Bolometric Bounds on the Antineutrino Mass

Abstract

High statistics calorimetric measurements of the β spectrum of 187 Re are being performed with arrays of silver perrhenate crystals operated at low temperature. After a modification of the experimental set-up, which allowed to substantially reduce the background of spurious counts and therefore to increase the sensitivity on the electron antineutrino mass, a new measurement with 10 silver perrhenate microbolometers is running since July 2002. The crystals have masses between 250 and 350 µg and their average FWHM energy resolution, constantly monitored by means of fluorescence X-rays, is of 28.3 eV at the β end-point. The Kurie plot collected during 4485 hours×mg effective running time has an end-point energy of 2466.1 ± 0.8stat ± 1.5syst eV, while the half lifetime of the decay is found to be 43.2 ± 0.2stat ± 0.1syst Gy. These values are the most precise obtained so far for 187 Re. From the fit of the Kurie plot we can deduce a value for the squared electron antineutrino mass m 2 νe of 147 ± 237stat ± 90syst eV 2 . The corresponding 90% C.L. upper limit for m νe is 21.7 eV. The interest in direct measurements of the neutrino mass m ν from the β decay spectrum has been recently stimulated by the evidence of a non zero value of ∆m 2 ν detected in searches on solar and atmospheric neutrino oscillations [1,2,3].Limits on direct measurements of m ν have been so far obtained by experiments with electrostatic spectrometers investigating the β decay of tritium. Recent results [4,5], have set an upper limit of 2.2 eV at 90% C.L. These experiments are based on the measurement of the spectrum of the emitted electron. One cannot therefore exclude "a priori" that the decay could partially occur on a excited state of the daughter molecule. This and other systematic effects have given in the past years a negative value for m ν 2 . Even if now these problems seem to be almost completely solved we think it is important to carry out a measurement in a different approach.Calorimetric measurements where all the energy released in the decay is recorded, appear therefore complementary to those carried out with spectrometers. In addition they allow to measure the entire β decay spectrum, and can therefore test any possible distortion of the Kurie plot. A particularly suitable approach appears the bolometric one [6,7] where detectors, operated at low * CEE fellow in the Network on Cryogenic Detectors, under contract FMRXCT980167 temperature, include absorbers of a material containing the β active nucleus. If the absorbers are diamagnetic and dielectric crystals their heat capacity can be very low, since it is proportional to the cube of the operating temperature. As a consequence even the tiny energy delivered by a particle can give rise to a measurable pulse in a suitable thermal sensor.The present experiment is carried out on the first forbidden unique decay:187 Re → 187 Os + e − + ν e which is particularly promising [8] due to its low transition energy (∼2.5 keV). In addition the large isotopic abundance of 187 Re (62.8 %) allows th...

Assessment of the 187Re decay constant by cross calibration of Re–Os molybdenite and U–Pb zircon chronometers in magmatic ore systems

“…Recent direct counting experiments have resulted in k 187 Re values with much improved precision over previous studies of this type (Galeazzi et al, 2001;Arnaboldi et al, 2003). Nevertheless, they are ca.…”

“…Re-Os meteorite data cross calibration with Pb-Pb meteoric age Shukolyukov and Lugmair (1997) 1.61 ± 0.26 · 10 À11 a À1 Microcalorimetric determinations Alessandrello et al (1999) 1.682 ± 0.045 · 10 À11 a À1 Microcalorimetric determinations Galeazzi et al (2001) 1.604 ± 0.004 · 10 À11 a À1 Microcalorimetric determinations Arnaboldi et al (2003) uncertainty of ±3% (1.64 ± 0.05 · 10 À11 a À1 ) was applied to the Lindner et al (1989) value of k 187 Re, however, because incomplete equilibration of tracer ( 190 Os) and radiogenic ( 187 Os) Os in batches of the Re-bearing solutions, and systematic uncertainties in the calibration of Os and Re spike and standard solutions. Geological determinations of k 187 Re have also been made over the past 50 years using terrestrial material and meteorites (Table 1).…”

“…The precision of these studies has been improved by mircocalorimetric determinations (Ashktorab et al, 1993;Alessandrello et al, 1999;Galeazzi et al, 2001;Arnaboldi et al, 2003), but even these modern methods yield results with uncertainties at the several percent level (Galeazzi et al, 2001). In addition, similar protocols (cryogenic bolometry with Re metal and AgReO 4 ) yield precise values that are significantly different, e.g., 1.682 ± 0.045 · 10 À11 a À1 (Galeazzi et al, 2001) and 1.604 ± 0.004 · 10 À11 a À1 (Arnaboldi et al, 2003;Audi et al, 2003a,b), making these k 187 Re values unsuitable for high-resolution Re-Os geochronology, particularly when compared with other isotopic systems in use in the Earth Sciences. Lindner et al (1986Lindner et al ( , 1989) determined a k 187 Re value of 1.64 ± 0.05 · 10 À11 a À1 by measuring in-growth of 187 Os in solutions containing precisely known quantities of Re.…”

“…Many studies used direct counting experiments and determined k 187 Re values between 2.31 · 10 À11 and 1.39 · 10 À13 a À1 (Sugarman and Richter, 1948;Suttle and Libby, 1954;Watt and Glover, 1962;Wolf and Johnston, 1962;Brodzinski and Conway, 1965;Naldrett, 1984;Ashktorab et al, 1993;Alessandrello et al, 1999;Galeazzi et al, 2001;Arnaboldi et al, 2003) ( Table 1). The precision of these studies has been improved by mircocalorimetric determinations (Ashktorab et al, 1993;Alessandrello et al, 1999;Galeazzi et al, 2001;Arnaboldi et al, 2003), but even these modern methods yield results with uncertainties at the several percent level (Galeazzi et al, 2001). In addition, similar protocols (cryogenic bolometry with Re metal and AgReO 4 ) yield precise values that are significantly different, e.g., 1.682 ± 0.045 · 10 À11 a À1 (Galeazzi et al, 2001) and 1.604 ± 0.004 · 10 À11 a À1 (Arnaboldi et al, 2003;Audi et al, 2003a,b), making these k 187 Re values unsuitable for high-resolution Re-Os geochronology, particularly when compared with other isotopic systems in use in the Earth Sciences.…”

MARE-1 in Milan: Status and Perspectives

“…Also dielectric compounds can be used. Up to now, only two β decay experiments have been carried out with thermal detectors: MANU [7,8] and MIBETA [5,6] experiments. MANU used metallic rhenium single crystal as absorber, while MIBETA used AgReO 4 crystals.…”