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تسجيل مستخدم جديدSearch for the Theta+ pentaquark in the gamma d -> Lambda n K+ reaction measured with CLAS
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For the first time, the reaction gamma d -> Lambda n K+ has been analyzed in order to search for the exotic pentaquark baryon Theta+(1540). The data were taken at Jefferson Lab, using the Hall-B tagged-photon beam of energy between 0.8 and 3.6 GeV and the CEBAF Large Acceptance Spectrometer (CLAS). No statistically significant structures were observed in the nK+ invariant mass distribution. The upper limit on the gamma d -> Lambda Theta+ integrated cross section has been calculated and found to be between 5 and 25 nb, depending on the production model assumed. The upper limit on the differential cross section is also reported.
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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 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 gamma d to K^+K^-pn reaction has been studied to search for the evidence of the Theta^+ by detecting K^+K^- pairs at forward angles. The Fermi-motion corrected nK^+ invariant mass distribution shows a narrow peak at 1.524 +- 0.002 + 0.003 GeV/c^2
. The statistical significance of the peak calculated from a shape analysis is 5.1 sigma, and the differential cross-section for the gamma n to K^- Theta^+ reaction is estimated to be 12 +- 2 nb/sr in the photon energy range from 2.0 GeV to 2.4 GeV in the LEPS angular range by assuming the isotropic production of the Theta^+ in the gamma n center-of-mass system. The obtained results support the existence of the Theta^+.
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 $Theta^+$ 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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