We present results on inelastic J/PSI-production from muon interactions with hydrogen and deuterium at an incident muon energy of 280 GeV. The measured cross section ratio per nucleon for muon-induced J/PSI-production in deuterium and hydrogen was found to be R(D2/H2) = 1.01 +/- 0.15. The colour singlet model is shown to provide a good description of the observed differential cross section apart from a normalisation factor. The comparison between the observed cross section and the colour singlet model prediction allows the extraction of the gluon structure function G(chi) of the nucleon. The momentum fraction-chi of the nucleon carried by the gluon is measured in the range of chi = [0.02, 0.30]. The normalised gluon distribution of free nucleons thus found can be parametrised as chi-G(chi) = 1/2 (eta + 1)(1 - chi)eta, with eta = 5.1 +/- 0.9 (stat).
We present a re-evaluation of the structure function ratios F-2(He)/F-2(D), F-2(C)/F-2(D) and F-2(Ca)/F-2(D) measured in deep inelastic muon-nucleus scattering at an incident muon momentum of 200 GeV. We also present the ratios F-2(C)/F-2(Li), F-2(Ca)/F-2(Li) and F-2(Ca)/F-2(C) measured at 90 GeV. The results are based on data already published by NMC; the main difference in the analysis is a correction for the masses of the deuterium targets and an improvement in the radiative corrections. The kinematic range covered is 0.0035 < x < 0.65, 0.5 < Q(2) < 90 GeV2 for the He/D, C/D and Ca/D data and 0.0085 < x < 0.6, 0.84 < Q(2) < 17 GeV2 for the Li/C/Ca ones.
Experimental results obtained at the CERN Super Proton Synchrotron on the structure-function ratio F2n/F2p in the kinematic range 0.004 < x < 0.8 and 0.4 < Q2 < 190 GeV2, together with the structure function F2d determined from a fit to published data, are used to derive the difference F2p(x) - F2n(x). The value of the Gottfried sum integral (F2p - F2n) dx/x = 0.240 +/- 0.016 is below the quark-parton-model expectation of 1/3.
Results are presented on the difference in R, the ratio of longitudinally to transversely polarised virtual photon absorption cross sections, for the deuteron and the proton. They are obtained by comparing the ratio of cross sections for the deep inelastic scattering of muons from deuterium and hydrogen targets at 90 and 280 GeV incident energy. The results cover the range x = 0.01 -0.30, at an average Q2 of 9 GeV2. The measured difference R(d)-R(p) shows no significant x dependence and is compatible with zero, as well as with expectations from perturbative QCD. We use the same method to obtain the difference R(Ca)-R(C) from cross section ratios measured on carbon and calcium targets at 90 and 200 GeV incident energy.
The structure function ratios F2C/F2Li, F2Ca/F2Li and F2Ca/F2C were measured in deep inelastic muon-nucleus scattering at an incident muon energy of 90 GeV, covering the kinematic range 0.0085 < x < 0.6 and 0.8 < Q2 < 17 GeV2. The sensitivity of the nuclear structure functions to the size and mean density of the target nucleus is discussed.
We present the structure function ratios F2He/F2D, F2C/F2D and F2Ca/F2D measured in deep inelastic muon-nucleus scattering at an incident muon momentum of 200 GeV. The kinematic range 0.0035 < x < 0.65 and 0.5 < Q2 < 90 GeV2 is covered. At low x the three ratios are significantly smaller than unity and the size of the depletion grows with decreasing x and increasing mass number A. At intermediate x the ratios show an enhancement of about 2% above unity for C/D and Ca/D, possibly less for He/D. There are indications of some Q2 dependence in the Ca/D data. The integrals of the structure function differences F2A-F2D are discussed.
The structure functions F2p and F2d measured by deep inelastic muon scattering at incident energies of 90 and 280 GeV are presented. These measurements cover a large kinematic range, 0.006 less-than-or-equal-to x less-than-or-equal-to 0.6 and 0.5 less-than-or-equal-to Q2 less-than-or-equal-to 55 GeV2, and include the first precise data at small x, where large scaling violations are observed. The data agree with earlier results from SLAC and BCDMS but exhibit differences with respect to those of EMC-NA2. Extrapolations to small x of recent phenomenological parton distributions are shown to disagree with the present results.
Results are presented on the ratio of neutron and proton structure functions, F2n/F2p, deduced from deep inelastic scattering of muons from hydrogen and deuterium. The data, which were obtained at the CERN muon beam at 90 and 280 GeV incident energy, cover the kinematic range x = 0.002-0.80 and Q2 = 0.1-190 GeV2. The measured structure function ratios have small statistical and systematic errors, particularly at small and intermediate x. The observed Q2 dependence in the range x = 0.1-0.4 is stronger than predicted by perturbative QCD. From the present data together with results from other experiments it is suggested that the twist-four coefficient for the proton is smaller than that for the neutron for x larger than 0.2.
We have studied transverse momentum distributions for exclusive rho(0) muoproduction on protons and heavier nuclei at 2 < Q2 < 25 GeV2. The Q2 dependence of the slopes of the p(t)2 and t' distributions is discussed. The influence of the non-exclusive background is investigated. The p(t)2-slope for exclusive events is 4.3 +/- 0.6 +/- 0.7 GeV-2 at large Q2. The p(t)2 spectra are much softer than inclusive p(t)2 spectra of leading hadrons produced in deep inelastic scattering.
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Data are presented on exclusive ρ0 and φ{symbol} production in deep inelastic muon scattering from a target consisting mainly of nitrogen. The ratio of the total cross sections for ρ0 and φ{symbol} production is found to be 9:(1.6±0.4) at 〈Q2〉=7.5 GeV2, consistent with the SU(3) prediction of 9:2. The t dependence for exclusive ρ0 production is found to become shallover as Q2 increases and, for large Q2, the t dependence is typical of that for a hard scattering process. Furthermore, the ratio of the cross sections for coherent: incoherent production from nitrogen is found to decrease rapidly with Q2. Such behaviour indicates that even for exclusive vector meson production the virtual photon behaves predominantly as an electromagnetic probe.
Results are presented on the ratios of the nucleon structure function in copper to deuterium from two separate experiments. The data confirm that the nucleon structure function, F2, is different for bound nucleons than for the quasi-free ones in the deuteron. The redistribution in the fraction of the nucleon's momentum carried by quarks is investigated and it is found that the data are compatible with no integral loss of quark momenta due to nuclear effects.
Final data measured with the EMC forward spectrometer are presented on the production of forward charged hadrons in mu-p and mu-d scattering at incident beam energies between 100 and 280 GeV. The large statistic of 373000 events allows a study of the semi-inclusive hadron production as a function of z, p(T)2 and <p(T)2> in small Q2, x(Bj) and W bins. Charge multiplicity ratios and differences as a function of z and x(Bj) are given for p, d and n-targets. From the differences of charge multiplicities the ratio of the valence quark distributions of the proton d-upsilon(x)/u-upsilon(x) is determined for the first time in charged lepton scattering. The Gronau et al. sum rule is tested, the measured sum being 0.31 +/- 0.06 stat. +/- 0.05 syst., compared with the theoretical expectation of 2/7 almost-equal-to 0.286. The measured sum corresponds to an absolute value of the ratio of the d and u quark charge of 0.44 +/- 0.10 stat. +/- 0.08 syst.
Measurements are presented of the inclusive distributions of the J/psi meson produced by muons of energy 200 GeV from an ammonia target. The gluon distribution of the nucleon has been derived from the data in the range 0.04 < x < 0.36 using a technique based on the colour singlet model. An arbitrary normalisation factor is required to obtain a reasonable integral of the gluon distribution. Some comments are made on the use of J/psi production by virtual photons to extract the gluon distribution at HERA.