Lambda Re-Scattering On the Proton

A complete study of the structure of the proton requires knowledge of its interaction with other particles. One such particle is the $\Lambda $, which is similar in structure to the proton, but with different quark content. Studying the interaction of the $\Lambda $ with the proton is difficult, since the $\Lambda $ does not exist naturally, and decays rapidly. The CLAS collaboration at the Thomas Jefferson National Accelerator Facility is able to produce large numbers of $\Lambda $'s via the photo production process $\gamma $p$\to $K$^{\mathrm{+}}\Lambda $. By using a long hydrogen target, the $\Lambda $ produced in this reaction can sometimes interact with a second proton in the target. The simplest process between a $\Lambda $ and a proton is the elastic scattering process $\Lambda $p$\to \Lambda $p. Determining the cross section for the process $\Lambda $p$\to \Lambda $p requires the detection of the outgoing proton, the decay products of the $\Lambda $, and the K$^{\mathrm{+}}$ from the original $\Lambda $ production. Since the main decay mode of the $\Lambda $ is to $\pi ^{\mathrm{-}}$p, the complete final state for this process is K$^{\mathrm{+}}\pi^{\mathrm{-}}$pp, which is an apparent violation of baryon number conservation. The first step in this study is the identification of events that have two protons and a K$^{\mathrm{+}}$. This talk will discuss the physics motivation behind this work, and will present the current status of the analysis of $\Lambda $ photo production in events with two protons.