BR subgroup meeting: focus on Dalitz decay


Time to be confirmed

BR (phone) meeting with focus on the Dalitz decay - 23 September 2019

People connected: Alexander Mueck, Alexei Maslennikov, Andreay Pazdnyakov, Anthony Morley, 
Artem Basalaev, Daniel Rauch, Daniela Rebuzzi (DR), Ansgar Denner, Fabio Cerutti (FC), Giacinto
Piacquadio, Hanna Borecka-Bielska, Hongtao Yang, Ivica Puljak, Jan Kretzschmar,
John Adams Villamoran, Joseph Cordero Mercado, Kerstin Tackmann, Kurt
Brendlinger, Mayda Velasco, Michael Spira (MS), Chia-Ming Kuo (CMK), Reisaburo Tanaka,
Robert Harlander, Ruggero Turra, Russel Turner, Shilpi (?), Sven Heinemeyer, Tom

DR: short introdution on motivation for this meeting
MS: theoretical updates on EW and Strong Dalitz processes. Details of the contributions that will be included in HDECAY:

(i) certain bins (to be chosen in an input file) in m_ff, i.e.

m_ff = M_H +- dM_H for "H -> ff"
m_ff = M_Z +- dM_Z for "H -> gamma Z"
m_ff < cut for "photon conversion".

The residual mass ranges in m_ff will then be given as separate contributions (integrated). 
All these contributions will probably be given in a separate output file, i.e. not 
added automatically to the primary output of Hdecay. In this way the user will have the option 
to choose between omitting/including the Dalitz contributions. This is at least what MS has thought. 
If this is wanted in a different way, please let us know.

(ii) Concerning the very first bin (m_ff = M_H +- dM_H) MS has to merge this with the elw. 
(QED) corrections to H -> ff. He still has to think about the proper procedure, but very 
likely this will not require an explicit cut on the photon energy (or M_fgamma). 
Remember that Hdecay is *inclusive* (or semi-inclusive in this particular case.) 
But this will probably result in a negative contribution to H -> ff in several cases (small but negative).

FC: it would be useful to have a tool that includes all the three contributions in pg 2, to evaluate them
MS: Careful on what is gauge invariant

CMK: CMS studies on H-> ll gamma with 2016 data

- Giacinto + Kerstin + Fabio (ATLAS) - Mayda + Chia-Ming (CMS) --> agreement on
the cuts to define the phase space
  Should be done independently:
  - to assess the contamination from Dalitz H->ee to H->ee gamma to H->Z gamma phase space
  - to allow for comparison to the theory prediction of Dalitz decay BR.
- MS --> implement in HDECAY the needed processes (H -> l^+l^-\gamma) 
  and the possibility to apply invariant mass cuts on M_{\gamma l^\pm} and M_{l^+l^-}.

There are minutes attached to this event. Show them.
    • 14:25 14:35
      Introduction 10m
      Speakers: Daniela Rebuzzi (INFN Pavia and Pavia University) , Daniela Rebuzzi (Universita and INFN (IT)) , Reisaburo Tanaka (Centre National de la Recherche Scientifique (FR))
    • 14:35 15:00
      Dalitz decay: updates on Th calculations 25m
      Speakers: Michael Spira (Unknown) , Michael Spira (Paul Scherrer Institut (CH))
    • 15:00 15:20
      CMS searches with 2016 data 20m
      Speaker: Chia-Ming Kuo (National Central University (TW))