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Jamal Jalilian-Marian

Publications and source records attributed to Jamal Jalilian-Marian.

70 records · Page 4Linked to original sources
arXiv2002

Photon production in high energy proton-nucleus collisions

We calculate the photon production cross-section in $pA$ collisions under the assumption that the nucleus has reached the saturation regime, while the proton can be described by the standard parton distribution functions. We show that due to the strong classical field $O(1/g)$ of the nucleus, bremsstrahlung diagrams become dominant over the direct photon diagrams. In particular, we show that $γ-$jet transverse momentum spectrum and correlations are very sensitive to gluon saturation effects in the nucleus.

hep-ph↗
arXiv2002

Forward Quark Jets from Protons Shattering the Colored Glass

We consider the single-inclusive minijet cross section in pA at forward rapidity within the Color Glass Condensate model of high energy collisions. We show that the nucleus appears black to the incident quarks except for very large impact parameters. A markedly flatter p_t distribution as compared to QCD in the dilute perturbative limit is predicted for transverse momenta about the saturation scale, which could be as large as Q_s^2 ~ 10 GeV^2 for a gold nucleus boosted to rapidity ~10 (as at the BNL-RHIC).

hep-ph↗
arXiv2002

Polarized Gluon Distribution Function from $η'$ Production

Using the recently proposed $ggη'$ effective vertex, we investigate the production of $η'$ from gluon fusion in polarized pp collisions. We show that by measuring $A_{LL}$ in $η'$ production, one can extract the polarized gluon distribution $ΔG(x,Q^2)$ at $Q^2 \sim 1 \GeV^2$ and in a wide range of x.

hep-ph↗
arXiv2001

Probing Gluons in Nuclei: the Case of $η'$

Using the recently proposed $gg --> eta'$ effective vertex, we investigate the production of $η'$ from gluon fusion in $pA$ collisions. We show that measuring $η'$ production cross-section at moderate $x_{η'}$ yields direct information on the small $x$ gluon distribution function of the nucleus. At RHIC, the smallest accessible $x$ turns out to be $O(10^{-5})$ and at LHC, it is $O(10^{-8})$. Therefore, $η'$ is an excellent probe of the Color Glass Condensate.

hep-ph↗
arXiv2001

Nuclear Effects in Prompt Photon Production at the Large Hadron Collider

We present a detailed study of prompt photon production cross section in heavy-ion collisions in the central rapidity region at energy of $\sqrt{s}=5.5$ TeV, appropriate to LHC experiment. We include the next-to-leading order radiative corrections, $O(α_{em}α_s^2)$, nuclear shadowing and the parton energy loss effects. We find that the nuclear effects can reduce the invariant cross section for prompt photon production by an order of magnitude at $p_t=3$ GeV. We discuss theoretical uncertainties due to parton energy loss and nuclear shadowing parameters. We show that the K-factor, which signifies the importance of next-to-leading order corrections, is large and has a strong $p_t$ dependence.

hep-ph↗
arXiv2000

Wong's equations and the small x effective action in QCD

We propose a new form for the small x effective action in QCD. This form of the effective action is motivated by Wong's equations for classical, colored particles in non-Abelian background fields. We show that the BFKL equation, which sums leading logarithms in x, is efficiently reproduced with this form of the action. We argue that this form of the action may be particularly useful in computing next-to- leading-order results in QCD at small x.

hep-ph↗
arXiv2000

Shadowing of gluons in perturbative QCD: A comparison of different models

We investigate the different perturbative QCD-based models for nuclear shadowing of gluons. We show that in the kinematic region appropriate to RHIC experiment, all models give similar estimates for the magnitude of gluon shadowing. At scales relevant to LHC, there is a sizable difference between predictions of the different models.

hep-ph↗
arXiv1999

Minding one's P's and Q's : from the one loop effective action in quantum field theory to classical transport theory

The one loop effective action in quantum field theory can be expressed as a quantum mechanical path integral over world lines, with internal symmetries represented by Grassmanian variables. In this paper, we develop a real time, many body, world line formalism for the one loop effective action. In particular, we study hot QCD and obtain the classical transport equations which, as Litim and Manuel have shown, reduce in the appropriate limit to the non-Abelian Boltzmann-Langevin equation first obtained by Bödeker. In the Vlasov limit, the classical kinetic equations are those that correspond to the hard thermal loop effective action. We also discuss the imaginary time world line formalism for a hot $ϕ^4$ theory, and elucidate its relation to classical transport theory.

hep-ph↗
arXiv1999

Small x Gluons in Nuclei and Hadrons

We numerically study the effects of high gluon density at small x on the evolution of gluon distribution function in both hadrons and nuclei. Using a newly derived, Wilson renormalization group-based evolution equation which includes n to 1 gluon ladder fusion, we find significant reduction in nuclear gluon distribution function for large nuclei at zero impact parameter at energies relevant for RHIC and LHC experiments.

hep-ph↗
arXiv1998

Unitarization of Gluon Distribution in the Doubly Logarithmic Regime at High Density

We analyze the general nonlinear evolution equations for multi gluon correlators derived in hep-ph/9709432 by restricting ourselves to a double logarithmic region. In this region our evolution equation becomes local in transverse momentum space and amenable to simple analysis. It provides a complete nonlinear generalization of the GLR equation. We find that the full double log evolution at high density becomes strikingly different from its linear doubly logarithmic DGLAP counterpart. An effective mass is induced by the nonlinear corrections which at high densities slows down the evolution considerably. We show that at small values of impact parameter the gluonic density grows as a logarithm of energy. At higher values of impact parameter the growth is faster, since the density of gluons is lower and nonlinearities are less important.

hep-ph↗
arXiv1997

The BFKL Equation from the Wilson Renormalization Group

We discuss the Wilson renormalization group approach to the effective action for low $x$ physics. It is shown that in the linearized, weak field regime the RG equation reduces to the BFKL equation for the evolution of the unintegrated gluon density. We discuss the relation of this approach with that of Lipatov.

hep-ph↗
arXiv1996

Saturation of Gluon Density at Small x

Gluon distribution function at small x is computed using the extended McLerran-Venugopalan model. A lipatov like enhancement is seen as well as a non-trivial transverse momentum dependence which is estimated. It is shown that gluon density saturates at small x which would lead to unitarization of cross sections computed with this distribution function.

hep-ph↗
arXiv1996

The Intrinsic Glue Distribution at Very Small x

We compute the distribution functions for gluons at very small x and not too large values of transverse momenta. We extend the McLerran-Venugopalan model by using renormalization group methods to integrate out effects due to those gluons which generate an effective classical charge density for Weizsäcker-Williams fields. We argue that this model can be extended from the description of nuclei at small x to the description of hadrons at yet smaller values of x. This generates a Lipatov like enhancement for the intrinsic gluon distribution function and a non-trivial transverse momentum dependence as well. We estimate the transverse momentum dependence for the distribution functions, and show how the issue of unitarity is resolved in lepton-nucleus interactions.

hep-ph↗
arXiv1995

The Gluon Propagator in non-Abelian Weizsäcker-Williams fields

We carefully compute the gluon propagator in the background of a non--Abelian Weizsäcker--Williams field. This background field is generated by the valence quarks in very large nuclei. We find contact terms in the small fluctuation equations of motion which induce corrections to a previously incorrect result for the gluon propagator in such a background field. The well known problem of the Hermiticity of certain operators in Light Cone gauge is resolved for the Weizsäcker--Williams background field. This is achieved by working in a gauge where singular terms in the equations of motion are absent and then gauge transforming the small fluctuation fields to Light Cone gauge.

hep-ph↗
arXiv1994

Rare Decays of Z-boson

We study radiative decay modes of the Z-boson into heavy quark bound states. We find that the widths for these decays are extremely small. We conclude that these decays will not be detectable for the time being unless there is a significant increase in the number of Z-bosons produced at the electron- positron colliders.

hep-ph↗