Experimental studies on Electromagnetic Properties of Neutrinos with sub-Kev Germanium Detectors
Lakhwinder Singh1*, H. T. Wong1
1Institute of Physics, Academia Sinica, Taipei, Taiwan
* presenting author:Lakhwinder Singh, email:lakhwinder@phys.sinica.edu.tw
The experimental verification of the existence of a non-zero neutrino mass and mixing between different neutrino flavors has triggered intensive studies of non-trivial electromagnetic properties. The investigation of neutrino electromagnetic properties with neutrino-electron scattering at low energy regime naturally demands the detectors having low threshold, low background and high recoil electron energy resolution. Such requirements naturally lead us toward Point Contact high-pure Germanium (PCGe) detector which has excellent energy resolution and detection threshold down to 300 eV. As the kinematic parameter in neutrino-electron scattering like energy transfer starts to overlap with atomic scale, the proper treatment of the atomic effects in neutrino-electron scattering is necessary, but experimental measurement of the response of atomic systems to the neutrino scattering is still not known. Therefore, we have to rely on a pure theoretical analysis in interpreting the low energy neutrino-electron scattering data. To understand the detector’s response in low energy regime and in order to include the atomic effect, we have studied various different approaches: Free Electron Approximation (FEA), Equivalent-Photon Approximation (EPA), and ab-initio many body theory multi-configuration relativistic random phase approximation (MCRRPA). The MCRRPA enables us to reliably understand the germanium detector response at the sub-keV level [1]. The interaction cross sections induced by millicharged neutrinos are evaluated with MCRPA. There is significant enhancement at atomic binding energies compared to that when the electrons are taken as free particles [2, 3].

The current best direct limits on the neutrino millicharges and magnetic moments are both derived from data taken with germanium detectors with low thresholds at sub-keV levels [1, 2]. The best upper limit on charge radius squared is derived from data taken with 180 kg- CsI(Tl) scintillating crystal detector [4].

[1] Jiunn-Wei Chen et al., Physics Letters B 731, 159 (2014).
[2] Jiunn-Wei Chen et al., Phys. Rev. D 90, 011301(R) (2014).
[3] Jiunn-Wei Chen et al., arXiv: 1411.0574.
[4] M. Deniz et al. Phys. Rev. D 81, 072001 (2010).

Keywords: Electromagnetic properties of neutrino, MCRRPA