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Register a new userCross Sections and Beam Asymmetries for K+ Sigma*- photoproduction from the deuteron at 1.5-2.4 GeV
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The $Sigma(1385)$ resonance, or $Sigma^*$, is well-known as part of the standard baryon decuplet with spin $J=3/2$. Measurements of the reaction $gamma p to K^+ Sigma^{*0}$ are difficult to extract due to overlap with the nearby $Lambda(1405)$ resonance. However, the reaction $gamma n to K^+ Sigma^{*-}$ has no overlap with the $Lambda(1405)$ due to its charge. Here we report the first measurement of cross sections and beam asymmetries for photoproduction of the sigs from a deuteron target. % where the $K^+$ and $pi^-$ are detected in the LEPS spectrometer. The cross sections at forward angles range from 0.4 to 1.2 $mu$b, with a broad maximum near $E_gamma simeq 1.8$ GeV. The beam asymmetries are negative, in contrast to postive values for the $gamma n to K^+Sigma^-$ reaction.
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Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)sigma0 reactions are measured for the first time for Egamma=1.5-2.4 GeV and 0.6<cos(theta_cm(K+))<1.0 by using linearly polarized photons at the Laser-Electron-Photon facility at SPring-8 (LEPS). The observed asymmetries are positive and gradually increase with rising photon energy. The data are not consistent with theoretical predictions based on tree-level effective Lagrangian approaches. Including the new results in the development of the models is, therefore, crucial for understanding the reaction mechanism and to test the presence of baryon resonances which are predicted in quark models but are sofar undiscovered.
Differential cross sections and photon beam asymmetries have been measured for the gamma n -> K+ Sigma- and gamma p -> K+ Sigma0 reactions separately using liquid deuterium and hydrogen targets with incident linearly polarized photon beams of Egamma=1.5-2.4 GeV at 0.6<cosTheta<1. The cross section ratio of sigma(K+Sigma-)/sigma(K+Sigma0), expected to be 2 on the basis of the isospin 1/2 exchange, is found to be close to 1. For the K+Sigma- reaction, large positive asymmetries are observed indicating the dominance of the K*-exchange. A large difference between the asymmetries for the K+Sigma- and K+Sigma0 reactions can not be explained by simple theoretical considerations.
Differential cross sections for $gamma p to K^+Lambda(1405)$ and $gamma p to K^+Sigma^0(1385)$ reactions have been measured in the photon energy range from 1.5 to 2.4 GeV and the angular range of $0.8<cos(Theta)<1.0$ for the $K^+$ scattering angle in the center-of-mass system. This data is the first measurement of the $Lambda(1405)$ photoproduction cross section. The lineshapes of LamS measured in $Sigma^+pi^-$ and $Sigma^-pi^+$ decay modes were different with each other, indicating a strong interference of the isospin 0 and 1 terms of the $Sigmapi$ scattering amplitudes. The ratios of LamS production to SigS production were measured in two photon energy ranges: near the production threshold ($1.5<E_gamma<2.0$ GeV) and far from it ($2.0 <E_gamma<2.4$ GeV). The observed ratio decreased in the higher photon energy region, which may suggest different production mechanisms and internal structures for these hyperon resonances.
Differential cross sections for the reaction $gamma p to K^{*0} Sigma^+$ are presented at nine bins in photon energy in the range from 1.7 to 3.0 GeV. The kstar was detected by its decay products, $K^+pi^-$, in the CLAS detector at Jefferson Lab. These data are the first kstar photoproduction cross sections ever published over a broad range of angles. Comparison with a theoretical model based on the vector and tensor $K^*$-quark couplings shows good agreement with the data in general, after adjusting the models two parameters in a fit to our data. Disagreement between the data at forward angles and the global angle-energy fit to the model suggests that the role of scalar $kappa$ meson exchange in $t$-channel diagrams should be investigated.
Differential cross sections and photon beam asymmetries for $pi^0$ photoproduction have been measured at $E_gamma$ = 1.5--2.4 GeV and at the $pi^0$ scattering angles, --1 $<$ cos$Theta_{c.m.} <$ --0.6. The energy-dependent slope of differential cross sections for $u$-channel $pi^0$ production has been determined. An enhancement at backward angles is found above $E_gamma$ = 2.0 GeV. This is inferred to be due to the $u$-channel contribution and/or resonances. Photon beam asymmetries have been obtained for the first time at backward angles. A strong angular dependence has been found at $E_gamma >$ 2.0 GeV, which may be due to the unknown high-mass resonances.
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