RareZdecays and neutrino flavor universality

Abstract

We study rare four-body decays of the Z-boson involving at least one neutrino and one charged lepton. Large destructive interferences make these decays very sensitive to the Z couplings to neutrinos. As the identified charged leptons can determine the neutrino flavors, these decays probe the universality of the Z couplings to neutrinos. The rare four-body processes could be accurately measured at future lepton colliders, leading to percent level precision.

Measurement of the branching fraction and search for $CP$ violation in $D^0\rightarrow K^0_S\,K^0_S\,π^+π^-$ decays at Belle

“…The results for A cor CP are combined according to Eqs. ( 10) and (11) To measure a T CP , we divide the data into four subsamples: D 0 decays with C T > 0 (yield = N 1 ) and C T < 0 (yield = N 2 ); and D 0 decays with −C T > 0 (N 3 ) and −C T < 0 (N 4 ). Thus, A T = (N 1 − N 2 )/(N 1 + N 2 ), ĀT = (N 3 − N 4 )/(N 3 + N 4 ), and a T CP = (A T − ĀT )/2.…”

“…proportional to sin(φ) sin(δ) [11][12][13], and, unlike A CP , δ = 0 results in the largest CP asymmetry. The observable a T CP is advantageous to measure experimentally, as any production or detection related non CP asymmetry contribution cancels out.…”

CP-violation, Asymmetries and Interferences in $t \bar{t} ϕ$

“…allowing us to construct simpler CP-odd observables [62]. In our paper, we will consider two most sensitive CP-odd observables from previous studies [37,38], where the tensor products already mentioned are evaluated at the t t CM frame, resulting in a single triple product of the form p t • ( p l + × p l − ).…”

Exposing dark sector with futureZ-factories

“…There have been previous work on constraining dark sector related new physics from Z properties at future e + e − colliders, including dark photon [41,42], sterile neutrino model [43,44], Z invisible width e.g. [45], rare SM Z decays [46][47][48][49][50], light CP-odd Higgs bosons and supersymmetric models [51][52][53][54][55], . Recently, this topic has been addressed for some specific models [56][57][58][59][60].…”