Saturation physics and angular correlations at RHIC and LHC

We investigate the angular correlation between pions and photons produced in deuteron-gold collisions at RHIC and proton-lead collisions at LHC using the Color Glass Condensate formalism and make predictions for the dependence of the production cross section on the angle between the pion and photon at different rapidities and transverse momenta. Measuring this dependence would shed further light on the role of high gluon density and saturation dynamics at RHIC and LHC.Comment: 2-column EPJ C format, requires svjour.cls and svepj.clo; 4 pages, 4 figure

Probing colored glass via qqˉq\bar{q} photoproduction

In this paper, we calculate the cross-section for the photoproduction of quark-antiquark pairs in the peripheral collision of ultra-relativistic nuclei, by treating the color field of the nuclei within the Color Glass Condensate model. We find that this cross-section is sensitive to the saturation scale $Q_s^2$ that characterizes the model. In particular, the transverse momentum spectrum of the produced pairs could be used to measure the properties of the color glass condensate.Comment: 25 pages LaTeX document - A reference and some footnotes added (version to appear in Nucl. Phys. A

Quark production in high energy proton-nucleus collisions

In this note, we discuss the problem of quark-antiquark pair production in the framework of the color glass condensate. The cross-section can be calculated in closed form for the case of proton-nucleus collisions, where the proton can be considered to be a dilute object. We find that kt-factorization is broken by rescattering effects.Comment: 6 pages, 3 figures, based on talks given at Hard Probes 2004 by H. Fujii and F. Geli

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 $\gamma-$jet transverse momentum spectrum and correlations are very sensitive to gluon saturation effects in the nucleus.Comment: 15 pages, 2 figure

Dilepton production from the Color Glass Condensate

We consider dilepton production in high energy proton-nucleus (and very forward nucleus-nucleus) collisions. Treating the target nucleus as a Color Glass Condensate and describing the projectile proton (nucleus) as a collection of quarks and gluons as in the parton model, we calculate the differential cross section for dilepton production in quark-nucleus scattering and show that it is very sensitive to the saturation scale characterizing the target nucleus.Comment: 9 pages LaTeX document, 1 postscript figur

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).Comment: 9 pages, no figure

The initial energy density of gluons produced in very high energy nuclear collisions

In very high energy nuclear collisions, the initial energy of produced gluons per unit area per unit rapidity, $dE/L^2/d\eta$, is equal to $f(g^2\mu L) (g^2\mu)^3/g^2$, where $\mu^2$ is proportional to the gluon density per unit area of the colliding nuclei. For an SU(2) gauge theory, we perform a non--perturbative numerical computation of the function $f(g^2\mu L)$. It decreases rapidly for small $g^2\mu L$ but varies only by $\sim 25$%, from $0.208\pm 0.004$ to $0.257\pm 0.005$, for a wide range 35.36--296.98 in $g^2\mu L$, including the range relevant for collisions at RHIC and LHC. Extrapolating to SU(3), we estimate the initial energy per unit rapidity for Au-Au collisions in the central region at RHIC and LHC.Comment: 11 pages, Latex, 3 figures; revised version-includes additional numerical data; reference adde

Prompt photons at RHIC

We calculate the inclusive cross section for prompt photon production in heavy-ion collisions at RHIC energies ($\sqrt{s}=130$ GeV and $\sqrt{s}=200$ GeV) in the central rapidity region including next-to-leading order, $O(\alpha_{em}\alpha_s^2)$, radiative corrections, initial state nuclear shadowing and parton energy loss effects. We show that there is a significant suppression of the nuclear cross section, up to $\sim 30$ at $\sqrt{s}=200$ GeV, due to shadowing and medium induced parton energy loss effects. We find that the next-to-leading order contributions are large and have a strong $p_t$ dependence.Comment: 9 pages, 5 figures, expanded discussion of the K facto