Results from the CUORE-0 experiment

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1 Journal of Physics: Conference Series PAPER OPEN ACCESS Results from the CUORE- experiment To cite this article: L Canonica et al 16 J. Phys.: Conf. Ser View the article online for updates and enhancements. Related content - Low energy analysis in CUORE- Gabriele Piperno and CUORE Collaboration - CUORE- detector: design, construction and operation C. Alduino, K. Alfonso, D.R. Artusa et al. - The CUORE and CUORE- experiments at LNGS C Alduino, K Alfonso, F T Avignone III et al. This content was downloaded from IP address on /1/18 at 6:37

2 XIV International Conference on Topics in Astroparticle and Underground Physics (TAUP 15) IOP Publishing Results from the CUORE- experiment L Canonica 1, C Alduino, K Alfonso 3, D R Artusa 1,, F T Avignone III, O Azzolini, T I Banks 5,6, G Bari 7, J W Beeman 8, F Bellini 9,1, A Bersani 11, M Biassoni 1,13, C Brofferio 1,13, C Bucci 1, A Caminata 11, X G Cao 1, S Capelli 1,13, L Cappelli 11,3,15, L Carbone 13, L Cardani 9,1, P Carniti 1,13, N Casali 9,1, L Cassina 1,13, D Chiesa 1,13, N Chott, M Clemenza 1,13, S Copello 11,16, C Cosmelli 9,1, O Cremonesi 13, R J Creswick, J S Cushman 17, I Dafinei 1, A Dally 18, C J Davis 17, S Dell Oro 1,19, M M Deninno 7, S Di Domizio 11,16, M L Di Vacri 3,, A Drobizhev 5,6, D Q Fang 1, M Faverzani 1,13, G Fernandes 11,16, E Ferri 1,13, F Ferroni 9,1, E Fiorini 1,13, B K Fujikawa 6, A Giachero 13, L Gironi 1,13, A Giuliani 1, L Gladstone, P Gorla 1, C Gotti 1,13, T D Gutierrez 3, E E Haller 8,, K Han 6,17, E Hansen 9,1, K M Heeger 17, R Hennings-Yeomans 5,6, K P Hickerson 3, H Z Huang 3, R Kadel 5, G Keppel, Yu G Kolomensky 5,5, K E Lim 17, X Liu 3, Y G Ma 1, M Maino 1,13, L Marini 11,16, M Martinez 9,1,6, R H Maruyama 17, Y Mei 6, N Moggi 7,7, S Morganti 1, P J Mosteiro 1, C Nones 8, E B Norman 9,3, A Nucciotti 1,13, T O Donnell 5,6, F Orio 1, J L Ouellet 5,6,, C E Pagliarone 1,15, M Pallavicini 11,16, V Palmieri, L Pattavina 1, M Pavan 1,13, G Pessina 13, V Pettinacci 1, G Piperno 9,1, S Pirro 1, S Pozzi 1,13, E Previtali 13, C Rosenfeld, C Rusconi 13, E Sala 1,13, S Sangiorgio 9, D Santone 1,, N D Scielzo 9, V Singh 5, M Sisti 1,13, A R Smith 6, L Taffarello 31, M Tenconi 1, F Terranova 1,13, C Tomei 1, S Trentalange 3, G Ventura 3,33, M Vignati 1, S L Wagaarachchi 5,6, B S Wang 9,3, H W Wang 1, J Wilson, L A Winslow, T Wise 17,18, L Zanotti 1,13, G Q Zhang 1, B X Zhu 3, S Zimmermann 3, S Zucchelli 7,35 1 INFN - Laboratori Nazionali del Gran Sasso, Assergi (L Aquila) I Italy Department of Physics and Astronomy, University of South Carolina, Columbia, SC 98-3 Department of Physics and Astronomy, University of California, Los Angeles, CA INFN - Laboratori Nazionali di Legnaro, Legnaro (Padova) I-35 - Italy 5 Department of Physics, University of California, Berkeley, CA 97-6 Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 97-7 INFN - Sezione di Bologna, Bologna I-17 - Italy 8 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 97-9 Dipartimento di Fisica, Sapienza Università di Roma, Roma I Italy 1 INFN - Sezione di Roma, Roma I Italy 11 INFN - Sezione di Genova, Genova I Italy 1 Dipartimento di Fisica, Università di Milano-Bicocca, Milano I-16 - Italy 13 INFN - Sezione di Milano Bicocca, Milano I-16 - Italy Content from this work may be used under the terms of the Creative Commons Attribution 3. licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1

3 XIV International Conference on Topics in Astroparticle and Underground Physics (TAUP 15) IOP Publishing 1 Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 18 - China 15 Dipartimento di Ingegneria Civile e Meccanica, Università degli Studi di Cassino e del Lazio Meridionale, Cassino I-33 - Italy 16 Dipartimento di Fisica, Università di Genova, Genova I Italy 17 Department of Physics, Yale University, New Haven, CT Department of Physics, University of Wisconsin, Madison, WI INFN - Gran Sasso Science Institute, L Aquila I Italy Dipartimento di Scienze Fisiche e Chimiche, Università dell Aquila, L Aquila I Italy 1 CSNSM, Univ. Paris-Sud, CNRS/INP3, Université Paris-Saclay, 915 Orsay - France Massachusetts Institute of Technology, Cambridge, MA Physics Department, California Polytechnic State University, San Luis Obispo, CA Department of Materials Science and Engineering, University of California, Berkeley, CA 97-5 Physics Division, Lawrence Berkeley National Laboratory, Berkeley, CA 97-6 Laboratorio de Fisica Nuclear y Astroparticulas, Universidad de Zaragoza, Zaragoza 59 - Spain 7 Dipartimento di Scienze per la Qualità della Vita, Alma Mater Studiorum - Università di Bologna, Bologna I Italy 8 Service de Physique des Particules, CEA / Saclay, Gif-sur-Yvette - France 9 Lawrence Livermore National Laboratory, Livermore, CA Department of Nuclear Engineering, University of California, Berkeley, CA INFN - Sezione di Padova, Padova I Italy 3 Dipartimento di Fisica, Universit a di Firenze, Firenze I Italy 33 INFN - Sezione di Firenze, Firenze I Italy 3 Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA Dipartimento di Fisica e Astronomia, Alma Mater Studiorum - Università di Bologna, Bologna I-17 - Italy lucia.canonica@lngs.infn.it Abstract. The CUORE- experiment searched for neutrinoless double beta decay in 13 Te using an array of 5 tellurium dioxide crystals, operated as bolometers at a temperature of 1 mk. It took data in the Gran Sasso National Laboratory (Italy) since March 13 to March 15. We present the results of a search for neutrinoless double beta decay in 9.8 kg years 13 Te exposure that allowed us to set the most stringent limit to date on this half-life. The performance of the detector in terms of background and energy resolution is also reported. 1. Introduction Neutrinoless double-beta (νββ) decay is an hypothesized nuclear decay that violates lepton number conservation. In this transition a nucleus (A, Z) decays into (A, Z+) nucleus with the emission of two electrons and no neutrino, resulting in a peak in the sum energy spectrum of the emitted electrons. This process, first hypothesized in [1,, 3], has never observed so far. Its discovery would demonstrate the lepton number violation, the Majorana nature of neutrinos and would constrain the absolute neutrino mass scale. Given its importance, an intense experimental effort is ongoing to search for this decay in several nuclei [, 5, 6]. The Cryogenic Underground Observatory for Rare Events (CUORE) [7], presently in the final stages of construction at the Gran Sasso National Laboratory (LNGS), will be one of the most sensitive upcoming νββ-decay experiments. It is an array of 988 TeO low-temperature calorimeters with the goal of searching for the νββ decay of 13 Te. The detectors are arranged in a compact structure of 19 towers, each one containing 5 TeO crystals, disposed on 13 floors. CUORE has been designed on the experience of the predecessor experiment Cuoricino [8]. It was a single tower of 6 bolometers ( kg of TeO ) which ran in the LNGS from 3 to

4 XIV International Conference on Topics in Astroparticle and Underground Physics (TAUP 15) IOP Publishing 8. Cuoricino did not observe any evidence for the νββ decay of 13 Te and set a limit on its hals file of Tν >.8 1 yr (9% C.L.) [9]. Scaling from Cuoricino to CUORE, we aim to improve the sensitivity to the νββ half life of 13 Te. This goal can be achieved by increasing the exposure (increasing the active mass) and by reducing the background in the Region Of Interest (ROI), using an improved material selection, cleaning and handling procedures. Before starting the construction of the 19 CUORE towers, an additional tower, named CUORE-, was produced according to the CUORE requirements.. The CUORE- experiment CUORE- is a single CUORE-like tower, the first one built using the low-background assembly techniques developed for CUORE [1]. It is made of 5 TeO bolometers, for a total mass of 39 kg. The TeO crystals are held in an ultra-pure copper frame by Polytetrafluoroethylene (PTFE) supports and they are arranged in 13 floors, with crystals per floor (see Fig. 1). Each TeO detector is instrumented with a Neutron Transmutation Doped (NTD) Ge thermistor glued on its surface, to measure the temperature change of the absorber and convert it into an electric signal. Each crystal is instrumented also with a silicon resistor ( heater ) to generate reference pulses. A custom design semi-automated system was developed in order to reproduce the mechanical coupling between the crystals and the chips, namely the glue. The results on the detector performance uniformity serves as evaluation parameters for validating the system operations. The tower was operated in Hall A of LNGS, in the same dilution refrigerator that previously hosted the Cuoricino experiment, and it took data between March 13 and March 15. Technical details are reported in [11], while the CUORE- physics results can be found in [1]. Figure 1. Picture of the CUORE detector: the 5 TeO crystals are arranged in 13 floors of crystals each..1. Thermistor uniformity One of the CUORE- goals was to test and compare the major upgrades in the uniformity of the bolometric performance achieved with the new CUORE-style assembly line, with respect to its predecessor Cuoricino. Figure shows the comparison of the bolometric performance of CUORE- and Cuoricino. The RMS of the base temperature distributions (lowest detector temperature) is evaluated to be 3

5 XIV International Conference on Topics in Astroparticle and Underground Physics (TAUP 15) IOP Publishing 9% for the Cuoricino detector while for CUORE- is %. The narrower distribution of CUORE- temperatures compared to the Cuoricino ones is a demonstration of the efficient operation of the semi-automated system for the sensor-to-absorber coupling. 18 Cuoricino 16 1 CUORE- Entries / T / T avg Figure. Comparison of the base temperatures of the CUORE- (red solid line) and Cuoricino (blue dashed line) bolometers normalized to the average temperature of the whole detectors... Detector performance CUORE- acquired data for the νββ search accumulating a total exposure of 9.8 kg y of 13 Te. Data are collected in month-long blocks called datasets. At the beginning and end of each dataset we calibrate the detector by placing a 3 Th source next to the outer vessel of the cryogenic system. We use the calibration line with the highest intensity and next to the ROI, 615 kev from 8 Tl, in order to study the detector response function to a mono energetic energy deposit for each bolometer and dataset. We estimate the shape parameters of the 615 kev line with a simultaneous, unbinned extended maximum likelihood (UEML) fit to calibration data. The physics- exposure-weighted effective mean of the FWHM values for each bolometer and dataset is.9 kev, with a corresponding RMS of.9 kev. We evaluate the background level in the alpha-dominated region (7-39) kev to be.16±.1 counts/(kev kg y), 6 times smaller with respect to the Cuoricino background in the same region..3. νββ decay result We search for νββ decay of 13 Te in the final CUORE- energy spectrum performing a simultaneous UEML fit in the energy region 7-57 kev (Fig. 3). The fit function is composed by three parameters: a posited signal peak at the Q-value of the transition, a peak at 57 kev from 6 Co double-gammas, and a smooth continuum background attributed to multi-scatter Compton events from 8 Tl and surface decays. The best-fit values are Γ ν =.1 ±.1(stat)±.1(syst) 1 yr 1 for the νββ decay rate and.58±.(stat)±.(syst) counts/(kev kg y) for the background index in the ROI. This result is 3 times lower than the Cuoricino background,.169±.6 counts/(kev kg y), in the same ROI. Using a Bayesian approach, we set a 9% C.L. lower bound on the decay half-life of.7 1 yr [1]. When combined with the kg y exposure of 13 Te from the Cuoricino experiment, we find a Bayesian 9% C.L. limit of T ν >. 1 yr, which is the most stringent limit to date on the 13 Te νββ half-life. Additional details on the analysis techniques can be found in [13].

6 XIV International Conference on Topics in Astroparticle and Underground Physics (TAUP 15) IOP Publishing Residual (σ) Events / ( kev) χ /NDF = 3.9/ Reconstructed Energy (kev) kg yr)) Event Rate (counts /(kev Figure 3. The best-fit model from the UEML fit (solid blue line) overlaid on the spectrum of νββ decay candidates in CUORE- (data points). The vertical dot-dashed black line indicates the position of Q-value. Top: The normalized residuals of the best-fit model and the binned data... Acknowledgments The CUORE Collaboration thanks the directors and staff of the Laboratori Nazionali del Gran Sasso and the technical staff of our laboratories. This work was supported by the Istituto Nazionale di Fisica Nucleare (INFN); the National Science Foundation under Grant Nos. NSF- PHY-65119, NSF-PHY-5337, NSF-PHY-85531, NSF-PHY-9171, and NSF-PHY ; the Alfred P. Sloan Foundation; the University of Wisconsin Foundation; and Yale University. This material is also based upon work supported by the US Department of Energy (DOE) Office of Science under Contract Nos. DE-AC-5CH1131 and DE-AC5-7NA73; and by the DOE Office of Science, Office of Nuclear Physics under Contract Nos. DE-FG- 8ER1551 and DEFG3-ER1138. This research used resources of the National Energy Research Scientific Computing Center (NERSC). References [1] Goeppert-Mayer M 1935 Phys. Rev. 8 6 [] Furry W H 1939 Phys. Rev [3] Pontecorvo B 1968 Sov. Phys. JETP 6 98 [] Agostini M et al 13 Phys. Rev. Lett [5] Albert J B et al 1 Nature 51 9 [6] Gando A et al 13 Phys. Rev. Lett [7] Artusa D R et al 15 Advances in High Energy Physics 15 1 [8] Arnaboldi C et al 8 Phys. Rev. C [9] Andreotti E et al 11 Astropart. Phys. 3 8 [1] Buccheri E et al 1 Nucl. Instrum. Meth. A [11] Artusa D R et al 1 Eur. Phys. J. C 7 8 [1] Alfonso K et al 15 Phys. Rev. Lett [13] Alduino C et al 15 Submitted to Phys. Rev. C (arxiv: [nucl-ex]) 5