46 research outputs found
Has saturation physics been observed in deuteron-gold collisions at RHIC?
In the framework of the recently proposed saturation picture, we examine in a
systematic way whether the nuclear modification factor measured for d-Au
collisions at RHIC may be simply explained. The Cronin peak which is obtained
at mid-rapidity around GeV may be reproduced at the proper
height only by boosting the saturation momentum by an additional nuclear
component as already shown in the literature. In this respect, mid-rapidity
RHIC data cannot necessarily be seen as a probe of the saturation picture. The
large rapidity () region allows us to test the shape of the
unintegrated gluon distribution in the nucleus, investigating various
parameterizations inspired by large rapidity solutions (of the BFKL and) of the
Balitsky-Kovchegov (BK) equation. A satisfactory description of at
RHIC is obtained in the BK picture.Comment: 13 pages, 5 figure
Single Inclusive Hadron Production at RHIC and the LHC from the Color Glass Condensate
Using the unintegrated gluon distribution obtained from numerical simulations
of the Balitsky-Kovchegov equation with running coupling, we obtain a very good
description of RHIC data on single inclusive hadron production at forward
rapidities in both p+p and d+Au collisions. No K-factors are needed for charged
hadrons, whereas for pion production a rapidity independent K-factor of order
1/3 is needed. Extrapolating to LHC energies, we calculate nuclear modification
factors for light hadrons in p+Pb collision, as well as the contribution of
initial state effects to the suppression of the nuclear modification factor in
Pb+Pb collisions.Comment: Abstract and 3 figures modifie
Scaling properties of high p_T inclusive hadron production
We analyze the scaling properties of inclusive hadron production in
proton-proton and in heavy ion collisions from fixed target to collider
energies. At large transverse momentum p_T, the invariant cross section
exhibits a power-like behavior Ed^3\sigma/d^3p\propto p_T^{-n} at fixed
transverse x, x_T=2p_T/\sqrt{s}, and fixed center-of-mass scattering angle
\theta_{cm}. Knowledge of the exponent n allows one to draw conclusions about
the production mechanisms of hadrons, which are poorly known, even at high p_T.
We find that high-p_T hadrons are produced by different mechanisms at
fixed-target and collider energies. For pions, higher-twist subprocesses where
the pion is produced directly dominate at fixed target energy, while
leading-twist partonic scattering plus fragmentation is the most important
mechanism at collider energies. High-p_T baryons on the other hand appear to be
produced by higher-twist mechanisms at all available energies. The higher-twist
mechanism of direct proton production can be verified experimentally by testing
whether high p_T protons are produced as single hadrons without accompanying
secondaries. In addition, we find that medium-induced gluon radiation in heavy
ion collisions can violate scaling.Comment: 14 pages, 3 figure
Interoperability in the OpenDreamKit project : the Math-in-the-Middle approach
OpenDreamKit - "Open Digital Research Environment Toolkit for the Advancement of Mathematics" - is an H2020 EU Research Infrastructure project that aims at supporting, over the period 2015-2019, the ecosystem of open-source mathematical software systems. OpenDreamKit will deliver a flexible toolkit enabling research groups to set up Virtual Research Environments, customised to meet the varied needs of research projects in pure mathematics and applications. An important step in the OpenDreamKit endeavor is to foster the interoperability between a variety of systems, ranging from computer algebra systems over mathematical databases to front-ends. This is the mission of the integration work package. We report on experiments and future plans with the Math-in-the-Middle approach. This architecture consists of a central mathematical ontology that documents the domain and xes a joint vocabulary, or even a language, going beyond existing systems such as OpenMath, combined with specifications of the functionalities of the various systems. Interaction between systems can then be enriched by pivoting around this architecture.Postprin
Constraining the nuclear gluon distribution in processes at RHIC
A systematic determination of the gluon distribution is of fundamental
interest in understanding the parton structure of nuclei and the QCD dynamics.
Currently, the behavior of this distribution at small (high energy) is
completely undefined. In this paper we analyze the possibility of constraining
the nuclear effects present in using the inclusive observables which
would be measured in the future electron-nucleus collider at RHIC. We
demonstrate that the study of nuclear longitudinal and charm structure
functions allows to estimate the magnitude of shadowing and antishadowing
effects in the nuclear gluon distribution.Comment: 6 pages, 3 eps figure
Back-to-Back Correlations of Di-hadrons in dAu Collisions at RHIC
We perform a complete theoretical analysis of the azimuthal angular
correlation of two-hadron productions in the forward collisions at RHIC
in the saturation formalism, and obtain a very good agreement with the
experimental data. It is demonstrated that the suppression and broadening of
the away side peak provide a unique signal for the onset of the saturation
mechanism at small- in a large nucleus. We emphasize that future experiments
of di-hadron correlations in collisions at both RHIC and LHC, and in
collisions at the planned electron-ion collider, shall provide us with a
thorough study and understanding of the strong interaction dynamics in the
saturation regime.Comment: 11 pages and 2 figures;v3 revised and update
Limiting fragmentation in hadron-hadron collisions at high energies
Limiting fragmentation in proton-proton, deuteron-nucleus and nucleus-nucleus
collisions is analyzed in the framework of the Balitsky-Kovchegov equation in
high energy QCD. Good agreement with experimental data is obtained for a wide
range of energies. Further detailed tests of limiting fragmentation at RHIC and
the LHC will provide insight into the evolution equations for high energy QCD.Comment: 28 pages, 10 figures (2 new figures, text slightly expanded, and some
additional references
The saturation scale and its x-dependence from Lambda polarization studies
The transverse polarization of forward Lambda hyperons produced in
high-energy p-A collisions is expected to display an extremum at a transverse
momentum around the saturation scale. This was first observed within the
context of the McLerran-Venugopalan model which has an x-independent saturation
scale. The extremum arises due to the k_t-odd nature of the polarization
dependent fragmentation function, which probes approximately the derivative of
the dipole scattering amplitude. The amplitude changes most strongly around the
saturation scale, resulting in a peak in the polarization. We find that the
observation also extends to the more realistic case in which the saturation
scale Q_s is x dependent. Since a range of x and therefore Q_s values is probed
at a given transverse momentum and rapidity, this result is a priori not
expected. Moreover, the measurement of Lambda polarization over a range of x_F
values actually provides a direct probe of the x dependence of the saturation
scale. This novel feature is demonstrated for typical LHC kinematics and for
several phenomenological models of the dipole scattering amplitude. We show
that although the measurement will be challenging, it may be feasible at LHC.
The situation at RHIC is not favorable, because the peak will likely be at too
low transverse momentum of the Lambda to be a trustworthy measure of the
saturation scale.Comment: 11 pages, 6 figure
The Surprising Transparency of the sQGP at LHC
We present parameter-free predictions of the nuclear modification factor,
R_{AA}^pi(p_T,s), of high p_T pions produced in Pb+Pb collisions at
sqrt{s}_{NN}=2.76 and 5.5 ATeV based on the WHDG/DGLV
(radiative+elastic+geometric fluctuation) jet energy loss model. The initial
quark gluon plasma (QGP) density at LHC is constrained from a rigorous
statistical analysis of PHENIX/RHIC pi^0 quenching data at sqrt{s}_{NN}=0.2
ATeV and the charged particle multiplicity at ALICE/LHC at 2.76 ATeV. Our
perturbative QCD tomographic theory predicts significant differences between
jet quenching at RHIC and LHC energies, which are qualitatively consistent with
the p_T-dependence and normalization---within the large systematic
uncertainty---of the first charged hadron nuclear modification factor,
R^{ch}_{AA}, data measured by ALICE. However, our constrained prediction of the
central to peripheral pion modification, R^pi_{cp}(p_T), for which large
systematic uncertainties associated with unmeasured p+p reference data cancel,
is found to be over-quenched relative to the charged hadron ALICE R^{ch}_{cp}
data in the range 5<p_T<20 GeV/c. The discrepancy challenges the two most basic
jet tomographic assumptions: (1) that the energy loss scales linearly with the
initial local comoving QGP density, rho_0, and (2) that \rho_0 \propto
dN^{ch}(s,C)/dy is proportional to the observed global charged particle
multiplicity per unit rapidity as a function of sqrt{s} and centrality class,
C. Future LHC identified (h=pi,K,p) hadron R^h_{AA} data (together with precise
p+p, p+Pb, and Z boson and direct photon Pb+Pb control data) are needed to
assess if the QGP produced at LHC is indeed less opaque to jets than predicted
by constrained extrapolations from RHIC.Comment: 13 pages, 8 figure
Nuclear shadowing in Glauber-Gribov theory with Q2-evolution
We consider deep inelastic scattering off nuclei in the Regge limit within
the Glauber-Gribov model. Using unitarized parton distribution functions for
the proton, we find sizeable shadowing effects on the nuclear total and
longitudinal structure functions, and , in the low-x limit.
Extending a fan-diagram analysis for the large-mass region of coherent
diffraction off nuclei to high Q2, we also find significant shadowing effects
in this kinematical regime. Finally, we discuss shortcomings of our approach
and possible extensions of the model to other kinematical regimes.Comment: 16 pages, 9 figure