In this paper the production cross section $pp\rightarrow (γ, Z) \to ν_τ\bar ν_τγ+X$ in $pp$ collisions at $\sqrt{s}=8, 13, 14, 33TeV$ is presented. Furthermore, we estimate bounds at the $95\%C. L.$ on the dipole moments of the tau-neutrino using integrated luminosity of ${\cal L}=20, 50, 100, 200, 500, 1000, 3000 fb^{-1}$ collected with the ATLAS detector at the LHC and we consider systematic uncertainties of $δ_{sys}=0, 5, 10\%$. It is shown that the process under consideration is a good prospect for probing the dipole moments of the tau-neutrino at the LHC.
The tau anomalous magnetic moment (a_tau) and electric dipole moment (d_tau) have not yet been observed. The present bounds on their values are of order 10^-2 and 10^-17 e*cm, respectively. We propose to measure a_tau with a precision of O(10^-3) or better and improve the existing limits on d_tau using precise tau- -> l- nu_tau \bar{nu}_l gamma (l=e or mu) data from high-luminosity B factories. A detailed feasibility study of this method is underway.
We discuss upper limits on the electric dipole moments (EDM) of the tau-lepton, heavy quarks, and W-boson, which follow from the precision measurements of the electron and neutron EDM.
We study the sensitivity of the LHC, with 20 inverse-fb of data, to lepton flavour violating Higgs boson decays h -> tau+ mu- (and h -> tau+ e-). We consider the large population of Higgses produced in gluon fusion, combined with leptonic decays of the tau, and estimate that the LHC could set a 95 % confidence level bound BR(h -> tau mu) < 4.5 \times 10^{-3}. This correponds to a coupling of order the Cheng-Sher ansatz y_{tau mu} = sqrt{m_tau m_mu/v^2}.
Motivated by the Galactic Center gamma-ray excess in the Fermi-LAT data, we study the signatures of a class of tau portal dark matter (DM) models where DM particles preferentially couple to tau leptons at the LHC. We consider the constraints from the DM direct detection and investigate the sensitivity of the LHC to di-tau plus missing energy signatures. We find that the LHC with a high luminosity of 3000 fb$^{-1}$ can test the tau portal DM models with fermionic mediators in the mass range of $120\sim450$ GeV.
Using the effective Lagrangian formalism, the anomalous magnetic and electric dipole moments of the tau-lepton in the $μ^{+}μ^{-} \rightarrow μ^{+}γ^{*} γ^{*} μ^{-}\rightarrow μ^{+}τ\barτμ^{-}$ process at the future muon colliders at the $\sqrt{s}=1.5, 3$ and $6$ TeV are investigated. In addition, the bounds at the $95\%$ confidence level on the dipole moments of the tau-lepton using different integrated luminosities are estimated. It is shown that the $μ^{+}μ^{-} \rightarrow μ^{+}γ^{*} γ^{*} μ^{-}\rightarrow μ^{+}τ\barτμ^{-}$ process leads to a remarkable improvement in the existing experimen…
The total cross-sections measured at LEP for e+e- annihilation into tau+tau-, c\bar{c} and b\bar{b} at 2E ~ 200 GeV are used to derive the upper limits 3*10^{-17}, 5*10^{-17}, 2*10^{-17} e*cm for the electric dipole moments and 4*10^{-17}, 7*10^{-17}, 2.5*10^{-17} e*cm for the weak dipole moments of the tau-lepton, c-, and b-quarks, respectively. Some of the existing limits on these moments are improved and for the b-quark the improvement is rather significant.
The tau lepton plays important role in distinguishing neutrino mass patterns and determining the chirality nature in heavy scalar mediated neutrino mass models, in the light of the neutrino oscillation experiments and its polarization measurement. We investigate the lepton flavor signatures with tau lepton at LHC upgrades, i.e. HL-LHC, HE-LHC and FCC-hh, through leptonic processes from doubly charged Higgs in the Type II Seesaw. We find that for the channel with one tau lepton in final states, the accessible doubly charged Higgs mass at HL-LHC can reach 655 GeV and 695 GeV for the neutrino mas…
We show how the sum of the two average tau polarisations in the decay chain chi20 -> stau1 tau -> tau tau chi10 in minimal supersymmetry with conserved R-parity can be measured at the LHC. This is accomplished by exploiting the polarisation dependence of the visible di-tau mass spectrum. Such a measurement provides information on the couplings of the involved SUSY particles and allows a more precise determination of the di-tau mass endpoint. If different tau decay modes can be distinguished, the polarisation and endpoint measurement can be improved even further.
It is shown that the electric dipole moment of the tau lepton several orders of magnitude larger than predicted by the standard model can be generated from mixings in models with vector like mutiplets. The EDM of the tau lepton arises from loops involving the exchange of the W, the charginos, the neutralinos, the sleptons, the mirror leptons, and the mirror sleptons. The EDM of the Dirac tau neutrino is also computed from loops involving the exhange of the W, the charginos, the mirror leptons and mirror sleptons. A numerical analysis is presented and it is shown that the EDMs of the tau lepton…
CP violation at low energy is investigated at the tau electromagnetic vertex. High statistics at B factories, and on top of the Upsilon resonances, allows a detailed investigation of CP-odd observables related to the tau-pair production. The contribution of the tau electric dipole moment is considered in detail. We perform an analysis independent from the high energy data by means of correlation and linear spin observables at low energy. We show that different CP-odd asymmetries, associated to the normal-transverse and normal-longitudinal correlation terms can be measured at low energy acceler…
We investigate the dipole moments of the tau- neutrino at high-energy and high luminosity at linear electron positron colliders, such as CLIC or ILC through the analysis of the reaction $e^{+}\, e^{-}\rightarrow ν\, \bar ν\,γ$ in the framework of the $SU(4)_L \times U(1)_X$ model. The limits on dipole moment were obtained for integrated luminosity of $\cal{L}$= 500-2000\, fb$^{-1}$ and center of mass between 0.5 and 3.0 TeV. The estimated limits for the tau-neutrino magnetic and electric dipole moments are improved by 2-3 orders of magnitude and complement previous studies on the dipole moment…
We obtain limits on the electromagnetic and weak dipole moments of the tau-lepton in the framework of a Left-Right symmetric model (LRSM) and a class of $E_6$ inspired models with an additional neutral vector boson $Z_θ$. Using as an input the data obtained by the L3 and OPAL Collaborations for the reaction $e^+e^-\to τ^+τ^-γ$, we get a stringent limit on the LRSM mixing angle $ϕ$, $-1.66\times 10^{-3}< ϕ<1.22\times 10^{-3}$, which in turn induces bounds on the tau weak dipole moments which are consistent with the bounds obtained recently by the DELPHI and ALEPH Collaborations from the reactio…
We study the implications of the searches based on H -> tau^+ tau^- by the ATLAS and CMS collaborations on the parameter space of the two Higgs doublet model (2HDM). In the 2HDM, the scalars can decay into a tau pair with a branching ratio larger than the SM one, leading to constraints on the 2HDM parameter space. We have also discussed the implications for the 2HDM of the recent di-muon search by the ATLAS collaboration for a CP-odd scalar in the mass range 4-12 GeV.
From the total cross section for the reaction $e^+e^-\to τ^+τ^-γ$ at the $Z_1$ pole and in the framework of a simplest little Higgs model (SLHM), we get a limit on the characteristic energy scale of the model $f$, $f \geq 5.4$ $TeV$, which in turn induces bounds on the electromagnetic and weak dipole moments of the tau-lepton. Our bounds on the electromagnetic moments are consistent with the bounds obtained by the L3 and OPAL collaborations for the reaction $e^+e^-\to τ^+τ^-γ$. We also obtained bounds on the tau weak dipole moments which are consistent with the bounds obtained recently by the …
If neutral Higgs bosons will be discovered at the CERN Large Hadron Collider (LHC) then an important subsequent issue will be the investigation of their CP nature. Higgs boson decays into tau lepton pairs are particularly suited in this respect. Analyzing the three charged pion decay modes of the tau leptons and taking expected measurement uncertainties at the LHC into account, we show that the CP properties of a Higgs boson can be pinned down with appropriately chosen observables, provided that sufficiently large event numbers will eventually be available.
In this paper, using the Bestest Little Higgs Model (BLHM) we calculate at the one-loop level the contributions to the Anomalous Magnetic Dipole Moment (AMDM) and Anomalous Weak Magnetic Dipole Moment (AWMDM) of the tau-lepton. The implications from this model are study, emphasizing the contributions of the new physics induced by the new scalar and vector bosons of the BLHM: $S_i=H_0, A_0, ϕ^{0}, η^{0}, σ, H^{\pm}, ϕ^{\pm}, η^{\pm}$, and $V_i=Z', W'$, because these quantify the new physics. With these new contributions we estimated bounds on both the real and imaginary parts of the AMDM and AW…
We discuss the possible enhancement of the tau lepton events at LHC when the left-handed stau doublet becomes light (which can be even lighter than the right-handed stau). This is illustrated in the constrained supersymmetric seesaw model where the slepton doublet mass is suppressed by the effects of a large neutrino Yukawa coupling. We study a few representative parameter sets in the sneutrino coannihilation regions where the tau sneutrino is NLSP and the stau coannihilation regions where the stau is NLSP both of which yield the thermal neutralino LSP abundance determined by WMAP.
We obtain limits on the anomalous magnetic and electric dipole moments of the $ν_τ$ through the reaction $e^{+}e^{-}\rightarrow ν\bar νγ$ and in the framework of a 331 model. We consider initial-state radiation, and neglect $W$ and photon exchange diagrams. The results are based on the data reported by the L3 Collaboration at LEP, and compare favorably with the limits obtained in other models, complementing previous studies on the dipole moments.
We conduce a study to probe the sensitivity of the process $e^+e^-\rightarrow (γ, Z) \to ν_τ\bar ν_τγ$ to the total cross section, the magnetic moment and the electric dipole moment of the tau-neutrino in a model-independent way. For this study, the beam polarization facility at the Compact Linear Collider (CLIC) along with the typical center-of-mass energies $\sqrt{s}=380-3000\hspace{0.8mm}GeV$ and integrated luminosities ${\cal L}=10-3000\hspace{0.8mm}fb^{-1}$ is considered. We estimate the sensitivity at the $95\%\hspace{1mm}$ Confidence Level (C.L.) and systematic uncertainties $δ_{sys}=0,…
In this study, we investigate the potential of the process $pp\rightarrow pγ^{*} p\rightarrow p τ\barν_τq^{\prime} X$ at the LHC to examine the anomalous electromagnetic moments of the tau lepton. We obtain $95\%$ confidence level bounds on the anomalous coupling parameters with various values of the integrated luminosity and center-of-mass energy. The improved bounds have been obtained on the anomalous coupling parameters of electric and magnetic moments of the tau lepton $a_τ$ and $\vert$$d_τ$$\vert$ compared to the current experimental sensitivity bounds. The $γp$ mode of photon reactions a…
The mSUGRA model predicts the polarization of the tau coming from the stau to bino decay in the co-annihilation region to be +1. This can be exploited to extract this soft tau signal at LHC and also to measure the tiny mass differences between the stau and the bino LSP. Moreover this strategy will be applicable for a wider class of bino LSP models, where the lighter stau has a right component at least of similar size as the left.
In this work we study the sensitivity on the anomalous magnetic and electric dipole moments of the tau-neutrino in the framework of the $SU(2)_L\times U(1)_Y\times U(1)_{B-L}$ electroweak model at future $e^+e^-$ linear colliders as the ILC and CLIC. For our study we consider the process $e^{+}e^{-}\rightarrow ( Z, Z', γ) \to ν_τ\bar ν_τγ$. For center-of-mass energies of $\sqrt{s}=1000-3000\hspace{0.8mm}GeV$ and integrated luminosities of ${\cal L}=500-2000\hspace{0.8mm}fb^{-1}$, we derive $95 \% \hspace{1mm}$ C.L. limits on the dipole moments $|μ_{ν_τ}(μ_B)| \leq 6.28 \times 10^{-9}$ and $|d_…
Spin effects in the tau-lepton pair induced by anomalous magnetic and electric dipole moments
NSC Kharkiv Institute of Physics and Technology（哈尔科夫物理与技术国立科学中心）；V. N. Karazin Kharkiv National University（瓦西里·卡扎金哈尔科夫国立大学）；M. Smoluchowski Institute of Physics, Jagiellonian University（雅盖隆大学M.斯莫卢霍夫斯基物理研究所）
We explore how the polarization of the tau leptons in the cascade decay $\tilde{q}\to q\tildeχ^0_2\to qτ\tildeτ\to qττ\tildeχ^0_1$ can be exploited to study mixing properties of neutralinos and staus. We present details of the analysis including experimental effects such as transverse momentum cuts for the $τ\toπν$ decay mode, and show that the di-pion invariant mass distribution provides valuable information on their properties.
Pair production of tau leptons in two photon collision ${γγ\to τ^{+}τ}^{-}$ is studied at CLIC to test CP violating QED couplings of tau leptons. CP violating effects are investigated using tau pair spin correlations which are observed through the hadronic decay of each $τ$ into $πν$. Competitive bounds with previous works on the electric dipole moment from CP odd terms have been obtained.
In this paper, we discuss application of the TauSpinner package as a simulation tool for measuring the CP state of the newly discovered Higgs boson using the transverse spin correlations in the H to tau tau decay channel. We discuss application for its main background Z/gamma* to tau tau as well. The TauSpinner package allows one to add, with the help of weights, transverse spin correlations corresponding to any mixture of scalar/pseudoscalar state, on already existing events using information from the kinematics of outgoing tau leptons and their decay products only. This procedure can be used…
Precise measurement of the Electric Dipole Moment (EDM) and anomalous magnetic moment ($g$-2) of particles are important tests of Beyond Standard Model (BSM) physics. It is generally believed that the tau lepton couples more strongly to BSM due to its large mass, and can be searched for at collider experiments. A new method to approximately reconstruct the neutrinos from the hadronic decays of $τ^-τ^+$ pairs produced at $e^-e^+$ tau factories is proposed. With all final state particle momenta available, observables based on matrix elements and sensitive to BSM are calculated. It is estimated t…
We obtain bounds on the anomalous magnetic and electric dipole moments of the tau-neutrino through the reaction $e^{+}e^{-}\to ν\bar νγ$ at the $Z_1$-pole in the framework of a Left-Right symmetric model and a class of $E_6$ inspired models with an additional neutral vector boson $Z_θ$. We use the data collected by the L3 Collaboration at LEP. For the parameters of the $E_6$ model we consider the mixing angle $θ_{E_6}=37.8^o$ and $M_{Z_θ}=7M_{Z_1}$. We find that our bounds are of the same order of magnitude as those obtained in other extensions of the Standard Model.
The tau-lepton plays an important role in the physics program at the Large Hadron Collider (LHC). It offers a probe in searches for New Physics and to measure parameters of the Standard Model. Spin of tau lepton is an interesting phenomenological quantity for separation of signal from background or in measuring properties of particles. A proper treatment of tau spin effects in the Monte Carlo simulations is important for understanding the detector acceptance as well as for the measurements/use of tau polarization and tau spin correlations. The TauSpinner is a tool to modify tau$spin effects in…
We analyze the sensitivity of hadronic tau decays to non-standard interactions within the model-independent framework of the Standard Model Effective Field Theory (SMEFT). Both exclusive and inclusive decays are studied, using the latest lattice data and QCD dispersion relations. We show that there are enough theoretically clean channels to disentangle all the effective couplings contributing to these decays, with the $τ\to ππν_τ$ channel representing an unexpected powerful New Physics probe. We find that the ratios of non-standard couplings to the Fermi constant are bound at the sub-percent l…
Supersymmetry (SUSY) with a long-lived stau is an attractive scenario in the LHC experiments because one can directly observe stau tracks in each SUSY event, and thus precise measurements of SUSY particle masses are possible. In this scenario, we discuss the possibility to observe/measure parity violation in interactions among SUSY particles. Such a measurement will be important in determining spins and chiralities of SUSY particles. We use the last step of the cascade-decay chain: $χ^0\to\tildeττ\to\tildeτ(lν\barν)$, where the polarization of the tau lepton can be determined statistically by …
In this work we estimate the heavy quark production in proton-proton and proton-nucleus collisions at LHC energies using the color dipole formalism and the solution of the running coupling Balitsky-Kovchegov equation. Nuclear effects are considered in the computation of the total cross sections and rapidity distributions for scattering on protons and nuclei.
A novel method for the direct measurement of the elusive magnetic and electric dipole moments of the tau lepton is presented. The experimental approach relies on the production of tau+ leptons from Ds+ -> tau+ nu_tau decays, originated in fixed-target collisions at the LHC. A sample of polarized tau+ leptons is kinematically selected and subsequently channeled in a bent crystal. The magnetic and electric dipole moments of the tau+ lepton are measured by determining the rotation of the spin-polarization vector induced by the intense electromagnetic field between crystal atomic planes. The exper…
The determination of the electromagnetic dipole moments of the top quark is one of the most important goals of the top quark physics program in the collider experiments. For this reason, the top quark pair production to investigate the sensitivity on the electric and magnetic dipole moments of the top quark via the process $pp\rightarrow p γp \rightarrow p t \bar{t} X$ at the Large Hadron Collider (LHC), the High-Luminosity Large Hadron Collider (HL-LHC) and High-Energy Large Hadron Collider (HE-LHC) is discussed. We apply pure leptonic and semileptonic decays for top quark pair production in …
We present a feasibility study, to search for dark matter at the LHC, in events with one soft hadronically decaying tau lepton and missing transverse energy recoiling against a hard $p_{T}$ jet from initial state radiation. This methodology allows the search for Supersymmetry in compressed mass spectra regions, where the mass difference between the lightest neutralino, $\tildeχ_1^0$, and the stau (the tau superpartner), $\tildeτ$, is small. Several theoretical models predict a direct connection between thermal Bino dark matter and staus within this scenario. We show that compressed regions, no…
We study the effect of operators generating dipole couplings of the light quarks to electroweak gauge bosons on several observables at LHC. We start by demonstrating that the determination of the gauge boson self-couplings from electroweak diboson production at LHC is robust under the inclusion of those quark dipole operators even when let them totally unconstrained in the analysis. Conversely, we determine the bounds that the diboson data imposes on the light-quark dipole couplings and show that they represent a significant improvement over the limits arising from Z and W electroweak precisio…
In this work we study the potential of the processes $e^+e^- \to e^+γ^* e^- \to e^+τ\barν_τν_e $ and $e^+e^- \to e^+γ^* γ^* e^- \to e^+ν_τ\barν_τe^- $ at a future high-energy and high-luminosity linear electron positron collider, such as the ILC and CLIC to study the sensibility on the anomalous magnetic and electric dipole moments of the tau-neutrino. For integrated luminosity of 590\hspace{1mm}$fb^{-1}$ and center-of-mass energy of 3\hspace{1mm}$TeV$, we derive $95 \% \hspace{1mm}C. L.$ limits on the dipole moments: $μ_{ν_τ}\leq 1.44 \times 10^{-6}μ_B$ and $d_{ν_τ}\leq 2.78 \times 10^{-17}\h…
