Proposal for an Electron Antineutrino Disappearance Search Using High-RateLi8Production and Decay

Abstract

This paper introduces an experimental probe of the sterile neutrino with a novel, high-intensity source of electron antineutrinos from the production and subsequent decay of 8 Li. When paired with an existing ∼1 kton scintillator-based detector, this Eν =6.4 MeV source opens a wide range of possible searches for beyond standard model physics via studies of the inverse beta decay interaction νe + p → e + + n. In particular, the experimental design described here has unprecedented sensitivity toνe disappearance at ∆m 2 ∼ 1 eV 2 and features the ability to distinguish between the existence of zero, one, and two sterile neutrinos.PACS numbers: 14.60.Pq, 14.60.StThe beta decay-at-rest of 8 Li produces an isotropic electron antineutrino flux with an average energy of 6.4 MeV. An underground liquid scintillator based detector can be used to detect these antineutrinos via the inverse beta decay (IBD) processν e + p → e + + n. The antineutrino rate and energy, peaking at 9 MeV, can be fully reconstructed by the detector. Precise energy and vertex reconstruction opens the possibility of searching for antineutrino disappearance due to oscillations, which, in the simplest two-neutrino form, has the probabilitywhere θ is the disappearance mixing angle; ∆m 2 (eV 2 ) is the squared mass splitting; L is the distance (in meters) from the antineutrino source to the detector; and E (MeV) is the antineutrino energy. This probability is maximized in the range of ∆m 2 ∼ E/L. An existing large scintillator-based antineutrino detector with a diameter of O(10 m), when combined with an 8 Li isotope decay-at-rest source, is sensitive to oscillations at ∆m 2 ∼ 1 eV 2 . This is an oscillation region of high interest due to anomalies that have been observed in the data from LSND [1], MiniBooNE [2], short-baseline reactor studies [3], and gallium source calibration runs [4]. These anomalies are often interpreted as being due to sterile neutrinos [5][6][7][8] and have motivated the development of the IsoDAR (Isotope Decay-At-Rest) concept.IsoDAR-style sources have been considered before [9][10][11]. The design presented here, consisting of an ion source, cyclotron, and target, is the first with a sufficiently high antineutrino flux to address the existence of one or more sterile neutrinos. 5 IBD interactions in a five year run. Such events allow a definitive search for antineutrino oscillations with the added ability to distinguish between models with one and two sterile neutrinos. A sample of more than 7200ν e -electron scatters is also accumulated during this time and can be used as a sensitive electroweak probe.The charged particle beam, used for electron antineutrino production, originates with a 60 MeV/amu cyclotron accelerating 5 mA of H + 2 ions. The design of this compact cyclotron [15] is ongoing and is envisaged as the injector for the accelerator system of the DAEδALUS physics program [16,17]. The IsoDAR design calls for about a factor of six increase in intensity compared to compact cyclotrons used in the medical isotope industry. ...

Neutrino physics with accelerator driven subcritical reactors

“…Note that, since the 8 Li spectrum is independent of the beam and target station parameters, for any deuterium beam energy and current and any target configuration, one may obtain 5 × 10 23 such decays for an experiment of some duration. Therefore, given any…”

“…As has been stressed in ref. [8], a deuterium beam is advantageous in that it directly brings neutrons to the target, which are liberated via proton stripping and deuterium breakup. The deuterium breakup fast neutrons have energies peaked around half of the deuterium beam energy and so they must travel a long distance before slowing enough to have a high interaction cross section with 7 Li.…”

“…These neutrons are moderated and multiplied by heavy water moderator and then absorbed by 99.99% isotopically pure 7 Li, producing 8 Li. The eventual β decay of the 8 Li produces our ν e with an energy spectrum peaked at 6 MeV but extending up to 13 MeV. These ν e travel isotropically and are eventually detected via the inverse beta decay reaction…”

“…[7,8], we use the 100 MeV/nucleon deuterium beam to knock neutrons out of 9 Be. These neutrons are moderated and multiplied by heavy water moderator and then absorbed by 99.99% isotopically pure 7 Li, producing 8 Li.…”

“…[7,8], we use the 100 MeV/nucleon deuterium beam to knock neutrons out of 9 Be. These neutrons are moderated and multiplied by heavy water moderator and then absorbed by 99.99% isotopically pure 7 Li, producing 8 Li. The eventual β decay of the 8 Li produces our ν e with an energy spectrum peaked at 6 MeV but extending up to 13 MeV.…”