arXiv subjects

Xilei Sun

Publications and source records attributed to Xilei Sun.

At least 19 recordsLinked to original sources

arXiv2026

Study of the intrinsic resolution of LaBr3(Ce,Sr) and NaI(Tl) crystals

The Gravitational wave burst high-energy Elec?tromagnetic Counterpart All-sky Monitor (GECAM) utilizes a large number of LaBr3 and NaI(Tl) crystals as sensitive materials for its gamma-ray detectors. To address the fitting issues of the energy resolution curves in the ground calibration of the GECAM detectors, this work conducts a comprehensive testing and comparative study of the energy resolution of 1-inch LaBr3(Ce,Sr) and NaI(Tl) crystals produced from the same batch. We employed a Hard X-ray Calibration Facility (HXCF), a PMT single-photoelectron calibration system, and Geant4 Monte Carlo simulation tools to quantify seven factors influencing energy resolution. The results indicate that the contributions of various components to energy resolution differ, with pho?toelectron statistical fluctuations and intrinsic resolution being predominant. For 100 keV X-rays, the total energy resolution of the LaBr3(Ce,Sr) crystal is 3.71% \pm 0.03% (expressed as 1-{\sigma}), with a contribution from photoelectron statistical fluctuations of 2.69% \pm 0.00% and an intrinsic resolution of 2.45% \pm 0.05%. For 100 keV X-rays, the total energy resolution of the NaI(Tl) crystal is 4.41% \pm 0.14% (expressed as 1-{\sigma}), with a contribution from photoelectron statistical fluctuations of 3.20% \pm 0.00% and an intrinsic resolution of 2.90% \pm 0.21%. We discussed the sources of intrinsic resolution, and the results indicate that the intrinsic resolution of the LaBr3(Ce,Sr) crystal primarily arises from luminescence non-proportionality, while that of the NaI(Tl) crystal mainly stems from fluctuations during energy transfer. This study emphasizes precise and specific experimental measurements and comparative research, demonstrating that both factors are important contributors to intrinsic resolution.

physics.ins-det↗

arXiv2026

SuperEM: A Sub-meV Threshold Detector Architecture for Cosmic Neutrino Background and Dark Matter Detection

Expanding the operational boundaries of radiation detection is imperative for contemporary particle physics, astrophysics, and cosmology. At this frontier, the direct detection of the Cosmic Neutrino Background (C$\nu$B), the determination of the absolute neutrino mass scale, and the search for sub-GeV Light Dark Matter (LDM) necessitate detector architectures capable of sub-millielectronvolt (sub-meV) energy thresholds, exceptional absolute energy resolution, fast time response, and massive scalability. Current technologies confront an intrinsic limit---the ``impossible triangle''---wherein optimizing for sub-meV thresholds inherently compromises either macroscopic timing response or spatial scalability. Here, we introduce the Superconductor-Coupled Semiconductor Electron-Multiplying (SuperEM) detector, a fundamentally novel structural paradigm designed to bypass this limitation. The architecture couples the ultra-low energy threshold of a superconducting absorber with the intrinsic high-gain digitization of a strongly biased, high-density semiconductor P-N junction. Incident energy yields a proliferation of non-equilibrium quasiparticles, which are subsequently extracted via quantum tunneling across an ultra-thin Atomic Layer Deposition (ALD) insulating barrier. Building upon our prior empirical validation of deep-cryogenic avalanche mechanics, this manuscript establishes the fundamental theoretical feasibility and structural foundation of the complete device. Signal transport simulations confirm that an undoped interface coupled with a strong drift field enables highly efficient, nanosecond-scale transient electron drift, resolving completely within 35 ns. The SuperEM architecture thus constitutes a scalable, high-resolution, and fast time-response framework for next-generation C$\nu$B and LDM observatories.

hep-ex↗

arXiv2026

Parameter Effects in Circumplanetary Disk Spectra and Prospects for Spectral Fitting

With the commissioning of the James Webb Space Telescope (JWST), near- and mid-infrared observations are rapidly extending into the wavelength regime where emission from small dust grains in circumplanetary disks (CPDs) is expected to dominate. We aim to systematically investigate how individual physical parameters of CPDs shape their infrared spectra and to improve the robustness of spectral fitting and physical interpretation of current and future observations. Building on our previous parametric CPD models, we employ a parameter-grid approach combined with radiative transfer simulations to explore the dependence of observable spectra on disk structure and dust properties. We identify the physical mechanisms responsible for the main spectral features and parameter degeneracies, and present the global trends emerging from the parameter study. We also demonstrate the applicability of the models by fitting representative observational data. Our results provide a structured theoretical framework for interpreting near- and mid-infrared observations of CPDs with JWST and related facilities.

astro-ph.EP↗

arXiv2026

Mixing plant for JUNO liquid scintillator: Design, construction, installation and commissioning

The most challenging part of building the Jiangmen Underground Neutrino Observatory (JUNO) is the production of 20 kilotons of ultra pure Liquid Scintillator (LS). This paper presents the design, construction, installation, and commissioning of the LS Mixing Plant, a core facility dedicated to blending the primary organic solvent (LAB) with essential functional solutes (PPO, bis-MSB, and BHT). The main purpose of the Mixing Plant is to prepare and purify the concentrated Master Solution (MS) to achieve a low radioactive contamination background. The amount of radioactive contaminants in the MS are lowered by approximately two orders of magnitude after acid and water extraction, followed by a multi-stage filtration procedure. The purified MS is mixed with LAB and then diluted into the LS for JUNO experiments. Commissioning results of the LS verify that the Mixing Plant achieved its design goal, delivering ultra pure LS that satisfies the stringent radiopurity requirements for neutrino physics.

physics.ins-det↗

arXiv2026

A Pathway to Sub-meV Detection of the Dark Universe: Robust Electron Avalanche in the PN junction at 10 mK

The search for light dark matter and cosmic primordial neutrinos necessitates detectors with sub-millielectronvolt (sub-meV) energy thresholds. While superconducting quantum sensors have approached this sensitivity, they often face significant challenges regarding readout complexity and scalability. To address these limitations, we propose a hybrid Superconductor-Insulator-P-N (S-I-P-N) detector architecture. This concept combines the high sensitivity of superconducting Cooper pair breaking with the massive intrinsic gain of semiconductor electron avalanches. A critical prerequisite for this scheme is operation at millikelvin (mK) temperatures, raising the critical fundamental question of whether silicon PN junctions can sustain avalanche multiplication in a regime where carrier freeze-out is severe. Here, we experimentally validate the critical semiconductor amplification stage of the proposed detector. We demonstrate that Silicon Photomultipliers (SiPMs) retain robust Geiger-mode avalanche capabilities at 10 mK. We report a single-photoelectron gain of order 10$^6$ and a dark count rate as low as 5~mHz/mm$^2$, 7 orders of magnitude lower than at room temperature. These results confirm the viability of high-gain semiconductor readout in the deep cryogenic regime, clearing the primary obstacle regarding the semiconductor component for the realization of scalable, sub-meV threshold S-I-P-N detectors.

physics.ins-det↗

arXiv2025

Characterization of SiPMs at 40 K for neutrino coherent detection based on pure CsI

Silicon photomultiplier (SiPM), as the core photoelectric sensor for coherent neutrino detection in low-temperature pure CsI, its working performance directly determines the measurement accuracy of the scintillator light yield. Our previous research has fully demonstrated the performance of pure CsI at liquid nitrogen temperature. More intriguingly, its performance is expected to be even better at 40 K. However, the performance characteristics of SiPM in the 40 K temperature range still remain to be explored. In this study, a self-developed adjustable temperature control system ranging from 30 K to 293 K was built to investigate the key performance parameters of SiPM at different temperatures, such as single photoelectron spectrum, gain, breakdown voltage, dark count rate, after-pulse, internal crosstalk, and single photoelectron resolution. Special emphasis was placed on examining the key performance parameters of SiPM in the 40 K temperature range to evaluate its feasibility for light yield measurement in this temperature range. The results show that this study obtained the parameter variation trends and optimal working conditions of 3 types of SiPM at different temperatures, thereby improving the sensitivity of the detector. This research provides important technical support for low-temperature detection in neutrino physics experiments.

physics.ins-det↗

arXiv2025

A Comprehensive Monte Carlo Simulation Tool on Electron Transport in Noble Gases and Liquids

For the particle detectors based on noble gases or liquids, it is essential to understand the transport dynamic and the properties of the electrons. We report the development of a tool for electron transport in noble gases He, Ne, Ar, Kr, or Xe, and liquids Ar, Kr, or Xe. The simulation, implemented in C++ and MATLAB, is based on electron-atom collisions, including elastic scattering, excitation and ionization. We validate the program through assessing the electron's swarm parameters, specifically the drift velocity and the diffusion coefficient. For electron transport in liquids, two models are discussed and both are used for the construction of the Monte Carlo framework based on the Cohen Leker theory. The results demonstrate the effectiveness and accuracy of the simulation tool, which offers a valuable support for detector design and data analysis.

physics.ins-det↗

arXiv2024

Observational characteristics of circum-planetary-mass-object disks in the era of James Webb Space Telescope

Recent observations have confirmed circumplanetary disks (CPDs) embedded in parental protoplanetary disks (PPDs). On the other hand, planetary-mass companions (PMCs) and planetary-mass objects (PMOs) are likely to harbor their own accretion disks. Unlike PPDs, CPDs and other disks around planet analogues are generally too compact to be spatially resolved by current instrumentation. In this study, we generate over 4,000 spectral energy distributions (SEDs) of circum-PMO-disks (CPMODs) with various host temperature and disk properties, which can be categorized into four prototypes, i.e., full, pre-transitional, transitional and evolved CPMODs. We propose a classification scheme based on their near-to-mid-infrared colors. Using those CPMOD models, we synthesize JWST (NIRCam and MIRI) photometry for F444W, F1000W and F2550W wide filters. We show F444W - F1000W and F444 - F2550W colors can be applied to distinguish different types of CPMODs, especially for those around hot hosts. Our results indicate that the ongoing and future JWST observations are promising to unveil structures and properties of CPMODs.

astro-ph.EP↗

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

The performance of SiPM-based gamma-ray detector (GRD) of GECAM-C

As a new member of GECAM mission, the GECAM-C (also called High Energy Burst Searcher, HEBS) is a gamma-ray all-sky monitor onboard SATech-01 satellite, which was launched on July 27th, 2022 to detect gamma-ray transients from 6 keV to 6 MeV, such as Gamma-Ray Bursts (GRBs), high energy counterpart of Gravitational Waves (GWs) and Fast Radio Bursts (FRBs), and Soft Gamma-ray Repeaters (SGRs). Together with GECAM-A and GECAM-B launched in December 2020, GECAM-C will greatly improve the monitoring coverage, localization, as well as temporal and spectral measurements of gamma-ray transients. GECAM-C employs 12 SiPM-based Gamma-Ray Detectors (GRDs) to detect gamma-ray transients . In this paper, we firstly give a brief description of the design of GECAM-C GRDs, and then focus on the on-ground tests and in-flight performance of GRDs. We also did the comparison study of the SiPM in-flight performance between GECAM-C and GECAM-B. The results show GECAM-C GRD works as expected and is ready to make scientific observations.

astro-ph.IM↗

arXiv2023

A Localization Method of High Energy Transients for All-Sky Gamma-Ray Monitor

Fast and reliable localization of high-energy transients is crucial for characterizing the burst properties and guiding the follow-up observations. Localization based on the relative counts of different detectors has been widely used for all-sky gamma-ray monitors. There are two major methods for this counts distribution localization: $χ^{2}$ minimization method and the Bayesian method. Here we propose a modified Bayesian method that could take advantage of both the accuracy of the Bayesian method and the simplicity of the $χ^{2}$ method. With comprehensive simulations, we find that our Bayesian method with Poisson likelihood is generally more applicable for various bursts than $χ^{2}$ method, especially for weak bursts. We further proposed a location-spectrum iteration approach based on the Bayesian inference, which could alleviate the problems caused by the spectral difference between the burst and location templates. Our method is very suitable for scenarios with limited computation resources or time-sensitive applications, such as in-flight localization software, and low-latency localization for rapid follow-up observations.

astro-ph.HE↗

arXiv2022

Calibration Strategy of the JUNO-TAO Experiment

The Taishan Antineutrino Observatory (JUNO-TAO, or TAO) is a satellite detector for the Jiangmen Underground Neutrino Observatory (JUNO). Located near the Taishan reactor, TAO independently measures the reactor's antineutrino energy spectrum with unprecedented energy resolution. To achieve this goal, energy response must be well calibrated. Using the Automated Calibration Unit (ACU) and the Cable Loop System (CLS) of TAO, multiple radioactive sources are deployed to various positions in the detector to perform a precise calibration of energy response. The non-linear energy response can be controlled within 0.6% with different energy points of these radioactive sources. It can be further improved by using $^{12}\rm B$ decay signals produced by cosmic muons. Through the energy non-uniformity calibration, residual non-uniformity is less than 0.2%. The energy resolution degradation and energy bias caused by the residual non-uniformity can be controlled within 0.05% and 0.3%, respectively. In addition, the stability of other detector parameters, such as the gain of each silicon photo-multiplier, can be monitored with a special ultraviolet LED calibration system.

physics.ins-det↗

arXiv2021

Gain stabilization and consistency correction approach for multiple SiPM-based gamma-ray detectors on GECAM

Each satellite of the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM, mission) consists of 25 SiPM based gamma-ray detectors (GRDs). Although SiPM based GRD has merits of compact size and low bias-voltage, the drift of the SiPM gain with temperature is a severe problem for GRD performance. An adaptive voltage supply source was designed to automatically adjust the SiPM bias voltage to compensate the temperature effects and keep the gain stable. This approach has been proved to be effective during both the on-ground and in-flight tests. The in-flight measured variation of the SiPM gain is within 2%. To reduce the gain non-uniformity of GRDs, an iterative bias voltage adjustment approach is proposed and implemented. The gain non-uniformity is reduced from 17% to 0.6%. In this paper, the gain stabilization and consistency correction approach are presented and discussed in detail.

physics.ins-det↗

arXiv2021

Development of water extraction system for liquid scintillatorpurification of JUNO

The Jiangmen Underground Neutrino Observatory (JUNO) uses 20k tons of liquid scintillator (LS)to detect neutrinos. The content of radioactive substances in the liquid scintillator will affect theexperimental results. JUNO will use counter current water extraction to reduce the radioactive metalions inside the LS. In this article, The factors that affect the final water extraction like the partitioncoefficient and the factors that affect it, the optimal mass transfer droplet size, the flow rate ratio,theoretical stage and different working mode (LS as continuous phase or dispersed phase) have beenstudied. We built counter current extraction prototype in the laboratory and a pilot plant in Daya Bay.We not only study the factors above, but also get a lot of engineering experience that worth sharing.

physics.ins-det↗

arXiv2020

A liquid scintillator for a neutrino Detector working at -50 degree

A liquid scintillator (LS) is developed for the Taishan Antineutrino Observatory (TAO), a ton-level neutrino detector to measure the reactor antineutrino spectrum with sub-percent energy resolution by adopting Silicon Photomultipliers (SiPMs) as photosensor. To reduce the dark noise of SiPMs to an acceptable level, the LS has to work at -50 degree or lower. A customized apparatus based on a charge-coupled device (CCD) is developed to study the transparency of the liquid samples in a cryostat. We find that the water content in LS results in transparency degradation at low temperature, which can be cured by bubbling dry nitrogen to remove water. Adding 0.05% ethanol as co-solvent cures the solubility decrease problem of the fluors PPO and bis-MSB at low temperature. Finally, a Gadoliniumdoped liquid scintillator (GdLS), with 0.1% Gd by weight, 2 g/L PPO, 1 mg/L bis-MSB, and 0.05% ethanol by weight in the solvent LAB, shows good transparency at -50 degree and also good light yield.

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

The liquid argon detector and measurement of SiPM array at liquid argon temperature

Particle detectors based on liquid argon (LAr) have recently become recognized as an extremely attractive technology for the direct detection of dark matter as well as the measurement of coherent elastic neutrino-nucleus scattering (CE$ν$NS). The Chinese argon group at Institute of High Energy Physics has been studying the LAr detector technology and a LAr detector has been operating steadily. A program of using a dual phase LAr detector to measure the CE$ν$NS at Taishang Nuclear Power Plant has been proposed and the R\&D work is ongoing. Considering the requirements of ultra-low radio-purity and high photon collection efficiency, SiPMs will be a good choice and will be used in the detector. In this proceeding, an introduction of the LAr detector and the measurement results of SiPM array at LAr temperature will be presented.

physics.ins-det↗

arXiv2017

The low temperature performance of CsI(Na) crystals for WIPMs direct searches

Previous studies showed that CsI(Na) crystals have significantly different waveforms between alpha and gamma scintillations. In this work, the light yield and PSD capability of CsI(Na) scintillators as a function of the temperature down to 80 K has been studied. As temperature drops, the fast component rises and the slow component decreases. By cooling the CsI(Na) crystals, the light yield of high ionization events are enhanced significantly, while the light yield of background gamma events are suppressed. At 110 K, CsI(Na) crystal achieves the optimal balance between low threshold and good background rejection performance. The different responses of CsI(Na) to gamma and alpha at different temperatures are explained with self-trapped and activator luminescence centers.

physics.ins-det↗