B. Drevillon

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.

Study of the Kππ system produced in K−p → KππN reactions at 14.3 GeV/c

We have studied the Kππ system in the 14.3 GeV/c reactions K−p → K−π+π−p, K−p → K0π−π0 and K−p → K0π+π−n. The data have been obtained from a 500 000 picture exposure of the CERN 2m HBC. The first two final states are dominated by Q-production in the Kππ system; there is also an L-signal at M (Kππ) ∼ 1.75 GeV. The reaction cross sections are compared to K−p data at other energies. We discuss the Kππ mass dependence of the diffractive production slope. Evidence is presented for a Q−p versus Q+p differential cross section cross-over around |t| = 0.17 GeV2. A t-channel isospin analysis for the KN → K∗(890)πN channels in the Q-region shows that the I = 1 exchange amplitude is ⋍ 10% of the dominant I = 0 exchange amplitude. The Kππ decay distributions indicate a predominant JP = 1+ state in the Q-region, and an important JP = 2− contribution in the L-region. We find neither s-channel nor t-channel helicity conservation at the meson vertex in the Q- or L-regions. The Kπ angular correlation moments within the Kππ diffractive system are characteristic of Kπ elastic scattering, suggesting a π-exchange Deck-type production mechanism. There is evidence for a Kf0 and κπ contribution (where κ is the JP(Kπ) = 0+ state) to the diffractive Kππ system. A fit to the K−π+π− and K0π−π0 Dalitz-plot distributions for the Q-re gion indicates that the ratio of Kϱ to K∗π decay amplitudes decreases with increasing Kππ mass.

Inclusive production of lambda and neutral kaon in K−p interactions at 3.93 GeV/c and 14.3 GeV/c

SummaryLambda and neutral-kaon production is studied in K−p interactions at 3.93 and 14.3 GeV/c. Topological inclusive cross-sections are given at both energies. Invariant cross-sections for lambdas and neutral kaons are presented as a function of the Feynmanx-variable and are found to decrease in magnitude and vary their shapes with energy. Thenn

Photoproduction of charmed D mesons at γ energies of 40–70 GeV

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Inclusive production of charged and neutral sigma hyperons in K−p interactions at 14.3 GeV/c

nn production, which represents (9±2)% and (29±3)% of the lambda inclusive cross-section at 3.93 GeV/c and 14.3 GeV/c respectively, yields mainly backward lambdas. The shapes of the transverse-momentum invariant distributions vary withx, but are roughly independent of energy. The lambda polarization is studied as a function ofx at both incident momenta: for fast lambdas it is negative, as observed in reactions where nucleon exchange is dominant.RiassuntoSi studia la produzione di particelle lambda e di kaoni neutri nelle interazioni K−p a 3.93 e 14.3 GeV/c. Per entrambi i valori dellenergia si danno le sezioni durto inclusive topologiche. Si presentano le sezioni durto invarianti per particelle lambda e kaoni neutri in funzione della variabilex di Feynman e si trova che diminuiscono in grandezza e cambiano di forma con lenergia. La produzione dinn

K−π− elastic scattering cross section measured in 14.3 GeV/c K−p interactions

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