A
bstract
A future high-luminosity
Z
-factory will offer the possibility to study rare
Z
decays, as those leading to lepton flavour violating final states. Processes such as
Z
→
ℓ
1
∓
ℓ
2
±
are ...potentially complementary to low-energy (high-intensity) observables of lepton flavour violation. In this work we address the impact of new sterile fermions on lepton flavour violating
Z
decays, focusing on potential searches at FCC-ee (TLEP), and taking into account experimental and observational constraints on the sterile states. We consider a minimal extension of the Standard Model by one sterile fermion state, and two well-motivated frameworks of neutrino mass generation, the Inverse Seesaw embedded into the Standard Model, and the
ν
MSM. Our study shows that sterile neutrinos can give rise to contributions to BR(
Z
→
ℓ
1
∓
ℓ
2
±
) within reach of the FCC-ee. We also discuss the complementarity between a high-luminosity
Z
-factory and low-energy charged lepton flavour violation facilities.
We consider measurements of exclusive rare semi-tauonic
b
-hadron decays, mediated by the
b
→
s
τ
+
τ
-
transition, at a future high-energy circular electron–positron collider (FCC-
ee
). We argue ...that the high boosts of
b
-hadrons originating from on-shell
Z
boson decays allow for a full reconstruction of the decay kinematics in hadronic
τ
decay modes (up to discrete ambiguities). This, together with the potentially large statistics of
Z
→
b
b
¯
, opens the door for the experimental determination of
τ
polarizations in these rare
b
-hadron decays. In the light of the current experimental situation on lepton flavor universality in rare semileptonic
B
decays, we discuss the complementary short-distance physics information carried by the
τ
polarizations and suggest suitable theoretically clean observables in the form of single- and double-
τ
polarization asymmetries.
Abstract We consider measurements of exclusive rare semi-tauonic b-hadron decays, mediated by the $$b \rightarrow s \tau ^+ \tau ^-$$ b→sτ+τ- transition, at a future high-energy circular ...electron–positron collider (FCC-ee). We argue that the high boosts of b-hadrons originating from on-shell Z boson decays allow for a full reconstruction of the decay kinematics in hadronic $$\tau $$ τ decay modes (up to discrete ambiguities). This, together with the potentially large statistics of $$Z\rightarrow b\bar{b}$$ Z→bb¯ , opens the door for the experimental determination of $$\tau $$ τ polarizations in these rare b-hadron decays. In the light of the current experimental situation on lepton flavor universality in rare semileptonic B decays, we discuss the complementary short-distance physics information carried by the $$\tau $$ τ polarizations and suggest suitable theoretically clean observables in the form of single- and double-$$\tau $$ τ polarization asymmetries.
We consider measurements of exclusive rare semi-tauonic b-hadron decays, mediated by the Formula omitted transition, at a future high-energy circular electron-positron collider (FCC-ee). We argue ...that the high boosts of b-hadrons originating from on-shell Z boson decays allow for a full reconstruction of the decay kinematics in hadronic Formula omitted decay modes (up to discrete ambiguities). This, together with the potentially large statistics of Formula omitted, opens the door for the experimental determination of Formula omitted polarizations in these rare b-hadron decays. In the light of the current experimental situation on lepton flavor universality in rare semileptonic B decays, we discuss the complementary short-distance physics information carried by the Formula omitted polarizations and suggest suitable theoretically clean observables in the form of single- and double- Formula omitted polarization asymmetries.
We consider measurements of exclusive rare semi-tauonic b-hadron decays, mediated by the $b \rightarrow s \tau ^+ \tau ^-$ transition, at a future high-energy circular electron–positron collider ...(FCC-ee). We argue that the high boosts of b-hadrons originating from on-shell Z boson decays allow for a full reconstruction of the decay kinematics in hadronic $\tau $ decay modes (up to discrete ambiguities). This, together with the potentially large statistics of $Z\rightarrow b\bar{b}$ , opens the door for the experimental determination of $\tau $ polarizations in these rare b-hadron decays. In the light of the current experimental situation on lepton flavor universality in rare semileptonic B decays, we discuss the complementary short-distance physics information carried by the $\tau $ polarizations and suggest suitable theoretically clean observables in the form of single- and double- $\tau $ polarization asymmetries.
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