Semileptonic decays and |V<sub>xb</sub>| determinations

Ricciardi, Giulia

doi:10.1051/epjconf/201818202104

Cited by 32 publications

(2 citation statements)

References 123 publications

(186 reference statements)

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“…We make these corrections explicit by including in addition to the subleading Isgur-Wise functions at order Λ QCD /m c,b corrections of order Λ 2 QCD /m 2 c in those HQET form factors that are protected from O(Λ QCD /m c ) corrections. 5 From comparison of the HQET predictions at O(α s , Λ QCD /m b,c ), using the three-point sum rule results for the subleading 4 The kinematic variable w is related to q 2 as w = (m 2 B + m 2 D ( * ) − q 2 )/(2mBm D ( * ) ). 5 Note that two of these corrections are implicitly included in [13] when the normalizations of the B → D ( * ) form factors hA 1 ,+ are decoupled from their HQET values.…”

Section: B → D ( * ) Form Factorsmentioning

confidence: 99%

Constraining new physics in b → cℓν transitions

Jung

Straub

2019

J. High Energ. Phys.

120

125

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B decays proceeding via b → c ν transitions with = e or µ are tree-level processes in the Standard Model. They are used to measure the CKM element V cb , as such forming an important ingredient in the determination of e.g. the unitarity triangle; hence the question to which extent they can be affected by new physics contributions is important, specifically given the long-standing tension between V cb determinations from inclusive and exclusive decays and the significant hints for lepton flavour universality violation in b → cτ ν and b → s decays. We perform a comprehensive model-independent analysis of new physics in b → c ν, considering all combinations of scalar, vector and tensor interactions occuring in single-mediator scenarios. We include for the first time differential distributions of B → D * ν angular observables for this purpose. We show that these are valuable in constraining non-standard interactions. Specifically, the zero-recoil endpoint of the B → D ν spectrum is extremely sensitive to scalar currents, while the maximum-recoil endpoint of the B → D * ν spectrum with transversely polarized D * is extremely sensitive to tensor currents. We also quantify the room for e-µ universality violation in b → c ν transitions, predicted by some models suggested to solve the b → cτ ν anomalies, from a global fit to B → D ν and B → D * ν for the first time. Specific new physics models, corresponding to all possible tree-level mediators, are also discussed. As a side effect, we present V cb determinations from exclusive B decays, both with frequentist and Bayesian statistics, leading to compatible results. The entire numerical analysis is based on open source code, allowing it to be easily adapted once new data or new form factors become available. arXiv:1801.01112v3 [hep-ph] 19 Dec 2018In the context of the Standard Model (SM), the element V cb of the Cabibbo-Kobayashi-Maskawa (CKM) matrix can be determined in various ways:• from a global fit including e.g. meson-antimeson mixing observables [1,2],[4] for a recent review).When considering the SM as the low-energy limit of a more fundamental theory of "new physics" (NP), these determinations are not applicable model-independently in general. Specifically, flavour-changing neutral current processes like meson-antimeson mixing could easily be affected by NP, invalidating the global fit. In this case, a potential disagreement between the global fit and the tree-level determinations from semi-leptonic B decays can signal the presence of NP. However, even the tree-level processes could in principle be significantly affected by NP. This possibility has been considered in the past in particular in view of the long-standing tensions between V cb from different decay channels. Clearly, these tensions could be due to statistical fluctuations or underestimated theoretical uncertainties. While the inclusive decay can be computed to high precision in an expansion in α s and 1/m c,b , see e.g.[3] for a recent overview, the exclusive decays require the knowledge of hadronic form...

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Section: B → D ( * ) Form Factorsmentioning

confidence: 99%

Constraining new physics in b → cℓν transitions

Jung

Straub

2019

J. High Energ. Phys.

120

125

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“…A number of flavour observables appear to indicate flavour-dependent coupling of BSM physics to SM particles. A strong hint of LFU violation exists in experimental measurements [15,16] of semileptonic B-meson decays. A summary of the most recent experimental and theoretical averages for these observables may be found in table 2.…”

Section: Anomalies In Flavourmentioning

confidence: 99%

A near-minimal leptoquark model for reconciling flavour anomalies and generating radiative neutrino masses

Bigaran

Gargalionis

Volkas

2019

J. High Energ. Phys.

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We introduce two scalar leptoquarks, the SU(2) L isosinglet denoted φ ∼ (3, 1, −1/3) and the isotriplet ϕ ∼ (3, 3, −1/3), to explain observed deviations from the standard model in semi-leptonic B-meson decays. We explore the regions of parameter space in which this model accommodates the persistent tensions in the decay observables R D ( * ) , R K ( * ) , and angular observables in b → sµµ transitions. Additionally, we exploit the role of these exotics in existing models for one-loop neutrino mass generation derived from ∆L = 2 effective operators. Introducing the vector-like quark χ ∼ (3, 2, −5/6) necessary for lepton-number violation, we consider the contribution of both leptoquarks to the generation of radiative neutrino mass. We find that constraints permit simultaneously accommodating the flavour anomalies while also explaining the relative smallness of neutrino mass without the need for cancellation between leptoquark contributions. A characteristic prediction of our model is a rate of muon-electron conversion in nuclei fixed by the anomalies in b → sµµ and neutrino mass; the COMET experiment will thus test and potentially falsify our scenario. The model also predicts signatures that will be tested at the LHC and Belle II.

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Gauge Theories of Weak Decays

Buras

2020

116

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We have mentioned already at the beginning of the book that the fundamental role in elementary particle physics, that is, the SM and its extensions, is played by Lagrangians. They encode the information about the particle content of a given theory and of fundamental interactions between these particles that are characteristic for this theory. Therefore, it is essential to start our presentation by discussing the general structure of various Lagrangians that we will encounter in this book.The theories we will discuss are relativistic quantum field theories, and it would appear at first sight that this first step of our expedition is extremely difficult. Yet, the seminal observation of Feynman that a given classical theory can be quantized by means of the path integral method simplifies things significantly. We can formulate the quantum field theory with the help of a Lagrangian of a classical field theory without introducing operators as done in canonical quantization. Having it, a simple set of steps allows us to derive the so-called Feynman rules and use them to calculate the implications of a given theory for various observables that can be compared with experiment.A very important role in particle physics is played by symmetries. They increase significantly the predictive power of a given theory, in particular by reducing the number of free parameters. In this context a very good example is quantum chromodynamics (QCD), the theory of strong interactions. With eight gluons and three colors for quarks, there is a multitude of interactions that, without the SU(3) symmetry governing them, could be rather arbitrary. But the SU(3) symmetry implies certain conservation laws, and at the end there is only a single parameter in QCD: the value of the strong coupling evaluated at some energy scale that can be determined in experiment. Once this is done, all effects of strong interactions can be uniquely predicted, even if this requires often very difficult calculations.The case of QCD is however special as it is based on an exact nonabelian symmetry. We will be more specific about this terminology later. In quantum electrodynamics (QED), which is based on an exact abelian symmetry U(1), in addition to the value of the electromagnetic coupling also the electric charges of quarks and leptons and generally fermions, scalars, and vector particles in a given theory are free. They have to be determined in experiment. In QCD all color charges are fixed by the SU(3) symmetry.Yet QED, similar to QCD, is a very predictive theory because it is based on an exact symmetry. This is generally not the case in nature, and on many occasions the symmetries that we encounter in particle physics are only approximate, and the manner in which 25

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Semileptonic decays and |V_xb| determinations

Cited by 32 publications

References 123 publications

Constraining new physics in b → cℓν transitions

Constraining new physics in b → cℓν transitions

A near-minimal leptoquark model for reconciling flavour anomalies and generating radiative neutrino masses

Gauge Theories of Weak Decays

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Semileptonic decays and |Vxb| determinations

Cited by 32 publications

References 123 publications

Constraining new physics in b → cℓν transitions

Constraining new physics in b → cℓν transitions

A near-minimal leptoquark model for reconciling flavour anomalies and generating radiative neutrino masses

Gauge Theories of Weak Decays

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Semileptonic decays and |V_xb| determinations