Associated hadronic production in μ-pair events at the CERN Intersecting Storage Rings

We have measured at s=62 GeV, at the CERN Intersecting Storage Rings, the associated charged hadrons with massive μ pairs, employing a vertex detector of ∼ 4π coverage. The experiment has provided the first data on hadron multiplicity, angular distributions, and correlations in lepton pair events at ISR energies. The average associated charged multiplicity 〈nch〉 is found to increase as the invariant mass of the hadronic system Mh increases, similarly to the observed s dependence in e+e− annihilation into hadrons at high energies. The multiplicity also increases with pT in the hemisphere opposite to the transverse momentum pT of the dimuon. Small clusters appear to be produced, whose correlation with the μ-pair can be explained in a simple Monte Carlo model incorporating the production of a weakly collimated jet of low multiplicity, recoiling against the dimuon.