S. Katsanevas

The reaction γp → pπ+π−π+π− for photon energies from 25 to 70 GeV

Abstract Measurements of the reaction γ p → p π + π − π + π − are presented, in which π + π − π + π − systems with masses up to 3 GeV are produced from fragmentation of the incident photon. The reaction is dominated by production of the large peak of the ϱ′(1600) meson and, at higher masses ≳2 GeV, y production of jet-like 4 π systems. The ϱ′(1600) meson is produced by a predominantly s -channel helicity conserving mechanism. At higher masses there are also indications of ϱπ peaks, of masses 1.3 GeV (the A 2 meson) and 1.75 GeV, produced with a recoiling π meson by a mechanism consistent with the Deck effect.

Observation of the ϱ′(1600) in the channel γp→π+π−p☆

Abstract A dipion enhancement of mass 1.59 GeV and width 0.23 GeV is observed in the channel γp→π + π − p. The spin-parity of the enhancement is consistent with being 1 − .

Observation of an ωπ0 state of mass 1.25 GeV produced by photons of energy 20–70 GeV☆

Abstract An analysis is presented of the channel γp→π + π − π 0 π 0 p. Evidence is found for an ωπ 0 enhancement of mass ≈1.25 GeV and width ≈0.3 GeV. The enhancement is a mixed spin-parity state with 1 − dominant.

Photoproduction of K+K− pairs on hydrogen at photon enegies of 20 to 36 GeV

The reaction γp→K+K−p has been investigated with photons in the energy range of 20<Eγ<36 GeV and with K+K− pairs in the mass range of MK+K−<2.0 GeV. The production of the φ(1019) contributes with a cross section σ(γp → φp) × BR(φ→K+K−) = 240±6 nb with an additional systematic error of ±20 nb. In the higher mass range of 1.05<MK+K−<2.0 GeV the production of K+K− pairs yields a cross section σ(γp→K+K−p) = 160±8 nb with an additional systematic error of +40−30 nb.

The reactions γp→ωπ+π−p and γp→ηπ+π−p at photon energies of 25–70 GeV

Measurements of ω and η production in the reaction γp→π+π−π+π−π0p are presented, showihg that the ωπ+π− channel is made up of an enhancement at ∼1.7 GeV of width ∼0.5 GeV, which is consistent with being a 1− state, together with a distribution at higher masses containing higher angular momentum terms. The ηπ+π− final state is produced with a similar cross section and also shows a low-mass enhancement.

Inclusive photoproduction of φ-mesons at photon energies of 25–70 GeV

Results are presented on inclusive φ photoproduction for incident energies between 25 and 70 GeV. Distributions in Feynman x, pT and decay angles are presented and interpreted in terms of quark fusion models. We demonstrate a similarity with the corresponding pion-induced reaction and obtain information on the hadronic nature of the photon.

Observation of a Charmed Neutral Meson Produced in a High-energy Photon Interaction

The production and decay of a D0 have been observed in a nuclear emulsion exposed to a photon beam from the CERN super proton synchroton in conjunction with the Omega spectrometer. All the decay products have been detected and measured in the emulsion and in the spectrometer. The mass of the charmed particle is 1866 ± 8 MeV/c2 and its decay time is (2.26 ± 0.05) × 10−14 s.

Jet-like structure in the reaction γp→π+π−π+π−π+π−p

Abstract We report on diffractive production of 6 π systems with a continuum of masses from 2 to 5 GeV/c 2 in the reaction γ p→ π + π − π + π − π + π - p. The event structure is compared in detail with Monte Carlo studies of p T limited phase space, and with the jets observed in hadronic systems produced by electron-positron annihilation. Strong similarities are found. For this jet-like structure of the 6 π system the axis is consistent with being along the incident photon direction.

Inclusive production of lambdas and antilambdas in γp interactions, for photon energies between 25 and 70 GeV

Abstract Results are presented on the inclusive photoproduction of λ and λ for incident photon energies between 25 and 70 GeV. The slope parameter of the pT2 distribution is found to be 2.83±0.1 GeV−2 for λ and 3.28±0.25 GeV−2 for λ . The xF distributions, measured in the range −0.2 to 0.7, show that while λ are produced centrally, λ production extends to more negative values of xF; the shapes show no energy dependence and are similar to those in pion-induced reactions. The polarization of the produced λ is less than 10%. The results are discussed in terms of vector dominance and quark fusion models.

Photoproduction of charmed F mesons at γ energies of 20–70 GeV

Abstract Evidence is presented for inclusive photoproduction of F ± mesons in three decay modes, ηπ ± , ηπ ± π + π − and ηπ ± π + π + π − π − . The average mass of the F ± is found to be 2.020±0.010 GeV.