摘要:

Differential cross sections are presented for eta production on the proton with photon beam energies of 725 and 750 MeV. Experiments of 20 years ago established the dominance of the S11(1535)N* resonance for higher photon energies. The purpose of this experiment was to investigate the coupling to other intermediate states in the H(&ggr;,&eegr;) reaction near threshold.

ISSN:0094-243X    

DOI:10.1063/1.40374

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

New, precise measurements of the differential cross sections fornp → d&pgr;0and &pgr;+d → ppand of analyzing powers forpp → d&pgr;+have been made at energies within 10 MeV (c.m.) of threshold. They allow the pion s‐wave and p‐wave parts of the production strength to be distinguished unambiguously, yielding an s‐wave strength at threshold which is signigicantly smaller than the previously accepted value. There is no evidence for Charge Independence Breaking nor for &pgr;NN resonances near threshold.

ISSN:0094-243X    

DOI:10.1063/1.40375

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The total cross section for the reaction p+p → p+p+&pgr;0was measured at nine center‐of‐mass energies from 1.5 MeV to 23 MeV above threshold. The experiment was carried out with the Indiana cooler, making use of the experimental advantages on a stored, electron‐cooled beam. Over most of the covered energy range only the lowest possible angular momentum state contributes to the exit channel. The energy dependence of the total cross section close to threshold is discussed.

ISSN:0094-243X    

DOI:10.1063/1.40376

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We present a brief overview of modernNN → &pgr;dandNN → NN&pgr; calculations. Our aim is to make a comparative study, emphasizing the relationship between a number of recent models. In view of current experimental interest, we complement this survey by discussing some results of aNN–&pgr; NNmodel for low energy pion production. We conclude by summarizing the present theoretical difficulties and discuss possible directions for the future.

ISSN:0094-243X    

DOI:10.1063/1.40378

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Production of the &eegr; meson near threshold has been studied with increased interest during the last 6–7 years. The present status of experimental investigation and theoretical understanding of &eegr; production by hadronic means in the threshold region is briefly reviewed.

ISSN:0094-243X    

DOI:10.1063/1.40379

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A sequential mechanism of meson production in proton–nucleus collisions leads to meson production at beam energies below the nucleon‐nucleon‐meson‐threshold. In a cascade‐like sequence, a light intermediate particle is created in first nucleon nucleon collision. In a second step, this intermediate particle produces a heavier outgoing meson by interacting with a second nucleon of the same target nucleus. If besides the light intermediate particle there is a deuteron produced in the first step, this can fuse with the nucleon N from the second step to form a bound final (3N) baryonic system. If thevelocities of the baryonsproduced in the two steps arematchedthen their relative energy is close to zero. Then the 3N fusion to one nucleus will be enhanced and the meson produced cross section for a two body channel should show a bump in the excitation function which has nothing to do with a resonance. Results of Monte‐Carlo simulations of this sequential reaction mechanism are shown.

ISSN:0094-243X    

DOI:10.1063/1.40356

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A number of physical phenomena related to reaction thresholds are discussed. Some history and some general remarks are included. The principal focus is on Coulomb‐bound systems, their formation in nuclear reactions, their structure, and their decay. Among the atom‐like systems considered are &pgr;A pionic atoms, Positronium, pionium (&pgr;+&pgr;−), and multipionic (N&pgr;A) atoms.

ISSN:0094-243X    

DOI:10.1063/1.40357

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The pp → pn&pgr;+reaction is one of the basic inelastic nucleon‐nucleon reactions, but it has been insufficiently explored near reaction threshold. The motivation for the experiment and the solutions chosen for the experimental difficulties are discussed.

ISSN:0094-243X    

DOI:10.1063/1.40358

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Results of full‐kinematics measurements of &pgr;−p → &pgr;−&pgr;+n, &pgr;−p → &pgr;−&pgr;0pand &pgr;+p → &pgr;+&pgr;+nin the threshold region are compared with current‐algebra calculations. Discrepancies can be largely attributed to isobar production, but even the threshold behavior is not adequately described by existing calculations.

ISSN:0094-243X    

DOI:10.1063/1.40383

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Cross sections for the reaction12C(p,&pgr;0)13Ng.s.have been measured at 153.5, 166.1, 186.0 and 204.0 MeV bombarding energy by detection of the13N recoil ions. The shapes of the differential cross section angular distributions agree well with those for the12C(p,&pgr;+)13Cg.s.reaction obtained by pion detection. The ratio of the (p,&pgr;+) to (p,&pgr;0) total cross section is close to two, as expected from isospin invariance, at 153.5, 186.0 and 204.0 MeV, but deviates significantly from this at 166.1 MeV bombarding energy. The (p,&pgr;+) and (p,&pgr;0) cross sections at the lower energies are both larger than expected from an extrapolation of the higher energy data.

ISSN:0094-243X    

DOI:10.1063/1.40359

出版商:AIP    

年代:1991

数据来源: AIP