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R. Ugoccioni

Publications and source records attributed to R. Ugoccioni.

At least 19 recordsLinked to original sources
arXiv2007

On Statistical Mechanics Developments of Clan Concept in Multiparticle Production

Clan concept has been introduced in multiparticle dynamics in order to interpret the wide occurrence of negative binomial (NB) regularity in n-charged particle multiplicity distributions (MDs) in various high energy collisions. The centrality of clan concept led to the attempt to justify its occurrence within a statistical model of clan formation and evolution. In this framework all thermodynamical potentials have been explicitly calculated in terms of NB parameters. Interestingly it was found that NB parameter k corresponds to the one particle canonical partition function. The goal of this paper is to explore a possible temperature and volume dependence of parameter k in various classes of events in high energy hadron-hadron collisions. It is shown that the existence of a phase transition at parton level from the ideal clan gas associated to the semihard component with k>1 to the ideal clan gas of the hard component with k<1 implies a discontinuity in the average number of particles at hadron level.

hep-ph↗
arXiv2006

Maps of zeroes of the grand canonical partition function in a statistical model of high energy collisions

Theorems on zeroes of the truncated generating function in the complex plane are reviewed. When examined in the framework of a statistical model of high energy collisions based on the negative binomial (Pascal) multiplicity distribution, these results lead to maps of zeroes of the grand canonical partition function which allow to interpret in a novel way different classes of events in pp collisions at LHC c.m. energies.

hep-ph↗
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

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

Clan structure analysis and QCD parton showers in multiparticle dynamics. An intriguing dialog between theory and experiment

This paper contains a review of the main results of a search of regularities in collective variables properties in multiparticle dynamics, regularities which can be considered as manifestations of the original simplicity suggested by QCD. The method is based on a continuous dialog between experiment and theory. The paper follows the development of this research line, from its beginnings in the seventies to the current state of the art, discussing how it produced both sound interpretations of the most relevant experimental facts and intriguing perspectives for new physics signals in the TeV energy domain.

hep-ph↗
arXiv2003

Signals of new physics in global event properties in pp collisions in the TeV energy domain: rapidity intervals

The study of possible new physics signals in global event properties in pp collisions in the TeV energy domain is extended from full phase-space to rapidity intervals experimentally accessible at LHC. The elbow structure in the total multiplicity distribution predicted in full phase-space is clearly present also in restricted rapidity intervals, leading to very strong charged particle correlations. It is also found that energy densities comparable to those reached in heavy ion collisions at RHIC could be attained in pp collisions at LHC.

hep-ph↗
arXiv2003

On signals of new physics in global event properties in pp collisions in the TeV energy domain

In the framework of the weighted superposition mechanism of different classes of minimum bias events (or substructures), described by the negative binomial multiplicity distribution, in possible scenarios for pp collisions in the TeV energy domain, we explore global properties of an eventual new class of events, characterised by high hadron and clan densities, to be added to the soft (without minijets) and semihard (with minijets) ones. It turns out that the main signal of the mentioned new physical expectations at 14 TeV c.m. energy would be an ``elbow structure'' in the tail of the total charged particle multiplicity distribution in complete disagreement with the second shoulder structure predicted by Pythia Monte Carlo calculations: a challenging problem for new experimental work.

hep-ph↗
arXiv2003

Open problems in forward-backward multiplicity correlations in hadron-hadron collisions in the TeV region

Continuing previous work on forward-backward multiplicity correlation properties in proton-proton collisions in the framework of the weighted superposition model of two components (each one described by a negative binomial multiplicity distribution) with the addition of the leakage parameter which controls clan spreading from one hemisphere to the opposite one, we examine E735 data on the c.m. energy dependence of the total correlation strength and of the forward variance at fixed total multiplicity. A comparison with the Chou-Yang approach to the problem is presented and extrapolations of the mentioned variables at LHC c.m. energy in possible scenarios in the new energy domain are discussed.

hep-ph↗
arXiv2002

Forward-backward multiplicity correlations in e+e- annihilation and pp collisions and the weighted superposition mechanism

Forward-backward multiplicity correlations in symmetric collisions are calculated independently of the detailed form of the corresponding multiplicity distribution. Applications of these calculations to e+e- annihilation and ppbar collisions confirm the existence of the weighted superposition mechanism of different classes of substructures or components. When applied to ppbar collisions in particular, clan concept and its particle leakage from one hemisphere to the opposite one become of fundamental importance. The increase with c.m. energy of the correlation strength as well as the behaviour of the average number of backward particles vs. the number of forward particles are correctly reproduced.

hep-ph↗
arXiv2002

Forward-backward multiplicity correlations and leakage parameter behaviour in asymmetric high energy collisions

Continuing previous work, forward-backward multiplicity correlations are studied in asymmetric collisions in the framework of the weighted superposition mechanism of different classes of events. New parameters for the asymmetric clan distribution and for the particle leakage from clans in one hemisphere to the opposite one are introduced to effectively classify different classes of collisions. This tool should be used to explore forward-backward multiplicity correlations in AB and pA collisions in present and future experiments at RHIC and LHC.

hep-ph↗
arXiv2002

Superposition effect and clan structure in forward-backward multiplicity correlations

The main purpose of this paper is to discuss the link between forward-backward multiplicity correlations properties and the shape of the corresponding final charged particle multiplicity distribution in various classes of events in different collisions. It is shown that the same mechanism which explains the shoulder effect and the H_n vs. n oscillations in charged particle multiplicity distributions, i.e., the weighted superposition of different classes of events with negative binomial properties, reproduces within experimental errors also the forward-backward multiplicity correlation strength in e+e- annihilation at LEP energy and allows interesting predictions for pp collisions in the TeV energy region, to be tested at LHC, for instance with the ALICE detector. We limit ourselves at present to study substructures properties in hadron-hadron collisions and e+e- annihilation; they are examined as ancillary examples in the conviction that their understanding might be relevant also in other more complex cases.

hep-ph↗
arXiv2001

Inclusive density of secondaries in heavy ion collisions

The inclusive density of charged secondaries produced in high energy heavy ion collisions are calculated in the framework of multiple scattering theory and quark-gluon string model. The obtained results are in agreement with the data only assuming rather large inelastic screening/percolation effects. We predict the total saturation of relative inclusive densities in dependence on the number of interacting nucleon. Predictions for LHC are also given.

hep-ph↗
arXiv2001

Particle rapidity density and collective phenomena in heavy ion collisions

We analyse recent results on charged particle pseudo-rapidity densities from RHIC in the framework of the Dual String Model, in particular when including string fusion. The model, in a simple way, agrees with all the existing data and is consistent with the presence of the percolation transition to the Quark-Gluon Plasma already at the CERN-SPS. It leads to strict saturation of the particle (pseudo-)rapidity density, normalised to the number of participant nucleons, as that number increases. A comparison with recent WA98 data is presented.

hep-ph↗
arXiv2000

Large Scale Structure and Cosmic Rays revisited

We investigate the possibility that ultra high energy cosmic rays (E > 10^19 eV) are related to the distribution of matter on large scales. The large scale structure (LSS) data stems from the recent IRAS PSCz redshift survey. We present preliminary predictions drawn from an anisotropic distribution of sources which follows the galaxy distribution.

astro-ph↗
arXiv2000

Particle Rapidity Density Saturation in Heavy Ion Collisions and the Dual String Model

We show that the Dual String Model with fusion leads, in heavy ion collisions, to strict saturation of the particle (pseudo-)rapidity density, normalised to the number of participant nucleons, as that number increases. Asymptotically, as the centre-of-mass energy goes to infinity with the number of participants fixed, this density approaches the nucleon-nucleon density. A comparison with recent WA98 data is presented.

hep-ph↗
arXiv2000

Particle Densities in Heavy Ion Collisions at High Energy and the Dual String Model

We analyse recent results on charged particle pseudo-rapidity densities from RHIC in the framework of the Dual String Model, in particular when including string fusion. The model, in a simple way, agrees with all the existing data and is consistent with the presence of the percolation transition to the Quark-Gluon Plasma already at the CERN-SPS.

hep-ph↗