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 Q 2 of 9 GeV 2 . 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.
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Average overall x values.
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The structure functions F p 2 and F d 2 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⩽ x ⩽0.6 and 0.5⩽ Q 2 ⩽55GeV 2 , 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.
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The decays η → γγ and η ′ → ηπ + π − have been observed in hadronic decays of the Z produced at LEP. The fragmentation functions of both the η and η ′ have been measured. The measured multiplicities for x > 0.1 are 0.298±0.023±0.021 and 0.068±0.016 for η and η ′ respectively. While the fragmentation function for the η is fairly well described by the JETSET Monte Carlo, it is found that the production rate of the η ′ is a factor of four less than the corresponding prediction.
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Additional 7 pct systematic error.
Additional 23 pct systematic error.
We present results on J/ψ production in muon interactions with tin and carbon targets at incident muon energies of 200 and 280 GeV. The ratio of cross sections per nucleon for J/ψ production on tin and carbon, R (Sn/C), is studied as a function of p T 2 , z and x . We find an enhancement for coherent J/ψ production R coh (Sn/C) = 1.54 ± 0.07, a suppression for quasielastic production R qe (Sn/C) = 0.79 ± 0.06 and for inelastic production R in (Sn/C) = 1.13 ± 0.08. The inelastic cross section ratio can be interpreted within the Colour Singlet model as an enhancement of the gluon distribution in tin with respect to that in carbon. The dependence of the ratio on z and p T 2 can explain the discrepancy between the results obtained in previous experiments.
Data for coherent events.
Data for quasielastic events.
Data for inelastic events.
Results are presented on the ratio of neutron and proton structure functions, F 2 n / F 2 p , deduced from deep inelastic scattering of muon 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 Q 2 = 0.1−190 GeV 2 . The measured structure function ratios have small statistical and systematic errors, particularly at small and intermediate x . The observed Q 2 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.
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Merged 90 and 280 GeV data.
The structure function ratiosF2C/F2Li,F2Ca/F2Li andF2Ca/F2C were measured in deep inelastic muonnucleus scattering at an incident muon energy of 90 GeV, covering the kinematic range 0.0085<x<0.6 and 0.8<Q2<17GeV2. The sensitivity of the nuclear structure functions to the size and mean density of the target nucleus is discussed.
Overall normalization error of 0.7%, due to uncertainties in target thickness, not included in the table.
Overall normalization error of 0.8%, due to uncertainties in target thickness, not included in the table.
Overall normalization error of 0.5%, due to uncertainties in target thickness, not included in the table.
We present the structure function ratiosF2He/F2D,F2C/F2D andF2Ca/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 lowx the three ratios are significantly smaller than unity and the size of the depletion grows with decreasingx and increasing mass numberA. At intermediatex 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 someQ2 dependence in the Ca/D data. The integrals of the structure function differencesF2A−F2D are discussed.
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Final data measured with the EMC forward spectrometer are presented on the production of forward charged hadrons in μp and μd scattering at incident beam energies between 100 and 280 GeV. The large statistic of 373 000 events allows a study of the semi-inclusive hadron production as a function ofz,pT2 and 〈pT2〉 in smallQ2,xBj andW bins. Charge multiplicity ratios and differences as a function ofz andxBj are given forp, d andn-targets. From the differences of charge multiplicities the ratio of the valence quark distributions of the protondv(x)/uv(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≈0.286. The measured sum corresponds to an absolute value of the ratio of thed andu quark charge of 0.44±0.10 stat.±0.08 syst.
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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 F(F2p-F2n)dx/x=0.240±0.016 is below the quark-parton-model expectation of 1/3.
No description provided.
The ratio of the structure function F 2 n / F 2 p ( x ) has been measured in deep inelastic scattering of 274 GeV muons on hydrogen and deuterium targets exposed simultaneously to the beam. The results were obtained from 0.3 (0.6) million events from hydrogen (deuterium) in the range 0.004 < x < 0.8 and 1 < Q 2 < 190 GeV 2 . At x < 0.25 both the statistical and the systematic error is below 2%. Implications for parton distributions and for the σ w / σ z production cross section ratio in p p collisions are discussed. When compared to other results obtained at lower energies, the data indicate a Q 2 dependence of the ratio.
No description provided.
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