Very High Multiplicity Physics Workshops

The following sections are included:

• PREFACE

• CONTENTS

The project of an ion collider accelerator complex NICA that is under development at JINR is presented. The article is based on the Conceptual Design Report (CDR)¹ of the NICA project delivered in January 2008. The article contains NICA facility scheme, the facility operation scenario, its elements parameters, the proposed methods of intense ion beam acceleration and achievement of the required luminosity of the collider. The symmetric mode of the collider operation is considered here and most attention is concentrated on the luminosity provision in collisions of uranium ions (nuclei).

A conceptual design of MultiPurpose Detector (MPD) is proposed to study the hot and dense baryonic matter in collisions of heavy ions over atomic mass range A = 1–238 at a center-of-mass energy up to . The MPD experiment is foreseen to be carried out at the future JINR accelerator complex for heavy ions – the Nuclotron Based Ion Collider fAcility which is designed to reach required parameters with an average luminosity of L = 10²⁷cm^-2s^-1.

We offer the parameter, interpreted as the "chemical potential", which is sensitive to the first order phase transition: it must decrease with number of evaporating (produced) particles (hadrons) if the (interacting hadron or/and QCD plasma) medium is boiling and it increase if no phase transition occur. The main part of the paper is devoted to the question: how one can measure the "chemical potential" in the hadron inelastic processes. Our definition of this parameter is quite general but assumes that the hadron multiplicity is sufficiently large. The simple transparent phenomenological lattice gas model is considered for sake of clarity only.

We consider the Bose-Einstein condensation (BEC) in a relativistic pion gas. The thermodynamic limit when the system volume V goes to infinity as well as the role of finite size effects are studied. At V → ∞ the scaled variance for particle number fluctuations, ω = 〈ΔN²〉/〈N〉, converges to finite values in the normal phase above the BEC temperature, T > T_C. It diverges as ω ∝ V^1/3 at the BEC line T = T_C, and ω ∝ V at T < T_C in a phase with the BE condensate. At high collision energy, in the samples of events with a fixed number of all pions, N, one may observe a prominent signal. When N increases the scaled variances for particle number fluctuations of both neutral and charged pions increase dramatically in the vicinity of the Bose-Einstein condensation line. As an example, the estimates are presented for p + p collisions at the beam energy of 70 GeV.

Along with π⁰ and η mesons, a resonance structure in the invariant mass spectrum of two γ-quanta at M = 360 ± 7 ± 9 MeV is first observed in the reaction dC → γ + γ + X at momentum 2.75 GeV/c per nucleon. Preliminary estimates of its width and cross section are Γ = 49.2 ± 18.6 MeV and σ_γγ ~ 98 μb. The collected statistics is 2339 ± 340 events of 1.5·10⁶ triggered interactions of a total number of ~ 10¹² dC-interactions. This structure is not observed in pC collisions at the beam momentum 5.5 GeV/c. Possible mechanisms of this ABC-like effect are discussed.

The predictions for correlation radii in the central Pb+Pb collisions for LHC are given in the frame of FAST HADRON FREEZE-OUT GENERATOR (FASTMC).

Experimental data on inclusive cross sections of jet, direct photon, and high-p_T hadron production in and AA collisions are analyzed in the framework of z-scaling. The analysis is performed with data obtained at ISR, , RHIC, and Tevatron. Scaling properties of z-presentation of the inclusive spectra are verified. Physical interpretation of the variable z and the scaling function ψ(z) is discussed. We argue that general principles of self-similarity, locality, and fractality reflect the structure of the colliding objects, interaction of their constituents, and particle formation at small scales. The obtained results suggest that the z-scaling may be used as a tool for searching for new physics phenomena beyond Standard Model in hadron and nucleus collisions at high transverse momentum and high multiplicity at U70, RHIC, Tevatron, and LHC.

The production of quarkonia is one of the most promising signals at the LHC for the study of the production properties of Quark Gluon Plasma. In addition to the J/ψ the extent to which ϒ is suppressed should give much insight into the new state of matter. The large muon acceptance and the high precision tracker make the CMS detector ideal for studies of this physics. The estimations of statistics and signal-to-background ratios for measurement of J/ψ and ϒ with CMS detector show the excellent capability to study the heavy-quarkonia cross-sections versus centrality, rapidity y and transverse momentum p_T, in Pb+Pb collisions at , via their dimuon decay channel. The differential cross-sections analyses will help significantly to clarify the physics mechanisms of quarkonia states production in high-energy nucleus-nucleus collisions.

The theory for Bose-Einstein correlations in case of neutral gauge bosons in pp collisions at high energies is presented. Based on quantum field theory at finite temperature the two-particle Bose-Einstein correlations of neutral gauge bosons are carried out for the first time. As a result, the important parameters of the correlation functions can be obtained for the Z⁰Z⁰ pairs. The correlations of two bosons in 4-momentum space presented in this paper offer useful and instructive complimentary viewpoints to theoretical and experimental works in multiparticle femtoscopy and interferometry measurements at hadron colliders.

Based on quantum field theory at finite temperature we carried out new results for two-particle Bose-Einstein correlation (BEC) function C₂(Q) in case of light hadrons. The important parameters of BEC function related to the size of the emitting source, mean multiplicity, stochastic forces range with the particle energy and mass dependence, and the temperature of the source are obtained for the first time. Not only the correlation between identical hadrons are explored but even the off-correlation between non-identical particles are proposed. The correlations of two bosons in 4-momentum space presented in this paper offer useful and instructive complimentary viewpoints to theoretical and experimental works in multiparticle femtoscopy and interferometry measurements at hadron colliders. This paper is the first one to the next opening series of works concerning the searching of BEC with experimental data where the parameters above mentioned will be retrieved.

We study the pion production process at high energy proton-nuclei peripheral collisions. The dominant contribution for the case of non-exited final state hadrons arises from kinematics of central region of pionization. The basic mechanism consist in of creation of pair of real gluons by exchanged reggeized gluons with subsequent conversion to a pair of pions.

We show that the mechanisms which include emission of two gluons in the same effective vertex contribution dominate compared with one with the creation of two separate gluons. Numerical estimations of cross section of pair of charged pions production for LHC facility give the value or order 10mb.

The problem of exceed of positively charged pions in cosmic ray interaction with earth atmosphere is as well considered. By close analogy to QED case of lepton pair creation at ion's collision we generalize our result to the case of pion pairs creation, providing to keep into account the screening effect.

The distribution of n pion pair production as a function of impact parameter is discussed. We estimate as well the behavior of total cross-section as a function of n as σ_n ~ 1/(n² · n!).

A simple cascade model which relates the energy dependence of mean charge multiplicity to the growth of the total cross-sections of strong interactions is presented. The main assumption, that the total time of hadronization is limited by the characteristic time of the strong interaction is explicitly used. The model describes well the available data on e⁺e^- annihilation and and is in qualitative agreement with the main results of the Bose-Einstein Correlation analysis in the hadron physics.

J/Ψ photo- and electroproduction is studied in the framework of the analytic S–matrix theory. It is argued that at low energies the background, which is the low-energy equivalent of the high-energy diffraction, replaces the Pomeron exchange. Detailed calculations and comparison with the data for the on shell J/Ψ photoproduction have been done in¹, based on Dual Model with Mandelstam Analyticity (DAMA). Here we discuss the generalization of the model for J/Ψ electroproduction in the framework of the off mass shell extension of DAMA².