New measurements of the (p)over-barp annihilation cross section at very low energy

Zenoni, A.; Bianconi, A.; Bocci, F.; Bonomi, G.; Corradini, M.; Donzella, A.; Rizzini, E. L.; Venturelli, L.; Bertin, A.; Bruschi, M.; Capponi, M.; Castro, S. D.; Dona, R.; Galli, D.; Giacobbe, B.; Marconi, U.; Massa, I.; Piccinini, M.; Cesari, N. S.; Spighi, R.; Vagnoni, V.; Vecchi, S.; Villa, M.; Vitale, A.; Zoccoli, A.; Cicalo, C.; Masoni, A.; Mauro, S.; Puddu, G.; Serci, S.; Usai, G.; Gorchakov, O. E.; Prakhov, S. N.; Rozhdestvensky, A. M.; Tretyak, V. I.; Poli, M.; Gianotti, P.; Guaraldo, C.; Lanaro, A.; Lucherini, V.; Petrascu, C.; Ableev, V. G.; Gastaldi, U.; Vannucci, L.; Bendiscioli, G.; Fontana, A.; Montagna, P.; Rotondi, A.; Salvini, P.; Mirfakhrai, N.; Balestra, Ferruccio; Botta, Elena; Bressani, Tullio; Bussa, Maria Pia; Busso, Luigi; Calvo, D.; Cerello, P.; Costa, Sergio; Denisov, O. Y.; E'Isep, F.; Feliciello, A.; Ferrero, Livio; Filippi, A.; Garfagnini, Raffaello; Grasso, Antonino; Maggiora, A.; Marcello, Simonetta; Panzarasa, A.; Tosello, F.; Agnello, M.; Iazzi, F.; Minetti, B.; Tessaro, S.

doi:10.1016/S0370-2693(99)00827-8

The (p) over bar p total annihilation cross section has been measured at four values of the (p) over bar incident momentum, between 70 MeV/c and 38 MeV/c, with the Obelix apparatus at LEAR. The new measurements are in agreement with the trend of previous measurements of the (p) over bar p, total annihilation cross section at low energy, performed by the Obelix experiment [A. Bertin et al., Phys. Lett. B 369 (1996) 77; A. Benedettini et al., Nucl. Phys. B (PI oc. Suppl.) 56A (1997) 58], as well as with a fit of the latter data based on a low energy expansion of the scattering amplitude [J. Carbonell, K.V. Plotasov, A. Zenoni, Phys. Lett. B 397 (1997) 345]. The departure of the annihilation cross section from a smooth behaviour, suggested by a previous measurement of the cross section around 34 MeV/c [A. Bertin ct al., Phys. Lett. B 369 (1996) 77], is not confirmed by the new data.