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Non-singlet vector current in lattice QCD: -improvement from large volumes
No full textIn previous work, we determined the improvement coefficients and required for the massless -improvement of the local and point-split discretizations of the non-singlet vector current for non-perturbatively -improved Wilson fermions and the Lüscher-Weisz gauge action, using ensembles of large-volume configurations generated by the Coordinated Lattice Simulations (CLS) initiative. A new estimate for the mass-dependent improvement coefficient has recently become available, differing from the one used in our earlier study, and on which our implementation via a massive axial Ward identity relied. Here, we update our analysis of the mass-independent vector improvement coefficients based on the new axial current improvement coefficient, and analyse additional ensembles with a different chiral trajectory in order to validate our results at two values of the bare coupling. We find that using the new estimate of improves the consistency between the two chiral trajectories, as well as with a previous determination of the improvement coefficients directly in the massless limit on small volumes
Combination of ATLAS and CMS searches for Higgs boson pair production at TeV
No full textThis note presents a combination of searches for Higgs boson pair (HH) production performed by the ATLAS and CMS Collaborations using proton-proton collision data sets recorded at at the LHC Run 2, corresponding to integrated luminosities ranging between 126 and 140. The upper limit at the 95% confidence level on the total HH production cross section corresponds to 2.5 times the standard model (SM) prediction with an expected value of 1.7 (2.8) assuming the absence (presence) of the SM HH signal. The strength of the HH signal is measured to be relative to the SM prediction. The observed significance is found to be 1.1 standard deviations when 1.3 are expected for the SM HH signal. Constraints are set on the Higgs boson trilinear self-coupling and on the couplings of two Higgs bosons to two vector bosons, both normalized to the SM predictions and denoted as and , respectively. The observed individual constraints at the 95% confidence level are and , while the expected constraints assuming the presence of the SM HH signal are and
First results from FASER at the LHC
No full textThe ForwArd Search ExpeRiment (FASER) is a new experiment at the Large Hadron Collider (LHC) designed to search for light, weakly-interacting particles. Placed 480 m downstream from the ATLAS interaction point along the beam collision axis, FASER detects particles that travel hundreds of meters. This paper presents the first physics results from FASER using data collected during LHC Run 3 in 2022-2023. We report on searches for dark photons decaying into electron-positron pairs and axion-like particles (ALPs) decaying into photon pairs, both of which can provide insights into physics beyond the Standard Model. We discuss the first direct observation of collider neutrinos with FASER and measurements of electron neutrino and muon neutrino interaction cross-sections in the unexplored TeV energy range using the FASERν emulsion detector. These results provide new opportunities for exploring both Standard Model and Beyond the Standard Model physics in the forward region of LHC proton-proton collisions. We also discuss future prospects, including an upgrade of a preshower calorimeter detector and plans for the Forward Physics Facility in the High-Luminosity LHC era
Large-scale simulations of lattice QCD for nucleon structure using Nf=2+1+1 flavors of twisted mass fermions
No full textUnderstanding the internal structure of protons and neutrons is a fundamental challenge in nuclear physics that requires both theoretical and computational advances. In this work, we present results from large-scale lattice Quantum Chromodynamics (QCD) simulations performed on European supercomputing facilities to calculate key nucleon structure quantities. Our calculations use gauge field configurations with Nf=2+1+1 twisted mass Wilson-clover fermions at physical quark masses and multiple lattice spacings, allowing for controlled continuum extrapolations. The highly optimized tmLQCD software, combined with the QUDA library for GPU acceleration, enables efficient execution on current heterogeneous computing architectures. We provide details of this computational approach and present our latest results on nucleon structure observables, including nucleon charges, electromagnetic form factors, and momentum fraction. These results include the first continuum extrapolation of nucleon structure quantities using only simulations at physical quark masses, eliminating systematic uncertainties associated with chiral extrapolations
Open Source at CERN in 2025/2026
No full textThis talk will be a brief exploration of what open source is, why has it gained such phenomenal success in the last decade and what does this mean for open source? Why do both the private and public sector turn to it in our digitalised environments?
In a world of AI, geopolitics and Sovereignty what are the challenges and where does open source fit?
The audience will leave with a better understanding of open source today and the challenges it faces.
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OpenUK CEO and Executive Producer State of Open Con, Amanda’s 25 years’ legal experience includes being instrumental in shaping open source’s legal frameworks and internet law in 2000’s. Sought-after international keynote speaker, tech press contributor and editor “Open Source: Law, Policy and Practice” (2022).
Recognition: Computer Weekly 50 Most Influential Women (2023, 2024) listed as #20 in 2024; Computing IT Leaders 100 (2023,2024,2025); Lifetime Achievement WIPL (2022); Women Who Will (2023); INvolve Heroes (2022, 2023); Novi Awards (2024); Raconteur 50 CEOs (2025).
Advisory: Boards -UK Open Standards Board; UKRI Digital Research Infrastructure; UKRI Exascale; KDE; Mimoto; Scarf; FerretDB and Space Aye; Fellow, Open Forum Academy; Distinguished Fellow, Rust Foundation; European Representative, OIN; Ambassador, Open Charge Alliance, Board Member Mojaloop Foundation and ITU Expert Network, Digital Innovation Board
Running Couplings in High-Temperature Effective Field Theory
No full textIn this work, we study the renormalization-group evolution of parameters in the three-dimensional effective field theory (3D EFT) that describes the thermally driven electroweak phase transition of the Higgs field. We focus on the first-order case, triggered by beyond the Standard Model physics. We compute the two-loop running of the 3D EFT couplings, including the effect of the leading non-renormalizable terms. We then analyze how the new contributions to the beta functions compare with those in the super-renormalizable case, highlighting their impact on perturbative computations of the scalar potential, which describes the vacuum structure of the theory. By incorporating higher-order corrections in the mass parameter evolution, as well as the running of other effective operators, we set the stage for testing their impact on phase transition dynamics in lattice simulations
Efficient evaluation of the dark-matter two-loop power spectrum in the EFT of LSS
No full textRapid progress in cosmological Large Scale Structure (LSS) surveys motivates precise theoretical predictions. The Effective Field Theory of Large-Scale Structure (EFTofLSS) is routinely applied to data, and requires fast computation of its predictions when sampling the large space of cosmological parameters. Going beyond existing one-loop techniques, we present a method to rapidly evaluate the two-loop power spectrum. Our method decomposes the typically small difference between a given linear power spectrum and a reference power spectrum into a cosmology-independent basis of functions resembling massive scalar propagators in Quantum Field Theory. By taking the leading terms in such a small difference, we numerically evaluate the cosmology-independent loop integrals where in the integrand only the relevant combinations of basis functions appear. We achieve an efficient numerical evaluation via physically motivated local ultraviolet subtractions and by arranging the cancellation of infrared singularities locally in the integrands. Final predictions are obtained by contracting these precomputed integrals with the cosmology-dependent coordinates of the expansion in the fixed basis. We present and publicly release the precomputed integrals for the renormalized two-loop dark-matter power spectrum in the EFTofLSS. These require eight EFT counterterms, which include the effect of generated vorticity, and are sufficient to analyze the lensing galaxy signal in LSS surveys at this order
New GPU developments in the Madgraph CUDACPP plugin: kernel splitting, helicity streams, cuBLAS color sums
No full textThe first production release of the CUDACPP plugin for the Madgraph5_aMC@NLO generator, which speeds up matrix element (ME) calculations for leading-order (LO) QCD processes using a data parallel approach on vector CPUs and GPUs, was delivered in October 2024. This has been described in previous publications by the team behind that effort. In this paper, I describe my work on some additional developments providing further optimizations of CUDACPP for GPUs, which I consider ready for inclusion in a new release of the software. The new approach mainly consists in splitting the calculation of the ME, which has been so far performed using a single large GPU kernel, into several smaller kernels. I also take this opportunity to describe more in detail some features of the CUDACPP software that are relevant to these new developments and that have not yet been documented
Rapid event extraction and tensorial event adaption: Libraries for efficient access and generic reweighting of parton-level events and their implementation in the MadtRex module
No full textWe present Rex and teaRex, C++17 libraries for efficient management of parton-level hard scattering event information and completely generic reweighting of such events, respectively. Rex is primarily an interfacing and I/O library for Les Houches Event format files and provides an internal event format designed with data parallelism in mind, and teaRex extends this format to provide full parton-level reweighting functionality with minimal code needing to be written by the end user. These libraries serve as the foundation for the MadtRex reweighting module for MadGraph5_aMC@NLO, extending the functionality of the CUDACPP plugin to allow for data-parallel model-generic leading order parameter reweighting on SIMD-enabled CPUs and SIMT GPUs, speeding up reweighting by more than two orders of magnitude compared to MadGraph5_aMC@NLO running on the exact same hardware while providing trivial scalability to larger and distributed systems