The AC-Coupled Low Gain Avalanche Diodes (AC-LGADs) represent an advanced silicon sensor technology that retains the exceptional time resolution of standard Low Gain Avalanche Diodes (LGADs) while enhancing position sensitivity through their resistive readout structure. This study addresses the position reconstruction challenge in pixel-type AC-LGADs. Based on a simplified 2D charge diffusion model derived from Ohm's law and current conservation, the position-dependent signal distributions were simulated for circular, square, and cross-shaped metal pads using MATLAB's PDE Toolbox, providing scanned datasets. By expanding the feature space and selecting the optimal number of nearest neighbors (k-value), the optimized K-Nearest Neighbors (KNN) algorithm achieved satisfactory reconstruction accuracy on the simulated datasets for circular and square metal pad configurations. Finally, experimental validation was performed using laser-scan data. With 3000 mu m pitch size, the optimized KNN algorithm achieved positional Root Mean Square Error (RMSE) of 11.2 mu m.

A low-gain avalanche diode (LGAD) is a new type of silicon detector with wide application prospects in particle physics experiments owing to its excellent timing resolution. LGAD sensors, with a pixel size of 1.3 mm × 1.3 mm, were used to construct a high-granularity timing detector (HGTD) in ATLAS experiments, to suppress the pileup caused by a large number of particles hitting the detector almost simultaneously, using timing information. Similarly, the CMS endcap timing layer (ETL) upgrade also plans to adopt LGAD sensors. However, pixel LGADs are characterized by higher readout electronics densities and costs, which limits their application. To decrease the readout electronics density, the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences has designed strip LGADs with larger areas. The strip LGADs each measure 19 mm in length, with varying widths of 1.0, 0.5, and 0.3 mm. The Circular Electron Positron Collider (CEPC) also proposes detectors using strip LGADs. This article provides a detailed introduction to the design parameters of these strip LGADs and their electrical characteristics, including leakage current, breakdown voltage, and depletion capacitance. The timing resolution and signal-to-noise ratio of three-strip LGAD sensors were investigated using a beta source test system. For the first time, a picosecond (ps) laser test system was used to test and analyze the position resolution parallel to the strip direction. The results demonstrate that the timing resolution of strip LGADs is approximately 37.5 ps, and the position resolution parallel to the strip direction is better than 1 mm.

Motivated by the stringent requirements of the Upstream Pixel (UP) tracker in the LHCb Upgrade II and the Inner Tracking detector (ITK) of the Circular Electron Positron Collider, the COFFEE series of pixel sensor chips have been developed using a 55 nm High-Voltage CMOS (HVCMOS) process. The primary objective is to achieve a time resolution of a few nanoseconds under a hit density of up to 100 MHz/cm(2), while maintaining fine spatial resolution (similar to 10 mu m) and reasonable power consumption (<200 mW/cm(2)). Building on the process validation of the COFFEE2 prototype, this work presents the design and preliminary test results of COFFEE3 - a prototype integrating two distinct readout architectures. Architecture 1, tailored for the current triple-well process, adopts NMOS-only in-pixel circuitry and innovative column-level readout to handle high hit densities. The time walk of pixel-level signal is controlled within 10 ns, and the Time of Arrival (TOA) and Time over Threshold (TOT) are measured with a system clock with the period of 25 ns in peripheral circuits. Architecture 2, developed for future possible processes with p-type buried layer isolation, features pixel-level time measurement and storage. A chip-level Time-to-Digital Converter (TDC) is used and the part of Voltage-Controlled Delay Line (VCDL) is copied in each pixel to get a high time resolution. The TOA resolution is estimated to be 4.2 ns and the TOT resolution 8.4 ns. COFFEE3, with a layout size of 3 & times;4 mm(2), was manufactured and has undergone preliminary tests. Charge injection tests for analog circuits, and laser tests for full readout chains, confirm that both architectures operate as expected. Next step work will focus on characterizing key performance such as the timing resolution, radiation hardness, and tracking performance of minimum ionising particles.

Low-Gain Avalanche Diodes (LGADs) provide moderate internal gain and time resolutions of a few tens of picoseconds, making them a key technology for ultrafast timing in high-energy physics and beyond. However, both their gain and timing characteristics vary strongly with reverse-bias voltage and temperature. This work establishes a compact analytical framework that describes multi-temperature LGAD gain and timing behavior through an equivalent representation of the gain layer. The non-uniform multiplication region is replaced by an equivalent rectangular gain layer, from which a first-order bias-compensation relation for constant gain is derived and validated. Using multi-temperature measurements of LGADs designed by IHEP and fabricated by IME, together with an independent HPK dataset, we show that the gain-voltage curve family can be reconstructed from a reference-temperature main curve, substantially reducing characterization effort. The same idea is then extended to timing by decomposing the total time resolution into jitter and intrinsic components and representing their temperature dependences as component-wise equivalent bias offsets. The resulting framework provides a function-level description of multi-temperature LGAD time-resolution curves and offers a practical tool for calibration, operation, and reduced-density characterization of LGAD-based ultrafast timing systems.

The AC-coupled Low Gain Avalanche Detector (AC-LGAD) is a kind of silicon detector with high time and spatial resolution, and can be used in the 4D-tracking systems in future colliders. Inside the collider detector, severe X-ray irradiation may impact the performance of silicon sensors. In this work, X-ray irradiation up to 1 MGy is employed to investigate the Total Ionizing Dose (TID) effect on the electrical characteristics, time resolution, and spatial resolution of strip-type AC-LGAD sensors. The results demonstrate that TID effects predominantly impact surface leakage current, while no significant change is found in spatial and time resolution.

Abstract Accurate luminosity measurements are essential for stable machine operation and precision physics at the High-Luminosity LHC (HL-LHC), where pileup levels exceeding 140 proton-proton interactions every 25 ns impose stringent requirements on fast and radiation-tolerant instrumentation. The Beam Monitoring detector for ATLAS (BMA) is an additional luminosity detector designed for HL-LHC. It is based on Low-Gain Avalanche Diodes (LGADs), which provide intrinsically fast signal rise times, high signal-to-noise ratio (SNR), and strong radiation tolerance — key features for resolving individual 25 ns bunch crossings in the HL-LHC environment. This contribution presents the BMA detector architecture, including the LGAD sensor layout and the readout chain, all designed to operate under the high particle fluences expected at the installation position. The amplification of the detector signal occurs far from the detector, thereby reducing radiation damage to the electronics, but still maintaining a high SNR. We report results from laboratory characterisation as well as the performance of prototype BMA detectors installed in ATLAS during the 2025 data-taking period. The LGADs performance — such as efficiency, gain stability, and gain degradation after irradiation — is analysed. The results provide an assessment of the LGAD technology as a beam-monitor and luminosity detector in the LHC environment, indicating that the gain and the particle detection efficiency, relevant for bunch-by-bunch luminosity measurements, can be retained under HL-LHC conditions.

This paper presents a study of position-dependent signal propagation delay in large-pitch pixelated AC-coupled Low-Gain Avalanche Detectors (AC-LGADs). In AC-LGADs, a continuous resistive N+ layer and segmented AC-coupled readout electrodes enable charge sharing and simultaneous timing and position measurements. However, lateral signal transport in the resistive layer can introduce a position-dependent delay in the measured signal arrival time. In this work, an IHEP-designed pixel AC-LGAD was characterized using a two-dimensional picosecond laser scan. The measured leading-edge arrival time shows an approximately linear dependence on an effective propagation distance, with a delay slope of about 194.7±1.3ps/mm for the tested device. After applying a position-dependent delay correction, the sigma of the combined arrival-time distribution over the scanned region is reduced from 88.3 ps to 48.6 ps. To interpret the observed delay, an equivalent two-dimensional lossy transmission-line model is developed for the continuous resistive layer. The model provides a semi-quantitative description of the leading-edge delay and indicates that, within the measured signal bandwidth, the transport is dominated by the resistive term and is therefore dispersive and diffusion-like. A distributed SPICE network including the pad-area response and capacitive charge sharing provides a complementary circuit-level cross-check of the approximately linear distance dependence. These results quantify the propagation-induced timing delay in large-pitch AC-LGADs and provide guidance for timing correction and future optimization of the resistive-layer sheet resistance.

We present a comprehensive theoretical study of linear wave scattering from magnetic domain walls with varied twist angles (sic) in spin-1/2 Bose-Einstein condensates (BECs). Using a gauge transformation, we show that scattering observables depend solely on the total twist (sic), independent of chirality. Within the Bogoliubov- de Gennes (BdG) framework, we develop a transfer-matrix method to compute reflection and transmission coefficients for incident phonons and free particles. Our results reveal a scattering threshold at the Zeeman energy E = h & strns;Omega(0), separating a pure phonon regime from multichannel scattering involving both collective and single-particle excitations above threshold. Above a critical twist angle (sic)(c), the effective spin rotation deviates from the imposed twist angle, leading to comb-like density modulations and Fano-like resonances below the threshold h & strns;Omega(0). The transition probability between phonon and particle channels is strongly tunable with (sic) < (sic)(c), enhanced for odd multiples of pi but suppressed for even multiples. These findings establish twist-engineered domain walls as a versatile platform for controlling quantum transport, with implications for atomtronic devices and quantum simulation.

The Circular Electron Positron Collider (CEPC) is a next-generation electron-positron collider for precision studies of Higgs, flavor physics and beyond. A key component of its tracking system is the Inner Tracker (ITK) using High Voltage Complementary Metal-Oxide-Semiconductor (HV-CMOS) sensor technology. The CEPC ITK consists of three barrel layers and four pairs of endcap disks, covering a total active area of about 20 m2. The HV-CMOS sensor fabricated with advanced 55 nm process is used to achieve a few-micrometer spatial resolution and a few-nanosecond timing resolution, with a moderate power consumption. The module design is shared between barrel and endcap to facilitate production. The whole system is designed for minimal material budget, with 0.7% X0 per layer in the barrel part. The design has been implemented in CEPC software framework for performance study and future optimization.

The Low Gain Avalanche Diode (LGAD) is a high-precision silicon-based timing sensor, with pixel sizes of 1.3 x 1.3 mm2 utilized in the High Granularity Timing Detector (HGTD) project at ATLAS. However, in future lepton colliders and space based experiments, the particle density is much lower than in Hadron colliders. Therefore, increasing the pixel area of the LGAD could lead to a reduction in the channel density of the readout electronics, resulting in cost and power consumption savings for experiments with low particle densities. It is essential to conduct detailed studies on the impact of area expansion on the time resolution and Signal-to Noise Ratio (SNR) of LGAD need to be studied in detail to provide a reference for the application of large-area LGADs. Different-area sensors are obtained by connecting different numbers of pixels in parallel within the LGAD array. These LGADs are designed by the Institute of High Energy Physics (IHEP, CAS) and manufactured by the Institute of Microelectronics (IME, CAS), feature an epitaxial layer thickness of 50 mu m. This paper studies the breakdown voltage, leakage current, and depletion process of devices with different areas, while also examining the time resolution, SNR, rise time and other parameters of sensors with varying areas using a beta source (90Sr) test system. The test results indicate that as the area of devices increases from 1.69 mm2 to 42.25 mm2, the time resolution deteriorates significantly from 37 ps to 65 ps. The depletion capacitance of the device increases with the area, resulting in a slower RC process for signal formation, longer signal rise time, and decreased SNR ratio, leading to a deterioration of time resolution.

Muon Spin Rotation/Relaxation/Resonance (μSR) is a versatile and powerful non-destructive technology for investigating the magnetic properties of materials at the microscopic level. The μSR technique typically utilizes fully spin polarized beams of positive muons generated at particle accelerator facilities and measures the evolution of the muon spin polarization inside a sample to extract information about the local magnetic environment in materials. With the development of accelerator technologies, intensities of muon beams are being continuously improved, which will cause a pile-up problem to the μSR spectrometer. The first muon source in China, named MELODY, is currently under construction and will be a pulsed source of muons operated at a repetition frequency of only 1 Hz due to limitations of the accelerator system at CSNS. Consequently, there is a strong motivation to operate MELODY at significantly higher muon intensities. This necessitates an upgrade of the detector system inside the spectrometer, which should be smaller and faster to accommodate the increased intensity per pulse of muons. The Low Gain Avalanche Diode (LGAD), characterized by a typical pulse width of 2 ns and a segmentation size in the centimeters range, has the potential to significantly improve the counting rates of μSR spectrometers that utilize a high intensity pulsed muon source. Thus, it is expected that the LGAD detector is a promising candidate to enhance the performance of μSR spectrometers at the new MELODY muon source.To validate this, tests on the LGAD were conducted at the ISIS pulsed muon source at the Rutherford Appleton Laboratory, UK. This paper will describe the setup of the candidate LGAD devices and the subsequent analysis of the experiment data.

The AC-coupled Strip LGAD (Strip AC-LGAD) is a novel LGAD design that diminishes the density of readout electronics through the use of strip electrodes, enabling the simultaneous measurement of time and spatial information. The Institute of High Energy Physics has designed a long Strip AC-LGAD prototype with a strip electrode length of 5.7 mm and pitches of 150 μm, 200 μm, and 250 μm. Spatial and timing resolutions of the long Strip AC-LGAD are studied by pico-second laser test and beta source tests. The laser test demonstrates that spatial resolution improves as the pitch size decreases, with an optimal resolution achieved at 8.3μm. Furthermore, the Beta source test yields a timing resolution of 37.6 ps.

The Low-Gain Avalanche Diode (LGAD) is a new silicon detector and holds wide application prospects in particle physics experiments due to its excellent timing resolution. The LGAD with a pixel size of 1.3 mm $\times$ 1.3 mm was used to construct a High Granularity Timing Detector (HGTD) in ATLAS experiments to solve the pile-up problem. Meanwhile, the Circular Electron Positron Collider (CEPC) also proposes detectors using the LGAD. However, pixel LGAD exhibits higher readout electronics density and cost, which somewhat limits the application of LGADs. To decrease the readout electronics density, the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences has designed strip LGADs with larger areas. These strip LGADs are all 19 mm in length but with different widths of 1.0 mm, 0.5 mm, and 0.3 mm. This article provides a detailed introduction to the design parameters of these strip LGADs and tests their electrical characteristics, including leakage current, break-down voltage, depletion capacitance, etc. The timing resolution and signal-to-noise ratio of the three strip LGAD sensors were investigated using a beta source test system. The position resolution parallel to the strip direction was tested and analyzed for the first time using a pico-second laser test system. Tests have demonstrated that the timing resolution of strip LGADs can reach about 37.5 ps, and position resolution parallel to the strip direction is better than 1 mm.

High-Voltage CMOS (HVCMOS) sensors, featuring a deep n-well separating the transistors and the depletion region, are intrinsically radiation hard and a good candidate for tracking systems in future high energy physics experiments. In hope of reducing the power density and incorporating more functionality in the same area, we are looking for foundries where HVCMOS sensors can be implemented in smaller feature size. In this paper we report the feasibility study in two MPWs using 55 nm processes. Sensor diodes are designed with deep n-well serving as electrode in Low-Leakage process, and the test results are reported. Design and first results for MPW in 55 nm HVCMOS process will also be described.

The DarkSHINE experiment proposes a novel approach to single-electron-on-fixed-target exploration that focuses on the search for dark photons through their invisible decay into dark matter particles. Central to this initiative is an advanced tracking detector designed to achieve exceptional sensitivity in the detection of light dark matter candidates. This study evaluates the performance of several prototype AC-coupled low-gain avalanche diode(AC-LGAD) strip sensors specifically developed for the DarkSHINE tracking detector. The electrical properties of the sensors from two batches of wafers with different +n doses are thoroughly evaluated. Spatial and temporal resolutions are measured using an infrared laser source. The spatial resolutions range from 6.5 to 8.2 μm and from 8.8 to 12.3 μm for the sensors from two distinct dose batches, each with a 100 μm pitch size. Furthermore, the sensors demonstrate time resolutions of 8.3 and 11.4 ps, underscoring the potential of AC-LGAD technology in enhancing the performance of the DarkSHINE tracking detector.

AC-coupled LGAD Strip (AC-LGAD Strip) is a new design of LGAD that allows high-precision detection of particle spatiotemporal information whereas reducing the density of readout electronics by using strip electrodes. Increasing the length of the electrodes is beneficial for reducing the electronic readout density. The Institute of High Energy Physics has designed a long AC-LGAD Strip prototype with a strip electrode length of 5.7 mm and pitches of 150 $\mu m$, 200 $\mu m$, and 250 $\mu m$. Timing and spatial resolutions of the long AC-LGAD Strip are studied by TCT laser scan test and Beta test. The TCT laser scan test demonstrates that spatial resolution improves as the pitch size decreases, with an optimal resolution achieved at 8.3 $\mu$m. Conversely, the jitter remains relatively stable at 14.7 ps, regardless of pitch size. Additionally, the Beta test yields a timing resolution of 37.6 ps. Enhancing the Signal-to-Noise Ratio (SNR) and mitigating signal attenuation can further bolster spatial resolution, either by reducing the pitch size or optimizing the readout electronics. The outstanding performance exhibited by the Long AC-LGAD Strip positions it as a highly promising choice for 4D tracking applications in future particle physics experiments.

AC-coupled LGAD (ac-LGAD) is a new 4-D detector developed based on the low-gain avalanche diode (LGAD) technology, which can accurately measure the time and spatial information of particles. The Institute of High Energy Physics (IHEP) designed a large-size ac-LGAD with a pitch of $2000~\mu \text{m}$ and ac pad of $1000~\mu \text{m}$ and explored the effect of N+ layer dose on the spatial resolution and time resolution. The spatial resolution varied from 36 to $16~\mu \text{m}$ depending on N+ dose for a charge corresponding to about 12 minimum ionizing particles (MIPs). The jitter component of the time resolution does not change significantly with different N+ doses, and it is about 15–17 ps measured by laser. The ac-LGAD with a low N+ dose has a large attenuation factor and better spatial resolution in the central region between pads. In these specific conditions, large signal attenuation factors and low noise levels are beneficial to improve the spatial resolution of the ac-LGAD sensor.

The low gain avalanche detectors (LGADs) are thin sensors with fast charge collection which in combination with internal gain deliver an outstanding time resolution of about 30 ps for Minimum Ionizing Particles (MIP). High collision rates and consequent large particle rates crossing the detectors at the upgraded Large Hadron Collider (LHC) in 2028 will lead to radiation damage and deteriorated performance of the LGADs. The main consequence of radiation damage is loss of gain layer doping (acceptor removal) which requires an increase of bias voltage to compensate for the loss of charge collection efficiency and consequently time resolution. The Institute of High Energy Physics (IHEP), Chinese Academy of Sciences (CAS) has developed a process based on the Institute of Microelectronics (IME), CAS capability to enrich the gain layer with carbon to reduce the acceptor removal effect by radiation. After 1 MeV neutron equivalent fluence of 2.5 x 10(15) n(eq)/cm(2), which is the maximum fluence to which sensors will be exposed at ATLAS High Granularity Timing Detector (HGTD), the IHEP-IME second version (IHEP-IMEv2) 50 mu m LGAD sensors already deliver adequate charge collection >4 fC and time resolution <50 ps at voltages <400 V. The operation voltages of these 50 mu m devices are well below those at which single event burnout may occur.