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Prasad, V. et al, Lacasta, C., Marinas, C., Mazorra de Cos, J., & Molina-Bueno, L. (2027). Upgrade of the Belle II vertex detector with depleted monolithic CMOS active pixel sensors. Nucl. Instrum. Methods Phys. Res. A, 1093, 171963–5pp.
Abstract: The Belle II experiment, operating at the asymmetric SuperKEKB e+e-collider, is preparing an upgrade of its vertex detector to cope with an increased luminosity of 6 & times; 1035 cm-2s-1. The upgraded vertex detector (VTX) will consist of five or six layers of depleted monolithic active pixel sensors (DMAPS), with a total material budget of approximately 3% X/X0. The OBELIX chip, derived from the TJ-Monopix2 sensor and fabricated using Tower-Jazz Semiconductor 180 nm CMOS technology, is being developed for this upgrade. It features a 33 & micro;m pixel pitch with a time-stamping binning of 50-100 ns, along with a dedicated digital periphery compatible with the Belle II trigger system, supporting rates up to 30 kHz. The sensor is designed to operate under the high background conditions expected at the target luminosity, with radiation tolerance up to 5 & times;1014 neq/cm2 and 100 Mrad, while targeting a power density of about 200 mW/cm2. This corresponds to hit rates up to 120 MHz/cm2. Beam test and irradiation studies of TJ-Monopix2 demonstrate that the operating sensor temperature should stay below 40 degrees C after irradiation up to 5 & times; 1014 neq/cm2. This report reviews the proposed VTX concept, sensor performance, and ongoing R&D activities.
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Ardu, M., Calibbi, L., Fedele, M., & Mescia, F. (2026). ALP production in lepton flavour violating meson, tau and gauge boson decays. J. High Energy Phys., 08(8), 217–36pp.
Abstract: In this paper we study axion-like particles (ALPs) with lepton-flavour-violating (LFV) couplings in the mass regime above the muon threshold, m(a) > m(mu), where the strong bound from the exotic muon decay μ-> ea no longer apply and the decay channel a -> e μbecomes kinematically accessible. In this region, the ALP typically decays promptly, motivating new search strategies based on its production in decays involving virtual muons. We analyse charged-meson and W decays, neutral-current processes such as Z and quarkonium decays, and, when couplings to the third generation are present, LFV tau decays. The subsequent decay a -> e μleads to striking LFV signatures with negligible Standard Model backgrounds. Combining these production modes with current low-energy constraints, we assess the sensitivity of future high-energy e (+) e (-) colliders, flavour factories such as Belle II and STCF, fixed-target experiments such as NA62, and proton beam-dump facilities such as SHiP. Overall, our results identify LFV ALP production in meson, gauge-boson, quarkonium and tau decays (with displaced vertices) as a promising and largely unexplored avenue to test ALP interactions with charged leptons above the muon mass threshold.
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Zhuo, J., Oyanguren, A., Fernandez Casani, A., Fiorini, L., & Kholoimov, V. (2026). Energy efficiency of a GPU-based computing system for high energy physics experiments. Front. Physics, 14, 1868616–8pp.
Abstract: In this paper we introduce the energy efficiency as a new metric for evaluating both hardware platforms based on Graphic Processor Units (GPU), and algorithm optimisations at High Energy Physics (HEP) experiments. We develop a method to compute the energy efficiency for the case of the first high level trigger (HLT1) of the LHCb experiment, relating the throughput with GPU specifications such as the number of cores, clock frequency, memory bandwidth and thermal design power. The model can be extended to other HEP experiments to make decisions and reach sustainable computing ecosystems.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Libralon, S., Lucio Martinez, M., Martinez-Vidal, F., et al. (2026). Study of the B0 → Λc+ (Λ)over-barc- KS0 decay. Phys. Rev. D, 114(1), 012012–14pp.
Abstract: The decay B-0 -> Lambda(+)(c) (Lambda) over bar (-)(c) K-S(0) is studied at LHCb for the first time using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of root s = 13 TeV, corresponding to an integrated luminosity of 5.4 fb(-1). The branching ratio relative to the decay B+ -> Lambda(+)(c) (Lambda) over bar (-)(c) K+ is measured to be [B(B-0 -> Lambda(+)(c) (Lambda) over bar (-)(c) K-S(0))/[B(B+ -> Lambda(+)(c) (Lambda) over bar (-)(c) K+)] = 0.53 +/- 0.05 +/- 0.05 where the first uncertainty is statistical and the second is systematic. Evidence is found for contributions from two resonant states, Xi(c) (2923)(+) and Xi(c) (2939)(+), in the Lambda(+)(c) K-S(0) system. The two states show a significance of 3.9 sigma relative to the nonresonant hypothesis. These two Xi(+)(c) states are consistent with being the isospin partners of the states observed in the Lambda(+)(c) K- system.
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LHCb Collaboration(Aaij, R. et al), Fernandez Casani, A., Jaimes Elles, S. J., Jashal, B. K., Libralon, S., Lucio Martinez, M., et al. (2026). Machine learning techniques for jet reconstruction at LHCb and application to the search for H → b(b)over-bar and H → c(c)over-bar in √s=13 TeV pp collisions. J. High Energy Phys., 07(7), 276–32pp.
Abstract: Two machine learning techniques for jet measurements at the LHCb experiment are presented: a regression-based method for jet-energy calibration and a deep neural network algorithm for jet flavour tagging, distinguishing between b-quark, c-quark, and light parton jets. These techniques are applied to a search for inclusive H -> b (b) over bar and H -> c (c) over bar decays using a LHCb dataset corresponding to an integrated luminosity of 1.6 fb(-1). The observed (expected) 95% confidence level upper limits correspond to 6.6 (11.1) times the SM cross-section for the H -> b (b) over bar process, and 1003 (1834) times the SM cross-section for the H -> c (c) over bar process.
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