the nuclear modification factor of open heavy mesons produced in ultrarelativistic heavy ion collisions.
Some recent experimental results obtained in collisions of heavy nuclei ($\sqrt{s}=200$ GeV) at BNL Relativistic Heavy-Ion Collider (RHIC) are discussed. The probes of dense matter created in heavy-ion collision by quarkonia, $D$ and $B$ mesons containing heavy charm and beauty quarks are considered. The centrality, rapidity and transverse momentum dependences of the nuclear modification factor and elliptic flow coefficient are presented and their possible theoretical interpretation is provided.
The spin and flavor symmetries of the heavy quark effective theory are employed to discuss the exclusive cross sections for pair production of heavy mesons in photon-photon collision. The ratios of the exclusive cross sections for heavy mesons are obtained explicitly and the validity of results is discussed.
A simple geometrical model (often quoted in literature as the Glauber model) of heavy ion collisions is recapitulated. It is shown that the transverse energy distribution of heavy ion collisions follow the geometry of the collision. An extension of the model to include rapidity and transverse mass particle spectra is discussed.
We consider the electromagnetic production of positron and electron in collisions of slow heavy nuclei. This process is dominated by emission of positron, with the electron captured by nucleus.
We review various production mechanisms of photons and small mass dileptons at large transverse momentum in heavy ion collisions at the LHC. Their relevance as a signal for quark-gluon plasma formation is discussed.
We estimate the impact parameter dependence of the production cross section for $η_c$ and $η_b$ mesons in peripheral heavy-ion collisions collisions. Total and elastic $γγ$ cross sections are calculated in an equivalent photon approximation.
From existing hadron and heavy ion collisions data on \bar{p}/p central production we estimate the value of the percolation parameter at RHIC energies.
Recent work on chemical equilibrium in heavy ion collisions is reviewed. The energy dependence of thermal parameters is discussed. The centrality dependence of thermal parameters at SPS energies is presented.
Based on the factorization formalism of nonrelativistic quantum chromodynamics (NRQCD), we calculate the production cross section for the charmonium and the bottomonium produced by the hard photoproduction processes and fragmentation processes in relativistic heavy ion collisions. It is shown that the existing experimental data on heavy quarkonium production at the Large Hadron Collider (LHC) can be described in the framework of the NRQCD formalism, and the phenomenological values of matrix elements for color-singlet and color-octet components give the main contribution. The numerical results …
We discuss the model predictions for antibaryon/baryon production ratios in high energy heavy ion collisions. The role of string junction mechanism of baryon number transfer seems to be very important here and we consider some quantitative results.
We consider (anti-)baryons production in heavy ion collisions as production of topological defects during the chiral phase transition. Non-zero quark masses which explicitly break chiral symmetry supress the (anti-)baryon density. Hardly any (anti-)baryons will be produced in the central rapidity region of a heavy ion collision.
The simple method for simulation of ``thermal'' hadron spectra in ultrarelativistic heavy ion collisions including longitudinal, transverse and elliptic flow is developed. The model is realized as fast Monte-Carlo event generator.
We study the effect of energy loss on charm and bottom quarks in high-energy heavy-ion collisions including hadronization, longitudinal expansion and partial thermalization. We consider in detail the detector geometry and single lepton energy cuts of the ALICE and CMS detectors at the Large Hadron Collider (LHC) to show the large suppression of high $p_T$ heavy quarks and the consequences of their semileptonic decays.
Some topics on heavy-ion collisions are reviewed with emphasis on those which are expected to be specially relevant at the Large Hadron Collider programme.
Various forms of matter may be produced in ultra-relativistic heavy ion collisions. These are the Quark Gluon Plasma, the Color Glass Condensate, the Glasma and Quarkyonic Matter. A novel effect that may be associated with topological charge fluctuations is the Chiral Magnetic Effect. I explain these concepts and explain how they may be seen in ultra-relativistic heavy ion collisions.
The single diffractive cross section for heavy quarks production is calculated in next-no-leading order (NLO) in nucleus-nucleus collisions. Such processes are expected to occur at the LHC. We start using the hard diffractive factorization formalism, taking into account the recent experimental parameterization for the Pomeron Structure Function (DPDF). Absorptive corrections are accounted by the multiple Pomeron contributions considering a gap survival probability, where its theoretical uncertainty for nuclear collisions is discussed. We estimate the diffractive ratios for single diffraction p…
The method for simulation of medium-induced rescattering and energy loss of hard partons in ultrarelativistic heavy ion collisions is developed. The model is realized as fast Monte-Carlo tool implemented to modify standard PYTHIA jet event.
Modelling correlations in heavy ion collisions is reviewed from model independent characterization of the two-particle correlations to Buda-Lund hydro model fits to correlations and spectra in Au + Au collisions at sqrt{s}=130 AGeV at RHIC.
We analyse the cluster structure of the final multihadron states resulting from heavy ion collisions using the concept of Jaynes - Shannon entropy. Further evidence for an interesting differentiation of events is provided.
The method of equivalent quanta is applied both to photon-photon and, by analogy, to double pomeron exchange in heavy-ion collisions. This Weizsäcker-Williams approach is used to calculate production cross sections for the glueball candidate $f_J(1710)$ meson via photon-photon and pomeron-pomeron fusion in peripheral heavy-ion collisions at both RHIC and LHC energies. The impact-parameter dependence for total and elastic cross sections are presented, and are compared to results for proton-proton collisions.
Due to coherence, there are strong electromagnetic fields of short duration in very peripheral heavy ion collisions. They give rise to photon-photon and photon-nucleus collisions with high flux. Photon-photon and photon-hadron physics at various invariant mass scales are discussed.
Combining results on single-particle distributions with those of the Bose-Einstein correlation analysis in the same experiment, the space-time emission function is extracted as a function of time and longitudinal coordinate, as well as a function of transverse coordinates. While the former function resembles a boomerang for both types of collision (only shifted in the time direction due to the larger freeze-out time in heavy-ion collisions), the latter function is Gaussian for heavy-ion collisions, but ring-shaped for hadron-hadron collisions.
We present a simple model with string absorption and percolation to describe the J/psi suppression in heavy ion collisions. The NA50 data are fairly well explained by the model.
Systematic trends of baryon transport, chemical freeze-out, and kinetic freeze-out in high energy nuclear collisions are presented. Further measurements of particles with heavy flavors are proposed in order to shed light on collision dynamics at parton level.
We investigate the impact parameter dependence of the $\cos 4ϕ$ azimuthal asymmetry for electromagnetic lepton pair production in heavy ion collisions. The asymmetry induced by linearly polarized coherent photons exhibits strong impact parameter dependence.
We propose to measure the linear polarization of the external electromagnetic fields of a relativistic heavy ion through azimuthal asymmetries in dilepton production in ultraperipheral collisions. The asymmetries estimated with the equivalent photon approximation are shown to be sizable.
Magnetic monopoles may be produced by the dual Schwinger effect in strong magnetic fields. Today, the strongest known magnetic fields in the universe are produced fleetingly in heavy-ion collisions. We use the complex worldline instanton method to calculate the momentum distribution of magnetic monopoles produced in heavy-ion collisions, in an approximation that includes the effect of the magnetic field to all orders but neglects monopole self-interactions. The result saturates the preparation time-energy uncertainty principle, and yields a necessary ingredient for experimental monopole search…
Current theoretical framework for the calculation of heavy quark production in $γγ$ collisions is reviewed. The importance of including direct photon contributions up to the order $α^2α_s^2$ and of the proper choice of renormalization and factorization scales in the evaluation of $σ(γγ\to Q\bar{Q})$ is emphasized.
The effect of collective potentials on pion spectra in ultrarelativistic heavy ion collisions is investigated. We find the effect of these potential to be very small, too small to explain the observed enhancement at low transverse momenta. (7 figures, bill be send on request)
We study open heavy flavor meson production in proton-nucleus (pA) collisions at RHIC and LHC energies within the Color Glass Condensate framework. We use the unintegrated gluon distribution at small Bjorken's x in the proton obtained by solving the Balitsky-Kovchegov equation with running coupling correction and constrained by global fitting of HERA data. We change the initial saturation scale of the gluon distribution for the heavy nucleus. The gluon distribution with McLerran-Venugopalan model initial condition is also used for comparison. We present transverse momentum spectra of single D …
A rotationally-symmetrical ellipsoidal flow model is proposed for the relativistic heavy-ion collisions and compared with the 14.6 A GeV/c Si-Al and 10.8 A GeV/c Au-Au collision data. The large stopping in the heavier collision system and heavier produced particles is accounted for by using the ellipsoidal flow picture. The central dip in the proton and deuteron rapidity distributions for Si-Al collision are reproduced.
The ratios of particle densities in lead-lead and proton-lead collisions to particle density in proton-proton collision in the central rapidity region at the LHC energy are predicted on the basis of wounded quark-diquark model.
We analyze the centrality dependence of thermal parameters describing hadron multiplicities, hadron spectra and dilepton spectra in heavy-ion collisions at SPS and RHIC energies.
Particle production mechanisms in high-energy heavy-ion collisions are reviewed in connection with recent experimental data from RHIC. Implications on mini-jet production, parton saturation and jet quenching are discussed.
Are heavy quarks produced thermally or only by hard parton collisions? What is the probability that a produced heavy quark or antiquark is observed in a given resonance?
The diffusion coefficients of heavy quarks from the coherent color electromagnetic fields which are generated in the early stage of relativistic heavy-ion collisions are calculated at midrapidity, and compared with those obtained from collisions within a thermalized quark-gluon plasma. The coherent color fields are modeled such that they are initially longitudinal and then become isotropic. We found that the diffusion coefficients from the coherent color fields are larger than those from collisions except for very fast heavy quarks, and the color fields are less effective for heavy-quark energ…
We review the theoretical aspects relevant in the description of high energy heavy ion collisions, with an emphasis on the learnings about the underlying QCD phenomena that have emerged from these collisions.
It is argued that in heavy ion collisions at LHC there could be a sizeable production of baryons containing two or three heavy quarks from statistical coalescence. This production mechanism is peculiar of Quark Gluon Plasma and the predicted rates, in heavy ion collisions at LHC energy, exceed those from a purely hadronic scenario, particularly for Xi_bc and Omega_ccc. Thus, besides the interest in the discovery of these new states, enhanced ratios of these baryons over singly heavy flavoured hadrons, like B or D, in heavy ion collisions with respect to pp at the same energy, would be a clear …
We review our recent results on exclusive production of $μ^+ μ^-$, heavy quark-antiquark, and meson-antimeson pairs in ultraperipheral, ultrarelativistic heavy ion collisions.
Many of the hadron-hadron cross sections required for the study of the dynamics of matter produced in relativistic heavy-ion collisions can be calculated using the quark-interchange model. Here we evaluate the low-energy dissociation cross sections of $J/ψ$, $ψ'$, $χ$, $Υ$, and $Υ'$ in collision with $π$, $ρ$, and $K$, which are important for the interpretation of heavy-quarkonium suppression as a signature for the quark gluon plasma. These comover dissociation processes also contribute to heavy-quarkonium suppression, and must be understood and incorporated in simulations of heavy-ion collisi…
Heavy flavor supplies a chance to constrain and improve the hadronization mechanism. We have established a sequential coalescence model with charm conservation and applied it to the charmed hadron production in heavy ion collisions. The charm conservation enhances the earlier hadron production and suppresses the later production. This relative enhancement (suppression) changes significantly the ratios between charmed hadrons in heavy ion collisions.
This is a review of the Quantum Chromodynamics Cosmological Phase Transitions, the Quark-Gluon Plasma, the production of heavy quark states via p-p collisions and RHIC (Relativistic Heavy Ion Collisions) using the mixed hybrid theory for the $Ψ(2S)$ and $Υ(3S)$ states; and the possible detection of the Quark-Gluon Plasma via heavy quark production using RHIC. Recent research on fragmentation for the production of D mesons is reviewed, as is future theoretical and experimental research on the Collins and Sivers fragmentation functions for pions produced in polarized p-p collisions.
We calculate the centrality dependence of inclusive cross section of large-pT charmed-meson ($D^{0}$, $D^{*}$, $D^{*+}$, and $D_{s}^{+}$) from heavy quark fragmentation by the hard photoproduction processes for the nucleus-nucleus collisions in ultrarelativistic heavy ion collisions. The numerical results indicate that the modification of the hard photoproduction processes cannot be negligible for the charmed-meson production in Au-Au collisions at Relativistic Heavy Ion Collider (RHIC) and Pb-Pb collisions at Large Hadron Collider (LHC).
In this short article we discuss the properties of electromagnetic fields in heavy-ion collisions and consequences for observables. We address quantitatively the issue of the magnetic field lifetime in a collision including the electric and chiral magnetic conductivities. We show that for reasonable parameters, the magnetic field created by spectators in a collision is not modified by the presence of matter. Based on this, we draw definite conclusions on observed effects in heavy-ion collisions.
