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CUORE: Cryogenic Underground Observatory for Rare Events

  • by Han Ke

The Cryogenic Underground Observatory for Rare Events (CUORE) searches for $0\nu\beta\beta$ of ${}^{130}Te$ with 988 5-cm-cubic crystals running as bolometers at 10 mK. At this temperature, the heat capacity of a CUORE crystal is so tiny that the crystal temperature increase by 0.1 mK per MeV energy input. This temperature change is measured precisely with a thermistor attached to the crystal. In recent years we have built and analyzed data from the prototype bolometric detectors Cuoricino and CUORE-0. The next stage, planned to start operations in 2016, is the largest bolometric detector ever built: CUORE. With a total natTeO2 detector mass of 741 kg (${}^{130}Te$ active mass 204 kg) and energy resolution of 5 keV FWHM at 2.527 MeV, CUORE is one of the most competitive $0\nu\beta\beta$ experiments under construction.

CUORE实验寻找碲-130同位素的无中微子双贝塔衰变。它的988块5厘米的立方晶体,在10mK的低温下作为热辐射量能器。在如此低的温度 下,CUORE晶体的热容量变得很小,MeV量级的能量就可以使晶体温度升高0.1mK。这种量级的温度变化可以非常精确地用热敏电阻计来精确测量。最近 几年,我们合作组建造了原型探测器Cuoricino和CUORE-0,并进行了相应的数据分析。下一步,我们将在2016年开始运行世界上最大的低温量 能器阵列:CUORE。CUORE包含741公斤的TeO2晶体,其包含自然丰度的Te-130共204公斤。预期的能量分辨率在2.526MeV将达到 5keV的半高全宽。CUORE是在建的最具竞争力的$0\nu\beta\beta$ 实验之一。

Schematic of a CUORE bolometer

To cool our detectors to 10 mK, we have custom-built the world’s largest dilution refrigerator. The cryostat consists of 6 thermal layers, all made of radio-pure oxygen-free copper. The experimental space inside is ~1$m^{3}$. We proudly claimed “the coldest cubic meter in the known universe” when CUORE cryostat successfully commissioned at a record of 5.9 mK.

为了把我们的探测器温度降低到10mK,我们建造了世界上最大的稀释制冷机。制冷机的包含6层嵌套的热屏蔽罐体,全部由高纯无氧铜制成。10mK级 的制冷空间体积约为1立方米。CUORE稀释制冷机在试运行时达到了5.9mK的低温,我们也非常自豪地宣称我们创造了“已知宇宙的最冷的一个立方米”。

In experiments, we measure the energies of two emitting electrons from $0\nu\beta\beta$. Since no energy is taken away by neutrinos, the sum of electron energy from $0\nu\beta\beta$ is constant at Q-Value. On the contrary, the sum of electron energy from $2\nu\beta\beta$ is a continuous spectrum. We have discovered $2\nu\beta\beta$ from a dozen or so isotopes, including ${}^{136}Xe$, ${}^{76}Ge$, ${}^{82}Se$, ${}^{100}Mo$, ${}^{130}Te$. Many international collaborations are searching for $0\nu\beta\beta$ in those isotopes. The next generation of experiments will use ton-scale detectors, with superb energy resolution and exquisitely low backgrounds in the energy region of interest. If observed, the experimental signature would be quite clear but very rare. The signature would be a narrow peak at the energy of the decay. In the current generation of experiments, we expect at most a few events every year in our detectors.

在实验中,我们测量双贝塔衰变释放的两个电子的能量。$0\nu\beta\beta$的两个电子能量之和是一个定值,即Q-Value,而$2\nu\beta\beta$的电子能量和为连续谱。我们已经在多种同位素源中发现了$2\nu\beta\beta$,例如${}^{136}Xe$, ${}^{76}Ge$, ${}^{82}Se$, ${}^{100}Mo$, and ${}^{130}Te$。目前国际上的热门议题就是在这些同位素中寻找$0\nu\beta\beta$。这一代和下一代的实验将使用百公斤到一顿的低本底,高能量分辨率的超大探测器。我们期望每年在衰变能量附近观测到的几个事例组成的一个小小的峰。

Status and Outlook

CUORE Towers

All 19 CUORE towers have been assembled and installed in the cryostat. We assayed all detector components and took extra care cleaning and transporting them. All assembly was done in 5 gloveboxes, which were flushed with nitrogen gas continuously. The expected background level at our region of interest (@2.527 MeV) is about 0.01 c/keV/kg/y.

Commissioning of the detectors and cryostat is on-going and we expect data taking by the end of 2016. With 5 years of data taking, CUORE will have a half-life sensitivity of 1026 years (90% CL) and corresponding Majorana mass of 50 to 110 meV.

The collaboration is also actively developing the next generation of bolometer for rare events – CUPID, CUORE with Particle ID.

所有的19个CUORE的模块都已建成并安装到了制冷机里面。我们建造探测器时,对探测器材料的放射性本底进行了仔细筛选,并对尽量避免在清洗和运 输过程中二次污染各个部件。最后的探测器组装完全在5个手套箱里面完成,不停地循环氮气避免空气中的杂质污染我们的探测器。预期的实验本底将在0.01每 keV每公斤每年。


CUORE合作组同时也在积极研发下一代CUORE探测器阵列,我们将它命名为CUPID(CUORE with Particle ID)。


SJTU is an official collaborating institution of CUORE. We’re actively working on many projects within CUORE and CUPID:

  • CUORE data analysis. Commission data will be available by the end of 2016
  • CUORE muon veto design and construction. This involves hardware work onsite at Gran Sasso, Italy
  • R&D of next generation crystal production with emphasis on radio-purity. This takes advantage our good working relationship with SICCAS (Shanghai), our crystal vendor.



  • 探测器调试与运行(意大利)
  • 无中微子双贝塔衰变物理分析
  • 下一代提纯晶体性能研究