Meeting: https://indico.cern.ch/event/607365/
Main Topic: neutral aTGCs
Introduction
Celine's presentation on EFT parametrization
- Page 20, does neutral aTGCs do produce better sensitivity due to unsuppressed interference? Not very clear about the size of interference w.r.t. charged aTGCs. But for the final sensitivity, charge aTGCs constrain slightly higher new physics mass scale than neutral aTGCs at the time being; although numerically nTGCs look more precise.
- Page 28, vertex function parametrization (h, f parameters) gives more freedom in terms of parameters, and therefore some of them has to be set to zero in the translation to EFT limits. However, once the constrains are made, EFT and h, f parameters can be converted into each other without problem.
- Page 29, study of the CB~W parameter in the ZZ case seems to be safe concerning unitarization, how about the case in the Zg, from the original vertex function approach, there seemed to have larger dependence of limits on form factors? This is also checked, the CB~W parameter is also unitarity safe in Zg. The previous form factor dependence is probably related to these CP-odd operators.
- Page 31, 35, commented that optimization with angular variables could potentially bring better sensitivity to neutral aTGCs study, since the interference term is relatively more enhanced when focusing on the case with one longitudinal Z boson. However, how much one can gain is not clear, studies have to be carried out. And dedicated variables could also be considered for CP-odd parameters.
- Page 32, 33, 36, what is the dominant term in usual neutral aTGCs studies? Given current sensitivity, the dominat term is (NP)2 term.
- Page 37, is that a typo that interference should vanish for CP odd instead? Indeed, yes.
- Page 39, commented that much more precise neutral aTGCs limits are needed to constrain physics beyond LHC reach in these channels, and current limits only correspond to NP around 1 TeV. This can motivate experimentalists to pursue better neutral aTGCs analysis with 13 TeV data and increased luminosity.
- Is the EFT parametrization implemented in Madgraph and available to experimentalists? YES
- Is vertex function approach already obsolete? It is hard to say, h/f parametrization gives more freedom in regions where the effects could be extremely small. Assuming some of the h/f parameters to be zero, the vertex function approach and the EFT approach can be translated into each other.
- Commented that high order effects can affect the anomalous coupling analysis. High order QCD effects can be factorized, while the high order EWK effects are more complicate (in general not able to factorize between SM and aTGCs). Currently do not know the impact of that in the EFT studies, but could check with Madgraph (if implemented later).
- Unfolding could be the ultimate goal for these analyses, one can reinterpret the results later? This is mostly true, however, in some cases, one may need to optimize the sensitivity by looking at multi-variables (angular distributions and etc.) to enhance the ultimate sensitivity to reach out the mass scale.
- Do we need to consider unitarization in this EFT approach? In principle not, but can be checked. In the case that unitarization plays a big role to the observed limits, it could be just because that the analyses can only constrain NP mass scale around or below TeV, and therefore not quite sensitive. And the argument is that unitarization is not that important give the low sensitivity.
- Again, about the unitarization, ATLAS and CMS will further discuss how to treat it consistently for future precise measurements
Concluding discussion
- This EFT parametrization seems straightforward to implement and translated from the original h/f limits. Therefore, in principle we should simply report limits on them in next publication. However, both ATLAS and CMS will discuss internally about how to proceed for the next step, whether analyzers are happy to implement the EFT limits in future publications.
- And possibly come back in the future with MC studies.