Pseudorapidity Distributions Research Articles

Open charm meson production at LHC

We discuss charm production at the LHC. The production of single $c \bar c$ pairs is calculated in the $k_t$-factorization approach. We use Kimber-Martin-Ryskin unintegrated gluon distributions in the proton. The hadronization is included with the help of Peterson fragmentation functions. Transverse momentum and pseudorapidity distributions of charmed mesons are presented and compared to recent results of the ALICE, LHCb and ATLAS collaborations. Furthermore we discuss production of two pairs of $c \bar c$ within a simple formalism of double-parton scattering (DPS). Surprisingly large cross sections, comparable to single-parton scattering (SPS), are predicted for LHC energies. We discuss perspectives how to identify the double scattering contribution. We predict much larger cross section for large rapidity distance between charm quarks from different hard parton scatterings compared to single scattering.

Predictions from a simple hadron rescattering model for pp collisions at the LHC

With studies of heavy ion and pp physics already under way at the LHC, it is necessary to consider how hadronic rescattering will affect the observed results from experiments. Through the use of a simple relativistic kinematics-based hadron rescattering model we show that the hadron rescattering phase can obscure some signals for radial flow in pp collisions at LHC energies. It is shown that the hadron rescattering model does not distort pseudorapidity distributions for pp collisions at , 7, 10 and 14 TeV, but does effect two-boson Hanbury–Brown Twiss (HBT) observables. We also compare HBT results from the model with recent measurements of ππ HBT in 0.9 TeV pp collisions. We show that there is very good agreement between the rescattering model and experiment in terms of multiplicity dependence of 1D HBT radii. There is also considerable agreement between the two on the kT dependence of 1D HBT radii. Predictions are also made for 1D and 3D identical pion and kaon correlation functions from pp collisions using the rescattering model for , 7, 10 and 14 TeV. These correlation functions are binned by multiplicity and kT, both separately and together. Fits to these correlation functions indicate that any kT signal of radial flow in pp collisions would be largely obscured by rescattering in the post-hadronization phase.

Pseudorapidity Distributions of Charged Particles Produced in pp Collisions at the CERN LHC Energies

Pseudorapidity Distributions of Charged Particles Produced in pp Collisions at the CERN LHC Energies

Diffraction dissociation in proton–proton collisions at = 0.9, 2.76 and 7 TeV with ALICE at the LHC

The relative rates of single- and double-diffractive processes were measured with the ALICE detector by studying properties of gaps in the pseudorapidity distribution of particles produced in proton–proton collisions at = 0.9, 2.76 and 7 TeV. ALICE triggering efficiencies are determined for various classes of events using a detector simulation validated with data on inclusive particle production. Cross-sections are determined using the van der Meer scans to measure beam properties and obtain a measurement of the luminosity.

Scaling violation and the inelasticity of very high energy proton–proton interactions

The pseudorapidity measurements at LHC, although in the central region only, allows us to perform preliminary tests of the multiparticle production extrapolation formula inspired by the analysis of recent cosmic ray data. Feynman scaling violation in the form proposed originally by Wdowczyk and Wolfendale in the 1970s has been applied to the Pierre Auger Observatory and the Hi-Res group measurements. The consistency of the average extensive air shower development with the hypothesis of protons being the primary particles, as indicated by anisotropy observations, was found for a smooth rise of the scaling violation parameter. We have shown that the longitudinal momenta of the produced particles determined inclusively as rapidity (pseudorapidity) distributions measured by LHC experiments follow the same universal high energy distribution scaled respectively. The high degree of Feynman scaling violation is confirmed. The decrease of the very high energy interaction inelasticity suggested by the cosmic ray data analysis is found to be consistent with LHC measurements up to 7 TeV.

System size, energy, centrality and pseudorapidity dependence of charged-particle density in Au+Au and Cu+Cu collisions at RHIC

Charged particle pseudorapidity distributions are presented from the PHOBOS experiment at RHIC, measured in Au+Au and Cu+Cu collisions at $\sqrt {s_{NN} } $ =19.6, 22.4, 62.4, 130 and 200 GeV, as a function of collision centrality. The presentation includes the recently analyzed Cu+Cu data at 22.4 GeV. The measurements were made by the same detector setup over a broad range in pseudorapidity, |η| < 5.4, allowing for a reliable systematic study of particle production as a function of energy, centrality and system size. Comparing Cu+Cu and Au+Au results, we find that the total number of produced charged particles and the overall shape (height and width) of the pseudorapidity distributions are determined by the number of nucleon participants, N part. Detailed comparisons reveal that the matching of the shape of the Cu+Cu and Au+Au pseudorapidity distributions over the full range of η is better for the same N part/2A value than for the same N part value, where A denotes the mass number. In other words, it is the geometry of the nuclear overlap zone, rather than just the number of nucleon participants that drives the detailed shape of the pseudorapidity distribution and its centrality dependence.

Centrality dependence of pseudorapidity distributions of baryons in heavy ion collisions at RHIC

The energy and centrality independence of the limiting fragmentation for produced mesons have been used to extract the reduced pseudorapidity (η′ = η − η beam ) distributions of charged baryons at forward rapidity. The distribution crosses at η′ ≈ = −1 suggesting the prominence of beam protons above that rapidity. The loss of beam rapidity has been extracted which has been found to increase with centrality.

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.

Charged-particle multiplicity and pseudorapidity distributions measured with the PHOBOS detector inAu+Au,Cu+Cu,d+Au, andp+pcollisions at ultrarelativistic energies

Pseudorapidity distributions of charged particles emitted in $Au+Au$, $Cu+Cu$, $d+Au$, and $p+p$ collisions over a wide energy range have been measured using the PHOBOS detector at RHIC. The centrality dependence of both the charged particle distributions and the multiplicity at midrapidity were measured. Pseudorapidity distributions of charged particles emitted with $|\eta|<5.4$, which account for between 95% and 99% of the total charged-particle emission associated with collision participants, are presented for different collision centralities. Both the midrapidity density, $dN_{ch}/d\eta$, and the total charged-particle multiplicity, $N_{ch}$, are found to factorize into a product of independent functions of collision energy, $\sqrt{s_{_{NN}}}$, and centrality given in terms of the number of nucleons participating in the collision, $N_{part}$. The total charged particle multiplicity, observed in these experiments and those at lower energies, assumes a linear dependence of $(\ln s_{_{NN}})^2$ over the full range of collision energy of $\sqrt{s_{_{NN}}}$=2.7-200 GeV.

Pseudorapidity distributions of charged particles inp−p̄orp−pcollisions at high energies and predictions at ultrahigh energies

Pseudorapidity distributions of charged particles produced in $p\ensuremath{-}\mathrm{p\ifmmode \bar{}\else \={}\fi{}}$ or $p\ensuremath{-}p$ collisions at different energies were reported by the UA5, UA1, P238, CDF, and ALICE collaborations. A multisource ideal gas model is used to fit the experimental data in this paper. According to the parameter values obtained from fitting the data, we find different linear relationships between different parameters and logarithmic center-of-mass energy. A prediction for the pseudorapidity distributions of charged particles produced in $p\ensuremath{-}\mathrm{p\ifmmode \bar{}\else \={}\fi{}}$ or $p\ensuremath{-}p$ collisions at the higher Large Hadron Collider energies is given.

Systematic study of photon production at forward rapidity in STAR

We present the measurement of multiplicity and pseudorapidity distributions of photons production at forward rapidity (−2.3 ≤ η ≤ −3.8) for Cu + Cu collisions at \( \sqrt {S_{NN} } \) = 62.4 and 200 GeV. Photons are measured using the Photon Multiplicity Detector (PMD) in STAR experiment at RHIC. The distributions of (η−ηbeam), where ηbeam is beam rapidity is presented. Pseudorapidity distributions of photons at forward rapidities, when ob-served in the frame of one of the colliding particles show the signature of energy independent scaling at forward rapidities known as Limiting Fragmentation. Measurement of inclusive photons reflect the distribution for π0 as most of the photons come from π0 decay. Gluon saturation at initial conditions of the collisions is one of the possible explanations for this scaling. Study of system-size and incident energy dependence of this phenomenon help us understand the mechanisms better. The system-size and energy dependence of the widths of scaling in pseudorapidity and comparison with model predictions are presented.

Rapidity and Pseudorapidity Distributions of theVarious Hadron-Species Produced in High EnergyNuclear Collisions: A Systematic Approach

With the help of a phenomenological approach outlined in the text in some detail, we have dealt here with the description of the plots on rapidity and pseudorapidity spectra of some hadron-secondaries produced in various nucleus-nucleus interactions at high energies. The agreement between the measured data and the attempted fits are, on the whole, modestly satisfactory excepting a very narrow central region in the vicinity of y = η = 0. At last, hints to how the steps suggested in the main body of the text to proceed with the description of the measured data given in the plots could lead finally to a somewhat systematic methodology have also been made.

Inclusive light hadron production inppscattering at the LHC

The inclusive production of light mesons in pp-scattering is considered in the framework of reggeon phenomenology with supercritical Pomeron. Available low-energy data can be explained with three reggeon particles taken into account. With the obtained results rapidity and pseudorapidity distributions for light-meson production at LHC energies are predicted.

Charged Hadron Spectra Measurement with the CMS detector in pp collisions at [formula omitted], 2.36, and 7 TeV

The CMS measurement of the charged hadron pseudorapidity and transverse momentum distributions in minimum bias pp collisions at s = 0.9 , 2.36 and 7 TeV, is presented. The charged hadron yield results were obtained using the inner silicon tracker, by means of 3 different methods: counting the number of reconstructed hits, the number of hit pairs (tracklet-based algorithm), and the number of fully reconstructed particle tracks. The obtained data is compared with other experiment results, several Monte-Carlo models and tunes, as well as some current theoretical models.

Erratum: Scaled momentum spectra in deep inelastic scattering at HERA

Charged particle production has been studied in neutral current deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 0.44 fb^-1. Distributions of scaled momenta in the Breit frame are presented for particles in the current fragmentation region. The evolution of these spectra with the photon virtuality, Q^2, is described in the kinematic region 10<Q^2<41000 GeV^2. Next-to-leading-order and modified leading-log-approximation QCD calculations as well as predictions from Monte Carlo models are compared to the data. The results are also compared to e+e- annihilation data. The dependences of the pseudorapidity distribution of the particles on Q^2 and on the energy in the \gamma p system, W, are presented and interpreted in the context of the hypothesis of limiting fragmentation.

VALIDITY OF NAKAMURA–KUDO SCALING OF CHARGED PARTICLE PSEUDORAPIDITY DISTRIBUTION IN RELATIVISTIC HIGH-ENERGY h–A INTERACTIONS

Nakamura and Kudo proposed a scaling form for charged particle pseudorapidity distributions on the basis of scaling in the mean hypothesis. This scaling form was tested primarily for hadron–hadron interaction data. But no attempt was made to verify this for hadron–nucleus interaction which offers unique opportunity to learn about the space–time structure of a strongly interacting process. In view of this we report an analysis of p–AgBr interaction data at 400 GeV/c and 200 GeV/c, π-–AgBr interaction data at 200 GeV/c and 350 GeV/c to test its (Nakamura–Kudo scaling) validity in hadron–nucleus interaction. In all cases the data show a remarkable agreement with the scaling behavior of Nakamura and Kudo.

Centrality dependences of the pseudorapidity distributions of charged particles in Au+Au collisions at RHIC energies

By employing the Glauber model, we give the centrality dependences of the numbers of participants and binary nucleon-nucleon collisions in nucleus-nucleus collisions. By taking into account the energy loss of the participants in their multiple collisions, we then present the pseudorapidity distributions of charged particles in nucleus-nucleus collisions as a function of beam energy and impact parameter. Finally, we analyze the centrality dependence of the pseudorapidity of the charged particles in Au+Au collisions at energies from = 19.6 to 200 GeV. The theoretical results are in good agreement with the experimental observations of the RHIC-PHOBOS collaboration.

(3+1)D hydrodynamic simulation of relativistic heavy-ion collisions

We present music, an implementation of the Kurganov-Tadmor algorithm for relativistic 3+1 dimensional fluid dynamics in heavy-ion collision scenarios. This Riemann-solver-free, second-order, high-resolution scheme is characterized by a very small numerical viscosity and its ability to treat shocks and discontinuities very well. We also incorporate a sophisticated algorithm for the determination of the freeze-out surface using a three dimensional triangulation of the hypersurface. Implementing a recent lattice based equation of state, we compute ${p}_{T}$-spectra and pseudorapidity distributions for Au+Au collisions at $\sqrt{s}=200 \mathrm{GeV}$ and present results for the anisotropic flow coefficients ${v}_{2}$ and ${v}_{4}$ as a function of both ${p}_{T}$ and pseudorapidity $\ensuremath{\eta}$. We were able to determine ${v}_{4}$ with high numerical precision, finding that it does not strongly depend on the choice of initial condition or equation of state.

Transverse-Momentum and Pseudorapidity Distributions of Charged Hadrons inppCollisions ats=7 TeV

Charged-hadron transverse-momentum and pseudorapidity distributions in proton-proton collisions at sqrt(s) = 7 TeV are measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield is obtained by counting the number of reconstructed hits, hit-pairs, and fully reconstructed charged-particle tracks. The combination of the three methods gives a charged-particle multiplicity per unit of pseudorapidity, dN(charged)/d(eta), for |eta| < 0.5, of 5.78 +/- 0.01 (stat) +/- 0.23 (syst) for non-single-diffractive events, higher than predicted by commonly used models. The relative increase in charged-particle multiplicity from sqrt(s) = 0.9 to 7 TeV is 66.1% +/- 1.0% (stat) +/- 4.2% (syst). The mean transverse momentum is measured to be 0.545 +/- 0.005 (stat) +/- 0.015 (syst) GeV/c. The results are compared with similar measurements at lower energies.

Hadron Multiplicities in Pb+Pb Collisions at the Large Hadron Collider and Pomeron Loop Effects

We study the pseudo-rapidity distribution of hadron multiplicities of high energy Pb+Pb collisions by using color glass condensate dynamics at LHC/ALICE in the fixed coupling case. It is found that after including the pomeron loop effects the charged hadron multiplicities at central rapidity are about 1500 for central Pb+Pb collisions, which are significantly smaller than the saturation based calculations, ∼ 1700 ÷ 2500 and compatible with that based on a study of multiplicities in the fragmentation region.