Fluctuations and transverse momentum distributions in the color clustering approach

We present our results on transverse momentum fluctuations, multiplicity fluctuations and transverse momentum distributions for baryons and mesons in the framework of the clustering of color sources. We determine under what conditions the initial state configurations can lead to color connection, and more specifically, if variations of the initial state can lead to a transition from disconnected to connected color clusters, modifying the number of effective sources. We find that beyond a critical point, one has a condensate, containing interacting and hence color-connected sources. This point thus specifies the onset of color deconfinement. We show that the transverse momentum and multiplicity distributions are related to each other in a defined way. We obtain a non-monotonic dependence of the p _T and multiplicity fluctuations with the number of participants. We present our results for the fluctuations and the transverse momentum distributions at RHIC energies compared to the existing experimental data and our predictions for LHC energies.     

Multiplicity fluctuations of particles produced in interactions of light nuclei with carbon nuclei at a momentum of 4.2 <Emphasis Type="Italic">A</Emphasis> GeV/<Emphasis Type="Italic">c</Emphasis> and their theoretical interpretation

New experimental data on fluctuations in the multiplicities of negatively charged particles in interactions of light nuclei (p, d, ⁴He, ¹²C) with carbon nuclei at a momentum of 4.2 A GeV/c in 4π geometry are reported. The data indicate a behavior similar to that earlier observed by the NA49 Collaboration. The cascade evaporation model, FRITIOF model, and UrQMD 1.3 model are used to analyze the data. The dependence of the fluctuations on nuclear collision centrality is theoretically described without any exotic assumptions. According to the FRITIOF model, the dependence of the multiplicity fluctuations on the collision centrality is to a large extent governed by fluctuations in the number of “wounded” nucleons that are associated with the experimental observation conditions. The NA49 Collaboration data are also described.     

Analysis of the semi-inclusivep T distributions at the CERNp\bar p collider based on the two-temperature model

A two-temperature model is proposed for the semi-inclusive transverse momentum (p _T ) distributions at the CERN \(p\bar p\) collider. Our model accounts well characteristic multiplicity dependence of thep _T distributions. Energy dependence of thep _T distributions is investigated in comparison with the data at ISR energies. High temperature state becomes more important at high energy and multiplicity regions. The ratio between high and normal temperature is almost independent of energy and multiplicity.     

Scaling properties of fluctuation results from the PHENIX experiment at RHIC

The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has made measurements of event-by-event fluctuations in the charged-particle multiplicity as a function of collision energy, centrality, collision species, and transverse momentum in several heavy-ion collision systems. It is observed that the fluctuations in terms of σ ²/μ ² exhibit a universal power law scaling as a function of N_participants that is independent of the transverse momentum range of the measurement.     

Multiplicity fluctuations of particles produced in interactions of light nuclei with carbon nuclei at a momentum of 4.2 A GeV/ c and their theoretical interpretation

New experimental data on fluctuations in the multiplicities of negatively charged particles in interactions of light nuclei (p, d, ⁴He, ¹²C) with carbon nuclei at a momentum of 4.2 A GeV/c in 4π geometry are reported. The data indicate a behavior similar to that earlier observed by the NA49 Collaboration. The cascade evaporation model, FRITIOF model, and UrQMD 1.3 model are used to analyze the data. The dependence of the fluctuations on nuclear collision centrality is theoretically described without any exotic assumptions. According to the FRITIOF model, the dependence of the multiplicity fluctuations on the collision centrality is to a large extent governed by fluctuations in the number of “wounded” nucleons that are associated with the experimental observation conditions. The NA49 Collaboration data are also described. Original Russian Text ? A.S. Galoyan, E.N. Kladnitskaya, V.V. Uzhinsky, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 10, pp. 718–721.     

Indications for the onset of deconfinement in Pb+Pb collisions at the CERN SPS

Particle production in central Pb+Pb collisions was studied with the NA49 large acceptance spectrometer at the CERN SPS at beam energies of 20, 30, 40, 80 and 158 GeV per nucleon. A change of the energy dependence is observed around 30A GeV for the yields of pions and strange particles as well as for the shapes of the transverse mass spectra. The energy dependence of fluctuations and correlations shows no structure. At present only a reaction scenario with onset of deconfinement is able to reproduce the measurements.     

Multifragmentation of Gold nuclei in the interactions with photoemulsion nuclei at 10.7 GeV/nucleon

Recent results from the EMU-01/12 collaboration are presented for 10.7 GeV/nucleon gold nuclei interactions in emulsion. The distributions of “bound” charge (Z _bound , Z _b3 ), multiplicity distributions, fragment correlations and fluctuations are discussed. The data are compared to similar results obtained on the ALADIN setup at 600 MeV/nucleon. It is shown that multifragmentation of gold nuclei at high and intermediate energies has common features. It is also obtained that the IMFs have reduced multiplicity at high energies. The data are analyzed within the scope of the statistical model of multifragmentation. This model requires the following predetermined model ingredients: mass, charge and excitation energy of nuclear residuals. The simple estimation method of these characteristics is proposed in the framework of the Glauber approach. It is shown that the multifragmentation model reproduces qualitatively the present data. A dramatic discrepancy between the predicted and experimental yield of two charged fragments is found. The evolution of transverse momentum of fragments as a function of Z _bound is presented. It is shown that the model greatly underpredicts the transverse momentum of fragments. It is interpreted as evidence of a strong radial flow of spectator fragments.     

Transverse-momentum fluctuations in pi(+)p and K(+)p Collisions at 250 GeV/c

We report results on event-by-event fluctuations of transverse momentum, Phi(p(t)), in pi(+)p and K(+)p collisions at 250 GeV/c. For the first time, their dependence on rapidity region, transverse momentum acceptance, multiplicity, mean transverse momentum per event, and on the correlation between transverse momentum and multiplicity are systematically presented. The results are compared with those from the PYTHIA Monte Carlo generator. The fluctuations under the same acceptance cuts as used in current heavy-ion experiments are also presented.     

Multiple parton-parton interactions in an impact parameter picture

The possibility of having several independent parton-parton interactions in a hadron-hadron collision is studied. A simple framework is developed for the effects of varying impact parameters. The consequences of having several different matter distributions inside the colliding hadrons are explored. Properties studied include multiplicity distributions, minijet rates, average transverse momentum dependence on multiplicity and E_T density outside jet cores.     

Fluctuations and correlations in the string clustering approach

The fluctuations due to the clustering of color sources can explain the behaviour of the scaled multiplicity variance and transverse momentum fluctuations with centrality. They also predict a nonmonotonic behaviour with centrality for the multiplicity associated to high-p_T events. The clustering of color sources gives rise to an increase in the long-range correlations with centrality as well as to a supression at high centrality with respect to superposition models.     

Multiplicity dependence of particle spectra: A peripheral phase-space description with application to 19 GeV/c pp reactions

As an attempt to describe the overall features of spectra of particles produced in hadronic interactions at high energy, we propose a peripheral phase-space model which incorporates restricted transverse momenta to the outgoing particles as well as a leading particle effect. Simulating proton-proton interactions at 19 GeV/c beam momentum, we examine the effect of modifying Monte-Carlo generated events by a matrix element containing a factor (?bp_⊥²) for each outgoing particle and an exponential damping exp (at) in the momentum transfer to each of the final baryons. With a fixed set of cut-off constants, we give a survey of spectral shapes obtained for particles of different types, pions, kaons, nucleons and hyperons. In particular, the generated longitudinal spectra are shown to have a distinct dependence on multiplicity. A comparison is carried out with existing data on 19 GeV/c pp interactions obtained by the Scandinavian Bubble Chamber Collaboration.     

String and parton percolation

A brief review to string and parton percolation is presented. After a short introduction, the main consequences of percolation of color sources on the following observables in A-A collisions: suppression, saturation of the multiplicity, dependence on the centrality of the transverse momentum fluctuations, Cronin effect and transverse momentum distributions, strength of the two and three body Bose-Einstein correlations and forward-backward multiplicity correlations, are presented. The behavior of all of them can be naturally explained by the clustering of color sources and the dependence of the fluctuations of the number of these clusters on the density.Arrival of the final proofs: 21 March 2005PACS: 25.75.-q, 12.38.Mh, 24.85. + p     

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 behavior. 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 occur 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 behavior 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.Received: 15 July 2004, Revised: 17 December 2004, Published online: 15 February 2005     

Photon and neutral pion distributions in 60 and 200 A GeV16O+nucleus and proton+nucleus reactions

Transverse momentum (p_T) distributions of inclusive photons and neutral pions at midrapidity are measured with a lead glass calorimeter in $\text{60}\text{and}\text{200 A}\text{GeV}{}^{16}\text{O}\text{+}\text{nucleus and proton}\text{+}\text{nucleus reactions}$. The variation of the average transverse momentum is investigated as function of centrality, determined by measurements of the remaining energy of the projectile and the charged particle multiplicity. For small values of the entropy, deduced from the multiplicity density, an increase in average p_T is observed levelling off for larger values of entropy. The target-mass and energy dependence of π⁰ p_T distributions are presented.     

Hadron production ine +e− annihilation and μ-p collisions under the assumption of longitudinal phase space dominance

Rapidity and multiplicity distributions are calculated for the hadrons produced ine ⁺e^? annihilation and deep inelastic muon-proton collisions for c.m. energies of 10 to 40 GeV. The hypothesis of longitudinal phase space dominance leads to a probability distribution which is identical to that of a grand canonical ensemble of non-interacting particles. We successfully describe experimental rapidity distributions, domains of Feynman-x scaling and scaling violations and the rapidity dependence of the mean transverse momentum. Multiplicity distributions are derived to be close to negative binomial distributions even for finite rapidity intervals. The plateau in the rapidity distribution is the origin for the negative binomial distribution in multiplicity. The mean number of hadrons of each species and the mean overall transverse momentum are the main input parameters in our calculation and are taken from experiment.     

Inclusive production of protons, anti-protons and neutrons in p+p collisions at 158 GeV/c beam momentum

New data on the production of protons, anti-protons and neutrons in p+p interactions are presented. The data come from a sample of 4.8 million inelastic events obtained with the NA49 detector at the CERN SPS at 158 GeV/c beam momentum. The charged baryons are identified by energy loss measurement in a large TPC tracking system. Neutrons are detected in a forward hadronic calorimeter. Inclusive invariant cross sections are obtained in intervals from 0 to 1.9 GeV/c (0 to 1.5 GeV/c) in transverse momentum and from ?0.05 to 0.95 (?0.05 to 0.4) in Feynman x for protons (anti-protons), respectively. p _T integrated neutron cross sections are given in the interval from 0.1 to 0.9 in Feynman x. The data are compared to a wide sample of existing results in the SPS and ISR energy ranges as well as to proton and neutron measurements from HERA and RHIC.     

Neutron inelastic scattering study of transverse spin fluctuations in CsNiF3: A soliton-only central peak

We have observed a quasi-elastic contribution to the spectrum of the transverse spin fluctuations S^perp;(Q, ω), perpendicular to an applied magnetic field in the easy plane of the one-dimensional ferromagnet CsNiF₃. According to the present theoretical understanding this contribution is due solely to soliton quasi-particles and it should not contain two-magnon scattering. The observed dependence on momentum transfer is as expected for soliton scattering with zero intensity at q_c = 0 rising through a maximum with increasing q_c.     

Self-similarity in one and two dimension of 800 GeV proton interactions with AgBr nuclei

The normalized multiplicity moments in one and two dimensions were investigated for secondary particles produced in 800 GeV proton interactions with AgBr nuclei in nuclear emulsion. The fluctuations are found to be more in two dimensions as compared to one dimension. It has been shown that the self-similar cascade model describes well the observed fluctuations. The multiplicity shows a weaker dependence of moments for high multiplicity events in comparison to all multiplicity events. The slope ratios (r _q) are not different in one and two dimensions and are found to be independent of the multiplicity. Ther _q distribution is well represented by the logbinomial and Levy-stable distributions which follows from the self-similar cascade model.     

Production of high transverse momentum particles in p-p-collisions in the central region at the CERN ISR

The inclusive production al all charged particles of transverse momentum p_T between 1.5 and 4.4 GeV/c at centre of mass angles 90° and 59.4° from p-p-collisions with √s = 44 and 53 GeV has been measured. No strong energy dependence is observed for these transverse momenta.     

Inclusive highP T π0 production from π± and protons at 200 GeV/c

We have measured the inclusive cross-section for π⁰ production at large transverse momentum by 200 GeV/c positive and negative hadron beams on Carbon targets (2.9<P _T <6 GeV/c; ?0.4<y ^*<1.2). We used the NA3 spectrometer at the CERNSPS.