Search for the Pentaquark Θ+ via the π−p → K−X Reaction at J-PARC

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Springer, Feb 17, 2016 - Science - 123 pages

This theses reports on an experimental search for an exotic hadron, Θ+(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 Θ+ was strongly constrained.

The Θ+ pentaquark was searched for via the π- 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 Θ+. 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 π- p → K- X reaction, and the upper limit of the production cross section was found to be less than 0.28 μb/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 Θ+ was evaluated. The upper limits on the decay width were estimated to be 0.36 and 1.9 MeV for the Θ+ spin-parity of 1/2+ and 1/2-, respectively. These are quite small for a width of ordinary hadron resonances, and the existence of Θ+ was strongly constrained and is doubtful.

 

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Contents

1 Introduction to Pentaquark Search
1
2 Experimental Apparatus
27
3 Data Analysis
49
4 Results
85
5 Discussion
95
6 Conclusion
104
Appendix AAC Efficiency
107
Appendix BMiscellaneous Vertex Analyses
109
Appendix CStability of Magnetic Field
113
Appendix DSummary of Σ Production Cross Section
115
Appendix EAdditional Study of Background Processes
119
Curriculum Vitae
122
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