PHYSICAL REVIEW LETTERS 122, 211803 (2019)
Observation of CP violation in Charm Decays
R.Aaij et al.* (2019)
(LHCb Collaboration)
Tianqi Huang
What is CP violation?
Why is it important?
Wht did they do ?
How ?
𝐷" ∶ 𝑐 𝑢%
• Calculated the value of CP violation
' " ∶ 𝑢𝑐̅
𝐷
• Combined it with previous
LHCb result.
𝐷"
𝐾*𝐾+
𝜋+𝜋*
Decay Chain
𝐷
∗+
𝐷" 𝜋 +
𝐾*𝐾+𝜋+
𝜋+𝜋*𝜋+
𝜋 − 𝑡𝑎𝑔𝑔𝑒𝑑
𝐷∗*
'"𝜋*
𝐷
𝐾*𝐾+𝜋*
𝜋+𝜋*𝜋*
𝑝𝑝
𝐵
' " 𝜇+ 𝑋
𝐷
𝐾 * 𝐾 + 𝜇+ 𝑋
𝜋 + 𝜋 * 𝜇+ 𝑋
𝜇 − 𝑡𝑎𝑔𝑔𝑒𝑑
𝐵%
𝐷" 𝜇* 𝑋
𝐾 * 𝐾 + 𝜇* 𝑋
𝜋 + 𝜋 * 𝜇* 𝑋
Γ : time – dependent rate
Direct Asymmetry:
(theoratical)
𝐾 *𝐾 +
𝑓
𝜋 +𝜋 *
Raw Asymmetry:
(experimentally)
𝑁: number of events
can be approximated as
For either 𝜋 − 𝑡𝑎𝑔𝑔𝑒𝑑
or 𝜇 − 𝑡𝑎𝑔𝑔𝑒𝑑
Systematic Uncertainty
• Fit Model
• Mistag (Only B)
• Weighting (Only B)
.
.
.
Results
combining these with previous LHCb results
differs from zero by more than 5 standard deviation
Future?
• more measurements
(with charmed particles)
• theoretical improvements