Averages of b-hadron, c-hadron, and tau-lepton properties as of early 2012 (1207.1158v2)

Abstract: This article reports world averages of measurements of b-hadron, c-hadron, and tau-lepton properties obtained by the Heavy Flavor Averaging Group (HFAG) using results available through the end of 2011. In some cases results available in the early part of 2012 are included. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, CP violation parameters, parameters of semileptonic decays and CKM matrix elements.

• The paper presents world averages of heavy flavor measurements, including lifetimes, mixing, and CP violation parameters, to validate the Standard Model.
• It employs rigorous statistical methods by combining data from B-factories and collider experiments to resolve discrepancies and accurately quantify uncertainties.
• Refined results, such as a B0 lifetime near 1.519 ps and Δmd around 0.507 ps⁻¹, provide essential guidance for future experimental designs and theoretical model building.

Overview of Averages of Heavy Flavor Properties

The paper, prepared by the Heavy Flavor Averaging Group (HFAG), compiles and reports on world averages of measurements for properties related to $b$-hadron, $c$-hadron, and $\tau$-lepton. These measurements include branching fractions, lifetimes, neutral meson mixing parameters, $\CP$ violation parameters, semileptonic decay parameters, and CKM matrix elements. This document provides an invaluable resource for researchers in particle physics, offering standardized measurements that can be used for theoretical models and plans for future experimentation.

Highlights and Numerical Results

1. $b$-hadron Lifetimes:
   • The lifetimes of $B^+$, $B^0$, and $B^0_s$ mesons are meticulously measured, with particular attention to resolving discrepancies caused by experimental setups or systematic biases. The paper highlights an average B^0 lifetime of approximately 1.519 ps.
2. Neutral B-Meson Mixing:
   • The mixing parameters for neutral B mesons, denoted $\Delta m$ and $\Delta \Gamma$, are crucial for understanding $\CP$ violation. The reported $\Delta m_{d}$ (for the B^0 system) is approximately 0.507 ps$^{-1}$, a parameter which plays a critical role in tests of the Standard Model and searches for new physics.
3. $\CP$ Violation Parameters:
   • The paper covers measurements related to $\CP$ asymmetries in $b \to c\bar{c}s$ transitions, emphasizing consistency with the $\CP$ violation observations in $b \to s$ penguin processes. The results align well with the Standard Model predictions, demonstrating the robustness of the current theoretical understanding.
4. B-Factory and Collider Contributions:
   • The paper acknowledges the significant contributions from asymmetric B-factories and experiments at collider facilities like the LHC and Tevatron. These experiments have been vital in providing high-precision measurements necessary for these world averages.
5. Numerical Consistency and Correlations:
   • Particular emphasis is placed on the handling of correlations between measurements. Statistical and systematic uncertainties are meticulously considered to ensure that the averages provided are reliable and precise.

Implications and Future Directions

The derivation of world averages for heavy flavor properties paves the way for multiple avenues in both theoretical and experimental physics. These measurements are crucial for:

• Testing the Standard Model: The precise values for parameters like the mass and width differences in mixings and $\CP$ violation parameters can be used to test predictions of the Standard Model with high precision. Deviations from these predictions may indicate new physics beyond the model.
• Model Building: Averages and measurements of CKM matrix elements, with their associated uncertainties, serve as benchmarks for model builders in theoretical particle physics. This can ultimately inform predictions for processes not yet measured.
• Future Experiments: The aggregated data and the identification of remaining uncertainties serve as a guide for future experimental designs to target specific unresolved questions and improve measurement accuracy.

Conclusion

The work of the HFAG in compiling and disseminating averages of $b$-hadron, $c$-hadron, and $\tau$-lepton properties underscores the collaborative effort in the high-energy physics community to refine our understanding of particle interactions and fundamental forces. As new data becomes available, these averages will continue to evolve, providing a dynamic resource that both corroborates current theories and probes the unknowns in particle physics.