Large Hadronic Effects in $B \to K^* \mu\mu$?

TL;DR

Recent LHCb results on B to K* mu mu decays suggest large hadronic effects are responsible for observed anomalies, complicating the search for new physics signals.

Contribution

The paper argues that hadronic effects, not new physics, likely explain the P5' anomaly and S7 observable in B to K* mu mu decays, emphasizing the importance of hadronic contributions.

Findings

Hadronic effects can account for the P5' anomaly.

Non-zero S7 indicates significant hadronic contributions.

Combined fits constrain new physics Wilson coefficients.

Abstract

Recent results from LHCb have confirmed the long-standing $P_5^\prime$ anomaly, an intriguing discrepancy in the angular distribution of the $B \to K^* \mu^+\mu^-$ decay that might be a sign of new physics. In addition, the new results hint at a non-zero value for $S_7$, another observable that characterizes the $B \to K^* \mu^+\mu^-$ angular distribution. We stress that a non-zero $S_7$ cannot be explained by heavy new physics but instead necessarily requires a sizable hadronic effect that introduces a strong phase. We argue that, under plausible assumptions, the hadronic effect is of the correct size to also explain $P_5^\prime$. The direct CP asymmetry in $B \to K^* \mu^+\mu^-$ emerges in principle as a clean probe of new physics in such a scenario. We show that a combined fit of hadronic parameters and Wilson coefficients retains sensitivity to new physics and we find strong bounds on imaginary parts of new physics Wilson coefficients.