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ECFA meeting on e+e- to ZH angular measurements
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ECFA meeting on e+e- to ZH angular measurements
CP violation in the Higgs section (Henning Bahl)
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- CPV in HVV at loop level vs tree level in Hff via mixing
- EFTs limited to empirical CP constraints (hard to connect to matter-antimatter asymmetry)
o Study of strong 1st order phase transitions using EFTs is limited
- Complex 2HDM is a benchmark model
o CP-odd couplings induced via mixing with CP-odd A boson
o Does the mixing allow CP-odd HVV couplings at tree level? No, cannot have direct AVV coupling
- EDMs provide constraints but direct searches needed to break degeneracies
o Q: Are there tools to calculate EDMs? Should we use EFTs?
A: EFTs useful, need to run up to scale for neutron EDM, smaller effect for electron EDM
- Q: What about spontaneous CP violation? A: usually happens at high temperature
- Q: What about breaking vacuum at zero temperature? A: can occur in the dark sector
CP and entanglement in H->VV decays (J. A. Aguilar Saavedra)
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- Spin density operator has 8 polarisations each for V1 and V2, 64 spin correlations
o coefficients can be measured from charged lepton distributions
o density operator translates into a 4D distribution dependent on spherical harmonics
x L=1 terms have suppressed effect for ZZ
- Within narrow bins of mV* the VV pair is produced in an almost pure state
o the problem is reduced to a binned measurement of general helicity amplitudes a00, a11, a-1-1
- When testing entanglement you could assume CP conservation (CP violation must be small in HVV)
o then a11 = a-1-1 and there is a normalization constraint to reduce the number of parameters to one
- Entanglement measurements involving orbital angular measurements are rare and have not been done in HEP
- Spins highly entangled, orbital angular momentum less so
- H->ZZ does not look competitive with LHC due to low event yields
o H->ZZ->lltautau may be competitive using post-decay entanglement
- CP violation can be measured using certain polarizations, can be done in semileptonic decays
o Likely best done in H->WW
- Q: How well do you need to reconstruct the neutrinos in H-.WW->lvlv? A: Need to study
- Q: How do you explain entanglement? A: Inseparable states and density matrices
Polarized beams for CP tests (Cheng Li)
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- Need both beams to be transversely polarized to directly probe CP violation using beam polarization
o can also probe CP-violation via triple product of final-state particles
- Define asymmetries for polarized and unpolarized beams
- Longitudinally polarized beams give slightly better constraints than transversely polarized beams
o due to higher cross section and smaller statistical uncertainty
- Limit on cHZZ~ is O(10^-2), limit on fCP is O(10^-5)
- Q: What is the ILC polarization scenario? A: Conservatively 80% for electrons and 30% for positrons
(the latter reducing to 20% at 1 TeV). An upgrade could give 90% for electrons and 60% for positrons.
Beam polarization at CEPC (Zhe Duan)
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- Time to polarize beam longer than beam lifetime
o motivates a polarized injector for CEPC
o also trying to use beam self-polarization to generate polarized beams
- Depolarization in the booster can occur through spin precession and crossing through spin resonancnes
o however CEPC has weak spin resonance strength
- Potential to achieve 50%-70% polarization for electron bunches at Z pole
o studying positron polarization and longitudinal polarization at WW threshold
- Simulation suggests 10-30% polarization possible for ZH production
o need to reduce the spin resonance strength by a factor of 10
- Need to study effect of beam-beam interaction
- Q: does the polarization affect beam spread? We do not see any effect
- Q: what about for an energy of 62.5 GeV? A: should be similar to 45.6 GeV
o would see an effect if used wigglers
Probing CP properties at the CEPC in ee->ZH->llH using optimal variables (Qiyu Sha)
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- Use EFT framework and assume CP-even dim-6 Wilson coefficients are zero
- General differential cross section includes three angular coefficients that are CP-odd
- Define two observables that are the ratios of the AZ odd-to-even and ZZ-odd-to-even angular coefficients
- Perform log likelihood fit to the distributions of the observables
- constrain Wilson coefficients to |cZa| < 0.3 and |cZZ| < 0.06, as well as fCP <~ 9.2 x 10^-6
- Q: are the likelihood scans 1D? A: yes
- Q: Do you consider systematics such as cross-section uncertainty? A: no
- Q: did you compare the sensitivity of the likelihood fit to a simple asymmetry? A: no
- Comment: it would be intersting to perform a 2d fit of c~ vs c to see the impact of the CP-even operator
Updates to FCC-ee ZH CP studies using kinematic observables (Valdis Slokenbergs)
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- added a correction for the interference normalization that reduces the resolution
- added Z->ee channel
- sensitivity of combined Z->ll channels is fCP ~ 4 x 10^-5 at 68% CL
- Q: what about direct fits to Wilson coefficients? A: first priority is to add Z->qqbar
Higgs self-coupling sensitivity at the ILC (Bryan Bliewert)
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- previous study at 500 GeV gave a relative uncertainty of 26.6% on the Higgs self-coupling
- a range of ZHH analysis bottlenecks can be addressed by state-of-the-art tools
- Expect ~20% improvement from updating sensitivity projections using these tools
- Q: what about H->tau-tau? does it help reject background? Comment: it could help by selecting tau-tau
and avoiding jet clustering
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