Coherency in neutrino-nucleus elastic scattering

Abstract

Neutrino-nucleus elastic scattering provides a unique laboratory to study the quantum mechanical coherency effects in electroweak interactions, towards which several experimental programs are being actively pursued. We report results of our quantitative studies on the transitions towards decoherency. A parameter (α) is identified to describe the degree of coherency, and its variations with incoming neutrino energy, detector threshold and target nucleus are studied. The ranges of α which can be probed with realistic neutrino experiments are derived, indicating complementarity between projects with different sources and targets. Uncertainties in nuclear physics and in α would constrain sensitivities in probing physics beyond the standard model. The maximum neutrino energies corresponding to α>0.95 are derived. PACS numbers: 13.15.+g, 21.10.Ft The elastic scattering of a neutrino with a nucleus [1,2] νA el :where A(Z, N ) denotes the atomic nucleus with its respective atomic, charge and neutron numbers, is a fundamental electroweak neutral current process in the Standard Model (SM) which has never been experimentally observed. It can provide a sensitive probe to physics beyond SM (BSM) [3,4] and plays an important role in astrophysical processes [1,5]. It offers prospects to study neutron density distributions [6], to detect supernova neutrinos [7] and to provide a compact and transportable neutrino detector for real-time monitoring of nuclear reactors [8]. The νA el events from solar and atmospheric neutrinos are the irreducible background [9] to forthcoming generation of dark matter experiments [10].There are active experimental programs to observe and measure the processes with neutrinos from reactors [11] or from decay-at-rest pions (DAR-π) [4] with a spallation neutron source [12]. The νA el reaction provides a unique laboratory to study the quantum mechanical coherency effects in electroweak interactions. At low momentum transfer, the de Broglie wavelength of the neutrinos is large compared with the nucleus, and the scattering amplitude of individual nucleons will coherently add to contribute to the cross-sections. Typically the neutrino energy (E ν ) and the measurable nuclear recoil kinetic energy (T ) are much less than the target nucleus mass (M ) in the discussion of coherency. The three-momentum transfer * Corresponding Author: htwong@phys.sinica.edu.tw (q ≡ | q|) is given by q 2 =2M T + T 2 2M T . Kinematics places constraints to the maximum recoil energy to beMeV is usually taken to characterize the requirement of coherency. The theme of this article is to quantify this transition − the first such investigation in the literature. We parametrize the degree of coherency and study its dependence on E ν , nuclear recoil detection threshold (T min ), and the nucleus A(Z, N ). Potential reaches of the up-coming experimental programs are derived.The differential cross-section of νA el scattering in SM is given by [2]:or, equivalently, in the experimental measurable T aswhere F Z (q 2 ) and F N (q 2 ) are, ...

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