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تسجيل مستخدم جديدSearch for Theta(1540)^+ in exclusive proton-induced reaction p+C(N) to Theta^+ bar{K}^0 + C(N) at the energy of 70 GeV
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A search for narrow Theta(1540)^+, a candidate for pentaquark baryon with positive strangeness, has been performed in an exclusive proton-induced reaction p+C(N) to Theta^+ bar{K}^0 + C(N) on carbon nuclei or quasifree nucleons at E_{beam}=70 GeV (sqrt{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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We have studied the reaction K+ p -> K+ n pi+ using an 11 GeV/c K+ beam and the Large Acceptance Superconducting Solenoid (LASS) multiparticle spectrometer facility at SLAC. We put limits on the production of narrow theta+ baryons in this reaction.
The exclusive reaction $gamma p to bar K^0 K^+ n$ was studied in the photon energy range between 1.6-3.8 GeV searching for evidence of the exotic baryon $Theta^+(1540)to nK^+$. The decay to $nK^+$ requires the assignment of strangeness $S=+1$ to any
observed resonance. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility corresponding to an integrated luminosity of 70 $pb^{-1}$. No evidence for the $Theta^+$ pentaquark was found. Upper limits were set on the production cross section as function of center-of-mass angle and $nK^+$ mass. The 95% CL upper limit on the total cross section for a narrow resonance at 1540 MeV was found to be 0.8 nb.
The Theta+ was searched for via the K+p -> pi+X reaction using the 1.2 GeV/c K+ beam at the K6 beam line of the KEK-PS 12 GeV Proton Synchrotron. In the missing mass spectrum of the K+p -> pi+X reaction, no clear peak structure was observed. Therefor
e a 90 % C.L. upper limit of 3.5 ub/sr was derived for the differential cross section averaged over 2degree to 22degree in the laboratory frame of the K+p -> pi+Theta+ reaction. This upper limit is much smaller than the theoretical calculation for the t-channel process where a K0* is exchanged. From the present result, either the t-channel process is excluded or the coupling constant of g_{K*NTheta} is quite small.
The exclusive reactions $gamma p to bar K^0 K^+ n$ and $gamma p to bar K^0 K^0 p$ have been studied in the photon energy range 1.6--3.8 GeV, searching for evidence of the exotic baryon $Theta^+(1540)$ in the decays $Theta^+to nK^+$ and $Theta^+to p K
^0$. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. The integrated luminosity was about 70 pb$^{-1}$. The reactions have been isolated by detecting the $K^+$ and proton directly, the neutral kaon via its decay to $K_S to pi^+ pi^-$ and the neutron or neutral kaon via the missing mass technique. The mass and width of known hyperons such as $Sigma^+$, $Sigma^-$ and $Lambda(1116)$ were used as a check of the mass determination accuracy and experimental resolution. Approximately 100,000 $Lambda^*(1520)$s and 150,000 $phi$s were observed in the $bar K^0 K^+ n$ and $bar K^0 K^0 p$ final state respectively. No evidence for the $Theta^+$ pentaquark was found in the $nK^+$ or $pK_S$ invariant mass spectra. Upper limits were set on the production cross section of the reaction $gamma p to Theta^+ bar K^0$ as functions of center-of-mass angle, $nK^+$ and $pK_S$ masses. Combining the results of the two reactions, the 95% C.L. upper limit on the total cross section for a resonance peaked at 1540 MeV was found to be 0.7 nb. Within most of the available theoretical models, this corresponds to an upper limit on the $Theta^+$ width, $Gamma_{Theta^{+}}$, ranging between 0.01 and 7 MeV.
The $Theta^+$ pentaquark baryon was searched for via the $pi^-pto K^-X$ reaction in a missing-mass resolution of 1.4 MeV/$c^2$(FWHM) at J-PARC. $pi^-$ meson beams were incident on the liquid hydrogen target with the beam momentum of 1.92 GeV/$c$. No
peak structure corresponding to the $Theta^+$ mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2$^{circ}$ to 15$^{circ}$ in the laboratory frame was obtained to be 0.26 $mu$b/sr in the mass region of 1.51$-$1.55 GeV/$c^2$.The upper limit of the $Theta^+$ decay width using the effective Lagrangian approach was obtained to be 0.72 MeV/$c^2$ and 3.1 MeV/$c^2$ for $J^P_{Theta}=1/2^+$ and $J^P_{Theta}=1/2^-$, respectively.
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