First Evidence for Direct CP Violation in Beauty to Charmonium Decays.

Area of Science:

• Particle Physics
• High-Energy Physics
• Quantum Chromodynamics

Background:

• The Cabibbo-Kobayashi-Maskawa (CKM) matrix describes flavor mixing in weak interactions.
• CP symmetry violation is a key feature of the Standard Model of particle physics.
• Understanding CP violation in B meson decays is crucial for testing the Standard Model and searching for new physics.

Purpose of the Study:

• To precisely measure the CP asymmetry and branching fraction of the B+→J/ψπ+ decay.
• To compare these measurements with the favored B+→J/ψK+ decay.
• To search for evidence of direct CP violation in beauty decays to charmonium final states.

Main Methods:

• Analysis of proton-proton collision data collected at 13 TeV.
• Utilizing a large dataset with an integrated luminosity of 5.4 fb⁻¹.
• Relative measurements against the B+→J/ψK+ decay channel to minimize systematic uncertainties.

Main Results:

• The CP asymmetry difference ΔA^CP was measured to be (1.29±0.49±0.08)×10⁻².
• The branching fraction ratio R_{π/K} was measured to be (3.852±0.022±0.018)×10⁻².
• Combined results with previous LHCb data yield ΔA^CP = (1.42±0.43±0.08)×10⁻², deviating from zero by 3.2 standard deviations.

Conclusions:

• The combined ΔA^CP measurement provides the first evidence for direct CP violation in beauty decays to charmonium final states.
• This finding offers a new probe for CP violation beyond the kaon and B0 meson systems.
• Further investigation could refine the significance and explore implications for new physics models.