Charged Hadron Production Research Articles

Parametrization of the shape of hadron-production spectra in high-energy particle interactions

The transverse-momentum dependence of inclusive differential cross sections measured in various collider experiments for processes involving the production of long-lived charged hadrons was approximated by the sum of an exponential and a power-law function. The dependence of the parameters appearing in these functions on the colliding-particle energy and type was studied, and relationships between these parameters were established. A number of new regularities in the behavior of charged-particle spectra were discovered.

Charge separation measurements in Pb–Pb collisions at LHC energies

The prospect of observing parity violation from the strong interaction in relativistic heavy–ion collisions has recently gained great attention. We present the measurements of the azimuthal asymmetry of charged hadron production in Pb–Pb collisions at = 2.76 TeV via the study of a parity even 3- and 2-particle azimuthal correlator. The results for LHC energies are compared to the ones reported by RHIC experiments but also to different models and to predictions from theory. The possible implications of these measurements to the local parity violation and the contribution from background effects are discussed.

Anomalous behavior of pion production in high energy particle collisions

A shape of invariant differential cross section for charged hadron production as function of transverse momentum measured in various collider experiments is analyzed. Contrary to the behavior of produced charged kaons, protons and antiprotons, the pion spectra require an anomalously high contribution of an exponential term to describe the shape.

Pion fragmentation functions from e+e− production

We present the new sets of fragmentation functions for charged pions at leading order. They are fitted to data on inclusive charged-hadron production in e+e− annihilation taken by different collaborations, who discriminated between events with charm, bottom, and light-flavors fragmentation in their charged-hadron sample. They also agree with data on the production of neutral pions.

Suppression of high [formula omitted] hadrons in Pb + Pb collisions at LHC

Hadron production and their suppression in Pb+Pb collisions at LHC at a center-of-mass energy of sNN=2.76 TeV are studied within a multiphase transport (AMPT) model whose initial conditions are obtained from the recently updated HIJING 2.0 model. The centrality dependence of charged hadron multiplicity dNch/dη at midrapidity was found quite sensitive to the largely uncertain gluon shadowing parameter sg that determines the nuclear modification of the gluon distribution. We find final-state parton scatterings reduce considerably hadron yield at midrapidity and enforces a smaller gluon shadowing to be consistent with dNch/dη data at LHC. With such a constrained parton shadowing, charged hadron and neutral pion production over a wide transverse momenta range are investigated in AMPT. Relative to nucleon–nucleon collisions, the particle yield in central heavy ion collisions is suppressed due to parton energy loss. While the calculated magnitude and pattern of suppression is found consistent with that measured in Au+Au collisions at sNN=0.2 TeV at RHIC, at the LHC energy the suppression is overpredicted which may imply the medium formed at LHC is less opaque than expected from simple RHIC extrapolations. Reduction of the QCD coupling constant αs by ∼30% in the higher temperature plasma formed at LHC as compared to that at RHIC was found to reproduce the measured suppression at LHC.

Measurement of elliptic and higher order flow from ATLAS experiment at the LHC

We present a differential measurement of the azimuthal anisotropy of charged hadron production in Pb+Pb collisions at = 2.76 TeV. This azimuthal anisotropy is expanded into a Fourier series in azimuthal angle, where the coefficient for each term, vn, characterizes the magnitude of the anisotropy at a particular angular scale. We extract v2–v6 via a discrete Fourier analysis of the two-particle Δϕ–Δη correlation with a large Δη gap (|Δη| > 2), and via an event-plane method based on the forward calorimeter. Significant v2–v6 values are observed over a broad range in , η and centrality, and they are found to be consistent between the two methods in the transverse momentum region GeV. This suggests that the measured v2–v6 obtained from two-particle correlations at low with a large Δη gap are consistent with the collective response of the system to the initial-state geometry fluctuations, and is not the result of jet fragmentation or resonance decay.

Centrality dependence of charged particle spectra and RCP in Pb+Pb collisions at TeV with the ATLAS detector at the LHC

The ATLAS experiment at the LHC measures the charged particle spectra and the nuclear modification factor in Pb+Pb collisions at the TeV in a transverse momentum range up to 30 GeV and a pseudorapidity range up to |η| < 2.5. The measurement reveals the strong suppression of charged hadron production in the most central collisions at a pT of about 7 GeV. A suppression of more than a factor of 2 is also measured at the upper edge of the analyzed pT range. The suppression does not show any strong η dependence.

Dependence on pseudorapidity and on centrality of charged hadron production in PbPb collisions at $ \sqrt {{{s_{\text{NN}}}}} = 2.76 $ TeV

A measurement is presented of the charged hadron multiplicity in hadronic PbPb collisions, as a function of pseudorapidity and centrality, at a collision energy of 2.76 TeV per nucleon pair. The data sample is collected using the CMS detector and a minimum-bias trigger, with the CMS solenoid off. The number of charged hadrons is measured both by counting the number of reconstructed particle hits and by forming hit doublets of pairs of layers in the pixel detector. The two methods give consistent results. The charged hadron multiplicity density dN(ch)/d eta, evaluated at eta=0 for head-on collisions, is found to be 1612 +/- 55, where the uncertainty is dominated by systematic effects. Comparisons of these results to previous measurements and to various models are also presented.

Cross section and double-helicity asymmetry in charged hadron production in p + p collisions at √s = 62.4 GeV at PHENIX

The cross section and double-helicity asymmetry for production of non-identified positive and negative charged hadrons at midrapidity in p + p collisions at √s = 62.4 GeV have been measured by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) for a transverse momentum range of 0.5–4.5 GeV/c. The cross section measurements are compared to next-to-leading order and next-to-leading log perturbative QCD calculations, providing information on the applicability of these calculation techniques in the measured kinematic range. The double-helicity asymmetry measurement at this moderate energy provides sensitivity to ΔG, the gluon spin contribution to the spin of the proton, up to modestly larger values of the gluon momentum fraction than previous RHIC measurements at 200 GeV.

Hard quasi-real photo-production of charged hadrons at COMPASS energies

The Common Muon Proton Apparatus for Structure and Spectroscopy (COMPASS) at CERN with its use of beams of naturally polarized muons scattered of a polarized deuteron target, provides an environment of hard scattering between quasi-real photons and partons. Hard hadron quasi-real photo-production with polarized initial states is sensitive to the polarized gluon distribution ΔG through γ-gluon(g) direct channels as well as q-g resolved processes. Comparisons of unpolarized differential cross section measurements to next-to-leading order (NLO) pQCD calculations are essential to develop our understanding of proton-proton and lepton-nucleon scattering at varying center of mass energies. These measurements are important to asses the applicability of NLO pQCD in interpreting polarized processes. In this talk we will discuss unidentified charged separated hadron production at low Q2 (Q2 < 0.1 GeV2/c2) and high transverse momenta (pT > l.0GeV/c). < p2T > spectra of charged hadrons at Q2 > 1 GeV2/c2 will also be discussed.

High-p T spectra of charged hadrons in Au + Au collisions at √s NN = 9.2 GeV in STAR

The production of hadrons in heavy-ion collisions at high-p T provides an important information on mechanism of particle formation and constituent energy loss in medium. Such information is needed for search of a Critical Point and signatures of phase transition. Measurements by the STAR Collaboration of charged hadron production in Au + Au collisions at √s NN = 9.2 GeV over a wide transverse momentum p T = 0.2−4 GeV/c and at mid-rapidity range are reported. It allows for a first measurement of the spectra for charged hadrons at high p T at this energy. The spectra demonstrate the dependence on centrality which enhances with p T . The constituent energy loss and its dependence on transverse momentum of particle, and centrality of collisions are estimated in the z-scaling approach.

Produced charged hadrons in central [formula omitted] collisions at LHC energies in the RDM

The energy dependence of charged-hadron production in relativistic heavy-ion collisions is investigated in a nonequilibrium-statistical relativistic diffusion model (RDM) with three sources. Theoretical pseudorapidity distributions are compared with Au+Au data at RHIC energies of sNN=0.13 and 0.2 TeV, and computed for Pb+Pb central collisions at LHC energies of 2.76 and 5.52 TeV. The central, nearly equilibrated source arising from gluon–gluon collisions becomes the major origin of particle production at LHC energies. The midrapidity dip is determined by the interplay of the three sources.

First measurement of the underlying event activity at the LHC with $\sqrt{s} = 0.9$ TeV

A measurement of the underlying activity in scattering processes with transverse momentum scale in the GeV region is performed in proton-proton collisions at sqrt(s) = 0.9 TeV, using data collected by the CMS experiment at the LHC. Charged hadron production is studied with reference to the direction of a leading object, either a charged particle or a set of charged particles forming a jet. Predictions of several QCD-inspired models as implemented in PYTHIA are compared, after full detector simulation, to the data. The models generally predict too little production of charged hadrons with pseudorapidity eta < 2, p_T > 0.5 GeV/c, and azimuthal direction transverse to that of the leading object.

Hadron multiplicity inppandAAcollisions at LHC from the color glass condensate

We provide quantitative predictions for the rapidity, centrality and energy dependencies of inclusive charged-hadron productions for the forthcoming LHC measurements in nucleus-nucleus collisions based on the idea of gluon saturation in the color-glass condensate framework. Our formulation gives very good descriptions of the first data from the LHC for the inclusive charged-hadron production in proton-proton collisions, the deep inelastic scattering at HERA at small Bjorken-x, and the hadron multiplicities in nucleus-nucleus collisions at RHIC.

On saturation of charged hadron production in pp collisions at LHC

First results on charged hadron transverse momentum spectra in pp collisions obtained by the CMS Collaboration at the LHC are analyzed in the z-scaling approach. These LHC data confirm z-scaling. The saturation regime of the scaling function ψ(z) observed in pp and interactions at lower energies GeV is verified. The saturation of ψ(z) for charged hadrons is found down to a value of z ≃ 0.05 at the highest energy GeV currently reached by the colliders. A microscopic scenario of hadron production is discussed in connection with the search for new signatures of phase transitions in hadron matter. Constituent energy loss and its dependences on the transverse momentum and collision energy are estimated. We suggest that the beam energy scan program in the saturation region at the LHC could be of interest.

Inclusive single-particle production in two-photon collisions at LEP II with the DELPHI detector

A study of the inclusive charged hadron production in two-photon collisions is described. The data were collected with the DELPHI detector at LEP II. Results on the inclusive single-particle pT distribution and the differential charged hadrons dσ/dpT cross-section are presented and compared to the predictions of perturbative NLO QCD calculations and to published results.

Medium-modified DGLAP evolution of fragmentation functions from large to small x

The unified description of fragmentation function evolution from large to small x which was developed for the vacuum in previous publications is now generalized to the medium, and is studied for the case in which the complete contribution from the largest class of soft gluon logarithms, the double logarithms, are accounted for and with the fixed order part calculated to leading order. In this approach it proves possible to choose the remaining degrees of freedom related to the medium such that the distribution of produced hadrons is suppressed at large momenta while the production of soft radiation-induced charged hadrons at small momenta is enhanced, in agreement with experiment. Just as for the vacuum, our approach does not require further assumptions concerning fragmentation and is more complete than previous computations of evolution in the medium.

Inclusive Production of Charged Hadrons and Jets in Photon-Photon Collision at LEP2

The inclusive production of charged hadrons and jets in the collisions of quasi-real photons (e+e− → e+e−+X) has been measured using the OPAL [1] detector at LEP. This analysis used the data taken by the OPAL-detector 1997-2000, L=616 pb−1 (hadrons) and 1998-2000, L=593 pb−1 (jet). The differential cross-sections as a function of the transverse momentum and the pseudorapidity of the hadrons and jets are compared to theoretical calculations of up to next-to-leading order.

Extraction of g1p, g1d and δg/g from HERMES data

HERMES collected deep-inelastic scattering (DIS) events of 27.6 GeV longitudinally polarised positrons off longitudinally polarised hydrogen and deuterium gas targets internal the HERA storage ring. Double-spin asymmetries A∥p,d of cross sections in inclusive DIS allow the precise extraction of spin structure functions of the proton g1p(x,Q2) and the deuteron g1d(x,Q2) in the kinematic range 0.0041 ≤ x ≤ 0.9 and 0.18 GeV ≤ Q2 ≤ 20GeV2. Furthermore, double-spin asymmetries of inclusive production of charged hadrons as a function of transverse momentum pt have been measured. For pt > 1 GeV the asymmetries are sensitive to the spin dependent gluon distribution function δg. Using a Leading Order Monte Carlo model to obtain information on the background asymmetry and background process kinematics, δg/g has been extracted.

Particle production and spectroscopy at HERA

Recent results on production of neutral strange ( K s 0 , Λ , Λ ¯ ) , charged and exotic ( Θ + , Θ c ) hadrons in ep collisions at HERA are presented. Measurements are compared with various Monte Carlo calculations.