Heavy quark energy loss in proton proton collisions at LHC

A promising probe to study deconfined matter created in high energy nuclear collisions is the energy loss of (heavy) quarks. Experiments at the Relativistic Heavy Ion Collider (RHIC) have shown that heavy quarks, i.e. charm and bottom quarks show a remarkable high momentum suppression, comparable to light quarks. In this exploratory study we investigate the energy loss of heavy quarks in high multiplicity proton proton collisions at LHC energies. We will find a small, however non-negligible energy loss of high momentum charm quarks.     

Restoration of multiplicity scaling in high energy proton-proton and antiproton-proton collisions

The energy dependent parameter characterizing the leading particle effect allows to restore the scaling in proton-proton and antiproton-proton multiplicity distributions from Serpukhov until highest available CERN \(S \bar ppS\) collider energies. The identification of theoretical second dispersions with the experimental ones represents one of the basic ingredients in the quantum statistical bosonic approach applied in the present contribution. The KNO scaling at the ISR energies as well as the Worblewski relation for the second dispersions at the \(S \bar ppS\) collider energies arise quite naturally; similar phenomena might appear at higher energies too. Some predictions for 2 and 10 TeV cms energies are specified.     

Hadron multiplicity induced by top quark decays at the LHC

The European Physical Journal C - Oscillations of the F(R) dark energy around the phantom divide line, ω DE=−1, both during the matter era and also in the de Sitter epoch are...     

Hadron multiplicity induced by top quark decays at the LHC

The average charged hadron multiplicities induced by top quark decays are calculated in pQCD at LHC energies. Different modes of top production are considered. Proposed measurements can be used as an additional test of pQCD calculations independent of the fragmentation model.     

Valence quark effects in beam remnants in high Et proton-proton collisions at s=27.4 GeV

Charged particle trajectories have been reconstructed in pp collisions with transverse energies (E_t) ranging from 1 GeV to 20 GeV. Data were collected by triggering on E_t in a highly segmented calorimeter with full azimuthal coverage. Minimum bias triggers were also used. Valence quark effects are known to appear at low E_t in the differences between positive and negative particle multiplicities in the forward direction. We reproduce these known prominent effects at low E_t, but find them not present in the collisions with large E_t, disappearing by about E_t=8 GeV. Furthermore, events with high planarity do not show a strong forward net flow of charge and disagree with the predictions of ISAJET. The results suggest that for the triggers studied, more than a single pair of proton constituents scatter at this energy.     

Heavy quark production at LHC in the color dipole formalism

In this work we estimate the heavy quark production in proton-proton and proton-nucleus collisions at LHC energies using the color dipole formalism and the solution of the running coupling Balitsky-Kovchegov equation. Nuclear effects are considered in the computation of the total cross sections and rapidity distributions for scattering on protons and nuclei.     

Forward-backward multiplicity correlation in high energy hadron-hadron collisions

The forward-backward multiplicity correlation over the full pseudorapidity range forpp andp \(\bar p\) collisions at ISR and Collider energies have been analysed in terms of a Chou-Yang Type multiplicity distribution which consists of a stochastic (binomial) component forz=n _F ?n _B and a nonstochastic (negative binomial) component forn=n _F +n _B . Reasonable agreement with experimental data is obtained if the final-state particles are assumed, in a cluster model, to be created by the decay of clusters with a mean cluster size (charged particles per cluster) which is energy-dependent.     

Generators of nuclear collisions at the LHC energy

Current versions of the most popular generators of ultrarelativistic heavy-ion collisions are used to simulate central (b<3 fm) Pb + Pb collisions at the LHC energy, $\sqrt s = 6A$ TeV. The charged-particle density predicted by the generators for the mid-rapidity range, dN _ch/dη, varies in a wide range, from about 2000 to about 6000. Moreover, even for a given generator, it depends strongly on model parameters and can vary from 10 to 100%.     

Heavy quark energy loss in a nuclear medium

Multiple scattering, modified fragmentation functions, and radiative energy loss of a heavy-quark propagating in a nuclear medium are investigated in perturbative QCD. Because of the quark mass dependence of the gluon formation time, the medium size dependence of heavy-quark energy loss is found to change from a linear to a quadratic form when the initial energy and momentum scale are increased relative to the quark mass. The radiative energy loss is also significantly suppressed relative to a light quark due to the suppression of collinear gluon emission by a heavy quark.     

Negative binomial multiplicity distributions in high energy hadron collisions

We examine the 2⁺⁺ gluonium spectrum in the framework of the Gauss-Weierstrass and Finite Energy QCD sum rules. The results of our analysis support the interpretation of the θ(1710) as a tensor glueball, but they also suggest the existence of at least another state with a massM?2 GeV and a width of about 200 MeV.     

A model for multiplicity distributions in high energy collisions

A phenomenological model is presented which regards the system after collision as a single entity that emits hadrons directly. The evolution of this entity gives a new two parameter distribution which fits the high energypp, \(\bar pp\) ,e ⁺ e ^?, π⁺ p andK ⁺ p data reasonably well. The entity emits hadrons along the rapidity axis and exhibits intermittency behaviour under certain conditions.     

Charmonium production from secondary collisions at LHC energy

We consider the charmonium production in the thermalized hadronic medium created in ultrarelativistic heavy ion collisions at LHC energy. The calculations for secondary and production by annihilation are performed within a kinetic model taking into account the space-time evolution of a longitudinally and transversely expanding medium. We show that secondary charmonium production appears almost entirely during the mixed phase, and that it is very sensitive to the charmonium dissociation cross section with co-moving hadrons. Within the most likely scenario for the dissociation cross section of the mesons their regeneration in the hadronic medium will be negligible. The secondary production of mesons however, due to their large cross section above the threshold, can substantially exceed the primary yield. Received: 3 January 2000 / Published online: 6 July 2000     

Study of Monte Carlo event generators for proton-proton collisions at LHC energies in the forward region

In this paper we present a comparative study between PYTHIA,EPOS,QGSJET,and SIBYLL generators.The global event observables considered are the charged energy flow,charged particle distributions,charged hadron production ratios and V~0 ratios.The study is performed in the LHCb and TOTEM fiducial phase spaces on minimum bias simulated data samples for pp collisions at s~(1/2)= 7 TeV,using the reference measurements from these experiments.In the majority of cases,the measurements are within a band defined by the most extreme predictions.The observed differences between the predictions and the measurements seem to be,in most part,caused by extrapolation from the central pseudorapidity region(|η|≤2.5),in which the generators were mainly tuned.     

Modeling of exclusive parton distributions and long-range rapidity correlations in proton-proton collisions at the LHC energies

The soft part of proton-proton interaction is considered within a phenomenological model that involves the formation of color strings. Under the assumption that an elementary collision is associated with the interaction of two color dipoles, the total inelastic cross section and the multiplicity of charged particles are estimated in order to fix model parameters. Particular attention is given to modeling of exclusive parton distributions with allowance for the energy-conservation law and for fixing the center of mass, which are necessary for describing correlations. An algorithm that describes the fusion of strings in the transverse plane and which takes into account their finite rapidity width is developed. The influence of string-fusion effects on long-range correlations is found within this mechanism.     

Multiplicity distribution in proton-proton and proton-antiproton collisions at high energies

Multiplicity distributions of secondary hadrons produced in p $ \bar p $ \bar p and collisions are very different. There are three types of inelastic processes in p $ \bar p $ \bar p scattering. The first one is the production of a shower of secondary hadrons in gluon string decay. The second one is the shower produced from the decay of two quark strings, and the third one is the shower produced from the decay of three quark strings. At the same time, there are just two types of inelastic processes for pp scattering: the shower from the gluon string and the shower from two quark strings. The multiplicity distribution and the average multiplicity of charged hadrons for an energy of 14 TeV are predicted.     

Leading particle spectrum and the multiplicity distribution in high energy collisions

A relation between the leading particle spectrum and the Koba-Nielsen-Olesen scaling function is derived. It describes the peak-plateau structure of the leading proton spectrum observed at high energies. Furthermore the associated cluster multiplicity is discussed.     

Charm quark energy loss at RHIC

Heavy quark energy loss in a hot QCD plasma is computed taking into account the competing effects due to suppression of zeroth order gluon radiation below the plasma frequency and the enhancement of gluon radiation due to first order medium induced bremsstrahlung. The results suggest a surprising degree of cancellation between the two medium effects for charm quarks and provide a possible explanation for the null effect observed by PHENIX in the prompt electron spectrum in Au+Au at √s = 130 AGeV. In this paper only the main results for heavy quark energy loss will be presented. For more detailed version see [1] and references therein.     

Multifractal structure in high energy collisions and finite multiplicity corrections

There are established rigorous relations between scaling indices which reveal on one hand the presence of intermittency and on the other hand the presence of multifractal phenomena represented by the frequencyG-moments. In the procedure applied in present paper, also the corresponding intercepts as well as an effective average multiplicity are involved. The last mentioned quantity is introduced by extending the relation which characterizes appearance of the multifractality. It is shown that the relation between scaling indices and corresponding slopes is satisfied with sufficient accuracy by the data available so far on deep-inelastic muon-nucleon scattering at 280 GeV.