arXiv subjects

Alberto Accardi

Publications and source records attributed to Alberto Accardi.

53 records · Page 3Linked to original sources

arXiv2007

Final state interactions and hadron quenching in cold nuclear matter

I examine the role of final state interactions in cold nuclear matter in modifying hadron production on nuclear targets with leptonic or hadronic beams. I demonstrate the extent to which available experimental data in electron-nucleus collisions can give direct information on final state effects in hadron-nucleus and nucleus-nucleus collisions. For hadron-nucleus collisions, a theoretical estimate based on a parton energy loss model tested in lepton-nucleus collisions shows a large effect on mid-rapidity hadrons at fixed target experiments. At RHIC energy, the effect is large for negative rapidity hadrons, but mild at midrapidity. This final state cold hadron quenching needs to be taken into account in jet tomographic analysis of the medium created in nucleus-nucleus collisions.

nucl-th↗

arXiv2007

Multi-nucleon correlations in Deep Inelastic Scattering at large Bjorken xB

Using realistic nuclear many-body wave functions in the collinear factorization framework, we evaluate nuclear Deep Inelastic Scattering at large Bjorken xB, where correlations are needed to exceed the kinematic limits of a single free nucleon. We find that recent experimental data on cross-section ratios from the CLAS collaboration exhibit features that are not reproduced by modern 2- and 3-nucleon correlations in the nuclear wave function. New physical mechanisms are needed to explain data in the 2<xB<3 range.

nucl-th↗

arXiv2006

Formation time scaling and hadronization in cold nuclear matter

I propose a scaling analysis of the hadron multiplicity ratio measured in Deep Inelastic Scattering on nuclear targets as a tool to distinguish energy loss and nuclear absorption effects on hadron suppression in cold nuclear matter. The proposed scaling variable is a function of the hadron fractional energy and of the virtual photon energy. Its functional form, which depends on a parameter λ, can be fixed by general theoretical considerations and encompasses both energy loss and absorption models. The parameter λis fitted to HERMES experimental data and shown to favor prehadron nuclear absorption as leading mechanism for hadron suppression as opposed to quark energy loss.

nucl-th↗

arXiv2006

Hadronization in cold nuclear matter

I review a recently proposed scaling analysis of hadron suppression in Deeply Inelastic Scattering on nuclear targets measured at the HERMES experiment. The analysis can distinguish 2 competing explanations for the observed suppression, namely, quark radiative energy loss with long hadron formation times, and prehadron nuclear absorption with hadronization starting inside the nucleus. Experimental data are shown to favor short formation times and prehadron absorption.

nucl-th↗

arXiv2006

Space-time evolution of hadronization

Beside its intrinsic interest for the insights it can give into color confinement, knowledge of the space-time evolution of hadronization is very important for correctly interpreting jet-quenching data in heavy ion collisions and extracting the properties of the produced medium. On the experimental side, the cleanest environment to study the space-time evolution of hadronization is semi-inclusive Deeply Inelastic Scattering on nuclear targets. On the theoretical side, 2 frameworks are presently competing to explain the observed attenuation of hadron production: quark energy loss (with hadron formation outside the nucleus) and nuclear absorption (with hadronization starting inside the nucleus). I discuss recent observables and ideas which will help to distinguish these 2 mechanisms and to measure the time scales of the hadronization process.

nucl-th↗

arXiv2006

Can we distinguish energy loss from hadron absoprtion?

Knowing whether a hadron is formed inside or outside the nuclear medium is very important for correctly interpreting jet quenching in heavy-ion collisions. The cleanest experimental environment to study the space-time evolution of hadronization is semi-inclusive DIS on nuclear targets. Two frameworks are presently competing to explain the observed attenuation of hadron production: quark energy loss, with hadron formation outside the nucleus, and nuclear absorption with hadronization starting inside the nucleus. I demonstrate that the observed approximate A^(2/3) scaling of experimental data cannot conclusively establish the correctness of either energy loss or absorption.

nucl-th↗

arXiv2005

"Naked" Cronin effect in A+A collisions from SPS to RHIC

Baseline computations of the Cronin effect in nuclear collisions at energies spanning the SPS and the RHIC accelerators are performed in the Glauber-Eikonal model, which ascribes the effect to initial-state incoherent multiple parton scatterings. The model accounts very well for the mid-rapidity Cronin effect in hadron-nucleus collisions in the 27-200 GeV center of mass energy range, and will be extended to nucleus-nucleus collisions. The computations are performed under the assumption that the partons do not interact with the medium produced in the collision. Therefore, medium effects such as energy loss in a Quark-Gluon Plasma may be detected and measured as deviations from the presented baseline computation of the "naked" Cronin effect.

nucl-th↗

arXiv2004

Cronin effect from backward to forward rapidity

I discuss recent experimental data on the Cronin effect in deuteron-gold collisions at the top RHIC energy, in a pseudorapidity range [-2,3]. Two theoretical approaches are compared and contrasted: the pQCD-based Glauber-Eikonal model and Colour Glass Condensate models. Neither can describe the Cronin effect over the whole pseudorapidity interval up to now explored experimentally, its most mysterious and intriguing part being at negative rapidity.

nucl-th↗

arXiv2004

Cronin effect and geometrical shadowing in d+Au collisions: pQCD vs. CGC

Multiple initial state parton interactions in p(d)+A collisions are calculated in a Glauber-Eikonal formalism, which incorporates the competing pattern of low-pT suppression due geometrical shadowing, and a moderate-pT Cronin enhancement of hadron spectra. Dynamical shadowing effects, which are not included in the computation, may be extracted by comparing experimental data to the baseline provided by the Glauber-Eikonal model. Data for neutral pion production at midrapidity show absence of dynamical shadowing in the RHIC energy range, sqrt(s)~20-200 GeV. Recent preliminary data at forward rapidity are addressed, and their interpretation discussed.

nucl-th↗

arXiv2004

Cronin effect vs. geometrical shadowing in d+Au collisions at RHIC

Multiple initial state parton interactions in p(d)+Au collisions are calculated in a Glauber-Eikonal formalism. The convolution of perturbative QCD parton-nucleon cross sections predicts naturally the competing pattern of low-pT suppression due geometrical shadowing, and a moderate-pT Cronin enhancement of hadron spectra. The formal equivalence to recent classical Yang-Mills calculations is demonstrated, but our approach is shown to be more general in the large x>0.01 domain because it automatically incorporates the finite kinematic constraints of both quark and gluon processes in the fragmentation regions, and accounts for the observed spectra in elementary pp-->π+X processes in the RHIC energy range, sqrt{s} = 20-200 GeV. The Glauber-Eikonal formalism can be used as a baseline to extract the magnitude of dynamical shadowing effects from the experimental data at differente centralities and pseudo-rapidities.

nucl-th↗

arXiv2003

An interpretation of saturation phenomena as Glauber-Gribov multiple parton scatterings

We compare two formalism that describe minijet production in pA and AA collisions: pQCD supplemented by Glauber-Gribov multiple semihard parton scatterings (pQCD+Glauber), and the Colour Glass Condensate (CGC). We argue that in a suitable limit they are equivalent to each other, the PQCD+Glauber model being more accurate from a numerical point of view. Finally, we analyze RHIC data on Au-Au integrated charged multiplicities in the pQCD+Glauber framework, and conclude that at least at central rapidity there is no sign of gluon saturation.

nucl-th↗

arXiv2003

Cronin effect in proton-nucleus collisions: a survey of theoretical models

I compare the available theoretical models that describe the Cronin effect on hadron and minijet production in proton-nucleus collisions, pointing out similarities and differences among them. The effect may be summarized by the value of two variables. Their values computed in the different models are compared in the energy range 27.4 GeV - 5500 GeV. Finally, I propose to use the pseudorapidity systematics as a further handle to distinguish among the models.

hep-ph↗

arXiv2003

Hadron production in deep inelastic lepton-nucleus scattering

Predictions for semi-inclusive deep inelastic lepton-nucleus scattering are presented. Both the effects of gluon radiation by the struck quark and the absorption of the produced hadron are considered. The gluon radiation covers a larger window in virtuality $Q^2$ because of the increased deconfinement of quarks inside nuclei. The absorption of hadrons formed inside the nucleus is described with a flavor dependent cross section. Calculations for rescaled fragmentation functions and nuclear absorption are compared with the EMC and HERMES data for N, Cu and Kr targets with respect to the deuteron target. Predictions for Ne and Xe targets in the HERMES kinematic regime are given.

nucl-th↗

arXiv2002

Nuclear modifications of fragmentation functions and rescaling models

We discuss nuclear modification of fragmentation functions in the context of the so-called ``rescaling models''. These models implement partial deconfinement inside nuclei by modifying the fragmentation functions perturbatively. We apply these models to the analysis of nuclear hadron production in deep inelastic scattering processes at the HERMES and EMC experiments.

nucl-th↗

arXiv2001

Initial conditions and charged multiplicities in ultra-relativistic heavy-ion collisions

At ultra-relativistic energies the minijet production in heavy-ion collisions becomes sensitive to semi-hard parton rescatterings in the initial stages of the process. As a result global characteristics of the event, like the initial minijet density, become rather insensitive on the infrared cutoff that separates hard and soft interactions. This allows to define a nearly parameter-free {\it saturation cutoff} at which the initial conditions may be computed. As an application we study the centrality dependence of the charged particle multiplicity, which is compared with present RHIC data and predicted at higher energies.

hep-ph↗

arXiv1997

Renormalization trasformations of the 4D BFYM theory

We study the most general renormalization transformations for the first-order formulation of the Yang-Mills theory. We analyze, in particular, the trivial sector of the BRST cohomology of two possible formulations of the model: the standard one and the extended one. The latter is a promising starting point for the interpretation of the Yang-Mills theory as a deformation of the topological BF theory. This work is a necessary preliminary step towards any perturbative calculation, and completes some recently obtained results.

hep-th↗

arXiv1997

Cohomology and Renormalization of BFYM Theory in three Dimensions

The first order formalism for 3D Yang-Mills theory is considered and two different formulations are introduced, in which the gauge theory appears to be a deformation of the topological BF theory. We perform the quantization and the algebraic analysis of cohomology and renormalization for both the models, which are found to be anomaly free. We discuss also their stability against radiative corrections, giving the full structure of possible counterterms, requiring an involved matricial renormalization of fields and sources.

hep-th↗