The kaon physics programme, long heralded as a cutting-edge frontier by the European Strategy for Particle Physics, continues to stand at the intersection of discovery and innovation in high-energy physics (HEP). With its unparalleled capacity to explore new physics at the multi-TeV scale, kaon research is poised to unveil phenomena that could reshape our understanding of the Universe. This document highlights the compelling physics case, with emphasis on exciting new opportunities for advancing kaon physics not only in Europe but also on a global stage. As an important player in the future of HEP, the kaon programme promises to drive transformative breakthroughs, inviting exploration at the forefront of scientific discovery.

Embedded systems are increasingly adopting heterogeneous templates integrating hardware accelerators and application-specific processors, which poses novel challenges. In particular, it is difficult to have accurate control of task activities in Commercial Off-the-shelf (COTS) System on Chips (SoCs), due to complex main memory sharing mechanisms among different computing engines. To address this problem, bandwidth regulation approaches based on monitoring and throttling are widely adopted. Existing solutions, however, are either too coarse-grained, limiting the control over computing engines activities, or platform-dependent, addressing the problem only for specific SoCs. In this paper we propose an innovative, fine-grained and platform-independent approach that can accurately control main memory bandwidth usage in an FPGA-based Heterogeneous System on Chip (HeSoC). Experimental results conducted on the Xilinx Zynq UltraScale+ platform demonstrate that our approach enables solutions not feasible with state-of-the-art bandwidth regulation methods.

For the first time at the Beam Test Facility (BTF) of the DAΦNE accelerator complex at the Laboratori Nazionali di Frascati of INFN, 450 MeV positrons have been deflected with high efficiency, using the planar channeling process in a bent silicon crystal. The deflection angle obtained is beyond 1 mrad. This interesting result finds several applications for manipulation of this kind of beams, in particular for ultraslow extraction from lepton circular accelerators like DAΦNE. In this work, the experimental apparatus, the measurement procedure, and the experimental results are reported. Published by the American Physical Society 2025

Memory bandwidth contention may severely inflate the execution time of tasks co-running on modern Commercial Off-The-Shelf (COTS) multicores. An effective and widely deployed solution to mitigate the problem is bandwidth regulation, a technique to limit the available memory bandwidth for those cores that are not executing time-critical tasks. The granularity at which time-critical activities can be identified at the core level can be in fact even finer than a whole task, and just span smaller memory-critical section (MCS) therein. As the co-presence of MCS and non-critical task portions in the system dynamically changes over time, bandwidth regulators require more or less frequent reconfiguration of their parameters. Similar reconfiguration techniques thus represent a central component of dynamic Memory Bandwidth Management Schemes (MBMS). In particular, the overhead and latency of such a component determine the feasibility and control granularity of the overall bandwidth-regulation solution. The literature extensively covers low-level bandwidth regulation mechanisms and-to some extent-their integration in wider MBMSs, yet no in-depth analysis is currently available of the impact of reconfiguration techniques. This paper addresses this issue by proposing a comparative analysis of the two basic approaches to reconfiguring bandwidth regulators in a system: synchronous and asynchronous schemes. The analysis, performed on a real-world setup with both synthetic and real-world benchmarks, shows that the asynchronous technique improves the control granularity of a bandwidth regulator by a factor of up to 19x, moving from the ms to the mu s scale.

Commercial-off-the-shelf (COTS) multicore systems on chip (SoC) represent a cheap and convenient solution for deploying sophisticated workloads in various application domains. The combination of several CPU cores and dedicated acceleration units tightly sharing memory and interconnect systems can provide tremendous peak performance, but also threatens timing predictability due to memory interference. Even when focusing on main CPU cores only, it has been reported that task slowdown due to memory interference can surpass 10x. Such poorly predictable timing behaviors bar greater adoption of COTS multicore SoCs in the domain of timing-critical applications, and motivate the wide activity of the research community to study solutions aimed at mitigating the problem. Understanding worst-case interference patterns on such hardware platforms is fundamental for building any effective memory interference control mechanism. A common assumption in the literature is that worst-case interference is generated by (and therefore assessed through) read-intensive synthetic workloads with 100% cache miss rate. Yet certain real-life workloads exhibit worse slowdown than what is generated under said assumed worst-case, so we study the interference effects of both synthetic and real-life benchmarks on different multicore SoCs. Our experiments indicate that cache thrashing causes the worst interference experienced by real-life benchmarks - due to their different usage of caches - and that there is no universal worst-case workload for every platform.

An experimental setup to investigate ion channeling in the hundreds MeV/u energy range is described. A short bent crystal, aligned to the incoming beam by an angular actuator, should deflect ions into a single plane pixel detector used to identify channeled and unchanneled particles. In order to enhance the footprint of channeling on the recorded signals, the incoming particle emittance is tailored on the crystalline plane acceptance by means of massive collimators. Numerical simulations of low energy carbon ions are performed with FLUKA to fully understand the measurement conditions demonstrate the feasibility of the test, to be performed in the experimental room of the National Center for Oncological Hadrontherapy accelerator complex in Pavia, Italy.

A sample of 3984 candidates of the K+→π+γγ decay, with an estimated background of 291±14 events, was collected by the NA62 experiment at CERN during 2017–2018. In order to describe the observed di-photon mass spectrum, the next-to-leading order contribution in chiral perturbation theory was found to be necessary. The decay branching ratio in the full kinematic range is measured to be (9.61±0.17)×10−7. The first search for production and prompt decay of an axion-like particle with gluon coupling in the process K+→π+a, a→γγ is also reported.

During 2022 data taking (Run III) PADME searched for a resonant production and a visible decay of the X17 particle into e(+)e(-). A precise knowledge within 1% uncertainty of the number of positrons was required for the observation. To that purpose, an array of 2 x 6 Timepix3 (total of 512 x 1536 pixels) hybrid pixel detectors operated in data-streaming mode with ToA resolution of 1.56 ns for every pixel was employed. Two methods for data acquisition were developed. A frame-based method, integrating the number of hits for each individual pixel for a predefined period of time served for monitoring the beam conditions and to provide a rough estimation of the beam distribution and number of positrons. A data streaming mode exploiting the nanosecond time resolution of Timepix3 detector was used for precise characterization of the transverse beam profile and the distribution of the incident positrons within each bunch of similar to 200 ns duration.

Fusion for Energy is delivering 5 out of 6 ITER superconducting poloidal field coils (PF coils), which are composed of stacks of 6 to 8 double-layered circular coils - double pancakes (DPs). The double pancakes range from 17 m to 24 m in diameter and the wound conductor has a NbTi core inside a stainless steel squared jacked. Due to the size of the PF 2-4 coils, they have been manufactured on the ITER site, very close to the assembly hall. This article highlights the manufacturing processes, the learning curve, the main challenges and learned lessons during the winding activities of the 30 double pancakes that comprise 4 PF coils.

Abstract This paper presents a detailed characterization of the positron beam delivered by the Beam Test Facility at Laboratori Nazionali of Frascati to the PADME experiment during Run III, which took place from October to December 2022. It showcases the methodology used to measure the main beam parameters such as the position in space, the absolute momentum scale, the beam energy spread, and its intensity through a combination of data analysis and Monte Carlo simulations. The results achieved include an absolute precision in the momentum of the beam to within ~1–2 MeV/c, a relative beam energy spread below 0.25%, and an absolute precision in the intensity of the beam at the level of 2%.

Recent results from searches for rare kaon decays with the NA62 experiment at CERN are reported, together with the future prospects. A future experiment HIKE, to go beyond NA62, has been proposed to push kaon physics to an unprecedented frontier. The HIKE timescale and expected performance are described. Among the NA62 results, the measurement of the branching ratios of the flavour changing neutral current $K^+\rightarrow\pi^+\mu^+\mu^-$ and the radiative non leptonic $K^+\rightarrow\pi^+\gamma\gamma$ decays are reported, upper limits are given for lepton flavor and lepton number violating decays $K^+\rightarrow\mu^-\nu e^+e^+$ and $K^+\rightarrow\pi^-\pi^0 e^+e^+$. A search for new physics in the branching ratio of the decay $K^+\rightarrow\pi^+ e^+e^-e^+e^-$ is presented

Hot cathode ionization gauges will measure the neutral gas pressure in the vacuum vessel of ITER. Overall, 52 gauge heads based on the concept of the ASDEX pressure gauge but using novel ZrC emitters are located in the divertor, in equatorial ports and in pumping ducts. The initial lifetime tests of the novel gauge design have raised the concern that the pyrolytic graphite used to indirectly heat the ceramic ZrC emitter erodes too fast during operation. This effect might limit the lifetime of the gauges below the limits acceptable according to the inherent availability (ignoring operational delays) requirement of 99.8% for the diagnostic system over the lifetime of ITER. Long term operation tests have been performed using 0.1 mm thick W, Ir, and Mo foils as an interlayer between the pyrolytic graphite and the ZrC within a constant atmosphere of 20 Pa H2. The longest lifetime of 860 h has been achieved with the Ir foil. Subsequent vibration tests applying accelerations on a shaker with magnitudes typical for seismic and ITER disruption loads demonstrated that the emitter can survive such demanding loads even after far-progressed erosion of the pyrolytic graphite. Additional ON/OFF cycle tests demonstrated that the gauge is still fully operational. In combination with a revision and consolidation of the operational plan and the reliability, accessibility, maintainability, and inspectability (RAMI) analysis, ITER’s inherent availability requirement for the diagnostic system could be demonstrated successfully.

The first search for the lepton number violating decay K+ -> pi(0)pi(-)mu(+)e(+) and lepton flavour violating decays K+ -> pi(0)pi(+)mu-e(+), K+ -> pi(0)pi(+)mu(+)e(-) has been performed using a dataset collected by the NA62 experiment at CERN in 2016-2018. Upper limits of 2.9 x 10(-10), 3.1 x 10(-10) and 5.0 x 10(-10), respectively, are obtained at 90% CL for the branching ratios of the three decays on the assumption of uniform phase-space distributions.

The first search for ultra-rare K+ decays into the π+e+e−e+e− final state is reported, using a dataset collected by the NA62 experiment at CERN in 2017–2018. An upper limit of 1.4×10−8 at 90% CL is obtained for the branching ratio of the K+→π+e+e−e+e− decay, predicted in the Standard Model to be (7.2±0.7)×10−11. Upper limits at 90% CL are obtained at the level of 10−9 for the branching ratios of two prompt decay chains involving pair-production of hidden-sector mediators: K+→π+aa, a→e+e− and K+→π+S, S→A′A′, A′→e+e−.

In this article, we report on the SHERPA project, aiming at developing an efficient technique to extract a positron beam from one of the rings of the LNF DA & phi;NE collider, creating O(ms) long pulses. The most common slow extraction method is the resonant technique: after having created an unstable region in phase space, particles are gradually extracted from the circulating beam using a combination of electrostatic and magnetic septa. Instead, SHERPA proposes to use coherent processes in bent crystals, a cheaper and less complex alternative. This non-resonant technique, already used in hadron accelerators, will provide continuous multi-turn extraction with high efficiency. Various Geant4 simulations were carried out to study the channeling properties of positrons below GeV, in preparation for the first beam tests of the crystals produced for SHERPA. For positrons in this energy region, no experimental data exist on crystal channeling. Validation of the Geant4 simulations was obtained using a combination of analytical theoretical equations and other Monte Carlo simulations.

The flavor-changing neutral current decay [Formula: see text] ([Formula: see text]) is well suited to explore the Standard Model structure. A new measurement of this decay branching fraction and form factor has been performed by the NA62 experiment at CERN based on data collected in 2017–2018. From the selected sample of 28011 [Formula: see text] event candidates with a negligible background, the decay form factor parameters [Formula: see text] and [Formula: see text], as well as the branching fraction [Formula: see text] have been measured.

We report the results of a search for dark photon in-flight decays to μ + μ − pairs at NA62. Dark photons could be produced by dumping protons onto a copper-iron absorber, reach the NA62 decay volume more than 80 m downstream of the dump and decay therein. The measurement is based on data collected in 2021 which correspond to 1.4 × 1017 dumped protons.

The X17 particle, the E38 particle, and the anomalous soft photons are anomalous particles because they do not appear to belong to any known Standard Model families. We propose a QED meson description of the anomalous particles as composite systems of a light quark and a light antiquark bound and confined by the compact QED interaction, by combining Polyakov's transverse confinement of opposite electric charges in compact QED in (2+1)D and Schwinger's longitudinal confinement for massless opposite electric charges in QED in (1+1)D. With predicted QED meson masses close to the observed X17 and E38 masses, QED mesons may be good candidates for the description of the anomalous particles.