Absence of a day-night asymmetry in the 7Be solar neutrino rate in Borexino
Physics Letters B, Volume 707, Issue 1, 16 January 2012, Pages 22-26 – ISSN 0370-2693
(Submitted 18 October 2011,
Revised 10 November 2011,
Accepted 13 November 2011,
Available online 25 November 2011)
[doi:10.1016/j.physletb.2011.11.025] (preprint on arXiv)
This work is dedicated to the memory of our friend Raju Raghavan, one of the fathers of this experiment, and a great scientist.
We report the result of a search for a day-night asymmetry in the 7Be solar neutrino interaction rate in the Borexino detector at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. The measured asymmetry is A dn = 0.001 ± 0.012 (stat) ± 0.007 (syst), in agreement with the prediction of MSW-LMA solution for neutrino oscillations. This result disfavors MSW oscillations with mixing parameters in the LOW region at more than 8.5σ. This region is, for the first time, strongly disfavored without the use of reactor anti-neutrino data and therefore the assumption of CPT symmetry. The result can also be used to constrain some neutrino oscillation scenarios involving new physics.