Add CEvNS cross section option to IBD/ES tab

[stdye]

Coherent elastic neutrino-nucleus scattering (CEvNS) is a long predicted but recently observed interaction. Although the cross section is relatively large-

sigma_scat_hart.pdf

the recoil energy of the struck nucleus is very small-

coherent_recoil.pdf

There are practical applications for CEvNS- (e.g. spent nuclear fuel monitoring- https://arxiv.org/abs/2111.15398)

CEvNS is a background for dark matter searches- (e.g. https://indico.fnal.gov/event/44988/contributions/198368/attachments/135388/167898/20201001_COHERENTDM.pdf)

Let's add this to the web app!

[stdye]

Reactor antineutrinos from Dresden-II observed using CEvNS on 3-kg of germanium nuclei- https://arxiv.org/abs/2202.09672

The distance from the center of the detector to the center of the core is 10.4 m. Larger detectors deployed at deeper sites will accommodate longer standoff distances (e.g. the same rate at ~100 m takes ~300 kg of germanium target)

[stdye]

Implementation requires UI for selecting target nucleus- .../src/elements/elements.json

The cross section goes like the square of the weak nuclear charge, Q_w = (Z(4sin^2(theta_w) - 1)+N) for N neutrons and Z protons, hence the need for the UI

CEvNS kinematics are identical to ES, both are 2-body elastic scattering, so some existing equations for ES can be used by substituting the electron mass with the mass of the selected nucleus

[stdye]

The user-community at the Applied Antineutrino Physics 2023 workshop at York, UK expressed interest in seeing this implemented. CEvNS is already in the code on the SnNu tab. Are there any impediments preventing this? If so, what are they?

[stdye]

How about adding a CEvNS event calculator, basically cloning the one on the SnNu tab, to the GeoNu and Reactor tabs instead of the pIBD/eES tab?