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.
This article summarizes the status of the global fit of the Cabibbo-Kobayashi-Maskawa (CKM) parameters within the Standard Model performed by the CKMfitter group. Special attention is paid to the ...inputs for the CKM angles alpha and gamma and the status of Bs arrow right mu mu and Bd arrow right mu mu decays. We illustrate the current situation for other unitarity triangles. We also discuss the constraints on generic Delta F = 2 new physics. All results have been obtained with the CKMfitter analysis package, featuring the frequentist statistical approach and using RFIT to handle theoretical uncertainties.
We discuss tests of the charged Higgs sector of the Two Higgs Doublet Model (2HDM) of Type II in the light of recent flavour physics data. Particular attention is paid to recent measurement of purely ...leptonic decays of heavy-light mesons, which depart more or less significantly from the Standard Model (SM) predictions. We derive constraints on the parameters of the 2HDM type II from leptonic and semileptonic $\Delta F=1$ decays as well as loop processes ($b \to s \gamma$ or $Z\to\bar{b}b$) sensitive to charged Higgs contributions. The outcome of this work is that while 2HDM Type II can fit individual observable through fine-tuning schemes, in a combined analysis it does not perform better than the SM by favouring a decoupling solution. Assuming that 2HDM Type II is realized in Nature, constraints on its parameters ($m_{H^+}$ and $\tan \beta$) are derived. A limit on the charged Higgs mass $m_{H^+} > 304 {\rm GeV}$ at 95% CL is obtained irrespective of the value of $\tan \beta$. This limit is dominated by the $b\to s \gamma$ branching ratio measurement. All results have been obtained with the \ckmfitter analysis package, featuring the frequentist statistical approach \rfit to handle theoretical uncertainties.
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.
This letter gathers a selection of Standard Model predictions issued from the metrology of the CKM parameters performed by the CKMfitter group. The selection includes purely leptonic decays of ...neutral and charged B, D and K mesons. In the light of the expected measurements from the LHCb experiment, a special attention is given to the radiative decay modes of B mesons as well as to the B-meson mixing observables, in particular the semileptonic charge asymmetries a^d,s_SL which have been recently investigated by the D0 experiment at Tevatron. Constraints arising from rare kaon decays are addressed, in light of both current results and expected performances of future rare kaon experiments. All results have been obtained with the CKMfitter analysis package, featuring the frequentist statistical approach and using Rfit to handle theoretical uncertainties.
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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