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 $k_{\bot}\simeq 3$ 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 ($\eta\simeq 3$) 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 $R_{CP}$ 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 eAeA 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 $x$ (high energy) is completely undefined. In this paper we analyze the possibility of constraining the nuclear effects present in $xg^A$ 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 $dAu$ 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-$x$ in a large nucleus. We emphasize that future experiments of di-hadron correlations in $pA$ collisions at both RHIC and LHC, and in $eA$ 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, $F_2^A$ and $F_L^A$, 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