Y. Eisenberg

A search for B and ϱ′(1250) production in the reaction γp → pπ+π− + neutrals at 2.8, 4.7 and 9.3 GeV☆

Abstract We have studied the reaction γ p → p π + π − + neutrals in the LBL-SLAC 82″ hydrogen bubble chamber exposed to a linearly polarized photon beam at 2.8., 4.7 and 9.3. GeV. We observe an enhancement at 1.24 GeV in the mesonic mass recoiling against the proton. The enhancement is produced peripherally with slopes of 5−7 GeV −2 and cross sections of 1−3 μb. We show that ωπ o is likely to be the major decay mode and give upper limits for other decay modes. The enhancement can be either the J P = 1 + B meson, a yet unestablished J P = 1 − meson decaying via ωπ o , or a diffractively produced Deck-type background. The observed decay correlations are compatible with an s -channel helicity conserving production process. Our data at higher masses are consistent with a ϱϵ decay of the ϱ′(1600) and we obtain an upper limit of 4±1 μ b for ϱ′(1600) production in the final state p π + π − + neutrals at 9.3 GeV.

OBSERVATION OF A FOUR PION VECTOR - MESON STATE OF MASS approximately equal to 1.5-GeV PRODUCED BY LINEARLY POLARIZED 9.3-GeV PHOTONS

Abstract From a study of γp → 2 π + 2 π − p using 9.3 GeV linearly polarized photons, evidence is found for a J P = 1 − , I G = 1 + four pion enhancement of mass ∼ 1.5 GeV with a production cross section of 1.6 ± 0.4 μb .

Vector Meson Photoproduction, Amplitude Structure and S‐Channel Helicity Conservation Violation in Pomeron Exchange Reactions

The experimental data on vector meson photoproduction and Compton scattering is analyzed by utilizing the dual absorptive model. The s‐channel helicity conserving (SHC) Pomeron exchange amplitude in ρo and φ photoproduction is found to shrink with s, in the same way as in π‐ and K+‐nucleon elastic scattering. The small SHC‐violating amplitudes are also studied. The ratio of amplitudes for ∣Dgr;λ∣ = 1 to Δλ = 0 at the γ‐ρ vertex is shown to be similar to the ratio of corresponding πN amplitudes at the proton vertex and both seem to depend only weakly on s.

Photoproduction of a New Vector Meson by Linearly Polarized 9.3 GeV Gamma Rays

From a 275 events/μb exposure of the 82″ HBC to the SLAC linearly polarized monochromatic (9.3 GeV) γ beam, our preliminary analysis shows evidence for peripheral [exp (6t)] photoproduction of a JP = 1 −, meson with mass in the 1.5 GeV region, width ≳ 0.4 GeV (M and Γ both model dependent) and σ = 1.7 ± 0.3 μb in the reaction γp ⇒ ρ1 p, ρ1 ⇒ 2π+;2π−. The 4π system shows ρ0π+ π− substructure. Arguments for IG = 1+ are presented from the angular correlations (and the lack of clear evidence for a ρ0ρ0 decay mode).