L.S. Barabash

Apparatus for the measurement of spin dependent observables in np and pp elastic and quasi-elastic scattering

Abstract The present article describes an apparatus used for the measurement of spin dependent observables at SATURNE II. Observables for np elastic and quasi-elastic scattering were measured between 0.31 and 1.1 GeV, those for pp elastic scattering between 1.94 and 2.24 GeV. Measurements of pn and pp observables with an unpolarized 6LiD and 7LiH targets around 2 GeV were also carried out. Fast electronics, on-line data acquisition, event selection and off-line analysis are presented.

Observation of a narrow structure in the pp elastic scattering observable Aoonn at Tkin=2.11 GeV

Abstract The angular dependece of the pp elastic scattering spin correlation parameter was measured in the angular range from 60° to 97° CM at 14 energies between 1.96 and 2.23 GeV. A rapid decrease of the energy dependence of this observable at 90° CM is observed around 2.11 GeV kinetic energy. This agrees with the behavior of A oonn predicted on the basis of an exotic six-quark structure. The A oonn (90° CM ), together with the known differential cross section, allows the determination of the absolute value of the pure spin-singlet amplitude. The energy dependence of this amplitude shows a shoulder centered at 2.11 GeV, corresponding to a total mass of 2.735 GeV and an estimated width of 17 MeV.

Angular dependence of the beam and target analyzing powers Aoono and Aooon in np elastic scattering between 0.477 and 0.940 GeV

Abstract We present a total of 273 independent data points of the analyzing powers A oono (nP) and A ooon (nP) in a large angular interval at four energies between 0.477 and 0.940 GeV. The SATURNE II polarized beam of free neutrons obtained from the break-up of polarized deuterons was scattered on the polarized Saclay frozen-spin proton target. Part of the data was obtained with a CH 2 target. A comparison of the two measured observables allows one to determine the polarization of the neutron beam. The present results provide an important contribution to any future theoretical or phenomenological analysis.

Angular dependence of the spin correlation parameter Aoonn in np elastic scattering between 0.8 and 1.1 GeV

Abstract We present a total of 323 data points of the spin correlation parameter A oonn (np) in a large angular interval at eight energies between 0.8 and 1.1 GeV. The SATURNE II polarized beam of free neutrons obtained from the break-up of polarized deuterons was scattered on the polarized Saclay frozen-spin proton target. The present data are the first existing results above 0.8 GeV.

Angular dependence of pp spin correlation and rescattering observables between 1.80 and 2.10 GeV

A polarized proton beam extracted from SATURNE II and the Saclay polarized proton target were used to determine the spin correlation parameter Aoosk and the rescattering observablesKos″ so; Dos″ok, Nos″sn, andNonsk at 1.80 and 2.10 GeV. The beam polarization was oriented perpendicular to the beam direction in the horizontal scattering plane and the target polarization was directed either along the vertical axis or longitudinally. Left-right and up-down asymmetries in the second scattering were measured. A check for the beam optimization with the beam and target polarizations oriented vertically provided other observables, of which results forDonon andKonno at 1.80, 1.85, 2.04, and 2.10 GeV are listed here. The new data at 2.10 GeV suggest a smooth energy dependence of spin triplet scattering amplitudes at fixed angles in the vicinity of this energy.

Measurements of the total cross section differenceΔσ Т innp transmission between 0.86 and 0.94 GeV

We present results of the total cross section differenceΔσТ obtained in transmission measurements at the energies 0.86, 0.88, 0.91 and 0.94 GeV. The SATURNE II polarized beam of free neutrons obtained from the break-up of polarized deuterons was transmitted through the polarized Saclay frozen-spin proton target. The beam and target polarizations were oriented in the vertical direction. The present results agree with previous SATURNE measurements and improve the amplitude analysis in the forward direction.

Measurements of the two and three spin-index observables inn p elastic scattering between 0.80 and 1.10 GeV

We present data of several rescattering observables measured inn p elastic scattering between 0.80 and 1.10 GeV. The SATURNE II polarized beam of free neutrons obtained from the break-up of polarized deuterons was scattered on the Saclay polarized frozen-spin proton target. Three different configurations of beam and target polarization directions were used: the observablesDonon andKonno were measured with the normal-normal spin configuration at eight energies;Nonkk,Dos″ok andKos″ko were determined with the longitudinal-longitudinal configuration at six energies;Nonsk,Dos″ok andKos″so with the sideway-longitudinal configuration at six energies. Part of the data was obtained with an unpolarized CH2 target where only the two spin-index polarization transfer parametersKos″ko andKos″so were determined. Data are compared with phase shift analyses predictions and with the LAMPF results at 0.788 GeV. Present results are the first measurements of rescattering observables above 0.80 GeV. They provide an important contribution to any future theoretical or phenomenological analysis.

Total cross sections, elastic scattering observables and direct reconstruction of scattering matrix in np Interactions between 0.8 and 1.1 GeV at SATURNE II

Neutron-proton total cross section differences with the beam and target polarizations orientated either transversally or longitudinally with respect to the beam direction, as well as 11 spin dependent elastic scattering observables measured at SATURNE II as a function of energy and angle are presented. A major part of results was measured using the quasimonoenergetic polarized neutron beam and/or the polarized proton target. A small part of data was obtained using a polarized deuteron beam considered as a beam of quasifree neutrons and protons. The present paper represents a review of measured observables. Several sets of present data are compared with results obtained in other laboratories below 0.8 GeV. Imaginary parts of spin dependent forward amplitudes for np scattering and for the isospin stateI=0 were determined. First direct reconstruction of the np scattering matrix at 0.84 GeV is shown.