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Short description.

Physics Motivation: measure Higgs Yukawa coupling to muons, which provides useful test for ratio of Yukawa coupling between 2nd/3rd generation leptons (with H\tau \tau); between 2nd generation lepton/quark (with Hcc).

Search Channel: e^+e^- → \nu \overline{\nu} H with H→\mu ^+ \mu ^- at \sqrt{s} of 500 GeV.

Detector Benchmark: very sensitive to high momentum resolution/tracking efficiency, algorithm for isolated lepton tagging.

Two different works are ongoing or finish in soon.

  1. Work using DBD-world samples: explored at \sqrt{s} of 250/500 GeV, left-/right-handed beam polarization, two processes of e^+e^- \to q\overline{q}H and e^+ e^- \to \nu \overline{\nu} H 
  2. Work using IDR-world samples: written in above

Main observables.

final observable: precision on the cross section times branching ratio \sigma \times \mathrm{BR}(H \to \mu ^+ \mu ^-), branching ratio of H \to \mu ^+ \mu ^-.

intermediate observables: track momentum resolutions, muon pair invariant mass M_{\mu ^+ \mu ^-}, event-by-event mass resolution \sigma (M_{\mu ^+ \mu ^-}) which is calculable using the covariance matrix of momenta space.

Candidate plots for IDR.

Some comparison between IDR-L and IDR-S in reconstructed particle level has done. More details can be found in my talk on 2019Apr03. All plots are left-handed beam polarization. All histograms are normalized to 1.

Overall distribution after BDTG score cut: M_{\mu ^+ \mu ^-} and \sigma (M_{\mu ^+ \mu ^-})


Similar plot ("barrel category"); require both muons are in barrel region |\cos \theta _{\mu ^{\pm}}| < 0.7


Similar plot ("mixed category"); require one muon is in barrel region |\cos \theta _{\mu 1}| < 0.7, and another is in endcap/forward region |\cos \theta _{\mu 2}| > 0.7


Only ~5% events are the case with both muons flying in endcap/forward region.


A toy MC technique is applied by using overall M_{\mu ^+ \mu ^-} distribution after BDTG score cut to estimate the precision on \sigma \times \mathrm{BR}(H \to \mu ^+ \mu ^-). Two detector models and two beam polarization cases are considered. In addition, the theoretical number is provided which assumes 100% signal efficiency, no backgrounds, and no detector effects.


40.15 \pm 0.15{\%}

41.11 \pm 0.15{\%}



114.51 \pm 0.69{\%}

113.73 \pm 0.68{\%}


  • My real analysis is about a factor of 3 worse than the theoretical limit. There are several reasons mixed up: imperfection of cuts, existence of irreducible background mainly come from e^+ e^- \to W^+ W^- \to 2\mu 2\nu, detector effect, and so on.
  • The right-handed case does not provide good precision due to too small number of events, only ~8 events with 1600 fb-1 statistics.
  • IDR-L gives relatively ~2.4% better precision than IDR-S, because overall M_{\mu ^+ \mu ^-} distribution is better in IDR-L. In detail, IDR-L gives significantly better performance in "barrel category", and similar performance in "mixed category". Almost all events are categorized in these two groups, resulting better result with IDR-L.

IDR note.

You can see my private overleaf project from here. The contents are only IDR-world.


Shin-ichi Kawada (DESY)

Reviewed by Ivanka Bozovic and Filip Zarnecki


GitHub repository: LINK

(1) DBD-world references

Branching ratio measurement of h \to \mu ^+ \mu ^- at the ILC [Talk at LCWS2017]

Impact of Momentum Resolution on \mathrm{BR}(h \to \mu ^+ \mu ^-) Measurement [Talk at ILD Meeting 2018]

Branching ratio measurement of h \to \mu ^+ \mu ^- at the ILC [Talk at ALCW2018]

Prospects of measuring Higgs boson decays into muon pairs at the ILC [Talk at LCWS2018]

Shin-ichi Kawada, Jenny List, Mikael Berggren, "Branching ratio measurement of h \to \mu ^+ \mu ^- at the ILC" (LCWS2017 proceedings) [LINK]

Shin-ichi Kawada, Jenny List, Mikael Berggren, "Prospects of measuring Higgs boson decays into muon pairs at the ILC" (LCWS2018 proceedings) [LINK]

(2) IDR-world references

Talk at Wednesday ILD Analysis/Software Meeting [2018Oct10, 2018Nov21, 2019Jan30, 2019Apr03]

Status Report: h \to \mu ^+ \mu ^- Benchmark [Talk at ILD Benchmarking Days]

Status Report: h \to \mu ^+ \mu ^- Benchmark [Talk at ILD Benchmarking Days II]

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