Muon pair production in proton-nucleon interactions and new parton radiative processes

Abstract

An examination of experimental data bearing on the production of muon pairs in nucleon-nucleon interactions demonstrates the existence of a large continuum for pairs with invariant masses less than 1.0 GeV/${\mathit{c}}^2$. The ratio of the pairs to the production of pions, $\frac{I\left(\mu \mu \right)}{I\left({\pi }^0\right)}$, is of the order of 5 × ${10}^{-5\mathrm{}}$ in the fragmentation region. The production of the pairs obeys Feynman scaling in the fragmentation region; the cross sections $\frac{d^2\sigma }{\mathrm{dm}}$ $\mathrm{dx}$ are nearly the same for the interactions of 28-GeV protons and 150-GeV protons and the assumption of scaling is consistent with less detailed measurements at 400 GeV over a region of Feynman $x$ such that $0.15<x<\mathrm{}0.6\mathrm{}$ and for values of the invariant mass $m\lesssim 1.0$ GeV/${\mathit{c}}^2$. The invariant-mass spectrum of this continuum varies with $x$; the mean mass changes from about 450 MeV/${\mathit{c}}^2$ at $x=0.2\mathrm{}$ to about 700 MeV/${\mathit{c}}^2$ for $x\approx 0.6$. The dimuon production varies with the target nucleus as $A^{\frac{2}{3}}$ in an $x$ region where meson production varies as $A^{0.55}$. The production is discussed in terms of parton bremsstrahlung, the annihilation of parton pairs produced by the hadron interaction (the Bjorken-Weisberg process) and line broadening of $\rho$-meson production.