On Coherent Neutrino and Antineutrino Scattering off Nuclei

Abstract

Neutrino-nucleus νA → νA and antineutrino-nucleusνA →νA interactions, when the nucleus conserves its integrity, are discussed with coherent (elastic) and incoherent (inelastic) scattering regimes taken into account. In the first regime the nucleus remains in the same quantum state after the scattering and the cross-section depends on the quadratic number of nucleons. In the second regime the nucleus changes its quantum state and the cross-section has an essentially linear dependence on the number of nucleons. The coherent and incoherent cross-sections are driven by a nuclear nucleon form-factor squared |F | 2 term and a (1−|F | 2 ) term, respectively. One has a smooth transition between the regimes of coherent and incoherent (anti)neutrino-nucleus scattering. Due to the neutral current nature these elastic and inelastic processes are indistinguishable if the nucleus recoil energy is only observed. One way to separate the coherent signal from the incoherent one is to register γ quanta from deexcitation of the nucleus excited during the incoherent scattering. Another way is to use a very low-energy threshold detector and collect data at very low recoil energies, where the incoherent scattering is vanishingly small. In particular, for 133 Cs and neutrino energies of 30-50 MeV the incoherent cross-section is about 15-20% of the coherent one. Therefore, the COHERENT experiment (with 133 Cs) has measured the coherent elastic neutrino nucleus scattering (CEνNS) with the inelastic admixture at a level of 15-20%, if the excitation γ quantum escapes its detection.After Freedman's paper [1] it was confirmed [2-5] that in the Standard Model the cross-section of elastic neutrino scattering off a nucleus is enhanced with respect to neutrino scattering off a single nucleon. The amplification factor for a spinless even-evenHere T A is the kinetic energy of the scattered nucleus, m A is the nucleus mass, q is the momentum transfer, G F is the Fermi constant, Z and N are the numbers of protons and neutrons, g p/n V are the proton/neutron couplings of the nucleon vector current, and F p/n (q) are the proton/neutron form-factors of the nucleus. The form-factors vanish as |q| → ∞ and approach unity (F p/n (q) = 1) if |q|R A 1, where R A is the radius of the nucleus. The coherency requirement reads as |q|R 1. Freedman used the termin "coherent neutrino-nucleus scattering" (CNNS) [1] to emphasize the fact that the dependence of the corresponding cross-section is quadratic in terms of the number of nucleons.The importance of the CNNS was demonstrated for a number of observables in astrophysics, like stellar collapse [13,14], and Supernovae [12,[15][16][17], in studies of physics beyond the Standard Model (SM) [3,11,[18][19][20][21][22][23][24][25][26][27][28], and in investigation of the nuclear structure [4,[29][30][31][32][33]. Due to the neutral-current nature an observation of ν-oscillations with CNNS could be evidence for sterile neutrino(s) [34,35]. Coherent scattering off atomic systems was studied in [36,37]. There are some expe...

Recent Probes of Standard and Non-standard Neutrino Physics With Nuclei

“…At low-and intermediate-energies, the neutrino being a key input to understand open issues in physics within and beyond the SM (see below), necessitated a generation of neutrino experiments for exploring neutrino scattering processes with nucleons and nuclei for both charged-current (inelastic) and neutral-current (coherent elastic and incoherent scattering) processes. Theoretically, the neutral-current neutrino-nucleus scattering we are interested here, is a well studied process for both coherent [61] an incoherent channels [62,63]. The accurate evaluation of the required transition matrix elements describing the various interaction channels of the electroweak processes between an initial and a final (many-body) nuclear state, is obtained on the basis of reliable nuclear wavefunctions.…”

On the Possibility of Separating Coherent and Incoherent (Anti)neutrino Scattering on Nuclei

“…The total cross section for (anti)neutrino scattering on a nuclear target [9,10] has the form of the sum of coherent and incoherent terms; that is,…”

“…Here, s = (p + k) 2 is the square of the total energy of the neutrino and nucleon, where k is the initiallepton 4-momentum and p is the effective scatteringnucleon 4-momentum obtained by solving the equation of energy-momentum conservation for the nucleus [9,10].…”

“…It turned out, however, that the data coming from the COHERENT experiment and underlying the statement that this experiment detected elastic coherent scattering of neutrinos on nuclei (CEνNS) do not meet the condition in (1) (see, for example, [9,10]); therefore, it would be illegitimate to associate these data unambiguously with a pure CEνNS process. In these data, there is a substantial contribution of inelastic (anti)neutrino-nucleus interactions, which, in no way, could be discriminated from CEνNS, since only the recoil energy of the nucleus was recorded in the experiment [9,10]. We can state that the experiment in question recorded events of neutrino interactions with nuclei in the channel of weak neutral currents at energies in the MeV region, and this is a highly important achievement in and of itself.…”

“…The potential of the COHERENT experiment can be aimed at studying in detail a dynamical transition between elastic and inelastic neutrino-nucleus interactions in the kinematical region of this experiment. On this path, it seems possible to detect experimentally (perform estimations of respective cross sections) coherent and inelastic [9,10] neutrino-nucleus interactions (CIνNS-abbreviation proposed by Yu. Efremenko) by measuring, for example, the flux of photons from the removal of nuclear excitations caused by this interaction.…”