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E. G. Ferreiro

Publications and source records attributed to E. G. Ferreiro.

At least 91 records · Page 5Linked to original sources
arXiv2005

Universality of the transverse momentum distributions in the framework of percolation of strings

In the framework of percolation of color sources, the transverse momentum distribution in heavy ion and $p+p$ collisions at all centralities and energies are shown to follow a universal behaviour. The width of the distribution depends on the fluctuations of the number of color sources per cluster. At low densities, there are only independent single color sources, no fluctuations occurs and the distribution is described by a single exponential. At very high densities, only one cluster of many color sources appears and therefore there are not fluctuations either and the hardness of the distribution is suppressed. The Cronin effect in this framework is due to a maximum of the fluctuations which decreases as the density increases. We obtain a good agreement with experimental data including the low $p_T$ behaviour and the spectra for different particles. We show that the transverse momentum and multiplicity distributions are related to each other in a defined way. This point is satisfied by the experimental data on $p+p$ collisions at different energies.

hep-ph↗
arXiv2004

Anomalous suppression of $π^0$ production at large transverse momentum in Au + Au and d + Au collisions at $\sqrt{{\bf s}_{\bf NN}} =$ 200 GeV

We propose a model of suppression of large $p_T$-pions in heavy ion collisions based on the interaction of the large $p_T$ pion with the dense medium created in the collision. The model is practically the same as the one previously introduced to describe $J/ψ$ suppression. Both the $p_T$ and the centrality dependence of the data are reproduced. In deuteron-gold collisions, the effect of the final state interaction with the dense medium turns out to be negligibly small. Here the main features of the data are also reproduced both at mid and at forward rapidities.

hep-ph↗
arXiv2004

Density saturation and the decrease of the normalised width of the multiplicity distribution in high energy pp collisions

It is experimentally observed that the width of the KNO multiplicity distribution --or the negative binomial parameter 1/k-- for pp collisions, in the energy region 10 to 1800 GeV, is an increasing function of the energy. We argue that in models with parton or string saturation such trend will necessary change: at some energy the distribution will start to become narrower. In the framework of percolating strings, we have estimated the change to occur at an energy of the order of 5--10 TeV.

hep-ph↗
arXiv2004

Large transverse momentum suppression of $π^0$'s in Au+Au and d+Au collisions at $\sqrt{s}=200$ GeV

We propose a model of suppression of $π^0$'s based on two different effects: at low $p_T$ we take into account the shadowing corrections, while at large $p_T$ the suppression is produced due to the interaction of the large $p_T$ pion with the dense medium created in the collision. The main features of the data on $AuAu$ and $dAu$ collisions are reproduced both at mid and at forward rapidities.

nucl-th↗
arXiv2003

Transverse momentum fluctuations and percolation of strings

The behaviour of the transverse momentum fluctuations with the centrality of the collision shown by the Relativistic Heavy Ion Collider data is naturally explained by the clustering of color sources. In this framework, elementary color sources --strings-- overlap forming clusters, so the number of effective sources is modified. These clusters decay into particles with mean transverse momentum that depends on the number of elementary sources that conform each cluster, and the area occupied by the cluster. The transverse momentum fluctuations in this approach correspond to the fluctuations of the transverse momentum of these clusters, and they behave essentially as the number of effective sources.

hep-ph↗
arXiv2002

On the jet spectrum in nucleus-nucleus interactions

We derive the inclusive transverse spectrum of minijets in nuclear collisions at very high energies by assuming that the nuclear S-matrix factorizes into a product of elastic S-matrices for elementary partonic collisions. Interference effects and, in particular, the contribution of loop diagrams are fully taken into account in the derivation of the spectrum, which is shown to coincide with the result earlier obtained by superposing the elementary interactions incoherently. A quantitative analysis confirms that the deformation induced by multiple collsions is a large effect at RHIC and LHC energies, for transverse momenta ~ 20 GeV.

hep-ph↗
arXiv2002

Aspects of the unitarized soft multipomeron approach in DIS and diffraction

We study in detail the main features of the unitarized Regge model (CFKS), recently proposed to describe the small-$Q^2$ domain. It takes into account a two-component description with two types of unitarized contributions: one is the multiple Pomeron exchanges contribution, interacting with the large dipole size configurations, and the other one consists on a unitarized dipole cross section, describing the interaction with the small size dipoles. We compare the resulting dipole cross section to that from the saturation model (GBW).

hep-ph↗
arXiv2002

Aspects of the Unitarized Soft Multipomeron Approach in DIS and Diffraction

We study in detail the main features of the unitarized Regge model (CFKS), recently proposed to describe the small-$Q^2$ domain. It takes into account a two-component description with two types of unitarized contributions: one is the multiple pomeron exchange contribution, interacting with the large dipole configurations, and the other one consists of a unitarized dipole cross section, describing the interaction with the small size dipoles. We analyze the ratio between soft and hard pieces as a function of the virtuality, and also compare the resulting dipole cross section to that from the saturation model. Diffraction dissociation is also considered, showing the scaling violations in diffractive DIS and estimating the corresponding logarithmic slope.

hep-ph↗
arXiv2001

Cumulative particle production and percolation of strings

Calculations of the production rate of particles with $x>1$ in nuclear collisions due to the interaction of colour strings are presented. Momentum and colour sum rules are used to determine the fragmentation functions of fused strings. Mechanisms of the string interaction are considered with total and partial overlapping in the transverse plane. The results reveal strong dependence of the chosen mechanism. In the percolation scenario with partial overlapping the $x$-dependence of the production rates agrees well with the existing data. The magnitude of the rates for $π^+$ production is in agreement with experiment. However the rates for the protons are substantially below the data.

hep-ph↗
arXiv2001

$J/Ψ$ suppression at SPS, RHIC and LHC energies and the percolation of strings

We study the enhancement of $c \bar c$ pair production that takes place in central heavy ion collisions due to the formation of clusters of strings. These clusters produce heavy flavors more efficiently due to their higher color. We discuss the competition between this mechanism and the well-known screening of color charge, which, above a critical string density, reduces strongly the probability of binding these $c \bar c$ pairs to form $J/Ψ$ particles. The dependence of $J/Ψ$ suppression on the centrality shows a peak at both RHIC and LHC energies corresponding to the percolation critical density.

hep-ph↗
arXiv2001

DIS data and the problem of saturation in small-x physics

New experimental data from HERA explore the region of very small x and small and moderate $Q^2$. We study the role of unitarity corrections in the description of these data. For that, we propose a model separating the small and large components of the $q\bar q$ fluctuation. This model gives a unified description of total and diffractive production in $γ^*p$ interactions. In this model unitarity corrections are controlled by diffraction data.

hep-ph↗
arXiv2001

J/psi suppression at SPS and RHIC in the comovers approach

The NA50 collaboration data on the $J/ψ$ suppression are compared with the results obtained in a comovers approach based on the Dual Parton Model (DPM). Predictions for the $J/ψ$ suppression versus the charged multiplicity - measured in the rapidity region of the dimuon trigger - are given for SPS and RHIC energies.

nucl-th↗
arXiv2000

Deep Inelastic Scattering Data and the Problem of Saturation in Small-x Physics

We investigate the role of unitarization effects in virtual photon-proton (γ^*p) interactions at small x. The q\bar{q}-fluctuation of the initial photon is separated into a small distance and a large distance component and a model for the unitarization of each component is proposed. The Born approximation for the small size component is calculated using QCD perturbation theory. Reggeon diagram technique is used in order to obtain a self-consistent scheme for both total γ^*p cross section and diffractive production. The model gives a good description of HERA data in the small-x region, with a single Pomeron of intercept 1.2.

hep-ph↗
arXiv2000

A unitary model for structure functions and diffractive production at small x

We propose a unified approach which describes both structure functions in the small-$x$ region and diffractive production in $γ^*p$-interactions. It is shown that the model, based on reggeon calculus and a quark-parton picture of the interaction, gives a good description of available experimental data in a broad region of $Q^2$ (including $Q^2 =0$) with a single Pomeron of intercept $α_P(0) = 1.2$. Predictions for very small $x$ are given and the problem of saturation of parton densities is discussed.

hep-ph↗
arXiv2000

Non-saturation of the J/psi suppression at large transverse energy in the comovers approach

We show that, contrary to recent claims, the $J/ψ$ suppression resulting from its interaction with comovers does not saturate at large transverse energy $E_T$. On the contrary, it shows a characteristic structure - change of curvature near the knee of the $E_T$ distribution - which is due to the $E_T$ (or multiplicity) fluctuation, and agrees with recent experimental results.

hep-ph↗
arXiv1999

Event-by-event fluctuations in heavy-ion collisions and the quark-gluon string model

We apply dynamical string models of heavy-ions collisions at high energies to the analysis of event-by-event fluctuations. Main attention is devoted to a new variable proposed to study "equilibration" in heavy-ions collisions. Recent results of the NA49 collaboration at CERN SPS are compared with predictions of the Quark-Gluon String Model (QGSM), which gives a good description of different aspects of multiparticle production for collisions of nucleons and nuclei. It is shown that the new observable and other results of the NA49 analysis of event-by-event fluctuations are correctly reproduced in the model. We discuss dynamical effects responsible for these fluctuations and give the predictions for p-p, p-Pb and Pb-Pb collisions at RHIC and higher energies.

hep-ph↗
arXiv1999

Baryon and Antibaryon Production in Hadronic and Nuclear Interactions

We introduce a new formulation of the diquark breaking mechanism which describes with no free parameters the huge nuclear stopping observed in central nucleus-nucleus collisions. Supplemented, in the dual parton model, with strings originating from diquark--antidiquark pairs from the nucleon sea, it gives a substantial increase of hyperon and antihyperon yields from $pPb$ to central $PbPb$ collisions. Compared to data, this increase is slightly underestimated for $Λ$'s and $Ξ$'s but is five times too small for $Ω$'s. Introducing final state interactions, a reasonable description of all baryon and antibaryon yields is achieved.

hep-ph↗