Branching fraction measurements of the rare $B^0_s\rightarrowφμ^+μ^-$ and $B^0_s\rightarrow f_2^\prime(1525)μ^+μ^-$ decays (2105.14007v2)

Abstract: The branching fraction of the rare $B^0_s\rightarrow\phi\mu^+\mu^-$ decay is measured using data collected by the LHCb experiment at center-of-mass energies of $7$, $8$ and $13\,\rm{TeV}$, corresponding to integrated luminosities of $1$, $2$ and $6\,{\rm fb}^{-1}$, respectively. The branching fraction is reported in intervals of $q^2$, the square of the dimuon invariant mass. In the $q^2$ region between $1.1$ and $6.0\,{\rm Ge\kern -0.1em V}^2!/c^4$, the measurement is found to lie $3.6$ standard deviations below a Standard Model prediction based on a combination of Light Cone Sum Rule and Lattice QCD calculations. In addition, the first observation of the rare $B^0_s\rightarrow f_2^\prime(1525)\mu^+\mu^-$ decay is reported with a statistical significance of nine standard deviations and its branching fraction is determined.

• The paper reports a 3.6σ deficit in the B0s→φμ⁺μ⁻ branching fraction compared to Standard Model predictions in the 1.1–6.0 GeV²/c⁴ q² range.
• It marks the first observation of the B0s→f₂′(1525)μ⁺μ⁻ decay with a nine sigma significance, consistent with SM expectations.
• Advanced LHCb detection and simulation methods were applied to minimize background interference and enhance measurement precision.

An Analysis of the Branching Fractions in Rare $B^0_s\rightarrow\phi\mu^+\mu^-$ Decays

This paper, authored by the LHCb collaboration and published in Physical Review Letters, reports on the measurement of the branching fraction for the rare decay process $B^0_s\rightarrow \phi\mu^+\mu^-$. This intricate paper explores data captured by the LHCb detector at CERN, spanning center-of-mass energies of 7, 8, and 13 TeV, which correspond to integrated luminosities of 1, 2, and 6 fb$^{-1}$, respectively. The analysis reveals noteworthy deviations from the Standard Model (SM) predictions, especially in the dimuon invariant mass squared ($q^2$) range of 1.1 to 6.0 GeV$^2$/c$^4$. The experimental data reveal a branching fraction lying 3.6 standard deviations below theoretical expectations determined by Light Cone Sum Rule and Lattice QCD calculations.

Key Findings and Observations

1. Branching Fraction Measurements: The $B^0_s\rightarrow \phi\mu^+\mu^-$ decay exhibited a branching fraction significantly lower than anticipated by SM predictions within specific $q^2$ intervals, notably in the 1.1 to 6.0 GeV$^2$/c$^4$ range. The measured value was $3.6\sigma$ below the SM estimate of $(5.37\pm0.66)\times10^{-8}$ GeV$^{-2}c^4$. This discrepancy reiterates previously observed tensions in semileptonic $b\rightarrow s\ell^+\ell^-$ transitions.
2. First Observation of $B^0_s\rightarrow f_2^\prime(1525)\mu^+\mu^-$ Decay: The research made the inaugural observation of the decay $B^0_s\rightarrow f_2^\prime(1525)\mu^+\mu^-$, noting a statistical significance of nine standard deviations with a discovered branching fraction aligning with SM expectations. This observation enriches our comprehension of semileptonic decays involving spin-2 mesons.
3. Methodological Rigor: The paper employed several advanced techniques and sophisticated models to eliminate background noise and enhance measurement precision. This includes leveraging the capabilities of the LHCb detector for muon detection and employing extensive simulation to refine efficiency determinations.

Implications and Future Directions

The observed deviations from the SM predictions in the $B^0_s\rightarrow \phi\mu^+\mu^-$ decay branching fractions signal potential avenues for new physics beyond the SM. These anomalies may hint at unaccounted interferences or the presence of new particles or forces that are yet to be incorporated within the current theoretical framework.

Further experimental investigations, enhanced with increased luminosity and detection precision, are critical to verify these findings. They also offer the possibility of unveiling new insights into leptonic universality and the internal dynamics of heavy mesons. The continuous paper of rare decays and their angular distributions could play a crucial role in testing the robustness of the SM and identifying deviations that could lead to a deeper understanding of fundamental particle interactions.

This paper contributes significantly to the ongoing discourse within particle physics regarding the limitations of the SM, emphasizing the need for comprehensive experimental validation and theoretical refinement moving forward. Future work may also focus on refining theoretical models such as Lattice QCD and exploring the parameter spaces of possible new physics scenarios to explain these intriguing observations.