D. Mercer

Photoproduction of ϱ0 and ω on hydrogen at photon energies of 20 to 70 GeV

Abstract We present results on photoproduction of ϱ 0 and ω in the reactions γ p→ π + π − p and γ p→ π + π − π 0 p by tagged photons in the energy ranges 20 to 70 GeV and 20 to 45 GeV, respectively. The production of the ϱ 0 shows dominantly the characteristics of a diffractive process with respect to the E γ and t dependence of the cross section and the spin density matrix. The ϱ 0 photoproduction yields on average over the photon energy range a total cross section of σ ( γ p→ ϱ 0 p) = 9.4±0.1 μ b with an additional systematic error of ±1 μ b, and average slope parameters of the t distribution d σ /d t ≈exp(− b | t | + ct 2 ), of b =9.1±0.1 GeV −2 and c = 3.1 ±±0.2 GeV −4 . The shape of the ϱ 0 peak in the π + π − invariant spectra shows a skewing similar to that observed at lower energies. The photoproduction of ω is also consistent with a diffractive process and has a cross section of σ ( γ p→ ω p) = 1.2± 0.1 μ b with an additional systematic error of ±0.2 μ b. The average slope parameters of the t distribution are b =8.3 ± 1.3 GeV −2 and c = 3.4±2.6 GeV −4 .

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.

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 charmed D mesons at γ energies of 40–70 GeV

Inclusive D0 photoproduction is observed in Kπ+π− and K+π−π0. Evidence is presented for an associated (CD) production mechanism. Cross section estimates and limits are given for D and D mesons.

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 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 − .

Inclusive photoproduction of single charged particles at highp T

Single charged-particle inclusive cross sections for photon, pion and kaon beams on hydrogen at the CERN-SPS are presented as functions ofpT andxF. Data cover the range 0.0<pT<5.0 GeV/c and 0.0<xF<1.0 at incident momenta from 70 to 170 GeV/c. The comparison between photon- and hadron-induced data indicates a relative excess of particles withpT>1.6 GeV/c for the photon-induced data. Using the hadron-induced data to estimate the hadronic behaviour of the photon, the difference distributions and ratios of cross sections are a measure of the contribution of the point-like photon interactions. The data are compared with QCD calculations and show broadly similar features.

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.

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.