1. General Seminars

K+ Xe interactions below 560 MeV/c.

by Dr V. A. Matveev (Institute of Theoretical and Experimental Physics, Moscow)

Aula Leale (Laboratori Nazionali di Frascatio)

Aula Leale

Laboratori Nazionali di Frascatio

The DIANA collaboration analyzed the K+ interactions in liquid Xenon at K+ momentum in the range 300 - 560 MeV/c. In the effective mass spectra of Ks and proton we observe a significant narrow peak at mass 1538 ± 2 MeV, which we identify as Theta+ pentaquark. For the next step we have examined pK+ effective mass. The scan conditions and cuts were as much as possible close to those in pKs analysis. The mass spectra in two data sets appeared to be very similar except Theta+ region, where a possible pK+ excess is compatible with zero. Therefore the observed peak is not a spurious structure created by systematics. We argue that it is a physical signal from the s-channel pentaquark baryon : K+n -> Theta+,Theta+ -> pK0. By comparing pKs and pK+ mass spectra, we tested the isospin I=0,1,2 hypotheses. We may conclude that Theta+ is most likely an isoscalar. The results of pK+ analysis are PRELIMINARY only. Currently we probe several intra nuclear cascade models and increase the statistics.