A.B. Clegg

A spin-parity analysis of the ωπ0 enhancement photoproduced in the energy range 20 to 70 GeV

Abstract A study is made of the ωπ 0 system produced near threshold in the reaction γ p→ π + π − π 0 π 0 p. A spin-parity analysis shows that the ωπ 0 enhancement is consistent with predominant 1 + B(1235) production, with ∼20% J P = 1 − background.

Photoproduction of π+π−π0 on hydrogen with linearly polarized photons of energy 20–70 GeV

Results on photoproduction of π+π−π0 in the photon energy range 20–70 GeV are presented. For the ω meson, the production cross-section is found to be 1010±15 (statistical)±290 (systematic) nb and is constant over the incident photon energy range. Spin-density matrix elements are evaluated for ω meson production. The φ meson is observed with a total photoproduction cross section (corrected for branching ratio to π+π−π0) of 610±35±170 nb. A third resonance, at 1.67 GeV, is seen in the mass spectrum and its interpretation is discussed. The production of a broad π+π−π0 continuum, mainly via ϱπ, and peaking at 1.2 GeV, contributes with a cross section of about 2.5 ωb. The spin-parity content is analysed by the moments of the π+π−π0 decay angular distribution in the helicity frame and by maximum likelihood fits to the π+π−π0 Dalitz plot. It is found that production of JP = 1− states accounts for less than half of the total mass spectrum above 900 MeV. There is a broad enhancement in the 1+ wave around 1.15 GeV indicating photoproduction of the H(1190) meson.

Photoproduction of KK̄π final states in the photon energy range from 20 to 70 GeV

The reactions γp→K+K−π0(p) and γp→ Ks0K± π±(p) have been measured using tagged photons in the energy range 20 to 70 GeV. No resonance structure is observed in either of the KKπ invariant mass distributions, which range from threshold up to ∼ 3 GeV. The photoproduction cross sections for φπ0 and K∗(892)K are presented and are compared with theoretical predictions. No evidence has been found for the photoproduction of φ′ (1680).

Observation of a peak at 1.28 GeV in the ηππ system in the reaction γp→ηπ+π−p

CERN - WA57. OMEGA SPECTROMETER. OBSERVATION OF A PEAK AT 1.28 GEV IN THE ETA PI PI SYSTEM IN GAMMA P --& gt; ETA PI+ PI- P. SPIN PARITY ANALYSIS INDICATES POSSIBLE INTERPRETATION AS B(1235) MESON.Abstract A peak is reported in the ηπ + π − system, produced in the reaction γ p→ ηπ + π − p, at a mass of 1.28 ± 0.01 GeV with a width of 0.08 ± 0.02 GeV. Possible spin-parity assignments for the peak are shown to be J π = 1 − , J π = 1 + or J π = 2 + and interpretations of these assignments are discussed.Abstract A peak is reported in the {ce:inline-formula}ηπ +π-{/ce:inline-formula} system, produced in the reaction {ce:inline-formula}γp ηπ +π -p{/ce:inline-formula}, at a mass of {ce:inline-formula}1.28 ± 0.01GeV{/ce:inline-formula} with a width of {ce:inline-formula}0.08 ± 0.02GeV{/ce:inline-formula}. Possible spin-parity assignments for the peak are shown to be {ce:inline-formula}J π = 1 -, J π = 1 +orJ π = 2 +{/ce:inline-formula} and interpretations of these assignments are discussed.

Inclusive photoproduction of δ(980) and B(1235) at high xF

Inclusive photoproduction of δ±(980) and B±0(1235) at high xF is reported. Production of B0 is largely due to double diffractive dissociation. The charged states are produced as leading particles, their production being described by the quark recombination picture. The relatively strong production of the δ(980) by this process is evidence that it is a qq state rather than a qqqq state.

The reaction γp → pωπ+π− for photon energies of 25–50 GeV

Measurements of the reaction γp → pωπ+π− are reported for photon energies 25–50 GeV. Particular attention is paid to ωπ+π− masses < 2 GeV. A search is made for ω′ or φ′ partners of the ϱ′(1600). Evidence is presented against the existence of narrow states and against the production of a broad state by an s-channel helicity conserving mechanism.

Inclusive photoproduction of ϱ and ω in the photon energy range 20 to 70 GeV

Inclusive production of ϱ0, ω, and ϱ± at low transverse momentum has been measured in γp collisions with photons of energy 20 to 70 GeV. The vector mesons have been studied as functions of the Feynman variable χF, varying between −0.2 and 0.95, i.e. excluding the “elastic” peaks of ϱ0 and ω photoproduction. For χF ≲ 0.6 the vector meson cross sections are approximately equal; that is, σ(ϱ0) ≈ σ(ω) ≈ 12[σ(ϱ+) + σ(ϱ−)]. For χF > 0.6, it is observed that σ(ϱ0) > σ(ω) ⩾ 12[σ(ϱ+) + σ(ϱ−)] and the differences increase with increasing χF. Over the χF range −0.2 < χF < 0.95 the vector mesons are produced similarly to non-diffractive leading particles in hadron-hadron collisions with an extra diffractive component in ϱ0 and ω production.

The decay of the ϱ′ (1600) into π+π−π0π0

Abstract Measurements of the reaction γ p→ π + π − π 0 π 0 p are presented for the photon energy range 20 to 70 GeV. The 1.6 GeV peak in the mass spectrum of the π + π − π 0 π 0 system is shown to decay dominantly to ϱ ± π ∓ π 0 . The ratio of ϱ 0 π 0 π 0 to ϱ ± π ∓ π 0 is less than 0.15, thus eliminating ϱϵ as the dominant decay mode of ϱ ′ (1600).

Photoproduction of an isoscalar 3π resonance at 1.67 GeV

Abstract A ϱπ enhancement with mass 1.67 ± 0.02GeV and width 0.16 ± 0.02GeV is observed in the channel γp→pπ + π − π 0 . Assuming an incoherent background, the cross section × branching ratio is 100 ± 20 nb. A spin-parity analysis favours J P = 1 − . The enhancement is most simply interpreted as a radial recurrence of the ω meson.

Further evidence for photoproduction of charmedF-mesons

Further experimental evidence is given for theF meson through its decay into η′s. Results are presented for the decay channels ηπ±, ηπ0π± and ηπ+π−π±, and confirm those obtained in a previous experiment.