EOS -- A Software for Flavor Physics Phenomenology

I present EOS, an open-source software dedicated to a variety of tasks in the processing of flavor physics observables. EOS is written in C++ and offers both a C++ and a Python interface. It is developed for three main tasks, the production of theoretical predictions for flavor physics observables; the inference of theoretical parameters from an extensible database of likelihoods; and the production of Monte Carlo samples of flavor processes for sensitivity studies.Comment: 9 pages, 4 figure

Dispersive analysis of Λb→Λ(1520)\Lambda_b \to \Lambda(1520) local form factors

We perform an analysis of $\Lambda_b\to\Lambda(1520)$ local form factors. We use dispersive techniques to provide a model-independent parametrisation of the form factors that can be used in the whole kinematic region. We use lattice QCD data to constrain the free parameters in the form factors expansion, which is further constrained by endpoint relations, dispersive bounds, and SCET relations. We analyse different scenarios, where we expand the form factors up to different orders, and their viability. Finally, we use our results to obtain predictions for some observables in $\Lambda_b\to\Lambda(1520)\ell^+\ell^-$ decays, as the differential branching ratio, the forward-backwards lepton asymmetry and the branching ratio of $\Lambda_b\to\Lambda(1520)\gamma$. Finally, we provide a python notebook based on the software EOS to reproduce our result.Comment: 21 pages, 4 figures, 1 ancillary file, v2: correction of typos, v3: version accepted in JHE

Testable likelihoods for beyond-the-standard model fits

Studying potential BSM effects at the precision frontier requires accurate transfer of information from low-energy measurements to high-energy BSM models. We propose to use normalising flows to construct likelihood functions that achieve this transfer. Likelihood functions constructed in this way provide the means to generate additional samples and admit a “trivial” goodness-of-fit test in form of a χ2 test statistic. Here, we study a particular form of normalising flow, apply it to a multi-modal and non-Gaussian example, and quantify the accuracy of the likelihood function and its test statistic

Prospects for searches of b→sννˉb \to s \nu \bar{\nu} decays at FCC-ee

We investigate the physics reach and potential for the study of various decays involving a $b \to s \nu \bar{\nu}$ transition at the Future Circular Collider running electron-positron collisions at the $Z$-pole (FCC-ee). Signal and background candidates, which involve inclusive $Z$ contributions from $b\bar{b}$, $c\bar{c}$ and $uds$ final states, are simulated for a proposed multi-purpose detector. Signal candidates are selected using two Boosted Decision Tree algorithms. We determine expected relative sensitivities of $0.53\%$, $1.20\%$, $3.37\%$ and $9.86\%$ for the branching fractions of the $B^{0} \to K^{*0} \nu \bar{\nu}$, $B^{0}_{s} \to \phi \nu \bar{\nu}$, $B^{0} \to K^{0}_{S} \nu \bar{\nu}$ and $\Lambda_{b}^{0} \to \Lambda^{0} \nu \bar{\nu}$ decays, respectively. In addition, we investigate the impact of detector design choices related to particle-identification and vertex resolution. The phenomenological impact of such measurements on the extraction of Standard Model and new physics parameters is also studied

Dispersive analysis of B → K (*) and B s → ϕ form factors

We propose a stronger formulation of the dispersive (or unitarity) bounds à la Boyd-Grinstein-Lebed (BGL), which are commonly applied in analyses of the hadronic form factors for B decays. In our approach, the existing bounds are split into several new bounds, thereby disentangling form factors that are jointly bounded in the common approach. This leads to stronger constraints for these objects, to a significant simplification of our numerical analysis, and to the removal of spurious correlations among the form factors. We apply these novel bounds to B¯→K¯∗ and B¯s→ϕ form factors by fitting them to purely theoretical constraints. Using a suitable parametrization, we take into account the form factors’ below-threshold branch cuts arising from on-shell B¯sπ0 and B¯sπ0π0 states, which so-far have been ignored in the literature. In this way, we eliminate a source of hard-to-quantify systematic uncertainties. We provide machine readable files to obtain the full set of the B¯→K¯∗ and B¯s→ϕ form factors in and beyond the entire semileptonic phase space

Prospects for searches of b → sν ν ¯ decays at FCC-ee

We investigate the physics reach and potential for the study of various decays involving a b→sνν¯ transition at the Future Circular Collider running electron-positron collisions at the Z-pole (FCC-ee). Signal and background candidates, which involve inclusive Z contributions from bb¯, cc¯ and uds final states, are simulated for a proposed multi-purpose detector. Signal candidates are selected using two Boosted Decision Tree algorithms. We determine expected relative sensitivities of 0.53%, 1.20%, 3.37% and 9.86% for the branching fractions of the B0→K∗0νν¯, Bs0→ϕνν¯, B0→KS0νν¯ and Λb0→Λνν¯ decays, respectively. In addition, we investigate the impact of detector design choices related to particle-identification and vertex resolution. The phenomenological impact of such measurements on the extraction of Standard Model and new physics parameters is also studied

Analysis of the ψ ( 3770 ) resonance in line with unitarity and analyticity constraints

We study the inclusive and exclusive cross sections of e+e-→hadrons for center-of-mass energies between 3.70 and 3.83GeV to infer the mass, width, and couplings of the ψ(3770) resonance. By using a coupled-channel K-matrix approach, we setup our analysis to respect unitarity and the analyticity properties of the underlying scattering amplitudes. We fit several models to the full dataset and identify our nominal results through a statistical model comparison. We find that, accounting for the interplay between the ψ(2S) and the ψ(3770), no further pole is required to describe the ψ(3770) line shape. In particular we derive from the pole location Mψ(3770)=3778.8±0.3MeV and Γψ(3770)=25.0±0.5MeV. Moreover, we find the decay to D+D- and D0D¯0 to be consistent with isospin symmetry and derive an upper bound on the branching ratio B(ψ(3770)→non-DD¯)<6% at 90% probability

Toward a complete description of b → uℓ− v within the Weak Effective Theory decays

We fit the available data on exclusive semileptonic b → uℓ −ν¯ decays within the Standard Model and in the Weak Effective Theory. Assuming Standard Model dynamics,we find |Vub| = 3.59+0.13−0.12 × 10−3. Lifting this assumption, we obtain stringent constraintson the coefficients of the ub`ν sector of the Weak Effective Theory. Performing a Bayesian model comparison, we find that a beyond the Standard Model interpretation is favoured over a Standard Model interpretation of the available data. We provide a Gaussian mixturemodel that enables the efficient use of our fit results in subsequent analyses beyond the Standard Model, within and beyond the framework of the Standard Model Effective Field Theory

Maximizing the physics potential of B±→π±μ+μ− decays

We present a method that maximizes the experimental sensitivity to new physics contributions in ±→±⁢+⁢− decays. This method relies on performing an unbinned maximum likelihood fit to both the measured dimuon 2 distribution of ±→±⁢+⁢− decays, and theory calculations at spacelike 2, where QCD predictions are most reliable. Using known properties of the decay amplitude we employ a dispersion relation to describe the nonlocal hadronic contributions across spacelike and time like 2 regions. The fit stability and the sensitivity to new physics couplings and new sources of ⁢-violation are studied for current and future data-taking scenarios, with the LHCb experiment as an example. The proposed method offers a precise and reliable way to search for new physics in these decays

Constructing model-agnostic likelihoods, a method for the reinterpretation of particle physics results

Experimental High Energy Physics has entered an era of precision measurements. However, measurements of many of the accessible processes assume that the final states’ underlying kinematic distribution is the same as the Standard Model prediction. This assumption introduces an implicit model-dependency into the measurement, rendering the reinterpretation of the experimental analysis complicated without reanalysing the underlying data. We present a novel reweighting method in order to perform reinterpretation of particle physics measurements. It makes use of reweighting the Standard Model templates according to kinematic signal distributions of alternative theoretical models, prior to performing the statistical analysis. The generality of this method allows us to perform statistical inference in the space of theoretical parameters, assuming different kinematic distributions, according to a beyond Standard Model prediction. We implement our method as an extension to the pyhf software and interface it with the EOS software, which allows us to perform flavor physics phenomenology studies. Furthermore, we argue that, beyond the pyhf or HistFactory likelihood specification, only minimal information is necessary to make a likelihood model-agnostic and hence easily reinterpretable. We showcase that publishing such likelihoods is crucial for a full exploitation of experimental results