Search for Pentaquark Theta+ in Hadronic Reaction at J-PARC

TL;DR

This experiment at J-PARC searched for the pentaquark Theta+ in hadronic reactions but found no evidence, setting upper limits on its production cross section and decay width, thus constraining theoretical models.

Contribution

First experiment at J-PARC to search for Theta+ in pi- p reactions with high missing-mass resolution, providing new upper limits on its production and decay properties.

Findings

No significant Theta+ signal observed.

Upper limit on production cross section: 0.28 μb/sr.

Decay width upper limits: 0.36 MeV (J^P=1/2+) and 1.9 MeV (J^P=1/2-).

Abstract

A variety of nuclear and hadron physics experiments are being performed using meson beams at the J-PARC Hadron Facility. As the first experiment at the facility, the pentaquark Theta+ was searched for in the pi- p -> K- X reaction with a missing-mass resolution of 2 MeV (FWHM). The number of accumulated beam pions are 7.8x10^10 and 8.1x10^10 for different beam momenta of 1.92 and 2.01 GeV/c, respectively. No significant structure was observed in the missing mass spectra. Upper limits of the production cross section are obtained to be 0.28ub/sr in the laboratory frame at 90% confidence level for each beam momenta. With a help of theoretical models, an upper limit of the total decay width of Theta+ was estimated to be 0.36 and 1.9 MeV for J^P = 1/2+ and 1/2- states, respectively.