China Jinping Underground Laboratory Research Articles

PandaX-III high pressure xenon TPC for Neutrinoless Double Beta Decay search

The PandaX-III experiment uses high pressure Time Projection Chambers (TPCs) to search for Neutrinoless Double Beta Decay (NLDBD) of 136Xe, with high energy resolution and sensitivity at the China Jin-Ping underground Laboratory II (CJPL-II). Fine-pitch Microbulk Micromegas will be used for charge amplification and readout in order to reconstruct both the energy and track of the NLDBD event. In the first phase of the experiment, the detector, which contains 200 kg of 90% 136Xe enriched gas operated at 10 bar, will be immersed in a large water tank to ensure 5 m of water shielding. For the final phase, a ton-scale experiment with multiple TPCs will be constructed to improve the detection probability and sensitivity. A 20-kg scale prototype TPC with 7 Micromegas modules has been built to optimize the design of Micromegas readout modules, and to study the energy calibration of the gaseous TPC . The preliminary results of the PandaX-III prototype TPC will be also presented in this paper.

A low-cost slow control system for the PandaX-4T experiment

The PandaX-4T experiment is a next-generation dark matter search program located in the China Jinping Underground Laboratory. To ensure the stability of the complex instrument during the planned operation, the status of the facility should be monitored continuously. The paper reports the design of the slow control system for the experiment. The system is used to monitor the facility status and generate an alarm signal while the detector is in abnormal status. Low-cost hardware is employed for the distributed data collection. Python-based data collection program was developed. We also used the open source software for data storage, visualization and anomaly detection, so that the development of the system is simplified. We finally achieved a low-cost and robust slow control system for the prototype detector in short time. It is running well currently. The system will be integrated with the PandaX-4T facility in late 2019.

Comparative Study of Tunnel Blast-Induced Vibration on Tunnel Surfaces and Inside Surrounding Rock

In tunnel blast applications, vibration monitors are typically placed on tunnel surfaces to measure the responses of rock to explosion loads for statutory compliance. Few publications in the open literature have focused on the differences between the blasting vibration on tunnel surfaces and inside the surrounding rock. During blasting excavation of the experimental tunnels in the China Jinping Underground Laboratory, velocity sensors were arranged both on the tunnel walls and inside the surrounding rock to monitor far-field vibrations. In this paper, the vibration characteristics on the tunnel surfaces and inside the surrounding rock are presented based on the recorded field data. Corresponding empirical formulae for peak particle velocity (PPV) attenuation and dominant frequency variation are derived from these data. A three-dimensional dynamic finite-element model is used to verify the site survey results. The field and numerical studies show that compared with the inside vibration, the tunnel surface vibration has a higher, more readily attenuated PPV and a lower frequency with a slower rate of decline in the dominant frequency. The mechanisms that cause the differences between the surface and inside vibration are discussed in detail. The tunnel surface vibration in the far field is dominated by surface waves, which occupy more than 75% of the total vibrational energy. For this reason, the results presented in this paper do not apply to vibration in the near field, where body waves are expected to be dominant.

Influence of initial stresses and unloading rates on the deformation and failure mechanism of Jinping marble under true triaxial compression

To investigate the deformation and failure mechanism of rock influenced by initial stress and unloading rates, this study presents minimum principal stress unloading tests of Jinping marble under true triaxial compression conditions under various initial stresses and unloading rates based on the in situ stresses measured in the China Jinping Underground Laboratory Phase II (CJPL-II). The effects of initial stresses and unloading rates on the bearing capacity and the deformation and failure characteristics of Jinping marble were analysed. The relationship between the strains in the three principal stress directions and the unloading extent of σ3 is defined using parameters such as the strain-unloading extent ratio and the unloading strain rate. With an increase in the initial σ1, the increase in strain-unloading extent ratio and unloading strain rate changed from linear to exponential earlier, and sample failure occurred with a smaller unloading extent. Meanwhile, the number of acoustic emission rings and the amount of cumulative energy increased, and the sample failure changed from tensile failure to a mixture of tensile and shear failure that showed more transgranular cracks in the microscopic images. With an increase in the initial σ2 or σ3, the overall trend of the failure characteristics was similar to that with an increase in the initial σ1, but the sample failed with a larger unloading extent, and the increase in strain-unloading extent ratio and unloading strain rate changed from linear to exponential later. The influence of unloading strain rate shows that as unloading strain rate increased, the sample failed with a larger unloading extent and changed from a mixture of tensile and shear to tensile failure, and more transgranular cracks were observed in the microscopic images.

Stability analysis of deep-buried hard rock underground laboratories based on stereophotogrammetry and discontinuity identification

In a tunnel, instabilities in the surrounding rock mostly occur within the sidewalls and crown. After acquiring the rock mass structure, a combination of laboratory experiments, numerical simulations, and in situ monitoring data can permit a more reasonable stability analysis of the surrounding rock and engineering support design to ensure a safer engineering project. To overcome the shortcomings (e.g., inefficiency, high labor costs, and safety risks) of traditional methods for mapping the rock mass structures of the sidewalls and crowns of tunnels, this study proposes a safe, rapid, and efficient method that can acquire a 3D digital elevation model (DEM) of the sidewalls and crown of a tunnel and the corresponding rock mass structures by using digital photogrammetry (DP). The proposed method was then tested in an engineering tunnel. Error analysis of check points and discontinuity orientations showed that the errors were within a reasonable range. The method was further applied to traffic tunnel #1 of the China Jinping Underground Laboratory Phase II (CJPL-II), and the spatial coordinates and orientations of the joints were obtained. A 3D quasi-deterministic discrete model was subsequently established by converting the coordinates and orientations of the joints from a geological coordinate system to a local coordinate system in discrete element software. The quasi-deterministic model was then used to confirm that the joint persistence has an important influence on the stability of the surrounding rock of a tunnel and, thus, affects the support installation. Finally, the joint persistence value was determined by the size of the onsite unstable block. The results of this study provide a reference for the design, construction, and support of similar deep-buried jointed hard rock tunnels.

Characteristics of the microseismicity resulting from the construction of a deeply-buried shaft

The China Jinping Underground Laboratory phase II (CJPL-II) is currently the world’s deepest laboratory with a maximum overburden over 2.4 km. For this project, a deeply-buried shaft was constructed on the floor of the existing large-span laboratories under conditions involving high geo-stress. To explore the failure characteristics encountered and optimize the excavation and support scheme of the shaft, an in situ microseismic (MS) monitoring experiment was carried out. Firstly, an appropriate monitoring scheme was developed for this special project (i.e. the details of the sensor array required, velocity model, and system protection). Secondly, the location accuracy of the monitoring system was analyzed. On this basis, the effect of excavation and support on the fracturing processes induced in the surrounding rock was analyzed by interpreting the MS information. Thirdly, the spatial relationship between the potential damage zones and direction of the maximum principal stress was validated by analyzing the spatiotemporal evolution of the MS activity with the help of numerical simulations. In addition, some suggestions for excavation and support schemes are provided based on the monitoring results. Hence, the MS monitoring scheme and results described in this paper constitute a reference for construction design and MS monitoring of similar projects.

PandaX: A deep underground dark matter search experiment in China using liquid xenon

The nature of dark matter is one of the most fundamental scientific unknowns. Particle physicists have spent decades searching for evidence of dark matter particles. The PandaX project is a staged xenon-based dark matter direct detection experiment located at the China Jinping Underground Laboratory. In this paper, we give an overview of the PandaX experiment, discuss its recent scientific results, and outline the plan for the future.

The CR-39 etching optimization and measurement for radon in China Jinping Underground Laboratory

The optimum radon measurement conditions for a kind of passive radon dosimeter containing CR-39 detector with large effective area were studied in detail. The optimum etching conditions were experimentally determined to be 6.25 mol L−1 NaOH solution at 75 °C for 6 h and the calibration factor was 1.1 ± 0.1 track cm−2/kBq m−3 h. Based on these parameters, these CR-39 detectors were used to measure radon concentration in China Jinping Underground Laboratory (CJPL). The measured results showed that radon concentrations in CJPL-I were lower than many other international underground laboratories.

Performances of a prototype point-contact germanium detector immersed in liquid nitrogen for light dark matter search

The CDEX-10 experiment searches for light weakly-interacting massive particles, a form of dark matter, at the China JinPing underground laboratory, where approximately 10 kg of germanium detectors are arranged in an array and immersed in liquid nitrogen. Herein, we report on the experimental apparatus, detector characterization, and spectrum analysis of one prototype detector. Owing to the higher rise-time resolution of the CDEX-10 prototype detector as compared with CDEX-1B, we identified the origin of an observed category of extremely fast events. For data analysis of the CDEX-10 prototype, we introduced and applied an improved bulk/surface event discrimination method. The results of the new method were compared to those of the CDEX-1B spectrum. Both sets of results showed good consistency in the 0--12 keVee energy range, except for the 8.0 keV K-shell X-ray peak from the external copper.

Dark matter direct search sensitivity of the PandaX-4T experiment

The PandaX-4T experiment, a four-ton scale dark matter direct detection experiment, is being planned at the China Jinping Underground Laboratory. In this paper we present a simulation study of the expected background in this experiment. In a 2.8-ton fiducial mass and the signal region between 1 to 10 keV electron equivalent energy, the total electron recoil background is found to be 4.9x10^{-5} /(kg day keV). The nuclear recoil background in the same region is 2.8x10^{-7}/(kg day keV). With an exposure of 5.6 ton-years, the sensitivity of PandaX-4T could reach a minimum spin-independent dark matter-nucleon cross section of 6x10^{-48} cm^{2} at a dark matter mass of 40 GeV/c^{2}.

Signal-background discrimination with convolutional neural networks in the PandaX-III experiment using MC simulation

The PandaX-III experiment will search for neutrinoless double beta decay of $^{136}$Xe with high pressure gaseous time projection chambers at the China Jin-Ping underground Laboratory. The tracking feature of gaseous detectors helps suppress the background level, resulting in the improvement of the detection sensitivity. We study a method based on the convolutional neural networks to discriminate double beta decay signals against the background from high energy gammas generated by $^{214}$Bi and $^{208}$Tl decays based on detailed Monte Carlo simulation. Using the 2-dimensional projections of recorded tracks on two planes, the method successfully suppresses the background level by a factor larger than 100 with a high signal efficiency. An improvement of $62\%$ on the efficiency ratio of $\epsilon_{s}/\sqrt{\epsilon_{b}}$ is achieved in comparison with the baseline in the PandaX-III conceptual design report.

Constraining Dark Matter Models with a Light Mediator at the PandaX-II Experiment.

We search for nuclear recoil signals of dark matter models with a light mediator in PandaX-II, a direct detection experiment in the China Jinping underground laboratory. Using data collected in 2016 and 2017 runs, corresponding to a total exposure of 54ton day, we set upper limits on the zero-momentum dark matter-nucleon cross section. These limits have a strong dependence on the mediator mass when it is comparable to or below the typical momentum transfer. We apply our results to constrain self-interacting dark matter models with a light mediator mixing with standard model particles, and set strong limits on the model parameter space for the dark matter mass ranging from 5GeV to 10TeV.

Limits on Light Weakly Interacting Massive Particles from the First 102.8 kg×day Data of the CDEX-10 Experiment.

We report the first results of a light weakly interacting massive particles (WIMPs) search from the CDEX-10 experiment with a 10kg germanium detector array immersed in liquid nitrogen at the China Jinping Underground Laboratory with a physics data size of 102.8kg day. At an analysis threshold of 160eVee, improved limits of 8×10^{-42} and 3×10^{-36} cm^{2} at a 90%confidence level on spin-independent and spin-dependent WIMP-nucleon cross sections, respectively, at a WIMP mass (m_{χ}) of 5 GeV/c^{2} are achieved. The lower reach of m_{χ} is extended to 2 GeV/c^{2}.

Taiwan EXperiment On NeutrinO — History and Prospects

We present a retrospective on the foundation, evolution, contributions and future prospects of the TEXONO Collaboration and its research programs on neutrino physics and dark matter searches at the Kuo-Sheng Reactor Neutrino Laboratory in Taiwan and, as a founding partner of the CDEX program, at the China Jinping Underground Laboratory in China. a a This retrospective paper is an expansion and update of one that appeared in “The Universe” newsletter of the Asia Pacific Organization for Cosmology and Particle Astrophysics (APCosPA Org).1

In situ observation and evaluation of zonal disintegration affected by existing fractures in deep hard rock tunneling

Zonal disintegration refers to the phenomenon whereby fractured zones and intact zones appear alternately in surrounding hard rocks under high stress conditions. In this study, zonal disintegration within hard surrounding rocks of deep tunnels at the China Jinping Underground Laboratory Phase II (CJPL-II) was observed by using a digital borehole televiewer in pre-drilled boreholes. The results revealed that fractured zones within intact high-strength marbles were small and exhibited a higher degree of fracturing, whereas fractured zones within low-strength, low-integrity, marbles showed fewer, yet larger fractures. An evaluation method based on rock mass integrity index using digital borehole televiewer data (RMIBT) has been proposed for the analysis of zonal disintegration process in the deep hard rocks surrounding the tunnels. By using the method we were able to quantify the initiation and evolution of fractures during zonal disintegration. The formation mechanism of the second and third fractured zones induced by the existing fractures was further investigated using numerical analysis. The data provide an insight into the evolution of failures in, and a basis for support design and stability control of, deep engineering works in hard rock.

In Situ Observation of Rock Spalling in the Deep Tunnels of the China Jinping Underground Laboratory (2400 m Depth)

To study rock spalling in deep tunnels at China Jinping Underground Laboratory Phase II (CJPL-II), photogrammetry method and digital borehole camera were used to quantify key features of rock spalling including orientation, thickness of slabs and the depth of spalling. The failure mechanism was analysed through scanning electron microscope and numerical simulation based on FLAC3D. Observation results clearly showed the process of rock spalling failure: a typical spalling pattern around D-shaped tunnels after top-heading and bottom bench were discovered. The orientation and thickness of the slabs were obtained. The slabs were parallel to the excavated surfaces of the tunnel and were related to the shape of the tunnel surface and orientation of the principal stress. The slabs were alternately thick and thin, and they gradually increased in thickness from the sidewall inwards. The form and mechanism of spalling at different locations in the tunnels, as influenced by stress state and excavation, were analysed. The result of this study was helpful to those rethinking the engineering design, including the excavation and support of tunnels, or caverns, at high risk of spalling.

Limits on light WIMPs with a 1 kg-scale germanium detector at 160 eVee physics threshold at the China Jinping Underground Laboratory**Supported by the National Key Research and Development Program of China (2017YFA0402200, 2017YFA0402201), the National Natural Science Foundation of China (11175099, 11275107, 11475117, 11475099, 11475092, 11675088), the National Basic Research Program of China (973 Program) (2010CB833006). We thank the support

We report results of a search for light weakly interacting massive particle (WIMP) dark matter from the CDEX-1 experiment at the China Jinping Underground Laboratory (CJPL). Constraints on WIMP-nucleon spin-independent (SI) and spin-dependent (SD) couplings are derived with a physics threshold of 160 eVee, from an exposure of 737.1 kg-days. The SI and SD limits extend the lower reach of light WIMPs to 2 GeV and improve over our earlier bounds at WIMP mass less than 6 GeV.

Design of the FPGA-based gigabit serial link for PandaX-III prototype TPC

PandaX-III is aimed to search for neutrinoless double beta decay of $$^{136}$$ Xe at China Jinping Underground Laboratory. To test various design features of PandaX-III detector, a prototype TPC with 20 kg Xe containing inside is built. Front-end boards installed inside the waterproof vessel integrate charge of Micromegas signal, digitize signal waveform and send data packet to back-end board. Front-end boards receive synchronous information (global clock, global trigger, etc.), as well as command messages from back-end board. In order to satisfy the requirement of high data throughput and multiple types of synchronous data transmission, we propose an optical fiber link to communicate between front-end board and back-end board. Communication of serial transmission is performed using FPGA-based gigabit transceiver with a 1 Gbit/s point-to-point speed. A dedicated user-defined protocol is implemented for various kinds of data transmission. To validate the performance of this link, bit error rate and eye diagram were tested. Preliminary joint test with detector was conducted in Shanghai. All test results showed sufficient data bandwidth and stable performance. To satisfy the requirement for data transmission between front-end board and back-end board in PandaX-III TPC detector readout, an FPGA-based gigabit serial link is designed and tested. This design shows good performance and will be applied to the R&D of PandaX-III TPC.

Assay of low-background stainless steel by smelting for the neutrino experiment at Jinping

To ensure compliance with the experimental requirement for ultra-low background, in this study the radioactivity of stainless steels manufactured by smelting is thoroughly investigated. Raw materials, stage samples, and commercial samples are investigated by glow discharge mass spectrometry (GDMS) and/or with high-purity germanium detectors (HPGe) at both the ground level and/or the China Jinping Underground Laboratory. Custom-made stainless steel samples are found to have radioactivity levels comparable to those in other low-background experiments. The comprehensive results regarding the radioactivity level in materials to be used in the proposed Jinping Neutrino Experiment are reported.

Limits on Axion Couplings from the First 80 Days of Data of the PandaX-II Experiment.

We report new searches for solar axions and galactic axionlike dark matter particles, using the first low-background data from the PandaX-II experiment at China Jinping Underground Laboratory, corresponding to a total exposure of about 2.7×10^{4} kg day. No solar axion or galactic axionlike dark matter particle candidate has been identified. The upper limit on the axion-electron coupling (g_{Ae}) from the solar flux is found to be about 4.35×10^{-12} in the mass range from 10^{-5} to 1 keV/c^{2} with 90%confidence level, similar to the recent LUX result. We also report a new best limit from the ^{57}Fe deexcitation. On the other hand, the upper limit from the galactic axions is on the order of 10^{-13} in the mass range from 1 to 10 keV/c^{2} with 90%confidence level, slightly improved compared with the LUX.