H.-P. Jakob

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).

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.

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).

Comparison of photon and hadron induced production of ρ0 mesons in the energy range of 65 to 175 GeV

The inclusive production of ρ0 mesons was measured in γp andh±p collisions at beam energies of 65 GeV≦Eγ≦175 GeV andEh=80, 140 GeV, respectively, whereh is π orK. Cross sections were determined for all beams and energies as functions ofxF (−0.1≦xF≦1.0),pT (0≦pT≦3.5 GeV/c) and the polar decay angle of the ρ0 by fitting the ρ0 signal in π+π- mass distributions. The ρ0 line shape is found to be distorted from a pure Breit-Wigner distribution throughout most of thexF−pT plane for both photon and hadron beams and a simple explanation is suggested. Throughout the paper emphasis is put on the comparison of photon and hadron beam data. The comparison of cross sections of γp andhp data provides a measure of the Vector Meson Dominance factor throughout thexF−pT range of the ρ0. The ρ0 production at lowpT can be described for both photon and hadron beams by a triple regge model at largexF. Similarly central production is well described by the quark-antiquark fusion model. At largepT there is an excess of ρ0 photoproduction which is consistent with the expected onset of pointlike photon interactions.