K. Freudenreich

Angular Distributions of Muon Pairs Produced by 194-{GeV}/

We present the angular distributions of muon pairs obtained in a high-statistics experiment using a 194-GeV/c π- impinging on a tungsten target. Our results are based on the analysis of 145,000 events with positive Feynmanx and mass above 4.07 GeV/c2, excluding the ϒ region. Simple first-order QCD relations allow us to determine the ratio of annihilation with hard-gluon emission to the sum of annihilation with hard-gluon emission and hard-gluon Compton scattering, which is found to be about 58% to 75%. We determine the parton square intrinsic transverse momenta to be of the order of 0.6 (GeV/c)2, and about 30% larger in the pion than in the nucleon. At largex1, our data agree with the higher-twist hypothesis, and support the interpretation of the relevant scale parameter as the dimuon square transverse momentum.

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We present the angular distributions of high-mass muon pairs produced in a high-statistics experiment by 140 and 194 GeV/c π− beams impinging on a tungsten target, and by 286 GeV/c π− beam on deuterium and tungsten targets. We find no evidence for a center-of-mass energy dependence or a nuclear dependence of the angular distribution parameters. The two parameters λ and μ are found to be essentially independent of any kinematical variable. In contrast, the parameterv increase with the dimuon transverse momentumPT, at variance with recent perturbative QCD predictions. Our statistics at largex1 are insufficient to substantiate the highertwist prediction.

Negative Pions

We compare the differential cross sections of high-mass muon pair production on deuterium and tungsten by incident negative pions of 140 and 286 GeV. We find an indication of a nuclear effect on the nucleon quark distributions comparable in magnitude to what is observed in muon-iron deep inelastic scattering, whereas the pion-quark distribution is unaffected, compatibly with QCD factorization.

Angular Distributions of Muon Pairs Produced by Negative Pions on Deuterium and Tungsten

Abstract We present the first clear evidence for a nuclear dependence of the transverse momentum distribution of massive muon pairs produced in hadronic interactions. Comparing the cross sections for high-mass dimuon production by incident negative pions (140 and 286 GeV) off tungsten and deuterium, we find that their ratio increases with the dimuon transverse momentum. The resulting difference in the mean transverse momentum squared amounts to 0.15±0.03 (syst.) GeV 2 / c 2 and is shown to be independent of the dimuon mass and longitudinal momentum.

Nuclear effects on the nucleon structure functions in hadronic high-mass dimuon production

Abstract We describe the design, construction and performance of a high-resolution spectrometer used at CERN to study the production of high-mass muon pairs by intense hadron beams. We also discuss the on- and off-line software used with this spectrometer.

Observation of a Nuclear Dependence of the Transverse Momentum Distribution of Massive Muon Pairs Produced in Hadronic Collisions

AbstractWe present a measurement of the production of muon pairs in 194 GeV/c π−-tungsten interactions. A sample of 155,000 events with mass higher than 4.07 GeV/c2 has been used to determine the differential cross-section as a function of the scaling variablesn

Differential cross-section of high-mass muon pairs produced by a 194 GeV/c π− beam on a tungsten target

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A-dependence of muon pair production in π-nucleus interactions at 280 GeV/c

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