arXiv subjects

Eluned Smith

Publications and source records attributed to Eluned Smith.

6 recordsLinked to original sources

arXiv2026

Accelerating fits in high-energy physics and beyond

Data analysis in particle physics often involves optimizing a loss function that quantifies how well a theoretical model describes the observed data, in order to estimate the parameters of the model. This is referred to as fitting. As datasets grow larger and more expensive analysis methods are used, the time required to perform this parameter estimation can be a limiting factor. This work explores techniques for accelerating the fitting process, and measures their performance on a set of models representative of a variety of physics fits. We compare the speed and precision of variants of well-known optimization algorithms, namely Newton's method, BFGS, and the Migrad algorithm (commonly used in particle physics fits). We observe significant speedups when using some algorithms: most notably, some variants of BFGS are about ten times faster than Migrad, while achieving the same precision. For quasi-Newtonian algorithms like BFGS and Migrad, we find that the initial value of the Hessian matrix has a large impact on the runtime. We additionally discuss methods for accelerating the evaluation of the loss function and its derivatives, using algebraic simplifications, automatic differentiation, and modern hardware features. We explore techniques for achieving good precision with 32-bit operations, which can achieve significantly higher throughput on the GPU. Lastly we explore efficient parallelization strategies for the CPU and GPU. All of the techniques and algorithms in this paper are implemented in our new FastFit library, which was used for all of our benchmarks.

physics.data-an↗

arXiv2026

Non-parametric and continuous extraction of amplitudes in realistic electroweak penguin decays

A novel approach to extract decay amplitudes in $B\to V(\to M_1M_2)\ell^+\ell^-$ processes, where $V$ represents a meson with either $J = 0$ (S-wave) or $J = 1$ (P-wave), was recently proposed. In this method, the dependence of the amplitudes on the dihadron and dimuon invariant masses is extracted model-independently through a fit to the helicity angles and a subsequent calculation of sPlot weights. In this paper, we show that this method still performs well when applied to data with experimental realism, namely in the presence of detection efficiencies and background candidates, both of which can have non-factorising dependencies between the fitted helicity angles and extracted two-particle masses. We show that a non-factorising efficiency can be accommodated with a small change to the conventional calculation of the sPlot weights, and a non-factorising background by expanding the description of the background distribution into individually factorising terms. We illustrate the method using simulated $B\to K^+π^-μ^+μ^-$ data, containing both S- and P-wave contributions to the $K^+π^-$ system, mixed with non-factorising background candidates and generated with a realistic function for the detection efficiency. We also show that this method can be applied over a much larger dimuon invariant-mass range than studied previously. This work suggests that the method is suitable for application to real experimental data, where it could provide model-independent decay-amplitude shapes for direct comparison with theoretical predictions. A measurement using this technique can improve sensitivity to potential new-physics effects in $b\to s\ell\ell$ transitions, as well as the understanding of hadronic form factors, particularly in the S-wave system.

hep-ex↗

arXiv2026

Flavor-physics benchmarks for tracker-based particle identification at the FCC-ee

The correct identification of charged hadrons plays a crucial role in flavor-physics measurements. The final detector configurations at the proposed Future Circular Collider are yet to be determined and this study aims to contribute to this discussion by benchmarking the particle-identification (PID) performance of the proposed CLD and IDEA detectors using fully simulated events. At present, neither detector proposal includes dedicated PID systems, relying instead on information from the tracking subsystems. We estimate the expected level of contamination due to misidentified charged hadrons for $b$-flavor tagging, rare $b\to s$ transitions, and $s$-jet tagging. The PID information provided by silicon trackers, namely time-of-flight and energy-deposit measurements, leads to significant background suppression with high signal efficiency for the low-momentum hadrons considered for same-side $b$-flavor tagging. In order to improve the contamination in rare decays where momenta are in the medium range, only good timing resolution of 30ps and below can yield an improvement of one order of magnitude below the level achieved by kinematic criteria alone. Light-quark jet-flavor tagging requires identification of particles with very large momentum, which is not possible using only time-of-flight or energy-deposit information in silicon. Access to the number of clusters in a drift-chamber setup, as proposed for the IDEA detector however, results in strong background suppression in every case. This suppression can be further improved in some scenarios by time-of-flight resolution of 30-50ps or better. The PID quality generally exhibits only a small dependence on the cluster-counting efficiency. Whether dedicated PID detectors could further enhance flavor-physics sensitivity should be the subject of future study.

hep-ex↗

arXiv2026

Constraints on new physics from decays of polarized $Λ_b^0$ baryons at the FCC-ee

The $Z^0$ bosons produced in electron-positron collisions at the potential Future Circular Collider (FCC-ee) provide unique opportunities for flavour physics. The non-zero polarization of \Lb baryons produced in $Z^0$ decays enables access to a much larger set of observables than at the LHC, where the $Λ_b^0$ baryons are produced unpolarized. This paper presents a toy angular analysis of $Λ_b^0\to Λ(\to pπ^-)μ^+μ^-$ decays using simulation samples of collisions at the FCC-ee reconstructed using the IDEA detector concept and assuming a dataset of $6\times 10^{12}$ $Z^0$ bosons. While the statistical sensitivity achieved for individual angular observables is not expected to significantly exceed that from the LHCb Upgrade II experiment, the addition of the polarized observables leads to a significant improvement of the knowledge on the Wilson coefficients $C_{9^{(\prime)}}$ and $C_{10^{(\prime)}}$.

hep-ex↗

arXiv2026

Prospects for Measuring $CP$-Violation in $B_s^0 \rightarrow ϕμ^+μ^-$ via Time-Dependent Angular Analysis

This work investigates the prospects for performing a time-dependent angular analysis of $B_s^0 \rightarrow ϕμ^+μ^-$ decays at hadron colliders, and introduces new optimised angular observables associated with $B_s^0$-mixing in the decay rate. The time-dependent normalised decay rate and corresponding probability density function is presented both for when the flavour of the $B_s^0$ meson at production is tagged and when it is untagged. The normalised angular terms linked to $B_s^0$-mixing in the tagged (untagged) case are denoted $\mathcal{Z}_i$ ($\mathcal{H}_i$), and their optimised counterparts as $Q_i$ ($\mathcal{M}_i$). The expected sensitivities of these observables at the end of Run 3, Run 4, and Run 5 of the LHC are determined using pseudoexperiments generated with a decay-time resolution, background level, and signal yield similar to those reported by the LHCb collaboration. It is found that all observables can be extracted with Run 3 statistics, and that the $\mathcal{H}_i$ and $\mathcal{Z}_i$ observables have similar sensitivity, despite the former being suppressed by mixing terms. Moreover, the angular observables only accessible via flavour tagging, such as the equivalent of $P_5^{\prime}$ in the $B^0_s$ system, are found to exhibit sensitivities comparable to current measurements in $B^0 \rightarrow K^{\ast 0} μ^+μ^-$ decays once Run 5 datasets are available. Fits to the observables to extract the Wilson coefficients show a significant increase in precision when either the observables accessible via time-dependent analysis, or flavour tagging, are included. A marked increase in sensitivity to $CP$-violating short-distance effects is observed for a subset of the new optimised $M_i$ and $Q_i$ observables.

hep-ex↗

arXiv2025

Non-parametric and continuous extraction of amplitudes in electroweak penguin decays

We introduce a novel approach to extract the decay-amplitudes in $B\to V(\to M_1M_2)\ell^+\ell^-$ processes, where $V$ represents a meson with either $J = 0$ (S-wave) or $J = 1$ (P-wave). This approach enables the decay-amplitudes across the dihadron and dilepton invariant-masses to be extracted from data in a model-independent and continuous way. To achieve this, the angular decay rate is expressed in a way that allows the application of the \sPlot technique to likelihood fits of the decay angles. We illustrate the abilities of this method on simulated $B^0\to K^+π^-\ell^+\ell^-$ data, containing both S- and P-wave contributions to the $K^+π^-$ system. We provide the weight functions and show that they allow the extraction of the absolute value of the P-wave and S-wave transversity amplitudes as a function of the dihadron and dimuon invariant-masses in a continuous, unbiased, and statistically-powerful way, while only relying on the angular distribution. As a consequence, the extracted amplitude shapes are model-independent -- up to the angular terms included in the fit -- and can be directly compared to theoretical predictions. A measurement using this technique can improve the sensitivity to potential new physics effects in $b\to s\ell^+\ell^-$ transitions, as well as the understanding of hadronic form factors, particularly in the S-wave system.

hep-ex↗