V. Sossi

Pion-induced pion production on deuterium: a quasifree process

Abstract A detailed experimental analysis of the π + d → π + π − pp in-plane coincidence data first presented by Rui et al. is compared to an expanded version of the Oset and Vicente-Vacas model for pion-induced pion production on a free nucleon. This extended model averages over Fermi motion to describe the assumed quasifree nature of the process occurring on the deuteron and includes nine additional diagrams to account for the N ∗ → N (ππ) p-wave reaction channels. Experimental effects such as pion energy loss in the target and in the detectors, pion decay and muon detection are investigated and incorporated into the comparison of experimental data and theory. Inclusion of Fermi motion was found to be essential to provide good agreement between data and model confirming the quasifree nature of the reaction. When compared to the total-cross-section measurements of Manley et al. , the free-reaction model yields a model-dependent estimate of the overall strength of the diagram containing the N ∗ → N (ππ) s-wave vertex.

The (π,2π) reaction on few body systems

Abstract A review of the (π,2π) reaction studies is presented in this paper, together with some very recent results from experiments performed at TRIUMF and at PSI. The comparison of the experimental results with the available models for the πN → ππN indicates that the (π,2π) reaction provides informations on the chiral symmetry breaking parameter, as well as on the pionic couplings g ΔΔπ and g NN ∗ ππ .

Vector analyzing power iT11 in pi d elastic scattering at 49 MeV

Measurements of the vector analyzing power {ital iT}{sub 11} in {pi}{ital d} elastic scattering at 49 MeV have been performed using a dynamically polarized target and a magnetic spectrometer. Data at seven {pi}{sup +} laboratory scattering angles between 50{degree} and 130{degree} were taken together with a complementary measurement at 60{degree} for {pi}{sup {minus}}{ital d} elastic scattering. In general, we find agreement with models that include the {pi}{ital N} P{sub 11} amplitude and disagreement with models that exclude or suppress it.

Vector analyzing power {ital iT}{sub 11} in {pi}{ital d} elastic scattering at 49 MeV

Measurements of the vector analyzing power {ital iT}{sub 11} in {pi}{ital d} elastic scattering at 49 MeV have been performed using a dynamically polarized target and a magnetic spectrometer. Data at seven {pi}{sup +} laboratory scattering angles between 50{degree} and 130{degree} were taken together with a complementary measurement at 60{degree} for {pi}{sup {minus}}{ital d} elastic scattering. In general, we find agreement with models that include the {pi}{ital N} P{sub 11} amplitude and disagreement with models that exclude or suppress it.

Multinucleon pion absorption in the He4(,ppp)n reaction

Three-proton emission cross sections for the {sup 4}He({pi}{sup +},{ital ppp}){ital n} reaction were measured at an incident pion kinetic energy of {ital T}{sub {pi}}{sup +}=165 MeV over a wide angular range in a kinematically complete experiment. Angular correlations, missing momentum distributions, and energy spectra are compared with three- and four-body phase-space Monte Carlo calculations. The results provide strong evidence that most of the three-proton coincidences result from three-nucleon absorption. From phase-space integration the total three-nucleon absorption cross section is estimated to be {sigma}{sup 3{ital N}}=4.8{plus minus}1.0 mb. The cross section involving four nucleons is small and is estimated to be {sigma}{sup 4{ital N}}{lt}2 mb. On the scale of the total absorption cross section in {sup 4}He, multinucleon pion absorption seems to represent only a small fraction.

Multinucleon pion absorption in theHe4(π+,ppp)nreaction

Three-proton emission cross sections for the {sup 4}He({pi}{sup +},{ital ppp}){ital n} reaction were measured at an incident pion kinetic energy of {ital T}{sub {pi}}{sup +}=165 MeV over a wide angular range in a kinematically complete experiment. Angular correlations, missing momentum distributions, and energy spectra are compared with three- and four-body phase-space Monte Carlo calculations. The results provide strong evidence that most of the three-proton coincidences result from three-nucleon absorption. From phase-space integration the total three-nucleon absorption cross section is estimated to be {sigma}{sup 3{ital N}}=4.8{plus minus}1.0 mb. The cross section involving four nucleons is small and is estimated to be {sigma}{sup 4{ital N}}{lt}2 mb. On the scale of the total absorption cross section in {sup 4}He, multinucleon pion absorption seems to represent only a small fraction.