Identification of thed+p→He3+ηReaction Very Near Threshold: Cross Section and Deuteron Tensor Analyzing Power

Abstract

From the interactions of a deuteron beam in a liquid-hydrogen target at energies near the d+p-+ 3 He + 77 threshold, r? events were selected on the basis of the momentum-analyzed 3 He with a background of less than 2%. This opens the way to a 3 He-tagged r\ beam at Saturne, with a possible flux of 10 4 -10 5 77' s per pulse. The present data allow an evaluation of the cross section down to less than 0.5 MeV above threshold. The deuteron tensor analyzing power f 20 has also been measured: The small negative value found at threshold (-0.15 ±0.05) seems incompatible with models based on one-pion exchange.

Search for quasi boundηmesons

“…Data are from Refs. [106], [107], [108], [109], [110], [111], [112]. Those close to threshold are shown in Fig.…”

Production of η and η′ mesons on nucleons and nuclei

“…39 reaches a plateau so close to threshold, it means that the multipion background under the η peak at low Q is very limited [181]. It was already suggested at the time of the first near-threshold measurements [241] that this reaction could be a useful source of tagged η-mesons to study their decay properties.…”

“…Although this had been investigated at a few energies in earlier experiments [241,243], more detailed measurements were carried out by two groups at COSY [181,182] using a deuteron beam, where the spectrometer acceptance is enhanced. The two data sets are broadly consistent and only the ANKE results for the total cross section are shown in Fig.…”

“…The data are taken from Refs. [241] (black filled circles), [243] (open magenta triangles), [244] (open green circle), [245] (red crosses), and [247] (blue stars). Systematic errors are not shown.…”

“…There have been numerous measurements of the pd → 3 He η reaction at low energies over the last 30 years, where the 3 He nucleus was detected and the η meson identified through the missing mass in the reaction [181,182,239,240,241,242,243,244,245,246,247,248]. The statistical precision is generally reasonable but the systematic uncertainties, mainly associated with the overall normalization, range from about 7% in the Saclay measurement [243] up to twice that in most of the other data, except for the large errors at COSY-11 [246].…”