K+ Xe interactions below 560 MeV/c.

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

Tuesday 29 Jul 2014, 15:00 → 16:00 Europe/Rome

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 K_s 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 pK_s 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 pK_s 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.