Minutes for CEPC Flavor White Paper Discussion
Date: 2023.05.05 9:00-11:30 (Beijing time)
Participants (11): Lorenzo, Lingfeng Li, Anson, Yadi Wang, Xuhui Jiang, Shanzhen Chen, Manqi Ruan, Hao Liang, Hanhua Cui, Yongfeng Zhu, Yuexin Wang
Lingfeng’s talk: Viable inputs for the Flavor White Paper
- Still remain a lot of stuff dominated by theory
- e.g. lattice, top elements, K constant, loop factor, not given by experiments
- need to figure out how much theory was put in
- CKM physics expert: Wenbin Qian (UCAS)
- Vus measurement from tau decay
- Dominated by systematics from kaon tagging (still challenging)
- Not even from theoretical uncertainty
- Need money plot of kaon identification at CEPC (i.e. kaon v.s. pion for f_k)
- Need experts to know whether the high order QCD, lattice correction, and isospin violation are well controlled.
- Tau decays to kaon channels with k_L and k_s final states should be noticed.
Hao’s talk: Vcb measurement via W decay
- Flavor tagging and the high purity sample are key for the success of this analysis
- Maybe the jet charge measurement (work by Hnahua) could bring some insight in suppressing bkg.
- Further optimization of forward region (of vertex system) by some new algorithms may further enhance the analysis
- Hao’s comment on GNN: not as stable as BDT, e.g. over-fitting
Anson’s talk: Tau exotic decay for ALP search
- Comparison with Belle II
- Current result is nearly one order of magnitude better than Belle II (It will be more informative and conclusive to figure out where the improvement comes from.)
- Belle II uses different methodology and techniques
- Vertex information is not so clear, and tau are very boosted (do not have good separation) at Belle II
- Do not have very strong ISR (which is different at Z-pole and already included in the current analysis)
- More references from Lorenzo will be helpful
- Need to check the mismatch of some parameters, e.g. w(m)?
- Beam spread, a leading term
- Need to communicate with accelerator colleagues if the numbers used in analysis make sense
Hanhua’s talk: Jet charge measurement
- In slide 32, anything greater than 40% is skeptical (too good to be true.)
- The problem is from the broad assumption that leading hadrons are perfectly separated, which is not always true.
- Need to take impact parameters into consideration. Also, how good the flavor tagging performance could be are needed to clarify.
- Further studies like quantification and cross check with full simulation are required.
- LingFeng suggests using the current jet flavor tagging algorithm to incorporate new information for jet charge tagging and then to apply on full simulation data sets.
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