The background in the neutrinoless double beta decay experiment GERDA
The GERDA collaboration, M. Agostini, M. Allardt, E. Andreotti, A. M. Bakalyarov, M. Balata, I. Barabanov, M. Barnabe Heider, N. Barros, L. Baudis, C. Bauer, N.… 展开作者
The GERDA collaboration, M. Agostini, M. Allardt, E. Andreotti, A. M. Bakalyarov, M. Balata, I. Barabanov, M. Barnabe Heider, N. Barros, L. Baudis, C. Bauer, N. Becerici-Schmidt, E. Bellotti, S. Belogurov, S. T. Belyaev, G. Benato, A. Bettini, L. Bezrukov, T. Bode, V. Brudanin, R. Brugnera, D. Budjas, A. Caldwell, C. Cattadori, A. Chernogorov, F. Cossavella, E. V. Demidova, A. Domula, V. Egorov, R. Falkenstein, A. Ferella, K. Freund, N. Frodyma, A. Gangapshev, A. Garfagnini, C. Gotti, P. Grabmayr, V. Gurentsov, K. Gusev, K. K. Guthikonda, W. Hampel, A. Hegai, M. Heisel, S. Hemmer, G. Heusser, W. Hofmann, M. Hult, L. V. Inzhechik, L. Ioannucci, J. Janicsko Csathy, J. Jochum, M. Junker, T. Kihm, I. V. Kirpichnikov, A. Kirsch, A. Klimenko, K. T. Knoepfle, O. Kochetov, V. N. Kornoukhov, V. V. Kuzminov, M. Laubenstein, A. Lazzaro, V. I. Lebedev, B. Lehnert, H. Y. Liao, M. Lindner, I. Lippi, X. Liu, A. Lubashevskiy, B. Lubsandorzhiev, G. Lutter, C. Macolino, A. A. Machado, B. Majorovits, W. Maneschg, I. Nemchenok, S. Nisi, C. O'Shaughnessy, D. Palioselitis, L. Pandola, K. Pelczar, G. Pessina, A. Pullia, S. Riboldi, C. Sada, M. Salathe, C. Schmitt, J. Schreiner, O. Schulz, B. Schwingenheuer, S. Schoenert, E. Shevchik, M. Shirchenko, H. Simgen, A. Smolnikov, L. Stanco, H. Strecker, M. Tarka, C. A. Ur, A. A. Vasenko, O. Volynets, K. von Sturm, V. Wagner, M. Walter, A. Wegmann, T. Wester, M. Wojcik, E. Yanovich, P. Zavarise, I. Zhitnikov, S. V. Zhukov, D. Zinatulina, K. Zuber, G. Zuzel
The GERmanium Detector Array (GERDA) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double beta decay of 76Ge. The signature of the signal is a monoenergetic peak at 2039 keV, the Q-value of the decay, Q_bb. To avoid bias in the signal search, the present analysis does not consider all those events, that fall in a 40 keV wide region centered around Q_bb. The main parameters needed for the neutrinoless double beta decay analysis are described. A background model was developed to describe the observed energy spectrum. The model contains several contributions, that are expected on the basis of material screening or that are established by the observation of characteristic structures in the energy spectrum. The model predicts a flat energy spectrum for the blinding window around Q_bb with a background index ranging from 17.6 to 23.8*10^{-3} counts/(keV kg yr). A part of the data not considered before has been used to test if the predictions of the background model are consistent. The observed number of events in this energy region is consistent with the background model. The background at Q-bb is dominated by close sources, mainly due to 42K, 214Bi, 228Th, 60Co and alpha emitting isotopes from the 226Ra decay chain. The individual fractions depend on the assumed locations of the contaminants. It is shown, that after removal of the known gamma peaks, the energy spectrum can be fitted in an energy range of 200 kev around Q_bb with a constant background. This gives a background index consistent with the full model and uncertainties of the same size.
Final Results of GERDA on the Search for Neutrinoless Double-$β$ Decay
锗探测器阵列（GERDA）实验寻找$^{76}$ Ge的轻子数破坏的无中微子双$β$（$0νββ$）衰变，其发现将在宇宙学和粒子物理学中产生深远的影响。通过在有源液氩屏蔽中操作富含$^{76}$ Ge的裸锗二极管，GERDA在信号区实现了前所未有的低本底指数$5.2\times10^{-4}$计数/（keV $\cdot$ kg $\cdot$ yr），并满足了在无本底状态下收集100 kg $\cdot$ yr暴露量的设计目标。当结合第一阶段的结果时，在127.2 kg $\cdot$/年的总暴露量后未观察到信号。$^{76}$ Ge中$0νββ$衰变半衰期的限值设定为90% C.L.时的$T_{1/2}>1.8\times10^{26}$年，这与假定没有信号时的灵敏度一致。
Pulse shape discrimination studies with a Broad-Energy Germanium detector for signal identification and background suppression in the GERDA double beta decay experiment
Improved limit on neutrinoless double beta decay of $^{76}$Ge from GERDA Phase II
GERDA实验研究了$^{76}$ Ge（$^{76}$ Ge $\rightarrow$ $^{76}$ Se +2 e $^-$）的轻子数违反无中微子双β衰变的情况，该双β衰变是在液态氩中用富集的$^{76}$ Ge部分操作裸Ge二极管。BEGe型探测器的曝光量比我们以前发布的数据增加了三倍。BEGe探测器的特点是通过对探测器信号的时间曲线进行分析，可以实现出色的背景抑制。在分析窗口中，已达到$1.0_{-0.4}^{+0.6}\cdot10^{-3}$ cts/（keV $\cdot$ kg $\cdot$ yr）的背景水平;如果归一化为能量分辨率，则这是任何0 $νββ$实验中达到的最低水平。未观察到信号，新的90% C.L.结合我们以前的数据，确定了$8.0\cdot10^{25}$年半衰期的下限。假设无信号，预期灵敏度中位数为$5.8\cdot10^{25}$年。
Isotopically modified Ge detectors for {\sc Gerda}: from production to operation
\textsc{Gerda}实验通过新颖的脉冲形状鉴别（PSD）技术来搜索无中微子双β（$0νβ$ β $) decay of $ ^{76} $Ge using high-purity germanium detectors made of material enriched in $ ^{76} $Ge. For Phase II of the experiment a sensitivity for the half life $ T_{1/2} ^{0ν}\，\，\sim 2 \cdot 10^{26} $ yr is envisioned. Modified Broad Energy Germanium detectors (BEGe) with thick n$ ^+ $ electrodes provide the capability to efficiently identify and reject background events, while keeping a large acceptance for the $ 0νβ $beta$ -衰变信号。生产厚窗口BEGe型探测器的\textsc{Gerda}实验的可行性证明了通过测试所有的生产步骤，从采购的同位素改性锗工作BEGe探测器。对\textsc{Gerda} Phase II原型BEGe探测器的光谱…
Design and Performance of the GERDA Low-Background Cryostat for Operation in Water
在寻找$^{76}$ Ge的无中微子双β衰变过程中，在INFN国立大萨索实验室进行的锗探测器阵列（GERDA）实验在感兴趣的区域获得了远低于10 $^{-3}$ cts/（keV $\cdot$ kg $\cdot$ yr）的前所未有的低本底。它利用了第一次实现的一种新的屏蔽概念的基础上，一个大型低温恒温器充满了液体惰性气体，浸没在水箱。锗探测器无需在液氩中封装即可工作。氩气和水将实验室和低温恒温器构造材料的环境背景屏蔽到可忽略的水平。在此期间，各种实验都采用了同样的方法。本文概述了64 m $^3$液氩低温恒温器及其相关基础设施的设计和运行经验。讨论包括与水箱中大型低温恒温器的操作相关的具有挑战性的安全问题。
