Search

The first measurement of the cross section of the quasifree $p\stackrel{\ensuremath{\rightarrow}}{n}\mathrm{pn}\ensuremath{\eta}$ reaction has been carried out at the CELSIUS storage ring using a deuterium internal cluster jet target. The energy dependence of the cross section is extracted using a fixed incident proton energy of ${T}_{p}=1350 \mathrm{MeV}$ and exploiting the Fermi momentum of the struck neutron. The data cover a range of center-of-mass excess energies from 16 to 109 MeV. The shape of the excitation function is broadly similar to that of the $p\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{pp}\ensuremath{\eta}$ reaction, though with a cross section about a factor of 6.5 larger.

The quasifree p + n --> d + eta reaction cross section has been measured at the threshold using 1295 MeV protons in the CELSIUS storage ring and an internal cluster-jet deuterium target. The kinematics is chosen such that the target proton can be assumed

The quasifree p+n{r_arrow}d+{eta} reaction cross section has been measured in the near-threshold region using deuterium from an internal cluster-jet target and 1350 MeV protons in the CELSIUS storage ring of the The Svedberg Laboratory, Uppsala. The energy dependence of the cross section is extracted by exploiting the Fermi momentum of the target neutron and reconstructing the kinematics on an event-by-event basis. The data cover center of mass excess energies from 16 to 113 MeV. {copyright} {ital 1997} {ital The American Physical Society}

A detector setup for the cooler storage ring CELSIUS is described. The setup detects particles produced in interactions between the internal beam and a cluster-jet target. Particles emitted in the forward direction are measured by means of arrays of plastic scintillators and proportional counters. Particles, particularly photons, emitted more isotropically are measured by means of two calorimeters containing CsI(Na) crystals. The performance of the setup is given for neutral meson production in proton-proton and proton-deuteron interactions in the energy range 290–1360 MeV.

The pd-->pdeta reaction has been studied in a kinematically complete experiment at five beam energies 927, 961, 996, 1032, and 1096 MeV. In contrast to our measurement of the pd-->(3)Heeta at the same energies, all the c.m. angular distributions are consistent with isotropy. The energy dependence of the total cross section seems to follow a three-body phase space as modified by a proton-deuteron final-state interaction, and such an extrapolation is consistent with other near-threshold data. The distributions of the pd and peta invariant mass at fixed beam energy are both close to those of phase space. However, this is not the case for the deta invariant mass, which shows significant structure in the first few MeV above threshold. This behavior is similar to that observed in the energy variation of the pn-->deta total cross section and is the sign of a large eta-deuteron scattering length that has been predicted in many theoretical models.

Exclusive measurements of the $p\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{pp}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ reaction have been carried out at ${T}_{p}=775\mathrm{MeV}$ at CELSIUS using the PROMICE/WASA setup. Together with data obtained at lower energy, they point to a dominance of the Roper excitation in this process. From the observed interference of its decay routes ${N}^{*}\ensuremath{\rightarrow}N\ensuremath{\sigma}$ and ${N}^{*}\ensuremath{\rightarrow}\ensuremath{\Delta}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\pi}}N\ensuremath{\sigma},$ their energy-dependent relative branching ratio is determined.

The CLAMSUD spectrometer has been recently installed at the jet-target position of the CELSIUS ring at “THE SVEDBERG LABORATORY.” The physical purpose is the study of kaon production at energies below the N-N threshold. Due to the low cross-section and short lifetime of kaons we increased the solid angle by means of two quadrupoles positioned at the entrance of the dipole. The experimental quality of the measurements due both to the beam characteristics and to the CLAMSUD detector will be shown.

A new type of compact pair spectrometer is developed for studies of radiative capture reactions and internal pair production at intermediate energies. The first results from capture reactions on 11B are presented together with theoretical predictions based on a continuum shell model calculation.

The neutron pickup reaction (p,d) has been studied at a proton energy of 800 MeV on targets of /sup 7/Li, /sup 12/C, /sup 13/C, /sup 16/O, /sup 25/Mg, /sup 28/Si, and /sup 40/Ca. States known to correspond to single-hole excitations are seen and in most cases the data are properly understood through distorted-wave Born approximation calculations. High-spin final states are prominent, and some are shown to be excited through multiple step processes. The strongest states seen in the data do not correspond to known levels.

We have measured the reactions $^{3,4}\mathrm{He}({\ensuremath{\pi}}^{\ensuremath{-}}, n)^{2,3}\mathrm{H}$ at ${T}_{\ensuremath{\pi}}=285, 428, 525, \mathrm{and} 575$ MeV over an angular range ${\ensuremath{\theta}}_{n}=18\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}134\ifmmode^\circ\else\textdegree\fi{}$ in the center-of-momentum frame, and the reaction $^{3}\mathrm{He}({\ensuremath{\pi}}^{\ensuremath{-}}, {\ensuremath{\pi}}^{0})^{3}\mathrm{H}$ at ${T}_{\ensuremath{\pi}}=285, 428, \mathrm{and} 525$ MeV over an angular range ${\ensuremath{\theta}}_{{\ensuremath{\pi}}^{0}}=60\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}140\ifmmode^\circ\else\textdegree\fi{}$. The pion absorption is found to proceed by a two-nucleon mechanism, with an energy dependence consistent with the formation of an $I=\frac{1}{2}$ resonance in the intermediate state. The pion single-charge exchange is discussed within the framework of the optical and Glauber models, and the dependence on the $^{3}\mathrm{He}$ electromagnetic form factors is discussed. We also examine the isospin dependence of the $\ensuremath{\pi}$-nuclear Hamiltonian.NUCLEAR REACTIONS $^{3,4}\mathrm{He}({\ensuremath{\pi}}^{\ensuremath{-}}, n)^{2,3}\mathrm{H}$, ${T}_{\ensuremath{\pi}}=285\ensuremath{-}575$ MeV, ${\ensuremath{\theta}}_{n}=18\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}134\ifmmode^\circ\else\textdegree\fi{}$; and $^{3}\mathrm{He}({\ensuremath{\pi}}^{\ensuremath{-}}, {\ensuremath{\pi}}^{0})^{3}\mathrm{H}$,, ${T}_{\ensuremath{\pi}}=285\ensuremath{-}525$ MeV, ${\ensuremath{\theta}}_{{\ensuremath{\pi}}^{0}}=60\ifmmode^\circ\else\textdegree\fi{}\ensuremath{-}140\ifmmode^\circ\else\textdegree\fi{}$; measured $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}$; discussed reaction mechanism, effects of form factors.

We have measured the cross section of /sup 3/He(..pi../sup -/,..pi../sup 0/)/sup 3/H at T = 285, 428, and 525 MeV for angles in the range of 60/sup 0/< or approx. =theta< or approx. =135/sup 0/ covering the momentum transfer range 0.5< or approx. =q< or approx. =1.0 GeV/c. Comparison is made with Glauber model calculations to discuss the sensitivity to nuclear structure and pion-nucleus interaction effects.

Angular distributions of the differential cross section and the analyzing power for the 9Be( p , π+)10Be and the 9Be( p , π−)10C reactions have been measured at 650 MeV. A phenomenological comparison, based on a model for pion emission from the target nucleus, is made between the analyzing power from the ( p , π) data and polarization data from πN scattering.

The (..pi../sup +/, p) reaction has been studied at T/sub ..pi../ = 90 and 180 MeV on /sup 12/C, and at T/sub ..pi../ = 90 and 170 MeV on /sup 13/C. The resolution was sufficient to resolve many single levels in the residual nuclei, and angular distributions were obtained between laboratory angles of 10/sup 0/ and 115/sup 0/. A comparison between the present (..pi.., p) data and existing high-energy (p,d) data in terms of a model assuming intermediate pion exchange in the (p,d) reaction indicates that the (..pi..,p) reaction is an important subprocess in the (p,d) reaction. The present data also suggest that pion rescattering is likely to be a fundamental part of the (..pi.., p) reaction mechanism.

The instrument described is intended for the detection and measurement of α particles from coherent interactions of high-energy particles with 4 He nuclei. It allows the determination of the magnitude and the direction of the momenta of the helium recoils from interactions in a pressurized gas target. The measurements are carried out with spark chambers and scintillation counters. Recoils emitted at angles greater than 65° with respect to the beam direction are accepted and the range of azimuth angles covered is 294°.

Asymmetries for elastic scattering of transversely polarised 800 MeV protons from Hydrogen in the coulomb interference region are presented and compared with the predictions of a recent phase shift analysis.