清华大学高能物理研究中心 Center for High Energy Physics, Tsinghua University CPV phase 𝜷 in 𝑩 𝟎 →𝑱/𝝍 𝝅 + 𝝅 − decays and limits on penguin effects 1. CP-violating phase 𝜙 𝑠 New Physics (NP) processes can modify the value of 𝜙 𝑠 if new particles contribute to box diagrams: 𝜙 𝑠 𝑚𝑒𝑎𝑠 =−2 𝛽 𝑠 + 𝛿 𝑃 + 𝛿 𝑁𝑃 𝜙 𝑠 measured value Tree Penguin New Physics The phase −2 𝛽 𝑠 =− 37.6 −0.7 +0.8 mrad is well predicted by Standard Model (SM). In order to search for NP, penguin phase 𝛿 𝑃 should be estimated. 2. World average on 𝜙 𝑠 World average: 𝜙 𝑠 =−30±33 mrad Combination of LHCb’s 𝐽/𝜓𝜙 & 𝐽/𝜓𝜋𝜋 𝜙 𝑠 =−10±39 mrad NP is not a large effect ⇒ Need to control SM effects (penguins) Tree Penguin 3. Methodology of penguin pollution control ⇒ Using 𝐵 0 →𝐽/𝜓 𝜌 0 decay as control channel: (a) tree diagram (b) penguin diagram Penguin pollution can be measured using observables from a 𝑏→𝑐 𝑐 𝑑 decay, and assuming approximate SU(3) flavour symmetry it is possible to apply these results on 𝜙 𝑠 (𝑏→𝑐 𝑐 𝑠). Two possible control channels (P2VV) can be used in a separated way: ⇒ Using 𝐵 𝑠 0 →𝐽/𝜓 𝐾 ∗0 decay as control channel: Penguin phase 𝛿 𝑃 can be calculated from measuring the mixing-induced CP-violating phase 𝛽 𝑒𝑓𝑓 and direct CP violation 𝛼 𝐶𝑃 in this channel. Penguins suppressed to tree level by 𝜆 2 ≃ 𝑉 𝑢𝑠 2 ≃ 0.22 2 4. Analysis strategy in 𝐵 0 →𝐽/𝜓 𝜋 + 𝜋 − A time-dependent amplitude analysis is performed to determine the CP-violating 𝛽, by measuring simultaneously the CP-even and CP-odd decay amplitudes for each contributing resonance, without any assumption on the CP content. Fit the entire 𝜋 + 𝜋 − mass spectrum using a six-resonance model. The most important is 𝐽/𝜓𝜌. [PLB 742 (2015) 38-49] (a) Tree diagram (b) Penguin diagram Penguins not suppressed to tree level! 5. Measurements of CP asymmetry Polarization-independent results 𝛼 𝐶𝑃 ≡ 1−| 𝜆 𝑖 | 1+ 𝜆 𝑖 = −32± 28 −7 +9 × 10 −3 2𝛽 𝐽/𝜓 𝜌 0 = 41.7± 9.6 −6.3 +2.8 ∘ rf. 2𝛽 𝑐 𝑐 𝑠 = 42.8 −1.5 +1.6 ∘ [HFAG] [PLB 742 (2015) 38-49] 6. Measurement of penguin pollution phase 𝛿 𝑃 The penguin phase 𝛿 𝑃 measured in 𝐵 0 →𝐽/𝜓 𝜌 0 decay: 𝛿 𝑃 =0.9±9.8 mrad Taking the maximum breaking in phase (𝜃≠ 𝜃 ′ ) and a range of SU(3) breaking in size [0.5, 1.5], the uncertainty on 𝛿 𝑃 becomes ±18 mrad. Our limit ± 18 mrad is smaller than the current 𝜙 𝑠 uncertainty ±33 mrad mostly due to S-wave modelling 𝜃− 𝜃 ′ : penguin strong phase difference between 𝑏→𝑐 𝑐 𝑑 and 𝑏→𝑐 𝑐 𝑠 清华大学工程物理系 Contact: feng.jiang@cern.ch