MDPI - Publisher of Open Access Journals

8 pages, 1341 KB

Open AccessReview

Semileptonic and Missing Energy B Decays at Belle II

by Giovanni Gaudino

Particles 2025, 8(2), 60; https://doi.org/10.3390/particles8020060 - 4 Jun 2025

Viewed by 986

The Belle II experiment has collected a 364 fb⁻¹ sample of collisions at the

Υ (4 S)

resonance. This dataset, with its low particle multiplicity and well-constrained initial state, provides an ideal environment for studying semileptonic and missing energy B [...] Read more.

The Belle II experiment has collected a 364 fb⁻¹ sample of collisions at the

Υ (4 S)

resonance. This dataset, with its low particle multiplicity and well-constrained initial state, provides an ideal environment for studying semileptonic and missing energy B decays. In this paper, I will present recent results on these decays, emphasizing their impact on the determination of CKM matrix elements and potential new physics. I will also discuss the techniques used for missing energy reconstruction and the challenges of signal-background discrimination. Future analysis prospects with larger datasets will also be highlighted. Full article

(This article belongs to the Special Issue Selected Papers from the 13th International Conference on New Frontiers in Physics (ICNFP 2024))

► Show Figures

Figure 1

9 pages, 1080 KB

Open AccessReview

Lepton Flavour Universality Tests Using Semileptonic b-Hadron Decays at the LHCb Detector

by Bogdan Kutsenko

Particles 2025, 8(1), 5; https://doi.org/10.3390/particles8010005 - 14 Jan 2025

Cited by 1 | Viewed by 1330

Abstract

This review highlights advancements in testing Lepton Flavour Universality (LFU) through semileptonic b-hadron decays at the LHCb detector. Measurements of the LFU

R (D)

and

R (D^{*})

provide evidence of deviations from Standard Model (SM) predictions, suggesting [...] Read more.

This review highlights advancements in testing Lepton Flavour Universality (LFU) through semileptonic b-hadron decays at the LHCb detector. Measurements of the LFU

R (D)

and

R (D^{*})

provide evidence of deviations from Standard Model (SM) predictions, suggesting the presence of possible New Physics (NP). However, the

D^{★}

longitudinal polarisation results are in good agreement with SM expectations, placing constraints on potential NP theories, such as the leptoquarks or charged Higgs models. Further improvements in the measurements’ precision are expected with the new data from LHCb Run 3, collected with higher instantaneous luminosity and improved trigger. Full article

(This article belongs to the Special Issue Selected Papers from the 13th International Conference on New Frontiers in Physics (ICNFP 2024))

► Show Figures

Figure 1

23 pages, 940 KB

Open AccessEditor’s ChoiceReview

Overview of B→K^(∗)ℓℓ Theoretical Calculations and Uncertainties

by Farvah Mahmoudi and Yann Monceaux

Symmetry 2024, 16(8), 1006; https://doi.org/10.3390/sym16081006 - 7 Aug 2024

Cited by 15 | Viewed by 2085

Abstract

The search for New Physics (NP) beyond the Standard Model (SM) has been a central focus of particle physics, including in the context of B-meson decays involving

b \to s ℓ ℓ

transitions. These transitions, mediated by flavour-changing neutral currents, are highly [...] Read more.

The search for New Physics (NP) beyond the Standard Model (SM) has been a central focus of particle physics, including in the context of B-meson decays involving

b \to s ℓ ℓ

transitions. These transitions, mediated by flavour-changing neutral currents, are highly sensitive to small NP effects due to their suppression in the SM. While direct searches at colliders have not yet led to NP discoveries, indirect probes through semi-leptonic decays have revealed anomalies in observables such as the branching fraction

B (B \to K μ μ)

and the angular observable

P_{5}^{'} (B \to K^{*} μ μ)

. In order to assess the observed tensions, it is essential to ensure an accurate SM prediction. In this review, we examine the theoretical basis of the

B \to K^{(*)} ℓ ℓ

decays, addressing in particular key uncertainties arising from local and non-local form factors. We also discuss the impact of QED corrections to the Wilson coefficients, as well as the effect of CKM matrix elements on the predictions and the tension with the experimental measurements. We discuss the most recent results, highlighting ongoing efforts to refine predictions and to constrain potential signs of NP in these critical decay processes. Full article

(This article belongs to the Special Issue Symmetries and Anomalies in Flavour Physics)

► Show Figures

Figure 1

26 pages, 1071 KB

Open AccessReview

Lepton Flavor Universality Tests in Semileptonic b→c Decays

by Suzanne Klaver and Marcello Rotondo

Symmetry 2024, 16(8), 964; https://doi.org/10.3390/sym16080964 - 29 Jul 2024

Viewed by 1897

Abstract

Semileptonic decays of b- to c-hadrons provide an exciting environment to probe new physics and currently present some of the most compelling anomalies in the field of flavor physics. Measurements of the lepton flavor universality ratios

R (D^{*})

, comparing [...] Read more.

Semileptonic decays of b- to c-hadrons provide an exciting environment to probe new physics and currently present some of the most compelling anomalies in the field of flavor physics. Measurements of the lepton flavor universality ratios

R (D^{*})

, comparing branching fractions with

τ

and

μ

leptons, show a discrepancy of over 3σ with respect to the Standard Model, and suggest that the coupling to

τ

leptons is stronger than predicted. Measurements of angular distributions as well as polarization in b- to c-hadron decays provide additional sensitivity to new physics. This review article offers an overview of the theory of semileptonic b- to c-hadron decays, presents the experiments and experimental techniques used to perform measurements of these decays, and summarizes the latest experimental results with their implications. Full article

(This article belongs to the Special Issue Symmetries and Anomalies in Flavour Physics)

► Show Figures

Figure 1

12 pages, 806 KB

Open AccessReview

The Neutron Lifetime Discrepancy and Its Implications for Cosmology and Dark Matter

by Fred E. Wietfeldt

Symmetry 2024, 16(8), 956; https://doi.org/10.3390/sym16080956 - 26 Jul 2024

Cited by 4 | Viewed by 5256

Abstract

Free neutron decay is the prototype for nuclear beta decay and other semileptonic weak particle decays. It provides important insights into the symmetries of the weak nuclear force. Neutron decay is important for understanding the formation and abundance of light elements in the [...] Read more.

Free neutron decay is the prototype for nuclear beta decay and other semileptonic weak particle decays. It provides important insights into the symmetries of the weak nuclear force. Neutron decay is important for understanding the formation and abundance of light elements in the early universe. The two main experimental approaches for measuring the neutron lifetime, the beam method and the ultracold neutron storage method, have produced results that currently differ by 9.8 ± 2.0 s. While this discrepancy probably has an experimental origin, a more exciting prospect is that it may be explained by new physics, with possible connections to dark matter. The experimental status of the neutron lifetime is briefly reviewed, with an emphasis on its implications for cosmology, astrophysics, and dark matter. Full article

(This article belongs to the Special Issue The Dark Universe: The Harbinger of a Major Discovery)

► Show Figures

Figure 1

51 pages, 1692 KB

Open AccessFeature PaperReview

B Meson Decays in the Covariant Confined Quark Model

by Stanislav Dubnička, Anna Z. Dubničková, Mikhail A. Ivanov and Andrej Liptaj

Symmetry 2023, 15(8), 1542; https://doi.org/10.3390/sym15081542 - 4 Aug 2023

Cited by 1 | Viewed by 3171

Abstract

The aim of this text is to present the covariant confined quark model (CCQM) and review its applications in the decays of B mesons. We do so in the context of existing experimental measurements and theoretical results of other authors, which we also [...] Read more.

The aim of this text is to present the covariant confined quark model (CCQM) and review its applications in the decays of B mesons. We do so in the context of existing experimental measurements and theoretical results of other authors, which we also review. The physics principles are, in detail, exposed for the CCQM; the other results (theoretical and experimental) are surveyed in an enumerative way with comments. We proceed by considering, successively, three categories of decay processes: leptonic, semileptonic and non-leptonic. Full article

(This article belongs to the Special Issue Review on Quantum Field Theory)

► Show Figures

Figure 1

14 pages, 407 KB

Open AccessArticle

A Proposal to the ‘12 vs. 32 Puzzle’

by Qiang Li, Wei Feng and Guo-Li Wang

Symmetry 2023, 15(7), 1457; https://doi.org/10.3390/sym15071457 - 21 Jul 2023

Cited by 1 | Viewed by 1531

Abstract

We reconsider the semileptonic decays of

B \to D_{1}^{(')} l {\bar{ν}}_{l}

. The previous theoretical calculations predict a significantly smaller rate for the semileptonic decay of B to [...] Read more.

We reconsider the semileptonic decays of

B \to D_{1}^{(')} l {\bar{ν}}_{l}

. The previous theoretical calculations predict a significantly smaller rate for the semileptonic decay of B to

D_{1}^{'} (J_{l} = \frac{1}{2})

compared with that to the

D_{1} (J_{l} = \frac{3}{2})

, which is not consistent with the current experimental data. This conflict is known as the so-called ‘

\frac{1}{2}

vs.

\frac{3}{2}

puzzle’. In this work, we propose a simple scheme to fix this problem, where we suppose the strong eigenstates

D_{1}^{(')}

that do not coincide with the eigenstate of the weak interaction, since no experimental results show that the weak and the strong interactions have to share the same eigenstates. Within the framework of this tentative scheme, meson B first weakly decays to the weak eigenstates

D_{α (β)}

and then the latter are detected as the

D_{1}^{(')}

by the strong decay products

D^{*} π

. We predict that there exist two new particles

D_{α (β)}

with

J^{P} = 1^{+}

, which were not previously identified. The good performance of the new scheme in describing the experimental data may hint at new symmetry in the weak decays of

B_{q}

to

1^{+}

heavy–light mesons. To test the scheme proposed here, we suggest an experiment to detect the difference in the invariant mass spectra of

D_{1}

that is reconstructed from the B weak decay and from the strong decay products. Full article

(This article belongs to the Section Physics)

► Show Figures

Figure 1

21 pages, 459 KB

Open AccessReview

A Light Shed on Lepton Flavor Universality in B Decays

by Sonali Patnaik and Rajeev Singh

Universe 2023, 9(3), 129; https://doi.org/10.3390/universe9030129 - 1 Mar 2023

Cited by 9 | Viewed by 2038

Abstract

Behind succeeding measurements of anomalies in semileptonic decays at LHCb and several collider experiments hinting at the possible violation of lepton flavor universality, we undertake a concise review of theoretical foundations of the tree- and loop-level b-hadron decays, [...] Read more.

Behind succeeding measurements of anomalies in semileptonic decays at LHCb and several collider experiments hinting at the possible violation of lepton flavor universality, we undertake a concise review of theoretical foundations of the tree- and loop-level b-hadron decays,

b \to c l ν_{l}

and

b \to s l^{+} l^{-}

along with experimental environments. We revisit the world averages for

R_{D (D^{*})}

,

R_{K (K^{*})}

,

R_{J / ψ}

, and

R_{η_{c}}

, for the semileptonic transitions and provide results within the framework of the relativistic independent quark model in addition to the results from model-independent studies. If the ongoing evaluation of the data of LHC Run 2 confirms the measurements of Run 1, then the statistical significance of the effect in each decay channel is likely to reach 5

σ

. A confirmation of these measurements would soon turn out to be the first remarkable observation of physics beyond the Standard Model, providing a wider outlook on the understanding of new physics. Full article

(This article belongs to the Special Issue Search for New Physics at the LHC and Future Colliders)

► Show Figures

Figure 1

7 pages, 342 KB

Open AccessReview

Recent Progress in

Λ_{c}^{+}

Decays

by Cong Geng and Xiaorong Zhou

Symmetry 2023, 15(1), 20; https://doi.org/10.3390/sym15010020 - 22 Dec 2022

Cited by 1 | Viewed by 1797

Abstract

Studying

Λ_{c}^{+}

decays provides important and complementary information to help understand the effects of non-perturbative quantum chromodynamics. Recently, many interesting results about

Λ_{c}^{+}

decays have been reported thanks to the high luminosity in Belle and dedicated operation at the [...] Read more.

Studying

Λ_{c}^{+}

decays provides important and complementary information to help understand the effects of non-perturbative quantum chromodynamics. Recently, many interesting results about

Λ_{c}^{+}

decays have been reported thanks to the high luminosity in Belle and dedicated operation at the

Λ_{c}^{+}

pair production threshold in BESIII. This paper reviews the recent progress in experimental measurements, containing sections about the hadronic weak decay, semileptonic decay, and decay asymmetry parameters and CP violation. Full article

(This article belongs to the Collection Symmetry/Asymmetry in Baryon Decay: Polarization, Hyperon Asymmetry Parameters and CP Violation)

► Show Figures

Figure 1

7 pages, 538 KB

Open AccessCommunication

Prospects for Probing Axionlike Particles at a Future Hadron Collider through Top Quark Production

by Yasaman Hosseini and Mojtaba Mohammadi Najafabadi

Universe 2022, 8(6), 301; https://doi.org/10.3390/universe8060301 - 26 May 2022

Cited by 5 | Viewed by 2258

Abstract

Axionlike particles (ALPs) emerge from spontaneously broken global symmetries in high energy extensions of the Standard Model (SM). This causes ALPs to be among the objectives of future experiments that intend to search for new physics beyond the SM. We discuss the reach [...] Read more.

Axionlike particles (ALPs) emerge from spontaneously broken global symmetries in high energy extensions of the Standard Model (SM). This causes ALPs to be among the objectives of future experiments that intend to search for new physics beyond the SM. We discuss the reach of future pp collider FCC-hh in probing the ALP model parameters through top quark pair production associated with ALP (

t \bar{t} + ALP

) in a model-independent approach. The search is performed in the semi-leptonic decay mode of

t \bar{t}

and the analysis is performed using a parametric simulation of the detector response for a projected integrated luminosity of

30 {ab}^{- 1}

. It is shown that

t \bar{t} + ALP

production at the FCC-hh is a promising channel with significant sensitivity to probe the ALP coupling with gluons. The ALP coupling with gluons obtained from HL-LHC and other experiments is presented for comparison. Full article

(This article belongs to the Special Issue Top Quark at the New Physics Frontier)

► Show Figures

Figure 1

20 pages, 533 KB

Open AccessArticle

QED-Corrections to Weak Decays

by Roman Zwicky

Symmetry 2021, 13(11), 2036; https://doi.org/10.3390/sym13112036 - 28 Oct 2021

Cited by 8 | Viewed by 2490

Abstract

Important aspects of QED-corrections to hadronic decays are reviewed with emphasis on conceptual points such as infrared divergences and structure dependence. These matter are illustrated for the

e^{+} e^{-} \to h a d r o n s

, the leptonic decay [...] Read more.

Important aspects of QED-corrections to hadronic decays are reviewed with emphasis on conceptual points such as infrared divergences and structure dependence. These matter are illustrated for the

e^{+} e^{-} \to h a d r o n s

, the leptonic decay

π^{+} \to ℓ^{+} \bar{ν}

and the semileptonic decay

B \to π ℓ^{+} \bar{ν}

. Aspects of structure dependence include the (non)-cancellation of hard-collinear logs (e.g.,

ln m_{ℓ}

and

ln m_{π}

) of charged final states. Full article

(This article belongs to the Special Issue Search for New Phenomena in Heavy-Quark Physics)

► Show Figures

Figure 1

71 pages, 2928 KB

Open AccessEditor’s ChoiceReview

Radiative Corrections to Semileptonic Beta Decays: Progress and Challenges

by Chien-Yeah Seng

Particles 2021, 4(4), 397-467; https://doi.org/10.3390/particles4040034 - 28 Sep 2021

Cited by 20 | Viewed by 5629

Abstract

We review some recent progress in the theory of electroweak radiative corrections in semileptonic decay processes. The resurrection of the so-called Sirlin’s representation based on current algebra relations permits a clear separation between the perturbatively-calculable and incalculable pieces in the [...] Read more.

We review some recent progress in the theory of electroweak radiative corrections in semileptonic decay processes. The resurrection of the so-called Sirlin’s representation based on current algebra relations permits a clear separation between the perturbatively-calculable and incalculable pieces in the

O (G_{F} α)

radiative corrections. The latter are expressed as compact hadronic matrix elements that allow systematic non-perturbative analysis such as dispersion relation and lattice QCD. This brings substantial improvements to the precision of the electroweak radiative corrections in semileptonic decays of pion, kaon, free neutron and

J^{P} = 0^{+}

nuclei that are important theory inputs in precision tests of the Standard Model. Unresolved issues and future prospects are discussed. Full article

(This article belongs to the Special Issue Beta-Decay Processes in Nuclear Systems)

► Show Figures

Figure 1

22 pages, 1316 KB

Open AccessArticle

Optimized Probes of the CP Nature of the Top Quark Yukawa Coupling at Hadron Colliders

by Darius A. Faroughy, Blaž Bortolato, Jernej F. Kamenik, Nejc Košnik and Aleks Smolkovič

Symmetry 2021, 13(7), 1129; https://doi.org/10.3390/sym13071129 - 24 Jun 2021

Cited by 2 | Viewed by 2237

Abstract

We summarize our recent proposals for probing the

C P

-odd

i \tilde{κ} \bar{t} γ^{5} t h

interaction at the LHC and its projected upgrades directly using associated on-shell Higgs boson and top quark or top quark pair production. We [...] Read more.

We summarize our recent proposals for probing the

C P

-odd

i \tilde{κ} \bar{t} γ^{5} t h

interaction at the LHC and its projected upgrades directly using associated on-shell Higgs boson and top quark or top quark pair production. We first recount how to construct a

C P

-odd observable based on top quark polarization in

W b \to t h

scattering with optimal linear sensitivity to

\tilde{κ}

. For the corresponding hadronic process

p p \to t h j

we then present a method of extracting the phase-space dependent weight function that allows to retain close to optimal sensitivity to

\tilde{κ}

. For the case of top quark pair production in association with the Higgs boson,

p p \to t \bar{t} h

, with semileptonically decaying tops, we instead show how one can construct manifestly

C P

-odd observables that rely solely on measuring the momenta of the Higgs boson and the leptons and b-jets from the decaying tops without having to distinguish the charge of the b-jets. Finally, we introduce machine learning (ML) and non-ML techniques to study the phase-space optimization of such

C P

-odd observables. We emphasize a simple optimized linear combination

α \cdot ω

that gives similar sensitivity as the studied fully fledged ML models. Using

α \cdot ω

we review sensitivity projections to

\tilde{κ}

at HL-LHC, HE-LHC, and FCC-hh. Full article

(This article belongs to the Special Issue Higher Order Radiative Corrections in QCD)

► Show Figures

Figure 1

9 pages, 309 KB

Open AccessArticle

Constraints on the Anomalous Wtb Couplings from B-Physics Experiments

by Anastasiia Kozachuk and Dmitri Melikhov

Symmetry 2020, 12(9), 1506; https://doi.org/10.3390/sym12091506 - 14 Sep 2020

Cited by 4 | Viewed by 2077

Abstract

We analyze constraints on the anomalous

W t b

couplings from B-physics experiments, performing a correlated analysis and allowing all anomalous couplings to differ simultaneously from their Standard Model (SM) values. The B-physics observables allow one to probe three linear combinations [...] Read more.

We analyze constraints on the anomalous

W t b

couplings from B-physics experiments, performing a correlated analysis and allowing all anomalous couplings to differ simultaneously from their Standard Model (SM) values. The B-physics observables allow one to probe three linear combinations out of the four anomalous couplings, which parameterize the

W t b

vertex under the assumption that the SM symmetries remain the symmetries of the effective theory. The constraints in this work are obtained by taking into account the following B-physics observables: the

{\bar{B}}^{0} - B^{0}

oscillations, the leptonic

B \to μ^{+} μ^{-}

decays, the inclusive radiative

B \to X_{s} γ

decays, and the differential branching fractions in the semileptonic inclusive

B \to X_{s} μ^{+} μ^{-}

and exclusive

B \to (K, K^{*}) μ^{+} μ^{-}

decays at small

q^{2}

, with q the momentum of the

μ^{+} μ^{-}

pair. We find that the SM values of the anomalous couplings belong to the 95% CL allowed region obtained this way, but lie beyond the 68% allowed region. We also report that the distributions of the anomalous couplings obtained within our scenario differ from the results of the 1D scenario, when only one of the couplings is allowed to deviate from its SM value. Full article

(This article belongs to the Special Issue QCD- and QED-Like Theories and Symmetry)

► Show Figures

Figure 1

15 pages, 680 KB

Open AccessEditor’s ChoiceArticle

Semileptonic Decays of Heavy Baryons in the Relativistic Quark Model

by Rudolf N. Faustov and Vladimir O. Galkin

Particles 2020, 3(1), 208-222; https://doi.org/10.3390/particles3010017 - 6 Mar 2020

Cited by 8 | Viewed by 3371

Abstract

Semileptonic and rare semileptonic decays of heavy baryons are studied in the framework of the relativistic quark model based on the quark-diquark picture, quasipotential approach, and quantum chromodynamics (QCD). The form factors parametrizing the matrix elements of the weak transitions are calculated in [...] Read more.

Semileptonic and rare semileptonic decays of heavy baryons are studied in the framework of the relativistic quark model based on the quark-diquark picture, quasipotential approach, and quantum chromodynamics (QCD). The form factors parametrizing the matrix elements of the weak transitions are calculated in the whole accessible kinematical range with the comprehensive account of the relativistic effects. The obtained results for the branching ratios and other observables agree well with the available experimental data. Full article

(This article belongs to the Special Issue Quantum Field Theory at the Limits: From Strong Fields to Heavy Quarks)

► Show Figures

Figure 1

Search Results (21)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI

Saved Queries

Search Filter Reset All

Years

Feature Papers

Subjects

Journals

Article Types

Countries / Regions

Search Results (21)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI