scholarly journals Probing μτ flavor-violating solutions for the muon g − 2 anomaly at Belle II

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Syuhei Iguro ◽  
Yuji Omura ◽  
Michihisa Takeuchi
Keyword(s):  
Particle Physics ◽  
Standard Model Prediction ◽  
Mass Range ◽  
Loop Correction ◽  
Lepton Flavor ◽  
Highly Sensitive ◽  
The Standard Model ◽  
Belle Ii ◽  
The One ◽  
Mass Enhancement

Abstract The discrepancy between the measured value and the Standard Model prediction of the muon anomalous magnetic moment is one of the most important issues in the particle physics. It is known that introducing a mediator boson X with the μτ lepton flavor violating (LFV) couplings is one good solution to explain the discrepancy, due to the τ mass enhancement in the one-loop correction. In this paper, we study the signal of this model, i.e. the same-sign leptons, in the Belle II experiment, assuming the flavor-diagonal couplings are suppressed. We show that the Belle II experiment is highly sensitive to the scenario in the mediator mass range of O(1–10) GeV, using the e+e−→ μ±τ∓X → μ±μ±τ∓τ∓ process induced by the X .

scholarly journals Relativistic effects in the search for new intra-atomic force with isotope shifts

2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
Minoru Tanaka ◽  
Yasuhiro Yamamoto
Keyword(s):  
Particle Physics ◽  
Relativistic Effects ◽  
Mass Range ◽  
New Physics ◽  
Wave Functions ◽  
Isotope Shifts ◽  
Atomic Force ◽  
The Standard Model ◽  
Nonrelativistic Calculation ◽  
New Physics Search

Abstract Isotope shift of atomic spectra is considered as a probe of new interaction between electrons and neutrons in atoms. We employ the method of seeking a breakdown of King’s linearity in the isotope shifts of two atomic transitions. In the present work, we evaluate the magnitudes of the nonlinearity using relativistic wave functions and the result is compared with that of nonrelativistic wave functions from our previous work. It turns out that the nonrelativistic calculation underestimates the nonlinearity owing to the new interaction in the mass range of the mediator greater than 1 MeV. Further, we find that the nonlinearity within the standard model of particle physics is significantly magnified by the relativistic effect in the $\text{p}_{1/2}$ state. To get rid of this obstacle in the new physics search, we suggest avoiding $\text{p}_{1/2}$ and that e.g. $\text{p}_{3/2}$ should be used instead.

scholarly journals Matching and running sensitivity in non-renormalizable inflationary models

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Jacopo Fumagalli ◽  
Marieke Postma ◽  
Melvin van den Bout
Keyword(s):  
Particle Physics ◽  
Higgs Field ◽  
Effective Field ◽  
Large Field ◽  
Tree Level ◽  
Planck Data ◽  
The Standard Model ◽  
Set Up ◽  
The One ◽  
Inflationary Models

Abstract Most of the inflationary models that are in agreement with the Planck data rely on the presence of non-renormalizable operators. If the connection to low energy particle physics is made, the renormalization group (RG) introduces a sensitivity to ultraviolet (UV) physics that can be crucial in determining the inflationary predictions. We analyse this effect for the Standard Model (SM) augmented with non-minimal derivative couplings to gravity. Our set-up reduces to the SM for small values of the Higgs field, and allows for inflation in the opposite large field regime. The one-loop beta functions in the inflationary region are calculated using a covariant approach that properly accounts for the non-trivial structure of the field space manifold. We run the SM parameters from the electroweak to the inflationary scale, matching the couplings of the different effective field theories at the boundary between the two regimes, where we also include threshold corrections that parametrize effects from UV physics. We then compute the spectral index and tensor-to-scalar ratio and find that RG flow corrections can be determinant: a scenario that is ruled out at tree level can be resurrected and vice versa.

scholarly journals Possible bilepton resonances in like-sign pairs

2019 ◽  
Vol 34 (10) ◽  
pp. 1950076 ◽  
Author(s):  
Claudio Corianò ◽  
Paul H. Frampton
Keyword(s):  
Standard Model ◽  
Pair Production ◽  
Model Prediction ◽  
Standard Model Prediction ◽  
Mass Range ◽  
Entire Mass Range ◽  
Large Ratio ◽  
The Standard Model ◽  
Integrated Luminosity

We consider pair production of bileptons Y[Formula: see text]Y[Formula: see text] at the LHC for the presently accumulated integrated luminosity of 150/fb. It is shown that the entire mass range 800 GeV [Formula: see text]M(Y) [Formula: see text] 2000 GeV can be successfully searched. A bilepton resonance will have an exceptionally large ratio of signal to background because the Standard Model prediction is so infinitesimal. A 5[Formula: see text] discovery is quite feasible.

scholarly journals Form Factor Measurements at BESIII for an Improved Standard Model Prediction of the Muon g-2

2018 ◽  
Vol 46 ◽  
pp. 1860026
Author(s):  
Marco Destefanis
Keyword(s):  
Form Factor ◽  
Standard Model ◽  
Model Prediction ◽  
Particle Physics ◽  
Standard Model Prediction ◽  
Final States ◽  
Direct Measurements ◽  
The Standard Model ◽  
Data Driven Approach

The anomalous part of the magnetic moment of the muon, (g-2)[Formula: see text], allows for one of the most precise tests of the Standard Model of particle physics. We report on recent results by the BESIII Collaboration of exclusive hadronic cross section channels, such as the 2[Formula: see text], 3[Formula: see text], and 4[Formula: see text] final states. These measurements are of utmost importance for an improved calculation of the hadronic vacuum polarization contribution of (g-2)[Formula: see text], which currenty is limiting the overall Standard Model prediction of this quantity. BESIII has furthermore also intiatated a programme of spacelike transition form factor measurements, which can be used for a determination of the hadronic light-by-light contribution of (g-2)[Formula: see text] in a data-driven approach. These results are of relevance in view of the new and direct measurements of (g-2)[Formula: see text] as foreseen at Fermilab/USA and J-PARC/Japan.

scholarly journals Scalar leptoquarks in leptonic processes

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Andreas Crivellin ◽  
Christoph Greub ◽  
Dario Müller ◽  
Francesco Saturnino
Keyword(s):  
Standard Model ◽  
Magnetic Moment ◽  
Anomalous Magnetic Moment ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Lepton Flavor ◽  
Interaction Terms ◽  
The Standard Model ◽  
The One ◽  
Scalar Leptoquarks

Abstract Leptoquarks are hypothetical new particles, which couple quarks directly to leptons. They experienced a renaissance in recent years as they are prime candidates to explain the so-called flavor anomalies, i.e. the deviations between the Standard Model predictions and measurements in b → sℓ+ℓ− and b → cτν processes and in the anomalous magnetic moment of the muon. At the one-loop level these particles unavoidably generate effects in the purely leptonic processes like Z → ℓ+ℓ−, Z →$$ v\overline{v} $$ v v ¯ , W → ℓν and h → ℓ+ℓ− and can even generate non-zero rates for lepton flavor violating processes such as ℓ → ℓ′γ, Z → ℓ+ℓ′−, h → ℓ+ℓ′− and ℓ → 3ℓ′. In this article we calculate these processes for all five representations of scalar Leptoquarks. We include their most general interaction terms with the Standard Model Higgs boson, which leads to Leptoquark mixing after the former acquires a vacuum expectation value. In our phenomenological analysis we investigate the effects in modified lepton couplings to electroweak gauge bosons, we study the correlations of the anomalous magnetic moment of the muon with h → μ+μ− and Z → μ+μ− as well as the interplay between different lepton flavor violating decays.

scholarly journals On the Second Dipole Moment of Dirac’s Particle

2021 ◽  
Author(s):  
Engel Roza
Keyword(s):  
Dipole Moment ◽  
Electric Dipole Moment ◽  
Electric Dipole ◽  
Particle Physics ◽  
Critical Survey ◽  
Majorana Particle ◽  
Nuclear Domain ◽  
The Standard Model ◽  
Charge Parity ◽  
The One

An analysis is presented of the possible existence of a second anomalous dipole moment of Dirac’s particle next to the one associated with the angular momentum. It includes a discussion why, in spite of his own derivation, Dirac has doubted about its relevancy. It is shown why since then it has been overlooked and why it has vanished from leading textbooks. A critical survey is given on the reasons of its reject, including the failure of attempts to measure and the perceived violations of time reversal symmetry and charge-parity symmetry. It is emphasized that the anomalous electric dipole moment of the pointlike electron (AEDM) is fundamentally different from the quantum field type electric dipole moment of an electron (eEDM) as defined in the standard model of particle physics. The analysis has resulted into the identification of a third type Dirac particle, next to the electron type and the Majorana particle. It is shown that, unlike as in the case of the electron type, its second anomalous dipole moment is real valued and is therefore subject to polarization in a vector field. Examples are given that it may have a possible impact in the nuclear domain and in the gravitational domain.

scholarly journals The Search for μ+ → e+γ with 10–14 Sensitivity: The Upgrade of the MEG Experiment

Symmetry ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1591
Author(s):  
Alessandro M. Baldini ◽  
Vladimir Baranov ◽  
Michele Biasotti ◽  
Gianluigi Boca ◽  
Paolo W. Cattaneo ◽  
...  
Keyword(s):  
Particle Physics ◽  
Rate Capability ◽  
Muon Beam ◽  
Paul Scherrer Institute ◽  
Current Status ◽  
Elementary Particle Physics ◽  
Lepton Flavor ◽  
The Standard Model ◽  
Stringent Limit ◽  
Paul Scherrer

The MEG experiment took data at the Paul Scherrer Institute in the years 2009–2013 to test the violation of the lepton flavor conservation law, which originates from an accidental symmetry that the Standard Model of elementary particle physics has, and published the most stringent limit on the charged lepton flavor violating decay μ+→e+γ: BR(μ+→e+γ) <4.2×10−13 at 90% confidence level. The MEG detector has been upgraded in order to reach a sensitivity of 6×10−14. The basic principle of MEG II is to achieve the highest possible sensitivity using the full muon beam intensity at the Paul Scherrer Institute (7×107 muons/s) with an upgraded detector. The main improvements are better rate capability of all sub-detectors and improved resolutions while keeping the same detector concept. In this paper, we present the current status of the preparation, integration and commissioning of the MEG II detector in the recent engineering runs.

scholarly journals Challenges in semileptonic $${\varvec{B}}$$ decays

2020 ◽  
Vol 80 (10) ◽  
Author(s):  
P. Gambino ◽  
A. S. Kronfeld ◽  
M. Rotondo ◽  
C. Schwanda ◽  
F. Bernlochner ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
B Decays ◽  
Lepton Flavor ◽  
The Standard Model ◽  
Model Predictions ◽  
Theoretical Predictions ◽  
Working Together ◽  
Mixing Matrix ◽  
Belle Ii ◽  
The Rich

AbstractTwo of the elements of the Cabibbo–Kobayashi–Maskawa quark mixing matrix, $$|V_{ub}|$$ | V ub | and $$|V_{cb}|$$ | V cb | , are extracted from semileptonic B decays. The results of the B factories, analysed in the light of the most recent theoretical calculations, remain puzzling, because for both $$|V_{ub}|$$ | V ub | and $$|V_{cb}|$$ | V cb | the exclusive and inclusive determinations are in clear tension. Further, measurements in the $$\tau $$ τ channels at Belle, Babar, and LHCb show discrepancies with the Standard Model predictions, pointing to a possible violation of lepton flavor universality. LHCb and Belle II have the potential to resolve these issues in the next few years. This article summarizes the discussions and results obtained at the MITP workshop held on April 9–13, 2018, in Mainz, Germany, with the goal to develop a medium-term strategy of analyses and calculations aimed at solving the puzzles. Lattice and continuum theorists working together with experimentalists have discussed how to reshape the semileptonic analyses in view of the much higher luminosity expected at Belle II, searching for ways to systematically validate the theoretical predictions in both exclusive and inclusive B decays, and to exploit the rich possibilities at LHCb.

scholarly journals HEAVY-NEUTRINO EFFECTS ON τ-LEPTON DECAYS

1994 ◽  
Vol 09 (38) ◽  
pp. 3595-3604 ◽  
Author(s):  
A. PILAFTSIS
Keyword(s):  
Standard Model ◽  
Heavy Neutrino ◽  
Lepton Flavor ◽  
Grand Unified Theories ◽  
The Standard Model ◽  
Unified Theories ◽  
Lepton Decays ◽  
The One

Minimal extensions of the standard model that are motivated by grand unified theories or superstring models with an E6 symmetry can naturally predict heavy neutrinos of Dirac or Majorana nature. Such heavy neutral leptons violate the decoupling theorem at the one-loop electroweak order and hence offer a unique chance for possible lepton-flavor decays of the τ-lepton, e.g. τ→eee or τ→μμμ, to be seen in LEP experiments. We analyze such decays in models with three and four generations.

scholarly journals COMET, an Experiment to Search for mu-e Conversion in a Nuclear Field

2018 ◽  
Vol 46 ◽  
pp. 1860065
Author(s):  
Hiroaki Natori
Keyword(s):  
Elementary Particle ◽  
Particle Physics ◽  
New Physics ◽  
Experimental Limit ◽  
Elementary Particle Physics ◽  
Lepton Flavor ◽  
Nuclear Field ◽  
Past Experiment ◽  
The Standard Model ◽  
Current Experimental Limit

Charged lepton flavor violating (CLFV) process is predicted to be out of experimental reach by the Standard Model of elementary particle physics (SM). However, many models of the new physics beyond the SM predicts that it is just below the current experimental limit. COMET searches for one of the CLFV process, mu-e conversion in a nuclear field, improving the sensitivity by a factor of approximately [Formula: see text] for Phase-I and [Formula: see text] for Phase-II experiment from a past experiment.

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