Artur M. Ankowski

Construction of spectral functions for medium-mass nuclei

This article is aimed at improving the description of lepton-nucleus interactions in the sub-GeV energy range. Approximate spectral functions for oxygen, calcium, and argon are constructed and used to obtain the electron cross sections in a given scattering angle. Comparison with a sample of available experimental data shows satisfactory agreement. Discrepancy between the presented model and the systematic computations available for oxygen [O. Benhar et al., Phys. Rev. D 72, 053005 (2005)] is also found to be very small. Analysis of appropriate kinematical regions leads to the conclusion that the obtained argon spectral function should describe well neutrino scattering in the 800-MeV energy region. Several approximations used in the model are critically reviewed. All the details needed to implement the presented approach in Monte Carlo simulations are given.

Argon spectral function and neutrino interactions

The argon spectral function is constructed and applied to neutrino-argon cross section computations in the plane wave impulse approximation with the Pauli blocking final state interaction effect taken into account. The approximations of the construction method are critically analyzed using the example of oxygen for which more detailed computations are available. An effective description of the nucleus based on the information contained in a spectral function is proposed. It is demonstrated that its predictions are close to those obtained from the complete spectral function. The effective description can be easily applied in Monte Carlo event generators.

Spectral functions for medium-sized nuclei

The spectral functions for calcium and argon are constructed. It is verified that their predictions for the quasielastic electron‐nucleus cross sections in the energy range ∼1 GeV agree with the data. The argon spectral function is then used to obtain the quasielastic neutrino‐nucleus cross section.

The γ‐ray production in neutral‐current neutrino‐oxygen interaction in the energy range above 100 MeV

We calculate the cross section of the γ‐ray production from neutral‐current neutrino‐oxygen quasi‐elasticinteraction, ν+16O→ν+p+15N*, or ν+16O→ν+n+15O*, in which the residual nuclei (15N* or 15O*) lead to the γ‐ray emission with Eγ>6 MeV at thebranching ratio of 41%. Above 200 MeV, this cross section dominates over that of γ‐ray production from the inelastic reaction, ν+16O→+16O*. In the present calculation, spectral function and the spectroscopic factors of 1p1/2, 1p3/2 and 1s1/2 states areessential. The γ‐ray production is dominated by the deexcitation of 1p3/2 state of the residual nucleus.

Spectral function of argon and calcium

Precise knowledge of the cross sections for neutrino interactions with nuclei is important not only for existing experiments but also for development of future detectors. When momentum transferred to the nucleus by the probe is high enough, the impulse approximation is valid, i.e. the nucleus can be described as composed of independent nucleons and the interaction happens between neutrino and a single bound nucleon. The cross section of the nucleus is then expressed as an integral of the free cross section (modified by the off-shell effect) folded with the so-called spectral function, describing the distribution of nucleon momenta and energies. I present results obtained for the approximate spectral functions of argon and calcium. The accuracy of the approach is verified by comparison with a broad spectrum of precise electronscattering data for the calcium target. Some of these data lie in the kinematical region corresponding to neutrino interactions what indirectly shows that a similar level of accuracy is achieved for neutrinos. The calculated Ar(νμ ,μ−) cross section is significantly lower than the one predicted within the Fermi gas model.