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تسجيل مستخدم جديدPhotoproduction of Lambda(1405) and Sigma^{0}(1385) on the proton at E_gamma = 1.5-2.4 GeV
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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.
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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.
The aim of the present analysis is to determine the relative production cross sections of the $Lambda$(1405) and $Sigma(1385)^{0}$ resonances in p+p collisions at E$_{kin}$=3.5 GeV measured with HADES. Upper and lower limits have been determined for
the ratio $sigma_{(Sigma(1385)^{0}+p+K^{+})}/sigma_{(Lambda(1405)+p+K^{+})}=0.76_{-0.26}^{+0.54}$. The knowledge of this ratio is an essential input for the analysis of the decay $Lambda(1405)rightarrowSigma^{pm}pi^{mp}$, where an unambiguous separation of the $Lambda$(1405) and $Sigma(1385)^{0}$ signals is not possible.
We report measurements of the photon beam asymmetry $Sigma$ for the reactions $vec{gamma}pto ppi^0$ and $vec{gamma}pto peta $ from the GlueX experiment using a 9 GeV linearly-polarized, tagged photon beam incident on a liquid hydrogen target in Jeffe
rson Labs Hall D. The asymmetries, measured as a function of the proton momentum transfer, possess greater precision than previous $pi^0$ measurements and are the first $eta$ measurements in this energy regime. The results are compared with theoretical predictions based on $t$-channel, quasi-particle exchange and constrain the axial-vector component of the neutral meson production mechanism in these models.
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 $Lambda(1405)$ resona
nce. 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.
We report the measurement of the $gamma p rightarrow K^{+}Lambda$ and $gamma p rightarrow K^{+}Sigma^{0}$ reactions at SPring-8. The differential cross sections and photon-beam asymmetries are measured at forward $K^{+}$ production angles using linea
rly polarized tagged-photon beams in the range of $E_{gamma}=1.5$--3.0 GeV. With increasing photon energy, the cross sections for both $gamma p rightarrow K^{+}Lambda$ and $gamma p rightarrow K^{+}Sigma^{0}$ reactions decrease slowly. Distinct narrow structures in the production cross section have not been found at $E_{gamma}=1.5$--3.0 GeV. The forward peaking in the angular distributions of cross sections, a characteristic feature of $t$-channel exchange, is observed for the production of $Lambda$ in the whole observed energy range. A lack of similar feature for $Sigma^{0}$ production reflects a less dominant role of $t$-channel contribution in this channel. The photon-beam asymmetries remain positive for both reactions, suggesting the dominance of $K^{*}$ exchange in the $t$ channel. These asymmetries increase gradually with the photon energy, and have a maximum value of +0.6 for both reactions. Comparison with theoretical predictions based on the Regge trajectory in the $t$ channel and the contributions of nucleon resonances indicates the major role of $t$-channel contributions as well as non-negligible effects of nucleon resonances in accounting for the reaction mechanism of hyperon photoproduction in this photon energy regime.
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