Search for lepton flavor violation via the intense high-energy muon beam
S. Kanemura, Y. Kuno, M. Kuze, T. Ota
备注：
Contribution to the 6th International Workshop on Neutrino Factories & Superbeams(NuFact04), Jul. 26-Aug. 1, 2004, Osaka Univerisity, Osaka, Japan, talk given by S.K., to appear in the Proceedings, 3 pages, 4 figures
A deep inerastic scattering process \mutau is discussed to study lepton flavor violation between muons and tau leptons. In supersymmetric models, the Higgs boson mediated diagrams could be important for this reaction. We find that at a muon energy ($E_μ$) higher than 50 GeV, the predicted cross section significantly increases due to the contribution from sea $b$-quarks. The number of produced tau leptons can be $\mathcal{O}(10^4)$ at $E_μ$= 300 GeV from $10^{20}$ muons, whereas $\mathcal{O}(10^2)$ events are given at $E_μ= 50$ GeV.
We examine single chargino production in conjunction with R-parity lepton number violation in future lepton-lepton collisions. Present bounds on R-parity violating couplings allow for a production cross section of the order of ${\cal{O}} (10 {fb})$ for a wide range of sneutrino and chargino masses. Scenarios of chargino decay which lead to purely leptonic signals in the final state and without missing energy are also discussed.
We propose a model for the vector-like lepton to explain the small muon mass by a seesaw mechanism, based on lepton-specific two Higgs doublet models with a local $U(1)'$ symmetry. There is no bare muon mass for a nonzero $U(1)'$ charge of the leptophilic Higgs doublet, so the physical muon mass is generated due to the mixing between the vector-like lepton and the muon after the leptophilic Higgs doublet and the dark Higgs get VEVs. In this scenario, the non-decoupling effects of the vector-like lepton give rise to leading contributions to the muon $g-2$, thanks to the light $Z'$ and the light…
We explore the possibility of the existence of excited leptons in the light of recent data on muon $g - 2$ from BNL. We have been able to put stringent bounds on the relevant parameter space.
Electron-positron pair production in combined laser and Coulomb fields is studied. To this end, the Feynman diagram for multiphoton pair creation by muon impact on a circularly polarized high-frequency laser beam is evaluated within the framework of laser-dressed quantum electrodynamics employing relativistic Volkov states. In the limit of low laser intensity, the result is shown to coincide with the known expression for multiphoton pair creation by a proton which is treated as an external Coulomb field. A scaling of the total pair creation rate is analyzed. The recoil distribution is calculat…
In this paper, we consider the Standard Model (SM) with one family of vector-like (VL) leptons, which couple to all three families of the SM leptons. We study the constraints on this model coming from the heavy charged lepton mass bound, electroweak precision data, the muon anomalous magnetic moment, lepton flavor violation, Higgs decay constraints and a recently measured lepton non-universality observable, $R_{K^{*0}}$. We find that the strongest constraints are coming from the muon $g-2, \ R_{μμ}=Γ(h\toμμ)/Γ(h\toμμ)_\text{SM}, \ R_{γγ}$ and $\text{BR}(μ\to eγ)$. Although VL leptons couple to…
The differential energy distribution for electrons and taus produced from lepton pair production from muons in transit through materials is numerically evaluated. We use the differential cross section to calculate underground lepton fluxes from an incident atmospheric muon flux, considering contributions from both conventional and prompt fluxes. An approximate form for the charged current differential neutrino cross section is provided and used to calculate single lepton production from atmospheric neutrinos. We compare the fluxes of underground leptons produced from incident muons with those …
Coherent production of lepton pair in muon scattering by nucleus is considered. With the help of different approaches (equivalent photon approximation, direct numerical and analytical calculations) we obtain total cross section of this reaction and distributions over invariant masses of final leptons. Special attention is paid to influence of final lepton identity on total and differential cross sections. We also study the role of coherence condition. Total cross sections of charmonia production in muon interaction with electromagnetic field of nucleus are also presented.
An accurate simulation of the propagation of muons through matter is needed for the analysis of data produced by muon/neutrino underground experiments. A muon may sustain hundreds of interactions before it is detected by the experiment. Since a small systematic uncertainty repeated hundreds of times may lead to sizable errors, requirements on the precision of the muon propagation code are very stringent. A new tool for propagating muon and tau charged leptons through matter that is believed to meet these requirements is presented here. An overview of the program is given and some results of it…
The leptons are viewed as composite objects, exhibiting anomalous magnetic moments and anomalous flavor-changing transition moments. The decay $μ\to e γ$ is expected to occur with a branching ratio of the same order as the present experimental limit.
Lepton number is promoted to an $U(1)_L$ gauge symmetry in a simple extension of the standard model. The spontaneous breaking of $U(1)_L$ by three units allows a conserved $Z_3^L$ lepton symmetry to remain, guaranteeing that neutrinos are Dirac fermions, which acquire naturally small masses from a previously proposed mechanism. Dark matter appears as a singlet scalar, with dark symmetry $Z_3^D$ derivable from $Z_3^L$. Muon $g-2$ may be explained.
We show that the observed anomalies in the lepton sector can be explained in extensions of the Standard Model that are natural and, therefore, resolve the Higgs sector hierarchy problem. The scale of new physics is around the TeV and Technicolor-like theories are ideal candidate models.
The recent experimental status, including the confirmation of the muon $g-2$ anomaly at Fermilab, indicates a Beyond Standard Model (BSM) satisfying the following properties: 1) it enhances the $g-2$ 2) suppresses flavor violations, such as $μ\to e γ$, 3) suppresses CP violations, such as the electron electric dipole moment (EDM). In this letter, I show that if the masses of heavy leptons are generated radiatively, the eigenbasis of the mass matrix and higher dimensional photon operators can be automatically aligned. As a result, the muon $g-2$ is enhanced but the EDM of the electron and $μ\to…
In light of the ongoing effort on reducing the theoretical uncertainties and an upcoming experiment concerning muon magnetic moment, we perform a detailed study of an 3-4-1 electroweak gauge extension of the standard model that contains exotic charged leptons in its spectrum. We discuss flavor changing neutral current, collider and electroweak bounds on the model and derive $1σ$ limits using current and projected limits on the muon magnetic moment. In summary, we exclude the masses of new gauge bosons that couple to muons and heavy charged leptons up to $700$~GeV. Moreover, we find a projected…
We propose a SUSY scenario to explain the current electron and muon $g-2$ discrepancies without introducing lepton flavor mixings. Threshold corrections to the Yukawa couplings can enhance the electron $g-2$ and flip the sign of the SUSY contributions. The mechanism predicts a flavor-dependent slepton mass spectrum. We show that it is compatible with the Higgs mediation scenario.
Combining the multi-lepton searches at the LHC, we study the possibilities of accommodating the new data of muon and electron $g-2$ anomalies in the lepton-specific inert two-Higgs-doublet model. We take the heavy CP-even Higgs as the 125 GeV Higgs, and find the muon and electron $g-2$ anomalies can be explained simultaneously in the region of 5 GeV $< m_h<60$ GeV, 200 GeV $<m_A< 620$ GeV, 190 GeV $<m_{H^\pm}< 620$ GeV for appropriate Yukawa couplings between leptons and inert Higgs. Meanwhile, the model can give a better fit to the data of lepton universality in $τ$ decays than the SM. Furthe…
We estimate the beam-normal single-spin asymmetry in elastic lepton-proton scattering without employing the ultrarelativistic approximation. Our calculation is relevant for analyses of muon scattering at energies of few hundred MeV and below -- when effects of the muon mass become essential. At such energies, the transverse polarization of the muon beam is expected to contribute significantly to the systematic uncertainty of precision measurements of elastic muon-proton scattering. We evaluate such systematics using an example of the MUSE experiment at PSI. The muon asymmetry is estimated at a…
A discrepancy between the experimental and theoretical results was reported for the anomalous magnetic moment of the muon. In leptogenesis scenarios which are due to a decay of right-handed neutrinos, this anomaly leads to large violations of lepton flavour within the framework of supersymmetric see-saw models. It is shown that for a hierarchical right-handed neutrino mass spectrum, we generically expect to observe μ\to e γin the near future experiment.
Radiative muon and tau lepton decays are described within the model-independent approach with the help of generalized Michel parameters. The exact dependence on charged lepton masses is taken into account. The results are relevant for modern and future experiments on muon and tau lepton decays.
A non-universal interaction, which involves only the third family leptons induces lepton flavor violating couplings and contributes to the anomalous magnetic moment of muon. In this paper, we study the effects of non-universal interaction on muon (g-2) and rare decay $τ\to μγ$ by using an effective lagrangian technique, and a phenomenological $Z^\prime$ model where $Z^\prime$ couples only to the third family lepton. We find that the deviation from the theory can be explained and the induced $τ\to μγ$ rate could be very close to the current experimental limit. In the $Z^\prime$ model, $M_{Z^\pr…
Any observation of charged lepton flavor violation (CLFV) implies the existence of new physics beyond the SM in charged lepton sector. CLFV interactions may also contribute to the muon magnetic moment and explain the discrepancy between the SM prediction and the recent muon $g-2$ precision measurement at Fermilab. We consider the most general SM gauge invariant Lagrangian of $ΔL=0$ bileptons with CLFV couplings and investigate the interplay of low-energy precision experiments and colliders in light of the muon magnetic moment anomaly. We go beyond previous work by demonstrating the sensitivity…
In this work we compute all relevant contributions stemming from the economical 3-3-1 model to the muon magnetic moment and the lepton flavor violation decay $μ\rightarrow eγ$. Using the current bounds on these phenomena, we derive lower limits on the scale of symmetry breaking of the model. Moreover, taking into account existing limits from meson and collider studies we show that there is still room for a possible signal in $μ\rightarrow eγ$ in the near future.
We calculate the anomalous magnetic moment for muons at one loop level arising from left right symmetric excited leptons which are excited states of known standard model leptons. Such excited states arise in compositeness theories where the known leptons are assumed to be made of more fundamental particles. In this work, we assume that the excited leptons possess a left right symmetry also. We show that at the one loop level, the QED contribution to the muon anomalous magnetic moment from these excited leptons comes from only one Feynman diagram, which turns out to be a natural analog of the o…
We study the lepton-flavor-violating reaction $μ^+ e^- \to e^+ e^-$ within two extensions of the standard model that include heavy neutrinos. The reaction is studied in the low energy limit in the form of muonium decay $M\to e^+ e^-$ and in the high energy regime of a muon collider. The two theoretical models we consider are: model I, a typical see-saw model that violates lepton flavor and number by inclusion of extra right handed neutrinos, and model II, a variant where lepton number is conserved and which includes extra right handed as well as left handed neutrinos, singlets under the gauge …
We consider a simple extension of the Standard Model (SM) with a vector-like lepton and a local $U(1)'$ symmetry, motivated by the recent experimental anomalies in the muon $g-2$ and the $W$ boson mass. The $U(1)'$ symmetry is spontaneously broken by the VEVs of the dark Higgs scalar and the second Higgs doublet, giving rise to the mixing between the muon and the vector-like lepton. As a result, we obtain the desirable corrections to the muon $g-2$ and the $W$ boson mass simultaneously, dominantly due to the $Z'$ gauge interactions for the vector-like lepton and the second Higgs doublet, respe…
A lepton-flavor violating (LFV) Z' boson may mimic some of the phenomena usually attributed to supersymmetric theories. Using a conservative model of LFV Z' bosons, the recent BNL E821 muon g-2 deviation allows for a LFV Z' interpretation with a boson mass up to 4.8 TeV while staying within limits set by muon conversion, mu -> e gamma, and mu -> eee. This model is immediately testable as one to twenty e^+e^- -> mu tau events are predicted for an analysis of the LEP II data. Future muon conversion experiments, MECO and PRIME, are demonstrated to have potential to probe very high boson masses wi…
Structure of leptons and hadrons within the framework of electrodynamics is considered. Muon and tau-lepton have the structure of 3 electrons. The mass of muon is defined by the section of two-photon annihilation. The mass of tau-lepton is defined by the section of three-photon annihilation. Hadrons are characterized by the structure of 5 electrons. The masses of hadrons are defined via the masses of muon and tau-lepton.
We study effects of unparticle physics on muon g-2 and LFV tau decay processes. LFV interactions between the Standard Model sector and unparticles can explain the difference of experimental value of muon g-2 from the Standard Model prediction. While the same couplings generate LFV tau decay, we found that LFV coupling can be of O(0.1 ... 1) without conflict with experimental bounds of LFV tau decay if the scaling dimension of unparticle operator d_{U} > 1.6.
We investigate the kinetic heating of neutron stars due to dark matter scattering in minimal models with scalar lepton partners mediating interactions which can account for the anomalous magnetic moment of the muon. In particular, such models in which the dark matter is a thermally produced Majorana fermion can be extremely difficult to detect at conventional searches. We demonstrate that future infrared observations of an old neutron star population could definitively probe the entire parameter space of this scenario.
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…
The coherent muon-electron conversion rates in various nuclei are calculated for general lepton flavor violating interactions. We solve the Dirac equations numerically for the initial state muon and the final state electron in the Coulomb force, and perform the overlap integrals between the wave functions and the nucleon densities. The results indicate that the conversion branching ratio increases for a light nucleus up to the atomic number Z ~ 30, is largest for Z = 30 -- 60, and becomes smaller for a heavy nucleus with Z > (~ 60). We also discuss the uncertainty from the input proton and neu…
The confirmation of the discrepancy with the Standard Model predictions in the anomalous magnetic moment by the Muon g-2 experiment at Fermilab points to a low scale of new physics. Flavour symmetries broken at low energies can account for this discrepancy but these models are much more restricted, as they would also generate off-diagonal entries in the dipole moment matrix. Therefore, if we assume that the observed discrepancy in the muon $g-2$ is explained by the contributions of a low-energy flavor symmetry, lepton flavour violating processes can constrain the structure of the lepton mass m…
We show that in a two Higgs doublet model type-II extended by vectorlike leptons the contributions from heavy neutral and charged Higgs bosons to the anomalous magnetic moment of the muon simultaneously feature chiral enhancement from masses of new leptons and $\tan^2 β$ enhancement from couplings of Higgs bosons. Assuming moderate values of new Yukawa couplings, not exceeding one, that can remain perturbative to very high energy scales, the measured value of muon $g-2$ can be explained within one standard deviation even with 6.5 TeV leptons or 20 TeV Higgs bosons. Allowing new couplings near …
We describe a possibility to explain the $2.6σ$ deviation from lepton flavour universality observed by the LHCb collaboration in $B^+\to K^+\ell^+\ell^-$ decays in the context of minimal composite Higgs models. We find that a sizable degree of compositeness of partially composite muons can lead to a good agreement with the experimental data. Our construction predicts a new physics contribution to $B_s$-$\bar{B}_s$ mixing. Additionally, it accounts for the deficit in the invisible $Z$ width measured at LEP.
Current experimental data from the $g-2$ muon factor, seems to show the necessity of physics beyond the Standard Model (SM), since the difference between SM and experimental predictions is 2.6$σ$. In the framework of the General Two Higgs Doublet Model (2HDM), we calculate the muon anomalous magnetic moment to get lower and upper bounds for the Flavour Changing (FC) Yukawa couplings in the leptonic sector. We also obtain lower bounds for the mass of the pseudoscalar Higgs ($m_{A^0}$) as a function of the parameters of the model.
We present a new class of constraints to the lepton-family number and R-parity violating couplings from muonium conversion, $μ^{-} + {_{22}^{48}} Ti \to e^{-} + {_{22}^{48}} Ti$, a class of tau decays, $τ\to l +$ (light meson) with $l= μor e$, and $J/ψ$ and $π^0$ decays into a lepton pair. We find that $μ^{-} + {_{22}^{48}} Ti \to e^- + {_{22}^{48}} Ti$ provides one of the strongest constraints along with $Δm_{K}, Δm_{B}$, $μ\to e γ$ and the neutrinoless double $β$ decay. Search for these lepton-family number violating (LFNV) decays forbidden in the standard model is clearly warranted in vario…
The effect on particle physics processes by intense electromagnetic fields in the charge bunch collisions at future lepton colliders is considered. Since the charge bunch fields are tied to massive sources (the $e^{+}e^{-}$ charges), a reference frame is chosen in which the fields appear to be co-propagating. Solutions of the Dirac equation minimally coupled to the electromagnetic fields reasonably associated with two intense overlapping charge bunches are obtained and found to be a Volkov solution with respect to a null 4-vector whose 3-vector part lies in the common propagation direction. Th…
We study the search potential of heavy triplet leptons in Type III Seesaw mechanism at future high-energy and high-luminosity muon colliders. The impact of up-to-date neutrino oscillation results is taken into account on neutrino parameters and the consequent decay patterns of heavy leptons in Type III Seesaw. The three heavy leptons in the Casas-Ibarra parametrization with diagonal unity matrix are distinguishable in their decay modes. We consider the pair production of charged triplet leptons $E^+ E^-$ through both $μ^+μ^-$ annihilation and vector boson fusion (VBF) processes. The leading-or…
We reevaluate electron-positron pair production from electromagnetic interactions of muons in transit through materials. Our approach, through the use of structure functions for inelastic and elastic scattering and including hadronic recoil, make the formalism useful for tau pair production at high energies. Our results for electron-positron pair production agree well with prior evaluations. Tau pair production, has a significant contribution from inelastic scattering in addition to the usual coherent scattering with the nucleus and scattering with atomic electrons.
New heavy Majorana and Dirac neutrinos production at future electron-muon colliders are investigated. The production of a single heavy neutrino is shown to be more relevant than pair production when comparing cross sections and neutrino mass ranges. The process $e^\pm μ^\mp \longrightarrow ν \ell^{\pm} W^{\mp}$ is studied including on-shell and off-shell heavy neutrino effects. Distributions are calculated including hadronization effects and experimental cuts that suppress background, in order to have a clear signal for heavy neutral leptons.
We consider the contributions to $g_μ-2$ from fourth generation heavy neutral and charged leptons, $N$ and $E$, at the one-loop level. Diagrammatically, there are two types of contributions: boson-boson-$N$, and $E$-$E$-boson in the loop diagram. In general, the effect from $N$ is suppressed by off-diagonal lepton mixing matrix elements. For $E$, we consider flavor changing neutral couplings arising from various New Physics models, which are stringently constrained by $μ\to eγ$. We assess how the existence of a fourth generation would affect these New Physics models.
In the framework of the MSSM extension with local gauged baryon and lepton numbers (BLMSSM), we calculate the muon anomalous magnetic dipole moment (MDM) and lepton $(e, μ, τ)$ electric dipole moment (EDM), and discuss how the muon MDM and lepton EDM depend on the parameters within the mass insertion approximation. Among many parameters, $\tanβ$,~$g_L$,~$m_L$ and $μ_H$ are more sensitive parameters for $a^{BL}_μ$. Considering the experimental limitations, our best numerical result of $a^{BL}_μ$ is around $2.5 \times 10^{-9}$, which can well compensate the departure between the experiment data …
Lepton Flavor Violation: From Muon Decays to Muon Colliders
University of California Santa Cruz（加州大学圣克鲁兹分校）；University of Oregon（俄勒冈大学）；University of Chicago（芝加哥大学）；Harvard University（哈佛大学）；University of California, Berkeley（加州大学伯克利分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；University of Pittsburgh（匹兹堡大学）；Cornell University（康奈尔大学）；Institute for Advanced Study（普林斯顿高等研究院）；New York University（纽约大学）
We consider the contributions to $g_μ-2$ from fourth generation neutral and charged leptons, $N$ and $E$, at the one-loop level. Diagramatically, there are two types of contributions: boson-boson-$N$, and $E$-$E$-boson in the loop diagram. In general, the effect from $N$ is suppressed by off-diagonal PMNS matrix element $V_{Nμ}$, from the Standard Model to the Two-Higgs Doublet Models. With contribution from $E$, we consider flavor changing neutral couplings.
We propose a novel model for lepton flavor and dark matter based on the $SU(2)_D$ gauge symmetry and vector-like leptons in its fundamental representations. We introduce a dark $SU(2)_D$ Higgs doublet and a Higgs bi-doublet for the mass mixing between the vector-like lepton and the lepton. As a result, the seesaw lepton masses are generated and there are sizable one-loop contributions to the muon $g-2$ via the $SU(2)_D$ gauge bosons and the relatively heavy vector-like lepton, as indicated in Fermilab E989. The tree-level mass mixing between the $Z$ boson and the isospin neutral gauge boson of…
We investigate the muon anomalous magnetic dipole moment (MDM), the muon electric dipole moment (EDM) and the lepton-flavour-violating decays of the $τ-$lepton, $τ\to μγ$ and $τ\to 3μ$, in the CP-violating Minimal Supersymmetric Standard Model (MSSM) with nonuniversal soft-supersymmetry breaking. We evaluate numerically the muon EDM and the branching ratios $B(τ\to μγ)$ and $B(τ\to 3μ)$, after taking into account the experimental constraints from the electron EDM and muon MDM. Upon imposition of the experimental limits on our theoretical predictions for the aforementioned branching ratios and …
We show that new physics explanations of the muon $g-2$ anomaly by the contributions of new leptons mediated by the standard model Higgs boson necessarily lead to large rates for $μ^+ μ^- \to hh$ and $μ^+ μ^- \to hhh$ irrespectively of details of the model or the scale of new physics. For new leptons with the same quantum numbers as the standard model leptons, cross sections are expected to be about 240 ab for $μ^+ μ^- \to hh$ independently of the center of mass energy, $\sqrt{s}$, and about 2.7 ab for $μ^+ μ^- \to hhh$ for $\sqrt{s} = 1$ TeV and growing quadratically with $\sqrt{s}$. Predicti…
We give a thorough analysis of the correlation between the muon anomalous magnetic moment and the radiative lepton flavor violating (LFV) processes within the minimal supersymmetric standard model. We find that in the case when the slepton mass eigenstates are nearly degenerate, $δa_μ$, coming from SUSY contributions, hardly depends on the lepton flavor mixing and, thus, there is no direct relation between $δa_μ$ and the LFV processes. On the contrary, if the first two generations' sleptons are much heavier than the 3rd one, i.e., in the effective SUSY scenario, the two quantities are closely …
We examine the lepton dipole moments in an extension of the Standard Model (SM), which contains vector-like leptons that couple only to the second-generation SM leptons. The model naturally leads to sizable contributions to the muon $g-2$ and the muon electric dipole moment (EDM). One feature of this model is that a sizable electron EDM is also induced at the two-loop level due to the existence of new vector-like leptons in the loops. We find parameter regions that can explain the muon $g-2$ anomaly and are also consistent with the experimental constraints coming from the electron EDM and the …
