Open and hidden charm production in dA collisions at RHIC and LHC

We discuss aspects of open and hidden charm production in deuterium-nucleus collisions at RHIC and LHC energies. We describe calculations of the total cross section and the charm quark transverse momentum distributions. We next explain how shadowing and moderate nuclear absorption can explain the PHENIX d Au/pp ratios and predict the combined effect of shadowing and absorption in 6.2 TeV d + Pb collisions.Arrival of the final proofs: 28 April 2005     

Midrapidity production of secondaries in pp collisions at RHIC and LHC energies in the quark–gluon string model

We consider the phenomenological implications of the assumption that baryons are systems of three quarks connected through a gluon string junction. The transfer of baryon number in rapidity space due to the string junction propagation is considered in detail. At high energies this process leads to a significant effect on the net baryon production in hN collisions at midrapidities. The numerical results for midrapidity inclusive densities of different secondaries in the framework of the quark–gluon string model are in reasonable agreement with the experimental data. One universal value, λ≃0.25, for the strangeness suppression parameter correctly describes the yield ratios of Λ/p, Ξ/Λ, and Ω/Ξ. The predictions for pp collisions at LHC energies are also presented. PACS 25.75.Dw     

Strange particle production in relativistic nucleus-nucleus collisions at RHIC and LHC energy regions

PACIAE, a parton and hadron cascade model, is utilized to systematically investigate strange particle production and strangeness enhancement in Au＋Au collisions and in Pb＋Pb collisions with the √SNN = 200 GeV at the RHIC and 2.76 TeV at the LHC, respectively. The experimental results at different centralities, using data from the STAR collaboration and the ALICE collaboration, are well described by the PACIAE model. This may represent the importance of the parton and hadron rescatterings, as well as the reduction mechanism for strange quark suppression, that are implemented in the PACIAE model.     

Description of pp collisions at LHC energies

The Monte Carlo version of quark-gluon string model is employed to study the multiplicity, rapidity and pr spectra of particles in pp collisions at energies from √s = 200 GeV to 14 TeV. A good quantitative agreement with the experimental data is found in a broad energy range. It means that the general features of ultrarelativistic pp interactions can be well understood in terms of soft- and hard-Pomeron exchanges. Predictions are made for the top LHC energy √s = 14TeV.     

Photon-photon luminosities in relativistic heavy ion collisions at LHC energies

Effective – luminosities are calculated for various realistic hadron collider scenarios. The main characteristics of photon-photon processes at relativistic heavy-ion colliders are established and compared to the corresponding –-luminosities ate ⁺-e ^– — and future photon linear colliders (PLC). Higher order corrections as well as inelastic processes are discussed. It is concluded that feasible high luminosity Ca–Ca collisions at the Large Hadron Collider (LHC) are an interesting option for – physics up to about 100 GeV – CM energy.     

VISHNU hybrid model for the viscous QCD matter at RHIC and LHC energies

In this proceeding, we briefly describe the viscous hydrodynamics + hadron cascade hybrid model VISHNU for relativistic heavy ion collisions and report the current status on extracting the QGP viscosity from elliptic flow data.     

Charmed hadrons from coalescence plus fragmentation in relativistic nucleus-nucleus collisions at RHIC and LHC

In a coalescence plus fragmentation approach we calculate the heavy baryon/meson ratio and the \(p_T\) spectra of charmed hadrons \(D^{0}\), \(D_{s}\) and \(\varLambda _{c}^{+}\) in a wide range of transverse momentum from low \(p_T\) up to about 10 GeV and discuss their ratios from RHIC to LHC energies without any change of the coalescence parameters. We have included the contribution from decays of heavy hadron resonances and also the one due to fragmentation of heavy quarks which do not undergo the coalescence process. The coalescence process is tuned to have all charm quarks hadronizing in the \(p_T\rightarrow 0\) limit and at finite \(p_T\) charm quarks not undergoing coalescence are hadronized by independent fragmentation. The \(p_T\) dependence of the baryon/meson ratios are found to be sensitive to the masses of coalescing quarks, in particular the \(\varLambda _{c}/D^{0}\) can reach values of about \(\mathrm 1\div 1.5 \) at \(p_T \approx \, 3\) GeV, or larger, similarly to the light baryon/meson ratio like \(p/\pi \) and \(\varLambda /K\), however a marked difference is a quite weak \(p_T\) dependence with respect to the light case, such that a larger value at intermediate \(p_T\) implies a relatively large value also for the integrated yields. A comparison with other coalescence model and with the prediction of thermal model is discussed.     

Electromagnetic interactions at RHIC and LHC

At LHC energies, the Lorentz factor will be 3400 for Pb+Pb collisions, and the electromagnetic interactions will play important roles. The cross sections for the electromagnetic particle productions are very large and cannot be ignored for the lifetimes of the beams and background. In this article, we are going to study some of the electromagnetic processes at the RHIC and the LHC and show the cross section calculations of the electron-positron pair production with the giant dipole resonance of the ions.     

Jet-Photon Production at RHIC and LHC

We calculate the production of prompt and thermal photons which includes the contribution of gluons in relativistic heavy ion collisions with the equilibrium and non-equilibrium quark-gluon plasma. We develop a new thermal jet-photon conversion mechanism which plays a vital role in the low transverse momentum region. The effect of the non-equilibrium quark-gluon plasma enhances the contribution of the thermal photons. The shadowing and iso-spin of the nucleus which can properly estimate the prompt photon production are also considered in our calculation.     

Unified model for small-t and high-t scattering at high energies: predictions at RHIC and LHC

The urgency of predictions in the large-t region at LHC stimulated us to present a unified model of small- and high-t scattering at high energies. Our model is based on safe theoretical ground: analyticity, unitarity, Regge behavior, gluon exchange and saturation of bounds established in axiomatic quantum field theory. We make precise predictions for the behavior of the differential cross sections at high t, the evolution of the dip–shoulder structure localized in the region 0.5 ≲ |t| ≲ 0.8 GeV² and the radical violation of the exponential behavior of the first diffraction cone at small t. PACS  12.40.Nn; 13.75.Cs; 13.85.Dz; 13.85.Lg     

Cold nuclear modifications at RHIC and LHC

We use recent nuclear parton distributions, among them the Hirai — Kumano — Nagai (HKN) and Eskola — Paukkunen — Salgado (EPS08) parameterizations, in our pQCD-improved parton model to calculate the nuclear modification factor, R _AA′ (p _T ), at RHIC and at the LHC. At RHIC, the deuteron-gold nuclear modification factor for pions, measured at p _T ≥ 10 GeV/c in central collisions, appears to deviate more from unity than the model results. The slopes of the calculated R _dAu (p _T ) are similar to the slopes of the PHENIX pion and photon data. At LHC, without final-state effects we see a small enhancement of R _dPb (p _T ) in the transverse momentum range 10 GeV/c ≥ p _T ≥ 100 GeV/c for most parameterizations. The inclusion of final-state energy loss will reduce the R _dPb (p _T ) values.     

Low-mass Drell-Yan pairs at RHIC and LHC

We summarize the calculation of Drell-Yan transverse-momentum distributions using QCD perturbation theory. In particular, the transversemomentum spectrum of low-mass Drell-Yan pairs is calculated with all-order resummation. We demonstrate that the transverse-momentum distribution of low-mass Drell-Yan pairs is an advantageous source of constraints on the gluon distribution and its nuclear dependence. We argue that low-mass Drell-Yan pairs in the forward region provide a good and clean probe of small-x gluons at RHIC and LHC.     

Charmonium dissociation and recombination at RHIC and LHC

Charmonium production at heavy-ion colliders is considered within the comovers-interaction model. The formalism is extended by including possible secondary J/ψ production through recombination and an estimate of recombination effects is made without adjusting the model parameters. The comovers-interaction model also includes a comprehensive treatment of initial-state nuclear effects, which are discussed in the context of such high energies. With these tools, the model properly describes the centrality and the rapidity dependence of experimental data at RHIC energy,  GeV, for both Au+Au and Cu+Cu collisions. Predictions for LHC,  TeV, are presented and the assumptions and extrapolations involved are discussed.     

Direct-photon production in heavy-ion collisions from SPS to RHIC energies

Direct photons are an important tool for the detection of the quark-gluon plasma in ultra-relativistic nucleus-nucleus collisions. Direct-photon measurements were made in Pb + Pb collisions at GeV and in Au + Au collisions at GeV. These results are reviewed and compared with model calculations.Arrival of the final proofs: 9 May 2005PACS: 25.75.DwThis revised version was published online in July 2005 with a correction to the article category and incorporation of the revised date.     

A first look at Au+Au collisions at RHIC energies using the PHOBOS detector

The PHOBOS detector has been used to study Au + Au collisions at√^sNN = 56,130, and 200 GeV Several global observables have been measured and the results are compared with theoretical models. These observables include the charged-particle multiplicity measured as a function of beam energy, pseudo-rapidity, and centrality of the collision. A unique feature of the PHOBOS detector is its almost complete angular coverage such that these quantities can be studied over a pseudo-rapidity interval of |η|≤5.4. This allows for an almost complete integration of the total charged particle yield, which is found to be about N _ch ^tot = 4200 ±470 at √^sNN = 130 GeV and N _ch ^tot = 5300 ±530 at √^sNN = 200 GeV. The ratio of anti-particles to particles emitted in the mid-rapidity region has also been measured using the PHOBOS magnetic spectrometer. Of particular interest is the ratio of anti-protons to protons in the mid-rapidity region, which was found to be (i.e.921-1) at √^sNN = 130 GeV. This high value suggests that an almost baryon-free region has been produced in the collisions.     

High energy Cherenkov gluons at RHIC and LHC

The collective effect of emission by the forward moving partons of high energy Cherenkov gluons in nucleus-nucleus collisions at RHIC and LHC energies is considered. It can reveal itself as peaks in the pseudorapidity distribution of jets at midrapidities, or as a ring-like structure of individual events in event-by-event analysis. The pseudorapidity distribution of centers of dense isolated groups of particles in the HIJING model is determined. It can be considered as the background for Cherenkov gluons. If peaks above this background are found in experiments, they indicate new collective effects. In memory of E.L. Feinberg