Results on the following π−p reactions involving a hyperon are studied at 4.5 and 6.0 GeV/c from a high-statistics bubble-chamber experiment. (1) π−p→(Λ, Σ0)K0: Differential cross sections and hyperon polarizations are presented. Comparison with the line-reversed reactions K¯N→(Λ, Σ0)π indicates the failure of the predictions of K*(890) and K*(1420) exchange degeneracy. Effective trajectories for these two reactions are compared. Shrinkage is observed in K¯N→Λπ and not in π−p→ΛK0. (2) π−p→(Λ, Σ0)K*(890)0: Differential cross sections, hyperon polarizations, and K*(890)0 density-matrix elements are determined. ΛK*(890)0 decay correlations are found to impose strong constraints on the scattering amplitudes. The data indicate that both natural- and unnatural-parity exchanges contribute large, but opposite, Λ polarizations. This behavior cannot be explained by a simple exchange model utilizing K and the exchange-degenerate K*(890) and K*(1420) only. Additional trajectories or absorption effects are required to obtain the observed Λ-polarization effects. Comparison of ΛK*(890)0 and Σ0K*(890)0 indicates the greater importance of unnatural-parity exchange in the former reaction. We observe no evidence for deviations from isospin predictions in ΛK*(890)0 production where K*(890)0→K+π− and KS0π0. (3) π−p→ΛK*(1420)0 and ΛK*(1300)0: K*(1420)0 density-matrix elements satisfying positivity constraints are determined allowing for s-wave interference effects. Evidence of the existence of a narrow K*(1300)0→Kππ with a dominant K+ρ− decay mode is observed in the 4.5- and 6-GeV/c data. (4) Σ(1385), Λ(1405), Λ(1520) production: Differential cross sections for the quasi-two-body reactions π−p→Y0K0, where Y0 is Λ(1405), Λ(1520), or Σ(1385)0, are presented and found to have a very similar flat slope in the forward direction. Data for forward K+ scattering in the reaction π−p→Σ(1385)−K+ are presented and discussed. It is argued that this forward peak cannot be explained by kinematic reflection or an s-channel effect and therefore must be due to either two-particle exchange or a single exotic exchange in the t channel.
No description provided.
No description provided.
FIT FOR FORWARD CROSS SECTION AND SLOPE.
The reactionsπ−p→K0(890) Λ,K0(890)Σ0 andK0(890)Σ0 are studied at an incident momentum of 3.95 GeV/c using data from a high statistics bubble chamber experiment corresponding to ∼90 events/μb. The differential cross sections, density matrix elements of the vector meson and hyperon polarizations are presented. A transversity amplitude analysis is performed for each of the reactions. The results are compared with those obtained for the SU(3) related processesK−p→ϕΔ, ϕΣ0, ϕΣ0(1385) andϱ−Σ+(1385) and with predictions of the additive quark model and SU(6) sum rules.
BREIT-WIGNER FIT WITH BACKGROUND POLYNOMIAL.
BACKWARD CROSS SECTION.
TOTAL CROSS SECTION USING SLICING TECHNIQUE. FORWARD (-TP < 1.2 GEV**2) CROSS SECTION IS 25 +- 2 MUB: DOUBLE MASS CUT GIVES 20 +- 7 PCT BACKGROUND CONTAMINATION.
Photoproduction is studied at 2.8 and 4.7 GeV using a linearly polarized monoenergetic photon beam in a hydrogen bubble chamber. We discuss the experimental procedure, the determination of channel cross sections, and the analysis of the channel γp→pπ+π−. A model-independent analysis of the ρ0-decay angular distribution allows us to measure nine independent density-matrix elements. From these we find that the reaction γp→pρ0 proceeds almost completely through natural parity exchange for squared momentum transfers |t|<1 GeV2 and that the ρ production mechanism is consistent with s-channel c.m. helicity conservation for |t|<0.4 GeV2. A cross section for the production of π+π− pairs in the s-channel c.m. helicity-conserving p-wave state is determined. The ρ mass shape is studied as a function of momentum transfer and is found to be inconsistent with a t-independent Ross-Stodolsky factor. Using a t-dependent parametrization of the ρ0 mass shape we derive a phenomenological ρ0 cross section. We compare our phenomenological ρ0 cross section with other experiments and find good agreement for 0.05<|t|<1 GeV2. We discuss the discrepancies in the various determinations of the forward differential cross section. We study models for ρ0 photoproduction and find that the Söding model best describes the data. Using the Söding model we determine a ρ0 cross section. We determine cross sections and nine density-matrix elements for γp→Δ++π−. The parity asymmetry for Δ++ production is incompatible with simple one-pion exchange. We compare Δ++ production with models.
FROM QUOTED TOPOLOGICAL CROSS SECTIONS. 1.44 GEV CROSS SECTION PUBLISHED PREVIOUSLY.
No description provided.
NO TMIN CORRECTION HAS BEEN MADE.
THE study of elastic scattering at high energies in the region of the diffraction maximum has gained in interest recently in connection with the verifica- tion of the asymptotic expressions obtained by cal- culating the Regge-pole trajectories. We have in- vestigated the elastic scattering of 3. 5- Be VIc 7r- mesons by protons. The measurements were made with the aid of a liquid-hydrogen bubble chamber 25 em in diameter, placed in a 14 kOe magnetic field.
No description provided.
DATA READ FROM GRAPH BY SRS.
No description provided.
The dissociation of virtual photons, $\gamma^{\star} p \to X p$, in events with a large rapidity gap between $X$ and the outgoing proton, as well as in events in which the leading proton was directly measured, has been studied with the ZEUS detector at HERA. The data cover photon virtualities $Q^2>2$ GeV$^2$ and $\gamma^{\star} p$ centre-of-mass energies $40<W<240$ GeV, with $M_X>2$ GeV, where $M_X$ is the mass of the hadronic final state, $X$. Leading protons were detected in the ZEUS leading proton spectrometer. The cross section is presented as a function of $t$, the squared four-momentum transfer at the proton vertex and $\Phi$, the azimuthal angle between the positron scattering plane and the proton scattering plane. It is also shown as a function of $Q^2$ and $\xpom$, the fraction of the proton's momentum carried by the diffractive exchange, as well as $\beta$, the Bjorken variable defined with respect to the diffractive exchange.
The differential cross section DSIG/DT for the LRG and the LPS data samples.
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
Differential and total cross-sections for photoproduction of gamma proton to proton pi0 omega and gamma proton to Delta+ omega were determined from measurements of the CB-ELSA experiment, performed at the electron accelerator ELSA in Bonn. The measurements covered the photon energy range from the production threshold up to 3GeV.
Differential cross section as a function of the OMEGA angle.
Differential cross section as a function of the OMEGA angle.
Differential cross section as a function of the PI0 angle.
We studied the exclusive reaction e p --> e' p' phi using the phi --> K^+ K^- decay mode. The data were collected using a 4.2 GeV incident electron beam and the CLAS detector at Jefferson Lab. Our experiment covers the range in Q^2 from 0.7 to 2.2 GeV^2, and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of phi production on the proton. Our measurement shows the expected decrease of the t-slope with the vector meson formation time c Delta tau below 2 fm. At = 0.6 fm, we measure b_phi = 2.27 +- 0.42 GeV^-2. The cross section dependence on W as W^{0.2+-0.1} at Q^2 = 1.3 GeV^2 was determined by comparison with phi production at HERA after correcting for threshold effects. This is the same dependence as observed in photoproduction.
Slope of the DSIG/DT distribution in different Q**2 regions.
Cross section as a function of Q**2 and W.
The differential cross section for exclusive PHI electroproduction off the photon, (TP=T-TMIN).
We have measured ρ0, ω (combined) and ϕ electroproduction over a range of virtual-photon four-momentum Q2 from 0.4 to 2.2 GeV2 and for photon energies ν from 2.7 to 8.6 GeV. We find that the slope of the t (momentum transfer) dependence of the ρ0 and ω forward peak decreases with increasing Q2 to less than half of the photoproduction slope.
The cross section for virtual photon are derived from E- P cross section bydividing on the virtual-photon flux factor.
We present results on vector-meson photoproduction via γp→Vp in the LBL-SLAC 82-in. hydrogen bubble chamber exposed to a linearly polarized photon beam at 2.8, 4.7, and 9.3 GeV. We find ρ0 production to have the characteristics of a diffractive process, i.e., a cross section decreasing slowly with energy and a differential cross section with slope of ∼ 6.5 GeV−2. Within errors the ρ0 production amplitudes are entirely due to natural-parity exchange. s-channel helicity is conserved to a high degree in the γ→ρ0 transition. We find evidence for small helicity-flip amplitudes for ππ pairs in the ρ0 region. Photoproduction of ω mesons is separated into its natural- (σN) and unnatural- (σU) parity-exchange contributions. The Eγ and t dependence and the spin density matrix of the unnatural-parity-exchange contribution are consistent with a one-pion-exchange process. The natural-parity-exchange part has characteristics similar to ρ0 production. At 9.3 GeV the ratio of σ(ρ0) to σN(ω) is ∼ 7. The slope of the φ differential cross section is ∼ 4.5 GeV−2, smaller than that of ρ0 and ω production. Natural-parity exchange is the main contributor to φ production. No evidence for higher-mass vector mesons is found in ππ, πππ, or KK¯ final states. The s and t dependences of Compton scattering as calculated from ρ, ω, and φ photoproduction using vector-meson dominance agree with experiment, but the predicted Compton cross section is too small by a factor of 2.
No description provided.
No description provided.
No description provided.
Data of the ηπ − system were obtained in the reaction π − p → ηπ − p at 6.3 GeV/ c beam momentum. About 17 k events of ηπ − were collected in the mass range 0.8 ⩽ M ηπ - ⩽ 1.8 GeV/ c 2 and in the range of the momentum transfer squared 0.075 ⩽ | t ′| ⩽ 0.60 (GeV/ c ) 2 . A large forward-backward asymmetry was observed around 1.3 GeV/ c 2 in the Gottfried-Jackson frame of the ηπ − system. A partial wave analysis of the data was performed. A peak of the D + wave attributed to a 2 (1320) is clearly seen. An enhancement is observed around 1.3 GeV/ c 2 in the P + wave.
No description provided.
No description provided.
Forum