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 ?
𝐷0 ∶ 𝑐𝑢
• Calculated the value of CP violation
𝐷0 ∶ 𝑢𝑐
• Combined it with previous
LHCb result.
𝐷0
𝐾−𝐾+
𝜋+𝜋 −
Decay Chain
𝐷 ∗+
𝐷0 𝜋 +
𝐾−𝐾+𝜋+
𝜋 +𝜋−𝜋+
𝜋 − 𝑡𝑎𝑔𝑔𝑒𝑑
𝐷 ∗−
𝐷0 𝜋 −
𝐾−𝐾+𝜋−
𝜋 +𝜋−𝜋−
𝑝𝑝
𝐵
𝐷0 𝜇+ 𝑋
𝐾 − 𝐾 + 𝜇+ 𝑋
𝜋 + 𝜋 − 𝜇+ 𝑋
𝜇 − 𝑡𝑎𝑔𝑔𝑒𝑑
𝐵
𝐷0 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