arXiv subjects

Marianne Bouchard

Publications and source records attributed to Marianne Bouchard.

5 recordsLinked to original sources

arXiv2026

Searching for New Physics with Reinforcement Learning

Finding new physics (NP) is the most important problem in particle physics today. Studying ``anomalies'', i.e., measurements of low-energy observables whose values disagree with the predictions of the Standard Model (SM), is a powerful search strategy. The SM Effective Field Theory (SMEFT) provides a general model-independent framework for parameterizing NP; it is natural to try to find the SMEFT operator(s) that can explain such anomalies. This is a challenging task because (i) the number of SMEFT operators is enormous, and (ii) at loop level there are very complicated correlations among the operators. Analyses by humans typically rely on phenomenological intuition to decide which operators are relevant. This is often biased and does not explore the complete SMEFT operator space. Interestingly, reinforcement learning (RL) techniques excel at tasks that require decision making to achieve their goals. In this paper, we introduce an RL method that can be used to find the SMEFT operators that explain any anomalies. We test it on the CDF $W$-mass anomaly, and show that it reproduces (and improves upon) known results. We then consider a far more complicated situation with multiple anomalies and show that, even here, this method is able to find the SMEFT operators that explain the data. Our RL method can therefore be used to efficiently search for NP at the level of SMEFT.

hep-ph↗

arXiv2026

Anomalies in Hadronic $B$ Decays

The decays $B\to PP$, where the pseudoscalar $P$ is a $\pi$ or $K$, have been studied under the assumption of flavour SU(3) symmetry [SU(3)$_F$]. The global fit shows a 3.6$\sigma$ discrepancy with the Standard Model (SM). Separate fits for $\Delta S = 0$ and $\Delta S = 1$ decays find parameter sets that differ by a factor of 10, suggesting 1000% SU(3)$_F$ breaking, significantly larger than the $\sim$ 30% breaking expected in the SM. This study has been extended to include final states with $\eta$ and $\eta'$ mesons. The resulting global fit, once again under the assumption of SU(3)$_F$ symmetry, is worse, with a 4.1$\sigma$ deviation from the SM. When theoretical constraints $|\widetilde C/\widetilde T| = 0.2$ or $\widetilde A = 0$ are imposed, the fits worsen, with the discrepancy approaching 5$\sigma$. These results hint at new-physics contributions to these decays.

hep-ph↗

arXiv2026

Anomalies in Hadronic $B \to VV$ Decays

Recently, a fit of charmless $B\to PP$ decays ($B \in \{B^0, B^+, B_s^0\}$, $P \in \{ \pi, K, \eta, \eta' \}$) to the latest data was performed under the assumption of flavour SU(3) symmetry [SU(3)$_F$]. It was found that there is a $4.1\sigma$ disagreement with the SU(3)$_F$ limit of the Standard Model [$\rm SM_{SU(3)_F}$]. In this paper, we extend this analysis to charmless $B \to VV$ decays ($V \in \{\rho, K^*, \phi, \omega\}$). The fit examining $B \to \rho K^*$ decays, assuming only isospin symmetry, is found to be acceptable. When we fit to $B \to VV$ decays with $V \in \{ \rho, K^* \}$ within SU(3)$_F$, we find a $5.2\sigma$ discrepancy with SM$_{SU(3)_F}$. Finally, when $B \to VV$ decays with $V \in \{ \rho, K^*, \phi, \omega \}$ are considered, the discrepancy grows to $>7\sigma$. The theoretical input in this analysis is modest, so our results are quite rigorous, group theoretically, and hold almost exactly in the SU(3)$_F$ limit. Although it seems unlikely that the introduction of $\sim 30$% SU(3)$_F$-breaking effects can account for this discrepancy, this must be verified.

hep-ph↗

arXiv2025

Isospin-based EWP-tree Relations

In 1998, it was shown that, if flavor SU(3) symmetry [SU(3)$_F$] is assumed in charmless $B \to PP$ decays ($P$ is a light pseudoscalar meson), some reduced matrix elements involving electroweak penguin (EWP) operators are related to those involving tree operators. Similarly, EWP diagrams are related to tree diagrams. These SU(3)$_F$ EWP-tree relations were recently used in global analyses of $B \to PP$ decays. They have also been used over the years in analyses of the $B \to \pi K$ puzzle, even though the $B \to \pi K$ amplitudes are related by isospin symmetry [SU(2)$_I$], and not the full SU(3)$_F$. In this paper, we show that, even if only SU(2)$_I$ is assumed, there are still EWP-tree relations. In $\Delta S=0$ decays, these relations are similar to those of SU(3)$_F$, and can be used to take into account the EWP contributions in the extraction of the CP phase $\alpha$ from $B \to \pi\pi$ decays. In $\Delta S=1$ decays, the SU(2)$_I$ EWP-tree relations are quite different from those of SU(3)$_F$; when these are used to analyze the $B \to \pi K$ puzzle, one now finds a 4-5$\sigma$ discrepancy with the Standard Model, much larger than what was previously found. We argue that, if one analyzes a set of hadronic $B$ decays whose amplitudes are related by isospin, one must use the SU(2)$_I$ EWP-tree relations for that set of decays in the analysis.

hep-ph↗

arXiv2025

Anomalies in Hadronic $B$ Decays: an Update

Recently, $B\to PP$ decays ($B = \{B^0, B^+, B_s^0\}$, $P = \{ π, K \}$) were analyzed under the assumption of flavor SU(3) symmetry (SU(3)$_F$). Although the individual fits to $ΔS=0$ or $ΔS=1$ decays are good, it was found that the combined fit is very poor: there is a $3.6σ$ disagreement with the SU(3)$_F$ limit of the standard model (SM$_{\rm{SU(3)}_F}$). One can remove this discrepancy by adding SU(3)$_F$-breaking effects, but 1000\% SU(3)$_F$ breaking is required. In this paper, we extend this analysis to include decays in which there is an $η$ and/or $η'$ meson in the final state. We now find that the combined fit exhibits a $4.1σ$ discrepancy with the SM$_{\rm{SU(3)}_F}$, and 1000\% SU(3)$_F$-breaking effects are still required to explain the data. These results are rigorous, group-theoretically -- no theoretical assumptions have been made. But when one adds some theoretical input motivated by QCD factorization, the discrepancy with the SM$_{\rm{SU(3)}_F}$ grows to $4.9σ$.

hep-ph↗