Below are some highlights from our recent results. Click on each image to download a PDF version.
CUORE-0 two-neutrino double beta decay half-life
In September 2016, we reported the results of a search for two-neutrino double beta decay in a 9.8 kg⋅yr exposure of 130Te with CUORE-0. From an exposure of 33.4 kg⋅y of TeO2, we determined the half-life to be T1/22ν = [8.2 ± 0.2 (stat.) ± 0.6 (syst.)] × 1020 y. We obtained this result after a detailed reconstruction of the sources responsible for the CUORE-0 counting rate, with a specific study of those contributing to the 130Te neutrinoless double beta decay region of interest.
CUORE-0 neutrinoless double beta decay half-life
In April 2015, we reported the results of a search for neutrinoless double beta decay in a 9.8 kg⋅yr exposure of 130Te with CUORE-0. We set a half-life limit of T1∕20ν > 2.7 × 1024 yr at 90% C.L. from CUORE-0 alone, and T1∕20ν > 4.0 × 1024 yr at 90% C.L. when combined with Cuoricino. The background index in the region of interest for this decay was 0.058 ± 0.004 (stat.) ± 0.002 (syst.) counts/(keV⋅kg⋅yr). Shown here is the best-fit model (solid blue line) overlaid on the spectrum of 0νββ decay candidates in CUORE-0 (data points); the data are shown with Gaussian error bars. The peak at 2507 keV is due to 60Co and the dash-dotted line indicates the position at which we expect a potential neutrinoless double beta decay decay signal. The dashed black line indicates the continuum background component in the ROI. The top panel shows the normalized residuals of the best fit model and the binned data points.
CUORE-0 Majorana neutrino mass sensitivity
Constraints on the effective Majorana neutrino mass (mββ) vs. the lightest neutrino mass (mlightest). For the inverted (IH, green) and normal (NH, red) hierarchies the central dark band is derived from the best-fit neutrino oscillation parameters; the lighter outer band includes their 3σ uncertainties . The horizontal bands delineated by the long-dashed black lines (a), the dashed beige lines (b), and the dot-dashed blue lines (c) are the range of 90% C.L. upper limits on mββ coming from (a) 130Te (CUORE-0 combined with Cuoricino), (b) 136Xe (EXO-200, KamLAND-Zen independently), and (c) 76Ge (combined limit from Gerda, IGEX, HDM). The vertical arrows aim to emphasize the range currently probed with each isotope. The horizontal, hashed grey band indicates the range of limits on mββ expected from CUORE assuming its target 90% C.L. lower limit half-life sensitivity of 9.5 × 1025 yr is attained.
CUORE-0 energy spectrum
Energy spectrum of physics (blue) and calibration (red) data in CUORE-0; the latter is normalized relative to the former at 2615 keV. The peaks are identified as (1) e+e− annihilation, (2) 214Bi, (3) 40K, (4) 208Tl, (5) 60Co, and (6) 228Ac.
The energy resolution of the calibration data in CUORE-0 was determined from a fit to the 2615 keV 208Tl γ-ray line. This gives an effective FWHM value of 4.9 keV at 2615 keV;. Shown here is the calibration data near this line, integrated over all bolometers in all datasets. The solid blue line is the projection of the best model fit. In addition to (a) a double-Gaussian line shape for the main photopeak, the fit function includes (b) a multiscatter Compton continuum, (c) a ~30 keV Te X-ray escape peak, and (d) a continuum background. We extrapolate the resolution from calibration data to our background data at the 0νββ region of interest and obtain a background resolution at the Q-value of 5.1 ± 0.3 keV.
CUORE-0 and Cuoricino backgrounds
Backgrounds at all energies were reduced moving from Cuoricino (black line) to CUORE-0 (red shaded region). In CUORE-0, the background index in the region 2700–3900 keV, excluding the 190Pt peak at 3290 keV, is 0.016 ± 0.001 counts/(keV⋅kg⋅yr), a factor of 6.8 reduction compared to Cuoricino. The background in the region of interested was reduced to 0.058 ± 0.004 counts/(keV⋅kg⋅yr), a factor of 2.7 over Cuoricino. This is consistent with our models that place the origin of the γ contamination in the cryostat materials, which are common to both CUORE-0 and Cuoricino. This γ background forms an irreducible background for CUORE-0, but is expected to be significantly reduced in CUORE due to better material selection, better shielding, and more efficient anti-coincidence rejection.