The EXFLU batches of thin LGAD sensors with substrates of thickness between 20 and 45 & micro;m were tested for timing performance at the DESY Test Beam Facility. The sensor designs are optimised for excellent timing resolution, and are manufactured by Fondazione Bruno Kessler. The timing performance is reported for both non-irradiated LGAD sensors and a set of 30 & micro;m sensors irradiated up to 2.5 & times; 10(15 )n1 (MeV eq.) cm(-2). In addition, a new approach to the analysis of thin sensors is considered using differential programming to optimise a signal probability model. The results using the conventional method and this approach using machine learning are presented.

The paper reports on the timing resolution achieved with Low-Gain Avalanche Diodes (LGADs), optimised for extreme-fluence conditions, at the DESY Test Beam Facility using 4 GeV/c electrons. The LGADs adopt an n-in-p technology with a p+-type boron gain implant, co-implanted with carbon to mitigate acceptor deactivation due to irradiation. The substrate thickness of the sensors varies from 20 to 45 & micro;m, with an active area spanning from 0.75 & times; 0.75 to 1.28 & times; 1.28 mm2. The experimental setup consisted of a 45 & micro;m-thick trigger sensor with an active area of 3.6 & times; 3.6 mm2, two device-under-test (DUT) planes, and a Photonis micro-channel plate photomultiplier tube (MCP) as a time reference. Data taking was performed at the ambient temperature of the facility, at 18 degrees C. The gain was measured between 7 and 40 across all non-irradiated sensors in the study. The timing resolution was calculated from a Gaussian fitting of the difference in times of arrival of a particle at the DUT and the MCP, using the constant fraction discriminator technique. A timing resolution of 26.4 ps was achieved in 45 & micro;m-thick sensors, down to 16.6 ps in 20 & micro;m-thick sensors, in the non-irradiation study. The combination of two 20 & micro;m-thick LGADs reached a timing resolution of 12.2 ps. A set of 30 & micro;m-thick sensors irradiated with neutrons at fluences between 0.4 & times; 1015 and 2.5 & times; 1015 neqcm-2 were tested in the beam. These irradiated sensors achieved a gain between 7 and 30 using a similar apparatus but cooled with solidified CO2 to-42 degrees C. A timing resolution of 20 ps was obtained in these irradiated sensors.

A new gain implant design has recently been introduced to enhance the radiation resistance of low-gain avalanche diodes (LGADs) to the extreme fluences anticipated in future hadron colliders like FCC-hh. This design utilises an engineered compensation of two opposing types of doping implants, requiring a thorough analysis of their evolution due to irradiation. To this end, the experimental measurements of their initial test structures have been compared with Technology CAD simulations both before and after irradiation. From the measurement-simulation comparison regarding C-V characteristics, the donor removal at high initial donor concentrations (>10^16 at/cm^3) used in Compensated LGADs has been studied, along with how donor co-implantation influences the beneficial effect of carbon to slow acceptor removal. Furthermore, an innovative application of van der Pauw test structures, typically employed by foundries to monitor process quality, has been implemented. The doping removal of the single implants used in Compensated LGADs has been estimated by examining the variation in sheet resistance with irradiation through these structures.

Future high-energy physics experiments require a paradigm shift in radiation detector design. In response to this challenge, resistive LGADs that combine Low Gain Avalanche Diode technology with resistive readout have been developed. The prototypes created so far, employing AC-coupled contacts, have demonstrated impressive performance, achieving a temporal resolution of 38 ps and a spatial resolution of 15 µm with a pixel pitch of 450 µm. To tackle some of the issues encountered up to this point, particularly the non-uniform response across the entire surface of the detector, a new version with DC-coupled contacts has recently been developed. The Synopsys ® Sentaurus TCAD simulations that have guided the design of their first production, released by the Fondazione Bruno Kessler in November 2024, will be presented below along with a concise summary of the history of the prototypes with AC-coupled contacts.

Soft X-ray experiments at synchrotron light sources are essential for a wide range of research fields. However, commercially available detectors for this energy range often cannot deliver the necessary combination of quantum efficiency, signal-to-noise ratio, dynamic range, speed, and radiation hardness within a single system. While hybrid detectors have addressed these challenges effectively in the hard X-ray regime, specifically with single photon counting pixel detectors extensively used in high-performance synchrotron applications, similar solutions are desired for energies below 2 keV. In this work, we introduce a single photon counting hybrid pixel detector capable of detecting X-ray energies as low as 550 eV, utilizing the internal amplification of Low Gain Avalanche Diode (LGAD) sensors. This detector is thoroughly characterized in terms of Signal-to-Noise Ratio and Detective Quantum Efficiency. We demonstrate its capabilities through ptychographic imaging at MAX IV 4th-generation synchrotron light source at the Fe L3-edge (707 eV), showcasing the enhanced detection performance of the system. This development sets a benchmark for soft X-ray applications at synchrotrons, paving the way for significant advancements in imaging and analysis at lower photon energies. The internal amplification of Low-Gain Avalanche Diode sensors can enhance the signal-to-noise ratio, improving the detection of low-energy X-rays. In this work, the authors demonstrate a single photon counting hybrid pixel detector detecting X-ray energies down to 550 eV, and test it in ptychographic imaging at the Fe L3-edge.

The Analog Spectral Imager for X-rays is a technology demonstrator of a small-pixel Hybrid Pixel Detector (HPD) designed for applications such as X-ray diffraction, synchrotron-based material science, and soft X-ray astrophysics requiring energy-resolved imaging. The ASIX architecture aims at mitigating the adverse effects of charge sharing, typical of small-pixel devices. In contrast to other frame-based photon counters or multi-threshold devices, ASIX employs, along with a 50 μm pixel, an ultra-low-noise (<30 e− ENC), fully analog, asynchronous, single-photon readout, targeting 10μm spatial resolution and 350 eV FWHM at 8 keV within the same exposure. In 2025, we began developing a small scale (∼5×5 mm2) HPD coupling a 300 μm-thick, n-on-p, edgeless silicon sensor with 50 μm pixels arranged in a hexagonal pattern to a newly designed 65-nm CMOS readout ASIC, featuring single-photon readout and on-chip analog to digital conversion, with a target rate capability of 108 ph/s/cm2. While the baseline for the ASIX R&D sensor is silicon for ≤20 keV operation, the design of the readout ASIC is compatible with High-Z materials sensors, such as cadmium-telluride or gallium-arsenide, for higher energies X-rays imaging, enabling potential extension to biomedical and preclinical research. This paper describes the ASIX imager architecture and reports on the development and testing of two Minimum Viable Products (MVPs), developed by coupling XPOL-III, a readily available 180-nm CMOS readout ASIC, to a 300 μm thick silicon sensor with 50 μm pixels and to a 750 μm thick CdTe sensor with 100 μm pixels, respectively. The MVPs achieved estimated energy resolution of 780eV FWHM at 17.5 keV (CdTe), and 620eV FWHM at 9.7 keV (silicon) and spatial resolution of 20μm (CdTe) and 7μm (silicon). These results confirm our preliminary models predicting the feasibility of simultaneous high energy and spatial resolution in such a small-pixel devices, thus securing the ASIX specifications. Finally, the paper highlights the technology gaps that ASIX would potentially fill in both terrestrial and space applications.

We present the application of LGAD technology for time-of-flight measurements of heavy ions and for precise diagnostics of radiation damage in diamond sensors. The polycrystalline CVD (pcCVD) diamond sensor used in this work was irradiated with heavy ion beams at GSI, Darmstadt, Germany during several experimental campaigns and subsequently investigated at MedAustron, Wiener Neustadt, Austria. To mitigate radiation-induced performance degradation, we propose a dedicated amplification system originally developed for LGAD sensors, which significantly extends the operational lifetime of diamond detectors. For precise sensor diagnostics, we employed strip LGAD sensors - commonly used for minimum ionizing particle (MIP) detection - and demonstrated their excellent performance for heavy ion (He/C) detection, achieving timing resolutions below 40 ps.

Low Gain Avalanche Diodes (LGADs) are silicon sensors designed to achieve an internal gain in the order of 10 through the impact ionization process. The development of LGADs was pushed forward by their application in High Energy Physics (HEP) experiments, where they will be employed to provide measurements of the time of arrival of minimum ionizing particles with a resolution of around 30 ps. The initial technological implementation of the sensors constrains their minimum channel size to be larger than 1 mm2, in order to reduce inefficiencies due to the segmentation of the gain structure. The gain of the sensors is kept in the order of 10 to limit the sensor shot noise and their power consumption. In photon science, the gain provided by the sensor can boost the signal-to-noise ratio of the detector system, effectively reducing the x-ray energy threshold of photon counting detectors and the minimum x-ray energy where single photon resolution is achieved in charge integrating detectors. This can improve the hybrid pixel and strip detectors for soft and tender x-rays by simply changing the sensor element of the detector system. Photon science applications in the soft and tender energy range require improvements over the LGADs developed for HEP, in particular the presence of a thin entrance window to provide a satisfactory quantum efficiency and channel size with a pitch of less than 100 μm. In this review, the fundamental aspects of the LGAD technology are presented, discussing also the ongoing and future developments that are of interest for photon science applications.

In recent years, Low Gain Avalanche Detectors (LGADs) have shown the capability of timing measurements in the tens of ps range for minimum ionizing particles. However, the segmentation of LGADs creates regions with no gain and provides a hindrance in achieving 100% fill factor (FF) for many applications and using LGADs as 4-dimensional (4D) tracking devices. The new LGAD design based on the trench isolation technique (TI-LGAD) is very promising in reducing the no-gain region and hence increased FF which in turn makes them capable of 4D tracking. This paper describes the features of a new TI-LGAD sensors production by FBK, in which the no-gain region is reduced significantly by replacing Junction Termination Extension (JTE) and p-stop implant with slender trenches. A new R&D batch is produced in FBK within the RD50 collaboration, in which several border layouts and fabrication processes are implemented. The new TI-LGAD batch enables a systematic study to select the best fabrication process and border layout. In this paper, the electrical and laser characterization, isolation between pixels, and the results on the measurement of no-gain region between pixels are presented.

Combined measurements of the production and decay rates of the Higgs boson, as well as its couplings to vector bosons and fermions, are presented. The analysis uses the LHC proton-proton collision data set recorded with the CMS detector in 2016 at $\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The combination is based on analyses targeting the five main Higgs boson production mechanisms (gluon fusion, vector boson fusion, and associated production with a W or Z boson, or a top quark-antiquark pair) and the following decay modes: H $\to$ $\gamma\gamma$, ZZ, WW, $\tau\tau$, bb, and $\mu\mu$. Searches for invisible Higgs boson decays are also considered. The best-fit ratio of the signal yield to the standard model expectation is measured to be $\mu$ $=$ 1.17 $\pm$ 0.10, assuming a Higgs boson mass of 125.09 GeV. Additional results are given for parametrizations with varying assumptions on the scaling behavior of the different production and decay modes, including generic ones based on ratios of cross sections and branching fractions or coupling modifiers. The results are compatible with the standard model predictions in all parametrizations considered. In addition, constraints are placed on various two Higgs doublet models.

Low gain avalanche detectors (LGADs), silicon sensors with intrinsic charge amplification, are being considered as a possible technology for tracking and timing in the high luminosity upgrade of the CERN Large Hadron Collider. In order to work in such an environment, LGADs must be sufficiently radiation hard. The characterisation before and after irradiation of properties, such as gain, charge collection, spatial homogeneity, space charge, and leakage current, is vital for assessing the performance and viability of LGADs. This paper presents the results obtained from the study of LGADs irradiated with 24-GeV/c protons up to a maximum fluence of 10(15) n(eq)/cm(2). The characterisation was performed mainly by means of the transient current technique with red and infrared laser pulses. It was found that the gain decreases with increasing fluence. At a fluence of 10(15) n(eq)/cm(2), the charge collected is similar to that of a normal p-i-n diode. Whilst this might be explained by an effective acceptor removal, it was also found that there are clear signs of a double junction in these devices, after irradiation. In addition, the spatial charge collection homogeneity before and after irradiation was evaluated.

A search for new physics using events containing an imbalance in transverse momentum and one or more energetic jets arising from initial-state radiation or the hadronic decay of W or Z bosons is presented. A data sample of proton-proton collisions at $\sqrt{s} = $ 13 TeV, collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb$^{-1}$, is used. The observed data are found to be in agreement with the expectation from standard model processes. The results are interpreted as limits on the dark matter production cross section in simplified models with vector, axial-vector, scalar, and pseudoscalar mediators. Interpretations in the context of fermion portal and nonthermal dark matter models are also provided. In addition, the results are interpreted in terms of invisible decays of the Higgs boson and set stringent limits on the fundamental Planck scale in the Arkani-Hamed, Dimopoulos, and Dvali model with large extra spatial dimensions.

This Letter presents the observation of the rare Z boson decay Z → ψl^+l^−. Here, ψ represents contributions from direct J/ψ and ψ(2S)→J/ψX, l^+l^− is a pair of electrons or muons, and the J/ψ meson is detected via its decay to μ^+μ^−. The sample of proton-proton collision data, collected by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV, corresponds to an integrated luminosity of 35.9  fb−1. The signal is observed with a significance in excess of 5 standard deviations. After subtraction of the ψ(2S) → J/ψX contribution, the ratio of the branching fraction of the exclusive decay Z→J/ψl+l− to the decay Z → μ^+μ^−μ^+μ^− within a fiducial phase space is measured to be B(Z → J/ψl^+l^−)/B(Z → μ^+μ^−μ^+μ^−) = 0.67 ± 0.18(stat) ± 0.05(syst).

Modifications of the properties of jets in PbPb collisions, relative to those in pp collisions, are studied at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV via correlations of charged particles with the jet axis in relative pseudorapidity ($\Delta \eta$), relative azimuth ($\Delta \phi$), and relative angular distance from the jet axis $\Delta \mathrm{r} = \sqrt{{(\Delta\eta)^{2}+(\Delta\phi)^{2}}}$. This analysis uses data collected with the CMS detector at the LHC, corresponding to integrated luminosities of 404 $\mu$b$^{-1}$ and 27.4 pb$^{-1}$ for PbPb and pp collisions, respectively. Charged particle number densities, jet fragmentation functions, and jet shapes are presented as a function of PbPb collision centrality and charged-particle track transverse momentum, providing a differential description of jet modifications due to interactions with the quark-gluon plasma.

A search has been performed for heavy resonances decaying to ZZ or ZW in 2l2q final states, with two charged leptons (l = e, μ) produced by the decay of a Z boson, and two quarks produced by the decay of a W or Z boson. The analysis is sensitive to resonances with masses in the range from 400 to 4500 GeV. Two categories are defined based on the merged or resolved reconstruction of the hadronically decaying vector boson, optimized for high- and low-mass resonances, respectively. The search is based on data collected during 2016 by the CMS experiment at the LHC in proton-proton collisions with a center-of-mass energy of √s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb^(−1). No excess is observed in the data above the standard model background expectation. Upper limits on the production cross section of heavy, narrow spin-1 and spin-2 resonances are derived as a function of the resonance mass, and exclusion limits on the production of W′ bosons and bulk graviton particles are calculated in the framework of the heavy vector triplet model and warped extra dimensions, respectively.

The angular distribution of the flavor-changing neutral current decay B+ -> K+mu(+)mu(-) is studied in proton-proton collisions at a center-of-mass energy of 8 TeV. The analysis is based on data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 20.5 fb(-1). The forward-backward asymmetry A(FB) of the dimuon system and the contribution F-H from the pseudoscalar, scalar, and tensor amplitudes to the decay width are measured as a function of the dimuon mass squared. The measurements are consistent with the standard model expectations.

Measurements are presented of associated production of a $mathrm {W}$ boson and a charm quark ( $mathrm {W}+mathrm {c}$ ) in proton–proton collisions at a center-of-mass energy of 13 $,text {Te}text {V}$ . The data correspond to an integrated luminosity of 35.7 $,text {fb}^{-1}$ collected by the CMS experiment at the CERN LHC. The $mathrm {W}$ bosons are identified by their decay into a muon and a neutrino. The charm quarks are tagged via the full reconstruction of ${mathrm {D}^{*}(2010)^{pm }}$ mesons that decay via ${mathrm {D}^{*}(2010)^{pm }}rightarrow mathrm {D}^0 + {pi ^{pm }}rightarrow mathrm {K}^{mp } + {pi ^{pm }}+ {pi ^{pm }}$ . A cross section is measured in the fiducial region defined by the muon transverse momentum $p_{mathrm {T}} ^{mu } u003e 26,text {Ge}text {V} $ , muon pseudorapidity $|eta ^{mu } | 5,text {Ge}text {V} $ . The inclusive cross section for this kinematic range is $sigma (mathrm {W}+mathrm {c})=1026pm 31,text {(stat)} begin{array}{c} +76 -72 end{array},text {(syst)} text { pb} $ . The cross section is also measured differentially as a function of the pseudorapidity of the muon from the $mathrm {W}$ boson decay. These measurements are compared with theoretical predictions and are used to probe the strange quark content of the proton.