Experimental determination of $V_{us}$ from kaon decays

Moulson, M.

doi:10.22323/1.291.0033

Cited by 67 publications

(89 citation statements)

References 31 publications

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“…Three volumes together with one-loop chiral perturbation theory (ChPT) [7] allow for a good estimate of the finite-volume effects. After chiral and continuum extrapolation, the total uncertainty is expected to be reduced to 0.2%, which is close to the current experimental uncertainty [2]. Open green symbols correspond to different volumes for a=0.12 fm and ml = 0.1 ms.…”

Section: Introductionsupporting

confidence: 82%

Recent progress in applying lattice QCD to kaon physics

Feng

2018

EPJ Web Conf.

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Abstract. Standard lattice calculations in kaon physics are based on the evaluation of matrix elements of local operators between two single-hadron states or a single-hadron state and the vacuum. Recent progress in lattice QCD has gone beyond these standard observables. I will review the status and prospects of lattice kaon physics with an emphasis on non-leptonic K → ππ decay and long-distance processes including K 0 -K 0 mixing and rare kaon decays.

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Section: Introductionsupporting

confidence: 82%

Recent progress in applying lattice QCD to kaon physics

Feng

2018

EPJ Web Conf.

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“…where s = q 2 = (p K + p π ) 2 , and λ(s, (41) is determined most precisely from the analysis of semileptonic kaon decays [68,69]. S EW = 1.0201(3) encodes the short-distance electroweak correction [70], and is simply written as an overall constant, although it only affects the SM contribution [25].…”

Section: Model-independent Analysismentioning

confidence: 99%

CP asymmetry in τ→KSπντ decays within the standard model and beyond

Chen

Yang

et al. 2019

Phys. Rev. D

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This work aims to explore the 2.8σ discrepancy observed between the BaBar measurement and the Standard Model prediction of the CP asymmetry in τ → K S πν τ decays. Firstly, we reproduce the known CP asymmetry due to K 0 −K 0 mixing by means of the reciprocal basis, which is convenient when a K S(L) is involved in the final state. As the Kπ tensor form factor plays a crucial role in generating an extra direct CP asymmetry that can arise only from the interference of vector and tensor operators, we then present a dispersive representation of this form factor, with its phase obtained in the context of chiral theory with resonances, which fulfills the requirements of unitarity and analyticity. Finally, the τ → K S πν τ decays are analyzed both within a model-independent low-energy effective theory framework and in a scalar leptoquark scenario. It is observed that the CP anomaly can be accommodated in the model-independent framework, even at the 1σ level, together with the constraint from the branching ratio of this decay; it can be, however, marginally reconciled only at the 2σ level, due to the specific relation between the scalar and tensor operators in the scalar leptoquark scenario.

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“…The element |V us | can be determined from analysis of semileptonic K 3 decays (K L µ3, K L e3, K ± e3, etc.) [4]: f + (0)|V us | = 0.21654 ± 0.00041 (7) where f + (0) is the K → π ν vector form-factor at zero momentum transfer. On the other hand, by comparing the kaon and pion inclusive radiative decay rates K → µν(γ) and π → µν(γ), one obtains [5]:…”

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confidence: 99%

The CKM unitarity problem: a trace of new physics at the TeV scale?

2020

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After the recent high precision determinations of Vus and V ud , the first row of the CKM matrix shows more than 4σ deviation from unitarity. Two possible scenarios beyond the Standard Model can be investigated in order to fill the gap. If a 4th quark b participates in the mixing, with |V ub | ∼ 0.04, then its mass should be no more than 6 TeV or so. A different solution can come from the introduction of the gauge horizontal family symmetry acting between the lepton families and spontaneously broken at the scale of about 6 TeV. Since the gauge bosons of this symmetry contribute to muon decay in interference with Standard Model, the Fermi constant is slightly smaller than the muon decay constant so that unitarity is recovered. Also the neutron lifetime problem, that is about 4σ discrepancy between the neutron lifetimes measured in beam and trap experiments, is discussed in the light of the these determinations of the CKM matrix elements.1. The Standard Model (SM) contains three fermion families in the identical representations of the gauge symmetry SU (3)×SU (2)×U (1) of strong and electroweak interactions. One of its fundamental predictions is the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix of quark mixing in charged current(1)Deviation from the CKM unitarity can be a signal of new physics beyond the Standard Model (BSM). The experimental precision and control of theoretical uncertainties in the determination of the elements in the first row of V CKM are becoming sufficient for testing the conditionSince |V ub | 0.004 is very small, its contribution is negligible and (2) reduces essentially to the check of the Cabibbo mixing: |V us | = sin θ C , |V ud | = cos θ C and |V us /V ud | = tan θ C . In essence, this is the universality test for the W -boson coupling (g/ √ 2)W + µ J µ L + h.c. to the relevant part of the charged left-handed currentFor energies smaller than W -boson mass this coupling gives rise to the effective current × current interactionswhich are responsible for leptonic decays of the neutron, pions, kaons etc., as well as to the interaction − 4G F √ 2 e L γ µ ν e ν µ γ µ µ L (5) * responsible for the muon decay. All these couplings contain the Fermi constant G F / √ 2 = g 2 /8M 2 W . Precision experimental data on kaon decays, in combination with the lattice QCD calculations of the decay constants and form-factors, provide accurate information about |V us |. On the other hand, recent calculations of short-distance radiative corrections in the neutron decay allow to determine |V ud | with a remarkable precision.In this paper we analyze the present individual determinations of V ud and V us and find significant (more than 4σ) deviation from the CKM unitarity (2). We discuss two possible BSM scenarios which can explain this deviation. In the first one the three-family unitarity is extended to four species, by introducing the 4th down-type quark b with mass of few TeV. The second scenario assumes the existence of horizontal gauge symmetry between the lepton families which is spontaneously br...

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Experimental determination of $V_{us}$ from kaon decays

Cited by 67 publications

References 31 publications

Recent progress in applying lattice QCD to kaon physics

Recent progress in applying lattice QCD to kaon physics

CP asymmetry in τ→KSπντ decays within the standard model and beyond

The CKM unitarity problem: a trace of new physics at the TeV scale?

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