Hyperon Beams in Modern Baryon Spectroscopy*

The use of multiple diverse incident particle probes is vital for our understanding of baryon spectroscopy, since each unique probe provides a different aspect of the particle being studied.  Commonly used primary beams include protons and electrons; secondary beams produced from these include photons, pions, and kaons. The use of other probes is limited by our ability to determine both the beam flux and the effective target thickness. The primary beam flux is typically measured by the accelerator, while the geometric length of the target can be easily measured; secondary beam flux is measured by the experimenter. Short-lived beam particles, like the Λ or K_S, provide additional information that cannot be obtained in any other way, but determination of the beam flux and the target thickness is much more complicated; bubble chamber experiments measured these quantities directly. In modern large-acceptance detectors, the beam particle is not detected, but is inferred using the final-state particles. With significantly higher data rates, they can compete with bubble chambers. A recent CLAS publication used this technique to study the process Λp→Λp. The scattered Λ was inferred via its decay to π^-p, and event selection compared the missing mass m_X in Xp→Λp to the known Λ mass m_Λ=1.115 GeV. The process γp→K⁺Λ was used to verify the beam Λ, and detection of the K⁺ in missing mass was required. The number of detected events exceeded all previous measurements for this process. Inclusively produced beams, as in γp→ΛX, can increase greatly both the overall flux and the momentum range of the beam Λ. The CSUDH Hadronic Structure Laboratory is testing this technique using the process pp→pp, where the beam proton comes from γp→pX. In parallel, we are revisiting  Λp→Λp using a different CLAS dataset, as well as K⁰p→K_Sp. This talk will present the motivations for the development of short-lived beams, the present status of this project with the CLAS Collaboration, and place it in context with other, similar projects.