We present a study of pp¯ collisions at s=1800 and 630 GeV collected using a minimum bias trigger by the CDF experiment in which the data set is divided into two classes corresponding to “soft” and “hard” interactions. For each subsample, the analysis includes measurements of the multiplicity, transverse momentum (pT) spectrum, and the average pT and event-by-event pT dispersion as a function of multiplicity. A comparison of results shows distinct differences in the behavior of the two samples as a function of the center of mass (c.m.) energy. We find evidence that the properties of the soft sample are invariant as a function of c.m. energy.
We present an analysis of multiplicity distributions of charged particles produced inZ0 hadronic decays. The results are based on the analysis of 82941 events collected within 100 MeV of theZ0 peak energy with the OPAL detector at LEP. The charged particle multiplicity distribution, corrected for initial-state radiation and for detector acceptance and resolution, was found to have a mean 〈nch〉=21.40±0.02(stat.)±0.43(syst.) and a dispersionD=6.49±0.02(stat.)±0.20(syst.). The shape is well described by the Lognormal and Gamma distributions. A negative binomial parameterisation was found to describe the shape of the multiplicity distribution less well. A comparison with results obtained at lower energies confirms the validity of KNO(-G) scaling up to LEP energies. A separate analysis of events with low sphericity, typically associated with two-jet final states, shows the presence of features expected for models based on a stochastic production mechanism for particles. In all cases, the features observed in the data are well described by the Lund parton shower model JETSET.
Measurements are presented from proton-proton collisions at centre-of-mass energies of sqrt(s) = 0.9, 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimum-bias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase-space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections. The results are compared to each other and to various Monte Carlo models, including a new AMBT1 PYTHIA 6 tune. In all the kinematic regions considered, the particle multiplicities are higher than predicted by the Monte Carlo models. The central charged-particle multiplicity per event and unit of pseudorapidity, for tracks with pT >100 MeV, is measured to be 3.483 +- 0.009 (stat) +- 0.106 (syst) at sqrt(s) = 0.9 TeV and 5.630 +- 0.003 (stat) +- 0.169 (syst) at sqrt(s) = 7 TeV.
Average transverse momentum in proton-proton collisions at a centre-of mass energy of 900 GeV as a function of the number of charged particles in the event for events with the number of charged particles >=1 having transverse momentum >500 MeV and absolute(pseudorapidity) <2.5.
The energy and centrality dependence of local particle pseudorapidity densities as well as validity of various parametrizations of the distributions are examined. The dispersion, σ, of the rapidity density distribution of produced particles varies slowly with centrality and is 0.80, 0.98, 1.21 and 1.41 for central interactions at 3.7, 14.6, 60 and 200A GeV incident energy, respectively, σ is found to be independent of the size of the interacting system at fixed energy. A novel way of representing the window dependence of the multiplicity as normalized variance versus inverse average multiplicity is outlined.
Charged-particle production was studied in proton-proton collisions collected at the LHC with the ALICE detector at centre-of-mass energies 0.9 TeV and 2.36 TeV in the pseudorapidity range |$\eta$| < 1.4. In the central region (|$\eta$| < 0.5), at 0.9 TeV, we measure charged-particle pseudorapidity density dNch/deta = 3.02 $\pm$ 0.01 (stat.) $^{+0.08}_{-0.05}$ (syst.) for inelastic interactions, and dNch/deta = 3.58 $\pm$ 0.01 (stat.) $^{+0.12}_{-0.12}$ (syst.) for non-single-diffractive interactions. At 2.36 TeV, we find dNch/deta = 3.77 $\pm$ 0.01 (stat.) $^{+0.25}_{-0.12}$ (syst.) for inelastic, and dNch/deta = 4.43 $\pm$ 0.01 (stat.) $^{+0.17}_{-0.12}$ (syst.) for non-single-diffractive collisions. The relative increase in charged-particle multiplicity from the lower to higher energy is 24.7% $\pm$ 0.5% (stat.) $^{+5.7}_{-2.8}$% (syst.) for inelastic and 23.7% $\pm$ 0.5% (stat.) $^{+4.6}_{-1.1}$% (syst.) for non-single-diffractive interactions. This increase is consistent with that reported by the CMS collaboration for non-single-diffractive events and larger than that found by a number of commonly used models. The multiplicity distribution was measured in different pseudorapidity intervals and studied in terms of KNO variables at both energies. The results are compared to proton-antiproton data and to model predictions.
Mean CQ moments of the multiplicity distributions for the pseudorapidity range -1.0 to 1.0 in P P NSD collisions at centre-of-mass energies 900 and 2360 GeV.
The growth and development of “charged particle jets” produced in proton-antiproton collisions at 1.8 TeV are studied over a transverse momentum range from 0.5 GeV/c to 50 GeV/c. A variety of leading (highest transverse momentum) charged jet observables are compared with the QCD Monte Carlo models HERWIG, ISAJET, and PYTHIA. The models describe fairly well the multiplicity distribution of charged particles within the leading charged jet, the size of the leading charged jet, the radial distribution of charged particles and transverse momentum around the leading charged jet direction, and the momentum distribution of charged particles within the leading charged jet. The direction of the leading “charged particle jet” in each event is used to define three regions of η−φ space. The “toward” region contains the leading “charged particle jet,” while the “away” region, on the average, contains the away-side jet. The “transverse” region is perpendicular to the plane of the hard 2-to-2 scattering and is very sensitive to the “underlying event” component of the QCD Monte Carlo models. HERWIG, ISAJET, and PYTHIA with their default parameters do not describe correctly all the properties of the “transverse” region.
Average number of charged particles as a function of the relative azimuthal angle between the individual charged particle and the overall leading jet angle.
Average scalar PT sum of charged particles as a function of the relative azimuthal angle between the individual charged particle for 3 different lower limits of the leading jet PT. and the overall jet angle.
The average number of toward(DPHI < 60 DEG), transverse (DPHI 60 TO 120 DEG) and away (DPHI > 120 DEG) charged particles as a function of the PT of the leading charged jet. The data in this table are from the Min-Bias events.
Quark and gluon jets with equal energies are identified in three-jet hadronicZ0 events, using reconstructed secondary vertices from heavy quark decay in conjunction with energy orderi
No description provided.
Quark and gluon jets in e + e − three-jet events at LEP are identified using lepton tagging of quark jets, through observation of semi-leptonic charm and bottom quark decays. Events with a symmetry under transposition of the energies and directions of a quark and gluon jet are selected: these quark and gluon jets have essentially the same energy and event environment and as a consequence their properties can be compared directly. The energy of the jets which are studied is about 24.5 GeV. In the cores of the jets, gluon jets are found to yield a softer particle energy spectrum than quark jets. Gluon jets are observed to be broader than quark jets, as seen from the shape of their particle momentum spectra both in and out of the three-jet event plane. The greater width of gluon jets relative to quark jets is also visible from the shapes of their multiplicity distributions. Little difference is observed, however, between the mean value of particle multiplicity for the two jet types.
QUARK means QUARK or QUARKBAR.
We describe a cone-based jet finding algorithm (similar to that used in\(\bar p\)p experiments), which we have applied to hadronic events recorded using the OPAL detector at LEP. Comparisons are made between jets defined with the cone algorithm and jets found by the “JADE” and “Durham” jet finders usually used ine+e− experiments. Measured jet rates, as a function of the cone size and as a function of the minimum jet energy, have been compared with O(αs2) calculations, from which two complementary measurements\(\alpha _s \left( {M_{Z^0 } } \right)\) have been made. The results are\(\alpha _s \left( {M_{Z^0 } } \right)\)=0.116±0.008 and\(\alpha _s \left( {M_{Z^0 } } \right)\)=0.119±0.008 respectively, where the errors include both experimental and theoretical uncertainties. Measurements are presented of the energy flow inside jets defined using the cone algorithm, and compared with equivalent data from\(\bar p\)p interactions, reported by the CDF collaboration. We find that the jets ine+e− are significantly narrower than those observed in\(\bar p\)p. The main contribution to this effect appears to arise from differences between quark- and gluon-induced jets.
Measured 2 jet production rate as a function of EPSILON, the minimum energy of a jet for a fixed cone radius R = 0.7 radians.
Measured 2 jet production rate as a function of R, the jet cone radius, for a fixed value of the minimum jet energy, EPSILON, of 7 GeV.
Measured 3 jet production rate as a function of EPSILON, the minimum energy of a jet for a fixed cone radius R = 0.7 radians.
This paper describes an analysis of sub-jet multiplicities, which are expected to be sensitive to the properties of soft gluon radiation, in hadronic decays of theZ0. Two- and three-jet event samples are selected using thek⊥ jet clustering algorithm at a jet resolution scaley1. The mean sub-jet multiplicity as a function of the sub-jet resolution,y0, is determined separately for both event samples by reapplying the same jet algorithm at resolution scalesy0<y1. These measurements are compared with recent perturbative QCD calculations based on the summation of leading and next-to-leading logarithms, and with QCD Monte Carlo models. The analytic calculations provide a good description of the sub-jet multiplicity seen in three- and two-jet mvents in the perturbative region (y0≈y1)), and the measured form of the data is in agreement with the expectation based on coherence of soft gluon radiation. The analysis provides good discrimination between Monte Carlo models, and those with a coherent parton shower are preferred by the data. The analysis suggests that coherence effects are present in the data.
Ratio of multiplicities of sub-jets from 3 and 2 jet samples. Data are corrected to the hadron level and have combined statistical and systematic errors.
Sub-jet multiplicity for 3 jet sample. Data corrected to the hadron level and have combined statistical and systematic errors.
Sub-jet multiplicity for 2 jet sample. Data corrected to the hadron level and have combined statistical and systematic errors.
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