Abstract

High-statistics measurements of differential cross sections and recoil polarizations for the reaction $\gamma p \rightarrow K^+ \Sigma^0$ have been obtained using the CLAS detector at Jefferson Lab. We cover center-of-mass energies ($\sqrt{s}$) from 1.69 to 2.84 GeV, with an extensive coverage in the $K^+$ production angle. Independent measurements were made using the $K^{+}p\pi^{-}$($\gamma$) and $K^{+}p$($\pi^-, \gamma$) final-state topologies, and were found to exhibit good agreement. Our differential cross sections show good agreement with earlier CLAS, SAPHIR and LEPS results, while offering better statistical precision and a 300-MeV increase in $\sqrt{s}$ coverage. Above $\sqrt{s} \approx 2.5$ GeV, $t$- and $u$-channel Regge scaling behavior can be seen at forward- and backward-angles, respectively. Our recoil polarization ($P_\Sigma$) measurements represent a substantial increase in kinematic coverage and enhanced precision over previous world data. At forward angles we find that $P_\Sigma$ is of the same magnitude but opposite sign as $P_\Lambda$, in agreement with the static SU(6) quark model prediction of $P_\Sigma \approx -P_\Lambda$. This expectation is violated in some mid- and backward-angle kinematic regimes, where $P_\Sigma$ and $P_\Lambda$ are of similar magnitudes but also have the same signs. In conjunction with several other meson photoproduction results recently published by CLAS, the present data will help constrain the partial wave analyses being performed to search for missing baryon resonances.

Highlights

  • Searches for missing baryon resonances in the strange sector have seen intense activity in recent years [1,2,3,4,5,6,7], following theoretical predictions that several of these missing states have strong couplings to strange baryons [8]

  • At forward angles, we find that P is of the same order of magnitude but opposite sign as P, in agreement with the static SU(6) quark model prediction of P ≈ −P

  • In conjunction with several other meson photoproduction results recently published by CEBAF Large Angle Spectrometer (CLAS), the present data will help constrain the partial-wave analyses being performed to search for missing baryon resonances

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Summary

Introduction

Searches for missing baryon resonances in the strange sector have seen intense activity in recent years [1,2,3,4,5,6,7], following theoretical predictions that several of these missing states have strong couplings to strange baryons [8]. It is closely related to the γp → K+ reaction but differs in an important intermediate aspect. Parity relations reduce the number of independent complex amplitudes to four [11], or the number of independent real observables to eight, one of them being the differential cross section (dσ/d cos θcK.m+.) and the rest being a carefully chosen set of seven polarization observables [12]. Because of the selfanalyzing nature of the hyperon ( and 0) decays, all seven of these polarization observables can be measured using different

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