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Light Mass Higgs subgroup

Goal of the group

Quoting from the "letter of intent":

  1. issues concerning XS * BR, in particular issues connected to the decays H -> gamma+gamma, tau+tau, bb, WW and ZZ
  2. Higgs property measurements: Higgs mass, (width), sigma*BR, J^PC, couplings (HVV, Yukawa, trilinear, quartic).

Discuss main theoretical issues (concerning XS * BR) and create tools to be used by ATLAS and CMS (+CDF+D0) to analyze Higgs boson data available in 2012 and beyond, including branching fractions, couplings to SM particles, anomalies in the present data (gamma+gamma and WW signals), evidence of spin zero and how this possibility could be confirmed in the near future, separation of signal and backgrounds and strategy for measuring the mass and other characteristics of a putative signal.

Group Contacts

Michael Dührssen (CERN) Markus Schumacher (Freiburg) André David (LIP) Marco Zanetti (MIT) Ansgar Denner (Würzburg) Massimiliano Grazzini (Zurich) Georg Weiglein (DESY)

Work plan

  1. Coupling parameter models (X is still to be exactly defined. Functional expressions for X(γ) and X(g) are needed for 2. and 5.)
    1. One parameter model with an overall scale (μ). Already used in 2011 results.
    2. Two parameter model with X(V) scaling the gauge couplings and X(F) scaling the Yukawa couplings. Ratios within the gauge and fermion couplings fixed to the SM. Interference terms, if they can't be factorized by a clever choice of X, as in the SM.
    3. Four parameter model with X(V), X(F) and effective parameters X(γ) for the photon decay and X(g) for the gluon decay/production. Ratios within the gauge and fermion couplings as in the SM. Interference terms, if they can't be factorized by a clever choice of X, as in the SM.
    4. A model with X(W), X(Z), X(τ), X(b), X(γ), X(g), (+ X(t) if ttH production becomes available). Interference terms, if they can't be factorized by a clever choice of X, as in the SM.
    5. A model with X(W), X(Z), X(τ), X(b), and X(t) (assuming no new particles in the photon and gluon loops). Interference terms, if they can't be factorized by a clever choice of X, as in the SM.
  2. Available options for X (discussion is ongoing and so far no agreement on a representation. Proposals are welcome!):
    1. Coupling strength scale factor gi that would appear directly at the Higgs vertex (e.g. σ(WH) ~ gW2 for i = W)
    2. The partial decay width Gi (e.g. σ(WH) ~ GW for i = W)
    3. Separate by observable initial/final states (e.g. 4μ instead of ZZ) -> postpone for now because of limited available data
  3. Relative and absolute measurements
    1. Without further assumptions one can fit for (If all correlations are kept in the fit, both are strictly identical)
      1. ratios Xi/Xj and one global scale μ=Xi2 / ΓH
      2. Xi / sqrt(ΓH)
    2. Assumptions for an absolute coupling measurement:
      1. no invisible/undetectable decays
      2. only the undetectable SM decays from H→cc, H→gg, ... and these are calculated by assuming that Xc=Xb or something similar.
      3. ΓW < ΓW(SM)
      4. Anything else?
    3. Start with C.1, C.2.b, C.2.c
  4. Can combine any option in C with every coupling parameter model in A.

A. Determination of Spin and CP quantum numbers

Action items

  1. Agree on a definition for coupling parameters that is well defined from the theory side and usable in an experimental fit
  2. Calculate theory uncertainties for whatever coupling parameters are used or give at least some limit estimate on the uncertainty
  3. If we have to continue with LO coupling parameter definitions, give some rough estimates for the uncertainties
  4. Check with jet group if additional uncertainties appear for a coupling fit due to analysis in exclusive jet bins

  1. Derive recipe how to simulate resonances with different SPIN and CP quantum numbers. Check possibility of reweighting fully simulated SM MC events by ratio of matrix elements, Compare different parametrization for anomalous couplings of an observed resonance.

Available Tools





-- ReiTanaka - 23-Apr-2012

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