Production Dependence of theA2(1300)Mass Distribution

Abstract

We demonstrate that much of the variation in mass shape and position of the A~(1300) meson from experiment to experiment is consistent with a model of two coupled or interfering wide-and narrow-width particles which may be close to forming a double-pole system. We find _that the double-pole limit of this model leads to reasonably good fits for the mass spectra of the a p and KK decay channels produced in ?r-p and pp collisions. Also, the model is consistent within experimental resolution with the available rp-decaychannel mass spectra found in the reaction K-n -+ Az-A. Predictions for other reactions involving AX production are made. N a recent Letter1 the prediction was made that the I TP mass distribution expected from decay of A2(1300) mesons produced in K-n+ Ai-A reactions should be a relatively narrow single peak. Since a BNL experiment2 appears to confirm this prediction except for an apparent mass shift, it would seem worthwhile to examine these data and other recently available data3 with respect to the model used in Ref. 1. We find that these data on the Az mass can be explained in consistent fashion and that enough parameters (though not too precisely fixed by data) are now determined so that predictions almost can be made.I t is quite possible that the A2 mass region has a different explanation than that of two closely mixed (coupled) or, equivalently, interfering resonances. However, this seems to be one of the simpler models one can propose if one accepts the totaled results of CERN experiments4 as correct. These data are well fitted by either interfering Breit-Wigner resonances4 or by a dipole Either case can be described, e.g., by Scarr, Phys. Rev. Letters 22, 1327 (1969). Although the singlepeak result is as predicted by the double-pole model used in Ref. 1. these authors find that JP= 1-is preferred over 2+, but 2+ is not'con~lusivel~ ruled out. The cleanest interpretation of the CERN missing-mass and spectrometer measurements of the A2 mass (if one does not uuestion the addition of results from their many different experim^ents) requires the same spin-parity for the two peaks, in which case 2+ appears most likely. a M. Aguilar-Benitz et al., Phys. Letters 29B, 62 (1969). We use only the recent, small-bin data in this analysis. 4 G. Chikovani et al., Phys. Letters 25B, 44 (1967); H. Benz et al., ibid. 28B, 233 (1968). The comment in the text refers to the total tabulation of events. Unfortunately, each individual result is not sufficiently good to back this statement solidly and independently. J. S. Bell, CERN Report No. TH.784 (unpublished). 6 K. E. Lassila and P. V. Ruuskanen, Phys. Rev, Letters 19,762 (1967).Eq. (4) of Ref. 6,7 which assumes a production amplitude Gi and a decay amplitude Fi (i= 1, 2) with a general 2 x 2 propagator matrix for the two particles connecting G to F. Interfering particles of the same JP mixed, for example, because of some symmetrybreaking interaction or common decay modes, can be reliably treated this way. The special dipole limit6 of this equation has the advanta...

Model analyses of elementary particle scattering amplitudes

“…0.06 at 10% probability limits (14). Thus, the model is able to explain the structure of the mass as observed in all these statistically good experiments.…”

“…A second possibility is that the mass matrix itself has isospin dependence that has not yet been exploited. A third, rather remote, possibility is that the A2 system is formed with three strongly coupled mesons, the third meson now coupling only to KK the same way as mg does in the earlier analyses (13,14). The first method seems most likely, however, as an analogous effect occurs in the nit decay channel of the p° and u mesons.…”

“…Originally it was assumed that m^ would couple mainly to (11) with -0.5 <€ <0.2 and £, <0.5 P ^ 2 (at 10% X probability levels), consistent with the smaller values of above (14). The data (10) for the reaction p + p -»• (îi + P) + 71, on the other hand, require -0.2 < £^<0.1, with in the previous range for (14).…”

“…Within 40% X probability levels it is found that 0.14<£^ <0.40 and -0.23 < <£ <-0.07, the best fit (55% probability) occurring near £, = P K 0.25 and = -0.15 (14). In a separate test on all data the assumption that m^ does not couple to Tip is verified:…”

“…The data (10) for the reaction p + p -»• (îi + P) + 71, on the other hand, require -0.2 < £^<0.1, with in the previous range for (14).…”