A bstract A measurement of the $$ {K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$ K + → π + ν ν ¯ decay by the NA62 experiment at the CERN SPS is presented, using data collected in 2021 and 2022. This dataset was recorded, after modifications to the beamline and detectors, at a higher instantaneous beam intensity with respect to the 2016–2018 data taking. Combining NA62 data collected in 2016–2022, a measurement of $$ \mathcal{B}\left({K}^{+}\to {\pi}^{+}\nu \overline{\nu}\right)=\left({13.0}_{-3.0}^{+3.3}\right)\times {10}^{-11} $$ B K + → π + ν ν ¯ = 13.0 − 3.0 + 3.3 × 10 − 11 is reported. With 51 signal candidates observed and an expected background of $$ {18}_{-2}^{+3} $$ 18 − 2 + 3 events, $$ \mathcal{B}\left({K}^{+}\to {\pi}^{+}\nu \overline{\nu}\right) $$ B K + → π + ν ν ¯ becomes the smallest branching ratio measured with a signal significance above 5 σ .

The NA62 experiment at the CERN SPS reports the first detection of a tagged neutrino candidate based on the data collected in 2022. The candidate consists of a K+ -> mu(+)nu(mu) decay where the charged particles are reconstructed and the neutrino is detected through a charged-current interaction in a liquid krypton calorimeter.

A measurement of the K^+→π^+νν decay by the NA62 experiment at the CERN SPS is presented, using data collected in 2021 and 2022. This dataset was recorded, after modifications to the beamline and detectors, at a higher instantaneous beam intensity with respect to the 2016–2018 data taking. Combining NA62 data collected in 2016–2022, a measurement of ℬ(K^+→π^+νν)=(13.0_-3.0^+3.3)×10^-11 is reported. With 51 signal candidates observed and an expected background of 18_-2^+3 events, ℬ(K^+→π^+νν) becomes the smallest branching ratio measured with a signal significance above 5σ.

The NA62 experiment at CERN utilises a differential Cherenkov counter with achromatic ring focus (CEDAR) for tagging kaons within an unseparated monochromatic beam of charged hadrons. The CEDAR-H detector was developed to minimise the amount of material in the path of the beam by using hydrogen gas as the radiator medium. The detector was shown to satisfy the kaon tagging requirements in a test-beam before installation and commissioning at the experiment. The CEDAR-H performance was measured using NA62 data collected in 2023.

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.

We present a case for ARM chips as an alternative to standard x86 at WLCG sites to help reduce power consumption. New measurements are presented on the performance and energy consumption of two machines (one ARM and one x86), that were otherwise similar in specification and cost. The comparison was extended to a dual socket x86 node, representative of our site. These new results include the energy-efficiency and speed of singleand multithreaded jobs; the effect of hyper-threading; and an initial look at clock throttling as a way of shaping power-load. We observe significantly lower power consumption and often slightly better performance on the ARM machine and, noting the increased availability of ARM software builds from all LHC experiments and beyond, we plan to install a 2k-core ARM cluster at our WLCG Tier2 site at Glasgow in the summer of 2023. This will enable testing, physicsvalidation, and eventually an ARM production environment that will inform and influence other WLCG sites in the UK and worldwide.

As the scientific community continues to push the boundaries of computing capabilities, there is a growing responsibility to address the associated energy consumption and carbon footprint. This responsibility extends to the Worldwide LHC Computing Grid (WLCG), encompassing over 170 sites in 40 countries, supporting vital computing, disk, tape storage and network for LHC experiments. Ensuring efficient operational practices across these diverse sites is crucial beyond mere performance metrics. This paper introduces the HEP Benchmark suite, an enhanced suite designed to measure computing resource performance uniformly across all WLCG sites, using HEPScore23 as performance unit. The suite expands beyond assessing only the execution speed via HEPScore23. In fact the suite incorporates metrics such as machine load, memory usage, memory swap, and notably, power consumption. Its adaptability and user-friendly interface enable comprehensive acquisition of system-related data alongside benchmarking. Throughout 2023, this tool underwent rigorous testing across numerous WLCG sites. The focus was on studying compute job slot performance and correlating these with fabric metrics. Initial analysis unveiled the tool's efficacy in establishing a standardized model for compute resource utilization while pinpointing anomalies, often stemming from site misconfigurations. This paper aims to elucidate the tool's functionality and present the results obtained from extensive testing. By disseminating this information, the objective is to raise awareness within the community about this probing model, fostering broader adoption and encouraging responsible computing practices that prioritize both performance and environmental impact mitigation.

The NA62 experiment at CERN, configured in beam-dump mode, has searched for dark photon decays in flight to electron-positron pairs using a sample of 1.4×1017 protons on dump collected in 2021. No evidence for a dark photon signal is observed. The combined result for dark photon searches in lepton–antilepton final states is presented and a region of the parameter space is excluded at 90% confidence level, improving on previous experimental limits for dark photon mass values between 50 and 600 MeV/c2 and coupling values in the range 10−6 to 4×10−5. An interpretation of the e+e− search result in terms of the emission and decay of an axionlike particle is also presented. Published by the American Physical Society 2024

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

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 WLCG infrastructure provides the compute power and storage capacity needed by the Large Hadron Collider (LHC) experiments at CERN. The infrastructure is distributed across over 170 data centres in more than 40 countries. The amount of energy consumed by the WLCG to support the scientific program of the LHC experiments, and its evolution, depends on different factors: the luminosity of the LHC and its operating conditions; the data volume and the data complexity; the evolving computing models and the offline software of the experiments; the ongoing R&D program in preparation for the next LHC phase (HL-LHC); the evolution of computing hardware technology towards better energy efficiency; and the modernization of the facilities hosting the data centres to improve Power Usage Effectiveness. This contribution presents a study of the WLCG energy needs and their potential evolution during the future LHC program based on the factors mentioned above. Some of the information is obtained from the CERN experience but then extrapolated to the whole of WLCG. The study provides, therefore, a holistic view for the infrastructure rather than a detailed prediction at the level of the individual facilities. It presents a clear view of the trends and offers a model for more refined studies.

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−.

The NA62 experiment at CERN, designed to study the ultra-rare decay K+ → π+ νν , has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to μ+μ− pairs is reported, based on a sample of 1.4 × 1017 protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90

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 NA62 experiment at CERN, designed to study the ultra-rare decay $K^+ \to \pi^+\nu\overline{\nu}$, has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to $\mu^+\mu^-$ pairs is reported, based on a sample of $1.4 \times 10^{17}$ protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV$/c^2$.

The K+ -> pi(+) nu(nu) over bar decay, with a very precisely predicted branching ratio of less than 10(-10), is among the best processes to reveal indirect effects of new physics. The NA62 experiment reports the branching ratio measurement BR(K+ -> pi(+) nu(nu) over bar) = (1.06(-0.34)(+0.40)vertical bar(stat) +/- 0.09 vertical bar syst) . 10(-10) at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016-2018. This provides evidence for the very rare K+ -> pi(+)nu(nu) over bar decay, observed with a significance of 3.4 sigma. This measurement is also used to set limits on BR(K+ -> pi(+) X), where X is a new feebly interacting scalar or pseudo-scalar particle, foreseen in several new physics scenarios.