G.M. Lewis

The total photon deuteron hadronic cross-section in the energy range 0.265-4.215 gev

Abstract The total cross section for photoproduction of hadrons on the deutron, σTd, has been measured for photon energies in the range 0.265–40215 GeV. From this, using results for the photon total cross section, obtained previously with the same apparatus, the neutron total cross section has been determined in the resonance region. The resonant structure is found to be quite different from that for the proton. Thereafter the neutron cross section falls off steadily with energy, and the values obtained are consistently lower than those for the proton. Forward scattering amplitudes have been evaluated for the deuteron.

Evidence for a narrow width boson of mass 2.95 GeV

Abstract In a search for resonances coupled to the p pπ − system, we have studied π − p interactions at 16 GeV/ c giving a forward antiproton, using the Omega spectrometer at CERN. In the final states involving a p , p and π − we observe a 5.6 (6.3) standard deviation enhancement in the p pπ − mass spectrum at (2.95 ± 0.01) GeV with a width consistent with the resolution ( σ = 15 MeV). The production cross section × branching ratio is estimated to be of the order 1 μb. The data are consistent with a resonance decaying partly via intermediate p p final states.

Inclusive φ production in π− p interactions at 16 GeV/c

Abstract Inclusive φ production is studied in π − p collisions at 16 GeV/ c . The φ cross section for Feynman variable x φ > 0.2 is found to be (15.5 ± 3.6) μb. This leads to an extrapolated cross section of (29.9 ± 7.0) μb for x φ > 0.0. Fitting the momentum transfer squared distribution of the φ to the form e −bp 2 T gives an average slope of b = (2.4 ± 0.3) (GeV/ c −2 for x φ > 0.5.

Observation in the K+K− system of a new structure at 2.20 GeV

Abstract A sample of 56 909 events of the reaction π − p→K + K − n at 10 GeV/ c has been measured in the Omega Spectrometer at CERN. In the K + K − system, besides production of mesons in the S ∗ /φ, f 0 / A 2 , g /ω ∗ and h regions we observe a new structure at 2.20 GeV with a width of the order of 200 MeV.

The total photon-proton cross-section for hadron production

Abstract The total hadronic cross section, σ T has been measured for tagged γ -rays, using electron beams in the GeV range, and narrow energy bins. Preliminary data are given covering the γ -energy region 275 MeV-1850 MeV, where interesting structure characteristics are observed.

Measurement of the L+M+…/K electron capture ratio in the decay of 125I

Abstract Using the “well-type” internal source scintillation spectrometer technique, a value of 0.253±0.005 was obtained for the L+M+…/K electron capture ratio in the decay of 125 I to the 35.4 keV excited state of 125 Te. This corresponds to an atomic mass difference of (153 ± 5) keV between the ground states of 125 I and 125 Te. Less than 1 % of capture transitions were found to go directly to the ground state of 125 Te.

Evidence for a narrow resonant state with strangeness +1 and charge +2

Abstract A narrow peak has been observed in Λ Δ ++ (1232) and Σ + (1385)p combinations produced in the reaction K+p → Λ pnπ+. This peak has a mass of 2.46 GeV/c2 and a width which is consistent with the experimental resolution.

Analysis of the reaction π−p→ppn at 10 and 16 GeV/c

Abstract Antiproton-proton pairs and antiproton-neutron pairs produced in the reaction π − p → p pn , were studied in the mass range from threshold to 2.6 GeV on the basis of 4 · 104 events at 10 GeV/c and 2 · 104 events at 16 GeV/c incident momentum. The cross section for peripheral production of p n pairs is significantly larger than for p p pairs. The p p production mechanism is consistent with the predictions of the one-pion exchange model, whereas the p n production cannot be sufficiently described by that model. A partial-wave analysis of the p p system, assuming pure one-pion exchange, shows that we need for a reasonable description of our data in addition to the JP = 3− resonance at 2.11 GeV and the 4+ resonance at 2.26 GeV found in an analysis of a formation experiment ( p p → π + π − ), two further resonances: a 1− state at 1.92 GeV and a 2+ state at 2.02 GeV.

K∗0(890) polarization measurements in the hypercharge exchange reaction π−p→K∗0(890) Λ0Σ0 at 10 GeV/c

K∗0(890) production in the hyperchange exchange reaction π−p→K∗0(890) Λ0Σ0 at 10 GeV/c (28 448 events) is discussed. An amplitude analysis in the t′ range up to 1 GeV2 shows that the production mechanism is dominated by natural parity exchange (∼84%). Comparisons are made with predictions from a Regge model and a quark model.

Search for narrow diquonium states in π−p interactions at 10 GeV/c

Narrow diquonium production in the reactions π−p→pπ−pp, pπ−pπ+n and pπ −ppπ0 is investigated in a 5.3 ev/nb experiment performed at the Omega Spectrometer. The computed upper limits are compared with the predictions of the Chan-Hogaasen model.