Incoherent neutrinoproduction of photons and pions in a chiral effective field theory for nuclei

Abstract

We study the incoherent neutrinoproduction of photons and pions with neutrino energy E ν 0.5 GeV. These processes are relevant to the background analysis in neutrino-oscillation experi- Rev. Lett. 100, 032301 (2008)]. The calculations are carried out using a Lorentz-covariant effective field theory (EFT) which contains nucleons, pions, the Delta (1232) (∆s), isoscalar scalar (σ) and vector (ω) fields, and isovector vector (ρ) fields, and has SU(2) L ⊗ SU(2) R chiral symmetry realized nonlinearly. The contributions of one-body currents are studied in the local fermi gas approximation. The current form factors are generated by meson dominance in the EFT Lagrangian. The conservation of the vector current and the partial conservation of the axial current are satisfied automatically, which is crucial for photon production. The ∆ dynamics in nuclei, as a key component in the study, are explored. Introduced ∆-meson couplings explain the ∆ spin-orbit (S-L) coupling in nuclei, and this leads to interesting constraints on the theory. Meanwhile a phenomenological approach is applied to parametrize the ∆ width. To benchmark our approximations, we calculate the differential cross sections for quasi-elastic scattering and incoherent electroproduction of pions without a final state interaction (FSI). The FSI can be ignored for photon production.

Low-energy photon production in neutrino neutral-current interactions

“…We have used m ω = (782.65± 0.12) MeV. The expression (15) holds for all a 1 charge states. The branching fractions in Table II are quite small because of the large a 1 total width.…”

“…This strengthens the conclusions of Refs. [9][10][11][12][13][14][15][17][18][19] that if the MiniBooNE signal is indeed found to be photons, the WZW anomaly is unlikely to be their dominant source.…”

“…Although neutral-current nucleon excitation followed by photon emission was originally suggested as a source of the signal, it was found insufficient as well in Refs. [14][15][16][17][18][19]. A comprehensive review of neutrino-induced quasielastic scattering and single photon production is given in a workshop summary [20].…”

Weak charged and neutral current induced one pion production off the nucleon

“…Indeed a theoretical calculation by Fogli and Nardulli [55,56] in an effective Lagrangian field theoretical model has shown that the inclusion of pion pole, nucleon pole, and other I = 1 2 resonance contribution leads to a better explanation of ANL [28], BNL [29] and CERN [57][58][59] data. In recent times, the need for inclusion of non-resonant and resonant (I = 1 2 channel) background terms to the dominant ∆(1232) contributions to explain the neutrino induced single pion production has been emphasized by many authors [53,[60][61][62][63] and numerical calculations have been performed to explain the present data. These calculations have been done either phenomenologically [61][62][63] or in an effective Lagrangian field theoretical model [53,60].…”

“…In recent times, the need for inclusion of non-resonant and resonant (I = 1 2 channel) background terms to the dominant ∆(1232) contributions to explain the neutrino induced single pion production has been emphasized by many authors [53,[60][61][62][63] and numerical calculations have been performed to explain the present data. These calculations have been done either phenomenologically [61][62][63] or in an effective Lagrangian field theoretical model [53,60]. However, there is no consensus on the treatment of background terms whether they should be added coherently or incoherently to the dominant ∆(1232) contribution.…”