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Register a new userSearch for invisible decays of the Higgs boson at the ILC
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Authors
Akimasa Ishikawa
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The existence of dark matter has been established in astrophysics. However, there are no dark matter candidates in the Standard Model~(SM). If the dark matter particles or their mediator can not interact with SM fermions or gauge bosons, the Higgs boson is the only portal to the dark matter. We present a simulation study to search for invisible decays of the Higgs boson at the ILC with the ILD detector.
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The existence of dark matter has been established in astrophysics. However, there is no candidate for DM in the Stand Model (SM). In SM, the Higgs boson can only decay invisibly via $Hrightarrow ZZ^ast rightarrow ubar{ u} ubar{ u}$ or DM, so any evidence of invisible Higgs decay that exceeds BR (H$rightarrow$inv.) will immediately point to a phenomenon that is beyond the standard model (BSM). In this paper, we report on the upper limit of BR (H$rightarrow$invisible) estimated for three channels, including two leptonic channels and one hadronic channel, under the assumption predicted by SM. With the SM ZH production rate, the upper limit of BR (H$rightarrow$inv.) could reach 0.24% at the 95% confidence level.
We study the prospects of measuring the decay of the Higgs boson into a pair of muons at the International Linear Collider (ILC). The study is performed at center-of-mass energies of 250,GeV and 500,GeV, with fully-simulated Monte-Carlo samples based on the International Large Detector (ILD). The expected precision on cross section times branching ratio $sigma times mathrm{BR}(h to mu ^+ mu ^-)$ has been evaluated to be 24.9{%} for an integrated luminosity of 2,ab$^{-1}$ at 250,GeV. This result improves to 17.5{%} in combination with 4,ab$^{-1}$ of 500,GeV data. We also quantify the impact of the transverse momentum resolution on this analysis, and found that it is very important reach the design goal of an asymptotic resolution of $sigma_{1/P_t} = 2 times 10^{-5}$,GeV$^{-1}$.
We report on a direct search for sub-GeV dark photons (A) which might be produced in the reaction e^- Z to e^- Z A via kinetic mixing with photons by 100 GeV electrons incident on an active target in the NA64 experiment at the CERN SPS. The As would decay invisibly into dark matter particles resulting in events with large missing energy. No evidence for such decays was found with 2.75cdot 10^{9} electrons on target. We set new limits on the gamma-A mixing strength and exclude the invisible A with a mass < 100 MeV as an explanation of the muon g_mu-2 anomaly.
Deviations from the standard Higgs sector generated by some new physics at an energy scale $Lambda$ could be described by an effective $SU(3)_c times SU(2)_L times U(1)$ invariant non-renormalizable Lagrangian terms of dimension six. A systematic study of various Higgs boson production channels ($gamma gamma$, $ZZ$, $WW$, $b bar b$, $tau bar tau$) at the International Linear Collider (ILC) in the SM extension by effective operators is carried out. Statistical methods are used to establish a degree of consistency for the standard Higgs sector with the forthcoming data, using the expected ILC accuracies of the Higgs boson production channels. Global fits in the two-parametric anomalous coupling space indicating to possible deviations from the standard Higgs-fermion and Higgs-gauge boson couplings are performed.
We examine the prospects for extending the Tevatron reach for a Standard Model Higgs boson by including the semileptonic Higgs boson decays h --> WW --> l nu jj for M_h >~ 2 M_W, and h --> W jj --> l nu jj for M_h <~ 2 M_W, where j is a hadronic jet. We employ a realistic simulation of the signal and backgrounds using the Sherpa Monte Carlo event generator. We find kinematic selections that enhance the signal over the dominant W+jets background. The resulting sensitivity could be an important addition to ongoing searches, especially in the mass range 120 <~ M_h <~ 150 GeV. The techniques described can be extended to Higgs boson searches at the Large Hadron Collider.
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