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

Abstract

Purpose: Study coherent productions with Eν 0.5 GeV. Also address the contributions of two contact terms in Neutral Current (NC) photon production that are partially related to the proposed anomalous ω(ρ), Z boson and photon interactions. Methods: We work in the framework of 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 incorporates a nonlinear realization of (approximate) SU(2) L ⊗ SU(2) R chiral symmetry. A revised version of the so-called "optimal approximation" is applied, where one-nucleon interaction amplitude is factorized out and the medium-modifications and pion wave function distortion are included. The calculation is tested against the coherent pion photoproduction data. Results: The computation shows an agreement with the pion photoproduction data, although precisely determining the ∆ modification is entangled with one mentioned contact term. The uncertainty in the ∆ modification leads to uncertainties in both pion and photon neutrinoproductions. In addition, the contact term plays a significant role in NC photon production. Conclusions: First, the contact term increases NC photon production by ∼ 10% assuming a resonable range of the contact coupling, which however seems not significant enough to explain the MiniBooNE excess. A high energy computation is needed to gain a firm conclusion and will be presented elsewhere. Second, the behavior of coherent neutrinoproductions computed here is significantly different from the expectation at high energy by ignoring the vector current contribution.

Progress and open questions in the physics of neutrino cross sections at intermediate energies

“…The πEx terms vanish exactly for isospin symmetric nuclei because amplitudes for protons and neutrons cancel with each other. The results from the Δ Δ + + + P C P NP CNP part of the model of [237,258] are within the uncertainty band of those in [238] up to (anti) neutrino energies of 1.4-1.5 GeV.…”

“…Finally we briefly review other approaches. The model of [258] starts from Lorentzcovariant effective field theories with nucleon, pion, Δ (1232) but also scalar (σ) and vector (ρ, ω) mesons as the relevant degrees of freedom, and exhibit a nonlinear realization of (approximate) ⊗ SU SU (2) (2) L R chiral symmetry. This is the same scheme as that employed in [189] for the neutrino-production of pions from nucleons.…”

“…The nucleus is treated as a scalar particle, including a nuclear form factor to ensure that the coherence is restricted to low-momentum transfers. The microscopical approaches of [258] and [238] are more robust and rely on the same formalism and approximations used to study COH π processes [211,258]. In [238], the NCγ model on the nucleon is directly applied by summing the different amplitudes coherently.…”

Recent advances and open questions in neutrino-induced quasi-elastic scattering and single photon production

“…They largely focused on extension of their previous work [110][111][112] to higher neutrino energies. This approach is very different from that employed by the Valencia group in that it has nucleons and ∆ resonances moving in relativistic mean fields with strong vector and scalar potentials.…”

Modeling neutrino-induced charged pion production on water at T2K kinematics

“…The CC1π + signal in this energy region mostly consists of elementary single-pion production through the decay of the delta resonance. The delta region is the main focus of most models describing SPP [10][11][12][13][14][15][16][17][18][19][20][21][22]. Most models that aim at describing the low energy resonance region tend to exhibit problematic behavior when they are extended to large values of invariant mass (W 1.4 GeV) because only first-order diagrams are taken into account [23].…”