arXiv subjects

Zeyuan Yu

Publications and source records attributed to Zeyuan Yu.

16 recordsLinked to original sources

arXiv2026

Long-Delayed Afterpulse Measurement of JUNO 20-inch Photomultiplier Tubes

In large-scale liquid scintillator detectors such as the Jiangmen Underground Neutrino Observatory (JUNO), high-intensity events like cosmic muons induce photomultiplier tube (PMT) afterpulses that can interfere with the analysis of delayed physics signals. To systematically evaluate this instrumental background, we present a dedicated measurement of long-delayed afterpulses in two types of JUNO 20-inch PMTs: a dynode-based PMT and a microchannel-plate (MCP) PMT. The afterpulse time profiles were first characterized within a direct 1.8~ms waveform window and were further extended to 20~ms using a sliding-window readout strategy. Distinct long-delayed components are observed, revealing a strong dependence on the PMT multiplication structure. The dynode PMT exhibits a broad afterpulse component peaking at approximately 260~$\mu$s, whereas the MCP-PMT shows a pronounced peak around 90~$\mu$s, an additional component around 550~$\mu$s, and a much smaller, broadly distributed millisecond-scale component. For the microsecond-scale components, the afterpulse yield per primary photoelectron is at the $10^{-3}$ level in the selected delayed windows and increases approximately linearly with the primary light intensity. The accumulated delayed activity can therefore become non-negligible following high-intensity events. These quantitative findings provide critical inputs for PMT response characterization and for the accurate modeling of delayed correlated backgrounds in high-precision neutrino experiments.

hep-ex↗

arXiv2026

An eightfold equivalence-preserving speedup of the JUNO OMILREC vertex and energy reconstruction

The Jiangmen Underground Neutrino Observatory (JUNO) reconstructs each event's vertex and energy with OMILREC, a maximum-likelihood fit that scans all $17{,}612$ large photomultiplier tubes (LPMTs) in every Minuit function evaluation, about $470$ times per event. This inner loop dominates the reconstruction CPU cost. Profiling shows that the production algorithm is latency-bound, sustaining only $9.9%$ of scalar floating-point peak because of virtual-function dispatch, ROOT-histogram pointer chasing, and repeated computation. We apply staged \emph{equivalence-preserving} optimizations: flattened data layouts, vectorizable geometry, hoisting of Minuit-invariant work, per-event precomputation, fit-phase loop splitting and indexing, and reduced-precision fast paths. Each stage is checked against a frozen reference from the unmodified code. The optimized implementation achieves single-thread speedups of $8.06\times$ ($1524.8 \rightarrow 189.2$~ms/event) on an Intel Xeon Platinum~8358P and $5.22\times$ ($705.1 \rightarrow 134.9$~ms/event) on an AMD~EPYC~9654, increasing to $8.6\times$ ($177.7$~ms/event) after further optimization. The likelihood remains bit-identical through the first seven releases and later agrees within a relative drift of $1.3\times10^{-14}$, below the $10^{-13}$ contract. For typical events, reconstructed vertex and energy agree with the baseline within $4$~mm and $7$~keV; a few boundary cases reach different valid minima owing to an improved minimizer seed. An eight-metric physics-acceptance test also passes on about $861{,}000$ $^{68}$Ge calibration events. Developed with assistance from an AI coding agent operating under these verification gates, this workflow offers a transferable template for accelerating likelihood-based reconstruction in large neutrino and collider detectors without changing physics output.

physics.ins-det↗

arXiv2026

A unified quenching model in Geant 4 simulation for $\alpha$, proton and electron particles in liquid scintillator detectors

The liquid scintillator (LS) detectors are widely used in reactor neutrino experiments. To precisely measure the oscillated neutrino spectrum, it is crucial to understand the LS energy response, especially the quenching effect. Numerous bench-top measurements have been conducted on quenching effects for $\alpha$ particles, protons, and electrons. These results have typically been described by Birks' law, but with different Birks' coefficients required for different particle species. In this study, we find that if more secondary electrons are allowed to be generated in Geant4 simulations, the bench-top results for all particles can be well fitted using a single Birks' coefficient of about $0.013~{\rm g\,cm^{-2}\,MeV^{-1}}$. The underlying reason is that a large fraction of the primary energy is deposited through the generation of $\delta$-electrons with energies below 4~keV, which should be tracked separately due to their different quenching behavior compared to primary particles. This study provides a unified framework for comparing Birks' coefficients from different bench-top measurements and helps experiments like JUNO and SNO+ better tune their simulations for precision energy measurements.

hep-ex↗

arXiv2026

Test of the JUNO 20-inch PMTs during Installation

Photomultiplier tubes (PMTs) are widely used in neutrino experiments. As a new-generation neutrino observatory, JUNO requires an excellent energy resolution of 3% at 1 MeV. This will be realized with a 20 kton liquid scintillator detector instrumented with more than 20000 20-inch PMTs and 25600 3-inch PMTs. These PMTs were successfully installed in JUNO from October 2022 to December 2024. During the installation, seven test campaigns were performed to validate the PMT functionality, including measurements dark count rate, gain, waveform, and charge spectrum. In this paper, we present the implementation of these tests and the corresponding results for the 20-inch PMTs throughout the installation process.

physics.ins-det↗

arXiv2026

Impact of the $^5$Li resonance in $\alpha$-$p$ elastic scattering on precision measurements of neutrino oscillation parameters

Precision measurements of four neutrino oscillation parameters, $\theta_{12}$, $\theta_{13}$, $\Delta m^2_{21}$, and |$\Delta m^2_{31}$|, face significant interference from a previously overlooked correlated background. Recent findings from the SNO+ and JUNO experiments reveal that cascade decays of $^{214}$Bi-$^{214}$Po in liquid scintillator detectors can mimic inverse beta decay signals from reactor and geoneutrinos, with a misidentification probability on the order of $10^{-4}$ when hydrogen neutron capture is used, a rate ten times higher than Geant4 simulations predicted. This work identifies the $^5$Li resonance in $\alpha$-$p$ elastic scattering as the underlying cause. For alpha energies above 5~MeV, the cross section is hundreds of times larger than that of Rutherford scattering. After correctly incorporating the differential cross section into Geant4, the misidentification probability is recalculated as 1.9$\times$10$^{-4}$. The simulated shape of the long tail in the alpha deposited energy also differs from the extrapolation models currently used by SNO+ and JUNO. These results will assist both experiments in more accurately estimating this novel background, thereby refining measurements of neutrino oscillation parameters and the geoneutrino flux. Additionally, the study implies an overlooked background with a rate of 0.5 events per detector per day in the Daya Bay $\theta_{13}$ analysis using hydrogen neutron capture, leading to an increase of $\sin^22\theta_{13}$ by approximately 0.012. Consequently, the Particle Data Group's reported $\sin^2\theta_{13}$ value shall increase by about 0.006~(1$\sigma$).

nucl-ex↗

arXiv2024

A novel measurement method for SiPM external crosstalk probability at low temperature

Silicon photomultipliers (SiPMs) are being considered as potential replacements for conventional photomultiplier tubes (PMTs). However, a significant disadvantage of SiPMs is crosstalk (CT), wherein photons propagate through other pixels, resulting in secondary avalanches. CT can be categorized into internal crosstalk and external crosstalk based on whether the secondary avalanche occurs within the same SiPM or a different one. Numerous methods exist for quantitatively estimating the percentage of internal crosstalk (iCT). However, external crosstalk (eCT) has not been extensively studied. This article presents a novel measurement method for the probability of emitting an external crosstalk photon during a single pixel avalanche, using a setup involving two identical SiPMs facing each other, and without the need for complex optical designs. The entire apparatus is enclosed within a stainless steel chamber, functioning as a light-tight enclosure, and maintained at liquid nitrogen temperature. The experimental setup incorporates two Sensl J-60035 SiPM chips along with two 0.5-inch Hamamatsu Photonics (HPK) VUV4 S13370-6050CN SiPM arrays. The findings show a linear relationship between the probability of emitting an external crosstalk photon and the SiPM overvoltage for both SiPM samples. Surprisingly, this novel measurement method also rovides measurements of the SiPM photon detection efficiency (PDE) for eCT photons at low temperature.

physics.ins-det↗

arXiv2023

A note on the stabilizer formalism via noncommutative graphs

In this short note we formulate a stabilizer formalism in the language of noncommutative graphs. The classes of noncommutative graphs we consider are obtained via unitary representations of compact groups, and suitably chosen operators on finite-dimensional Hilbert spaces. Furthermore, in this framework, we generalize previous results in this area for determining when such noncommutative graphs have anticliques.

cs.IT↗

arXiv2022

Model Independent Approach of the JUNO $^8$B Solar Neutrino Program

The physics potential of detecting $^8$B solar neutrinos will be exploited at the Jiangmen Underground Neutrino Observatory (JUNO), in a model independent manner by using three distinct channels of the charged-current (CC), neutral-current (NC) and elastic scattering (ES) interactions. Due to the largest-ever mass of $^{13}$C nuclei in the liquid-scintillator detectors and the {expected} low background level, $^8$B solar neutrinos would be observable in the CC and NC interactions on $^{13}$C for the first time. By virtue of optimized event selections and muon veto strategies, backgrounds from the accidental coincidence, muon-induced isotopes, and external backgrounds can be greatly suppressed. Excellent signal-to-background ratios can be achieved in the CC, NC and ES channels to guarantee the $^8$B solar neutrino observation. From the sensitivity studies performed in this work, we show that JUNO, with ten years of data, can reach the {1$\sigma$} precision levels of 5%, 8% and 20% for the $^8$B neutrino flux, $\sin^2\theta_{12}$, and $\Delta m^2_{21}$, respectively. It would be unique and helpful to probe the details of both solar physics and neutrino physics. In addition, when combined with SNO, the world-best precision of 3% is expected for the $^8$B neutrino flux measurement.

hep-ex↗

arXiv2021

Radiogenic neutron background in reactor neutrino experiments

We report a novel correlated background in the antineutrino detection using the inverse beta decay reaction. Spontaneous fissions and $(\alpha,n)$ reactions in peripheral materials of the antineutrino detector, such as borosilicate glass of photomultipliers, produce fast neutrons and prompt gamma rays. If the shielding from the material to the detector target were not thick enough, neutrons and gammas could enter the target volume and mimic antineutrino signals. This paper revisits the yields and energy spectra of neutrons produced in B$(\alpha,n)$N and F$(\alpha,n)$Na reactions. A Geant4 based simulation has been carried out using a simplified detector geometry for the present generation reactor neutrino experiments. The background rates in these experiments are estimated. If this background was not taken into account, the value of the neutrino mixing angle $\sin^22\theta_{13}$ would be underestimated. We recommend that Daya Bay, RENO, Double Chooz, and JUNO, carefully examine the masses and radiopurity levels of detector materials that are close to the target and rich in boron and fluorine.

physics.ins-det↗

arXiv2021

Improving the energy uniformity for large liquid scintillator detectors

It is challenging to achieve high precision energy resolution for large liquid scintillator detectors. Energy non-uniformity is one of the main obstacles. To surmount it, a calibration-data driven method was developed previously to reconstruct event energy in the JUNO experiment. In this paper, we investigated the choice of calibration sources thoroughly, optimized the calibration positions and corrected the residual detector azimuthal asymmetry. All these efforts lead to a reduction of the energy non-uniformity near the detector boundary, from about 0.64% to 0.38%. And within the fiducial volume of the detector it is improved from 0.3% to 0.17%. As a result the energy resolution could be further improved.

physics.ins-det↗

arXiv2020

The replacement system of the JUNO liquid scintillator pilot experiment at Daya Bay

The Jiangmen Underground Neutrino Observatory (JUNO), a multi-purpose neutrino experiment, will use 20 kt liquid scintillator (LS). To achieve the physics goal of determining the neutrino mass ordering, 3$\%$ energy resolution at 1 MeV is required. This puts strict requirements on the LS light yield and the transparency. Four LS purification steps have been designed and mid-scale plants have been built at Daya Bay. To examine the performance of the purified LS and find the optimized LS composition, the purified LS was injected to the antineutrino detector 1 in the experimental hall 1 (EH1-AD1) of the Daya Bay neutrino experiment. To pump out the original gadolinium loaded LS and fill the new LS, a LS replacement system has been built in EH1 in 2017. By replacing the Gd-LS with purified water, then replacing the water with purified LS, the replacement system successfully achieved the designed goal. Subsequently, the fluorescence and the wavelength shifter were added to higher concentrations via the replacement system. The data taken at various LS compositions helped JUNO determine the final LS cocktail. Details of the design, the construction, and the operation of the replacement system are reported in this paper.

physics.ins-det↗

arXiv2020

Making Robots Draw A Vivid Portrait In Two Minutes

Significant progress has been made with artistic robots. However, existing robots fail to produce high-quality portraits in a short time. In this work, we present a drawing robot, which can automatically transfer a facial picture to a vivid portrait, and then draw it on paper within two minutes averagely. At the heart of our system is a novel portrait synthesis algorithm based on deep learning. Innovatively, we employ a self-consistency loss, which makes the algorithm capable of generating continuous and smooth brush-strokes. Besides, we propose a componential sparsity constraint to reduce the number of brush-strokes over insignificant areas. We also implement a local sketch synthesis algorithm, and several pre- and post-processing techniques to deal with the background and details. The portrait produced by our algorithm successfully captures individual characteristics by using a sparse set of continuous brush-strokes. Finally, the portrait is converted to a sequence of trajectories and reproduced by a 3-degree-of-freedom robotic arm. The whole portrait drawing robotic system is named AiSketcher. Extensive experiments show that AiSketcher can produce considerably high-quality sketches for a wide range of pictures, including faces in-the-wild and universal images of arbitrary content. To our best knowledge, AiSketcher is the first portrait drawing robot that uses neural style transfer techniques. AiSketcher has attended a quite number of exhibitions and shown remarkable performance under diverse circumstances.

cs.RO↗

arXiv2017

The Flash ADC system and PMT waveform reconstruction for the Daya Bay Experiment

To better understand the energy response of the Antineutrino Detector (AD), the Daya Bay Reactor Neutrino Experiment installed a full Flash ADC readout system on one AD that allowed for simultaneous data taking with the current readout system. This paper presents the design, data acquisition, and simulation of the Flash ADC system, and focuses on the PMT waveform reconstruction algorithms. For liquid scintillator calorimetry, the most critical requirement to waveform reconstruction is linearity. Several common reconstruction methods were tested but the linearity performance was not satisfactory. A new method based on the deconvolution technique was developed with 1% residual non-linearity, which fulfills the requirement. The performance was validated with both data and Monte Carlo (MC) simulations, and 1% consistency between them has been achieved.

physics.ins-det↗

arXiv2016

Neutron Beam Tests of Barium Fluoride Crystal for Dark Matter Direct Detection

In order to test the capabilities of Barium Fluoride (BaF2) Crystal for dark matter direct detection, nuclear recoils are studied with mono-energetic neutron beam. The energy spectra of nuclear recoils, quenching factors for elastic scattering neutrons and discrimination capability between neutron inelastic scattering events and {\gamma} events are obtained for various recoil energies of the F content in BaF2.

physics.ins-det↗

arXiv2016

Neutron Beam Tests of $CsI(Na)$ and $CaF_{2}(Eu)$ Crystals for Dark Matter Direct Search

In recent decades, inorganic crystals have been widely used in dark matter direct search experiments. To contribute to the understanding of the capabilities of $CsI(Na)$ and $CaF_{2}(Eu)$ crystals, a mono-energetic neutron beam is utilized to study the properties of nuclear recoils, which are expected to be similar to signals of dark matter direct detection. The quenching factor of nuclear recoils in $CsI(Na)$ and $CaF_{2}(Eu)$, as well as an improved discrimination factor between nuclear recoils and ${\gamma}$ backgrounds in $CsI(Na)$, are reported.

physics.ins-det↗

arXiv2013

13C(alpha,n)16O background in a liquid scintillator based neutrino experiment

Alpha from natural radioactivity may interact with a nucleus and emit a neutron. The reaction introduces background to the liquid scintillator (LS) based neutrino experiments. In the LS detector, alpha comes from 238U, 232Th and 210Po decay chains. For Gadolinium-doped LS (Gd-LS) detector, alpha also comes from 227Ac. The nucleus 13C is a natural component of Carbon which is rich in the LS. The background rate and spectrum should be subtracted carefully from the neutrino candidates. This paper describes the calculation of neutron yield and spectrum with uncertainty estimated. The results are relevant for many existing neutrino experiments and future LS or Gd-LS based experiments.

physics.ins-det↗