P.M. Heinen

Production and decay properties of the δ (970) meson

Abstract Using an 880 events per microbarn sample of K − p interactions at 4.2 GeV/ c the production and decay properties of the δ (970) have been investigated in the following reactions: K − p → Σ + (1385) ηπ − and K − p ar Σ + (1385)K 0 K − .

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.

A partial-wave analysis of the 3π system in the reaction K−p → π+π−π0 Λ at 4.2 GeV/c

A partial-wave analysis of the (3π)0 system produced peripherally in the reaction K−p → π+π−π0 Λ at 4.2 GeV/c is presented. The observation of the weak Λ decay allows a determination of all the transversity production amplitudes except for two phases. The production of known resonances having decay modes other than 3π is used to test the isobar model ansatz. Significant ω(783), φ(1020) and A2(1310) production is observed. The spin parity of the ω∗(1675) is established as 3−. No evidence for production of other resonances, such as axial vector-mesons, is found.

The reactions K−p → O−12+ at an incoming momentum of 4.25 GeV/c☆

A bubble-chamber study is presented of a 10 events/μb experiment using K− mesons of 4.25 GeV/c incident momentum. Differential and total cross sections are determined for 7 different reactions: K−p → K0n (la), → π0Λ (lb), → ηΛ (lc), → η′Λ (ld), → π−Σ (le), → π+Σ− (lf), K+ Ξ− (lg). The experimental characteristics in dσ/dt of each reaction are described: (la) shows a levelling off at t = 0 (GeV/c)2, a break at t = −0.6 (GeV/c)2 and no backward events, (lb) dσ/dt has a smooth behaviour and a measurable backward component with an indication of a dip at u = −0.2 (GeV/c)2, (1c) dσ/dt shows a dip in the region between t ≈ −0.2 and −0.4 (GeV/c)2, (ld) dσ/dt has a smooth behaviour; neither this reaction nor the preceding one shows a clear evidence for backward events, (le) dσ/dt has a break at t = −0.5 (GeV/c)2; there is a significant cross section in the backward region; (lf) and (lg) show mainly backward production. The polarization of the hyperon is measured in the reactions (lb), (lc), (ld) and (le) in the forward production peak. The statistics do not allow the detection of a definite structure in the polarization but the sign and magnitude are determined. An interpretation of the results is given in terms of a dual Regge model, including the effects of absorption as elaborated recently by several authors.

Lambda production in the fragmentation processes p→K− and K− →p Λ at 4.25 GeV/c

Abstract In the reaction K − +p→ Λ +X at 4.25 GeV/ c both the target fragmentation of the proton into lambda and the beam fragmentation of kaon into lambda have been studied. The sample consists of 21 000 Λ events with t >−1.0 (GeV/ c ) 2 and 9000 Λ events with u > −1.0 (GeV/ c ) 2 . Abundant π 0 and meson resonance production for residual masses M x c 2 is observed. In the t -channel of am effective exchange trajectory is deduced. which lies between the K and K(890) trajectories. In the u -channel the effective exchange trajectory is in good agreement with a nucleon trajectory. The extrapolated average pion multiplicities of the residual mass system in the t -channel are in very good agreement with the values measured in antiproton-proton annihilations at rest.

INCLUSIVE CROSS SECTIONS OF MEDIUM-ENERGY KAON REACTIONS.

The characteristics of the neutral kaons produced in the reaction 4.2 GeV/c K− + p → Ko + anything are compared with data at other momenta. A survey is made of medium-energy inclusive cross sections obtained by postulating σT(K−p) = σ−(K−) + σ−(Ko) + σ−(Y). The inclusive cross sections σ−(K−) and σ−(Ko) are found to be constant as functions of the incoming kaon momentum. Moreover, a comparison with inclusive K+ production in the reaction K+ + p shows σ−(K−) ≈ σ+(K+) ≈ 11.7 mb.

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.

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.

Production of Σ(1660) in K−p interactions at 4.2 GeV/c

The reaction of K−p → Σ+(1660)π− was studied in a 65 event/μb sample of Σππ(π), Λππ(π) and pK0π− final states. The main production features observed are that the Σ(1660) decaying into Σππ is mostly Λ(1405)π and is produced only at small t; the Σ(1660) decaying into Σπ shows both forward and backward production. This confirms earlier results suggesting the existence of two Σ(1660) resonances. An Adair analysis and a (model-dependent) moments analysis find a J = 32 preference for the Σ+ (1660)→ Λ(1405)π+ → Σ+π−π+; a Dalitz-Miller analysis of the decay Σ+(1660) → Λ(1405)π+ → Σ−π+π+ determines JP to be 32−. For the Σ+(1660) → Σ0π+ a moments analysis suggests J = 32. Branching ratios are determined, which (with the exceptation of the Λ(1405)π mode) are in reasonable agreement with results from formation experiments for the JP = 32− Σ(1660) resonance. We compare our branching ratios with SU(3) and SU(6) predictions; the latter comparison suggests that, unless there is strong configuration mixing, Σ(1660) → Λ(1405)π, if 32−, cannot be a member of the (70, 1−) multiplet.