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The Milano neutrino mass experiment with bolometric detectors: towards an improved sensitivity
Nuclear Physics B (Proc. Suppl.) 143 (2005) 522 www.elsevierphysics.com
The Milano neutrino mass experiment with bolometric detectors: towards an improved sensitivity M. Sistia , C. Arnaboldia , C. Brofferioa , F. Capozzia , O. Cremonesia , E. Fiorinia , A. Giulianib , B. Margesinc, A. Nucciottia , M. Pavana, M. Pedrettib , G. Pessinaa, S. Pirroa, E. Previtalia, M. Zenc a
Dip. di Fisica dell’Universtit` a di Milano-Bicocca and Sez. di Milano dell’INFN, Milano, Italy
b
Dip. di Fisica e Matematica dell’Universtit` a dell’Insubria, Como, Italy, and Sez. di Milano dell’INFN, Milano, Italy ITC-irst, Mycrosystems Division, Povo (Tn), Italy
0920-5632/$ – see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.nuclphysbps.2005.01.187
field and are expected in a second phase of the experiment [3].
N(E) pEF(Z,E)S(E) fit residuals
50
40
1.0 0.0 -1.0
10.0
√
30
20
√
In Milano we are developing thermal microcalorimeters to measure the β-decay spectrum of 187 Re with high statistics and high energy resolution [1]. 187 Re offers the best sensitivity to the direct measurement of mν , due to its low transition energy. Our detectors are made of AgReO4 crystals as absorbers, glued to doped silicon chip thermometers. Using an array of 8 such detectors, for a total mass of 2.2 mg, we have collected ∼ 6.2 × 106 187 Re decays above the common energy threshold of 750 eV [2]. The resulting Kurie plot, corresponding to 8751 hours×mg, is shown in Fig. 1. A fit in the energy interval 0.9 ÷ 4 keV gives 2465.3 ± 0.5(stat.) ± 1.6(syst.) eV for the β end-point, and −112 ± 207(stat.) ± 90(syst.) eV2 for the squared electron antineutrino mass. The 90 % C.L. upper limit to mν is 15 eV. Details of the experimental setup and of the data analysis are reported in [2]. With a Montecarlo code, we have devised the experimental arrangement needed to achieve, with the present technology, a sensitivity on mν below 3 eV, in order to validate the results of spectrometer experiments. In a first phase of the new Milano experiment, it should be possible to attain a limit Σ90 (mν ) ≈ 2.5 eV after running for 3 years 200 microcalorimeters with an individual 187 Re β activity of 0.25 Bq, an energy resolution of 10 ÷ 15 eV and a pile-up resolving time of 100 ÷ 200 µs [3]. Further improvements of the sensitivity to the sub-eV range would require new developments in the thermal detector
N(E) pEF(Z,E)S(E)
c
8.0 6.0 4.0 2.0 0.0 2.40 2.45 2.50 energy [keV]
10
0
1.0
1.5
2.0 2.5 energy [keV]
3.0
3.5
4.0
Figure 1. Final Kurie plot: p and E are the β momentum and kinetic energy, F (Z, E) is the Coulomb factor and S(E) is the shape factor.
REFERENCES 1. C. Arnaboldi et al., Phys. Rev. Lett. 91 (2003) 161802. 2. M. Sisti et al., Nucl. Instrum. Methods A 520 (2004) 125. 3. A. Nucciotti et al., Nucl. Instrum. Methods A 520 (2004) 148.
The Milano neutrino mass experiment with bolometric detectors: towards an improved sensitivity M. Sistia , C. Arnaboldia , C. Brofferioa , F. Capozzia , O. Cremonesia , E. Fiorinia , A. Giulianib , B. Margesinc, A. Nucciottia , M. Pavana, M. Pedrettib , G. Pessinaa, S. Pirroa, E. Previtalia, M. Zenc a
Dip. di Fisica dell’Universtit` a di Milano-Bicocca and Sez. di Milano dell’INFN, Milano, Italy
b
Dip. di Fisica e Matematica dell’Universtit` a dell’Insubria, Como, Italy, and Sez. di Milano dell’INFN, Milano, Italy ITC-irst, Mycrosystems Division, Povo (Tn), Italy
0920-5632/$ – see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.nuclphysbps.2005.01.187
field and are expected in a second phase of the experiment [3].
N(E) pEF(Z,E)S(E) fit residuals
50
40
1.0 0.0 -1.0
10.0
√
30
20
√
In Milano we are developing thermal microcalorimeters to measure the β-decay spectrum of 187 Re with high statistics and high energy resolution [1]. 187 Re offers the best sensitivity to the direct measurement of mν , due to its low transition energy. Our detectors are made of AgReO4 crystals as absorbers, glued to doped silicon chip thermometers. Using an array of 8 such detectors, for a total mass of 2.2 mg, we have collected ∼ 6.2 × 106 187 Re decays above the common energy threshold of 750 eV [2]. The resulting Kurie plot, corresponding to 8751 hours×mg, is shown in Fig. 1. A fit in the energy interval 0.9 ÷ 4 keV gives 2465.3 ± 0.5(stat.) ± 1.6(syst.) eV for the β end-point, and −112 ± 207(stat.) ± 90(syst.) eV2 for the squared electron antineutrino mass. The 90 % C.L. upper limit to mν is 15 eV. Details of the experimental setup and of the data analysis are reported in [2]. With a Montecarlo code, we have devised the experimental arrangement needed to achieve, with the present technology, a sensitivity on mν below 3 eV, in order to validate the results of spectrometer experiments. In a first phase of the new Milano experiment, it should be possible to attain a limit Σ90 (mν ) ≈ 2.5 eV after running for 3 years 200 microcalorimeters with an individual 187 Re β activity of 0.25 Bq, an energy resolution of 10 ÷ 15 eV and a pile-up resolving time of 100 ÷ 200 µs [3]. Further improvements of the sensitivity to the sub-eV range would require new developments in the thermal detector
N(E) pEF(Z,E)S(E)
c
8.0 6.0 4.0 2.0 0.0 2.40 2.45 2.50 energy [keV]
10
0
1.0
1.5
2.0 2.5 energy [keV]
3.0
3.5
4.0
Figure 1. Final Kurie plot: p and E are the β momentum and kinetic energy, F (Z, E) is the Coulomb factor and S(E) is the shape factor.
REFERENCES 1. C. Arnaboldi et al., Phys. Rev. Lett. 91 (2003) 161802. 2. M. Sisti et al., Nucl. Instrum. Methods A 520 (2004) 125. 3. A. Nucciotti et al., Nucl. Instrum. Methods A 520 (2004) 148.