A. Bertin

Measurement of the ortho-para transition rate in the pμp molecule and deduction of the pseudoscalar coupling constant gpμ

Abstract The ortho-para transition rate in the pμp molecule has been found experimentally to be λ OP = (4.1 ± 1.4) × 10 4 s −1 . Our recent result for the muon capture rate in liquid hydrogen can now be interpreted to extract the ortho-molecular capture rate: λ OM = (531 ± 33) s −1 . A deduction of the pseudoscalar coupling constant g p μ is presented: we find g p μ = 8.7 ± 1.9.

A novel measurement of the muon capture rate in liquid hydrogen by the lifetime technique

Abstract The muon nuclear capture rate by protons has been measured by comparing the lifetime τ μ − of negative muons stopped in liquid hydrogen with the lifetime τ μ + of positive muons. We get τ μ − = 2194.903 ± 0.066 ns and τ μ + = 2197.182 ± 0.121 ns. Taking into account also the previous determinations of τ μ + , we present the updated determination of the muon lifetime, and correspondingly we obtain for the capture rate of muons from the pμp molecular ions the value λ c = 460 ± 20 s −1 .

p̄p annihilation cross section at very low energy

Abstract The pp total annihilation cross section has been measured, with the Obelix apparatus at LEAR, at ten values of the antiproton incident momentum between 43 and 175 MeV/c. The values of the cross section show that the well known 1 p behaviour of the annihilation cross section is drastically modified at very low momenta, which demonstrates the important role of the Coulomb force in low energy pp interaction. Moreover, they do not present any explicit resonant behaviour. Finally, when compared to potential model calculations, the data suggest that the percentage of P-wave in pp interaction around 50 MeV/c antiproton incident momentum is less than 5%.

NEGATIVE PARTICLE PRODUCTION AT THE CERN INTERSECTING STORAGE RINGS.

Abstract Preliminary results on the production of negative particles in inclusive reactions at intermediate angles (80–200 mrad) at the CERN ISR are reported. Pion production is still the dominant process; within our experimental errors, scaling holds for negative pions or alternatively a limiting distribution is reached at relatively low energies. However the antiproton production cross-sections are apparently larger than smaller energies.

New measurements of the p̄p annihilation cross section at very low energy

Abstract The p p total annihilation cross section has been measured at four values of the p 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 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 (Proc. 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. Protasov, 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 44 MeV/c [A. Bertin et al., Phys. Lett. B 369 (1996) 77], is not confirmed by the new data.

Meson spectroscopy with antineutrons

Abstract First results on meson spectroscopy using antineutrons as projectiles are reported. Three-body (π + π + π − ) and five-body (π + π + π + π − π − ) final states following the annihilation of 100 to 290 MeV/ c antineutrons on hydrogen were analyzed. The (π + π − ) invariant mass spectrum in the three-body reaction is accounted for by the ϱ 0 anf f 2 (1270) resonances, together with an enhancement around 1540 MeV, in the region of the AX (1565) and the f 2 (1515) resonances, whereas the best fit for the (π + π + π − π − ) invariant mass in five-body events shows the already reported structure ζ(1480) and suggests the presence of a second structure around 1650 MeV.

φ and ω meson production in n¯p annihilation and the OZI rule

Abstract The φπ + /ωπ + ratio from n ¯ p annihilations on a liquid hydrogen target, for n ¯ momenta between 64 and 297 MeV/ c , was measured using the OBELIX spectrometer at LEAR. The ratio R ( ϕ π / ω π ) = σ ( n ¯ p → ϕ π + ) / σ ( n ¯ p → ω π + ) turned out 0.110±0.015 stat ±0.006 syst . Implications of this result on the OZI rule are discussed.

A new measurement of the positive muon lifetime

Abstract We present a new measurement of the positive muon lifetime by a pulsed-beam technique. The results is τ μ + = 2197.078 ±0.073 ns.

Transfer rates of negative muons from deuterium mesoatoms to helium, neon, argon, krypton, xenon and nitrogen atoms

SummaryWe have measured the rates of the processes μd+ZY→→μSY+d, in which the μp--meson is transferred from a μd mesic atom to an atomzY of higher atomic number (zY stands here for helium, nitrogen, neon, argon, krypton and xenon). The rates of the studied processes have been obtained, for each elementzY, by observing the time distribution of the electrons coming from the decay of negative muons stopped in gaseous deuterium (at a pressure of 6 abs atm) to which a known small proportion of the elementzY had been added. The data obtained are discussed in relation to those concerning the μp+ZY→μZY+P process (which were the result of a previous work) and to the existing theory.RiassuntoAbbiamo misurato le velocità dei processi μd+ZY→μZY+d, nei quali il mesone μp- viene trasferito da un atomo mesico μd ad un atomozY di numero atomico maggiore (zY sta qui per elio, azoto, neon, argon, krypton, xenon). Le velocità dei processi studiati sono state ricavate, per ogni elementozY, osservando la distribuzione temporale degli elettroni provenienti dal decadimento dei muoni negativi fermatisi in deuterio gassoso (alla pressione di 6 atm ass) al quale era stata aggiunta una proporzione dell’elementozY piccola e nota. I dati ottenuti sono discussi in rapporto a quelli concernenti il processo μp+ZY→μZY+p, ricavati in un lavoro precedente, ed alla teoria esistente.РезюмеМы измеряли скорости процессов μd+ZY→μZY+d, в которых μ-мезон переходит от мезоатома μp- дейтерия к атомыzY с более высоким атомным номером (zY стоит здесь для гелия, азота, неона, аргона, криптона, и ксенона). Были получены скорости изучаемых процессов для каждого элементаzY, посредством наблюдения распределения времени электронов, происходящих от распада отрицательных мюонов в газообразном дейтерии (при давлении 6 атм.), к которому добавляется известная малая доля элементаzY. Полученные данные рассматриваются относительно результатов, касающихся процесса μ+ZY→μZY+p (которые были получены в предыдущей работе), и существующей теории.

p̄D and p̄ 4He annihilation cross sections at very low energy

Abstract The p D and p 4 He total annihilation cross sections have been measured with the Obelix apparatus at LEAR at, respectively, three and two values of the p incident momentum between 70 MeV/c and 36 MeV/c. The values of the p D annihilation cross section, at such low energies, are in agreement with a surprising result obtained in a recent low statistics measurement of the antiprotonic deuterium K α X-rays [M. Augsburger et al., Phys. Lett. B 461 (1999) 417] (see following article), concerning the unexpected narrow width of the antiprotonic deuterium 1s level.