Search for Θ+ via π−p→K−X reaction near production threshold

Abstract

We have searched for Θ + via π − p → K − X reaction using 1.87 and 1.92 GeV/c π − beam at the K2 beam line of the KEK 12 GeV Proton Synchrotron. In the missing mass spectrum at beam momentum of 1.92 GeV/c, a bump has been found at 1530 MeV/c 2 which is consistent with the mass reported by several experiments. The statistical significance of this bump, however, is only 2.5−2.7σ. Therefore we have derived the upper limit of Θ + production cross section via π − p → K − Θ + reaction which is 3.9µb at 90% confidence level assuming that Θ + is produced isotropically in the center of mass system.

J-PARC E19 Experiment: Pentaquark Θ+ Search in Hadronic Reaction at J-PARC

“…5). These results are one order of magnitude smaller than the value of 2.9 µb/sr obtained in the previous KEK-PS E522 experiment [15].…”

Present status on experimental search for pentaquarks

“…Since the Θ + has the same quark constituents as the combination of nK + and pK 0 , these two modes are expected as the primary decay channel, and thus are usually used in reconstructions in the experiments. After the first report for the Θ + , the signals were observed by many groups [11,[48][49][50][51][52][53][54][55][56][57][58], and some groups confirmed their results with new data [59][60][61][62][63]. All these results are briefly listed in Table I.…”

“…This does not consist with a narrow resonance. The mass values in LEPS early experiment [11], DIANA experiments [48,[60][61][62], SAPHIR experiment [51] and JINR experiments [55,56] are around 1540 MeV/c 2 , while the values in HERMES experiment [50], SVD early experiment [49], ITEP's analysis on the old neutrino experiments [52,53] and E522 experiment [57] are near 1530 MeV/c 2 . Besides, the LEPS recent experiment [59], the SVD updated experiment [63] and the ZEUS experiment [54] provide even lower mass values close to 1520 MeV/c 2 , and the OBELIX experiment gives a much higher value.…”

“…The E522 experiment at the K2 beam line of the KEK 12 GeV proton synchrotron was performed to search for the pentaquark candidate Θ + via the reaction π − p → K − X [57]. In this experiment, a scintillation fiber ((CH) n ) and a bulk of polyethylene ((CH 2 ) n ) were used as the targets.…”

Spin-3/2 Pentaquark in QCD Sum Rules

“…After the first discovery, numerous theoretical and experimental papers on this pentaquark state have been published and the field of hadron spectroscopy has been strongly stimulated by these studies. Nevertheless, the question of the existence of Θ + is still a heavily disputed issue [3,4,5,6,7,8,9]. After reanalyzing the data with higher statistics, the LEPS group has recently again announced the observation of a significant peak [10], confirming their earlier results, which is a promising sign for further studies of Θ + .…”