H. Voorthuis

The real part of the elastic scattering amplitude in the Coulomb interference region of 4.2 GeV/c K− mesons on protons and a comparison with K+p scattering at 5 GeV/c.

Abstract Using the same method as applied before to 5 GeV/ c K + p scattering we analyzed 4.2 GeV/ c K − p elastic scattering down to | t | values of 0.01 (GeV/ c ) 2 . About 5500 events yielded the following results: the ratio of real to imaginary part of the nuclear amplitude α = 0.20 ± 0.07, the slope of the exponential A = 8.6 ± 0.2 (GeV/ c ) −2 , the total elastic nuclear cross-section σ el = 4.3 ± 0.1 mb and the total cross-section σ T = 25.0 ± 0.7 mb.

Study of the reaction

Abstract Results are presented on effective-mass distributions, differentisl cross sections and longitudinal c.m. momentum distributions for the channels K − p → K − p π o , K o p π − and K − π + n , obtained from a sample of approximately 28 000 inelastic two-pronged interactions at 4.2 GeV/ c incident momentum. The results are in satisfactory agreement with the prediction of a generalized Veneziano-model corrected for (non-dual) π -and pomeron exchange. For the channel K − pπ o pomeron exchange contributes about 20% of the cross section. In the channel K − π + n the dual, pion and pomeron contributions are responsible for resp. 15%, 65% and 20% of the total cross section. We also present results on total and differential cross sections and spin-density matrix elements for the quasi two-body reactions K − p → K ∗− (890) p and K ∗o (890) n . These results are compared with single Regge-pole exchange model predictions. The reaction mechanism of K ∗− (890) production is dominated by the ω(θ) trajectory exchange with some admixture of π -exchange. The mechanism for K ∗o (890) production is dominated by π -exchange with some admixture of (A 2 ) trajectory exchange.

Production and decay of Ξ∗ (1820) in K−p reactions at 4.2 GeV/c

Abstract Using a high statistics sample of K − p interactions at 4.2 GeV/ c , the production and decay properties of the Ξ ∗ (1820) are discussed. The mass and width are found to be M = (1823 ± 2) MeV and Γ = (21 ± 7) MeV. Evidence is found for Ξ ∗ (2030) in the Σ K channel and for a new Ξ ∗ at a mass of 2120 MeV in the ΛK − channel.

Spin-parity structure of the (Kππ)0 system produced in the charge-exchange reaction K−p → (K0π+π−)n at 4.2 GeVc

Abstract A partial wave analysis of the K 0 π + π − system produced in the charge exchange reaction K − p → ( K 0 π + π − ) n at 4.2 GeV/ c has been performed both as a function of Kππ mass and of t ′. The 1 + S wave forms the largest contribution to the K ππ system and peaks at roughly the same mass as the Q in diffractive K ππ production. The polarization properties of the 1 + S ( K ∗ π) and 1 + S (Kϱ) waves differ fromt those of the diffractive 1 + wave. There is some evidence for a resonance contribution to 1 + S ( K ∗ π) . The strong 2 + wave the K ∗ (1420) and the K ϱ/ K ∗ ϱ decay branching ratio determined to be 0.36±0.10. An enhancement with spin-parity 1 − is observed under K ∗ (1420) .

Spin Parity Structure of the (anti-K pi pi)0 System Produced in the Charge Exchange Reaction K- p --> (anti-K0 pi+ pi-) n at 4.2-GeV/c

Abstract A partial wave analysis of the K 0 π + π − system produced in the charge exchange reaction K − p → ( K 0 π + π − ) n at 4.2 GeV/ c has been performed both as a function of Kππ mass and of t ′. The 1 + S wave forms the largest contribution to the K ππ system and peaks at roughly the same mass as the Q in diffractive K ππ production. The polarization properties of the 1 + S ( K ∗ π) and 1 + S (Kϱ) waves differ fromt those of the diffractive 1 + wave. There is some evidence for a resonance contribution to 1 + S ( K ∗ π) . The strong 2 + wave the K ∗ (1420) and the K ϱ/ K ∗ ϱ decay branching ratio determined to be 0.36±0.10. An enhancement with spin-parity 1 − is observed under K ∗ (1420) .

Study of the I = 32 K−π− elastic scaterring from the reaction K−p→K−π−pπ+ at 4.25 GeV/c incident K− momentum☆

Abstract Results on the elastic K−π− scattering have been obtained from a study of the K−π− system in 15 000 events of the type K−p→K−π−pπ+ at a K− beam momentum of 4.25 GeV/c. The on-mass-shell values of the spherical harmonic moments of the K−π− scattering angular distribution and the K−π− elastic cross section have been obtained by extrapolation to the pion pole. From these values we determined the s- and p-wave phase shifts δ03 and δ13 as a function of the effective mass of the K−π− system between threshold and 1.25 GeV/c2. The value of |δ03| is smaller than 17° for all mass values and the existence of a p-wave cannot be neglected. At mK−π− = 1.18 GeV/c2 there are two solutions for the phase shifts. On the average, the cross section of the K−π− elastic scattering over the region of the effective mass considered amounts to approximately 2.5 mb.

Backward production of a spin-parity 1+ Kϱ resonance at 1.28 GeV

Abstract A (Kππ)+ mass enhancement is observed in the reactions K−p → Ξ −Ko+π+πo− when events with a small (K− → Ξ−) four momentum transfer squared are selected. The signal is also visible in the reaction K−p → Ξ−π++ neutrals. The enhancement, centered at 1.28 GeV, is seen to decay preferentially into Kϱ with spin-parity JP = 1+. The cross section for K−p→ Ξ−C+(1.28) with C+ → Kϱ at 4.15 GeV/c incident K− momentum is (6.2 ± 0.6) μb.

Interference between Δ++ and Q− production in K−p → K−π−π+p at 4.25 GeV/c☆

Abstract Evidence is found for overlap and interference between Δ ++ and Q − production in K − p → K − π − π + p at 4.25 GeV/ c . The strong forward asymmetry observed in the Δ ++ decay is such that it cannot be explained by the contribution of p π + S- and P-waves only. It finds a natural interpretation in terms of overlap between Δ ++ ar Q − production. The interference between Δ ++ and Q − production is constructive over essentially the whole Δ ++ region.

Partial-wave analysis of the low-mass (π+π−p) system produced in K−p interactions at 4.2 GeV/c

Abstract A partial-wave analysis of the low-mass (π+π−p) system produced in the reaction K−p → K−(π+π−p) at 4.2 GeV/c incident momentum is performed in order to study the two (π+π−p) enhancements around 1500 and 1700 MeV. It is found that the low-mass (π+π−p) system can be described using the spin-parity states J P = 1 2 + , 3 2 − and 5 2 + only. In the 1500 MeV region contributions are observed from the 1 2 + wave decaying into pϵ and the 3 2 − wave decaying into Δ++π−; in the 1700 MeV region contributions are found from the 1 2 + wave decaying into Δ++π−, the 3 2 − wave decaying into pϵ, and the 5 2 + wave decaying into pϵ.

(2030) production in K−p reactions at 4.2 GeV/c

Abstract Significant production of (2030) is observed in the channel K − p → (Σ K − K + from a high statistics bubble chamber exposure at 4.2 GeV/ c . The mass and width are determined to be 2024 ± 2 MeV and 16 ± 5 MeV respectively. Apart from Σ K , the only other decay channel is found to be Λ K .