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This report constitutes the roadmap document prepared by the Double Beta Decay APPEC Committee for the APPEC SAC on the future neutrinoless double beta decay experimental programme in Europe. It reviews the existing, planned and proposed technologies for neutrinoless double beta decay, their discovery potential and technical challenges, making a critical examination of resources and schedules. It also provides a concise discussion of the theoretical issues and of the status and uncertainties on the nuclear matrix element evaluation.
This Report provides an extensive review of the experimental programme of direct detection searches of particle dark matter. It focuses mostly on European efforts, both current and planned, but does it within a broader context of a worldwide activity in the field. It aims at identifying the virtues, opportunities and challenges associated with the different experimental approaches and search techniques. It presents scientific and technological synergies, both existing and emerging, with some other areas of particle physics, notably collider and neutrino programmes, and beyond. It addresses the issue of infrastructure in light of the growing needs and challenges of the different experimental searches. Finally, the Report makes a number of recommendations from the perspective of a long-term future of the field. They are introduced, along with some justification, in the opening Overview and Recommendations section and are next summarised at the end of the Report. Overall, we recommend that the direct search for dark matter particle interactions with a detector target should be given top priority in astroparticle physics, and in all particle physics, and beyond, as a positive measurement will provide the most unambiguous confirmation of the particle nature of dark matter in the Universe.
We propose a novel detection concept for neutrinoless double-beta decay searches. This concept is based on a Time Projection Chamber (TPC) filled with high-pressure gaseous xenon, and with separated-function capabilities for calorimetry and tracking. Thanks to its excellent energy resolution, together with its powerful background rejection provided by the distinct double-beta decay topological signature, the design discussed in this Letter Of Intent promises to be competitive and possibly out-perform existing proposals for next-generation neutrinoless double-beta decay experiments. We discuss the detection principles, design specifications, physics potential and R&D plans to construct a detector with 100 kg fiducial mass in the double-beta decay emitting isotope Xe(136), to be installed in the Canfranc Underground Laboratory.
The NEMO-3 experiment at the Modane Underground Laboratory has investigated the double-$beta$ decay of $^{48}{rm Ca}$. Using $5.25$ yr of data recorded with a $6.99,{rm g}$ sample of $^{48}{rm Ca}$, approximately $150$ double-$beta$ decay candidate events have been selected with a signal-to-background ratio greater than $3$. The half-life for the two-neutrino double-$beta$ decay of $^{48}{rm Ca}$ has been measured to be $T^{2 u}_{1/2},=,[6.4, ^{+0.7}_{-0.6}{rm (stat.)} , ^{+1.2}_{-0.9}{rm (syst.)}] times 10^{19},{rm yr}$. A search for neutrinoless double-$beta$ decay of $^{48}{rm Ca}$ yields a null result and a corresponding lower limit on the half-life is found to be $T^{0 u}_{1/2} > 2.0 times 10^{22},{rm yr}$ at $90%$ confidence level, translating into an upper limit on the effective Majorana neutrino mass of $< m_{betabeta} > < 6.0 - 26$ ${rm eV}$, with the range reflecting different nuclear matrix element calculations. Limits are also set on models involving Majoron emission and right-handed currents.
The CUPID-Mo experiment is searching for neutrinoless double beta decay in $^{100}$Mo, evaluating the technology of cryogenic scintillating Li$_{2}^{100}$MoO$_4$ detectors for CUPID (CUORE Upgrade with Particle ID). CUPID-Mo detectors feature background suppression using a dual-readout scheme with Li$_{2}$MoO$_4$ crystals complemented by Ge bolometers for light detection. The detection of both heat and scintillation light signals allows the efficient discrimination of $alpha$ from $gamma$&$beta$ events. In this proceedings, we discuss results from the first 2 months of data taking in spring 2019. In addition to an excellent bolometric performance of 6.7$,$keV (FWHM) at 2615$,$keV and an $alpha$ separation of better than 99.9% for all detectors, we report on bulk radiopurity for Th and U. Finally, we interpret the accumulated physics data in terms of a limit of $T_{1/2}^{0 u},> 3times10^{23},$yr for $^{100}$Mo and discuss the sensitivity of CUPID-Mo until the expected end of physics data taking in early 2020.
We report the results of a search for neutrinoless double-beta decay in a 9.8~kg$cdot$yr exposure of $^{130}$Te using a bolometric detector array, CUORE-0. The characteristic detector energy resolution and background level in the region of interest are $5.1pm 0.3{rm~keV}$ FWHM and $0.058 pm 0.004,(mathrm{stat.})pm 0.002,(mathrm{syst.})$~counts/(keV$cdot$kg$cdot$yr), respectively. The median 90%~C.L. lower-limit sensitivity of the experiment is $2.9times 10^{24}~{rm yr}$ and surpasses the sensitivity of previous searches. We find no evidence for neutrinoless double-beta decay of $^{130}$Te and place a Bayesian lower bound on the decay half-life, $T^{0 u}_{1/2}>$~$ 2.7times 10^{24}~{rm yr}$ at 90%~C.L. Combining CUORE-0 data with the 19.75~kg$cdot$yr exposure of $^{130}$Te from the Cuoricino experiment we obtain $T^{0 u}_{1/2} > 4.0times 10^{24}~mathrm{yr}$ at 90%~C.L.~(Bayesian), the most stringent limit to date on this half-life. Using a range of nuclear matrix element estimates we interpret this as a limit on the effective Majorana neutrino mass, $m_{betabeta}< 270$ -- $760~mathrm{meV}$.