We have measured the fraction of J/ψ mesons originating from χc meson decays in pp¯ collisions at s=1.8TeV. The fraction, for PTJ/ψ>4.0GeV/c and |ηJ/ψ|<0.6, not including contributions from b flavored hadrons, is 29.7%±1.7%(stat)±5.7%(syst). We have determined the cross sections for J/ψ mesons originating from χc decays and for directly produced J/ψ mesons. We have found that direct J/ψ production is in excess of the prediction of the color singlet model by the same factor found for direct ψ(2S) production.
Fraction of J/PSI mesons from CHI/C decays, excluding the the contributions from b-hadron decay.
Differential cross section for J/PSI's directly produced (ie excluding CHI/C and PSI/(25) decay contribution to the prompt production cross section). RE = PBAR P --> J/PSI X.
Differential cross section for J/PSI's produced in CHI/C decays.
The diffractive production of ρ0(770 @#@) mesons in muon-proton interactions is studied in the kinematic region 0.15 GeV2< Q2< 20 GeV2 and 20 GeV < ? < 420 GeV. The data were obtained in the Fermilab fixed-target experiment E665 with primary muons of 470 GeV energy. Results are presented on the Q2, x and ? dependence of the cross section, on the shape of the ρ+ρt - mass spectrum, on the slope of the diffraction peak and on the production and decay angular distributions of the ρ0(770). The cross section for diffractive production of ρ0 by virtual photons on protons depends mainly on Q2. At fixed Q2, no significant dependence on x or ? is observed. The extrapolation to Q2 = 0 yields a photoproduction cross section of (10.30 ± 0.33) μb. The slope of the t′ distribution has a value of (7.0 ± 0.2) GeV−2, with a tendency to decrease as Q2 increases. The production and decay angular distributions of the ρ0 depend strongly on Q2 and are consistent with s-channel helicity conservation. The ratio R = σl/σt deduced from the decay angular distributions rises strongly with Q2, passing the value of 1 at Q2≈ 2 GeV2.
Statistical errors only.
Statistical errors only.
Cross section extrapolated to Q**2 = 0.
Inclusive photoproduction of $\dspm$ in ep collisions at HERA has been measured with the ZEUS detector for photon-proton centre of mass energies in the range \linebreak \wrang and photon virtuality Q~2 < 4 \g2. The cross section $\sigma_{ep \to \ds X} $ integrated over the kinematic region \ptrangand \etarang is {\xsecs}. Differential cross sections as functions of $p_{\perp}~{\ds}$, $\eta~{\ds}$ and W are given. The data are compared with two next-to-leading order perturbative QCD predictions. For a calculation using a massive charm scheme the predicted cross sections are smaller than the measured ones. A recent calculation using a massless charm scheme is in agreement with the data.
Data from the (Kpi)pi channel.
Data from the (Kpipipi)pi channel.
Data from the (Kpi)pi channel.
A study is presented of the process gamma p -->XY, where there is a large rapidity gap between the systems X and Y. Measurements are made of the differential cross section as a function of the invariant mass mx of the system produced at the photon vertex. Results are presented at centre of mass energies of W_gp = 187 GeV and W_gp = 231 GeV, both where the proton dominantly remains intact and, for the first time, where it dissociates. Both the centre of mass energy and the mx~2 dependence of HERA data and those from a fixed target experiment may simultaneously be described in a triple-Regge model. The low mass photon dissociation process is found to be dominated by diffraction, though a sizable subleading contribution is present at larger masses. The pomeron intercept is extracted and found to be alpha_pom(0) = 1.068 \pm 0.016 (stat.) \pm 0.022 (syst.) \pm 0.041 (model), in good agreement with values obtained from total and elastic hadronic and photoproduction cross sections. The diffractive contribution to the process gamma p --> Xp with mx~2 / W_gp~2 < 0.05 is measured to be 22.2 \pm 0.6 (stat.) \pm 2.6 (syst.) \pm 1.7 (model) % of the total gamma p cross section at W_gp = 187 GeV.
Data for proton remaining intact.
Data for proton dissociating.
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.
We report on the measurement of W-boson pair-production with the L3 detector at LEP at a centre-of-mass energy of 161.34 GeV. In a data sample corresponding to a total luminosity of 11 pb −1 , we select four-fermion events with high invariant masses of pairs of hadronic jets or leptons. Combining all final states, the measured total cross section for W-pair production is: sigma WW = 2.89 −0.70 +0.81 (stat.) ± 0.14 (syst.) pb. Within the Standard Model, this corresponds to a mass of the W boson of: M W = 80.80 −0.42 +0.48 (exp.) ± 0.03 (LEP) GeV. Limits on anomalous triple-vector-boson couplings are derived.
No description provided.
No description provided.
We have measured the spin-dependent structure function $g_1~p$ in inclusive deep-inelastic scattering of polarized muons off polarized protons, in the kinematic range $0.003 < x < 0.7$ and $1 GeV~2 < Q~2 < 60 GeV~2$. A next-to-leading order QCD analysis is used to evolve the measured $g_1~p(x,Q~2)$ to a fixed $Q~2_0$. The first moment of $g_1~p$ at $Q~2_0 = 10 GeV~2$ is $\Gamma~p = 0.136\pm 0.013(stat.) \pm 0.009(syst.)\pm 0.005(evol.)$. This result is below the prediction of the Ellis-Jaffe sum rule by more than two standard deviations. The singlet axial charge $a_0$ is found to be $0.28 \pm 0.16$. In the Adler-Bardeen factorization scheme, $\Delta g \simeq 2$ is required to bring $\Delta \Sigma$ in agreement with the Quark-Parton Model. A combined analysis of all available proton and deuteron data confirms the Bjorken sum rule.
Data for Q**2 > 1 GeV**2.
Data for Q**2 > 0.2 GeV**2.
Statistical errors only.
Results from a 4π solid angle measurement of the reactions 3He(π+,ppp) and 4He(π+,ppp)n at incident pion energies of Tπ+=70, 118, 162, 239, and 330 MeV are presented. For 3He the total absorption cross sections and their decomposition into two-proton and three-proton components are evaluated; for 4He the three-proton absorption cross sections are given. The differential distributions of the three-proton multinucleon absorption mode of both nuclei are analyzed and compared to each other by making use of a complete set of variables. The data are investigated for signatures of initial and final state interactions: it is found that more than half of the three-proton yield cannot be accounted for by cascade mechanisms. The remaining strength shows dependence on the incident pion angular momentum, but also structures that are not explained by simple semiclassical models.
Absorption cross section. Total errors are presented.
First and second errors are due to fits and normalization uncertainties, respectively.
First and second errors are due to fits and normalization uncertainties, respectively.
The experimental setup and detection technique of the COSY-11 installation, an internal experimental facility at the cooler synchrotron and storage ring COSY Jülich, are described. The detection system has been designed for meson production studies with full geometrical acceptance close to threshold. Preliminary results of first measurements are presented, emphasis is put on strangeness production in the reactions pp → ppK + K − and pp → pK + Λ .
Excess energy of 6.1 MeV above threshold 3.3016 GeV.
Excess energy of 2 MeV above threshold 2.339 GeV.
We report the first observation of diffractively produced W bosons. In a sample of W -> e nu events produced in p-barp collisions at sqrt{s}=1.8 TeV, we find an excess of events with a forward rapidity gap, which is attributed to diffraction. The probability that this excess is consistent with non-diffractive production is 1.1 10^{-4} (3.8 sigma). The relatively low fraction of W+Jet events observed within this excess implies that mainly quarks from the pomeron, which mediates diffraction, participate in W production. The diffractive to non-diffractive W production ratio is found to be R_W=(1.15 +/- 0.55)%.
No description provided.
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