Charged Hadron Distributions Research Articles

Analyses of whole transverse momentum distributions in pp̄ and pp collisions by using a modified version of Hagedorn’s formula

To describe the transverse momentum [Formula: see text] distribution of charged hadrons at 1.96 TeV observed by the CDF collaboration, we propose a formula with two components, namely, hadron gas distributions and inverse power laws inspired by QCD calculus. The new formula based on a formula by Hagedorn in 1983 includes an integration of pseudo-rapidity [Formula: see text]. The data collected at 0.9, 2.76, 7 and 13 TeV by the ALICE, CMS, and ATLAS collaborations are also analyzed using various models including single component models as well as two-component models. The results by the use of the modified version of Hagedorn’s formula are compared with those by the use of the two-component model proposed by Bylinkin, Rostovtsev and Ryskin (BRR). We investigate whether or not there is an interrelation among our modified formula, a formula proposed by ATLAS collaboration, and the BRR formula. Moreover, formulas for the [Formula: see text] distributions in the nonextensive approach are discussed.

Decomposing energy balance contributions for quenched jets with CMS

Modification of energy balance in dijet events from heavy ion collisions, measured by CMS, was among the first jet quenching observations in the LHC energy domain. Here we further study the spatial extent of medium-induced modifications for such dijets, as well as potential medium response to propagating partons, using two-dimensional angular correlations of charged hadrons measured with respect to jets. New differential measurements of charged particle energy flow about the jet direction as a function of relative azimuth and relative pseudorapidity from 2.76 TeV PbPb collisions are compared with the reference pp data recorded by the CMS at the same energy. Modifications of correlated charged hadron distributions for both the leading and the subleading sides of the dijet are reported, together with comparisons of the long-range asymmetry of the underlying event in PbPb vs pp collisions.

Jet-track correlations in PbPb and pp collisions at 2.76 TeV

Jet quenching is one of the established signatures of the Quark Gluon Plasma, and this phenomenon has been studied extensively in high energy heavy ion experiments over the last decade. Despite significant progress made in those studies, the specifics of the energy loss mechanisms and the details of jet-medium interactions require further quantitative understanding. Studies of two-dimensional angular correlations of charged hadrons with respect to reconstructed jets make it possible to experimentally assess the energy radiation patterns of an energetic parton traversing the medium as well as its fragmentation function. In these proceedings, we present new differential measurements of charged particle densities and energy flow about the jet direction as a function of relative azimuth and relative pseudorapidity from 2.76 TeV PbPb and pp collisions recorded by the CMS Collaboration. With a sample of back-to-back dijets, previously used to reconstruct the event-wise momentum imbalance (missing pT), we explore modifications to correlated charged hadron distributions for both the leading and the subleading sides of the dijet. With this technique, we can individually assess the contribution of the medium-induced modifications to each side of the dijet and explore the extent of potential medium response to the jet propagation, while also extending these measurements to large angular and radial distances.

Charged hadron distributions in a two component model

Inclusive charged hadron cross sections, dσ/dη, and d2σ/(dηdpT2) are considered within the two component model, which combines the power-like and the exponential terms in pT. The observed dependences of the spectra shape on energy and pseudorapidity qualitatively agree with the proposed model for hadroproduction. A short overview of the results published recently is presented.

Charged particle production in Pb-Pb and p-Pb collisions measured by the ATLAS detector

The ATLAS experiment at the Large Hadron Collider measures charged hadron spectra in Pb+Pb and p+Pb collisions. The results are compared to the pp spectra of charged hadrons at the same centre-of-mass energy. Charged hadron distributions from Pb+Pb are compared to charged particle cross-sections in pp collisions at √s= 2.76 TeV, reference crosssection for p+Pb at √s NN = 5.02 TeV is reconstructed using √s = 2.76 TeV and 7 TeV pp results. These allow for a detailed comparison of the collision systems in a wide transverse momentum and rapidity ranges in different centrality intervals. The nuclear modification factors RAA and RpPb are presented as a function of centrality, pT, η The charged particle RAA is found to vary significantly as a function of transverse momentum, and shows a pronounced minimum at about 7 GeV. Above 60 GeV, RAA is consistent with a flat, centrality-dependent, value within the uncertainties. RpPb results show strong rapidity dependence in the region of so-called Cronin peak at about 2 GeV and above pT of 10 GeV show anomalous enhancement.

Energy dependent growth of nucleon and inclusive charged hadron distributions**Supported by Natural Science Foundation of Hebei Province (A2012210043)

In the Color Glass Condensate formalism, charged hadron pT spectra in p+p and p+Pb collisions are studied by considering an energy-dependent broadening of nucleon density distribution. Then, in the glasma flux tube picture, the n-particle multiplicity distributions at different pseudo-rapidity ranges are investigated. Both the theoretical results show good agreement with the recent experimental data from ALICE and CMS at LHC energies. The predictive results for pT or multiplicity distributions in p+p and p+Pb collisions at the Large Hadron Collider are also given in this paper.

Pseudorapidity distribution of charged hadrons in proton–proton collisions at [formula omitted

The pseudorapidity distribution of charged hadrons in pp collisions at s=13 TeV is measured using a data sample obtained with the CMS detector, operated at zero magnetic field, at the CERN LHC. The yield of primary charged long-lived hadrons produced in inelastic pp collisions is determined in the central region of the CMS pixel detector (|η|<2) using both hit pairs and reconstructed tracks. For central pseudorapidities (|η|<0.5), the charged-hadron multiplicity density is dNch/dη||η|<0.5=5.49±0.01(stat)±0.17(syst), a value obtained by combining the two methods. The result is compared to predictions from Monte Carlo event generators and to similar measurements made at lower collision energies.

Longitudinal Properties of High Energy Collisions

The rapidity distribution and longitudinal energy distribution are analysed within the thermodynamical formalism with the non-extensive Tsallis statistics. Our approach is based on a model for fireball rapidity distribution recently proposed where the fireball moves longitudinaly according to a q-Gaussian function rapidity distribution. We show that the rapidity distribution of charged hadrons are correctly obtained as compared to the experimental data for rapidities up to ∼ 10.5. The energy density as a function of the rapidity is studied for the first time. We show that most of the energy carried by hadrons are in the high rapidity region. Our results show that the energy density is a good tool for studying the logitudinal aspects of high energy collisions.

Analysis of pPb collisions at LHC energies in the relativistic diffusion model

Particle production sources in pPb collisions at LHC energies are investigated in pseudorapidity space as functions of centrality. The nonequilibrium-statistical relativistic diffusion model (RDM) with three sources is applied to the analysis of preliminary charged-hadron distributions measured by the ATLAS and ALICE collaborations in pPb collisions at 5.02 TeV. The size of the midrapidity source relative to the fragmentation sources in pPb collisions is considered as function of centrality, and incident energy. At LHC energies particle production from the mid-rapidity gluon-gluon source is larger than that from the fragmentation sources at all centralities. Conclusions regarding the statistical equilibration process are drawn.

Particle production sources inpPb and PbPb at the LHC

Hadron production in relativistic heavy-ion collisions at LHC energies is investigated. After a brief consideration of stopping, particle production is accounted for in a nonequilibrium-statistical model with two fragmentation sources, and a central source that is mostly due to low-x gluon-gluon collisions. The particle content and energy dependence of the three sources is discussed for AuAu (RHIC) and PbPb (LHC). Results for asymmetric pPb collisions are compared with preliminary ALICE and ATLAS data. A brief survey of several features of hadron production in relativistic heavy-ion collisions at LHC energies is given in this article, which is essentially based on results pub- lished in (1), and obtained in (2, 3). The stopping process in the very first phase of the col- lision is mostly characterized by the interaction of fast va- lence quarks with low-x gluons in the respective other nu- cleus. The fragmentation peaks in net-proton (proton - antiproton) rapidity distributions are clearly visible in SPS and RHIC data (4-7). When considering rapidity or pseu- dorapidity distributions of produced charged particles, the fragmentation distributions also play a significant role, but since they shift to large values of rapidity at LHC, particle production near mid rapidity is almost exclusively deter- mined by the central low-x gluon-gluon source. This source cancels out in net-proton distributions, but in charged-hadron distributions its importance rises strongly with incident energy. In this note the relative im- portance of the three sources is investigated as function of energy from a direct comparison of the analytical solutions of a nonequilibrium-statistical relativistic diffusion model (RDM) (8) with PHOBOS (9) and recent ALICE data (10) data. This allows also for predictions at the LHC design energy, and for an analysis of the asymmetric pPb system at the current LHC energy of 5.02 TeV.

Collective effects in light–heavy ion collisions

We present results for the azimuthal anisotropy of charged hadron distributions in A+A, p+A, d+A, and He3+A collisions within the IP-Glasma+MUSIC model. Obtained anisotropies are due to the fluid dynamic response of the system to the fluctuating initial geometry of the interaction region. While the elliptic and triangular anisotropies in peripheral Pb+Pb collisions at root-s=2.76 TeV are well described by the model, the same quantities in root-s=5.02 TeV p+Pb collisions underestimate the experimental data. This disagreement can be due to neglected initial state correlations or the lack of a detailed description of the fluctuating spatial structure of the proton, or both. We further present predictions for azimuthal anisotropies in p+Au, d+Au, and He3+Au collisions at root-s=200 GeV. For d+Au and 3He+Au collisions we expect the detailed substructure of the nucleon to become less important.

Scaling behaviour of charged hadron distributions in pp and collisions

We report on a scaling behaviour in the transverse momentum () distributions for charged hadrons produced in proton–proton (pp) collisions with different centre of mass energies ( = 0.9, 2.76 and 7 TeV) at the Compact Muon Solenoid detector. This scaling behaviour appears when the is replaced by , where K is a parameter and depends on . A similar scaling behaviour is observed in the pT distributions of charged hadrons produced in proton–antiproton () collisions with = 0.63, 1.8 and 1.96 TeV at the Collider Detector at Fermilab. The particle production mechanism behind the scaling behaviour in the pp or collisions could be explained by the model of percolation of strings.

Pseudo-rapidity distributions of charged hadrons in pp and pA collisions at the LHC

In the framework of the Color Glass Condensate, the pseudo-rapidity distributions of charged hadrons in pp and pA collisions at the LHC are studied with the UGD function from the GBW model. With a χ2 analysis of the CMS data in pp collisions at √s=0.9, 2.36, 7 TeV, the normalization factor is obtained and the theoretical results are in good agreement with the experimental data. Then, considering the influence of nucleon hard partons transverse distribution on the number of participants in pA collisions by using a Glauber Monte Carlo method, we also give the predictive results for the multiplicity distributions in pPb collisions at √s=4.4 TeV.

Initial state fluctuations and higher harmonic flow in heavy-ion collisions

A framework combining Yang-Mills dynamics of the pre-equilibrium glasma with relativistic viscous hydrodynamic evolution of the quark–gluon plasma and hadron gas phases is presented. Event-by-event fluctuations of nucleon positions and color charges are taken into account, leading to negative binomial fluctuations of gluon multiplicities. Experimental anisotropic flow coefficients v 2 – v 5 of charged hadron distributions in heavy-ion collisions at the Large Hadron Collider are well described. Furthermore, event-by-event distributions of v 2 , v 3 and v 4 measured by the ATLAS collaboration are reproduced.

Particle production sources at LHC energies

Particle production sources at RHIC and LHC energies are investigated in pseudorapidity space. A nonequilibrium-statistical relativistic diffusion model with three sources is applied to the analysis of charged-hadron distributions in AuAu collisions at RHIC energies, in PbPb collisions at the current LHC energy of 2.76 TeV, in pPb at 5.02 TeV, and in pp. The size of the midrapidity source relative to the fragmentation sources in heavy-ion collisions is investigated as function of incident energy. At LHC energies, the midrapidity value is mostly determined by particle production from gluon–gluon collisions.

Azimuthal distributions of charged hadrons, pions, and kaons produced in deep-inelastic scattering off unpolarized protons and deuterons

The azimuthal cos{\phi} and cos2{\phi} modulations of the distribution of hadrons produced in unpolarized semi-inclusive deep-inelastic scattering of electrons and positrons off hydrogen and deuterium targets have been measured in the HERMES experiment. For the first time these modulations were determined in a four-dimensional kinematic space for positively and negatively charged pions and kaons separately, as well as for unidentified hadrons. These azimuthal dependences are sensitive to the transverse motion and polarization of the quarks within the nucleon via, e.g., the Cahn, Boer-Mulders and Collins effects.

Charged-Hadron Pseudorapidity Distributions in p-p and Pb-Pb Collisions at LHC Energies

Pseudorapidity distributions of charged hadrons produced in p-p and Pb-Pb collisions at LHC energies were measured by the CMS and ALICE Collaborations, respectively. An improved Tsallis distribution in the two-cylinder model is used to describe the pseudorapidity spectra. We consider the rapidity shift at the longitudinal direction in the geometrical picture of the collisions. The calculated results are in agreement with the experimental data. The gap between the projectile cylinder and the target cylinder increases with the centralities. The rapidity shifts in the cylinders also increase with the centralities.

Gluon saturation and pseudo-rapidity distributions of charged hadrons at RHIC energy regions

We modified the gluon saturation model by rescaling the momentum fraction according to saturation momentum and introduced Cooper-Frye hydrodynamic evolution to systematically study the pseudo-rapidity distributions of final charged hadrons at different energies and different centralities for Au-Au collisions in relativistic heavy-ion collisions at the BNL Relativistic Heavy Ion Collider (RHIC). The features of both gluon saturation and hydrodynamic evolution at different energies and different centralities for Au-Au collisions are investigated in this paper.

Revised production cross-section of γ-rays in p–p collisions with LHC data for the study of TeV γ-ray astronomy

We present the production cross-section of γ-rays based on data of p–p collisions at the Large Hadron Collider (LHC), revising the previous semi-empirical formula mainly for (1) the inelastic cross-section in p–p collisions, σpp(E0), and 2) the inclusive γ-ray spectrum in the forward region, σpp→γ(E0,Eγ). We find that the previous cross-section gives a significantly softer spectrum than found in the data of LHC. In this paper, we focus our interest mainly upon the LHC forward (LHCf) experiment, giving γ-ray spectra in the very forward region with the pseudo-rapidity η∗≳8.8 in the center of mass system (CMS), which have not been reported so far. We also give the pseudo-rapidity distribution of charged hadrons with -3⩽η∗⩽3 obtained by ALICE and TOTEM experiments, both with LHC. We find that the revised cross-section reproduces quite well the accelerator data over the wide energy range from GeV to 30PeV for projectile protons, corresponding approximately to 100MeV to 3PeV for secondary γ-rays. The production cross-section of γ-rays produced in the forward region is essential for the study of γ-ray astronomy, while not important are those produced in the central region in CMS, and of much less importance in the backward. We discuss also the average transverse momentum of γ-rays, p¯t, and the average inelasticity transferred to γ-rays, k¯γ∗, obtaining that the former increases very slowly with p¯t=100∼220MeV/c for E0=1GeV∼26PeV, and the latter is almost independent of E0, with k¯γ∗≈1/6, while we cannot exclude the possibility of a small increase of k¯γ∗.

Blast-wave model with two freeze-out temperatures for hadrons produced in relativistic heavy-ion collisions

An expanding fireball model with two freeze-outs, which assumes that the chemical freeze-out occurs earlier at a higher temperature and the thermal freeze-out occurs later at a lower temperature, is developed and successfully applied to fit simultaneously the hadron ratios, the transverse momentum spectra of measured hadrons, and the rapidity distribution of charged hadrons measured in $\mathrm{Au}+\mathrm{Au}$ collisions at $200A$ GeV by the STAR, PHENIX, and PHOBOS Collaborations. The quality of all the fittings is very good, and the resulting parameters are in agreement with published values.