Thrust jet analysis of deep-inelastic large-rapidity-gap events

Abstract.

A thrust analysis of Large-Rapidity-Gap events in deep-inelastic $ep$ collisions is presented, using data taken with the H1 detector at HERA in 1994. The average thrust of the final states $X$, which emerge from the dissociation of virtual photons in the range $10 < Q^2 < 100 {\rm GeV}^2$, grows with hadronic mass $M_X$ and implies a dominant 2-jet topology. Thrust is found to decrease with growing $P_t$, the thrust jet momentum transverse to the photon-proton collision axis. Distributions of $P_t^2$ are consistent with being independent of $M_X$. They show a strong alignment of the thrust axis with the photon-proton collision axis, and have a large high$-P_t$ tail. The correlation of thrust with $M_X$ is similar to that in $e^+e^-$annihilation at $\sqrt s_{ee}=M_X$, but with lower values of thrust in the $ep$ data. The data cannot be described by interpreting the dissociated system $X$ as a $q\bar q$ state but inclusion of a substantial fraction of $q\bar q g$ parton configurations leads naturally to the observed properties. The soft colour exchange interaction model does not describe the data.