Recently, it was pointed out that the electron and muon g-2 discrepancies can be explained simultaneously by a flavor-violating axion-like particle (ALP). We show that the parameter regions favored by the muon g-2 are already excluded by the muonium-antimuonium oscillation bound. In contrast, those for the electron g-2 can be consistent with this bound when the ALP is heavier than 1.5 GeV. We propose to search for a signature of the same-sign and same-flavor lepton pairs and the forward-backward muon asymmetry to test the model at the Belle II experiment.
We report on the recent results of searches for lepton-flavor-violating tau decays as well as lepton-number-violating B decays with the world-highest data samples accumulated at the Belle.
We study charged lepton flavor violation associated with a light leptophilic axion-like particle (ALP), $X$, at the $B$-factory experiment Belle II. We focus on production of the ALP in the tau decays $τ\to X l$ with $l=e,μ$, followed by its decay via $X\to l^- l^+$. The ALP can be either promptly decaying or long-lived. We perform Monte-Carlo simulations, recasting a prompt search at Belle for lepton-flavor-violating $τ$ decays, and propose a displaced-vertex (DV) search. For both types of searches, we derive the Belle~II sensitivity reaches in both the product of branching fractions and the …
In this work, we study the lepton number violating tau decays via two intermediate on-shell Majorana neutrinos $N_j$ into two charged pions, and a charged lepton $τ^{\pm} \to π^{\pm} N_j \to π^{\pm} π^{\pm} \ell^{\mp}$. We consider the scenario where the heavy neutrino masses are within $0.5$ GeV $\leq M_N \leq 1.5$ GeV. We evaluated the possibility to measure the modulation of the decay width along the detector length for these processes at taus factories, such as Belle II. We study some realistic conditions which could lead to the observation of this phenomenon at futures $τ$'s factories.
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 sensi…
We report the recent results of a search for lepton-flavor-violating tau decays and a search for CP violation in tau to nu Ks pi using a large data sample accumulated with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. The sensitivity to these modes is significantly improved compared to previous experiments.
$L_μ-L_τ$ gauge boson ($Z'$) with a mass in the MeV to GeV region can resolve not only the muon $g-2$ excess, but also the gap in the high-energy cosmic neutrino spectrum at IceCube. It was recently proposed that such a light gauge boson can be detected during the Belle II experiment with a luminosity of 50 ab$^{-1}$ by the $e^+ e^- \to γ+\slashed{E}$ process through the kinetic mixing with the photon, where the missing energy $\slashed{E}$ is from the $Z' \to \barνν$ decays. We study the phenomenological implications when a pair of singlet vector-like leptons carrying different $L_μ- L_τ$ cha…
The present experimental status of searches for lepton flavor violating decays of the $τ$ lepton to a lighter mass lepton and a photon or a pseudoscalar meson is presented. The results obtained are from $e^+e^-$ annihilation data collected at a center-of-mass energy near 10.58 GeV by the \babar and the Belle detectors. In order to benefit from larger available datasets, the first $\babar-$Belle combinations of upper limits on the branching fractions of lepton flavor violating $τ$-decays are obtained.
The electroweak penguin B decays mediated by $b \to s \ell^+ \ell^- $ transitions are flavour-changing neutral current processes, and are thus sensitive to new physics owing to potential contributions of heavy particles in the quantum loop. Recently, LHCb has obtained interesting results, where the possible hints of lepton family universality violation (LFUV) could be seen. We report a new measurement of the LFUV observable $R_{K}$, the ratio of branching fractions of $B\to Kμ^{+}μ^{-}$ to $B\to Ke^{+}e^{-}$, based on the full data sample recorded by Belle at the $Υ(4S)$ resonance from $e^+e^-…
The impact of axion-like particles (ALPs) on the search of permanent electric dipole moments (EDMs) of molecules, atoms, nuclei and nucleons is systematically investigated. We classify first the full set of CP-violating Jarlskog invariants emerging in the ALP effective field theory (EFT) containing operators up to dimension-5. Then, we evaluate the leading short-distance effects to the EDMs up to two-loop order. The high sensitivity of EDMs to CP-violating ALP interactions is emphasised exploiting both the current and projected experimental sensitivities.
We consider the lepton number violating decays $B \to μ^{\pm} μ^{\pm} π^{\mp}$ and $B \to D^{(*)} μ^{\pm} μ^{\pm} π^{\mp}$ which may be detected at LHCb and Belle-II experiments; and $B \to μ^{\pm} μ^{\pm} e^{\mp} ν$ and $B \to D^{(*)} μ^{\pm} μ^{\pm} e^{\mp} ν$ decays which may be detected at Belle-II experiment. The projected total number of produced $B$ mesons is $4.8 \times 10^{12}$ at LHCb upgrade and $5 \times 10^{10}$ at Belle-II. For the case that the above decays are not detected, we deduce the new upper bounds (sensitivity limits) for the mixing parameter $|U_{μN}|^2$ of heavy steril…
We assess the status of past and future experiments on lepton flavor violating (LFV) muon and tau decays into a light, invisible, axion-like particle (ALP), $a$. We propose a new experimental setup for MEG II, the MEGII-fwd, with a forward calorimeter placed downstream from the muon stopping target. Searching for $μ\to e a$ decays MEGII-fwd is maximally sensitive to LFV ALPs, if these have nonzero couplings to right-handed leptons. The experimental set-up suppresses the (left-handed) Standard Model background in the forward direction by controlling the polarization purity of the muon beam. The…
We show that existing laboratory experiments have the potential to unveil the origin of matter by probing leptogenesis in the type-I seesaw model with three right-handed neutrinos and Majorana masses in the GeV range. The baryon asymmetry is generated by CP-violating flavour oscillations during the production of the right-handed neutrinos. In contrast to the case with only two right-handed neutrinos, no degeneracy in the Majorana masses is required. The right-handed neutrinos can be found in meson decays at BELLE II and LHCb.
Motivated by recent results from the LHCb, BABAR and Belle collaborations on B\to D^{(*)}\ell^-\barν_\ell decays, which significantly deviate from the Standard Model and hint the possible new physics beyond the Standard Model, we probe the R-parity violating supersymmetric effects in B^-_c\to \ell^-\barν_\ell and B\to D^{(*)}\ell^-\barν_\ell decays. We find that (i) \mathcal{B}(B^-_c\to e^- \barν_e) and \mathcal{B}(B^-_c\toμ^-\barν_μ) are sensitive to the constrained slepton exchange couplings; (ii) the normalized forward-backward asymmetries of B\to De^-\barν_{e} decays have been greatly affe…
I review the latest results on exotic, lepton flavor violating (LFV) and lepton number violating (LNV) decays of the B, D mesons and the tau leptons, obtained at the two B-factory experiments, Belle and BaBar. Where appropriate, results from other experiments are also described.
Now the bounds on the lepton-flavor violating (LFV) decay modes of tau lepton are being improved by the Belle experiment in the KEK B factory. In this paper the LFV decay of tau lepton is discussed in the supersymmetric seesaw model, using the current neutrino oscillation data.
In this paper, the production of Axion-Like Particles (ALPs) at $B$-factories via the process $e^+e^- \to γa$ is revisited. To this purpose, the relevant cross-section is computed via an effective Lagrangian with simultaneous ALP couplings to $b$-quarks and photons. The interplay between resonant and non-resonant contributions is shown to be relevant for experiments operating at $\sqrt{s}=m_{Υ(nS)}$, with $n=1,2,3$, while the non-resonant one dominates at $Υ(4S)$. These effects imply that the experimental searches performed at different quarkonia resonances are sensitive to complementary combi…
ALP production in Lepton Flavour Violating meson, tau and gauge boson decays
Instituto de Física Corpuscular, Universidad de Valencia and CSIC（瓦伦西亚大学与西班牙国家研究委员会联合粒子物理研究所）；School of Physics, Nankai University（南开大学物理学院）；PRISMA ++ Cluster of Excellence & Mainz Institute for Theoretical Physics Johannes Gutenberg University（约翰内斯·古腾堡美因茨大学美因茨理论物理研究所）；Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati（意大利国家核物理研究院弗拉斯卡蒂国家实验室）
$B$-meson decays involving radiative and electroweak penguin processes are sensitive probes to new physics beyond the standard model. The Belle experiment recently reported measurements of the inclusive radiative decay $B \to X^{}_{s} γ$, and exclusive radiative decays $B \to K^{\ast} γ$ and $B \to K^{0}_{S} ηγ$. A lepton-flavor dependent measurements of angular observables for the decays $B \to K^{\ast} \ell \ell$ by Belle hinted at possible deviation from lepton-flavor-universality. Any departure from lepton flavor universality is essentially accompanied by lepton flavor violation. Recently,…
We consider lepton-flavor violation in strangeness changing ($|ΔS|=1$) semileptonic $τ$-lepton decays arising from new physics encoded in a standard model effective Lagrangian. Its invariance under the standard model gauge group entails the relevance of other processes which can serve as complementary probes of the new physics operators. We show in particular that for some of them the bounds implied by current data on the rare kaon decays involving a neutrino pair, $K\to πν\barν$, are stronger than the existing limits from direct searches for lepton-flavor-violating semileptonic $τ$ decays. We…
Motivated by recent Belle measurement of the branching ratios $B^- \to π^+ π^- K^-$ and $B^- \to K^+ K^- K^-$ and $B^\pm \to χ_{c0} K^\pm$, we investigate the CP violating asymmetry in the partial widths for the decays $B^- \to π^+ π^- K^-$ and $B^- \to K^+ K^- K^-$, which results from the interference of the nonresonant decay amplitude with the resonant amplitude $B^\pm \to χ_{c0} K^\pm $ $ \toπ^+ π^- K^\pm $ and $B^\pm \to χ_{c0} K^\pm$ $ \to K^+ K^- K^-$. By taking $γ\simeq 58^o$ we predict that the partial widths asymmetry is reaching 10% for the $B^- \to π^+ π^- K^-$ decay and 16% for the…
The recent Belle and Babar measurements of the branching ratios $B^- \to π^+ π^- K^-$ and $B^- \to K^+ K^- K^-$ and $B^\pm \to χ_{c0} K^\pm$ have renewed interests in these decays as another mean to look for direct CP violation in B decays. In this talk, I would like to discuss a recent analysis of the CP violating asymmetry in the partial widths for the decays $B^- \to π^+ π^- K^-$ and $B^- \to K^+ K^- K^-$, which results from the interference of the non resonant amplitude with the resonant amplitude $B^\pm \to χ_{c0} K^\pm $ $ \rarrπ^+ π^- K^\pm $ and $B^\pm \to χ_{c0} K^\pm$ $ \to K^+ K^- K…
We search for lepton-number- and baryon-number-violating decays $τ^{-}\to\overline{p}e^{+}e^{-}$, $pe^{-}e^{-}$, $\overline{p}e^{+}μ^{-}$, $\overline{p}e^{-}μ^{+}$, $\overline{p}μ^{+}μ^{-}$, and $pμ^{-}μ^{-}$ using 921 fb$^{-1}$ of data, equivalent to $(841\pm12)\times 10^6$ $τ^{+}τ^{-}$ events, recorded with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. In the absence of a signal, $90\%$ confidence-level upper limits are set on the branching fractions of these decays in the range $(1.8$-$4.0)\times 10^{-8}$. We set the world's first limits on the first four channels …
Axion-Like Particles (ALPs) are pseudo Nambu-Goldstone bosons associated with spontaneously broken global $U(1)$ symmetries. Such particles can have lepton-flavor-violating (LFV) couplings to the SM charged leptons. LFV ALPs provide the possibility to address some of the SM long-lasting problems. We investigate the sensitivity of a future muon collider suggested by the Muon Accelerator Program (MAP) to the production of LFV ALPs in the ALP mass range $m_a\leq1$ MeV. ALPs are assumed to be produced through the LFV decay $τ\ra\ell a$ ($\ell=e,μ$) of one of the tau leptons produced in the muon-an…
Recently BABAR and Belle have measured anomalous large transverse polarizations in some pure penguin $B \to VV$ decays, which might be inconsistent with the Standard Model expectations. We try to explore its implications for R-parity violating (RPV) supersymmetry. The QCD factorization approach is employed for the hadronic dynamics of B decays. We find that it is possible to have parameter spaces solving the anomaly. Furthermore, we have derived stringent bounds on relevant RPV couplings from the experimental data, which is useful for further studies of RPV phenomena.
We speculate about the possible interpretations of the recently observed excess in the $h \to τμ$ decay. We derive a robust lower bound on the Higgs boson coupling strength to a tau and a muon, even in presence of the most general new physics affecting other Higgs properties. Then we reevaluate complementary indirect constraints coming from low energy observables as well as from theoretical considerations. In particular, the tentative signal should lead to $τ\to μγ$ at rates which could be observed at Belle II. In turn we show that, barring fine-tuned cancellations, the effect can only be acco…
We study the implication of R-parity violating Rp Minimal Supersymmetric Standard Model (MSSM) model in lepton polarization asymmetry ALP in B l l(bar) decays . The analysis show that the ALP is significant in a certain phenomenological parametric region of Yukawa couplings. We have also placed indirect bounds on Lambda' lambda couplings as obtained from B t t(bar).
Belle II is a Super $B$ Factory experiment, expected to record 50 ab$^{-1}$ of $e^+e^-$ collisions at the SuperKEKB accelerator until 2035. The large samples of $B$ mesons, charm hadrons, and tau leptons produced in the clean experimental environment of $e^+e^-$ collisions will provide the basis of a broad and unique flavor-physics program. Belle II will pursue physics beyond the Standard Model in many ways, for example: improving the precision of weak interaction parameters, particularly Cabibbo-Kobayashi-Maskawa (CKM) matrix elements and phases, and thus more rigorously test the CKM paradigm…
Probing the CP Property of ALP-photon Interactions at Future Lepton Colliders
Center for High Energy Physics, Peking University（北京大学高能物理中心）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）；Key Laboratory of Multiscale Spin Physics (Ministry of Education), Beijing Normal University（北京师范大学多尺度自旋物理教育部重点实验室）；State Key Laboratory of Nuclear Physics and Technology, Institute of Quantum Matter, South China Normal University（华南师范大学量子物质研究院核物理与技术国家重点实验室）；Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter, Guangdong Provincial Key Laboratory of Nuclear Science（广东省基础学科研究中心（物质结构与基本相互作用）、广东省核科学重点实验室）
We discuss constraints on soft CP-violating couplings of axion-like particles with photon and fermions by using data on electric dipole moments of Standard Model particles. In particular, for the ALP leptophilic scenario we derive bounds on CP-odd ALP-photon-photon coupling from data of the {\tt ACME} Collaboration on electron EDM. We also discuss prospects of the Storage Ring experiment to constrain the ALP-photon-photon coupling from data on proton EDM for the simplified hadrophilic interactions of ALP. The regarding constraints from experimental bounds on the muon and neutron EDMs are weak.…
We discuss a minimal solution to the long-standing $(g-2)_μ$ anomaly in a simple extension of the Standard Model with an extra $Z'$ vector boson that has only flavor off-diagonal couplings to the second and third generation of leptons, i.e. $μ, τ, ν_μ, ν_τ$ and their antiparticles. A simplified model realization, as well as various collider and low-energy constraints on this model, are discussed. We find that the $(g-2)_μ$-favored region for a $Z'$ lighter than the tau lepton is totally excluded, while a heavier $Z'$ solution is still allowed. Some testable implications of this scenario in fut…
Lepton flavor violating interactions are absent in the standard model but are expected in various beyond standard models. In this work, the potential of the future circular electron-positron collider to probe the four fermion lepton flavor couplings via the $e^{+}e^{-}\rightarrow e^{\pm}τ^{\mp}$ process is revisited by means of an effective field theory approach. We provide constraints at $95\%$ CL on the dimension-six Wilson coefficients including major sources of background processes and considering realistic detector effects at four expected operation energies $\sqrt{s}=157.5$, $162.5$, $24…
We speculate about the possible interpretations of the recently observed excess in the $h \to τμ$ decay. We derive a robust lower bound on the Higgs boson coupling strength to a tau and a muon, even in presence of the most general new physics affecting other Higgs properties. Then we reevaluate complementary indirect constraints coming from low energy observables as well as from theoretical considerations. In particular, the tentative signal should lead to $τ\to μγ$ at rates which could be observed at Belle II. In turn we show that, barring fine-tuned cancellations, the effect can be accommoda…
A lot of branching ratios of the exclusive $c \to d/s\ellν_\ell$ ($\ell=e,μ$) decays have been quite accurately measured by CLEO-c, BELLE, BABAR, BES(I,II,III), ALEPH and MARKIII collaborations. We probe the R-parity violating supersymmetric effects in the exclusive $c \to d/s\ellν_\ell$ decays. From the latest experimental measurements, we obtain new upper limits on the relevant R-parity violating coupling parameters within the decays, and many upper limits are obtained for the first time. Using the constrained new parameter spaces, we predict the R-parity violating effects on the observables…
Confining hidden sectors at the GeV scale are well motivated by asymmetric dark matter and naturalness considerations and can also give interesting collider signatures. Here we study such sectors connected to the Standard Model by a TeV scale mediator charged under both QCD and the dark force. Such a mediator admits a Yukawa coupling between quarks and dark quarks which is generically flavour and $CP$ violating. We show that in contrast to expectation, electric dipole moments do not place a strong constraint on this scenario even with $O(1)$ $CP$-violating phases. We also quantitatively explor…
Axion-like particles (ALPs) with lepton-flavor violating couplings can be probed in exotic muon and tau decays. The sensitivity of different experiments depends strongly on the ALP mass and its couplings to leptons and photons. For ALPs that can be resonantly produced, the sensitivity of three-body decays such as $μ\to 3e$ and $τ\to 3μ$ exceeds by many orders of magnitude that of radiative decays like $μ\to eγ$ and $τ\toμγ$. Searches for these two types of processes are therefore highly complementary. We discuss experimental constraints on ALPs with a single dominant lepton-flavor violating co…
Lepton flavour violating (LFV) processes are a smoking gun signal of new physics (NP). If the semileptonic $B$ decay anomalies are indeed due to some NP, such operators can potentially lead to LFV decays involving the second and the third generation leptons, like $τ\to 3μ$. In this paper, we explore how far the nature of NP can be unraveled at the next generation $B$-factories like Belle-II, provided the decay $τ\to 3μ$ has been observed. We use four observables with which the differentiation among NP operators may be achieved to a high confidence level. Possible presence of multiple NP operat…
