Experimental search for radiative decays of the pentaquark baryon \Theta^+(1540)

TL;DR

This study searched for radiative decay modes of the 540 pentaquark baryon using bubble chamber data but found no signals, setting upper limits on decay widths and measuring related reaction cross sections.

Contribution

It provides the first upper limits on radiative decay widths of the 540 baryon and measures specific K^+ induced reaction cross sections at 640 MeV.

Findings

No evidence for radiative decays of 540 was observed.

Upper limits on decay widths were established: <8 keV and <11 keV.

Measured cross sections for K^+N reactions involving  pions.

Abstract

The data on the reactions K^+Xe --> K^0 \gamma X and K^+Xe --> K^+ \gamma X, obtained with the bubble chamber DIANA, have been analyzed for possible radiative decays of the \Theta^+(1540) baryon: \Theta^+ --> K^0 p \gamma and \Theta^+ --> K^+ n \gamma. No signals have been observed, and we derive the upper limits \Gamma(\Theta^+ --> K^0 p \gamma) / \Gamma(\Theta^+ --> K^0 p) < 0.032 and \Gamma(\Theta^+ --> K^+ n \gamma) / \Gamma(\Theta^+ --> K^+ n) < 0.041 which, using our previous measurement of \Gamma(\Theta^+ --> KN) = (0.39+-0.10) MeV, translate to \Gamma(\Theta^+ --> K^0 p \gamma) < 8 keV and \Gamma(\Theta^+ --> K^+ n \gamma) < 11 keV at 90% confidence level. We have also measured the cross sections of K^+ -induced reactions involving emission of a neutral pion: \sigma(K^+n --> K^0 p \pi^0) = (68+-18) \mub and \sigma(K^+N --> K^+ N \pi^0) = (30+-8) \mub for incident K^+ momentum of 640 MeV.