William J. Metcalf

Muon pair production in 16 and 22 GeV πCu collisions

Abstract We have measured inclusive muon pair production by 16 and 22 GeV π − on a copper target in a wide aperture magnetic spectrometer. We interpret the data in terms of quark annihilation models and find approximate scaling in the variable τ = M 2 / s over a wide energy range. At large values of τ the yield of μ-pairs produced by π − is ∼ 100 times that produced by protons. This effect can be understood by assuming appropriate quark distributions for π − and p and thus provides experimental insight into the inner structure of these particles.

Production of Jψ in 16 and 22 GeVπCu collisions

Abstract We have measured the inclusive production of J ψ in 16 and 22 GeV π− copper collisions in a wide aperture magnetic spectrometer. The cross section per Cu nucleus for x > 0 corrected for branching ratio is 64 ± 38 nb at 16 GeV and 196 ± 38 nb at 22 GeV. As threshold is approached, the mean values of the Feynman x distribution increase and the cross section for J ψ production drops steeply. This can be understood in terms of the quark-fusion model where the antiquark content of the pion makes an increasingly significant contribution as M 2 s increases.

Experimental determination of the structure function of the pion

Abstract It was shown in the preceeding letter that dimuon production by 22 GeV pions proceeds in part through qq annihilations in agreement with the Drell-Yan model. Using these data we extract the quark distribution function of the pion. Comparison of our structure function with that obtained from data at higher energy reveals differences compatible with the QCD calculations of the Q 2 -dependence (scale breaking) of the pion structure function.

The magnitude of the parton intrinsic transverse momentum

Abstract We analyze data on the transverse momentum distribution of dimuons produced by 22 GeV and 16 GeV π − incident on a Cu target. We evaluate the quantum chromodynamic lowest order perturbation contributions and also introduce an intrinsic transverse momentum k T on the partons relative to their parent hadrons. The analysis of our data leads to 〈 k T 〉=0.30−0.35 GeV. We discuss our result in comparison with analyses of data at higher energies.

The contribution of qq̄ annihilations to dimuon production in πN interactions

We present data on dimuon production by 16 GeV π+ and π− beams on a Cu target. From the data we evaluate, for π−N collisions, the fraction of dimuon events that originate from the annihilation process qq → μ+μ−. Using this information the experimentally determined cross section for the process qq → μ+μ− is observed to be in agreement with the Drell-Yan model over a wide range of incident energies. The observed deviations from exact scaling are of the order predicted by QCD calculations for the Q2-dependence of the nucleon and the pion structure function.

Search for short-lived particles below charm threshold

We have searched for the production by virtual photons of short-lived particles that exhibit muonic decay. We used Brookhavens 10.5 GeV/c muon beam and examined the two and three-muon final states. The sample of 158 trimuon events is due almost entirely to QED tridents. The sample of 673 dimuons can be accounted for in part by asymmetric tridents and in part by the decay of π and K mesons. We obtain an upper limit for the production of other short-lived particles of the order of Bδ < 150 pb/nucleon, where B is the branching ratio for muonic decay. From the trident sample we establish that muons obey Fermi-Dirac statistics at the level of 8 standard deviations.

On the polarization of low mass dimuons produced in hadronic interactions

Abstract We have examined the angular distribution of massive μ+μ− pairs produced in 22 GeV/c π−Cu interactions. We find that the virtual photons which give rise to the process γv→μ+μ− are mainly longitudinally polarized. This contradicts the simple quark-antiquark annihilation model indicating that this is not the dominant production mechanism for the bulk of the data. However, for large fractional momentum of the incident q better agreement with the g q annihilation hypothesis is obtained.