Average Charged Particle Multiplicity Research Articles

Predictions on global properties in O+O collisions at the Large Hadron Collider using a multi-phase transport model

Oxygen (^{16}O) ions are planned to be injected at the Large Hadron Collider (LHC) in its next runs, and a day of physics run is anticipated for O+O collisions at sqrt{s_mathrm{{NN}}} = 7 TeV. As the system size of O+O collisions has the final state multiplicity overlap with those produced in pp, p+Pb and Pb+Pb collisions, the study of global properties in O+O collisions may provide a deeper insight into the heavy-ion-like behavior observed in small collision systems and its similarities/differences with a larger system like Pb+Pb collisions. In the present work, we report the predictions for global properties in O+O collisions at sqrt{s_mathrm{{NN}}} = 7 TeV using a multi-phase transport model (AMPT). We report the mid-rapidity charged-particle multiplicity, transverse mass, Bjorken energy density, pseudo-rapidity distributions, squared speed of sound, transverse momentum (p_mathrm{T}) spectra, the kinetic freeze-out parameters, and p_mathrm{T}-differential particle ratio as a function of collision centrality. Further, we have studied the transverse momentum-dependent elliptic flow of charged particles. The results are shown for Woods-Saxon and harmonic oscillator nuclear density profiles. In addition, we have compared the results with an alpha -clustered structure incorporated inside the oxygen nucleus. Average charged-particle multiplicity and the Bjorken energy density show a significant increase in most central collisions for the harmonic oscillator density profile, while other global properties show less dependence on the density profiles considered in this work. The results from the alpha -clustered structure incorporated inside the oxygen nucleus show similar initial energy density and final charged-particle multiplicity as observed for the harmonic oscillator density profile.

Study of charged particles produced in the 84Kr + nuclear emulsion interactions at 1 GeV per nucleon

Abstract The main focus of this article is to study the characteristics of charged pions and their correlation with shower particles emitted in the interaction of 84Kr + emulsion at 1 A GeV. Author have also studied the dependence of the average multiplicity of charged pions and shower particles with projectile mass. In this study author observed that the average multiplicity of charged pions and shower particles showing the linear dependency on the projectile mass.

Freeze-out scenarios in small systems at RHIC and LHC energies

We study the hadronic yields produced in two small collision systems [Formula: see text] at [Formula: see text][Formula: see text]TeV and [Formula: see text] at [Formula: see text][Formula: see text]TeV, and extracted the chemical freeze-out (CFO) parameters. The CFO parameters are obtained using a hadron resonance gas (HRG) model and in this study present the system size dependence of the parameters. We observe that with the strangeness suppression factor [Formula: see text] included in the model, a single freeze-out scenario can describe hadronic yields for all the centralities of [Formula: see text] collision at [Formula: see text][Formula: see text]TeV, indicating that the strange hadrons have not reached full equilibrium. On the other hand, for small average charged particle multiplicity ([Formula: see text]) bins of [Formula: see text] collision at [Formula: see text][Formula: see text]TeV strangeness is not fully equilibrated whereas strangeness equilibration seems to be reached in large [Formula: see text]. For both the collision systems, no significant system volume dependence of the temperature has been observed. However, in comparable [Formula: see text] values, temperatures are 10–20[Formula: see text]MeV larger for [Formula: see text] collision compared to [Formula: see text] collision. We observe that the volume of the system at the CFO increases with increase of charge multiplicity for both the collisions. The increase is much steeper in [Formula: see text] collision at [Formula: see text][Formula: see text]TeV than [Formula: see text] collision at [Formula: see text][Formula: see text]TeV. Further, we analyze the transverse momentum ([Formula: see text]) spectra of different hadrons produced in [Formula: see text] collision at [Formula: see text][Formula: see text]TeV in a combined freeze-out scenario. We show the [Formula: see text] dependence of freeze-out parameters. It is observed that with [Formula: see text] included in the model, a single freeze-out scheme can describe the [Formula: see text] spectra. For similar [Formula: see text] values, [Formula: see text] in both the collision systems are close to each other and overall values of [Formula: see text] increase with increase of [Formula: see text]. Unlike CFO scenario using the produced hadron yields only, freeze-out temperature in combined scenario of chemical and kinetic freeze-out, obtained from [Formula: see text] spectra, increases with increase of [Formula: see text]. For smaller [Formula: see text] values, the temperature in [Formula: see text] collision at [Formula: see text][Formula: see text]TeV is similar to that of [Formula: see text] collision at [Formula: see text][Formula: see text]TeV. However, temperatures are larger in [Formula: see text] collision than [Formula: see text] collision at larger [Formula: see text] values.

Multiplicity fluctuations in the Glauber Monte Carlo approach

We discuss multiplicity fluctuations of charged particles produced in nuclear collisions measured event-by-event by the NA49 experiment at CERN SPS within the Glauber Monte Carlo approach. We use the concepts of wounded nucleons and wounded quarks in the mechanism of multiparticle production to characterize multiplicity fluctuations expressed by the scaled variance of multiplicity distribution. Although Wounded Nucleon Model correctly reproduce the centrality dependence of the average multiplicity in Pb+Pb collisions, it completely fails in description of corresponding centrality dependence of scaled variance of multiplicity distribution. Using subnucleonic degrees of freedom, i.e. wounded quarks within Wounded Quark Model, it is possible to describe quite well the multiplicity distribution of charged particles produced in proton+proton interactions. However, the Wounded Quark Model with parameters describing multiplicity distribution of particles produced in proton+proton interactions substantially exceeds the average multiplicity of charged particles produced in Pb+Pb collisions. To obtain values of average multiplicities close to those experimentally measured in Pb+Pb collisions, the concept of shadowed quark sources is implemented. Wounded Quark Model with implemented shadowing source scenario reproduces the centrality dependence of scaled variance of multiplicity distribution of charged particles produced in Pb+Pb collisions in the range from the most central to mid-peripheral interactions.

Production of deuterons, tritons, He3 nuclei, and their antinuclei in pp collisions at s=0.9 , 2.76, and 7 TeV

Invariant differential yields of deuterons and anti-deuterons in pp collisions at $\sqrt{s}$ = 0.9, 2.76 and 7 TeV and the yields of tritons, $^{3}$He nuclei and their anti-nuclei at $\sqrt{s}$ = 7 TeV have been measured with the ALICE detector at the CERN Large Hadron Collider. The measurements cover a wide transverse momentum ($p_{\text{T}}$) range in the rapidity interval $|y|<0.5$, extending both the energy and the $p_{\text{T}}$ reach of previous measurements up to 3 GeV/$c$ for $A=2$ and 6 GeV/$c$ for $A=3$. The coalescence parameters of (anti-)deuterons and $^{3}\overline{\text{He}}$ nuclei exhibit an increasing trend with $p_{\text{T}}$ and are found to be compatible with measurements in pA collisions at low $p_{\text{T}}$ and lower energies. The integrated yields decrease by a factor of about 1000 for each increase of the mass number with one (anti-)nucleon. Furthermore, the deuteron-to-proton ratio is reported as a function of the average charged particle multiplicity at different center-of-mass energies.

Measurement of the charged-particle multiplicity inside jets from [Formula: see text][Formula: see text]pp collisions with the ATLAS detector.

The number of charged particles inside jets is a widely used discriminant for identifying the quark or gluon nature of the initiating parton and is sensitive to both the perturbative and non-perturbative components of fragmentation. This paper presents a measurement of the average number of charged particles with p_text {T}>500 {mathrm{MeV}} inside high-momentum jets in dijet events using 20.3 fb^{-1} of data recorded with the ATLAS detector in pp collisions at sqrt{s}=8 {mathrm{TeV}} collisions at the LHC. The jets considered have transverse momenta from 50 {mathrm{GeV}} up to and beyond 1.5 {mathrm{TeV}}. The reconstructed charged-particle track multiplicity distribution is unfolded to remove distortions from detector effects and the resulting charged-particle multiplicity is compared to several models. Furthermore, quark and gluon jet fractions are used to extract the average charged-particle multiplicity for quark and gluon jets separately.

Indication of transverse radial flow in high-multiplicity proton–proton collisions at the Large Hadron Collider

We analyze the measured spectra of π±, K±, p() in proton–proton (pp) collisions at = 0.9, 2.76 and 7 TeV in the light of blast-wave model to extract the transverse radial flow velocity and kinetic temperature at freeze-out for the system formed in pp collisions. The dependence of the blast-wave parameters on average charged particle multiplicity of event sample or the ‘centrality’ of collisions has been studied and compared with results of similar analysis in nucleus–nucleus (AA) and proton–nucleus (pA) collisions. We analyze the spectra of , Λ() and Ξ− also to see the dependence of blast-wave description on the species of produced particles. Within the framework of the blast-wave model, the study reveals indication of collective behavior for high-multiplicity events in pp collisions at LHC. Strong transverse radial flow in high-multiplicity pp collisions and its comparison with that in pA and AA collisions match with predictions from a very recent theoretical work (Shuryak and Zahed 2013 arXiv:hep-ph/1301.4470) that addresses the conditions for applicability of hydrodynamics in pp and pA collisions.

Decisive Test of Color Coherence in Proton-Nucleus Collisions at the LHC

Proton-nucleus collisions (p+A) at LHC energies provide a rigorous test of color glass condensate (CGC), a model proposed to describe the high energy limit of quantum chromodynamics. In the CGC the average multiplicity of charged particles at midrapidity in p+A collisions depends logarithmically on the number of participants, N(part). In contrast, the wounded nucleon model of independent nucleon-nucleon scatterings, verified at RHIC energies, predicts that multiplicity in p+A depends linearly on N(part). We argue that the dependence of mean multiplicity on N(part) in p+A collisions at LHC energies can single out a model of particle production, thus offering a stringent test of the CGC and the wounded nucleon model. Based on this observation we propose a novel experimental test of color coherence in p+A collisions.

Multiplicity of charged particles in electron-induced showers developing in oriented silicon and tungsten crystals

A more than twofold increase in the average multiplicity of charged particles in electromagnetic showers initiated by electrons with an energy of 26 GeV in tungsten crystals 2.7, 5.8, and 8.4 mm thick, oriented along the 〈111〉 axis, in comparison with misoriented crystals is shown. For a silicon crystal 20 mm thick, oriented along the 〈110〉 axis, at an electron energy of 28 GeV, the average multiplicity of charged particles increases by a factor of ∼1.6. The widths of the orientation dependences of the average multiplicity of charged particles in electron-induced showers in silicon and tungsten crystals are proportional to the crystal thickness and depend on the electron energy as E −1/2.

Wounded quarks and multiplicity at relativistic ion colliders

In this paper, we propose a parameterization which is based on a phenomenological model involving the wounded quarks interactions for explaining the average charged particle multiplicity $\ < n_{ch}\ >$, the central pseudo-rapidity density $\ < (dn/d\eta)_{\eta=0}\ >$ and complete rapidity dependence of $dn/d{\eta}$ in relativistic heavy-ion collider experiments. The model also interrelates nucleus-nucleus (A-A) collisions with p-A and p-p interactions. Our parameterization rests on simple assumptions regarding mean number of participating quarks and their average number of collisions. The results for $\ < n_{ch}\ >$ and their variations with the mass number of colliding nuclei, center-of-mass energy ($\sqrt{s_{NN}}$) and collision centrality are well supported by the available experimental data. Finally we give the predictions from our model for A-A collisions at the Large Hadron Collider (LHC) and Compressed Baryonic Matter (CBM) experiments. Our results indicate the existence of a possible universal production mechanism for p-p, p-A and A-A collisions.

Measurement of the centrality dependence of the charged particle pseudorapidity distribution in lead–lead collisions at [formula omitted] with the ATLAS detector

The ATLAS experiment at the LHC has measured the centrality dependence of charged particle pseudorapidity distributions over |η|<2 in lead–lead collisions at a nucleon–nucleon centre-of-mass energy of sNN=2.76 TeV. In order to include particles with transverse momentum as low as 30 MeV, the data were recorded with the central solenoid magnet off. Charged particles were reconstructed with two algorithms (2-point “tracklets” and full tracks) using information from the pixel detector only. The lead–lead collision centrality was characterized by the total transverse energy in the forward calorimeter in the range 3.2<|η|<4.9. Measurements are presented of the per-event charged particle pseudorapidity distribution, dNch/dη, and the average charged particle multiplicity in the pseudorapidity interval |η|<0.5 in several intervals of collision centrality. The results are compared to previous mid-rapidity measurements at the LHC and RHIC. The variation of the mid-rapidity charged particle yield per colliding nucleon pair with the number of participants is consistent with lower sNN results. The shape of the dNch/dη distribution is found to be independent of centrality within the systematic uncertainties of the measurement.

Charged particle multiplicity in showers formed by gamma-rays in oriented tungsten crystal

It is shown that the average charged particle multiplicity in electromagnetic showers induced by γ-rays with energies of 9–26 GeV in the tungsten crystal 1 mm thick (T = 77 K) oriented along the 〈111〉 axis approximately twofold increases in comparison with a misoriented crystal.

Extrapolation of multiplicity distribution in collisions to LHC energies

The multiplicity (Nch) and pseudorapidity distribution (dNch/dη) of primary charged particles in p + p collisions at Large Hadron Collider (LHC) energies of 10 and 14 TeV are obtained from extrapolation of existing measurements at lower . These distributions are then compared to calculations from PYTHIA and PHOJET models. The existing measurements are unable to distinguish between a logarithmic and power law dependence of the average charged particle multiplicity (⟨Nch⟩) on , and their extrapolation to energies accessible at LHC give very different values. Assuming a reasonably good description of inclusive charged particle multiplicity distributions by negative binomial distribution (NBD) at lower to hold for LHC energies, we observe that the logarithmic dependences of ⟨Nch⟩ are favored by the models at midrapidity. The dNch/dη versus η distributions for the existing measurements are found to be reasonably well described by a function with three parameters which accounts for the basic features of the distribution, height at midrapidity, central rapidity plateau and the higher rapidity fall-off. Extrapolation of these parameters as a function of is used to predict the pseudorapidity distributions of charged particles at LHC energies. dNch/dη calculations from PYTHIA and PHOJET models are found to be lower compared to those obtained from the extrapolated dNch/dη versus η distributions for a broad η range.

Number of nucleon-nucleon collisions vs. energy in modified Glauber calculations

We modified the standard Glauber model calculations of number of participants (Nw), number of collisions (Ncoll) and their dispertions using a simplified estimate of the energy loss in nucleon-nucleon collision. A fraction equal to 1-k of the initial nucleon momentum is allowed to be lost in each inelastic interaction, so that two "nucleon-like structures", emerging after the nucleon-nucleon inelastic process, have lower momenta. Therefore, further "nucleonnucleon" inelastic collisions take place at a lower energy sqrts and with the experimentally known cross-section (σinelpp(sqrts). We obtain a considerable reduction in the number of collisions Ncoll and in the total mean number of charged particles Nch, compared to the standard Glauber approach, while the number of participants Nw is practically unchanged. The model incorporates the experimental values of the average charged particle multiplicity for pp and pp̄ collisions as a function of sqrts, so that the total mean number of charged particles (Nch) could be calculated and compared with the heavy-ion collision data. This model has been used to describe the available data on the average multiplicity obtained for PbPb and AuAu collisions from AGS to RHIC energies. Possible applications of this model to the pA and dA multiplicity data analysis are also discussed.

Soft QCD phenomena in events with high-E T jets at tevatron

Presented are results from the recent jet fragmentation and underlying event structure studies carried out by the CDF Collaboration. Multiplicities of charged particles in quark and gluon jets are measured and their ratio is compared to pQCD predictions. The results are compared to the earlier measurements obtained at e+ e– colliders. Average charged particle multiplicities and energy flow in the underlying event are compared to Pythia Monte Carlo event generator; the necessary tuning of Pythia parameters needed to make it match the data is discussed.

Multiplicities of π 0, η, K 0 and of charged particles in quark and gluon jets

We measured the average multiplicities of inclusive charged particles, π 0, η and K 0 mesons in quark and in gluon jets as a function of a topological scale Q jet. The ratio of particle multiplicity in gluon jets to that in quark jets as a function of Q jet is found to be independent of the particle species, which is consistent with QCD expectation. We observed no evidence for an enhancement of η meson production in gluon jets with respect to quark jets, beyond that observed for charged particles. We measured the ratio of the slope of the average charged particle multiplicity in gluon jets to that in quark jets, C, and we compared it to a next-to-next-to-next-to leading order calculation. Our result, C = 2.27 ± 0.20(stat. + syst.), is about one standard deviation higher than the perturbative prediction.

Multiplicities of $\pi^0, \eta,\rm K^0$ and of charged particles in quark and gluon jets

We compared the multiplicities of $\pi^0, \eta, \rm K^0 $ and of charged particles in quark and gluon jets in 3-jet events, as measured by the OPAL experiment at LEP. The comparisons were performed for distributions unfolded to 100% pure quark and gluon jets, at an effective scale $\rm Q_{jet} $ which took into account topological dependences of the 3-jet environment. The ratio of particle multiplicity in gluon jets to that in quark jets as a function of $\rm Q_{jet}$ for $ \pi^0, \eta$ or $\rm K^0 $ was found to be independent of the particle species. This is consistent with the QCD prediction that the observed enhancement in the mean particle rate in gluon jets with respect to quark jets should be independent of particle species. In contrast to some theoretical predictions and previous observations, we observed no evidence for an enhancement of $ \eta $ meson production in gluon jets with respect to quark jets, beyond that observed for charged particles. We measured the ratio of the slope of the average charged particle multiplicity in gluon jets to that in quark jets, C, and we compared it to a next-to-next-to-next-to leading order calculation. Our result, $\rm C=2.27\pm 0.20(stat.+syst.),$ is about one standard deviation higher than the perturbative prediction.

Hadronization properties of b quarks compared to light quarks in [formula omitted] from 183 to 200 GeV

The DELPHI detector at LEP has collected 54 pb −1 of data at a centre-of-mass energy around 183 GeV during 1997, 158 pb −1 around 189 GeV during 1998, and 187 pb −1 between 192 and 200 GeV during 1999. These data were used to measure the average charged particle multiplicity in e +e −→b b ̄ events, 〈n〉 b b ̄ , and the difference δ bl between 〈n〉 b b ̄ and the multiplicity, 〈n〉 l l ̄ , in generic light quark (u,d,s) events: δ bl (183 GeV) =4.55±1.31( stat)±0.73( syst) , δ bl (189 GeV) =4.43±0.85( stat)±0.61( syst) , δ bl (200 GeV) =3.39±0.89( stat)±1.01( syst) . This result is consistent with QCD predictions, while it is inconsistent with calculations assuming that the multiplicity accompanying the decay of a heavy quark is independent of the mass of the quark itself.

Leading particle effect, inelasticity, and the connection between average multiplicities ine+e−andppprocesses

The Regge-Mueller formalism is used to describe the inclusive spectrum of the proton in $\mathrm{pp}$ collisions. From such a description the energy dependences of both average inelasticity and leading proton multiplicity are calculated. These quantities are then used to establish the connection between the average charged particle multiplicities measured in ${e}^{+}{e}^{\ensuremath{-}}$ and $pp/\overline{p}p$ processes. The description obtained for the leading proton cross section implies that Feynman scaling is strongly violated only at the extreme values of ${x}_{F},$ that is at the central region ${(x}_{F}\ensuremath{\approx}0)$ and at the diffraction region ${(x}_{F}\ensuremath{\approx}1),$ while it is approximately observed in the intermediate region of the spectrum.

Scaling in energy dependence of relative particle production rates and peak position of ξ distributions in e+e− annihilations

Abstract With the production rates, 〈 n part 〉, of the K 0 , K + , p and Λ and average charged particle multiplicities, 〈 n ch 〉, recently measured at LEP1.5–LEP2, scaling of the relative particle production rates 〈 n part 〉/〈 n ch 〉 is seen in a broad center of mass energy range from s = 29–35 to 183 GeV. The quantity ξ 0 /〈 n ch 〉 1/2 , where ξ 0 is the position of the maximum of the ξ=− ln (2p/ s ) distribution and p is the particle momentum, also scales from 14 to 183 GeV. It is shown that the gaussian shape of the ξ distribution is a simple consequence of longitudinal phase space. The slope parameter in the logarithmic increase of ξ 0 with the center of mass energy must be smaller than 1, as observed experimentally, but this does not necessary imply a manifestation of coherence.