Search for exotic baryons in double radiative capture on pionic hydrogen

Zolnierczuk, Piotr; Armstrong, D. S.; Christy, E.; Clark, James H.; Gorringe, T. P.; Hasinoff, M.; Kovash, M. A.; Tripathi, S.; Wright, D. H.

doi:10.1016/j.physletb.2004.07.008

Cited by 2 publications

(2 citation statements)

References 28 publications

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“…However, the signals for those exotic states could not be found in several recent experiments [17][18][19][20][21][22][23][24][25][26][27][28][29][30]. In addition, more reports have been given on possible candidates for various crypto-exotic baryons [31][32][33][34][35][36][37]. The existence of pentaquark baryons is thus not conclusive at the present time.…”

Section: Introductionmentioning

confidence: 82%

Pentaquark Θ+(1540) production in γN→KK¯N reactions

Nakayama

Lee

2006

Physics Reports

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The recent developments in the search of exotic pentaquark hadrons are briefly reviewed. We then focus on investigating how the exotic pentaquark Θ(1540) baryon production can be identified in the γN → KKN reactions, focusing on the influence of the background (non-Θ production) mechanisms. By imposing the SU(3) symmetry and using various quark model predictions, we are able to fix the coupling constants for evaluating the kaon backgrounds, the KK production through the intermediate vector meson and tensor meson photoproduction, and the mechanisms involving intermediate Λ (1116), Λ(1405), Λ(1520), Σ(1193), Σ(1385), and ∆(1232) states. The vector meson photoproduction part is calculated from a phenomenological model which describes well the experimental data at low energies. We point out that the neutral tensor meson production can not be due to π 0 -exchange as done by Dzierba et al. [Phys. Rev. D 69, 051901 (2004)] because of C parity. The neutral tensor meson production is estimated by considering the vector meson exchange and found to be too weak to generate any peak at the position near Θ(1540). For Θ(1540) production, we assume that it is an isoscalar and hence can only be produced in γn → K + K − n and γp → K 0 K 0 p reactions, but not in γp → K + K − p and γn → K 0 K 0 n. The total cross section data of γp → K + K − p is thus used to fix the form factors which regularize the background amplitudes so that the signal of Θ(1540) in γn → K + K − n and γp → K 0 K 0 p cross sections can be predicted.We find that the predicted K + K − and K + n invariant mass distributions of the γn → K + K − n reaction can qualitatively reproduce the shapes of the JLab data. However, the predicted Θ(1540) peak can not be identified unambiguously with the data. High statistics experiments are needed to resolve the problem. We also find that an even-parity Θ is more likely to be detected, while it will be difficult to identify an odd-parity Θ, even if it exists, from the background continuum, if its coupling constants are small as in the present quark model predictions.

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Section: Introductionmentioning

confidence: 82%

Pentaquark Θ+(1540) production in γN→KK¯N reactions

Nakayama

Lee

2006

Physics Reports

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“…A branching ratio upper limit ≤ 5.5×10 −4 for double radiative capture on pionic hydrogen was obtained by Vasilevsky et al[14] 2. In addition, in Refs [16,17]. we conducted searches for exotic baryon and dibaryon resonances by detection of photon-pairs following pion capture in hydrogen and deuterium.…”

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confidence: 93%

Double radiative pion capture on hydrogen and deuterium and the nucleon's pion cloud

et al. 2007

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We report measurements of double radiative capture in pionic hydrogen and pionic deuterium. The measurements were performed with the RMC spectrometer at the TRIUMF cyclotron by recording photon pairs from pion stops in liquid hydrogen and deuterium targets. We obtained absolute branching ratios of (3.02 ± 0.27(stat.) ± 0.31(syst.)) × 10 −5 for hydrogen and (1.42 ± 0.09 0.12 (stat.) ± 0.11(syst.)) × 10 −5 for deuterium, and relative branching ratios of double radiative capture to single radiative capture of (7.68 ± 0.69(stat.) ± 0.79(syst.)) × 10 −5 for hydrogen and (5.44 ± 0.34 0.46 (stat.) ± 0.42(syst.))×10 −5 for deuterium. For hydrogen, the measured branching ratio and photon energy-angle distributions are in fair agreement with a reaction mechanism involving the annihilation of the incident π − on the π + cloud of the target proton. For deuterium, the measured branching ratio and energyangle distributions are qualitatively consistent with simple arguments for the expected role of the spectator neutron. A comparison between our hydrogen and deuterium data and earlier beryllium and carbon data reveals substantial changes in the relative branching ratios and the energy-angle distributions and is in agreement with the expected evolution of the reaction dynamics from an annihilation process in S-state capture to a bremsstrahlung process in P-state capture. Lastly, we comment on the relevance of the double radiative process to the investigation of the charged pion polarizability and the in-medium pion field.

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Search for exotic baryons in double radiative capture on pionic hydrogen

Cited by 2 publications

References 28 publications

Pentaquark Θ+(1540) production in γN→KK¯N reactions

Pentaquark Θ+(1540) production in γN→KK¯N reactions

Double radiative pion capture on hydrogen and deuterium and the nucleon's pion cloud

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