Search for the Pentaquark Θ+ Via the π-P → K-X Reaction at J-Parc

This theses reports on an experimental search for an exotic hadron, +(1540) pentaquark, which is a genuine exotic hadron with a five-quark system of uuddsbar. The results of this book support that the existence of + was strongly constrained.

The + pentaquark was searched for via the - p K- X reaction using a beam momentum of 2.01 GeV/c at the J-PARC hadron experimental facility, taking advantage of high-statistics and high-resolution compared with previous experiments, some of which claimed the evidence of +. In order to realize a good missing-mass resolution of 2 MeV, the beam spectrometer and superconducting kaon spectrometer were constructed.

No clear peak was observed in the missing mass spectrum of the - p K- X reaction, and the upper limit of the production cross section was found to be less than 0.28 b/sr at the 90% confidence level in a mass region of 15001560 MeV/c2. This upper limit is an order of magnitude smaller than that of the previous KEK experiment. Compared with a theoretical calculation using the effective Lagrangian approach, the decay width of + was evaluated. The upper limits on the decay width were estimated to be 0.36 and 1.9 MeV for the + spin-parity of 1/2+ and 1/2-, respectively. These are quite small for a width of ordinary hadron resonances, and the existence of + was strongly constrained and is doubtful.

Nominated as an outstanding contribution by Kyoto University's Physics Department in 2015 Introduces the current status of the T+ pentaquark search Describes details of the experimental apparatus and analysis method of the J-PARC K1.8 beam line and superconducting kaon spectrometer Includes supplementary material: sn.pub/extras

Autorentext

Klappentext

This theses reports on an experimental search for an exotic hadron, +(1540) pentaquark, which is a genuine exotic hadron with a five-quark system of uuddsbar. The results of this book support that the existence of + was strongly constrained.

The + pentaquark was searched for via the - p K- X reaction using a beam momentum of 2.01 GeV/c at the J-PARC hadron experimental facility, taking advantage of high-statistics and high-resolution compared with previous experiments, some of which claimed the evidence of +. In order to realize a good missing-mass resolution of 2 MeV, the beam spectrometer and superconducting kaon spectrometer were constructed.

No clear peak was observed in the missing mass spectrum of the - p K- X reaction, and the upper limit of the production cross section was found to be less than 0.28 b/sr at the 90% confidence level in a mass region of 1500-1560 MeV/c2. This upper limit is an order of magnitude smaller than that of the previous KEK experiment. Compared with a theoretical calculation using the effective Lagrangian approach, the decay width of + was evaluated. The upper limits on the decay width were estimated to be 0.36 and 1.9 MeV for the + spin-parity of 1/2+ and 1/2-, respectively. These are quite small for a width of ordinary hadron resonances, and the existence of + was strongly constrained and is doubtful.

Inhalt

Introduction to Pentaquark Search.- Experimental Apparatus.- Data Analysis.- Results.- Discussion.- Conclusion.- Appendix.