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Register a new userAnomalies in B Decays: A Sign of New Physics?
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David London
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At the present time, there are a number of measurements of $B$-decay observables that disagree with the predictions of the standard model. These discrepancies have been seen in processes governed by two types of decay: (i) $b to s mu^+ mu^-u$ and (ii) $b to c tau^- {bar u}$. In this talk, I review the experimental results, as well as the proposed new-physics explanations. We may be seeing the first signs of physics beyond the standard model.
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While the LHC did not observe direct evidence for physics beyond the standard model, indirect hints for new physics were uncovered in the flavour sector in the decays $Bto K^*mu^+mu^-$, $Bto Kmu^+mu^-/Bto Ke^+e^-$, $B_stophimu^+mu^-$, $Bto D^{(*)}tau u$ and $htotau^pmmu^mp$. Each observable deviates from the SM predictions at the $2-3,sigma$ level only, but combining all $bto smu^+mu^-$ data via a global fit, one finds $4-5,sigma$ difference for NP compared to the SM and combining $Bto D^{*}tau u$ with $Bto Dtau u$ one obtains $3.9,sigma$. While $Bto D^{(*)}tau u$ and $htotaumu$ can be naturally explained by an extended Higgs sector, the $bto smu^+mu^-$ anomalies point at a $Z$ gauge boson. However, it is also possible to explain $Bto D^{(*)}tau u$ and $bto smu^+mu^-$ simultaneously with leptoquarks while their effect in $htotau^pmmu^mp$ is far too small to account for current data. Combining a 2HDM with a gauged $L_mu-L_tau$ symmetry allows for explaining the $bto smu^+mu^-$ anomalies in combination with $htotau^pmmu^mp$, predicting interesting correlations with $tauto3mu$. In the light of these deviations from the SM we also discuss the possibilities of observing lepton flavour violating $B$ decays (e.g. $Bto K^{(*)}tau^pmmu^mp$ and $B_stotau^pmmu^mp$).
Contributions to B - bar B mixing from physics beyond the standard model may be detected from CP-violating asymmetries in B decays. There exists the possibility of large new contributions that cannot be detected by first generation experiments because of a discrete ambiguity. Some possible strategies for resolving this are discussed.
We investigate the implications of the latest LHCb measurement of $R_K$ for NP explanations of the $B$ anomalies. The previous data could be explained if the $b to s mu^+ mu^-$ NP is in (I) $C_{9,{rm NP}}^{mumu}$ or (II) $C_{9,{rm NP}}^{mumu} = -C_{10,{rm NP}}^{mumu}$, with scenario (I) providing a better explanation than scenario (II). This continues to hold with the new measurement of $R_K$. However, for both scenarios, this measurement leads to a slight tension of $O(1sigma)$ between separate fits to the $b to s mu^+ mu^-$ and $R_{K^{(*)}}$ data. In this paper, we investigate whether this tension can be alleviated with the addition of NP in $b to s e^+ e^-$. In particular, we examine the effect of adding such NP to scenarios (I) and (II). We find several scenarios in which this leads to improvements in the fits. $Z$ and LQ models with contributions to both $b to s mu^+ mu^-$ and $b to s e^+ e^-$ can reproduce the data, but only within scenarios based on (II). If the tension persists in future measurements, it may be necessary to consider NP models with more than one particle contributing to $b to s ell^+ ell^-$.
If new physics (NP) is present in B -> pi pi decays, it can affect the isospin I=2 or I=0 channels. In this paper, we discuss various methods for detecting and measuring this NP. The techniques have increasing amounts of theoretical hadronic input. If NP is eventually detected in B -> pi pi -- there is no evidence for it at present -- one will be able to distinguish I=2 and I=0, and measure its parameters, using these methods.
Recent measurements of certain B decays indicate deviations from Standard Model (SM) predictions. We show that Supersymmetric effects can increase the Branching Ratios (BRs) of both $Bto D {tau} { u}_{tau}$ and $Bto D^ast {tau} { u}_{tau}$ with respect to the SM rates, thereby approaching their newest experimentally measured values.
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