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A study of the reaction p+p-->p+p+[pi][superscript 0] from 320 MeV to 500 MeV

University of British Columbia

The reaction p+p → p+p+π⁰ has been studied from threshold up to 500 MeV, by detecting the decay 7-rays of the π⁰ in coincidence in two large NaI crystals (TINA and MIN A). It was possible to measure the energy spectra, the differential cross sections and the asymmetry of the π⁰. The total cross sections and the angular distribution parameter b (defined by [Formula Omitted] determined in this measurement are consistent with previous measurements, but are of a much higher precision. The value obtained for b is very small indicating that most of the π⁰ mesons are isotropically distributed in the centre of mass. Assuming the energy spectra predicted by Gell-Mann, we have deduced the intensities of the Ss, Ps and Pp transitions by a global fit to all the energy spectra and the resulting cross sections. For Ss we obtained [Formula Omitted] which is smaller and more accurate than the previous measurements. A model independent [Formula Omitted] would have an uncertainty of about 6 µb. We have compared our results with those of the reaction n+p → N + N + π± and found them to be fairly similar. Any difference would demand inelasticities in the 1=0 channels, but the total cross sections indicate that σ₀₁ is small. The centre of mass pion energy spectra for pp → ppπ⁰ and np → nnπ⁺ are also similar. However a large cosΦ term is observed in the π± differential cross sections from the np reaction which is an indication of a significant value for σ₀₁. The analysing powers are fairly large and negative. This is the first measurement of this observable, although evidence from the reaction ¹³C(p, π⁻) had suggested that the asymmetry in the free pn → ppπ⁻ reaction might be positive.

Text

2010-10-21

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http://hdl.handle.net/2429/29429

Physics

University of British Columbia

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