Analysis of pp → ππ Data at Low Energy and its Implications

Abstract

This thesis is a study of data on pp → ππ in the range 0.36 ≤ P(_lab) ≤ 1.55 GeV/c taken by the PS 172 experiment at CERN's LEAR facility. The aim is to elucidate the nature of mesonic states coupling both to baryon-antibaryon and meson-meson channels. The PS 172 data are compared with, and found to be consistent with, earlier data on the same channel, and, in a model independent way, the consistency of the PS 172 results with BNL data on pp pp → π(^0)π(^0) is also established. The first amplitude analysis of pp → π(^0)π(^0) to incorporate the PS 172 data is performed and it is found that from the hundreds of possible amplitudes, only two are compatible with the BNL pp → π(^0)π(^0) data and with threshold conditions. The latter may be applied in a far more rigorous way than has been previously possible since the PS 172 momentum range extends so close to threshold. Both of the solutions found exhibit resonances with spins 0-5 and the masses, widths and couplings of these states are deduced. The lowest spin resonances are found to have such large couplings to NN that they are unlikely to be simple qq states.