WG2 STXS in Decay discussion



LHCHWG2 meeting
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Giacomo Ortona
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Introduction (M. Duehrssen0

  • This effort started ~10 years ago, but not much push for it until now
  • This is a first case study of its feasibility with H->4l events from CMS and ATLAS
  • We know STXS (in production) is affected by potentially large acceptance effects
  • If we define Lorentz invariant fiducial regions in decay, we can mitigate them. Lorentz invariance is crucial to reduce DoFs.
  • The goal is to have the same behaviour (or very close behaviour) between SM and BSM
  • Detector effects are not completely removable, but we can mitigate them.

ATLAS presentation

  • Fiducial selection close to Reco, but remove pT and eta dependance
  • Close behaviour between SM and BSM

Action items:

  • It would be nice to see the double ratio 
  • It would be nice to compare ZZ* vs gamma*gamma* vs Zgamma*
    A: the eigenvectors shown are in any case taken among the most extreme cases
  • It would be nice to compare ttH and ggH
    A: this was checked, the behaviour was the same

CMS presentation

  • The agreement seems worst than in ATLAS case
    A: it could be the CMS samples are more extreme, but most likely the fiducial volume was defined fine tuning it on the ATLAS selection and thus CMS pays a price for this. Some work is needed to adapt and compromise the fiducial selection across the 2 experiments.

Discussion / Action items

  • The 2 experiments need to work a bit more on the definition of the fiducial selection
  • Using the same samples should help making an apples-to-apples comparison
  • Material could be shared on the WG2 twiki
  • If the method works, the idea is to replace the decay defnition in STXS with the result of this study. To be noted: since the fiducial decay volume is not dependent on the production (Lorentz invariance), if we define M STXS production bins and N decay bins, the total number of bins is N+M (and not N*M). The (relative) number of events in each decay bin is the same for each production bin. So stage 0 would be to replace the definition of the decay final state, stage 1 we can introduce some binning (for example mZ2 which is sensitive to CP).
There are minutes attached to this event. Show them.
    • 2:00 PM 2:20 PM
      STXS in decay - motivations 20m
      Speaker: Michael Duehrssen-Debling (CERN)
    • 2:20 PM 2:40 PM
      ATLAS results on HZZ4l 20m
      Speakers: Andrea Gabrielli (University of Toronto (CA)), Han Li (Shandong University (CN)), Michael Duehrssen-Debling (CERN)
    • 2:40 PM 3:00 PM
      CMS results on HZZ4l 20m
      Speakers: Antra Gaile (Riga Technical University (LV)), Matteo Bonanomi (Hamburg University), Toni Sculac (University of Split Faculty of Science (HR))