Determining the CP parity of Higgs bosons at the LHC in the τ to 1-prong decay channels

Abstract

We investigate a method for determining the CP nature of a neutral Higgs boson or spin-zero resonance Φ at a future linear e + e − collider (ILC) in its Φ → τ − τ + decay channel. Our procedure is applicable if the production vertex of the Higgs boson can be measured. This will be the case, for example, for the Higgs-strahlung process e + e − → Z + Φ. We show that the method is feasible for both the leptonic and the hadronic 1-prong tau decay modes, τ Recently, the ATLAS and CMS experiments reported the discovery of a neutral boson of mass ∼ 126 GeV at the LHC [1,2]. The experimental findings disfavor the option of a spin J = 1 resonance. The experimental results [1,2] are compatible with the hypothesis of identifying this resonance with the Standard Model (SM) Higgs boson; however, much more detailed investigations will be necessary to establish this conjecture. The investigations of the properties of this resonance will probably be possible at the LHC to a large extent. A high-energy linear e + e − collider would be an ideal machine to investigate the properties of this resonance, i.e., its couplings, decay modes, spin, and CP parity, in great detail (and, of course, also of other, not too heavy resonances of similar type if they exist). As it is likely that the ATLAS and CMS resonance is a spin-zero (Higgs) boson, one may revert, for assessing the prospects of exploring this particle at a future linear collider, to the many existing phenomenological investigations, within the SM and many of its extensions, of Higgs-boson production and decay in e + e − collisions. As to the prospects of exploring the spin and CP properties of a Higgs boson, there have been a number of proposals and studies, including that are relevant for Higgs-boson production and decay at a linear collider. In this workshop contribution we apply a method [26,27] for the determination of the CP properties of a neutral spin-zero (Higgs) boson Φ in its τ + τ − decays to the production of Φ at a future e + e − linear collider (ILC). For definiteness, we consider e + e − → ZΦ, but the analysis outlined below is applicable to any other Φ production mode. In our analysis all major 1-prong τ decays are taken into account. We demonstrate that the CP properties of Φ can be determined with our method in an unambiguous way.

Large pseudoscalar Yukawa couplings in the complex 2HDM

“…For definiteness we focus on Type II. As previously discussed, a direct measurement involving the vertex hτ + τ − [69,72] …”

“…In reference [68] an exclusion of φ t > 40 • (φ t > 25 • ) for a luminosity of 50 fb −1 (300 fb −1 ) was obtained for 14 TeV and assuming φ t = 0 as the null hypothesis. A study of the τ + τ − h vertex was proposed in [69] (see also [70,71]) and a detailed study taking into account the main backgrounds [72] lead to an estimate in the precision of ∆φ τ of 27 • (14.3 • ) for a luminosity of 150 fb −1 (500 fb −1 ) and a center of mass energy of 14 Tev. Figure 9.…”

H →τ + τ − γ as a probe of the τ magnetic dipole moment

“…It is worth mentioning that the imaginary parts of c 1 and c 2 would also lead to a CPviolating electric dipole moment (and its Z analogue) for the τ . While interesting in their own right [26][27][28][29][30][31][32][33][34], CP symmetry prevents these new physics amplitudes from interfering with the SM contribution to h → τ + τ − γ, thus leading to greatly decreased LHC sensitivity (see also [35]). For this reason, we choose here to focus on the magnetic dipole moment for which Higgs decays are a more sensitive probe.…”

Search for CP violation effects in the $$h\rightarrow \tau \tau $$ h → τ τ decay with $$e^+e^-$$ e

“…Although difficult to reconstruct, the tau decays are complex enough to yield information of the tau spin correlation [16,17]. Hence h → τ + τ − is a golden channel for the measurement of the CP nature of the Higgs which has led to an enormous amount of studies on the prospects of the measurement of the CP mixing angle(φ) at LHC using either the ggF/ZH or the VBF production mode [18][19][20][21][22][23][24][25][26][27] as well as at e + e − colliders [28][29][30].…”