The production ofK0, Λ and\(\bar \Lambda \) particles is studied in the E665 muon-nucleon experiment at Fermilab. The average multiplicities and squared transverse momenta are measured as a function ofxF andW2. Most features of the data can be well described by the Lund model. Within this model, the data on the K0/π± ratios and on the averageK0 multiplicity in the forward region favor a strangeness suppression factors/u in the fragmentation process near 0.20. Clear evidence for QCD effects is seen in the average squared transverse momentum ofK0 and Λ particles.
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We present cross section measurements for inclusive jet production in almost-real photon-photon interactions at TRISTAN using the AMY detector. The results are compared with leading-order QCD calculations for different parameterizations of the parton density in the photon.
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The production of charmed mesons$$\mathop {D^0 }\limits^{( - )} $$,D
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The DSYS error is due to the error in the branching ratio.
The DSYS error is due to the error in the branching ratio.
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We report results on a precision measurement of the ratio R=σLσT in deep inelastic electron-nucleon scattering in the kinematic range 0.2≤x≤0.5 and 1≤Q2≤10 (GeV/c)2. Our results show, for the first time, a clear falloff of R with increasing Q2. Our R results are in agreement with QCD predictions only when corrections for target mass effects and some additional higher twist effects are included. At small x, the data on R favor structure functions with a large gluon contribution. We also report results on the differences RA−RD and the cross section ratio σAσD between Fe and Au nuclei and the deuteron. Our results for RA−RD are consistent with zero for all x, Q2 indicating that possible contributions to R from nuclear higher twist effects and spin-0 constituents in nuclei are not different from those in nucleons. The ratios σAσD from all recent experiments, at all x, Q2 values, are now in agreement.
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We report measurements of the proton form factors GEp and GMp extracted from elastic scattering in the range 1≤Q2≤3 (GeV/c)2 with total uncertainties < 15% in GEp and < 3% in GMp. Comparisons are made to theoretical models, including those based on perturbative QCD, vector-meson dominance, QCD sum rules, and diquark constituents in the proton. The results for GEp are somewhat larger than indicated by most theoretical parametrizations, and the ratios of the Pauli and Dirac form factors Q2(F2pF1p) are lower in value and demonstrate a weaker Q2 dependence than those predictions. A global extraction of the elastic form factors from several experiments in the range 0.1 0.1<Q2<10 (GeV/c)2 is also presented.
Point-to-point systematic uncertainty is 0.5%, overall normailzation uncertainty is 1.9%.
Point-to-point systematic uncertainty is 0.5%, overall normailzation uncertainty is 1.9%.
Point-to-point systematic uncertainty is 0.5%, overall normailzation uncertainty is 1.9%.
If quarks are composite particles then excited states are expected. We have searched in pp¯ collisions for excited quarks (q*) which decay to common quarks by emitting a W boson (q*→qW) or a photon (q*→qγ). The simplest model of excited quarks has been excluded for mass M*<540 GeV/c2 at 95% confidence level.
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The CERES experiment (CErenkov Ring Electron Spectrometer) studies the production of low mass e + e − pairs in proton-proton, proton-nucleus and nucleus-nucleus interactions at the CERN SPS. The CERES spectrometer, has a novel design based on two Ring Imaging Cherenkov (RICH) counters, and it operates close to its design specifications. Data were recorded with 200 GeV u sulfur beam and 450 GeV proton beam. The analysis is in progress. We have extracted first e + − -pairs samples for p+Be, p+Au and S+Au collisions. In addition other physics topics were addressed. Inclusive photon spectra were measured in S+Au interactions. No excess over known hadronic sources was found within our present systematic error of 11%. Results on high p i charged pion spectra are presented up to 4 GeV c . We also studied the production of e + e − -pairs m the strong electromagnetic fields of very peripheral S+Pt collisions. The data are well described by a first-order perturbative QED-calculation.
NON-DISRUPTIVE S+PT COLLISIONS.
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The proton Compton effect has been studied in the region between the threshold for pion photoproduction and the Δ(1232). The measurements were performed using bremmstrahlung from the high duty-factor electron beam available at the Saskatchewan Accelerator Laboratory. Elastically scattered photons were detected with an energy resolution of approximately 1.5% using a large NaI total absorption scintillation detector. Differential cross sections were measured for photon energies in the range 136 MeV≤Eγ≤289 MeV and for angles in the range 25°<θlab<135°. The angular distributions and the excitation functions derived from these data are in agreement with recent theoretical analyses. The results were interpreted within a formalism based in part on dispersion relations to obtain model-dependent estimates of the electric and magnetic polarizabilities, α¯ and β¯. We find, subject to the dispersion sum rule constraint α¯+β¯=(14.2±0.5)×10−4 fm3, that α¯=(9.8±0.4±1.1)×10−4 fm3 and β¯=(4.4∓0.4∓1.1)×10−4 fm3, which are consistent with the best previous measurements.
Axis error includes +- 3/3 contribution (DUE TO THE CALIBRATION).
Axis error includes +- 3/3 contribution (DUE TO THE CALIBRATION).
Axis error includes +- 3/3 contribution (DUE TO THE CALIBRATION).
The differential cross sections dσ/dxF for J/ψ produced inclusively in 800 GeV/c p-Cu and p-Be collisions have been measured in the kinematic range 0.30≤xF≤0.95 through the decay mode J/ψ→μ+μ−. They are compared with the predictions of the semilocal duality model for several sets of parton density functions. No evidence for a suggested intrinsic charm contribution to the cross section is observed. The ratio of the differential cross sections for Cu and Be targets confirms the suppression of J/ψ production in heavy nuclei at large xF.
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