Study of YY production in two, three and four body final states by 3.0, 3.6 and 4.0 GeV/c antiprotons in hydrogen

Abstract

We present the results on hyperon-antihyperon production by 3.0, 3.6 and 4.0 GeV/c antiprotons in hydrogen. We used about 300 000 pictures taken in an antiproton beam from the CERN proton synchrotron with the 81 cm Saclay hydrogen bubble chamber. A systematic study was made of interactions leading to a hyperon and an antihyperon with or without additional pions in the final states. The analysis indicates that the cross-sections for each of these processes are of the order of few tens of microbarns or less and that, whereas for the two-body final states the cross-sections decrease when the\(\bar p\) momentum increases from 3.0 to 4.0 GeV/c, the cross-sections for 3 and 4 body final states remain constant. For most of these events the angular distributions show a strong forward peaking of the antihyperon in the c.m.s. of the interaction. This suggests that a peripheral-type mechanism is predominant in these processes. About half of the events of the type\(\bar pp \to Y\bar Y\pi \) or\(\bar pp \to Y\bar Y\pi \pi \) proceed via the formation of hyperon or antihyperon resonances. The\(\overline {Y\mathop *\limits_1 } (1385)\),\(\overline {Y\mathop *\limits_0 } (1405)\),\(\overline {Y\mathop *\limits_0 } (1520)\) resonances and their charge con ugates are produced with masses, widths and decay branching ratios consistent with the values found in other experiments. The cross-sections for the reactions\(\bar pp \to A\bar Y\) or\(A\overline {Y*} \) are consistently larger by a factor varying from 2 to 6 than those corresponding to the reactions\(\bar pp \to \Sigma ^0 \bar Y\) or\(\Sigma ^0 \overline {Y*} \).