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Register a new userStudy of the $h gamma Z$ coupling at the ILC
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We studied the $e^+e^- to h gamma $ process at the International Linear Collider (ILC) at $sqrt{s}=250$ GeV, based on the full detector simulation of the International Large Detector (ILD). This process is loop-induced in the Standard Model (SM) and is sensitive to new physics which alters $h gamma gamma$ or $h gamma Z$ coupling. We performed the analysis by employing the leading signal channels with $h to b bar{b}$ and $h to WW^*$ and including full SM background processes. The results are obtained for two scenarios of beam polarisations each with an integrated luminosity of 900 fb$^{-1}$. We found the expected significance of the SM signal is 0.40$sigma$ for $P(e^-,e^+)=(-0.8,+0.3)$ (the left-handed polarisation), and 0.06$sigma$ for $P(e^-,e^+)=(+0.8,-0.3)$ (the right-handed polarisation). The bounds on new physics effects are reported as the 95% C.L. upper limit for the cross-section of $e^+e^- to h gamma$: $sigma_{hgamma}^L <$ 1.8 fb and $sigma_{hgamma}^R <$ 0.5 fb respectively for left- and right-handed polarisations. The constraints on effective $hgamma Z$ couplings are to be further studied.
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We study the $h gamma Z$ coupling, which is a loop induced coupling in the Standard Model (SM), to probe new physics. In a global fit based on the SM Effective Field Theory, measurement of the SM $h gamma Z$ coupling can provide a very useful constraint, in particular for the precise determination of $hZZ$ and $hWW$ couplings. At the International Linear Collider (ILC), there are two direct ways to study the $h gamma Z$ coupling: one is to measure the branching ratio of the $h to gamma Z$ decay and the other to measure the cross section for the $e^+e^- to h gamma$ process. We have performed a full simulation study of the $e^+e^- to h gamma$ process at the 250 GeV ILC, assuming 2 ab$^{-1}$ data collected by the International Large Detector (ILD). The expected 1$sigma$ bound on the effective $hgamma Z$ coupling ($zeta_{AZ}$) combining measurements of the cross section for $e^+e^- to h gamma$ followed by $h to b bar{b}$ and the $h to gamma Z$ branching ratio is $-0.0015<zeta_{AZ}<0.0015$. The expected significance for the signal cross section in the fully hadronic $h to WW^*$ channel is 0.09 $sigma$ for beam polarizations of $P(e^-,e^+)=(-80%,+30%)$.
Precise measurements of electroweak processes at the International Linear Collider (ILC) will provide unique opportunities to explore new physics beyond the Standard Model. Fermion pair production events are sensitive to new interactions involving a new heavy gauge boson or an electroweak interacting massive particle (EWIMP).We studied the mass reach of new particles at the ILC with $sqrt{s}=250$ GeV by using $e^+ e^-to e^+ e^-$and $e^+ e^-to mu^+ mu^-$ events. We show that a mass reach for BSM particles can be determined with 90% confidence level using a toy Monte Carlo technique.
We evaluate the expected measurement accuracy of the branching ratio of the Standard Model Higgs boson decaying into tau pairs at the ILC with a full simulation of the ILD detector concept. We assume a Higgs mass of 125 GeV, a branching ratio of BR($h to tau ^+ tau ^-$) = 6.32%, a beam polarization of electron (positron) of -0.8(+0.3), and an integrated luminosity of 250 fb$^{-1}$. The Higgs-strahlung process $e^+ e^- to Zh$ with $Z to qoverline{q}$ is analyzed. We estimate the measurement accuracy of the branching ratio $Delta (sigma times mathrm{BR}) / (sigma times mathrm{BR})$ to be 3.4% with using a multivariate analysis technique.
The Standard Model (SM) predicts a branching ratio of the Higgs boson decaying to invisible particles of $mathcal{O}$(0.001), though current measurements have only set upper limits on this value. The small SM-allowed rate can be enhanced if the Higgs boson decays into new particles such as dark matter. Upper limits have been placed on BR(H$rightarrow$inv.) by ATLAS and CMS at $mathcal{O}$(0.1), but the hadron environment limits precision. The ILC `Higgs factory will provide unprecedented precision of this electroweak measurement. Studies of the search for H$rightarrow$invisible processes in simulation are presented with SiD, a detector concept designed for the ILC. Preliminary results for expected sensitivity are provided, as well as studies considering potential systematics limitations.
Precise measurements of electroweak processes at the International Linear Collider (ILC) will provide unique opportunities to explore new physics beyond the Standard Model. Fermion pair productions are sensitive to a new contact interaction or a new heavy gauge boson by comparing cross section and angular distribution with expectations of the new physics models. In this proceedings we report a simulation study of fermion pair productions at a center-of-mass energy of 250 GeV, with a focus on lepton pairs, to demonstrate the potential of the first phase of the ILC.
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