Abstract
While the standard model is the most successful theory to describe all the interactions and constituents of elementary particle physics, it has been constantly scrutinized for over four ...decades. Weak decays of charm quarks can be used to measure the coupling strength between quarks in different families and serve as an ideal probe for CP violation. As the lowest charm-strange baryons with three different flavors,
baryons (composed of
or
) have been extensively studied in experiments. In this study, we use state-of-the-art lattice QCD techniques to generate 2+1 clover fermion ensembles with two lattice spacings,
. Then, we present the first
ab-initio
lattice QCD calculation of the
form factors. Our theoretical results for the
decay widths are consistent with and approximately two times more precise than the latest measurements by the ALICE and Belle collaborations. Based on the latest experimental measurements, we independently obtain the quark-mixing matrix element
, which is in good agreement with results from other theoretical approaches.
Using a systematic, symmetry-preserving continuum approach to the Standard Model strong-interaction bound-state problem, we deliver parameter-free predictions for all semileptonic Bc→ηc,J/ψ ...transition form factors on the complete domains of empirically accessible momentum transfers. Working with branching fractions calculated therefrom, the following values of the ratios for τ over μ final states are obtained: Rηc=0.313(22) and RJ/ψ=0.242(47). Combined with other recent results, our analysis confirms a 2σ discrepancy between the Standard Model prediction for RJ/ψ and the single available experimental result.
Continuum Schwinger function methods for the strong-interaction bound-state problem are used to arrive at a unified set of parameter-free predictions for the semileptonic K→π, D→π,K and Ds→K, ...B(s)→π(K) transition form factors and the associated branching fractions. The form factors are a leading source of uncertainty in all such calculations: our results agree quantitatively with available data and provide benchmarks for the hitherto unmeasured Ds→K0, B¯s→K+ form factors. The analysis delivers a value of |Vcs|=0.974(10) and also predictions for all branching fraction ratios in the pseudoscalar meson sector that can be used to test lepton flavour universality. Quantitative comparisons are provided between extant theory and the recent measurement of BBs0→K−μ+νμ. Here, further, refined measurements would be useful in moving toward a more accurate value of |Vub|.
We describe non-standard contributions to semileptonic processes in a model independent way in terms of an
SU
(
2
)
L
×
U
(
1
)
Y
invariant effective lagrangian at the weak scale, from which we ...derive the low-energy effective lagrangian governing muon and beta decays. We find that the deviation from Cabibbo universality,
Δ
CKM
≡
|
V
u
d
|
2
+
|
V
u
s
|
2
+
|
V
u
b
|
2
−
1
, receives contributions from four effective operators. The phenomenological bound
Δ
CKM
=
(
−
1
±
6
)
×
10
−
4
provides strong constraints on all four operators, corresponding to an effective scale
Λ
>
11
TeV
(90% CL). Depending on the operator, this constraint is at the same level or better then the
Z pole observables. Conversely, precision electroweak constraints alone would allow universality violations as large as
Δ
CKM
=
−
0.01
(90% CL). An observed
Δ
CKM
≠
0
at this level could be explained in terms of a single four-fermion operator which is relatively poorly constrained by electroweak precision measurements.
In terms of Pc1,c2=Pc(4380,4450)+ as the hidden charm pentaquark states to consist of cc̄uud, we study the semileptonic Λb→(Pc1,c2→)J∕ψpℓ−ν̄ℓ decays. In our discussion, while the main contribution to ...Λb→K−J∕ψp is from the non-perturbative process via the doubly charmful b→cc̄s transition, we propose that the Λb→Pc1,c2→J∕ψp transitions partly contribute to the Λb→K−(Pc1,c2→)J∕ψp decays, in which the required cc̄ pair is formed by the sea quarks, intrinsic charm, or both. We predict that B(Λb→J∕ψpℓ−ν̄ℓ)=(2.04−1.57+4.82,1.75−1.35+4.14)×10−6 for ℓ=(e,μ), which are about two orders of magnitude smaller than the observed decay of Λb→pμν̄μ. We also explore the angular correlations for the J∕ψp and ℓ−ν̄ℓ pairs. Our results of the decay branching ratios and angular asymmetries in Λb→J∕ψpℓ−ν̄ℓ, accessible to the ongoing experiments at the LHCb, can be used to improve the understanding of the hidden charm pentaquark states.
•Pentaquarks in the semileptonic Λb decays.•The branching ratios of the Λb decays through the pentaquarks are predicted.•The angular correlations in the decays are studied.•The physical observables are accessible to the LHCb experiments.
Power terms with NLO accuracy for B→Xcℓν Mannel, Thomas; Pivovarov, Alexei A.; Rosenthal, Denis
Nuclear and particle physics proceedings,
June-July 2015, Letnik:
263-264
Journal Article
Recenzirano
Within the Heavy Quark Expansion we analytically compute the QCD correction to the coefficient of power suppressed contribution of chromo-magnetic operator in the limit of vanishing mass of the final ...state quark.
In the framework of a non-relativistic quark model, the mass spectra of the ground and excited states of doubly heavy Ξ and Ω baryons are calculated. We estimate the mass difference between the Ω and ...corresponding Ξ baryons as MΩ−MΞ≃178 MeV for all the states containing cc,bc, or bb quarks. A simple form of the universal Isgur-Wise function, as the transition form factor between the doubly heavy baryons, is introduced. Working in the close-to-zero recoil limit, we investigate the b→c semileptonic decay widths and branching fractions of the doubly heavy baryons. The obtained results are compared with other theoretical predictions.
We discuss the computation of form factors for semi-leptonic decays of B-, Bs-mesons in lattice QCD. Considering in particular the example of the static Bs form factors we demonstrate that after ...non-perturbative renormalization the continuum limit can be taken with confidence. The resulting precision is of interest for extractions of Vub. The size of the corrections of order 1/mb is just estimated at present but it is expected that their inclusion does not pose significant difficulties.
We study the semileptonic decays in the framework of the Standard Model (SM), by employing the perturbative QCD (PQCD) factorization formalism combined with the lattice QCD input for the relevant ...transition form factors. We calculate the branching ratios with , the ratios of the branching fractions and , and the physical observables , and . The "PQCD+Lattice" predictions for and agree with the available experimental measurements within errors. For the ratios and , the "PQCD+Lattice" predictions agree with the other predictions. For and , our theoretical predictions agree with the measured values within errors. Our theoretical predictions of the semileptonic decays considered could be tested in the near future by the LHCb and Belle II experiments.
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