arXiv subjects

A. H. Rezaeian

Publications and source records attributed to A. H. Rezaeian.

16 recordsLinked to original sources

arXiv2017

Predictions for Cold Nuclear Matter Effects in $p+$Pb Collisions at $\sqrt{s_{_{NN}}} = 8.16$ TeV

Predictions for cold nuclear matter effects on charged hadrons, identified light hadrons, quarkonium and heavy flavor hadrons, Drell-Yan dileptons, jets, photons, gauge bosons and top quarks produced in $p+$Pb collisions at $\sqrt{s_{_{NN}}} = 8.16$ TeV are compiled and, where possible, compared to each other. Predictions of the normalized ratios of $p+$Pb to $p+p$ cross sections are also presented for most of the observables, providing new insights into the expected role of cold nuclear matter effects. In particular, the role of nuclear parton distribution functions on particle production can now be probed over a wider range of phase space than ever before.

hep-ph↗

arXiv2016

Heavy ions at the Future Circular Collider

The Future Circular Collider (FCC) Study is aimed at assessing the physics potential and the technical feasibility of a new collider with centre-of-mass energies, in the hadron-hadron collision mode, seven times larger than the nominal LHC energies. Operating such machine with heavy ions is an option that is being considered in the accelerator design studies. It would provide, for example, Pb-Pb and p-Pb collisions at sqrt{s_NN} = 39 and 63 TeV, respectively, per nucleon-nucleon collision, with integrated luminosities above 30 nb^-1 per month for Pb-Pb. This is a report by the working group on heavy-ion physics of the FCC Study. First ideas on the physics opportunities with heavy ions at the FCC are presented, covering the physics of the Quark-Gluon Plasma, of gluon saturation, of photon-induced collisions, as well as connections with other fields of high-energy physics.

hep-ph↗

arXiv2016

Predictions for $p+$Pb Collisions at $\sqrt{s_{NN}} = 5$ TeV: Comparison with Data

Predictions made in Albacete {\it et al} prior to the LHC $p+$Pb run at $\sqrt{s_{NN}} = 5$ TeV are compared to currently available data. Some predictions shown here have been updated by including the same experimental cuts as the data. Some additional predictions are also presented, especially for quarkonia, that were provided to the experiments before the data were made public but were too late for the original publication are also shown here.

hep-ph↗

arXiv2013

Predictions for $p+$Pb Collisions at sqrt s_NN = 5 TeV

Predictions for charged hadron, identified light hadron, quarkonium, photon, jet and gauge bosons in p+Pb collisions at sqrt s_NN = 5 TeV are compiled and compared. When test run data are available, they are compared to the model predictions.

hep-ph↗

arXiv2009

Cronin effect for protons and pions in pA collisions

Pions and protons production cross-sections are analyzed in proton-proton and proton-nucleus collisions at the RHIC energy at midrapidity. We employ the pQCD factorization scheme supplemented with the color-dipole formalism to investigate the Cronin effect. We calculate the broadening in the color-dipole approach for different centralities. Our main goal is to investigate, in a parameter-free manner within a unified framework, how much of the cronin effect for both pions and baryons comes from the transverse momentum broadening due to initial partons multi-scatterings. We conclude that final-state effects in pA collisions are important. Uncertainties in nuclear shadowing of various parton distributions and parton fragmentation functions are also discussed.

hep-ph↗

arXiv2009

Direct photons at forward rapidities in high-energy pp collisions

We investigate direct photon production in pp collisions at the energies of RHIC, CDF and LHC, at different rapidities employing various color-dipole models. The cross section peaks at forward rapidities due to the abelian dynamics of photon radiation. This opens new opportunities for measurement of direct photons at forward rapidities, where the background from radiative hadronic decays is strongly suppressed. Our model calculations show that photon production is sensitive to the gluon saturation effects, and strongly depends on the value of the anomalous dimension.

hep-ph↗

arXiv2009

Applied High Energy QCD

These lectures stress the theoretical elements that underlie a wide range of phenomenological studies of high-energy QCD, which include both soft and hard processes. After a brief introduction to the basics of QCD, various aspects of QCD-based phenomenology are covered: colour transparency, hadronization of colour charges, Regge phenomenology, parton model, Bjorken scaling and its violation, DGLAP evolution equation, BFKL formalism, GLR-MQ evolution equation and saturation. In the last part of the lecture, we employ the light-cone dipole formalism to describe deep inelastic lepton scattering, Drell-Yan processes, direct photon production, diffraction, quark and gluon shadowing in nuclei, the Cronin effect and nuclear broadening.

hep-ph↗

arXiv2008

Azimuthal Asymmetry of pions in pp and pA collisions

We investigate the azimuthal asymmetry v2 of produced pions in pp and pA collisions at both RHIC and SPS energies. In our approach, based on the pQCD parton model and the light-cone QCD-dipole formalism, the azimuthal asymmetry results from a correlation between the color-dipole orientation and the impact parameter of the collision. We introduce the color-dipole orientation within an improved Born approximation and the saturation model which satisfies available DIS data, showing that the azimuthal asymmetry of partons and pions is very sensitive to the choice of the model, and that it is reduced in the saturation model. We find that v2 of quarks and gluons in parton-nucleus collisions have very different patterns. The azimuthal asymmetry of gluons in gluon-nucleus collisions can be negative at small transverse momentum, changes the sign and becomes positive at high transverse momentum. The azimuthal asymmetry of quarks in quark-nucleus collisions is positive at all values of transverse momentum. We find that the azimuthal anisotropy v2 of produced pions in both pp and pA collisions is positive, albeit rather small.

hep-ph↗

arXiv2008

Handedness of direct photons

The azimuthal asymmetry of direct photons originating from primary hard scatterings between partons is calculated. This can be accounted for by the inclusion of the color dipole orientation, which is sensitive to the rapid variation of the nuclear profile. To this end we introduce the dipole orientation within the saturation model of Golec-Biernat and Wüsthoff, while preserving all its features at the cross-section level. We show that the direct photon elliptic anisotropy v2 coming from this mechanism changes sign and becomes negative for peripheral collisions, albeit it is quite small for nuclear collisions at the RHIC energy.

hep-ph↗

arXiv2008

Azimuthal Asymmetry of Prompt Photons in Nuclear Collisions

The azimuthal elliptic asymmetry v2 observed in heavy ion collisions, is usually associated with properties of the medium created in the final state. We compute the azimuthal asymmetry which is due to multiple interactions of partons at the initial stage of nuclear collisions, and which is also present in $pA$ collisions. In our approach the main source of azimuthal asymmetry is the combination of parton multiple interactions with the steep variation of the nuclear density at the edge of nuclei. We apply the light-cone dipole formalism to compute the azimuthal asymmetry of prompt photons yield from parton-nucleus, proton-nucleus and nucleus-nucleus collisions at the RHIC energy.

hep-ph↗

arXiv2008

Azimuthal anisotropy of direct photons

The electromagnetic bremsstrahlung produced by a quark interacting with nucleons or nuclei is azimuthally asymmetric. In the light-cone dipole approach this effect is related to the orientation dependent dipole cross section. Such a radiation anisotropy is expected to contribute to the azimuthal asymmetry of direct photons in pA and AA collisions, as well as in DIS and in the production of dileptons.

hep-ph↗

arXiv2007

Direct photons and dileptons via color dipoles

Drell-Yan dilepton pair production and inclusive direct photon production can be described within a unified framework in the color dipole approach. The inclusion of non-perturbative primordial transverse momenta and DGLAP evolution is studied. We successfully describe data for dilepton spectra from 800-GeV pp collisions, inclusive direct photon spectra for pp collisions at RHIC energies $\sqrt{s}=200$ GeV, and for $p\bar{p}$ collisions at Tevatron energies $\sqrt{s}=1.8$ TeV, in a formalism that is free from any extra parameters.

hep-ph↗

arXiv2007

Direct photons at LHC

The DGLAP improved color dipole approach provides a good description of data for inclusive direct photon spectra at the energies of RHIC and Tevatron. Within the same framework we predict the transverse momentum distribution of direct photons at the CERN LHC energies.

hep-ph↗

arXiv2006

Diquark Bose-Einstein Condensation and Nuclear Matter

We study a possible transition between symmetric nuclear matter and the diquark Bose-Einstein condensate (BEC) matter at zero temperature. We find that chiral restoration transition is first order and coincides with deconfinement. We investigate various possible coexistence patterns which may emerge from the first order deconfinement phase transition by assuming different values for the critical deconfinement chemical potential. If deconfinement takes place at higher chemical potential, there exists a mixed phase of nuclear and chirally restored diquark BEC matter. This coexistence region extends over a large density region for a bigger diquark BEC or a weaker diquark-diquark interaction. For model parameters with heavy diquark in vaccum, phase transition to diquark matter becomes of second-order. We also show that in the case of precocious deconfinement, droplets of nucleons and droplets of chirally restored Bose-Einstein condensed diquarks coexist surrounded by non-trivial vacuum. We show that a early deconfinement and a weak repulsive diquark-diquark interaction soften the equation of state. We propose a scenario in which nuclear matter saturates due to the formation of the diquark BEC and deconfinement phenomena. In this picture, instead of repulsive vector-meson exchange the compressibility of the equation of state is related to a repulsive diquark-diquark interaction. In general, we emphasize the importance of a diquark BEC phase at rather low density before quark BCS-pairing transition.

nucl-th↗

arXiv2006

Volume and Quark Mass Dependence of the Chiral Phase Transition

We investigate chiral symmetry restoration in finite spatial volume and at finite temperature by calculating the dependence of the chiral phase transition temperature on the size of the spatial volume and the current-quark mass for the quark-meson model, using the proper-time Renormalization Group approach. We find that the critical temperature is weakly dependent on the size of the spatial volume for large current-quark masses, but depends strongly on it for small current-quark masses. In addition, for small volumes we observe a dependence on the choice of quark boundary conditions.

hep-ph↗

arXiv2001

Trace anomaly and Casimir effect

The Casimir energy for scalar field of two parallel conductor in two dimensional domain wall background, with Dirichlet boundary conditions, is calculated by making use of general properties of renormalized stress tensor.We show that vacuum expectation values of stress tensor contain two terms which come from the boundary conditions and the gravitational background. In two dimensions the minimal coupling reduces to the conformal coupling and stress tensor can be obtained by the local and non-local contribution of the anomalous trace. This work shows that there exists a subtle relation between Casimir effect and trace anomaly in curved space time.

hep-th↗