The HLMA project: determination of high Δm2 LMA mixing parameters and constraint on |Ue3| with a new reactor neutrino experiment

Abstract

In the forthcoming months, the KamLAND experiment will probe the parameter space of the solar large mixing angle (LMA) MSW solution as the origin of the solar neutrino deficit withν e 's from distant nuclear reactors. If however the solution realized in nature is such that ∆m 2 sol > ∼ 2 · 10 −4 eV 2 (thereafter named the HLMA region), KamLAND will only observe a rate suppression but no spectral distortion and hence it will not have the optimal sensitivity to measure the mixing parameters. In this case, we propose a new medium baseline reactor experiment located at Heilbronn (Germany) to pin down the precise value of the solar mixing parameters. In this paper, we present the Heilbronn detector site, we calculate thē ν e interaction rate and the positron spectrum expected from the surrounding nuclear power plants. We also discuss the sensitivity of such an experiment to |U e3 | in both normal and inverted neutrino mass hierarchy scenarios. We then outline the detector design, estimate background signals induced by natural radioactivity as well as by insitu cosmic ray muon interaction, and discuss a strategy to detect the anti-neutrino signal 'free of background'.-1 -

Addendum: Neutrino mass hierarchy determination using reactor antineutrinos

“…The recently measured relatively large value of the angle θ 13 of the Pontecorvo, Maki, Nakagawa, Sakata (PMNS) neutrino mixing matrix in the Daya Bay [2] and RENO [3] experiments 3 opens up the possibility of the neutrino mass hierarchy determination in an experiment with reactorν e . This possibility was discussed first in [6] and later was further investigated in [7,8,9,10] (see also [11]). It is based on the observation that for cos 2θ 12 = 0 and sin θ 13 = 0, θ 12 being the solar neutrino mixing angle (see, e.g., [1]), the probabilities ofν e survival in the cases of NO (NH) and IO (IH) spectra differ [6,12]: P N H (ν e →ν e ) = P IH (ν e →ν e ), and |P N H (ν e →ν e ) − P IH (ν e →ν e )| ∝ sin 2 2θ 13 cos 2θ 12 .…”

Reactor as a source of antineutrinos: Thermal fission energy

“…The KamLAND Collaboration, which is recording antineutrinos at a distance of a few hundred kilometers from reactors, is able to determine the remaining two mixing-matrix elements U e1 and U e2 and to test the LMA MSW hypothesis of solar-neutrino oscillations [4]. In addition, it should be noted that a program of neutrino studies at the reactors on the Taiwan island is being developed [5] and that interesting proposals concerning searches for neutrino oscillations were put forth in Germany [6]. (More details on the motivation of those investigations, their status, and their prospects can be found, for example, in the review articles cited in [7].)…”

Precision neutrino oscillation physics with an intermediate baseline reactor neutrino experiment

“…The total number of expected events for the no oscillation case is given in Table I. We consider a single reactor plant with power of either 5 GW (achievable, e.g., at Heilbronn, Germany [31]) or 25 GW (achievable at Kashiwazaki, Japan), as the only relevant source of neutrinos, neglecting the possible contaminations due to other plants at larger distances. We also assume that the reactors have a 100% efficiency.…”

“…The bulk of this error comes from uncertainty in the overall flux normalization. The use of a near detector can improve this flux normalization error to as low as 0.8% [31]. The error on energy calibration could be taken as 0.5% [41].…”