Production of φ mesons in e+e− annihilation at a center-of-mass energy of 29 GeV has been observed with the time-projection chamber detector at the PEP storage ring. The φ production rate has been measured in the energy range 0.075<x<0.55 (x=2Eφs), giving 0.077±0.012(stat)±0.016(syst) φ's per event. The average value of pt2 relative to the thrust axis is 1.0±0.4 (GeV/c)2.
No description provided.
EXTRAPOLAATION TO ALL X USES LUND MONTE CARLO PREDICTIONS.
ERRORS ARE BOTH STATISTICAL AND SYSTEMATIC. PT IS MEASURED RELATIVE TO THE EVENT THRUST AXIS, AND IS FOUND TO HAVE A MEAN VALUE OF 1.0 +- 0.4 GEV.
UPPER LIMITS FOR DEL(1232)++ PRODUCTION.
UPPER LIMITS FOR SIG(1385)+- PRODUCTION.
Measurements of midrapidity charged particle multiplicity distributions, $dN_{\rm ch}/d\eta$, and midrapidity transverse-energy distributions, $dE_T/d\eta$, are presented for a variety of collision systems and energies. Included are distributions for Au$+$Au collisions at $\sqrt{s_{_{NN}}}=200$, 130, 62.4, 39, 27, 19.6, 14.5, and 7.7 GeV, Cu$+$Cu collisions at $\sqrt{s_{_{NN}}}=200$ and 62.4 GeV, Cu$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV, U$+$U collisions at $\sqrt{s_{_{NN}}}=193$ GeV, $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV, $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV, and $p$$+$$p$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV. Centrality-dependent distributions at midrapidity are presented in terms of the number of nucleon participants, $N_{\rm part}$, and the number of constituent quark participants, $N_{q{\rm p}}$. For all $A$$+$$A$ collisions down to $\sqrt{s_{_{NN}}}=7.7$ GeV, it is observed that the midrapidity data are better described by scaling with $N_{q{\rm p}}$ than scaling with $N_{\rm part}$. Also presented are estimates of the Bjorken energy density, $\varepsilon_{\rm BJ}$, and the ratio of $dE_T/d\eta$ to $dN_{\rm ch}/d\eta$, the latter of which is seen to be constant as a function of centrality for all systems.
Transverse energy in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV
Multiplicity in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV
Transverse energy in Au+Au collisions at $\sqrt{s_{NN}}$ = 130 GeV
The total hadronic cross-section sigma_gg(W) for the interaction of real photons, gg->hadrons, is measured for gg centre-of-mass energies 10<W<110 GeV. The cross-section is extracted from a measurement of the process e+e- -> e+e-g*g* -> e+e- hardrons, using a luminosity function for the photon flux together with form factors for extrapolating to real photons (Q^2=0 GeV^2). The data were taken with the OPAL detector at LEP at e+e- centre-of-mass energies 161, 172 and 183 GeV. The cross-section sigma_gg(W) is compared with Regge factorisation and with the energy dependence observed in gp and pp interactions. The data are also compared to models which predict a faster rise of sigma_gg(W) compared to gp and pp interactions due to additional hard gg interactions not present in hadronic collisions.
No description provided.
No description provided.
Exposures of the Ne/H 2 filled Big European Bubble Chamber (BEBC) to a dichromatic neutrino (antineutrino) beam produced by 400 GeV protons of the CERN SPS yielded ∼ 3100 events with a negative, and ∼ 1100 with a positive, muon. The neutrino flux is determined from the muon flux in the shielding. Assuming a linear energy dependence of the cross section, the values σ E between 20 and 200 GeV are found to be 0.657 ± 0.012 (stat.) ± 0.027 (syst.) and 0.309 ± 0.009 (stat.) ± 0.013 (syst.) cm 2 (GeV nucleon) −1 , for neutrinos and antineutrinos, respectively. The scaling variable q 2 E decreases significantly with increasing energy both for neutrinos and antineutrinos.
Measured charged current total cross section.
Measured charged current total cross section.
No description provided.
The charged-current cross sections for neutrinos and antineutrinos on nucleons in the energy range 20–200 GeV are given. Taken in conjunction with the previous Gargamelle results, they show that σ E is almost constant with energy for antineutrinos, and falls with energy for neutrinos. The value of 〈q 2 〉 E decreases with energy for both neutrinos and antineutrinos, and these deviations from exact Bjorken scaling are consistent with those observed in electron and muon inelastic scattering. We find no evidence for new heavy quark states with right-handed coupling.
Measured charged current total cross section.
Measured charged current total cross section.
Results on the hadronic final state in e/sup +/e/sup -/ annihilation at 13, 17 and 27.4 GeV are presented. There is no compelling evidence for the existence of the t quark in these data, which are in general agreement with a simple quark parton model. Some tentative indications of QCD effects are observed in the p/sub T//sup 2/ distributions.
TAU HEAVY LEPTON CONTRIBUTION SUBTRACTED.
INCLUSIVE HADRON SPECTRUM. THESE DATA AT 13, 17 AND 27.4 GEV ON S*D(SIG)/DX ARE INCLUDED IN THE RECORD OF R. BRANDELIK ET AL., PL 89B, 418 (1980).
We have observed τ pair production at average CM energies of 13.9, 22.3, 34.5 and 43.1 GeV. The cross-sections are consistent with QED, the cut off parameters beingΛ+>161 GeV andΛ−169 GeV (95% CL). The topological branching fraction of the τ to 1 charged particle,B1, is 0.847±0.011 (stat)−0.013+0.016(syst) and no decays to 5 charged particles were observed resulting inB5<0.007 (95% CL). Within the 3 charged track final stateB(τ−→π−π+π−v)/(B(τ−→π−π+π−v)+B(τ−→π−π+π−π0v))=0.37−0.20+0.35
No description provided.
No description provided.
We have measured the reactions e + e − → e + e − → μ + μ − and e + e − → γγ at c.m. energies between 12 and 31.6 GeV. Excellent agreement with the predictions of QED has been found, resulting in cut off parameters Λ + > 112 GeV and Λ − > 139 GeV for the first process and Λ + > 34 GeV and Λ − > 42 GeV (95% c.1.) for the last one. A limit on the Weinberg angle of sin 2 θ W < 0.55 (95% c.1.) has been obtained.
SIG(C=QED) QED predictions for the cross sections. Only statistical errors are given.
SIG(C=QED) QED predictions for the cross sections. Only statistical errors are given.
SIG(C=QED) QED predictions for the cross sections. Only statistical errors are given.
We present a test of the flavour independence of the strong coupling constant for charm and bottom quarks with respect to light (uds) quarks, based on a hadronic event sample obtained with the OPAL detector at LEP. Five observables related to global event shapes were used to measure alpha_s in three flavour tagged samples (uds, c and b). The event shape distributions were fitted by Order(alpha_s**2) calculations of jet production taking into account mass effects for the c and b quarks. We find: = 0.997 +- 0.038(stat.) +- 0.030(syst.) +- 0.012(theory) and = 0.993 +- 0.008(stat.) +- 0.006(syst.) +- 0.011(theory) for the ratios alpha_s(charm)/alpha_s(uds) and alpha_s(b)/alpha_s(uds) respectively.
No description provided.