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تسجيل مستخدم جديدThe $J=3/2$ $Theta^*$ partner to the $Theta(1540)$ baryon
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If the exotic baryon $Theta(1540)$ is $ududbar{s}$ with $J^P = {1/2}^+$, we predict that there is a 10bar with $J^P = {3/2}^+$ containing a $Theta^*(1540-1680)$. The width $Gamma(Theta^* to KN)$ is at least a factor of three larger than $Gamma(Theta)$. The possibilities of $Theta^* to KNpi$ or $Theta gamma$ via $M1$ and $E2$ multipoles are discussed.
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The data on the reactions K^+Xe --> K^0 gamma X and K^+Xe --> K^+ gamma X, obtained with the bubble chamber DIANA, have been analyzed for possible radiative decays of the Theta^+(1540) baryon: Theta^+ --> K^0 p gamma and Theta^+ --> K^+ n gamma. No s
ignals have been observed, and we derive the upper limits Gamma(Theta^+ --> K^0 p gamma) / Gamma(Theta^+ --> K^0 p) < 0.032 and Gamma(Theta^+ --> K^+ n gamma) / Gamma(Theta^+ --> K^+ n) < 0.041 which, using our previous measurement of Gamma(Theta^+ --> KN) = (0.39+-0.10) MeV, translate to Gamma(Theta^+ --> K^0 p gamma) < 8 keV and Gamma(Theta^+ --> K^+ n gamma) < 11 keV at 90% confidence level. We have also measured the cross sections of K^+ -induced reactions involving emission of a neutral pion: sigma(K^+n --> K^0 p pi^0) = (68+-18) mub and sigma(K^+N --> K^+ N pi^0) = (30+-8) mub for incident K^+ momentum of 640 MeV.
The QCD sum rule technique is employed to investigate pentaquark states with strangeness S = +1 and IJ^P = 0,1/2^pm, 1,1/2^pm, 0,3/2^pm, 1,3/2^pm. Throughout the calculation, emphasis is laid on the establishment of a valid Borel window, which corres
ponds to a region of the Borel mass, where the operator product expansion converges and the presumed ground state pole dominates the sum rules. Such a Borel window is achieved by constructing the sum rules from the difference of two independent correlators and by calculating the operator product expansion up to dimension 14. Furthermore, we discuss the possibility of the contamination of the sum rules by possible KN scattering states. As a result, we conclude that the 0,3/2^+ state seems to be the most probable candidate for the experimentally observed Theta^+(1540), while we also obtain states with 0,1/2^-, 1,1/2^-, 1,3/2^+ at somewhat higher mass regions.
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rt{s} = 11.5 GeV) studying nK^+, pK_S and pK_L decay channels of Theta(1540)^+ in four different final states of the Theta^+ bar{K}^0 system. In order to assess the quality of the identification of the final states with neutron or K_L we reconstructed Lambda(1520)to nK_S and phito K_LK_S decays in the calibration reactions p+C(N)to Lambda(1520)K^+ + C(N) and p+C(N)to pphi + C(N). We found no evidence for narrow pentaquark peak in any of the studied final states and decay channels. Assuming that the production characteristics of the Theta^+ bar{K^0} system are not drastically different from those of the Lambda(1520)K^+ and pphi systems, we established upper limits on the cross section ratios sigma(Theta^+bar{K}^0)/sigma(Lambda(1520)K^+) < 0.02 and sigma(Theta^+bar{K}^0)/sigma(pphi) < 0.15 at 90% CL and a preliminary upper limit for the forward hemisphere cross section sigma(Theta^+bar{K}^0) < 30 nb/nucleon.
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