Average Multiplicity Of Charged Hadrons Research Articles

Pseudorapidity distributions of charged hadrons in proton-lead collisions at sqrt{s_{mathrm{NN}}}=5.02 and 8.16 TeV

The pseudorapidity distributions of charged hadrons in proton-lead collisions at nucleon-nucleon center-of-mass energies sqrt{s_{mathrm{NN}}}=5.02 and 8.16 TeV are presented. The measurements are based on data samples collected by the CMS experiment at the LHC. The number of primary charged hadrons produced in non-single-diffractive proton-lead collisions is determined in the pseudorapidity range |ηlab| < 2.4. The charged-hadron multiplicity distributions are compared to the predictions from theoretical calculations and Monte Carlo event generators. In the center-of-mass pseudorapidity range |ηcm| < 0.5, the average charged-hadron multiplicity densities 〈dNch/dηcm〉|ηcm| < 0.5 are 17.31 ± 0.01 (stat) ± 0.59 (syst) and 20.10 ± 0.01 (stat) ± 0.85(syst) at sqrt{s_{mathrm{NN}}}=5.02 and 8.16 TeV, respectively. The particle densities per participant nucleon are compared to similar measurements in proton-proton, proton-nucleus, and nucleus-nucleus collisions.

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

Multiplicity distributions of secondary hadrons produced in p\( \bar p \) and collisions are very different. There are three types of inelastic processes in 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.

Can universality of the QCD evolution be checked in W boson decays into hadrons?

The average multiplicity of charged hadrons from W boson is calculated in pQCD. The agreement of our theoretical predictions with the LEP data is in favor of universality of the QCD evolution in hard processes.

Hadron multiplicity in e+e-events induced by top quark pairs at the ILC energy

The average charged hadron multiplicity in the $e^+e^-$ events with the primary $t\bar{t}$-pair at the collision energy 500 GeV, as well as the average multiplicity of charged hadrons from the top quark are calculated in QCD to be $86.7 \pm 1.11$ and $41.0 \pm 0.54$, respectively.

Nuclear shadowing, diffractive scattering and low momentum protons in μXe interactions at 490 GeV

The production of charged hadrons is studied in μXe and μD interactions at 490 GeV beam energy. The data were taken at the Tevatron at Fermilab with the E665 spectrometer, equipped with a streamer chamber as vertex detector. Differences between the μXe and μD data are explained by cascading of hadrons in the Xe nucleus. The average multiplicity of charged hadrons in μXe scattering is compared to previously published pXe scattering data and is found to be strongly reduced. This is traced back to the low number of ‘projectile’ collisions in μXe interactions. From a study of thex Bj dependence of hadron production in μXe scattering, and by considering events with a large rapidity gap, evidence is found for a significant contribution of diffractive scattering, which is enhanced in the kinematic region where shadowing of the cross section is observed. This result supports recent models in which diffractive scattering and nuclear shadowing are closely related.

Growth of the average multiplicity of particles in high-energy collisions.

The data on the growth of the average charged-hadron multiplicity in [ital p]([ital [bar p]])-[ital p] collisions from [radical][ital s] =5 to 900 GeV, and in [ital e][sup +][ital e[minus]] annihilation from 10 to 90 GeV, are described by the same slowly increasing power of [ital s]. The power approaches an asymptotic value of the order of 0.1 only at [radical][ital s] [similar to]1000 TeV. The ratio of the average multiplicity in [ital e][sup +][ital e[minus]] annihilation to that in [ital pp] collisions is nearly constant at 1.5; thus, the difference between these averages increases. A small but increasing energy fraction tends to be removed from particle production in the extreme fragmentation region; this sustains relatively increasing production of high multiplicities of soft particles.

W 2 andQ 2 dependence of charged hadron and pion multiplicities invp and $$\bar vp$$ charged current interactionscharged current interactions

Using data onvp and\(\bar vp\) charged current interactions from a bubble chamber experiment with BEBC at CERN, the average multiplicities of charged hadrons and pions are determined as functions ofW2 andQ2. The analysis is based on ∼20000 events with incidentv and ∼10000 events with incident\(\bar v\). In addition to the known dependence of the average multiplicity onW2 a weak dependence onQ2 for fixed intervals ofW is observed. ForW>2 GeV andQ2>0.1 GeV2 the average multiplicity of charged hadrons is well described by〈n〉=a1+a2ln(W2/GeV2)+a3ln(Q2/GeV2) witha1=0.465±0.053,a2=1.211±0.021,a3=0.103±0.014 for thevp anda1=−0.372±0.073,a2=1.245±0.028,a3=0.093±0.015 for the\(\bar vp\) reaction.

Quark models for hadronic reactions. Nucleon-nucleon scattering

A model for the development of scattered quarks into final-state hadrons is extended for application to hadronic reactions, focusing on nucleon-nucleon scattering in particular. Numerical calculations show that the model reproduces the main features of experimental data on secondary-hadron production in low-transverse-momentum nucleon-nucleon scattering at c.m. energies above about 3 GeV, including the variation of sigma/sub el//sigma/sub tot/ with energy, the average charged-hadron multiplicity, the moments of the charged-hadron multiplicity distribution, and the longitudinal-momentum distribution of final-state hadrons. In anticipation of the future availability of higher-energy nucleon colliding-beam machines, charged-hadron multiplicities are estimated for c.m. energies up to 2000 GeV.

Multiplicity distributions in a quark model for high-energy nucleon-nucleon scattering

A quark model for high-energy nucleon-nucleon scattering is outlined. The ratio of elastic to total cross section and the average transverse momentum of secondary hadrons are constant in this model. A constant value for the average three-momentum transfer in high-energy collisions is assumed based on the physical picture of two Lorentz-contracted disks colliding at infinite momentum in the c.m. Besides the nucleon and pion masses, only the three constants mentioned previously are needed to calculate hadronic multiplicity distributions, and these constants can be determined from experimental data. The average charged-hadron multiplicity calculated from the model grows as ${E}^{\frac{1}{4}}$ at asymptotic energies, where $E$ is the laboratory energy of the projectile. The calculated values of the higher moments of the multiplicity distribution show the same qualitative behavior as is experimentally observed.

Simple model fore+e−annihilation predicts rapid rise of hadron multiplicity observed at PETRA

The simple model for ${e}^{+}{e}^{\ensuremath{-}}$ annihilation developed in an article previously published in this journal [Phys. Rev. D 20, 1093 (1979)] is extended to the PETRA energy range (10 to 40 GeV in the c.m.). The calculated values of the average charged-hadron multiplicity are in reasonable agreement with experiment.

Hadron-jet production in high-energy electron-positron annihilation

A simple model is developed for the conversion of an initially produced quark-antiquark pair into hadron jets in electron-positron annihilation. The model assumes that only two quark flavors ($u$ and $d$) are produced, both quarks have the same mass, and all final-state hadrons are pions. In the model, hadrons are produced in two oppositely directed jets in the center-of-momentum (c.m.) frame of the annihilating electron and positron, and the average hadron momentum transverse to the jet direction is constant. The average multiplicity of charged hadrons and the average energy per charged hadron rise as ${s}^{\frac{1}{4}}$ at high energies, where $s$ is the square of the total c.m. energy. If the component of the final-state hadron momentum parallel to the jet direction is denoted by ${p}_{\ensuremath{\parallel}}$, and the average value of the momentum component perpendicular to the jet axis is calculated for hadrons with different values of ${x}_{\ensuremath{\parallel}}=\frac{2{p}_{\ensuremath{\parallel}}}{{s}^{\frac{1}{2}}}$, a seagull effect is observed. Particle-density distributions of the charged final-state hadrons can also be calculated as a function of ${x}_{\ensuremath{\parallel}}$. These distributions rise to a peak as ${x}_{\ensuremath{\parallel}}\ensuremath{\rightarrow}0$ and are not strongly dependent on the c.m. energy.

Hadron Production by Electron - Positron Annihilation at 5 GeV Center - of Mass Energy

We have measured the cross section \ensuremath{\sigma} for electron - positron annihilation into three or more hadrons, with at least two charged particles in the final state, at 5 GeV center-of-mass energy. We find a model-independent lower limit of $\ensuremath{\sigma}&gt;9.1\ifmmode\pm\else\textpm\fi{}1.0$nb; assuming invariant phase-space production of pions, we calculate the detection efficiency of our detector to be (45 \ifmmode\pm\else\textpm\fi{} 11)%, yielding a cross section $\ensuremath{\sigma}=21\ifmmode\pm\else\textpm\fi{}5$nb. The average charged hadron multiplicity is found to be $\overline{n}=4.3\ifmmode\pm\else\textpm\fi{}0.6$.

Study of electroproduction with a streamer chamber for 0.3 < Q2 < 1.5 GeV 2, mp ⩽ W < 2.8 GeV

Electroproduction in the kinematical region 0.3 < Q 2 < 1.5 GeV 2, m p ⩽ W < 2.8 GeV has been studied with a streamer chamber at DESY. The average multiplicity of charged hadrons is found to be somewhat smaller (∼ 10%) than for photoproduction. The normalized π − inclusive momentum spectra show less leading negative pions with increasing Q 2. The reaction ep → ep π + π − has been analyzed. The mass distributions show strong Δ ++ formation at low energies and dominant π 0 production for high energies. The cross sections for Δ ++ and ϱ 0 production have been determined by maximum-likelihood fits. The ratio of ϱ 0 to total inelastic production drops with Q 2 from (16.6 ± 0.8)% at Q 2 = 0 to (7.6 ± 2.1)% [(4.3 ± 2.9)%] at 〈 Q 2〉 = 0.6 [1.04] GeV 2. The t-distribution for events in the ϱ mass region becomes increasingly flat with Q 2. The ϱ 0 decay angular distribution has been analyzed in the helicity system. Near threshold (1.7 < W < 2 GeV) the ϱ 0 mesons are longitudinally polarized. For higher energies more transversely-aligned ϱ 0 mesons are being produced. Under the assumption of s-channel helicity conservation the ratio R = σ L(ep ϱ 0)/ σ T(ep ϱ 0) is found to be 0.30 ± 0.14 at 〈 Q 2〉 = 0.6 GeV 2, 〈 W〉 = 2.3 GeV.