Total and partial pion absorption cross sections on4Hein the Δ resonance region

Abstract

This paper presents a large solid angle measurement of the positive pion absorption cross section on 4 He and its decomposition into partial channels. The total absorption cross sections at incident pion kinetic energies of T ϩϭ 70, 118, 162, and 239 MeV are 35Ϯ5, 52Ϯ4, 51Ϯ5, and 27Ϯ2 mb, respectively. These values are lower than those reported in some previous experiments. At all pion energies a large fraction of the absorption cross section is due to multinucleon channels. ͓S0556-2813͑98͒03108-2͔

Metastable GeV-scale particles as a solution to the cosmological lithium problem

“…Again, one has to distinguish two types of reactions, inelastic scattering, π ± + 4 He → π + N , and absorption, π ± + 4 He → N where N represents a variety of multi-nucleon/nuclear final states. We use the results of experimental studies [38,39,40] to account for the pion-4 He reactions across the delta-resonances. We also Besides enhancing the number of free neutrons, the reactions on 4 He have an additional important effect: they produce energetic A = 3 elements that are able to participate in the non-thermal reactions leading to 6 Li.…”

“…Right : The top curve shows the total π ± -4 He inelastic scattering cross section as given in [38] and labeled as "Bin75". The data labeled "Mat98" [40] is the absorptive part; older data "Str90" on pion absorption is collected in [39]. We employ the model calculation of [102], scaled by a factor 0.8 to fit "Bin75".…”

“…The cross section breaks down into an absorptive part with no pion in the final state and the remaining inelastic part. We fit the in-flight absorption data "Mat98" [40] by scaling down the calculation of [102] by a factor of 0.8; older data "Str90" on absorption is collected in [39]. The dotted parts of the lines show the regions in which we had to extrapolate without data.…”

“…Again, one has to distinguish two types of reactions, inelastic scattering, π ± + 4 He → π + N , and absorption, π ± + 4 He → N where N represents a variety of multi-nucleon/nuclear final states. We use the results of experimental studies [38,39,40] to account for the pion-4 He reactions across the delta-resonances. We also extrapolate these results to the threshold regions, and calculate effective cross sections to the various (exclusive) final states by averaging over the pion "lifetime" trajectory while taking into account the respective energy-dependent branchings.…”