Exposing the dark sector with future Z factories

Confining hidden sectors are an attractive possibility for physics beyond the Standard Model (SM). They are especially motivated by neutral naturalness theories, which reconcile the lightness of the Higgs with the strong constraints on colored top partners. We study hidden QCD with one light quark flavor, coupled to the SM via effective operators suppressed by the mass M of new electroweak-charged particles. This effective field theory is inspired by a new tripled top model of supersymmetric neutral naturalness. The hidden sector is accessed primarily via the Z and Higgs portals, which also mediate the decays of the hidden mesons back to SM particles. We find that exotic Z decays at the LHC and future Z factories provide the strongest sensitivity to this scenario, and we outline a wide array of searches. For a larger hidden confinement scale Λ ∼ O(10) GeV, the exotic Z decays dominantly produce final states with two hidden mesons. ATLAS and CMS can probe their prompt decays up to M ∼ 3 TeV at the high luminosity phase, while a TeraZ factory would extend the reach up to M ∼ 20 TeV through a combination of searches for prompt and displaced signals. For smaller Λ ∼ O(1) GeV, the Z decays to the hidden sector produce jets of hidden mesons, which are long-lived. LHCb will be a powerful probe of these emerging jets.Furthermore, the light hidden vector meson could be detected by proposed dark photon searches.

Section: Original Tripled Top Model With Singlet Top Partnersmentioning

confidence: 50%

Light hidden mesons through the Z portal

Cheng

Salvioni

et al. 2019

“…(3.7) as in refs. [31,32]. 4 The asymmetric cut on the invariant mass of bb is required to take into account the effects of photons from initial-state radiation (ISR) [34] or unmeasured neutrinos from semi-leptonic b-decays [35].…”

Section: The H → Bb Casementioning

confidence: 99%

Measuring the ratio of HW W and HZZ couplings through W +W −H production

Chiang

2018

For a generic Higgs boson, measuring the relative sign and magnitude of its couplings with the W and Z bosons is essential in determining its origin. Such a test is also indispensable for the 125-GeV Higgs boson. We propose that the ratio of the HW W and HZZ couplings λ W Z can be directly determined through the W + W − H production, where H denotes a generic Higgs boson, owing to the tree-level interference effect. While this is impractical at the LHC due to the limited sensitivity, it can be done at future e + e − colliders, such as a 500-GeV ILC with the beam polarization P (e − , e + ) = (−0.8, +0.3) in the jj ± bb and ± ± ∓ jj channels. The discovery potential of a general ratio and the power to discriminate it from the SM value are studied in detail. Combining the cross section of e + e − → W + W − H with the measurements of HZZ coupling at the HL-LHC, one can further improve the sensitivity of λ W Z .

“…The values of corresponding to the sensitivity S/ √ B = 2 are summarized in tables 3, 4 and 5. The b-tagging efficiency, c quark mis-tagging rate and light quark mis-tagging rate are conservatively assumed to be 0.8, 0.09 and 0.01 [31,52], respectively. The τ -tagging efficiency and the probability of a jet faked as τ are assumed to be 0.6 and 0.02 [31,53], respectively.…”

Section: Jhep03(2018)139mentioning

confidence: 99%

Search for a heavy dark photon at future e+e− colliders

Huang

et al. 2018

A coupling of a dark photon A from a U(1) A with the standard model (SM) particles can be generated through kinetic mixing represented by a parameter . A non-zero also induces a mixing between A and Z if dark photon mass m A is not zero. This mixing can be large when m A is close to m Z even if the parameter is small. Many efforts have been made to constrain the parameter for a low dark photon mass m A compared with the Z boson mass m Z . We study the search for dark photon in e + e − → γA → γµ + µ − for a dark photon mass m A as large as kinematically allowed at future e + e − colliders. For large m A , care should be taken to properly treat possible large mixing between A and Z. We obtain sensitivities to the parameter for a wide range of dark photon mass at planed e + e − colliders, such as Circular Electron Positron Collider (CEPC), International Linear Collider (ILC) and Future Circular Collider (FCC-ee). For the dark photon mass 20 GeV m A 330 GeV, the 2σ exclusion limits on the mixing parameter are 10 −3 -10 −2 . The CEPC with √ s = 240 GeV and FCC-ee with √ s = 160 GeV are more sensitive than the constraint from current LHCb measurement once the dark photon mass m A 50 GeV. For m A 220 GeV, the sensitivity at the FCC-ee with √ s = 350 GeV and 1.5 ab −1 is better than that at the 13 TeV LHC with 300 fb −1 , while the sensitivity at the CEPC with √ s = 240 GeV and 5 ab −1 can be even better than that at 13 TeV LHC with 3 ab −1 for m A 180 GeV. We also comment on sensitivities of e + e − → γA with dark photon decay into several other channels at future e + e − colliders.