Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
27,997
result(s) for
"Leptons"
Sort by:
Neutrino
Discusses the development of the theory of the existence of neutrinos, and examines the struggle to detect and understand the tiny particles.
Book
A Note on the Barut Second-Order Equation
The second-order equation in the (1/2, 0) [direct sum] (0, 1/2) representation of the Lorentz group has been proposed by A. Barut in the 70s [1]. It permits to explain the mass splitting of leptons (e, [mu], [tau]). The interest is growing in this model (see, for instance, the papers by S. Kruglov [2] and J. P. Vigier et al. [3,4]). We note some additional points of this model.
Journal Article
Bc excitations at LHC: first observations and further research prospects
Status of the Bc meson excitatons search is presented in our work. We discuss the 2S Bc states first discovered by ATLAS and newly confirmed by CMS and LHCb collaborations. We review the observation prospects for the rest predicted states (B∗c, 2P wave, 3P wave and D wave) at LHC experiments. Cascade decays to the ground state as well as direct decays to the lepton pair are regarded for these states.
Conference Proceeding
The \\\\Upsilon (1S)\\ leptonic decay using the principle of maximum conformality
In the paper, we study the \\[\\Upsilon (1S)\\] leptonic decay width \\[\\Gamma (\\Upsilon (1S)\\rightarrow \\ell ^+\\ell ^-)\\] by using the principle of maximum conformality (PMC) scale-setting approach. The PMC adopts the renormalization group equation to set the correct momentum flow of the process, whose value is independent to the choice of the renormalization scale and its prediction thus avoids the conventional renormalization scale ambiguities. Using the known next-to-next-to-next-to-leading order perturbative series together with the PMC single scale-setting approach, we do obtain a renormalization scale independent decay width, \\[\\Gamma _{\\Upsilon (1S) \\rightarrow e^+ e^-} = 1.262^{+0.195}_{-0.175}\\] keV, where the error is squared average of those from \\[\\alpha _s(M_{Z})=0.1181\\pm 0.0011\\], \\[m_b=4.93\\pm 0.03\\] GeV and the choices of factorization scales within \\[\\pm 10\\%\\] of their central values. To compare with the result under conventional scale-setting approach, this decay width agrees with the experimental value within errors, indicating the importance of a proper scale-setting approach.
Journal Article
Search for lepton-flavor-violating tau-lepton decays to ℓγ at Belle
A
bstract
Charged lepton flavor violation is forbidden in the Standard Model but possible in several new physics scenarios. In many of these models, the radiative decays
τ
±
→
ℓ
±
γ
(
ℓ
=
e, μ
) are predicted to have a sizeable probability, making them particularly interesting channels to search at various experiments. An updated search via
τ
±
→
ℓ
±
γ
using full data of the Belle experiment, corresponding to an integrated luminosity of 988 fb
−
1
, is reported for charged lepton flavor violation. No significant excess over background predictions from the Standard Model is observed, and the upper limits on the branching fractions,
B
(
τ
±
→
μ
±
γ
) ≤ 4
.
2 × 10
−
8
and
B
(
τ
±
→
e
±
γ
) ≤ 5
.
6 × 10
−
8
, are set at 90% confidence level.
Journal Article
Effects of one-loop on-shell and off-shell decay H → VV at future lepton colliders
One-loop on-shell and off-shell decays H → VV with VV = γγ, Zγ, ZZ are presented in this paper. The effects of one-loop on-shell and off-shell Higgs decays via Higgs productions at future lepton colliders are also then examined. We find that the impacts of one-loop Higgs decays are significant and they are should be taken into account at future lepton colliders.
Journal Article
Modular A 4 symmetry models of neutrinos and charged leptons
We present a comprehensive analysis of neutrino mass and lepton mixing in theories with A4 modular symmetry, where the only flavon field is the single modulus field τ, and all masses and Yukawa couplings are modular forms. Similar to previous analyses, we discuss all the simplest neutrino sectors arising from both the Weinberg operator and the type I seesaw mechanism, with lepton doublets and right-handed neutrinos assumed to be triplets of A4. Unlike previous analyses, we allow right-handed charged leptons to transform as all combinations of 1, 1′ and 1′′ representations of A4, using the simplest different modular weights to break the degeneracy, leading to ten different charged lepton Yukawa matrices, instead of the usual one. This implies ten different Weinberg models and thirty different type I seesaw models, which we analyse in detail. We find that fourteen models for both NO and IO neutrino mass ordering can accommodate the data, as compared to one in previous analyses, providing many new possibilities.
Journal Article
Search for resonant and nonresonant new phenomena in high-mass dilepton final states at s = 13 TeV
A
bstract
A search is presented for physics beyond the standard model (SM) using electron or muon pairs with high invariant mass. A data set of proton-proton collisions collected by the CMS experiment at the LHC at
s
= 13 TeV from 2016 to 2018 corresponding to a total integrated luminosity of up to 140 fb
−
1
is analyzed. No significant deviation is observed with respect to the SM background expectations. Upper limits are presented on the ratio of the product of the production cross section and the branching fraction to dileptons of a new narrow resonance to that of the Z boson. These provide the most stringent lower limits to date on the masses for various spin-1 particles, spin-2 gravitons in the Randall-Sundrum model, as well as spin-1 mediators between the SM and dark matter particles. Lower limits on the ultraviolet cutoff parameter are set both for four-fermion contact interactions and for the Arkani-Hamed, Dimopoulos, and Dvali model with large extra dimensions. Lepton flavor universality is tested at the TeV scale for the first time by comparing the dimuon and dielectron mass spectra. No significant deviation from the SM expectation of unity is observed.
Journal Article
Modular S 4 and A 4 symmetries and their fixed points: new predictive examples of lepton mixing
In the modular symmetry approach to neutrino models, the flavour symmetry emerges as a finite subgroup ΓN of the modular symmetry, broken by the vacuum expec- tation value (VEV) of a modulus field τ. If the VEV of the modulus τ takes some special value, a residual subgroup of ΓN would be preserved. We derive the fixed points τS = i, τST = (−1 + i3\\[ \\sqrt{3} \\])/2, τTS = (1 + i3\\[ \\sqrt{3} \\])/2, τT = i∞ in the fundamental domain which are in-variant under the modular transformations indicated. We then generalise these fixed points to τf = γτS, γτST, γτTS and γτT in the upper half complex plane, and show that it is suffi-cient to consider γ ∈ ΓN. Focussing on level N = 4, corresponding to the flavour group S4, we consider all the resulting triplet modular forms at these fixed points up to weight 6. We then apply the results to lepton mixing, with different residual subgroups in the charged lepton sector and each of the right-handed neutrinos sectors. In the minimal case of two right-handed neutrinos, we find three phenomenologically viable cases in which the light neutrino mass matrix only depends on three free parameters, and the lepton mixing takes the trimaximal TM1 pattern for two examples. One of these cases corresponds to a new Littlest Modular Seesaw based on CSD(n) with n = 1 + 6\\[ \\sqrt{6} \\]≈ 3.45, intermediate between CSD(3) and CSD(4). Finally, we generalize the results to examples with three right-handed neutrinos, also considering the level N = 3 case, corresponding to A4 flavour symmetry.
Journal Article
Complementary signals of lepton flavor violation at a high-energy muon collider
A
bstract
A muon collider would be a powerful probe of flavor violation in new physics. There is a strong complementary case for collider measurements and precision low-energy probes of lepton flavor violation (as well as CP violation). We illustrate this by studying the collider reach in a supersymmetric scenario with flavor-violating slepton mixing. We find that the collider could discover sleptons and measure the slepton and neutralino masses with high precision, enabling event reconstruction that could cleanly separate flavor-violating new physics signals from Standard Model backgrounds. The discovery reach of a high-energy muon collider would cover a comparably large, and overlapping, range of parameter space to future
μ → e
conversion and electron EDM experiments, and unlike precision experiments could immediately shed light on the nature of new physics responsible for flavor violation. This complementarity strengthens the case that a muon collider could be an ideal energy-frontier laboratory in the search for physics beyond the Standard Model.
Journal Article