M.J. Vicente-Vacas

Computer simulation of inclusive pion nuclear reactions

Abstract We carry out a simultaneous calculation of all inclusive reactions in pion-nucleus scattering in the range T π = 85–350 MeV. The channels considered are, quasielastic, single charge exchange, double charge exchange and absorption. The method combines a microscopic calculation of the intrinsic probabilities for each reaction as a function of the nuclear density, followed by a computer simulation procedure in order to trace the fate of the pions through the different channels. Double, single and integrated differential cross sections for quasielastic and charge exchange reactions, as well as absorption cross sections are calculated. The agreement with experimental data for the different reactions, energies and nuclei is rather remarkable with some limitations enforced by the approximations used.

Chiral non-perturbative approach to the isoscalar s-wave ππ interaction in a nuclear medium

Abstract The s-wave isoscalar amplitude for ππ scattering in a nuclear medium is evaluated using a non-perturbative unitary coupled channels method and the standard chiral Lagrangians. The method has proved successful to describe the ππ properties in the scalar-isoscalar channel up to 1.2 GeV, giving rise to poles in the t matrix for the f0(980) and the σ. The extension of the method to the nuclear medium implies not only the renormalization of the pions in the medium, but also the introduction of interaction terms related to contact terms in the πN → ππN interaction. Off-shell effects are also shown to be important leading to cancellations which reduce the coupled channel integral equations to a set of algebraic equations. As the density increases we find a reduction of strength below the σ region and a certain accumulation of strength at energies around pion threshold. Our results, based on chiral Lagrangians, provide similar results to those obtained with phenomenological models which impose minimal chiral constraints.

Nuclear effects in neutrino production of Δ at intermediate energies

Abstract The neutrino production of Δ in 16 O has been studied at intermediate energies relevant to atmospheric neutrino experiments. The Δ production cross sections with electrons or muons in the final state is found to be reduced due to nuclear effects. This reduction is even larger for the accompanying one pion production cross sections. The ratio of electron to muon production cross sections, however, does not show any significant dependence on nuclear medium effects.

Erratum: Neutron and proton spectra from the decay ofΛhypernuclei [Phys. Rev. C55, 735 (1997)]

An error in the computer program which evaluated nucleon spectra following the decay of

Projectile delta excitation in alpha-proton scattering

\Lambda

Coherent pion production in the (3He,t) reaction in nuclei

hypernuclei has been detected. The error affected the final state interaction (FSI) of the nucleons, reducing by a factor ten the nucleon-nucleon (NN) collision probability. When correcting the error, some results and conclusions of Ref. [1] have changed substantially.

Pion production by pions in the 16O(π+,π+π−) reaction at Tπ+ = 280 MeV

Abstract The (α, α′) reaction in the Δ-region is a clear example of projectile delta excitation. We study the reaction theoretically and compare the results to a recent experiment. The agreement is rather good. On the other hand the reaction offers a test for models of coherent pion production. Finally, the use of the present model should provide the appropriate background to extract the excitation strength of the Roper resonance observed in the same reaction.

Coherent pion production induced by protons and light ions

Abstract We have evaluated the cross section for coherent pion production in the 3 He + 12 C → t + 12 C + π + reaction. The Δ peak of the energy distribution is considerably shifted with respect to the peak in the p( 3 He ,t)Δ ++ reaction. The coherent pions represent a sizable fraction of all pions produced and are a major ingredient in the interpretation of the shift of the Δ peak in the inclusive ( 3 He,t ) reaction in nuclei. The coherent production process qualifies as production of virtual pions followed by elastic scattering of the virtual pions with the nucleus and the investigation of this channel will offer information about pion nucleus interaction complementary to the one obtained from scattering of real pions.

Coherent π0 electroproduction

The results of an experiment of pion-induced pion production on 16O at a laboratory energy of 280 MeV are reported. The four-fold-differential cross section, d4σdΩπ+dΩπ+dEπ+dEπ, was measured, and the missing mass, Mx, for the reaction 16Ofs(π+,π+π−) at laboratory angles of 50°, 80° and 115° for the π−, and from 22° to 128° for the π+ was deduced. The angular and energy distributions of the many-fold differential cross sections are compared with an A(π+,π+π−) model for the reaction. The observed cross sections are reproduced in magnitude and shape when the theoretical calculations consider a proper pion dispersion relation, \gw(q), inside the nuclear medium. The total cross section, deduced by integrating the four-fold differential cross sections, is compared with the available theoretical predictions for the 16O(π+, π+π−) reaction.

Double pion photoproduction in nuclei

Abstract We study coherent pion production by means of the (p,n) and (He,t) reactions on different nuclei and at different energies of the projectile. Energy and angular distributions are calculated. The angular distributions are rather narrow along the direction of the momentum transfer, particularly in heavy nuclei. The reaction is sensitive to the longitudinal part of the elementary NN→NΔ interaction. It also provides a new tool to obtain information on the pion-nuclear interaction, complementary to that offered by reactions with real pions.