Measuring θ 12 despite an uncertain reactor neutrino spectrum

Abstract

The recently discovered 5 MeV bump highlights that the uncertainty in the reactor neutrino spectrum is far greater than some theoretical estimates. Medium baseline reactor neutrino experiments will deliver by far the most precise ever measurements of θ 12 . However, as a result of the bump, such a determination of θ 12 using the theoretical specrum would yield a value of sin 2 (2θ 12 ) which is more than 1% higher than the true value. We show that by using recent measurements of the reactor neutrino spectrum the precision of a measurement of θ 12 at a medium baseline reactor neutrino experiment can be improved appreciably. We estimate this precision as a function of the 9 Li spallation background veto efficiency and dead time.

Vetoing cosmogenic muons in a large liquid scintillator

“…The second instead requires a measurement of the depth of the solar oscillation maximum, a broad feature which extends across the spectrum visible at these experiments. This feature includes essentially all of the events in the sample, and so it will be measured extremely precisely at these experiments, with an uncertainty which is dominated by a systematic uncertainty in the reactor neutrino spectrum [26].…”

“…This motivates us to use the more recent determination of σ(sin 2 (2θ 12 )) from Ref. [26], shown in Fig. 14, which uses the observational uncertainty on the reactor neutrino flux from Daya Bay [17].…”

“…Of course, if we included the uncertainty in the detector's energy response then then the systematic errors would play a more Figure 14: The 1σ uncertainty with which sin 2 (2θ 12 ) can be measured at JUNO in 6 years with a fraction t l of live time and 9 Li rejection efficiency E c , from Ref. [26]. For the curves from bottom to top the fractions t l are 1.0, 0.9, 0.8, 0.7, 0.6 and 0.5.…”