Fits to measurements of rare heavy flavour decays

This write-up is intended to form part of the proceedings for Lepton-Photon 2023. We review the decays $b\rightarrow c \ell \nu_\ell$ (where $\ell \in \{e,\mu,\tau\}$) as well as $b\rightarrow s \mu^+ \mu^-$ and $b\rightarrow s e^+ e^-$, giving the current state of the art in terms of measurements. We review fits to such data of new physics weak effective field theory operators, before closing with simplified interpretations in terms of TeV-scale field theories.Comment: Talk for Lepton-Photon 2023. 11 pages, 10 figures. v2 has minor correction

The Case for Future Hadron Colliders From B→K(∗)μ+μ−B \to K^{(*)} \mu^+ \mu^- Decays

Recent measurements in $B \to K^{(*)} \mu^+ \mu^-$ decays are somewhat discrepant with Standard Model predictions. They may be harbingers of new physics at an energy scale potentially accessible to direct discovery. We estimate the sensitivity of future hadron colliders to the possible new particles that may be responsible for the anomalies: leptoquarks or $Z^\prime$s. We consider luminosity upgrades for a 14 TeV LHC, a 33 TeV LHC, and a 100 TeV $pp$ collider such as the FCC-hh. Coverage of $Z^\prime$ models is excellent: for narrow particles, with perturbative couplings that may explain the $b$-decay results for $Z^\prime$ masses up to 20 TeV, a 33 TeV 1 ab$^{-1}$ LHC is expected to cover most of the parameter space up to 8 TeV in mass, whereas the 100 TeV FCC-hh with 10 ab$^{-1}$ will cover all of it. A smaller portion of the leptoquark parameter space is covered by future colliders: for example, in a $\mu^+\mu^-jj$ di-leptoquark search, a 100 TeV 10 ab$^{-1}$ collider has a projected sensitivity up to leptoquark masses of 12 TeV (extendable to 21 TeV with a strong coupling for single leptoquark production), whereas leptoquark masses up to 41 TeV may in principle explain the anomalies.Comment: 24 pages, 10 figures. v2: Improved discussion and references added, version submitted to JHE

Multiple solutions in supersymmetry and the Higgs.

Weak-scale supersymmetry is a well-motivated, if speculative, theory beyond the Standard Model of particle physics. It solves the thorny issue of the Higgs mass, namely: how can it be stable to quantum corrections, when they are expected to be 1015 times bigger than its mass? The experimental signal of the theory is the production and measurement of supersymmetric particles in the Large Hadron Collider (LHC) experiments. No such particles have been seen to date, but hopes are high for the impending run in 2015. Searches for supersymmetric particles can be difficult to interpret. Here, we shall discuss the fact that, even given a well-defined model of supersymmetry breaking with few parameters, there can be multiple solutions. These multiple solutions are physically different and could potentially mean that points in parameter space have been ruled out by interpretations of LHC data when they should not have been. We shall review the multiple solutions and illustrate their existence in a universal model of supersymmetry breaking.This work was supported by STFCThis is the accepted manuscript. The final version is available from the Royal Society at http://rsta.royalsocietypublishing.org/content/373/2032/20140035

The Rumble in the Meson: a leptoquark versus a Z′Z^\prime to fit b→sμ+μ−b \rightarrow s \mu^+ \mu^- anomalies including 2022 LHCb RK(∗)R_{K^{(\ast)}} measurements

We juxtapose global fits of two bottom-up models (an $S_3$ scalar leptoquark model and a ${B_3-L_2}$ $Z^\prime$ model) of \bsll\ anomalies to flavour data in order to quantify statistical preference or lack thereof. The leptoquark model couples directly to left-handed di-muon pairs, whereas the $Z^\prime$ model couples to di-muon pairs with a vector-like coupling. $B_s-\overline{B_s}$ mixing is a focus because it is typically expected to disfavour $Z^\prime$ explanations. In two-parameter fits to 247 flavour observables, including $B_{s/d} \to \mu^+ \mu^-$ branching ratios for which we provide an updated combination and LHCb $R_{K^{(\ast)}}$ measurements from December 2022, we show that each model provides a similar improvement in quality-of-fit of $\sqrt{\Delta \chi^2}=3.6$ with respect to the Standard Model. The main effect of the $B_s-\overline{B_s}$ mixing constraint in the $Z^\prime$ model is to disfavour values of the $s_L-b_L$ mixing angle greater than about $5|V_{cb}|$. This limit is rather loose, meaning that a good fit to data does not require `alignment' in either quark Yukawa matrix. No curtailment of the $s_L-b_L$ mixing angle is evident in the $S_3$ model.Comment: 31 pages, 6 figures. v3 is updated with a new fit including December 2022 LHCb reanalysis of $R_{K^{(\ast)}}$ measurements. Plots and fits significantly changed but the main conclusion is left unchanged. v4 has minor changes. v5 has a typo fixed in the caption of Fig 6, v6 has corrected vertical lines in Fig

Flavonstrahlung in the B3−L2B_3-L_2 Z′Z' Model at Current and Future Colliders

The $B_3-L_2$ $Z^\prime$ model may explain some gross features of the fermion mass spectrum as well as $b\rightarrow s \ell \ell$ anomalies. A TeV-scale physical scalar field associated with gauged $U(1)_{B_3-L_2}$ spontaneous symmetry breaking, the flavon field $\vartheta$, affects Higgs phenomenology via mixing. In this paper, we investigate the collider phenomenology of the flavon field. Higgs and $W$ boson mass data are used to place bounds upon parameter space. We then examine flavonstrahlung (${Z^\prime} \rightarrow Z^\prime \vartheta$ production) at colliders as a means to directly produce and discover flavon particles, providing direct empirical evidence tying it to $U(1)_{B_3-L_2}$ symmetry breaking. A 100 TeV FCC-hh or a 10 TeV muon collider would have high sensitivity to flavonstrahlung, whereas the HL-LHC can observe it only in extreme corners of parameter space.Comment: 27 pages, 14 figure

Plan B: New Z′{Z^\prime} models for b→sl+l−b\rightarrow sl^+l^- anomalies

Measurements of $b \rightarrow s \mu^+ \mu^-$ transitions indicate that there may be a new physics field coupling to di-muon pairs associated with the $b$ to $s$ flavour transition. Including the 2022 LHCb reanalysis of $R_K$ and $R_{K^\ast}$, one infers that there may also be associated new physics in $b\rightarrow e^+ e^-$ transitions. Here, we examine the extent of the statistical preference for $Z^\prime$ models coupling to di-electron pairs taking into account the relevant constraints, in particular from experiments at LEP-2. We identify an anomaly-free set of models which interpolates between the $Z^\prime$ not coupling to electrons at all, to one in which there is an equal $Z^\prime$ coupling to muons and electrons (but where in all models in the set, the $Z^\prime$ boson can mediate $b\rightarrow \mu^+ \mu^-$ transitions). A $3B_3-L_e-2L_\mu$ model provides a close-to-optimal fit to the pertinent measurements along the line of interpolation. We have (re-)calculated predictions for the relevant LEP-2 observables in terms of dimension-6 SMEFT operators and put them into the ${\tt flavio2.3.3}$ computer program, so that they are available for global fits.Comment: 25 pages, 7 figure