Difference in Energy Dependence forA2−andA

Abstract

We present a comparison of A{" and ^ production. The cross section for the production of A 2° falls much more rapidly with increasing energy than the A{" cross section. The characteristics of the production processes seem to be very similar in other respects. These facts are hard to understand in terms of a Regge picture of the production process.We wish to report on three experiments which give results on the production of the A 2 meson. 1,2 We present results from 7-BeV/c ir'p and ir + d exposures in the 30-in. Argonne National Laboratory-Midwestern Universities Research Association chamber and a 25 BeV/c u""p experiment in the 80-in. Brookhaven National Laboratory chamber.The production characteristics of the A 2 are similar in each of the three experiments. The A 2 " is produced in a large J p = 1 + background coming from diffractive processes. In Figs. 1(a) and 1(c) we see that the A 2~ signal is greatly enhanced relative to the background by requiring that the momentum transfer to the recoil proton be larger than 0.1 (Be V/c) 2 [0.15 in Fig. 1(a)]. The diffractive background is not present for the A 2 in Fig. 1(b) and the A 2 cut does little to improve the signal. We have drawn on the mass plots the fitted Breit-Wigner (BW) curves. The error bars show the level of background obtained from a Zemach 3 analysis of the 2 + signal and the mass range considered in the analysis, respectively. The background assumed in making the BW fit is shown as a cross line. The mass values obtained in the fits were 1.29, 1.31, and 1.305 BeV/c 2 with widths of 0.102, 0.122, and 0.085 BeV/e 2 for the charged and neutral 7-BeV/ c data and the 25-BeV/c data, respectively.All three experiments yield a 7 distribution for (A) 7.0GeV/c 77 p 0 A 2 > 0.15 (B) 7.0GeV/c 7T + d 0 A 2 >0.l > CD o d > Id (0 25.0 GeV/c IT p 0 A 2 >0.l .5 2.0 2.5 3.0 M(3TT) GeV FIG. 1. (a) M(3ir) distribution from the reactions TTp-^p^TTtrand Tr^p-^pir'ir^w 0 at 7 Be V/c, 2.6 events/^b. (b) MOrVV) from the reaction ir+d-»p s pTr + ir~ir 0 at 7 BeV/c, 5.6 events/fib. This plot has lp s I < 0.3 BeV/c and includes three-prong events, (c) M(7r + 7r~ir~) from the reaction 7r~£-*£7r + 7r~7r~* at 25 BeV/c, 3.3 events/Mb. All of the mass plots have iv"*(1238) removed, (d) A^> 2 distribution from the reaction ir~p-^pA 2 "~ at 7 Be V/c with A 2~

THEORETICAL REMARKS ON THE A$sub 2$ MESON.

“…Given a pair f , E claimed to be necessary to fit data with a (34) i.e. a linear fractional transformation.…”