p t -Multiplicity correlations in a multi-pomeron-exchange model with string collective effects (original) (raw)
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Multi-pomeron exchange model for pp and pp̄ collisions at
2013
A new variant of the effective pomeron exchange model is proposed for the description of the correlation, observed in pp and pp collisions at center-of-mass energy from SPS to LHC, between mean transverse momentum and charged particles multiplicity. The model is based on the Regge-Gribov approach. Smooth logarithmic growth with the collision energy was established for the parameter k, the mean rapidity density of charged particles produced by a single string. It was obtained in the model by the fitting of the available experimental data on charged particles rapidity density in pp and pp collisions. The main effect of the model, a gradual onset of string collectivity with the growth of collision energy, is accounted by a free parameter β that is responsible in an effective way for the string fusion phenomenon. Another free parameter, t, is used to define string tension. We extract parameters β and t from the available experimental results on p tmultiplicity correlation at nucleon collision energy √ s from 17 GeV to 7 TeV. Smooth dependence of both β and t on energy allows to make predictions for the correlation behavior at the collision energy of 14 TeV. The indications to the string interaction effects in high multiplicity events in pp collisions at the LHC energies are also discussed.
Multi-pomeron exchange model for pppppp and pbarpp\bar{p}pbarp collisions at ultra-high energy
A new variant of the effective pomeron exchange model is proposed for the description of the correlation, observed in pppppp and pbarpp\bar{p}pbarp collisions at center-of-mass energy from SPS to LHC, between mean transverse momentum and charged particles multiplicity. The model is based on the Regge-Gribov approach. Smooth logarithmic growth with the collision energy was established for the parameter k, the mean rapidity density of charged particles produced by a single string. It was obtained in the model by the fitting of the available experimental data on charged particles rapidity density in pppppp and pbarpp\bar{p}pbarp collisions. The main effect of the model, a gradual onset of string collectivity with the growth of collision energy, is accounted by a free parameter {\beta} that is responsible in an effective way for the string fusion phenomenon. Another free parameter, t, is used to define string tension. We extract parameters {\beta} and t from the available experimental results on -multiplic...
EPJ Web of Conferences
The multiplicity dependence of heavy flavour production in pp-collisions at LHC energies is studied in the framework of the multi-pomeron exchange model. The model is introducing the string-string interaction collectivity effects in pp collisions, which modifies multiplicity and transverse momenta, leading to the non-trivial mean p t vs. multiplicity (p t N ch − N ch). correlation. The string collectivity strength parameter is fixed by experimental data on multiplicity and transverse momentum correlation in a wide energy range (from ISR to LHC). The particles discrimination is implemented according to Schwinger mechanism taking into account the strong decays of hadron resonances. We demonstrate, that the faster-than-linear growth of the open charm production with the event charged particle multiplicity, observed in experimental pp high energy collisions, can be explained by the modification of the string tension due to the increasing overlap and interaction of quark-gluon strings. The model is extended for p-A interactions and the calculations for p-Pb collisions are performed.
Charged particle multiplicity correlations in pp̄ collisions at =0.3−1.8
Physics Letters B, 1995
The correlations between charged particle multiplicities produced in forward and backward pseudorapidity regions in pp interactions have been measured with a 240 element scintillator hodoscope. The correlation coefficient and the variance of the difference of multiplicities in the two pseudorapidity regions were determined for fi = 0.3-1.8 TeV. These results have been interpreted in terms of a cluster model of particle production.
Physical Review Letters, 2002
The Ω/Ω ratio originating from string decays is predicted to be larger than unity in proton proton interactions at SPS energies (E lab =160 GeV). The anti-omega dominance increases with decreasing beam energy. This surprising behavior is caused by the combinatorics of quark-antiquark production in small and low-mass strings. Since this behavior is not found in a statistical description of hadron production in proton proton collisions, it may serve as a key observable to probe the hadronization mechanism in such collisions.
Charged particle correlations in \bar pp$$ collisions at c.m. energies of 200, 546 and 900 GeV
Zeitschrift für Physik C Particles and Fields, 1988
We present data on two-particle pseudo:rapidity and multiplicity correlations of charged particles for non single-diffractive pi6-collisions at c.m. energies of 200, 546 and 900 GeV. Pseudorapidity correlations interpreted in terms of a cluster model, which has been motivated by this and other experiments, require on average about two charged particles per cluster. The decay width of the clusters in pseudorapidity is approximately independent of multiplicity and of c.m. energy. The investigations of correlations in terms of pseudorapidity gaps confirm the picture of cluster production. The strength of forward-backward multiplicity correlations increases linearly with Ins and depends strongly on position and size of the pseudorapidity gap separating the forward and backward interval. All our correlation studies can be understood in terms of a cluster model in which clusters contain on average about two charged particles, i.e. are of similar magnitude to earlier estimates from the ISR. = D 2 --(n) =f2, (2.6)
Analysis of the first RHIC results in the string fusion model
Physics Letters B, 2002
First results from RHIC on charged multiplicities, evolution of multiplicities with centrality, particle ratios and transverse momentum distributions in central and minimum bias collisions, are analyzed in a string model which includes hard collisions, collectivity in the initial state considered as string fusion, and rescattering of the produced secondaries. Multiplicities and their evolution with centrality are successfully reproduced. Transverse momentum distributions in the model show a larger p T -tail than experimental data for central collisions, and this disagreement tends to disappear with decreasing centrality. Discrepancies with particle ratios are examined comparing with previous features of the model at SPS. With the first collisions at the Relativistic Heavy Ion Collider (RHIC) at BNL in June 2000, the study of nuclear collisions has entered the truly ultrarelativistic domain. While there exist predictions from many models , now experiments have presented results on several aspects of data, most of them corresponding to AuAu collisions at 130 GeV per nucleon in the center of mass. So it comes the time to examine the ability of models for ultrarelativistic heavy ion collisions, fitted to describe nuclear data at the much lower energies of the Super Proton Synchrotron (SPS) at CERN and nucleon data in the range of energies going from SPS to TeVatron at FNAL, to describe the new situation, and whether the evidences of Quark Gluon Plasma (QGP) already obtained at SPS are verified or not . The aim of this letter is to compare the results of the String Fusion Model (SFM) with some of the first RHIC data. Other comparisons can be found in 1 . After a very brief model description, charged multiplicities at midpseudorapidity in central collisions, evolution of charged multiplicities at midpseudorapidity with centrality, transverse momentum distributions of charged particles at different centralities and ratios of different particles will be compared with available data coming from the experiments. Finally some conclusions will be summarized. An exhaustive description of the model can be found in . Its main features are the following: Elementary inelastic collisions (binary nucleon-nucleon collisions) are considered as collisions between partons from nucleons of the projectile and the target, distributed in the transverse plane of the global collision. Some of these elementary collisions are taken as hard ones, and proceed as gluon-gluon -→ gluon-gluon through PYTHIA with GRV 94 LO parton density functions (pdf's) and EKS98 modification of pdf's inside nuclei , with subsequent radiation and fragmentation performed by ARIADNE [20] and JETSET . Those collisions not being considered hard produce soft strings in pairs. These strings are allowed to fuse if their parent partons are close enough in impact parameter ; as the number of strings increases with increasing energy, atomic number and centrality, this mechanism accordingly grows in importance. Fragmentation of soft strings is performed using the tunneling mechanism for mass and transverse momentum distributions, while longitudinal momenta are simulated by an invariant area law. The main consequences of string fusion are a reduction of multiplicities in the central rapidity region and an increase in heavy particle production. The produced particles are allowed to rescatter (between themselves and with spectators nucleons) using a very naive model with no proper space-time evolution, whose consequences are a small multiplicity reduction, an increase in strange and multistrange baryons and nucleon annihilation. Some comments are in order at this point: First, partons which generate both soft and hard strings can be valence quarks and diquarks, and sea quarks and antiquarks, so the number of soft strings is not simply proportional to the number of wounded nucleons but has some proportionality, increasing with increasing energy, centrality and nuclear size, on the number of binary nucleon-nucleon collisions 2 . Besides, only fusion of two strings in considered in the actual version of the model, and hard strings are not fused. Finally, the rescattering model is simplistic and has been included just to estimate the effects that such kind of physics could have and to tune the parameters of the model as an initial condition for a more sophisticated evolution; thus, results depending strongly on it should be taken with caution. All these aspects will be commented more extensively when the comparison with experimental data is performed. In Fig. results of the model (unless otherwise stated, results of the model correspond to its default version with the mentioned pdf's and string fusion and rescattering, see [14]) for the pseudorapidity distribution of charged particles in central collisions at SPS and RHIC are compared with experimental data. For central AuAu collisions at 130 GeV per nucleon in the center of mass, the model successfully reproduce the data, while at 56 GeV it overestimates the PHOBOS results [2]. Nevertheless, the situation at these energies is not clear: WA98 results [22] at SPS lie above the PHOBOS data at 56 GeV, and far above NA49 data [21] (as extracted in [2]) at SPS; NA49 results on multiplicities in central PbPb collisions at SPS are in agreement with those from WA97 [23]. So it is difficult to conclude anything definitive on the evolution of multiplicities with increasing energy in the model. Recently it has been proposed [24] that the evolution of multiplicities with centrality can be used as a tool to discriminate among several models for multiparticle production 2 Usually the soft contribution is taken as proportional to the number of wounded nucleons, while the contribution proportional to the number of binary nucleon-nucleon collisions is considered hard. Let us stress that this is a misleading (model dependent) statement: some proportionality with the number of binary nucleon-nucleon collisions is demanded by a basic requirement of the theory as unitarity, and has nothing to do with the soft or hard origin of these binary nucleon-nucleon collisions.
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 2012
We show that the dependence of the charged particle multiplicity on the centre-of-mass energy of the collision is, in the String Percolation Model, driven by the same power law behavior in both proton-proton and nucleusnucleus collisions. The observed different growths are a result of energymomentum constraints that limit the number of formed strings at low energy. Based on the very good description of the existing data, we provide predictions for future high energy LHC runs.
Scaling behaviour and correlations in the string fusion model for heavy ion collisions
Zeitschrift für Physik C Particles and Fields, 1995
The KNO scaling, the scaling of multiplicities, the behaviour of fluctuations in the transverse momentum as a function of the multiplicity and the long range correlations in nucleus-nucleus collisions are studied by a Monte Carlo code based on the string fusion model. It is shown that the fusion of strings produces a strong reduction of the long range correlations at high multiplicities, which could be detected experimentally. On the contrary the KNO scaling, the scaling of multiplicities and the behaviour of fluctuations in the transverse momentum are not modified when string fusion is included.