J.W.G. Wignall

Antiproton-deuteron annihilation into neutral strange particles at incident momenta below 1 GeV/c

Abstract Experimental data are presented on total and differential cross sections for the inclusive production of Λ and Ks0 in low-energy p d annihilations. The data, taken with p momenta in the range 0.4–0.9 GeV/c, are compared with the results of other experiments, including those with p momenta above the threshold for Λ Λ production on a single nucleon. The combined results from all these experiments suggest the dominance of a double-scattering mechanism, involving K exchange, both below and above threshold, although the details of the differential scattering cross sections are not well predicted by this model.

Antiproton-neutron annihilation in flight: A test of the Orfanidis-Rittenberg statistical model

Abstract We produce inclusive and exclusive branching ratios for pionic annihilations of p n in the range 450–920 MeV/ c . These are compared with a statistical, linear decay model for N N annihilations proposed by Orfanidis and Rittenberg, and we find good agreement using the same parameters as those adopted in previous fits of the model to p p data.

Resonance production in the reaction pd→psπ+π-π-π0 at 0.4 to 0.9 GeV/c antiproton momenta

Abstract Resonance production has been studied in the annihilation process p n aarπ + π - π - π 0 induced by antiprotons in the 0.4 to 0.9 GeV/ c momentum range. We observe strong production of ϱ mesons, together with some f 0 (predominantly in the ϱf 0 channel), ω 0 and A 2 mesons and there is a strong ϱϱ signal. We also observe a broad (~300 MeV/ c 2 ) enhancement at ~1100 MeV/c 2 in the π + π - π - invariant-mass distribution, whereas no such enhancement is seen in the π + π - π 0 channel; we have considered various explanations for this enhancement, including an “A 1 ” effect and interference between amplitudes for conventional resonance production.

Interpretation of enhancements in the pn spectrum from pD annihilations

Abstract Data are presented from a low energy p D experiment that show an enhancement near 1930 MeV in the p n mass spectrum. This, and other enhancements observed at nearby masses, may be interpreted in terms of a double-scattering effect.

Antiproton-nucleon scattering in deuterium below 1.0 GeV/c

The pp and pn elastic differential cross sections have been extracted from the reaction pd→ppn in which the deuteron breaks up. The incident antiproton momenta were 0.480, 0.735 and 0.940 GeV/c, and the range of the momentum transfers was 0.04 < ∣t∣ < 0.7 (GeV/c)2. Both pp and pn differential cross sections are diffraction-like, with structure similar to the higher-momentum data.

The reaction p̄d → 2π+3π−p for antiproton momenta in the range 0.35–0.92 GeV/c

A sample of 1657 pp→ps2π+3π− events in the p momentum range 0.35−0.92 GeV/c has been analysed, yielding data on the cross section, invariant-mass distributions, and pion-pion angular correlations. It was found that a conventional model in terms of non-interfering Breit-Wigner resonances did not fit the data as well as a novel hybrid model that included π-π phase shifts, especially in the case of the π+π− invariant-mass distributions.

A search for direct electron production inpp interactions at 70GeV/c

A search for directly produced electrons in 70 GeV/cpp interactions has been performed using BEBC equipped with a hydrogen filled track sensitive target surrounded by a hydrogen/neon blanket. No candidates for single electron production with momentump e >500 MeV/c were found in a sample of 66,000 primary interactions. This result places an upper limit of 2.5 μb on the cross section for singlee± production at the 90% confidence level. The corresponding upper limit on the charmed particle production cross section in 14 μb. From the observation of 7 events producing ane+e− pair with mass,\(m_{e^ + e^ - } > m_{\pi ^0 } \) thee±/π± ratio from this source is estimated to be (0.7±0.2)×10−4.

Elastic antiproton-deutron scattering below 1.0 GeV/c

Abstract We present differential cross sections for elastic p d scattering at beam momenta 0.735 and 0.940 GeV/c and momentum transfers in the range 0.04 p d elastic differential cross section is expressed in terms of a deutron form factor and the I=0 t-channel exchange N N amplitudes, enabling us to isolate the corresponding I=0 t-channel exchange cross sections.