Search For Lepton Flavor Violation Research Articles

Using the e ± µ∓ + E T miss signature in the search for supersymmetry and lepton-flavor violation in neutralino decays

The LHC (CMS) discovery potential in the search for supersymmetry and lepton-flavor violation in neutralino decays using the e ± µ∓ + E T miss signature is studied. A detailed study is done for the CMS test points LM1-LM9. It is shown that, for the point LM1, it is possible to detect lepton-flavor violation in neutralino decays with lepton-flavor-violating branching Br( $$\tilde \chi _2^0 $$ → µ± e ∓ $$\tilde \chi _1^0 $$ ) ≥ 0.04 Br( $$\tilde \chi _2^0 $$ → e + e − $$\tilde \chi _1^0 $$ , µ+ µ− $$\tilde \chi _1^0 $$ ) for an integral luminosity of 10 fb−1. The discovery potential in the mSUGRA-SUSY scenario with tan β = 10, sgn(µ) = + in the (m 0, m 1/2) plane using the e ± µ∓ + E T miss signature is determined.

Search for lepton-flavor violation at HERA

A search for lepton-flavor-violating interactions $e p \to \mu X $ and $e p\to \tau X $ has been performed with the ZEUS detector using the entire HERA I data sample, corresponding to an integrated luminosity of 130 pb^{-1}. The data were taken at center-of-mass energies, $\sqrt{s}$, of 300 and 318 GeV. No evidence of lepton-flavor violation was found, and constraints were derived on leptoquarks (LQs) that could mediate such interactions. For LQ masses below $\sqrt{s}$, limits were set on $\lambda_{eq_1} \sqrt{\beta_{\ell q}}$, where $\lambda_{eq_1}$ is the coupling of the LQ to an electron and a first-generation quark $q_1$, and $\beta_{\ell q}$ is the branching ratio of the LQ to the final-state lepton $\ell$ ($\mu$ or $\tau$) and a quark $q$. For LQ masses much larger than $\sqrt{s}$, limits were set on the four-fermion interaction term $\lambda_{e q_\alpha} \lambda_{\ell q_\beta} / M_{\mathrm{LQ}}^2$ for LQs that couple to an electron and a quark $q_\alpha$ and to a lepton $\ell$ and a quark $q_\beta$, where $\alpha$ and $\beta$ are quark generation indices. Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks in $R$-Parity-violating supersymmetric models. In some cases, especially when a higher-generation quark is involved and for the process $e p\to \tau X $, the ZEUS limits are the most stringent to date.

Hadronic EDM constraints on orbifold GUTs

We point out that the null results of the hadronic electric dipole moment (EDM) searches constrain orbifold grand unified theories (GUTs), where the GUT symmetry and supersymmetry (SUSY) are both broken by boundary conditions in extra dimensions and it leads to rich fermion and sfermion flavor structures. A marginal chromoelectric dipole moment (CEDM) of the up quark is induced by the misalignment between the CP violating left- and right-handed up-type squark mixings, in contrast to the conventional four-dimensional SUSY GUTs. The up quark CEDM constraint is found to be as strong as those from charged lepton flavor violation (LFV) searches. The interplay between future EDM and LFV experiments will probe the structures of the GUTs and the SUSY breaking mediation mechanism.

A SEARCH FOR LEPTON FLAVOR VIOLATION IN TAU DECAYS ATBABAR

We present a recent BABAR search for lepton flavor violation in tau decays. The search for τ → ℓℓℓ(ℓ = e, μ) decays is based on a data sample of 91.6 fb-1. No signal is found in any of six channels and 90% CL upper limits are set in the range of (1 - 3) × 10-7. The search for τ → μγ decay is done with a 63 fb-1data sample. The number of observed events is consistent with expected background level and a preliminary upper limit is set at 2 × 10-6at 90% CL.

Is it still interesting to search for lepton-flavor violation in rare kaon decays?

Further possibilities of experiments aimed at searches for lepton-flavor violation in kaon decays at present and future intermediate-energy accelerators are considered. It is shown that such investigations are complementary to searches for muonic lepton-flavor-violating processes and can possess, in some models featuring approximately conserved generation quantum numbers of fundamental fermions, a very high and even record sensitivity. Searches for lepton-flavor-violating processes in kaon decays should be considered as a very important and independent part of the general program of searches for the violation of lepton flavors in processes involving charged leptons.

Search for lepton flavor violation via the intense high-energy muon beam

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 ($E_{\mu}$) 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 $E_{\mu}$= 300 GeV from $10^{20}$ muons, whereas $\mathcal{O}(10^2)$ events are given at $E_{\mu}= 50$ GeV.

Lepton Flavor Violation in rare muon decays

The current status of the experimental search for lepton flavor violation in rare muon decays is reviewed. The possible benefits of increasing the muon source intensity is examined for the different experimental situations.

Search for Lepton Flavour Violation (LFV) in Three-Body Tau Decays at BaBar

The results of searches for Lepton Flavour Violating (LFV) decays at the BaBar detector located on the PEP-II collider, using data collected at an e+e− energy of 10.58 GeV, are presented. Upper limits at 90% Confidence Level (CL) are established in the range 1 - 3×10−7 for six τ→lll modes using 91.5 fb−1 of data and in the range 0.7 - 4.8×10−7 for fourteen τ→lhh modes using 221.4 fb−1 of data. The τ→lhh results are preliminary.

Physics at a Neutrino Factory Complex

A Neutrino Factory based on a muon storage ring is the most powerful tool invented so far to study neutrino oscillations, having the best sensitivity and precision on the mixing angles θ 23 and θ 13 as well as on the CP violating phase δ. Parameter ambiguities can be solved in most cases thanks to the availability of a well understood flux of ν e of high energy, allowing study of the golden and silver channels ν e → ν μ and ν e → ν τ respectively. Short baseline physics allows precision tests of the Standard Model and unprecedented DIS studies. The potent muon source should allow improved search for lepton flavour violation. Last but not least the Neutrino Factory is the first step towards muon colliders.

Search for Lepton Flavor Violation in the Higgs Boson Decay at a Linear Collider

Search for Lepton Flavor Violation in the Higgs Boson Decay at a Linear Collider

Indirect search for lepton flavor violation at CERN LEP via doubly charged bileptons

We search for lepton flavour violating couplings via doubly charged bilepton (or doubly charged Higgs) exchange in electron-positron annihilation process $ \text{e}^{+}\text{e}^{-}\to \mu^{+}\mu^{-}, \tau^{+}\tau^{-}$ using CERN LEP data at the center of mass energies between 189-207 GeV. Standard model program ZFITTER has been used to calculate radiative corrections. We find that $g_{L}^{2}/M_{L}^{2}<O(10^{-6})GeV^{-2}$ at 95% C.L. for flavour violating scalar and vector bilepton couplings.

Search for lepton flavor violation in the Higgs boson decay at a linear collider

We discuss possibility of direct search for lepton flavor violation (LFV) in Yukawa interaction by measuring the branching ratio for the decay of the lightest Higgs boson (h0) into a τ–μ pair at a linear collider (LC). We study the significance of the signal process, e+e−→Z*→Zh0→Zτ±μ∓, against the backgrounds such as e+e−→Zτ+τ−→Zτ±μ∓+ missings. After taking appropriate kinematic cuts, the number of the background event is considerably reduced, so that the signal can be visible when the branching ratio of h0→τ±μ∓ is larger than about 10−4. In a minimal supersymmetric Standard Model scenario, the effective coupling of h0τ±μ∓ can be generated at the loop level due to the slepton mixing. When supersymmetric mass parameters are larger than TeV scales, the branching ratio can be as large as several times 10−4. Therefore, the signal can be marginally visible at a LC. In the general two-Higgs-doublet model, the possible maximal value for the branching ratio of h0→τ±μ∓ can reach to a few times 10−3 within the available experimental bound, so that we can obtain larger significance.

Lepton Flavor Violation, Neutralino Dark Matter and the Reach of the LHC

We revisit the phenomenology of the Constrained MSSM with right-handed neutrinos (CMSSMRN). A supersymmetric seesaw mechanism, generating neutrino masses and sizable lepton flavour violating (LFV) entries is assumed to be operative. In this scheme, we study the complementarity between the `observable ranges' of various paths leading to the possible discovery of low energy SUSY: the reach of the Cern Large Hadron Collider (LHC), the quest for neutralino dark matter signals and indirect searches through LFV processes. Within the regions of the CMSSMRN parameter space compatible with all cosmo-phenomenological requirements, those which are expected to be probed at the LHC will be typically also accessible to upcoming LFV experiments. Moreover, parameter space portions featuring a heavy SUSY particle spectrum could be well beyond LHC reach while leaving LFV searches as the only key to get a glimpse on SUSY.

Search for leptoquark production and lepton flavour violation

Direct and indirect leptoquark searches performed at LEP, HERA and the Tevatron are reviewed. No signal of leptoquark production or exchange is observed. Complementary limits are obtained from different processes and different experiments. PACS: 13.85.Rm Limits on production of particles

Muon physics at a neutrino factory**Presented at NuFact02: The 4th International Workshop on Neutrino Factories, 1–6 June 2002. (A compilation of articles from this workshop was published in J. Phys. G: Nucl. Part. Phys. 29 (2003) issue 8.)

A neutrino factory could deliver beams of low-energy muons thousand times more intense than available today. In this paper I will review the field of muon physics and discuss what experiments could benefit most from such high-intensity beams. Emphasis will be given on experiments in particle physics, i.e. the determination of the muon anomalous magnetic moment and searches for charged lepton flavour violation.

The PRISM project at the high-intensity proton machine project

PRISM is a project in Japan to make a high-intensity low-energy muon source with a narrow energy-spread and high purity[1]. In this report, we give an overview of the PRISM project, its physics applications, especially to a search for muon lepton flavor violation and its future extension toward a neutrino factory.

Searching for muon to electron conversion below the 10 −16 level

The Muon-to-Electron COnversion, or MECO experiment [1] at Brookhaven National Laboratory seeks to detect coherent, neutrinoless conversion of a muon into an electron in the field of a nucleus with a rate sensitivity four orders of magnitude lower than existing limits. I will review the current limits of charged lepton flavor violation search experiments, which presently range from 10 to slightly below 10 [2]. Recent observations of neutrino oscillation at Super-Kamiokande [3] imply that neutrinos both have mass and mix, but neutrino mixing alone yields an inaccessibly low rate of μN → eN , hence observation of a signal requires fundamentally new physics. I will highlight a few of the numerous extensions of the Standard Model that predict an observable signal at the 10 level. I will present a detailed description of the MECO experiment, which utilizes several new techniques to reach this level. These include the use of a high Z target and an axially graded solenoidal field in the production region, transport in a combination of solenoids and toroidal sections to filter the muon beam, and situating the muon stopping target within a second axially graded field to increase the acceptance of conversion electrons. If Γ(μN → eN)/Γ(μN → νμN ) = 10 MECO should observe 5 events with a background of 0.45 events. I will conclude with a summary of the present status of the experiment.

PRISM Overview

The PRISM project has been proposed to obtain a high-intensity slow muon beam. By employing two novel techniques, i.e., high-field pion capture and a longitudinal phase rotation, an intense (10 11– 10 12 μ/ s ), monochromatic ( ΔE/E≃ a few %) , and low-energy ( 20 MeV ) muon beam can be produced. Muon beam with such features enable searches for lepton flavor violation at an unprecedented level as well as new field of muon application.

Neutrino masses and lepton-flavor violation in a supersymmetric model with lopsided Froggatt–Nielsen charges

We analyze in detail lepton-flavor violation (LFV) in the charged-lepton sector, such as μ→eγ and τ→μγ within the framework of supersymmetric models with lopsided Froggatt–Nielsen charges. We show that the present experimental limits on the LFV processes already exclude some of the models. The proposed future search for LFV, especially in muon processes, can provide a significant probe to this framework.

Flavor mixing in slepton production at the CERN Large Hadron Collider

The measurement of lepton-flavor violation (LFV) in the minimal SUSY standard model at the CERN Large Hadron Collider (LHC) is discussed based on a realistic simulation. We consider the LFV decay of the second-lightest neutralino, ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{2}^{0}\ensuremath{\rightarrow}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{l}{l}^{\ensuremath{'}}\ensuremath{\rightarrow}{\mathrm{ll}}^{\ensuremath{'}}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\chi}}}_{1}^{0},$ in the case where flavor mixing exists in the right-handed sleptons. We scan the parameter space of the minimal supergravity model (MSUGRA) and a more generic model in which we take the Higgsino mass $\ensuremath{\mu}$ as a free parameter. We find that the possibility of observing LFV at LHC is higher if $\ensuremath{\mu}$ is smaller than the MSUGRA prediction; the LFV search at LHC can cover the parameter range where the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\mu}}e\ensuremath{\gamma}$ decay can be suppressed by cancellation among the diagrams for this case.