Spacetime picture of baryon stopping in the color-glass condensate

McLerran LD, Schlichting S, Sen S. Spacetime picture of baryon stopping in the color-glass condensate. PHYSICAL REVIEW D. 2019;99(7): 074009.We discuss baryon stopping in the color glass condensate description of high energy scattering. We consider the scattering of a distribution of valence quarks on an ultrarelativistic sheet of colored charge. We compute the distribution of scattered quarks from a composite projectile, and calculate the baryon currents before and after the collisions and on an event by event basis. We obtain simple analytic estimates of the baryon number compression and rapidity shifts, which in the idealized case of plane wave scattering, produce results that agree with considerations of Anishetty-Koehler-McLerra

Gluon radiation from a classical point particle. II. Dense gluon fields

The goal of this paper is to extend the results of [K. Kajantie, L. D. McLerran, and R. Paatelainen, Gluon radiation from a classical point particle, Phys. Rev. D 100, 054011 (2019)., where formulas were derived for gluonic radiation for a high energy nucleus colliding with a classical colored particle. In [K. Kajantie, L. D. McLerran, and R. Paatelainen, Gluon radiation from a classical point particle, Phys. Rev. D 100, 054011 (2019).], we computed the amplitudes for radiation in the fragmentation region of the particle for a dilute gluonic field. In this paper, we compute the radiation by solving the fluctuation equations of the dense background field in a specific gauge, which makes it simple to solve the asymptotic radiation from an initial condition immediately after the passage of the nucleus. We identify and compute two components of gluon radiation, a bulk component which extends to the central region and bremsstrahlung, which may give rise to an experimentally observable intensity peak in the target fragmentation region.The goal of this paper is to extend the results of [K. Kajantie, L. D. McLerran, and R. Paatelainen, Gluon radiation from a classical point particle, Phys. Rev. D 100, 054011 (2019)., where formulas were derived for gluonic radiation for a high energy nucleus colliding with a classical colored particle. In [K. Kajantie, L. D. McLerran, and R. Paatelainen, Gluon radiation from a classical point particle, Phys. Rev. D 100, 054011 (2019)] we computed the amplitudes for radiation in the fragmentation region of the particle for a dilute gluonic field. In this paper, we compute the radiation by solving the fluctuation equations of the dense background field in a specific gauge, which makes it simple to solve the asymptotic radiation from an initial condition immediately after the passage of the nucleus. We identify and compute two components of gluon radiation, a bulk component which extends to the central region and bremsstrahlung, which may give rise to an experimentally observable intensity peak in the target fragmentation region.Peer reviewe

Open and hidden charm production in heavy ion collisions at ultrarelativistic energies

We consider the production of the open charm and J/psi mesons in heavy ion collisions at BNL RHIC. We discuss several recently developed pictures for J/psi production and argue that a measurement at RHIC energies is crucial for disentangling these di erent descriptions

Gluon Bremsstrahlung in Relativistic Heavy Ion Collisions

We study the process $qq\rightarrow qqg$ at lowest order in QCD perturbation theory to understand gluon radiation in the fragmentation region of relativistic heavy-ion collisions. We arrive at a formula for gluon multiplicity that interpolates between $\sim 1/k_{\bot}^2$ behavior at low $k_{\bot}$, to $\sim 1/k_{\bot}^4$ at large $k_{\bot}$.Comment: 5 pages, 2 figures Clarifying paragraphs added to Introduction and Section I

Trace anomaly as signature of conformality in neutron stars

We discuss an interpretation that a peak in the sound velocity in neutron star matter, as suggested by the observational data, signifies strongly-coupled conformal matter. The normalized trace anomaly is a dimensionless measure of conformality leading to the derivative and the non-derivative contributions to the sound velocity. We find that the peak in the sound velocity is attributed to the derivative contribution from the trace anomaly that steeply approaches the conformal limit. Smooth continuity to the behavior of high-density QCD implies that the matter part of the trace anomaly may be positive definite. We discuss a possible implication of the positivity condition of the trace anomaly on the $M$-$R$ relation of the neutron stars.Comment: 6 pages, 3 figure

Predictions for p+Pb at 4.4A TeV to Test Initial State Nuclear Shadowing at energies available at the CERN Large Hadron Collider

Collinear factorized perturbative QCD model predictions are compared for p+Pb at 4.4A TeV to test nuclear shadowing of parton distribution at the Large Hadron Collider (LHC). The nuclear modification factor (NMF), R_{pPb}(y=0,p_T<20 GeV/c) = dn_{p Pb} /(N_{coll}(b)dn_{pp}), is computed with electron-nucleus (e+A) global fit with different nuclear shadow distributions and compared to fixed Q^2 shadow ansatz used in Monte Carlo Heavy Ion Jet Interacting Generator (HIJING) type models. Due to rapid DGLAP reduction of shadowing with increasing Q^2 used in e+A global fit, our results confirm that no significant initial state suppression is expected (R_{pPb} (p_T) = 1 \pm 0.1) in the p_T range 5 to 20 GeV/ c. In contrast, the fixed Q^2 shadowing models assumed in HIJING type models predict in the above p_T range a sizable suppression, R_{pPb} (p_T) = 0.6-0.7 at mid-pseudorapidity that is similar to the color glass condensate (CGC) model predictions. For central (N_{coll} = 12) p+ Pb collisions and at forward pseudorapidity (\eta = 6) the HIJING type models predict smaller values of nuclear modification factors (R_{pPb}(p_T)) than in minimum bias events at mid-pseudorapidity (\eta = 0). Observation of R_{pPb}(p_T= 5-20 GeV/c) less than 0.6 for minimum bias p+A collisions would pose a serious difficulty for separating initial from final state interactions in Pb+Pb collisions at LHC energies.Comment: Revised version accepted for publication; Phys. Rev. C, in press, 16 pages, 4 figures, text modifications, added references, new figure 4, revtex

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 Weizs\"acker-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.Comment: 31 pages, Latex2e, 5 postecript figure included, using epsf, latexsym, amssymb and fancyheading