Symmetries and Asymmetries of B -> K* mu+ mu- Decays in the Standard Model and Beyond (0811.1214v5)

Abstract: The rare decay B -> K* (-> K pi) mu+ mu- is regarded as one of the crucial channels for B physics as the polarization of the K* allows a precise angular reconstruction resulting in many observables that offer new important tests of the Standard Model and its extensions. These angular observables can be expressed in terms of CP-conserving and CP-violating quantities which we study in terms of the full form factors calculated from QCD sum rules on the light-cone, including QCD factorization corrections. We investigate all observables in the context of the Standard Model and various New Physics models, in particular the Littlest Higgs model with T-parity and various MSSM scenarios, identifying those observables with small to moderate dependence on hadronic quantities and large impact of New Physics. One important result of our studies is that new CP-violating phases will produce clean signals in CP-violating asymmetries. We also identify a number of correlations between various observables which will allow a clear distinction between different New Physics scenarios.

• The paper presents a detailed analysis of angular distributions in B→K* μ⁺μ⁻ decays, elucidating SM symmetries and potential New Physics effects.
• It employs an effective Hamiltonian framework and NNLL QCD calculations to simplify complex form factors and improve predictive precision.
• The study explores various New Physics scenarios, offering both model-independent insights and specific predictions for CP-violating asymmetries and Wilson coefficients.

Overview of $B\to K^*\mu^+\mu^-$ Decays in the Standard Model and Beyond

The paper "Symmetries and Asymmetries of $B\to K^*\mu^+\mu^-$ Decays in the Standard Model and Beyond" offers an extensive theoretical investigation into the angular distributions in the rare decay $B\to K^*(\to K\pi)\mu^+\mu^-$. This rare decay is notable for its sensitivity to potential New Physics (NP) beyond the Standard Model (SM) due to its complex flavor structure encompassed within the $b\to s$ transition. Using the benefits of angular analysis and comprehensive QCD calculations, the authors aim to provide precise theoretical predictions for observables that can distinguish SM interactions from NP effects.

Theoretical Framework

The approach is rooted in using the effective Hamiltonian framework to separate short- and long-distance effects inherent in the decay process. This involves calculating matrix elements using operators derived primarily from QCD sum rules on the light-cone and taking into account next-to-next-to-leading logarithmic (NNLL) accuracy in the perturbative QCD calculations. The heavy-quark effective theory inspires simplifications allowing the reduction of seven independent $B\to K^*$ form factors to two, known as soft form factors, at leading order.

Observables and Angular Analysis

The paper discusses a full angular analysis of the decay process, focusing on constructing observables like forward-backward asymmetry ($A_{\rm FB}$) and CP-violating asymmetries which provide high sensitivity to NP effects. These observables benefit from the angular structure of the decay, which lends itself to precise measurements at collider experiments. The ability to express these observables in terms of the Wilson coefficients aids in quantifying potential NP contributions.

Implications for New Physics

The analysis covers several NP scenarios, including the Minimal Supersymmetric Standard Model (MSSM), Littlest Higgs models, and more. Each scenario allows for distinctive predictions about deviations from SM expectations, particularly through new CP-violating phases or scalar and pseudoscalar operators. Key insights include the potential for NP to induce significant changes in CP-violating observables or to adjust key parameters such as the Wilson coefficients tied to the decay process.

Model-Independent and Scenario-Specific Predictions

The paper takes a dual approach in its analysis—first, offering model-independent insights based on variation in Wilson coefficients and then exploring specific NP scenarios to offer broader predictions for angular coefficients and asymmetries. This layered approach is critical for disentangling complex NP effects and understanding the degree to which they can manifest in observable B-physics channels.

Future Prospects and Challenges

As the paper elucidates, the path forward involves harnessing advances in experimental capabilities at facilities like the LHC, where unprecedented sensitivity to angular distributions of rare decays can offer stark contrasts between NP predictions and SM consistency. These efforts will undoubtedly require cooperation between advanced theoretical models and cutting-edge experimental techniques to probe deeper into the flavor sector's potential for unveiling NP.

In conclusion, the paper's meticulous presentation of decay dynamics and critical observables offers a robust theoretical foundation upon which future discoveries in particle physics could rest. Its call for precise measurements combined with rigorous theoretical computation charts a path for unveiling new layers of fundamental physics through diligent scrutiny of rare B meson decays.