First Simultaneous Determination of Inclusive and Exclusive |V_{ub}|

Area of Science:

• High Energy Physics
• Particle Physics
• Quantum Chromodynamics

Background:

• The Cabibbo-Kobayashi-Maskawa (CKM) matrix describes quark mixing in weak interactions.
• Precise determination of CKM elements like V_{ub} is crucial for testing the Standard Model of particle physics.
• Discrepancies between inclusive and exclusive measurements of V_{ub} have been a long-standing issue.

Purpose of the Study:

• To perform the first simultaneous determination of the absolute value of V_{ub} using both inclusive and exclusive decays.
• To compare the results from inclusive and exclusive B meson decays to resolve tensions.
• To utilize the full Belle dataset for a high-precision measurement.

Main Methods:

• Analysis of the full Belle dataset at the ϒ(4S) resonance (711 fb^{-1}).
• Full reconstruction of B meson hadronic decays to isolate semileptonic b→uℓν decays.
• Two-dimensional fit using charged pion multiplicity and q^{2} to separate exclusive B→πℓν decays from inclusive B→X_{u}ℓν and backgrounds.
• Combination of experimental results with lattice QCD and QCD calculations.

Main Results:

• Determined |V_{ub}^{excl}| = (3.78 ± 0.23 ± 0.16 ± 0.14) × 10^{-3}.
• Determined |V_{ub}^{incl}| = (3.88 ± 0.20 ± 0.31 ± 0.09) × 10^{-3}.
• The ratio |V_{ub}^{excl}|/|V_{ub}^{incl}| = 0.97 ± 0.12, which is compatible with unity.

Conclusions:

• The first simultaneous measurement shows excellent agreement between inclusive and exclusive determinations of |V_{ub}|.
• This result alleviates tensions in previous measurements and provides a precise value for this fundamental parameter.
• The findings strongly support the consistency of the Standard Model and the underlying theoretical frameworks like QCD.