20-inch photomultiplier tube timing study for JUNO

Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid scintillator neutrino detector now under construction at Jiangmen, Guangdong, China for determination of neutrino mass ordering with 3% energy resolution at 1 MeV, a precise measurement of neutrino oscillation parameters, and other neutrino physics. The central detector is made up of a 35.4-meter diameter acrylic sphere which contains 20 kton of liquid scintillator and is surrounded by about 18k 20-inch photomultiplier tubes (PMTs). The PMTs performance is one of the JUNO’s key successes to reach the high resolution goal. In this study, the PMT characteristic and its timing related responses were determined via the PMT generated signals, extracted from the PMT in a scanning station system. About 2,400 of micro-channel plate PMTs (MCP-PMTs) and dynode PMTs were analyzed for their responses with LED source such as rise time, fall time, transit time spread (TTS), gain, etc., which relate to photon incident on different positions of PMT’s glass surface. Furthermore, we also observed the fluctuation of PMT performance under magnetic field which can decrease the PMT photon detection efficiency (PDE).

The stress measurement system for the JUNO Central Detector acrylic panels

The Jiangmen Underground Neutrino Observatory (JUNO) Central Detector (CD) is a huge acrylic spherical vessel containing 20,000 tons of liquid scintillator; the sphere is composed of 263 pieces of acrylic spherical panels bonded by the mass polymerization. The operation life time of the JUNO CD is 20 years. To ensure the structural safety during the JUNO CD life time, the acrylic stress of CD is required not to be greater than 3.5 MPa. The stresses of acrylic spherical panels are required to be measured during the installation on-site; unfortunately there is no suitable commercial measurement equipment that can meet JUNO's requirements. Therefore, a measurement setup based on photo-elastic principle and spectrometric methods was designed, developed and tested for on-site measurements. The measurement system performs accurate calibration of stress-optical coefficient of acrylic in JUNO, and gives reliable results of acrylic stresses. The measurement system has been tested in the Taixing Donchamp Acrylic Ltd mechanical workshop, and the achieved results meet the JUNO's requirements. The measurement principle, the system components, and the tooling design are introduced in the paper. Moreover, the calibration of stress-optical coefficient of the acrylic and measurements results on JUNO acrylic spherical panels are discussed in the following.

Accurate prediction of the Drell-Yan φ∗ η distribution in wide dilepton mass and rapidity ranges in pp collisions through NNLO+N3LL

This paper presents high-accuracy predictions for the differential cross sections as a function of the key observable φ*η of the neutral-current Drell-Yan (DY) dilepton production in proton-proton (pp) collisions. The differential distributions for the φ*η are presented by using the state-of-the-art predictions from the combined calculations of fixed-order perturbative QCD corrections at next-to-next-to-leading order (NNLO) accuracy and resummation of large logarithmic terms at next-to-next-to-leading logarithmic (NNLL) and next-to-NNLL (N3LL) accuracies, i.e., NNLO+NNLL and NNLO+N3LL, respectively. The predicted distributions are reported for a thorough set of the DY dilepton invariant mass mll ranges, spanning a wide kinematic region of 50 < mll< 1000 GeV both near and away from the Z-boson mass peak, and rapidity yll ranges in the central detector acceptance region of |yll| < 2.4. The differential φ*η distributions in the wide mll and yll ranges offer stringent tests to assess the reliability of the predictions, where the mll and yll are closely correlated with the parton distribution functions (PDFs) of the incoming partons. The merged predictions through NNLO+N3LL are observed to provide good description of the 13 TeV pp collision data for the φ*η (including the dilepton transverse momentum pll T as well) distributions in almost the entire mll and yll ranges, apart from the intermediate- to high-φ*η region in the lowest mass range 50–76 GeV which is assessed to constitute a challenge for the presented predictions. The merged predictions at NNLO+N3LL are also reported at 14 TeV for the upcoming high-luminosity running era of the LHC, in which increasing amount of data is expected to require more accurate and precise theoretical description. The most recent PDF models MSHT20 and CT18 are tested for the first time in addition to the NNPDF3.1 exploiting the merged φ*η predictions.

The design and sensitivity of JUNO’s scintillator radiopurity pre-detector OSIRIS

The OSIRIS detector is a subsystem of the liquid scintillator filling chain of the JUNO reactor neutrino experiment. Its purpose is to validate the radiopurity of the scintillator to assure that all components of the JUNO scintillator system work to specifications and only neutrino-grade scintillator is filled into the JUNO Central Detector. The aspired sensitivity level of $$10^{-16}\hbox { g/g}$$ 10 - 16 g/g of $$^{238}\hbox {U}$$ 238 U and $$^{232}\hbox {Th}$$ 232 Th requires a large ($$\sim 20\,\hbox {m}^3$$ ∼ 20 m 3 ) detection volume and ultralow background levels. The present paper reports on the design and major components of the OSIRIS detector, the detector simulation as well as the measuring strategies foreseen and the sensitivity levels to U/Th that can be reached in this setup.

Calibration strategy of the JUNO experiment

We present the calibration strategy for the 20 kton liquid scintillator central detector of the Jiangmen Underground Neutrino Observatory (JUNO). By utilizing a comprehensive multiple-source and multiple-positional calibration program, in combination with a novel dual calorimetry technique exploiting two independent photosensors and readout systems, we demonstrate that the JUNO central detector can achieve a better than 1% energy linearity and a 3% effective energy resolution, required by the neutrino mass ordering determination.

Comprehensive sensitivity analysis of rotational stability of a super-deep underground spherical structure considering uncertainty

Jiangmen Underground Neutrino Observatory central detector is located 700 m below the ground and also submerged into an ultrapure water pool. The main structure of the Jiangmen Underground Neutrino Observatory central detector is a hybrid spherical shell that is vulnerable to rotation under the buoyancy effect. The influences of the model parameters on the rotational stability of this complex and unique structure are investigated. Since the model parameters are inevitably subjected to many sources of uncertainties (e.g. manufacturing tolerances and geometrical imperfections), the parameter uncertainty is taken into account. In addition, linear and nonlinear rotational stabilities of this super-deep underground spherical structure are also under consideration. Specifically, the critical loading multiplier is used as the evaluation indicator of linear rotational stability and the load proportionality factor- θ curve is considered as the evaluation indicator of nonlinear rotational stability. The sensitivity of linear and nonlinear rotational stabilities to uncertain parameters is systematically studied in terms of univariate and multivariate global sensitivity analyses. The univariate global sensitivity analysis is able to evaluate the effects of uncertain parameters on each evaluation indicator, whereas multivariate global sensitivity analysis enables to assess the global influence of uncertain parameters on all evaluation indicators. A polynomial chaos expansion surrogate model is utilized to replace the time-consuming simulation model for analytical implementation of the univariate and multivariate global sensitivity analyses. The present polynomial chaos expansion-based univariate and multivariate global sensitivity analyses effectively and efficiently reveal the sensitivity of the rotational stability of this super-deep underground spherical structure to uncertain parameters, and provide a practical method for comprehensive sensitivity analysis of similar structures.