Study of Fermilab data for the reaction π− p→ηn

Fermilab data for the angular distribution measurements of the reaction ^– p n are investigated and it is shown that a good fit with experiment is obtained by using a simple Regge pole model with phenomenological residue functions. The energy dependence in this case is found to be different from that for the d/dt/ data obtained at Serpukhov.Work supported by the Pakistan Science Foundation under contract No. P-PU-PHY(11/1).     

On momentum dependence of the reaction π− p→ωn near threshold

We discuss the near–threshold behavior of the ω production amplitude in the reaction π⁻ p→ωn. In contrast to the results of earlier analyses we find that the averaged squared matrix element of the production amplitude must be a decreasing function of energy in order to describe the existing experimental data. Received: 11 August 1999     

Study of the reaction γp → pπ0η

The reaction γp → pπ⁰η has been studied with the CBELSA detector at the tagged photon beam of the Bonn electron stretcher facility. The reaction shows contributions from Δ⁺(1232)η , N(1535)⁺π⁰ and pa ₀(980) as intermediate states. A partial-wave analysis suggests that the reaction proceeds via formation of six Δ -resonances, Δ(1600)P ₃₃ , Δ(1920)P ₃₃ , Δ(1700)D ₃₃ , Δ(1940)D ₃₃ , Δ(1905)F ₃₅ , Δ(2360)D ₃₃ , and two nucleon resonances N(1880)P ₁₁ and N(2200)P ₁₃ , for which pole positions and decay branching ratios are given.     

Two-pion spectra for the reaction π− p → π0π0 n at a pion momentum of 38 GeV/c and combined analysis of GAMS, Crystal Barrel, and BNL data

We perform a K-matrix analysis of IJ ^PC =00⁺⁺, 10⁺⁺, 02⁺⁺, and 12⁺⁺ meson partial waves using GAMS data on π^? p → π⁰π⁰ n, ηηn, ηη'n that are supplemented with BNL data on π^? p → K $\bar K$ n and Crystal Barrel data on p $\bar p$ (at rest) → π⁰π⁰π⁰, π⁰ηη, π⁰π⁰η. The positions of the amplitude poles (physical resonances) are determined, together with the positions of the K-matrix poles (bare states) and the values of barestate couplings to two-meson channels. The nonet classification of the bare states found in the present analysis is discussed.     

Investigation of the reaction π − p → η′π 0 n at the VES spectrometer

Results obtained by investigating the reaction π ^? p → η′π ⁰ n at the VES spectrometer (Institute for High Energy Physics, Protvino) are presented. The effective-mass spectrum and angular distributions of η′π ⁰ events are compared with their counterparts for ηπ ⁰ and η′π ^? events selected from the same data sample. The ratio R of the branching fractions for the decays of a ₂ ⁰ (1320) mesons into η′π and ηπ is measured. The result is R=0.047±0.018, which agrees with the value measured previously for a ₂ ^? . An investigation of P-wave production in the η′π ⁰ and ηπ ⁰ systems over the effective-mass interval 1.45–1.9 GeV/c2 leads to the conclusion that the coupling of the exotic object π ₁ (1600) to the ρπ channel is suppressed in relation to its coupling to the η′π or the b ₁(1235)π channel.     

Measurement of the πmeson polarizabilities via the γp → γπ+n reaction

An experiment on the radiative ^{+}-meson photoproduction from the proton ( p ^{+}n) was carried out at the Mainz Microtron MAMI in the kinematic region 537MeV < E < 817MeV, 140^° 180^°. The ^{+}-meson polarizabilities have been determined from a comparison of the data with the predictions of two different theoretical models, the first one being based on an effective pole model with pseudoscalar coupling while the second one is based on diagrams describing both resonant and nonresonant contributions. The validity of the models has been verified by comparing the predictions with the present experimental data in the kinematic region where the pion polarizability contribution is negligible ( s₁ < 5m²) and where the difference between the predictions of the two models does not exceed 3%. In the region, where the pion polarizability contribution is substantial ( 5 < s₁/m² < 15, -12 < t/m² < - 2), the difference of the electric () and the magnetic () polarizabilities has been determined. As a result we find . This result is at variance with recent calculations in the framework of chiral perturbation theory.     

Description of initial-and final-state-interaction effects for the reaction γp → π−Δ++ in the region of nucleon-resonance excitation

A model has been developed for describing the cross section for the reaction γ_r,v p → π^?Δ⁺⁺ in the energy region of nucleon-resonance excitation, and relevant calculations have been performed. The model takes into account the contribution of all reliably established resonances with masses less than 2 GeV and the contributions of nonresonance mechanisms in the approximation of Born diagrams. On the basis of data on the amplitudes of pion-nucleon interactions, a method has been evolved for phenomenologically describing the coupling of initial and final states with open inelastic channels. Calculations performed in this study represent a first step in developing a method for determining the electromagnetic form factors for nucleon resonances in exclusive reactions of pion-pair production on a nucleon by real and virtual photons.     

Study of the K − → e − νπ 0 decay

The decay K ^? → e ^? νπ ⁰ has been studied using in-flight decays detected with the ISTRA₊ setup working at the 25-GeV negative secondary beam of the U-70 PS. About 130K events were used for the analysis. The λ ₊ parameter of the vector form factor has been measured: λ ₊=0.0293±0.0015(stat.)±0.002(syst.). The limits on the possible tensor and scalar couplings have been derived: f _T/f ₊(0)=?0.045±0.060(stat.) and f _S/f ₊(0)=?0.019 _?0.016 ^+0.025 (stat.).     

Study of theK + K − π+ π− system centrally produced in the reactions π+ p→π+(K + K − π+ π−)p andpp→p(K + K − π+ π−)p at 85 GeV/c

The reactions π⁺ p→π⁺(K ⁺ K ^? π⁺ π^? p andpp→p(K ⁺ K ^? π⁺ π^?)p where the (K ⁺ K ^? π⁺ π^?) system is centrally produced have been studied at 85 GeV/c. 48% of the final state proceeds through single or double vector meson resonant production i.e.,K ^*0(890) (37%), ? (4%),ρ ⁰ (7%). Evidence is found for associatedK ^*0 (890) \(\bar K\) ^*o (890) production (6.4±1.1%) with a cross section ten times higher than that found for associated ? ? production in the same experiment.     

Studies of the reactionπ − p→η ′ π 0 n at 38 and 100 GeV/c

The production of ⁰ system in ^– _p charge-exchange interactions at ^– momenta 38 GeV/c and 100 GeV/c has been studied. The 2 and ^{0 0} decay modes of leading to 4 and 8 final states respectively have been detected. No statistically significant peak is observed in the ⁰ mass spectrum in the range of 1.2 GeV÷2.1 GeV. An upper limit of 6·10^–3 has been established for thea ₂ ⁰ (1320) ⁰ branching ratio.     

TheK − d→pλπ− reaction

The (p) mass distribution is calculated for the reactionK ^– dp^– at rest and in flight at 700 MeV/c, for both BDI-1 and NRS-F potentials, with results which do not discriminate strongly between them. The in flight calculations can be brought into satisfactory agreement with experiment after some modification of the¯KNY amplitudes, but the at rest calculations show a strong disagreement with experiment which is not yet resolved, but which may partly reflect the experimental procedures adopted. The discrepancy with the earlier work reported by Dalitz, Hemming and Morris is accounted for, with the conclusion that further physics input may be needed to reach agreement with the data.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.     

Scaling in the mean of the p+p→π0+X inclusive reaction data and the energy dependence of Feynman variable

We have studied the p+p⁰+X inclusive reaction data of Carey et al. in the framework of the scaling in the mean hypothesis first proposed by Dao et al. These data have been used to obtain the gamma ray spectrum in terms of the average value of the Feynman variablex, written as x.A comparison with the observed gamma ray spectrum at Mt. Chacaltaya by the Japanese and Brazilian Group gives the energy dependence of x at very high energy.     

A study of the ϱ0 meson polarization in π− p reaction at 5 GeV/c

Experimental data on ⁰ meson polarization in ^– p reaction at 5 GeV/c are presented. Change in ⁰ meson polarization for mesons produced at smallP ² and atP ² 0·3 or produced in backward direction in CMS is demonstrated. Natural explanation of these phenomena is one pion exchange mechanism and mechanism of quark-antiquark annihilation as observed for ⁰ meson production in¯pp reactions.The authors are indebted to Ján Piút, Richard Lednický, V. S. Rumiancev and N. K. Koutsidi for discussions and critical comments.     

Observation of the leading K1 L-excitation series from JP = 1− through 5− in the reaction K− p → K− π+ n AT 11 GeV/c

High statistics data for the reaction K⁻p→K⁻π⁺n at 11 GeV/c have been obtained in the LASS spectrometer at SLAC. A spherical harmonic moments analysis provides clear evidence for the production of the complete leading orbitally excited K¹ series up through J^P = 5⁻. New measurements are made of the masses and widths of the 1⁻K¹(892), 2⁺K¹(1430 ), 3⁻ K¹(1780), and 4⁺ K¹(2060), and evidence is presented for the production of a new K¹ state at 2382 MeV/c² with spin-parity 5⁻.     

τ− → π−π0ντ decay in the extended NJL model

The width of the decay τ^? → π^?π⁰ν_τ was calculated in the extended NJL model. Contact interaction of W boson with a pion pair as well as the contribution of the ρ mesons in the ground and first radialexcited states are taken into account. The sum of the contact diagram and diagram with intermediate ρ meson in the ground state leads to the result which coincides with the result of the vector-dominance model. Our results are in satisfactory agreement with experimental data.