Understanding the B->K*mu+mu- Anomaly (1307.5683v3)

Abstract: We present a global analysis of the B->K*(->K pi)mu+mu- decay using the recent LHCb measurements of the primary observables P_{1,2} and P'_{4,5,6,8}. Some of them exhibit large deviations with respect to the SM predictions. We explain the observed pattern of deviations through a large New Physics contribution to the Wilson coefficient of the semileptonic operator O9. This contribution has an opposite sign to the SM one, i.e., reduces the size of this coefficient significantly. A good description of data is achieved by allowing for New Physics contributions to the Wilson coefficients C7 and C9 only. We find a 4.5 sigma deviation with respect to the SM prediction, combining the large-recoil B->K*(->K pi)mu+mu- observables with other radiative processes. Once low-recoil observables are included the significance gets reduced to 3.9 sigma. We have tested different sources of systematics, none of them modifying our conclusions significantly. Finally, we propose additional ways of measuring the primary observables through new foldings.

• The paper demonstrates a 4.5σ deviation in large-recoil observables in B→K*μ⁺μ⁻ decay, indicating a significant new physics contribution to the Wilson coefficient C9.
• It employs an effective Hamiltonian framework to isolate short-distance effects and minimizes uncertainties by focusing on observables with low form-factor dependence.
• The study underscores the need for further precision measurements, providing crucial insights for future experimental and theoretical exploration in flavor physics.

Analysis of the $B \to K^* \mu^+\mu^-$ Anomaly

The paper at hand presents an in-depth paper of the decay process $B \to K^* (\to K \pi) \mu^+\mu^-$, particularly in light of recent LHCb data exhibiting deviations from the Standard Model (SM) predictions. These deviations are observed across several primary observables, such as $P_{1,2}$ and $P'_{4,5,6,8}$. The authors focus on interpreting these anomalies through potential new physics (NP) contributions, primarily attributed to modifications in the Wilson coefficients associated with semileptonic operators, with particular attention to the coefficient of operator $O_9$.

Key Findings

The analysis draws significant conclusions by assessing the impact of NP on the Wilson coefficients, specifically focusing on coefficients $7$ and $9$. Among the results are:

• A $4.5\,\sigma$ deviation from the SM is observed when large-recoil observables are considered, implicating a notable NP contribution to $C_9$. This discrepancy reduces to $3.9\,\sigma$ upon including low-recoil observables.
• The analysis suggests that the NP contribution to $C_9$ has an opposite sign to the SM, reducing its effective value.

Methodological Approach

• The paper employs an effective Hamiltonian framework, allowing for the separation of short-distance NP effects from long-distance SM contributions.
• Observables were chosen based on their low sensitivity to hadronic form factors and their heightened sensitivity to potential NP contributions. The primary observables analyzed include $P_1$, $P_2$, and $P'_{4,5,6,8}$.
• Extensive testing of systematic uncertainties, including those arising from charm-loop effects and form-factor uncertainties, affirms the stability of the findings.

Implications and Future Directions

The implications of this paper are profound for both the physics community's understanding of flavor physics and the potential existence and identification of NP. Notably:

1. Model Building: The results, indicating NP effects discernible in modified Wilson coefficients, particularly $C_9$, provide crucial inputs into the construction of NP models, potentially involving new heavy gauge bosons or other exotic phenomena.
2. Experimental Focus: The paper underscores the importance of further precision measurements in the $B \to K^* \mu^+\mu^-$ decay channel, especially with increased data accumulations at LHCb and future experiments. The potential systematic effects from the S-wave component and systematics tied to charm-loop effects necessitate vigilant experimental strategies and refined theoretical models.
3. Broader Theoretical Landscape: These results contribute to broader efforts attempting to reconcile observed data with the SM or suggest scenarios requiring extensions. Future theoretical work could explore beyond tree-level contributions or alternative frameworks like supersymmetry or extra-dimensional theories.

The consistency of the anomaly across various classes of observables and its robustness against typical SM uncertainties suggest that the flavor physics of $B$ mesons may still hold valuable surprises, meriting continued investigation and possibly signaling physics beyond the current paradigm.