Measurements of the magnetic form factor of the proton in the timelike region at large momentum transfer

Abstract

The cross section for the reaction $\overline{p}\stackrel{\ensuremath{\rightarrow}}{p}{e}^{+}{e}^{\ensuremath{-}}$ has been measured at $s=8.8,$ $10.8,$ $12.4,$ $13.1,$ and $14.4 {\mathrm{GeV}}^{2}$ by Fermilab experiment E835. A non-magnetic spectrometer is used to identify the ${e}^{+}{e}^{\ensuremath{-}}$ final states generated by the antiproton beam intersecting an internal hydrogen gas jet target. From the analysis of the 144 observed events, new high-precision measurements of the proton magnetic form factor for timelike momentum transfers are obtained.