Steven J. Greene

Ratios of elastic scattering of pions from H-3 and He-3

We have measured the elastic-scattering ratios of normalized yields for charged pions from 3H and 3He in the backward hemisphere. At 180 MeV, we completed the angular distribution begun with our earlier measurements, adding six data points in the angular range of 119 deg to 169 deg in the pi-nucleus center of mass. We also measured an excitation function with data points at 142, 180, 220, and 256 MeV incident pion energy at the largest achievable angle for each energy between 160 deg and 170 deg in the pi-nucleus center of mass. This excitation function corresponds to the energies of our forward-hemisphere studies. The data, taken as a whole, show an apparent role reversal of the two charge-symmetric ratios r1 and r2 in the backward hemisphere. Also, for data > 100 deg we observe a strong dependence on the four-momentum transfer squared (-t) for all of the ratios regardless of pion energy or scattering angle, and we find that the superratio R data match very well with calculations based on the forward-hemisphere data that predicts the value of the difference between the even-nucleon radii of 3H and 3He. Comparisons are also made with recent calculations incorporating different wave functions and double scattering models.

High precision floating wire measurements of large dipole magnets at LAMPF

The current-carrying, floating wire technique was used to measure the particle momentum versus magnetic field calibration of the EPICS pion spectrometer at LAMPF. Wire orbits were measured through a pair of dipoles bending through 120° in the vertical plane. Measurements were made in situ and corrected for gravitational and frictional effects. The specific manner of correcting for gravitational effects is given. Magnetic field versus particle momentum calibrations were derived with an accuracy of 2 parts in 104.

Nonanalog 0+(g.s.)→0+(g.s.) transitions in pion double charge exchange reactions on 128Te and 130Te

Abstract Small-angle (π + , π − cross sections for the 0 + (g.s.)→0 + (g.s.) transition in ββ-decay-allowed nuclei 128 Te and 130 Te were measured in the Δ 33 resonance region. The ratio of the cross section for 130 Te to that for 128 Te is 2.92±1.38 , in opposite trend to the currently accepted A −4 3 dependence of the nonanalog (π + , π − ) transitions. Possible consequences on the interpretation of geochemical ββ-decay half-life ratio are discussed.

Elastic and Inelastic Pion Scattering on 3H and 3He

Over a period of several years, the UCLA-GWU-ACU-LAMPF Collaboration has carried out an extensive and systematic program of pion-scattering measurements on the A = 3 nuclei. By means of these measurements, we have probed the matter distributions of nucleons in these few-body nuclei, particularly the neutron distribution in 3H (which cannot be accessed with electron scattering), and have investigated the extent to which charge symmetry is broken in the strong interaction.

A large-angle pion-nucleus scattering facility for EPICS at LAMPF

Abstract A facility has been constructed to extend the measurements of pion-nucleus scattering with the EPICS system at LAMPF into the angular range of 115 to 180°. The design of the system is described, and results of tests on it are given. Comparisons of measurements of elastic scattering cross sections with previous data are presented.

Elastic scattering of pions from 3H and 3He into the backwards hemisphere

We have measured differential cross sections for the elastic scattering of charged pions from 3H and 3He into the backward hemisphere. Near the peak of the delta resonance, at Tπ=180 MeV, an angular distribution covering 114° to 168° in the laboratory extends our earlier measurements. At Tπ=142, 180, 220, and 256 MeV, we have measured an excitation function at angles approaching 170°. The cross sections for the reactions 3He(π+,π+)3He and 3H(π−,π−)3H show a rise at back angles which is not seen for 3He(π−,π−)3He and 3H(π+,π+)3H. There is a dip in the cross sections near 130°, for Tπ=180 MeV. We also present the values of the charge symmetric ratios r1 and r2, which cross each other near 120° and maintain this new relationship in the backwards hemisphere.

Pion elastic scattering from polarized 13C in the energy region of the P33 resonance.

Analyzing powers [ital A][sub [ital y]] were measured for [pi][sup +] and [pi][sup [minus]] elastic scattering from polarized [sup 13]C at incident pion energies [ital T][sub [pi]] near the [ital P][sub 33] [pi]-nucleon resonance. At [ital T][sub [pi]]=130 MeV, the values of [ital A][sub [ital y]] are significantly different from zero for [pi][sup [minus]] scattering. For [pi][sup +] at [ital T][sub [pi]]=130 MeV and for both [pi][sup [minus]] and [pi][sup +] at all other energies, the [ital A][sub [ital y]] are mostly consistent with zero. Elastic differential cross sections were measured using an unpolarized [sup 13]C target. Both the analyzing-power and cross-section data were compared with predictions using a variety of nuclear structure and reaction models. The analyzing power was found to be strongly sensitive to the quadrupole spin-flip part of the transition. The data of this work complement measurements of the magnetic form factor by electron scattering. The pion [ital A][sub [ital y]] data are not reproduced by calculations using wave functions that fit the magnetic form factor at low momentum transfers.

Pion elastic scattering from polarized [sup 13]C in the energy region of the [ital P][sub 33] resonance

Analyzing powers [ital A][sub [ital y]] were measured for [pi][sup +] and [pi][sup [minus]] elastic scattering from polarized [sup 13]C at incident pion energies [ital T][sub [pi]] near the [ital P][sub 33] [pi]-nucleon resonance. At [ital T][sub [pi]]=130 MeV, the values of [ital A][sub [ital y]] are significantly different from zero for [pi][sup [minus]] scattering. For [pi][sup +] at [ital T][sub [pi]]=130 MeV and for both [pi][sup [minus]] and [pi][sup +] at all other energies, the [ital A][sub [ital y]] are mostly consistent with zero. Elastic differential cross sections were measured using an unpolarized [sup 13]C target. Both the analyzing-power and cross-section data were compared with predictions using a variety of nuclear structure and reaction models. The analyzing power was found to be strongly sensitive to the quadrupole spin-flip part of the transition. The data of this work complement measurements of the magnetic form factor by electron scattering. The pion [ital A][sub [ital y]] data are not reproduced by calculations using wave functions that fit the magnetic form factor at low momentum transfers.

ALL at small momentum transfers for the first complete determination of the forward pp scattering amplitudes

Abstract The asymmetry A LL for pp elastic scattering has been measured at 650 and 800 MeV in the region of Coulomb-nuclear interference. The real part of the double-spin-flip amplitude extracted from these data completes our determination of the forward pp scattering amplitudes at these energies. Comparison with the predictions of forward dispersion relations reveals a discrepancy in the spin-dependent channels at 650 MeV.

MEASUREMENT OF DELTA SIGMA-l AND C (L, L) = (L, L : 0, 0) N PROTON PROTON SCATTERING BETWEEN 300-MEV AND 800-MEV

Measurements are reported of the difference ..delta..sigma/sub L/ between proton-proton total cross sections for parallel and antiparallel spin states and of the parameter C/sub L/L for proton-proton elastic scattering near 90/sup 0/, for thirteen energies between 300 and 800 MeV. The ..delta..sigma/sub L/ results agree well with previous ANL ZGS and SIN data, but disagree with recent results from TRIUMF. Attempts to understand the cause of the discrepancy have been unsuccessful, but possible sources are discussed. The ..delta..sigma/sub L/ and C/sub L/L results have been used with other experimental data to extract quantities which depend only on spin-singlet, coupled spin-triplet, and spin-triplet partial waves. Structure is found in these quantities, which appears to be associated with the resonantlike /sup 1/D/sub 2/ and /sup 3/F/sub 3/ partial waves. Additional similar structure is also found, which may be due either to the /sup 3/P/sub 0/ partial wave or the (/sup 3/P/sub 2/, /sup 3/F/sub 2/) partial-wave pair.