We report the first measurements of the kurtosis (\kappa), skewness (S) and variance (\sigma^2) of net-proton multiplicity (N_p - N_pbar) distributions at midrapidity for Au+Au collisions at \sqrt(s_NN) = 19.6, 62.4, and 200 GeV corresponding to baryon chemical potentials (\mu_B) between 200 - 20 MeV. Our measurements of the products \kappa \sigma^2 and S \sigma, which can be related to theoretical calculations sensitive to baryon number susceptibilities and long range correlations, are constant as functions of collision centrality. We compare these products with results from lattice QCD and various models without a critical point and study the \sqrt(s_NN) dependence of \kappa \sigma^2. From the measurements at the three beam energies, we find no evidence for a critical point in the QCD phase diagram for \mu_B below 200 MeV.
$\Delta N_p$ multiplicity distribution in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for 0-5 percent central collisions at midrapidity (| y |< 0.5).
$\Delta N_p$ multiplicity distribution in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for 30-40 percent central collisions at midrapidity (| y |< 0.5).
$\Delta N_p$ multiplicity distribution in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for 70-80 percent central collisions at midrapidity (| y |< 0.5).
We present the multiplicity and pseudorapidity distributions of photons produced in Au+Au and Cu+Cu collisions at \sqrt{s_NN} = 62.4 and 200 GeV. The photons are measured in the region -3.7 < \eta < -2.3 using the photon multiplicity detector in the STAR experiment at RHIC. The number of photons produced per average number of participating nucleon pairs increases with the beam energy and is independent of the collision centrality. For collisions with similar average numbers of participating nucleons the photon multiplicities are observed to be similar for Au+Au and Cu+Cu collisions at a given beam energy. The ratios of the number of charged particles to photons in the measured pseudorapidity range are found to be 1.4 +/- 0.1 and 1.2 +/- 0.1 for \sqrt{s_NN} = 62.4 GeV and 200 GeV, respectively. The energy dependence of this ratio could reflect varying contributions from baryons to charged particles, while mesons are the dominant contributors to photon production in the given kinematic region. The photon pseudorapidity distributions normalized by average number of participating nucleon pairs, when plotted as a function of \eta - ybeam, are found to follow a longitudinal scaling independent of centrality and colliding ion species at both beam energies.
Fig. 1. (Color online.) Top panel: Photon reconstruction efficiency $\left(\epsilon_{\gamma}\right)$ (solid symbols) and purity of photon sample $\left(f_{\mathrm{p}}\right)$ (open symbols) for PMD as a function of pseudorapidity $(\eta)$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ at $\sqrt{s_{\mathrm{NN}}}=$ $200 \mathrm{GeV}$. Bottom panel: Comparison between estimated $\epsilon_{\gamma}$ and $f_{\mathrm{p}}$ for PMD as a function of $\eta$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=62.4 \mathrm{GeV}$ using HIJING and AMPT models. The error bars on the AMPT data are statistical and those for HIJING are within the symbol size. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.
Fig. 1. (Color online.) Top panel: Photon reconstruction efficiency $\left(\epsilon_{\gamma}\right)$ (solid symbols) and purity of photon sample $\left(f_{\mathrm{p}}\right)$ (open symbols) for PMD as a function of pseudorapidity $(\eta)$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ at $\sqrt{s_{\mathrm{NN}}}=$ $200 \mathrm{GeV}$. Bottom panel: Comparison between estimated $\epsilon_{\gamma}$ and $f_{\mathrm{p}}$ for PMD as a function of $\eta$ for minimum bias $\mathrm{Au}+\mathrm{Au}$ at $\sqrt{s_{\mathrm{NN}}}=62.4 \mathrm{GeV}$ using HIJING and AMPT models. The error bars on the AMPT data are statistical and those for HIJING are within the symbol size. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.
Fig. 2. (Color online.) Event-by-event photon multiplicity distributions (solid circles) for $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Cu}+\mathrm{Cu}$ at $\sqrt{s_{\mathrm{NN}}}=62.4$ and $200 \mathrm{GeV} .$ The distributions for top $0-5 \%$ central $\mathrm{Au}+$ Au collisions and top $0-10 \%$ central $\mathrm{Cu}+\mathrm{Cu}$ collisions are also shown (open circles). The photon multiplicity distributions for central collisions are observed to be Gaussian (solid line). Only statistical errors are shown. NOTE: For points with invisible error bars, the point size was considered as an absolute upper limit for the uncertainty.
We present a study of the production of K_s^0 and Lambda^0 in inelastic pbar-p collisions at sqrt(s)= 1800 and 630 GeV using data collected by the CDF experiment at the Fermilab Tevatron. Analyses of K_s^0 and Lambda^0 multiplicity and transverse momentum distributions, as well as of the dependencies of the average number and <p_T> of K_s^0 and Lambda^0 on charged particle multiplicity are reported. Systematic comparisons are performed for the full sample of inelastic collisions, and for the low and high momentum transfer subsamples, at the two energies. The p_T distributions extend above 8 GeV/c, showing a <p_T> higher than previous measurements. The dependence of the mean K_s^0(Lambda^0) p_T on the charged particle multiplicity for the three samples shows a behavior analogous to that of charged primary tracks.
K0S inclusive invariant PT distribution for HARD events at a centre of massenergy 1800 GeV.
K0S inclusive invariant PT distribution for MB events at a centre of mass energy 1800 GeV.
K0S inclusive invariant PT distribution for SOFT events at a centre of massenergy 1800 GeV.
We have studied hadronic events produced at LEP at a centre-of-mass energy of 161 GeV. We present distributions of event shape variables, jet rates, charged particle momentum spectra and multiplicities. We determine the strong coupling strength to be αs(161 GeV) = 0.101±0.005(stat.)±0.007(syst.), the mean charged particle multiplicity to be 〈nch〉(161 GeV) = 24.46 ± 0.45(stat.) ± 0.44(syst.) and the position of the peak in the ξp = ln(1/xp) distribution to be ξ0(161 GeV) = 4.00 ±0.03(stat.)±0.04(syst.). These results are compared to data taken at lower centre-of-mass energies and to analytic QCD or Monte Carlo predictions. Our measured value of αs(161 GeV) is consistent with other measurements of αs. Within the current statistical and systematic uncertainties, the PYTHIA, HERWIG and ARIADNE QCD Monte Carlo models and analytic calculations are in overall agreement with our measurements. The COJETS QCD Monte Carlo is in general agreement with the data for momentum weighted distributions like Thrust, but predicts a significantly larger charged particle multiplicity than is observed experimentally.
Determination of alpha_s.
Multiplicity and higher moments.
Thrust distribution.
Gluon jets with about 39 GeV energy are identified in hadronic Z 0 decays by tagging two jets in the same hemisphere of an event as quark jets. Identifying the gluon jet to be all the particles observed in the hemisphere opposite to that containing the two tagged jets yields an inclusive gluon jet definition corresponding to that used in analytic calculations, allowing the first direct test of those calculations. In particular, this jet definition yields results which are only weakly dependent on a jet finding algorithm. We find r ch. =1.552±0.0041 ( stat ) ±0.061 ( syst. ) for the ratio of the mean charged particle multiplicity in gluon jets to that in light quark uds jets, where the uds jets are identified using an inclusive jet definition similar to that used for the gluon jets. Our result is in general agreement with the prediction of a recent analytic calculation which incorporates energy conservation into the parton shower branching processes, but is considerably smaller than analytic predictions which do not incorporate energy conservation.
Mean charged particle multiplicity in gluon jets.
Mean charged particle multiplicity in single hemisphere light quark jets.
We have studied hadronic events produced at LEP at centre-of-mass energies of 130 and 136 GeV. Distributions of event shape observables, jet rates, momentum spectra and multiplicities are presented and compared to the predictions of several Monte Carlo models and analytic QCD calculations. From fits of event shape and jet rate distributions to\({\mathcal{O}}(\alpha _s^2 ) + NLLA\) QCD calculations, we determineαs(133 GeV)=0.110±0.005(stat.)±0.009(syst.). We measure the mean charged particle multiplicity 〈nch〉=23.40±0.45(stat.) ±0.47(syst.) and the position ζ0 of the peak in the ζp = ln(1/xp) distribution ζ0=3.94±0.05(stat.)±0.11(syst.). These results are compared to lower energy data and to analytic QCD or Monte Carlo predictions for their energy evolution.
Determination of alpha_s.
Multiplicity and high moments.
Tmajor distribution.
Symmetric three-jet events are selected from hadronic Z0 decays such that the two lower energy jets are each produced at an angle of about 150° with respect to the highest energy jet. In some cases, a displaced secondary vertex is reconstructed in one of the two lower energy jets, which permits the other lower energy jet to be identified as a gluon jet through anti-tagging. In other cases, the highest energy jet is tagged as a b jet or as a light quark (uds) jet using secondary vertex or track impact parameter and momentum information. Comparing the two lower energy jets of the events with a tag in the highest energy jet to the anti-tagged gluon jets yields a direct comparison of b, uds and gluon jets, which are produced with the same energy of about 24 GeV and under the same conditions. We observe b jets and gluon jets to have similar properties as measured by the angular distribution of particle energy around the jet directions and by the fragmentation functions. In contrast, gluon jets are found to be significantly broader and to have a markedly softer fragmentation function than uds jets. For the k⊥ jet finder with ycut=0.02, we find $${«ngle n^{⤪ ch.}»ngle {⤪ gluon}⩈er «ngle n^{⤪ ch.}»ngle {⤪ b} {⤪ quark}}=1.089pm 0.024 ({⤪ stat.})pm0.024 ({⤪ syst.})$$ $${«ngle n^{⤪ ch.}»ngle {⤪ gluon}⩈er «ngle n^{⤪ ch.}»ngle {⤪ uds} {⤪ quark}}=1.390pm 0.038 ({⤪ stat.})pm0.032 ({⤪ syst.})$$ as the ratios of the mean charged particle multiplicity in the gluon jets compared to the b and uds jets. Results are also reported using the cone jet finder.
Two method of jet's reconstruction: 'kt' and 'cone' (see text).
Two method of jet's reconstruction: 'kt' and 'cone' (see text). QUARK meansUQ or DQ or SQ.
None
THETA is the angle between hadron and jet's axis. CONST is the parameter used in jet's definition (see text).
CONST is the parameter used in jet's definition (see text).
CONST is the parameter used in jet's definition (see text).
We have measured the multiplicity of charm quark pairs arising from gluon splitting in a sample of about 3.5 million hadronic Z 0 decays. By selecting a 3-jet event topology and tagging charmed hadrons in the lowest energy jet using leptons, we established a signature of heavy quark pair production from gluons. The average number of gluons splitting into a c c pair per hadronic event was measured to be n g→c c =(2.27±0.28±0.41) × 10 −2 .
Axis error includes +- 8.4/8.4 contribution (Total generator error for the electron channel due to the uncertainties in parameters of Peterson model of fragmentation, LAMBDA_QCD, ALPHA_S, Lund fragmentation parameters and lepton decay model).
We have used data from the OPAL detector at LEP to reconstruct D ∗ mesons and secondary vertices in jets. We have studied the hemispheres of the events opposite these jets and obtain values of the hemisphere charged particle multiplicity in Z 0 → u u , d d , s s , Z 0 → c c and Z 0 → b b events of n uds = 10.41 ± 0.06 ± 0.09 ± 0.19 ; n c = 10.76 ± 0.20 ± 0.14 ± 0.19 ; n b = 11.81 ± 0.01 ± 0.12 ± 0.21 where the first errors are statistical, the second systmatic and the third a common scale uncertainty. We find the difference in total charged particle multiplicity between c and b quark events and light (u, d, s) quark events to be δ cl = 0.69 ± 0.51 ± 0.35; δ bl = 2.79 ± 0.12 ± 0.27. These results are compared to the predictions of various models and QCD based calculations.
Second systematic error is a common scale uncertainty.
Difference in the TOTAL charged particle multiplicity.
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