William P. Swanson

The reaction γp → π+π−π+π−p at high energy and photon dissociation into four pions

Abstract The reaction γp → π+π−π+π−p has been studied using the SLAC 2-meter streamer chamber placed in an 18 GeV bremsstrahlung beam. We find evidence for a broad enhancement (ϱ′) in the 4π mass spectrum at a mass of 1620 MeV with a width of about 300 MeV. This state is produced peripherally with a cross section consistent with being energy independent. I-spin = 1 (C = −1) is deduced from the dominant ϱππ decay mode and J ≠ 0 from the observation of a polarization phenomenon. Assuming quantum numbers JP = 1−, s-channel helicity is conserved at the γ−ϱ′ vertex. Further support for the JP assignment is gathered when comparing our results to data from e+e− colliding-beam experiments.

A study of the decay KL0 → πeν

Abstract We report results from a Dalitz plot analysis of 17750 K e3 0 candidates obtained in an experiment designed to have high efficiency across the Dalitz plot. Assuming a vector interaction form factor ƒ + (q 2 ) = ƒ + (0) (1 + λ + q 2 /m π 2 ) we obtain λ + = 0.0348 ± 0.0044. Our upper limits for the scalar (ƒ s ) and tensor (ƒ t ) form factors at the 95% confidence level are ƒ s ƒ + (0) and ƒ t ƒ + (0) .

A study of the decay KLO → πμν

Abstract We report results from a Dalitz plot analysis of 16 386 K μ3 0 candidates obtained in an experiment with high efficiency across the Dalitz plot and very low background. We measure the vector and scalar from factors and obtain the following values for the linear expansion parameters: γ + = 0.028 ± 0.011, γ 0 = 0.039 ± 0.010.

The reaction γp → ϱOp at 5.5 to 18 GeV☆

The reaction γp→ϱOp in the energy range 5.5<Eγ<18 GeV was studied using a streamer chamber exposed to an 18 GeV bremsstrahlung beam. Our results differ from earlier counter experiments in the following ways: (i) the ϱ cross section is constant (≈ 12 μb) throughout the energy range and (ii) both dσdt|tmin and the slope parameter of dσdt are constant and have significantly smaller values (≈82 μbGeV2 and 6.6 GeV−2 respectively) at all our energies. The t-dependence of the ϱ density matrix in both s− and t-channel helicity frames shows that the production conserves the s-channel helicity at all t-values observed (up to −0.8 GeV2).

Performance of the SLAC 2-meter streamer chamber in a study of multibody photoproduction.

Abstract The performance of the SLAC 2-m streamer chamber is evaluated using the results of a high-statistics, multibody-photo-production experiment carried out with an 18 GeV bremsstrahlung beam. The instrumental arrangement is outlined, and the data-analysis procedures are described in detail. Special methods are then discussed for dealing with trigger, dip-angle, and hydrogen-target losses and for weighting the surviving events. Finally, the spatial resolution, instrumental efficiency, and overall normalization accuracy are given, and the momentum range over which particle types can be distinguished by ionization is discussed. The results of this evaluation indicate that the streamer chamber is successful in combining the high geometrical resolution, excellent multiple-track efficiency, nearly 4 π solid angle, and ionization capabilities of the bubble chamber with the high repetition rate and triggering facility of the spark chamber.

Analysis of πp reactions in the LPS framework at Eπ = 6–18 GeV☆

Abstract The reactions γ p → π + π − p and γ p → π + π − π + π − p in the energy range Eγ = 6–18 GeV from the SLAC 2m streamer chamber are analyzed in terms of the longitudinal-phase-space (LPS) method. The 3-body LPS hexagonal plots show accumulations which reflect the dominant diffractive ϱ o production. The five-body final state is divided into sixteen LPS sectors. The partial cross sections, invariant-mass and momentum-transfer distributions of the four populous sectors are presented and discussed. Within this framework, we attempt to isolate and study the dissociations γ → π + π − , γ → π + π − π + π − and the double dissociations γ → π + π − , p → p π + π − . The proton dissociation p → p π + π − is found to be in approximate agreement with results from πp and pp reactions. Assuming that pomeron exchangedominates, this result is consistent with pomeron factorization.

A multi-Regge model applied to high-energy quasi-inclusive photoproduction☆

Abstract We compare inclusive photoproduction data in the energy range E γ = 9.0−18.0 GeV to the multi-Regge model. The model incorporates vector-dominance coupling of the photon, the Chew-Pignotti algorithm for charge assignment, and correct treatment of n -body phase space. A technique of ordering the particles according to longitudinal momentum is used to enhance features of the data and provide a more sensitive test of the model. We compare the model to mass distributions, separation of particles in rapidity, longitudinal momentum distributions, topological cross-sections and charge orderings of secondaries. A reasonable description of the data is achieved, using parameters derived from pp and K + p experiments. Within this framework, it is found that the class of diagrams involving γ coupling to the ϱ are not adequate to describe all aspects of the data, and that other couplings are present to a significant degree.

ANALYSIS OF gamma p REACTIONS IN THE LPS FRAMEWORK AT E (gamma) = 6-GeV TO 18-GeV

Abstract The reactions γ p → π + π − p and γ p → π + π − π + π − p in the energy range Eγ = 6–18 GeV from the SLAC 2m streamer chamber are analyzed in terms of the longitudinal-phase-space (LPS) method. The 3-body LPS hexagonal plots show accumulations which reflect the dominant diffractive ϱ o production. The five-body final state is divided into sixteen LPS sectors. The partial cross sections, invariant-mass and momentum-transfer distributions of the four populous sectors are presented and discussed. Within this framework, we attempt to isolate and study the dissociations γ → π + π − , γ → π + π − π + π − and the double dissociations γ → π + π − , p → p π + π − . The proton dissociation p → p π + π − is found to be in approximate agreement with results from πp and pp reactions. Assuming that pomeron exchangedominates, this result is consistent with pomeron factorization.

THE REACTION gamma p ---> rho0 p AT 5.5-GeV TO 18-GeV

The reaction γp→ϱOp in the energy range 5.5<Eγ<18 GeV was studied using a streamer chamber exposed to an 18 GeV bremsstrahlung beam. Our results differ from earlier counter experiments in the following ways: (i) the ϱ cross section is constant (≈ 12 μb) throughout the energy range and (ii) both dσdt|tmin and the slope parameter of dσdt are constant and have significantly smaller values (≈82 μbGeV2 and 6.6 GeV−2 respectively) at all our energies. The t-dependence of the ϱ density matrix in both s− and t-channel helicity frames shows that the production conserves the s-channel helicity at all t-values observed (up to −0.8 GeV2).