Combining dark matter detectors and electron-capture sources to hunt for new physics in the neutrino sector
Pilar Coloma
0
1
2
Patrick Huber
0
1
2
Jonathan M. Link
0
1
2
Open Access
0
1
2
c The Authors.
0
1
2
0
850 West Campus Dr
,
Blacksburg, VA 24061
,
U.S.A
1
Center for Neutrino Physics, Physics Department
,
Virginia Tech
2
[20] C. Broggini, C. Giunti and A. Studenikin, Electromagnetic properties of neutrinos
In this letter we point out the possibility to study new physics in the neutrino sector using dark matter detectors based on liquid xenon. These are characterized by very good spatial resolution and extremely low thresholds for electron recoil energies. When combined with a radioactive e source, both features in combination allow for a very competitive sensitivity to neutrino magnetic moments and sterile neutrino oscillations. We find that, for realistic values of detector size and source strength, the bound on the neutrino magnetic moment can be improved by an order of magnitude with respect to the present value. Regarding sterile neutrino searches, we find that most of the gallium anomaly could be explored at the 95% confidence level just using shape information.
1 Introduction 2 3 4
Constraints on the neutrino magnetic moment
Sterile neutrino searches
Results for larger exposure
Summary and conclusions
Neutrinos have long been a rich hunting ground for physics beyond the Standard Model
(BSM). In fact, neutrino mass is so far the only BSM physics that has been established
in laboratory experiments. Astrophysical evidence of dark matter suggests the existence
of BSM particles, which have nevertheless not been observed yet. Among all feasible
candidates, weakly interacting massive particles (WIMPs) are theoretically rather appealing.
These may be observable through their interactions within detectors, as the earth moves
through the sea of WIMPs. This possibility has triggered a cornucopia of experimental
efforts of direct dark matter detection [1].
In this letter we examine the physics potential of combining a liquid xenon (LXe)
detector, designed to search for WIMP dark matter, with an intense electron-capture neutrinos
dark matter detectors has been proposed before in the literature, see for instance refs. [2
5]. Direct dark matter detection relies on observing nuclear recoils with electron-equivalent
tion cross section, large detector masses and low background levels are also required. A
LXe time projection chamber (TPC) can provide a large volume, low detection thresholds
(sub-keV) and a very low background rate at the energies of interest. At the same time
the electron density is higher in xenon than in any other stable noble gas, thus providing
the largest possible target density in any given volume near the source. The idea of using
never developed. As a by-product we also find non-negligible sensitivity to sterile neutrino
1 eV2 range suggested by recent terrestrial experiments [7].
When a nucleus decays via electron-capture almost all of the available energy goes into
a mono-energetic neutrino. Among possible nuclei which decay via electron-capture, 51Cr
offers several practical advantages: it is readily produced by thermal neutron capture [8],
has a mean lifetime of 39.96 days and produces two mono-energetic neutrino lines at 750 keV
(90%) and 430 keV (10%). Mega-curie-scale 51Cr sources have been produced in the past
and used to calibrate the gallium radiochemical solar neutrino detectors GALLEX [9, 10]
Constraints on the neutrino magnetic moment
increase in the number of events at low electron recoil energies. This makes two-phase
LXe TPCs [1217], with their low-energy detection threshold, ideal detectors for such a
. 3 1012B. The best constraint from terrestrial experiments, on the other hand,
has been obtained by the GEMMA experiment, < 2.9 1011B at 90% CL [19]. In
and references therein.
For our sensitivity estimate, we assume a data taking period of 100 days, using a
51Cr source with initial strength of 5 MCi. Our choice for the strength of the source is
based on simulations conducted for the SOX experiment [21] of the GALLEX enriched 50Cr
material [8] irradiated in the High Flux Isotope Reactor at Oak Ridge National Laboratory.
We consider a generic LXe detector, but for definiteness we chose a design similar to the
proposed LZ detector [17, 22]. We assume a cylindrical fiducial volume with equal diameter
source is placed 1 m below the fiducial volume, along the central axis of the cylinder.
Neutrinos are detected via electron elastic scattering in the detector, see eq. (2.1). Under
these assumptions, a total of 12, 518 signal events are expected for a 100 day run. Regarding
backgrounds, we have considered contributions from solar neutrino interactions, 222Rn and
is estimated to be 1.05 counts per ton and day for pp neutrinos and 0.51 counts per ton
and day for 7Be neutrinos. The 85Kr and 136Xe backgrounds have been taken directly
from figure 2 in ref. [23] and rescaled according to our run length and detector mass, while
reduction with respect to what has been achieved fo (...truncated)