Angular analysis and differential branching fraction of the decay $B^0_s\toφμ^+μ^-$

Abstract: An angular analysis and a measurement of the differential branching fraction of the decay $B^0_s\to\phi\mu^+\mu^-$ are presented, using data corresponding to an integrated luminosity of $3.0\, {\rm fb^{-1}}$ of $pp$ collisions recorded by the LHCb experiment at $\sqrt{s} = 7$ and $8\, {\rm TeV}$. Measurements are reported as a function of $q^{2}$, the square of the dimuon invariant mass and results of the angular analysis are found to be consistent with the Standard Model. In the range $1<q^2<6\, {\rm GeV}^{2}/c^{4}$, where precise theoretical calculations are available, the differential branching fraction is found to be more than $3\,\sigma$ below the Standard Model predictions.

Angular Analysis and Differential Branching Fraction of the Decay $B^0_s\to\phi\mu^+\mu^-$

This paper presents an in-depth study conducted by the LHCb collaboration on the decay $B^0_s\to\phi\mu^+\mu^-$. This decay process is a flavor-changing neutral current (FCNC) transition that is only permissible through loop-level interactions in the Standard Model (SM), providing a unique window into potential new physics beyond the SM.

Key Findings

1. Branching Fraction Measurement: The study measures the differential branching fraction of the decay as a function of $q^2$, the square of the dimuon invariant mass. While the results of the angular analysis were observed to be consistent with SM expectations, the differential branching fraction in the range $1 < q^2 < 6 \, \text{GeV}^2/c^4$ was found to be more than $3\,\sigma$ below SM predictions. This is a significant discrepancy and may hint at potential contributions from beyond the SM physics.

2. Angular Analysis: The research provides a full three-dimensional angular analysis using a dataset corresponding to an integrated luminosity of $3.0 \, \text{fb}^{-1}$ of $pp$ collisions recorded by the LHCb experiment. The angular analysis includes key observables such as $F_{\rm L}$, $S_{3,4,7}$, and the CP asymmetries $A_{5,6,8,9}$. Notably, all the angular observables were found to be in good agreement with the predictions from the SM.

3. Systematic and Statistical Robustness: The study incorporates detailed systematic uncertainty evaluations for both the branching fraction and the angular observables. These include potential biases from the modeling of the signal and background mass shapes, angular acceptance corrections, and contributions from peaking backgrounds, among others.

Implications and Future Directions

The findings of this research hold significant implications for the field of particle physics. The observed deviation from the SM prediction in the differential branching fraction suggests potential new physics. Such anomalies often investigate the possibility of new particles or interactions that could alter the characteristics of FCNC processes.

While the angular analysis shows consistency with the SM, further data, especially with greater precision, could help elucidate any subtle discrepancies that current analyses might not detect. Future work could aim to refine theoretical models and include higher-order corrections to better match the data or confirm deviations. Additionally, increasing the dataset through further LHC runs could provide a larger statistical basis for confirming or refuting these intriguing hints of new physics.

The study of rare decay processes like $B^0_s\to\phi\mu^+\mu^-$ continues to be at the forefront of probing the boundaries of the SM, and by extension, exploring the realms where new physics might emerge.