Antiproton reactions at 6 and 9 geV/c

Abstract

Interactions of antiprotons on protons at 6 and 9 GeV/c are investigated from a 520K picture exposure at the SLAC Hybrid Facility, using a baryon-exchange trigger. Double-differential cross-sections are presented for the inclusive processes pp →π(^±)x, and fits are made to the statistical thermodynamic model of Hagedorn and Hoang, where the shortcomings of the model are pointed out. Cross-section data are also given for exclusive annihilation channels. In the channel p →π(^+)π(^+)π(^-)π(^-) copious production of p and f mesons is observed. A Van Hove analysis indicates that; (i) there is a pronounced "leading particle" effect; (ii) resonances are favourably produced in the central region; (iii) there is associated production of resonances; and (iv) ∆ exchange makes only a small contribution. Two simple amplitude models incorporating these features are proposed and compared: one where the dominant process is a leading pion recoiling from a loose "cluster" of pions; in the other, where both vertices produce peripheral pions, with a centrally produced resonance. The latter model is found to describe the data much better. Figures for spin-density matrices and cross-sections are given and compared with previous data. Preliminary results of a search for narrow exotic mesons are given. For this, data taken with a deuterium target (amounting to 566K pictures) is also used. Upper cross-section limits are given for inclusive processes. A number of narrow effects are reported in exclusive channels, the most significant being in the channel pp →p(_f)nπ(^+)π (^-)π(^-) where a 6 standard deviation enhancement in the p(_f)n mass is seen at 2.02 GeV/c(^2), the mass of a previously found state. The cross-section is greater than 1 µb and the width is consistent with resolution (20 MeV/c(^2). Initial indications are that this state is also produced centrally. "The Shepherds, I say, whose names were Knowledge, Experience, Watchful, and Sincere, took them by the hand, and had them to their tents, and made them partake of that which was ready at present. They said, moreover, we would that you should stay here awhile, to be acquainted with us, and yet more to solace yourselves with the good of these Delectable Mountains....Then I saw in my dream, that in the morning the Shepherds called up Christian and Hopeful to walk with them upon the mountains. So they went forth with them, and walked a while, having a pleasant prospect on every side. Then said the Shepherds one to another, Shall we show these pilgrims some wonders? So, when they had concluded to do it, they had them first to the top of a hill called Error, which was very steep on the farthest side, and bid them look down to the bottom. So Christian and Hopeful looked down, and saw at the bottom several men dashed all to pieces by a fall that they had from the top. Then said Christian, what meaneth this?... Then I saw that they had them to the top of another mountain, and the name of that is Caution, and bid them look afar off; which when they did, they perceived, as they thought, several men walking up and down among the tombs that were there; and they perceived that the men were blind, because they stumbled sometimes upon the tombs, and because they could not get out from among them. Then said Christian, What means this?". From “The Pilgrim’s Process” by John Bunyan