Gluon jets are identified in hadronic Z0 decays as all the particles in a hemisphere opposite to a hemisphere containing two tagged quark jets. Gluon jets defined in this manner are equivalent to gluon jets produced from a color singlet point source and thus correspond to the definition employed for most theoretical calculations. In a separate stage of the analysis, we select quark jets in a manner to correspond to calculations, as the particles in hemispheres of flavor tagged light quark (uds) events. We present the distributions of rapidity, scaled energy, the logarithm of the momentum, and transverse momentum with respect to the jet axes, for charged particles in these gluon and quark jets. We also examine the charged particle multiplicity distributions of the jets in restricted intervals of rapidity. For soft particles at large transverse momentum, we observe the charged particle multiplicity ratio of gluon to quark jets to be 2.29 +- 0.09 +- 0.15 in agreement with the prediction that this ratio should approximately equal the ratio of QCD color factors, CA/CF = 2.25. The intervals used to define soft particles and large transverse momentum for this result, p<4 GeV/c and 0.8<p_t<3.0 GeV/c, are motivated by the predictions of the Herwig Monte Carlo multihadronic event generator. Additionally, our gluon jet data allow a sensitive test of the phenomenon of non-leading QCD terms known as color reconnection. We test the model of color reconnection implemented in the Ariadne Monte Carlo multihadronic event generator and find it to be disfavored by our data.
(C=GLUON) and (C=QUARK) stand for jets originated from gluon and any light quark (Q=u, d, s), correspondingly. The ratio of gluon to quark jets are evaluated for 40.1 GeV jet energy.
(C=GLUON) and (C=QUARK) stand for jets originated from gluon and any light quark (Q=u, d, s), correspondingly. The ratio of gluon to quark jets are evaluated for 40.1 GeV jet energy.
(C=GLUON) and (C=QUARK) stand for jets originated from gluon and any light quark (Q=u, d, s), correspondingly. The ratio of gluon to quark jets are evaluated for 40.1 GeV jet energy.
In this paper Au+Au collisions at 11.6A GeV/c are characterized by two global observables: the energy measured near zero degrees (EZCAL) and the total event multiplicity. Particle spectra are measured for different event classes that are defined in a two-dimensional grid of both global observables. For moderately central events (σ/σint<12%) the proton dN/dy distributions do not depend on EZCAL but only on the event multiplicity. In contrast the shape of the proton transverse spectra shows little dependence on the event multiplicity. The change in the proton dN/dy distributions suggests that different conditions are formed in the collision for different event classes. These event classes are studied for signals of new physics by measuring pion and kaon spectra and yields. In the event classes doubly selected on EZCAL and multiplicity there is no indication of any unusual pion or kaon yields, spectra, or K/π ratio even in the events with extreme multiplicity.
Table for event classification (from CLASS1 to CLASS8) where ZCAL energy solely used for event selection. Number of Projectile Participants Npp=197*(1-E(P=3)/EKIN(P=1)).
CLASS1 (see Table for event classification).
CLASS1 (see Table for event classification).
With the H1 detector at the ep collider HERA, D* meson production cross sections have been measured in deep inelastic scattering with four-momentum transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88 GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe the differential cross sections within theoretical and experimental uncertainties. Using these calculations, the NLO gluon momentum distribution in the proton, x_g g(x_g), has been extracted in the momentum fraction range 7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon momentum fraction x_g has been obtained from the measured kinematics of the scattered electron and the D* meson in the final state. The results compare well with the gluon distribution obtained from the analysis of scaling violations of the proton structure function F_2.
Total cross section for DIS D*+- production in the specified kinemtaic range.
DIS cross section as a function of the transverse D* momentum in the laboratory frame.
DIS cross section as a function of the transverse D* momentum in the hadronic centre-of-mass frame.
We report measurements of Xi and Xi-bar hyperon absolute yields as a function of rapidity in 158 GeV/c Pb+Pb collisions. At midrapidity, dN/dy = 2.29 +/- 0.12 for Xi, and 0.52 +/- 0.05 for Xi-bar, leading to the ratio of Xi-bar/Xi = 0.23 +/- 0.03. Inverse slope parameters fitted to the measured transverse mass spectra are of the order of 300 MeV near mid-rapidity. The estimated total yield of Xi particles in Pb+Pb central interactions amounts to 7.4 +/- 1.0 per collision. Comparison to Xi production in properly scaled p+p reactions at the same energy reveals a dramatic enhancement (about one order of magnitude) of Xi production in Pb+Pb central collisions over elementary hadron interactions.
Data are given at the midrapidity value.
Requested data from authors.
We present a measurement of Z0 boson and Drell-Yan production cross sections in p¯p collisions at s=1.8TeV using a sample of 107pb−1 accumulated by the Collider Detector at Fermilab. The Drell-Yan cross section is measured in the mass range of Mμμ>40GeV/c2. We compare the measurements with the predictions of quantum chromodynamics in both leading order and next-to-leading order, incorporating the recent parton distribution functions. The measurements are consistent with the standard model expectations.
The mesured Z0 cross sections for the two running periods and combined.
The mesured Z0 cross section, times the branching ratio Z0 --> MU+ MU- (3.362 PCT) for the two running periods and combined.
The mesured production cross section for the combined data sets for ABS(YRAP) < 1.
The NA44 collaboration has measured charged kaon and pion distributions at midrapidity in sulphur and proton collisions with nuclear targets at 200 and 450 GeV/c per nucleon, respectively. The inverse slopes of kaons are larger than those of pions. The difference in the inverse slopes of pions, kaons and protons, all measured in our spectrometer, increases with system size and is consistent with the buildup of collective flow for larger systems. The target dependence of both the yields and inverse slopes is stronger for the sulphur beam suggesting the increased importance of secondary rescattering for SA reactions. The rapidity density, dN/dy, of both K+ and K- increases more rapidly with system size than for pi+ in a similar rapidity region. This trend continues with increasing centrality, and according to RQMD, it is caused by secondary reactions between mesons and baryons. The K-/K+ ratio falls with increasing system size but more slowly than the pbar/p ratio. The pi-/pi+ ratio is close to unity for all systems. From pBe to SPb the K+/p ratio decreases while K-/pbar increases and ({K+*K-}/{p*pbar})**1/2 stays constant. These data suggest that as larger nuclei collide, the resulting system has a larger transverse expansion, baryon density and an increasing fraction of strange quarks.
No description provided.
No description provided.
No description provided.
The neutral π0 and η mesons are studied in 197Au−197Au collisions at an incident energy of 800AMeV, substantially below the threshold for η production in N−N collisions. While the gross π0 multiplicity increases almost linearly with the number of participant nucleons, the multiplicities of η and hard π0 mesons show a stronger than linear dependence. The nonlinearity is governed by the average transverse-mass excess 〈mt〉−(s−2mN) of the mesons and is insensitive to their final-state interaction in the nuclear medium.
No description provided.
No description provided.
No description provided.
The multiplicity structure of the hadronic system X produced in deep-inelastic processes at HERA of the type ep -> eXY, where Y is a hadronic system with mass M_Y< 1.6 GeV and where the squared momentum transfer at the pY vertex, t, is limited to |t|<1 GeV^2, is studied as a function of the invariant mass M_X of the system X. Results are presented on multiplicity distributions and multiplicity moments, rapidity spectra and forward-backward correlations in the centre-of-mass system of X. The data are compared to results in e+e- annihilation, fixed-target lepton-nucleon collisions, hadro-produced diffractive final states and to non-diffractive hadron-hadron collisions. The comparison suggests a production mechanism of virtual photon dissociation which involves a mixture of partonic states and a significant gluon content. The data are well described by a model, based on a QCD-Regge analysis of the diffractive structure function, which assumes a large hard gluonic component of the colourless exchange at low Q^2. A model with soft colour interactions is also successful.
The multiplicity moment MULT as a function of the mass of the charged hadron system in the full phase space and separately in the forward and backward hemispheres.
The multiplicity moment DISPERSION as a function of the mass of the charged hadron system in the full phase space and separately in the forward and backward hemispheres.
The multiplicity moment R2 as a function of the mass of the charged hadron system in the full phase space and separately in the forward and backward hemispheres.
In a joint effort the CERES/NA45 and TAPS collaborations have measured low-mass electron pairs in p–Be and p–Au collisions at 450 GeV/c at the CERN SPS. In the range covered up to ≈ 1.5 GeV/c2 the mass spectra from p–Be and p–Au collisions are well explained by electron pairs from decays of neutral mesons. For p–Au our result is new. For p–Be, the simultaneously measured electron pair inclusive pair spectrum in which instrumental uncertainties are highly reduced. We confirm the earlier finding of HELIOS-1 with significantly reduced systematic uncertainties of 23% in the mass range below 450 MeV/c2, and of 28% in the mass range above 750 MeV/c2 at 90% confidence limit. Any unconventional source of electron pairs is limited by these error margins as the percentage fraction of the hadronic contribution.
Relative production cross sections.
K − /K + and p ¯ / p ratios measured in 158 A·GeV Pb+Pb collisions are shown as a function of transverse momentum P T and centrality in top 8.5% central region. Little centrality dependence of the K − / K + and p ¯ / p ratios is observed. The transverse mass m T distribution and dN/dy of K + , K − , p and p ¯ around mid-rapidity are obtained. The temperature T ch and the chemical potentials for both light and strange quarks (μ q , μ s ) at chemical freeze-out are determined by applying simple thermodynamical model to the present data. The resultant μ q , μ s and T ch are compared with those obtained from similar analysis of SPS S+A and AGS Si+A data. The chemical freeze-out temperature T ch at CERN energies is higher than thermal freeze-out temperature T fo which is extracted from m T distribution of charged hadrons. At AGS energies T ch is close to T fo .
Data obtained from the fit of MT spectra.
Data obtained from the fit of MT spectra.
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