HXSWG OFF-SHELL AND INTERFERENCE TASK FORCE

Current task: produce a short summary document by 16th January

Review and discuss the status and future potential of
off-shell and signal-background interference enabled
experimental analyses for Higgs production at the LHC
and future colliders and related theoretical calculations/tools
and phenomenological studies.  Elaborate, prioritise
and coordinate theoretical and experimental efforts.

HXSWG open meeting on off-shell and sig-bkg interference
issues took place on 24th October 2014 with the following
invited presentations:

- Off-shell Higgs interference effects and width measurements in the ZZ
decay channel, Raoul Rontsch (Fermilab)
- EFT analysis of the off-shell Higgs data, Aleksandr Azatov (CERN)
- MC tools: MadGraph5_aMC@NLO status report, Fabio Maltoni (Louvain)
- MC tools: Sherpa status report, Frank Krauss (IPPP Durham)
- Interference effects in diphoton production for VBF, Nerina Fidanza
(Buenos Aires)
- Rare Higgs decays as probes for Higgs couplings to first- and second
generation quarks, Stoyan Stoynev (Northwestern)

A second open meeting dedicated to discussion will follow (possibly
during the 8th HXSWG Workshop @ CERN on 22-24 January 2015)

General topics:

1) ggF and VBF off-shell H --> ZZ,WW data at (HL-)LHC and (I)LC facilitates
  novel, complementary approach to constrain Higgs properties (width,
  coupling strength and structure)

2) gg --> H --> gamma gamma signal background interferometry
  (Higgs mass peak shift depending on Higgs width)

3) Hcc~ constraint via signal-signal interferometry

Discussion points:

- theoretical calculations and available tools: status, wish list and
prospects

- status of included higher order corrections and estimation of residual
 uncertainties

- what off-shell/interference-enabled constraints in SM, via EFT or specific BSM
 benchmarks are feasible and of interest at LHC Run1,2,3,HL and (I)LC?

- implications of off-shell-only coupling measurements for New Physics searches

- what value is added compared to on-shell Higgs measurements?

- Higgs width constraints: appropriate treatment of model dependence issues?

- analysis techniques: where is matrix element method essential?,
 are used kinematic discriminants optimal?, other improvements?