Polarization Observables in γp → K⁺ + Λ and K⁺ + Σ⁰ Using Circularly Polarized Photons on a Polarized Frozen Spin Target

Abstract

The search for undiscovered excited states of the nucleon continues to be a focus of experiments at the Thomas Jefferson National Accelerator Facility (JLab). A large effort using the CEBAF Large Acceptance Spectrometer (CLAS) detector has provided the database, which will allow nearly modelindependent partial wave analyses (PWA) to be carried out in the search for such states. Polarization observables play a crucial role in the effort, as they are essential in disentangling the contributing resonant and non-resonant amplitudes. Recent coupled-channel analyses have found strong sensitivity of the K + +Λ channel to several higher mass nucleon resonances. In 2008 and 2010, doublepolarization data were taken at JLab using circularly and linearly polarized tagged photons incident on a longitudinally and transversely polarized frozen spin butanol target (FROST), operated at the temperature of 30 mK. The reaction products were detected in CLAS. This work is based on the analysis of FROST data and the extraction of the T and F asymmetries of the K + Λ and K + Σ 0 final states and their comparison to predictions of recent multipole analyses. There are very few published measurements of the T asymmetry and none for the F asymmetry for the K + Λ final state. The K + Σ 0 final state has no published measurements for these asymmetries. Comparison of CLAS results with the phenomenological models MAID, Bonn Gatchina, and RPR-Ghent will be shown. This work is the first of its kind and will significantly broaden the world database for these reactions.

Measurement of polarization observables in vector meson photoproduction using a transversely-polarized frozen-spin target and polarized photons at CLAS, Jefferson Lab

“…The magnitude of φ ′ was also consistent with the CUA result [62]. CUA extracted the angle by studying the raw target asymmetry for the reaction γp → π + X.…”

“…Some quick fixes were carried out in order to resume data taking at the earliest possible. The quality of the data following the quench was studied in [62]. It was observed that the data taken after the quench had more background rendering the analysis more challenging.…”

“…Some TOF paddles of the CLAS spectrometer were dead or malfunctioning during the experiment. Reference [62] contains an extensive study on bad TOF paddles in FROST-g9b using single-track events. These paddles were identified by studying the reconstructed mass versus TOF counter number for all six sectors.…”

Polarization Observables T and F in the yp → pi p Reaction

“…The s-channel diagram of the single-pion photoproduction process with baryon excited states as the intermediate product. This figure is from[17].…”