R. Gilman

Systematics of pion double-charge-exchange reactions on T = 0 nuclei

Abstract Pion induced double charge exchange on 12 C, 16 O, 24 Mg, 28 Si, 32 S, and 40 Ca exhibits forward-angle cross sections that vary rapidly with pion energy and fall off roughly as A −4 3 . Angular distributions at 164 MeV appear diffractive for targets of 12 C, 16 O, and 40 Ca.

the Δ interaction contribution to double charge exchange

Abstract The Δ interaction mechanism and its contribution to the pion-induced double-charge exchange reaction to isobaric analogue states at energies around the resonance region is studied and is compared to the conventional mechanism which involves two sequential single-charge exchange steps. The Δ interaction mechanism is found to be very sensitive to the choice of form factors; it gives rise by itself to cross sections ranging from 5% of the results from the conventional mechanism to values comparable to the conventional mechanism. The amplitudes from the two processes are out of phase by approximately 90° near Tπ = 180 MeV and hence, there is little interference. In particular the minimum of the differential cross section at Tπ = 164 MeV is not changed by the inclusion of the Δ interaction mechanism.

The energy dependence of 18O(π+, π−)18Ne(gs)☆

Abstract Eight angular distributions measured for 18(π+, π−)18Ne(gs) across the Δ33 resonance show the details of the energy dependence of the reaction. At higher energies, the maximum is at q ≅ 0.85 fm−1, in agreement with simple sequential scattering models, but a lower energies it is at q ≅ 0.5 fm−1, with the transition occuring over a narrow energy range.

Two-amplitude model of pion DCX applied to the 18O angular distribution and excitation function☆

Abstract An earlier model developed to fit the DCX excitation function of 18O has been extended to account for the T π = 164 MeV 18 O DCX angular distribution in terms of that for 16O and a double-isobaric-analog transition.

Low-momentum delta production in the 13C(p, d)12C∗ reaction☆

Abstract Cross sections for the reaction 13 C(p, d) 12 C ∗ in coincidence with back-to-back, out-of-plane, two-proton decays at high excitation energies (140–420 MeV) are presented for E p = 800 MeV at deuteron laboratory angles of 2.5°, 5.0°, and 9.0°. At all angles a resonant-like enhancement in the cross section is observed at 241 MeV of excitation energy with a width of 55 MeV. Some features of these data indicate that this structure may be related to the formation of low-spin (ΔN −1 ) states in 12 C.

Pion scattering to 6- stretched states in Mg24 and Mg26

Inelastic {pi}{sup {plus minus}} cross-section measurements at pion incident energies of 150 and 180 MeV were made on 6{sup {minus}} states in {sup 24,26}Mg. In particular, we have determined the ({ital f}{sub 7/2}{ital d5/2}{sup {minus}1}){sub 6}{sup {minus}} isoscalar {ital Z}{sub 0}=0.21{plus minus}0.02 strength for the strongest {ital T}=0, {ital J} {sup {pi}}=6{sup {minus}} state located at 12.11{plus minus}0.05 MeV in {sup 24}Mg, and the isoscalar {ital Z}{sub 0}=0.17{plus minus}0.04 and isovector {ital Z}{sub 1}=0.21{plus minus}0.02 strength for the strongest {ital T}=1, {ital J} {sup {pi}}=6{sup {minus}} state located at 9.18 MeV in {sup 26}Mg. The distorted-wave impulse-approximation pion cross-section calculations required a multiplicative normalization factor of 1.2{plus minus}0.1 in order to reproduce the pure isovector strength deduced from electron scattering for the well-known {ital T}=1, {sup {pi}}=6{sup {minus}} state at 15.15 MeV in {sup 24}Mg and the {ital T}=2, {ital J} {sup {pi}}=6{sup {minus}} state at 18.05 MeV in {sup 26}Mg.

Pion scattering to 6 sup minus stretched states in sup 24 Mg and sup 26 Mg

Inelastic {pi}{sup {plus minus}} cross-section measurements at pion incident energies of 150 and 180 MeV were made on 6{sup {minus}} states in {sup 24,26}Mg. In particular, we have determined the ({ital f}{sub 7/2}{ital d5/2}{sup {minus}1}){sub 6}{sup {minus}} isoscalar {ital Z}{sub 0}=0.21{plus minus}0.02 strength for the strongest {ital T}=0, {ital J} {sup {pi}}=6{sup {minus}} state located at 12.11{plus minus}0.05 MeV in {sup 24}Mg, and the isoscalar {ital Z}{sub 0}=0.17{plus minus}0.04 and isovector {ital Z}{sub 1}=0.21{plus minus}0.02 strength for the strongest {ital T}=1, {ital J} {sup {pi}}=6{sup {minus}} state located at 9.18 MeV in {sup 26}Mg. The distorted-wave impulse-approximation pion cross-section calculations required a multiplicative normalization factor of 1.2{plus minus}0.1 in order to reproduce the pure isovector strength deduced from electron scattering for the well-known {ital T}=1, {sup {pi}}=6{sup {minus}} state at 15.15 MeV in {sup 24}Mg and the {ital T}=2, {ital J} {sup {pi}}=6{sup {minus}} state at 18.05 MeV in {sup 26}Mg.

The observation of energetic protons in coincidence with pion-induced double charge exchange on 12C and 48Ca

Abstract Angular distributions of recoil protons in coincidence with the scattered pions from the reaction ( π + , π − p) on targets of 12 C and 48 Ca are reported. The measurements were made at an incident pion energy of 250 MeV, for a scattered pion angle of 80° and energy of 139 MeV. The angular distribution of recoil protons is broader than expected from a model in which the reaction is assumed to proceed by two sequential pion charge-exchange scatterings from nucleous in a Fermi gas.

Resonances in C13(13C,)22Ne

Complete angular distributions (theta/sub c.m./ = 9/sup 0/--90/sup 0/) for the reaction /sup 13/C( /sup 13/C,..cap alpha..) /sup 22/ Ne in the energy range E/sub c.m./ = 6.25--13.38 MeV have been measured. The data exhibit significant resonancelike behavior and a portion of it has been fitted to extract the amplitudes and phases of the relevant l values with two methods. The first uses a least-squares procedure to fit the angular distributions to a linear sum of Legendre polynomials while the second makes a grid search to find a best fit to an amplitude squared equation.

Resonance with l>lgrIN12C+16O☆

Abstract In 12 C( 16 O, α) 24 Mg, an l =9 resonance is observed at a CM energy of 11.4 MeV — significantly lower in energy than one would have expected from grazing l -value considerations.