Review of Neutrino Coherent Scattering Belkis Cabrera-Palmer March 20, 2009 Sandia National Laboratories Lawrence Livermore National Laboratory

Outline physics of neutrino coherent scattering cross section and rates NPP monitoring solar neutrino background

Neutrino Coherent Scattering ,k’  ,k Z R N, q It has never been observed!

Cross section Coherence applies when momentum transfer q <<   1/R(Germanium) ~ 38 MeV R, M, Z,N   T, 1/R(Argon) ~ 47 MeV  Cross section enhanced by N2 (N is # of neutrons) Same for all neutrino flavors Estimation of events for reactor neutrinos:

Challenges: small recoil energy and smaller ionization energy the nucleus recoil energy is for heavy nuclei, the recoil energy is in the few keVs: quenching: detectable ionization energy is just a fraction of the recoil energy I ~ hundreds of eV

Challenges: fewer reactor neutrinos at larger energies the cross section increases with neutrino energy: but …there are fewer reactor neutrinos at higher energies the detectable recoil energy threshold constraints the access to lower neutrino energies, since, to produce an event with energy I, the minimum neutrino energy is Germanium target

Reactor neutrino spectra 52% Uranium yields 65% more neutrinos with E>8MeV than Plutonium Neutrinos per MeV fission from Uranium and Plutonium From: Klapdor, Metzinger PLB 112,1 (1982) Estimation of Events per eV, day, kg(Ge) vs. the minimum neutrino energy E that produces recoils with Uranium fission produces 67% more events with I> 300eV than Plutonium fission 57%

Sensitivity to NPP fuel composition About 20% variation in total events during a Nuclear Power Plant fuel cycle ~20 %

Scale of a Coherent Scattering Detector Estimated number of counts/day kg above threshold with a Germanium Detector above threshold(eV) for Uranium fraction 80% for Uranium fraction 50% Kgs for 3-signal (no bkgnd) in 15 days 300 2.6 2.2 12 200 8.3 7.1 3 100 35.9 31.3 1 A 100eV-improvement in detector threshold produces a large reduction in detector size.

Comparison to solar neutrino background Estimated counts/day kg above threshold with Germanium above threshold (eV) from reactor (U80%, R=20meters) from solar neutrinos Equivalent radius (Km) 300 2.6 3.7e-4 1.7 200 8.3 5.6e-4 2.5 100 35.9 8.4e-4 4.1 The solar neutrino background is comparable with the reactor neutrino signal at distances >1.5 km from the reactor core. The solar background prevents or at least greatly complicates using coherent scatter detectors as standoff reactor monitors beyond a kilometer or so. Detector

Conclusions Neutrino Coherent Scattering … is hard to detect since the detectable fraction of the released energy is less than few hundreds of eV, requires detector with very low noise threshold, can be used for NPP monitoring since it is sensitive to fuel composition.

Muito obrigada.