The exclusive photoproduction of J/psi mesons, gamma p->J/psi p, has been studied in ep collisions with the ZEUS detector at HERA, in the kinematic range 20<W<290 GeV, where W is the photon-proton centre-of-mass energy. The J/psi mesons were reconstructed in the muon and the electron decay channels using integrated luminosities of 38 pb^-1 and 55 pb^-1, respectively. The helicity structure of J/psi production shows that the hypothesis of s-channel helicity conservation is satisfied at the two standard-deviation level. The total cross section and the differential cross-section dsigma/dt, where t is the squared four-momentum transfer at the proton vertex, are presented as a function of W, for |t|<1.8 GeV^2. The t distribution exhibits an exponential shape with a slope parameter increasing logarithmically with W with a value b=4.15 \pm 0.05 (stat.)^{+0.30}_{-0.18} (syst.) GeV^-2 at W=90 GeV. The effective parameters of the Pomeron trajectory are alphapom(0) = 1.200 \pm 0.009(stat.)^{+0.004}_{-0.010}(syst.) and alphappom= 0.115 \pm 0.018(stat.)^{+0.008}_{-0.015}(syst.) GeV^-2.
The total exclusive J/PSI photoproduction cross section, the differential cross section extrapolated to t=0 and the slope parameter of the exponential t dependence as afunction of W, the photon-proton c.m. energy, for data from J/PSI muon decay.
The total exclusive J/PSI photoproduction cross section as a function of W,the photon-proton c.m. energy, for data from J/PSI electron decays.
The differential cross section extrapolated to t=0 and the slope parameter of the exponential t dependence for exclusive J/PSI photoproduction as a function of W, the photon-proton c.m. energy for data from J/PSI electron decays.
The photon-proton total cross section has been measured in the process e+ p -> e+ gamma p -> e+ X with the ZEUS detector at HERA. Events were collected with photon virtuality Q^2 < 0.02 GeV^2 and average gamma-p center-of-mass energy W_{gamma p} = 209 GeV in a dedicated run, designed to control systematic effects, with an integrated luminosity of 49 nb^{-1}. The measured total cross section is sigma_{tot}^{gamma p} = 174 +- 1 (stat.) +- 13 (syst.) microbarns. The energy dependence of the cross section is compatible with parameterizations of high-energy p-p and p-pbar data.
Total GAMMA P cross section.
The dijet cross section in photoproduction has been measured with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb$^{-1}$. The events were required to have a virtuality of the incoming photon, $Q^2$, of less than 1 GeV$^2$ and a photon-proton centre-of-mass energy in the range $134 < W_{\gamma p} < 277$ GeV. Each event contains at least two jets satisfying transverse-energy requirements of $E_{T}^{\rm jet1}>14$ GeV and $E_{T}^{\rm jet2}>11$ GeV and pseudorapidity requirements of $-1<\eta^{\rm jet1,2}<2.4$. The measurements are compared to next-to-leading-order QCD predictions. The data show particular sensitivity to the density of partons in the photon, allowing the validity of the current parameterisations to be tested.
Measured cross section as a function of COS(THETA*), where THETA* is the dijet angle in the parton-parton c.m. frame. The data are shown in two X(C=GAMMA) regions.
Measured cross section as a function of ET(JET1) for X(C=GAMMA) > 0.75 for:. -1 < ETARAP(JET1) < 0. -1 < ETARAP(JET2) < 0.
Measured cross section as a function of ET(JET1) for X(C=GAMMA) > 0.75 for:. 0 < ETARAP(JET1) < 1. -1 < ETARAP(JET2) < 0.
We report on measurements of the ϒ(1S), ϒ(2S), and ϒ(3S) differential cross sections (d2σ/dpTdy)|y|<0.4, as well as on the ϒ(1S) polarization in pp¯ collisions at s=1.8TeV using a sample of 77±3pb−1 collected by the collider detector at Fermilab. The three resonances were reconstructed through the decay ϒ→μ+μ−. The measured angular distribution of the muons in the ϒ(1S) rest frame is consistent with unpolarized meson production.
The differential cross section times the branching ratio into mu+ mu- for UPSILON(1S) production.
The differential cross section times the branching ratio into mu+ mu- for UPSILON(2S) production. The first DSYS error is the systematic error due to the polarization of the UPSILON which is shown seperately from the other systematic errors.
The differential cross section times the branching ratio into mu+ mu- for UPSILON(3S) production. The first DSYS error is the systematic error due to the polarization of the UPSILON which is shown seperately from the other systematic errors.
We present measurements of the B+ meson total cross section and differential cross section $d\sigma/ dp_T$. The measurements use a $98\pm 4$ pb^{-1} sample of $p \bar p$ collisions at $\sqrt{s}=1.8$ TeV collected by the CDF detector. Charged $B$ meson candidates are reconstructed through the decay $B^{\pm} \to J/\psi K^{\pm}$ with $J/\psi\to \mu^+ \mu^-$. The total cross section, measured in the central rapidity region $|y|<1.0$ for $p_T(B)>6.0$ GeV/$c$, is $3.6 \pm 0.6 ({\rm stat} \oplus {\rm syst)} \mu$b. The measured differential cross section is substantially larger than typical QCD predictions calculated to next-to-leading order.
Measured differential cross section for B+ production. The first (DSYS) error is the PT dependent systematic error and the second is the full correlated systematic error.
The total integrated B+ meson cross section. The first error is the combined statistical and PT dependent systematic error. The DSYS error is the fully correlated systematic error.
The interaction of virtual photons is investigated using the reaction e+e- -> e+e- hadrons based on data taken by the OPAL experiment at e+e- centre-of-mass energies sqrt(s_ee)=189-209 GeV, for W>5 GeV and at an average Q^2 of 17.9 GeV^2. The measured cross-sections are compared to predictions of the Quark Parton Model (QPM), to the Leading Order QCD Monte Carlo model PHOJET to the NLO prediction for the reaction e+e- -> e+e-qqbar, and to BFKL calculations. PHOJET, NLO e+e- -> e+e-qqbar, and QPM describe the data reasonably well, whereas the cross-section predicted by a Leading Order BFKL calculation is too large.
Total cross section in the given phase space and assuming ALPHA = 1/137.
Differential cross section as a function of X where X is the maximum value of X1 or X2, the upper and lower vertex values.
Differential cross section as a function of Q**2 where Q**2 is the maximum value of Q1**2 or Q2**2, the upper and lower vertex values.
The charged particle multiplicities of two- and three-jet events from the reaction e+e- -> Z0 -> hadrons are measured for Z0 decays to light quark (uds) flavors. Using recent theoretical expressions to account for biases from event selection, results corresponding to unbiased gluon jets are extracted over a range of jet energies from about 11 to 30 GeV. We find consistency between these results and direct measurements of unbiased gluon jet multiplicity from upsilon and Z0 decays. The unbiased gluon jet data including the direct measurements are compared to corresponding results for quark jets. We perform fits based on analytic expressions for particle multiplicity in jets to determine the ratio r = Ng/Nq of multiplicities between gluon and quark jets as a function of energy. We also determine the ratio of slopes, r(1) = (dNg/dy)/(dNq/dy), and of curvatures, r(2) = (d2Ng/dy2)/(d2Nq/dy2), where y specifies the energy scale. At 30 GeV, we find r = 1.422 +/- 0.051, r(1) = 1.761 +/- 0.071 and r(2) = 1.98 +/- 0.13, where the uncertainties are the statistical and systematic terms added in quadrature. These results are in general agreement with theoretical predictions. In addition, we use the measurements of the energy dependence of Ng and Nq to determine an effective value of the ratio of QCD color factors, CA/CF. Our result, CA/CF = 2.23 +/- 0.14 (total), is consistent with the QCD value of 2.25.
Measurements of the mean charged particle multiplicity of biased two-jet uds flavour events from Z0 decays as a function of the transverse momentum cutoff PT(C=LU) used to separate two- and three-jet events.
Measurements of the mean charged particle multiplicity of three-jet uds flavour 'Y events' from Z0 decays, as a function of the angle THETA1 between the lowest two energy jets. The results for the quark jet scale SQRT(S(C=QQBAR)) and the gluon jet scales PT(C=LU) and PT(C=LE) are also given.
Measurements of the unbiased gluon multiplicity as a function of the energy scale Q=PT(C=LU). The corresponding bins of THETA1 in 'Y events' are also indicated.
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.
Charged multiplicity at $\sqrt{s} = 630~\text{GeV}$, $|\eta| < 1$, $p_T > 0.4~\text{GeV}$.
Charged multiplicity at $\sqrt{s} = 1800~\text{GeV}$, $|\eta| < 1$, $p_T > 0.4~\text{GeV}$.
$\langle p_\perp \rangle$ vs. multiplicity at $\sqrt{s} = 630~\text{GeV}$, $|\eta| < 1$, $p_T > 0.4~\text{GeV}$.
We present a search for new heavy particles, $X$, which decay via $X \to WZ \to e\nu +jj$ in $p{\bar p}$ collisions at $\sqrt{s}$ = 1.8 TeV. No evidence is found for production of $X$ in 110 pb$^{-1}$ of data collected by the Collider Detector at Fermilab. Limits are set at the 95% C.L. on the mass and the production of new heavy charged vector bosons which decay via $W'\to WZ$ in extended gauge models as a function of the width, $\Gamma (W')$, and mixing factor between the $W'$ and the Standard Model $W$ bosons.
CONST(NAME=XI) is the mixing factor between WPRIME and W-boson.
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.
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