The measurement of B->tau nu at the B factories provides important constraints on the parameter tan beta/m_H^+- in the context of models with two Higgs doublets. Limits on this decay from e+e- collisions at the Z peak were sensitive to the sum of B->tau nu and B_c->tau nu. Due to the possibly sizeable contribution from B_c->tau nu we suggest that a signal for this combination might be observed if the LEP L3 Collaboration used their total data of ~3.6 10^6 hadronic decays of the Z boson. Moreover, we point out that a future Linear Collider operating at the Z peak (Giga Z option) could constrain tan beta/m_H^+- from the sum of these processes with a precision comparable to that anticipated at proposed high luminosity B factories from B-> tau nu alone.
The possibility of detecting the S-wave of the decays tau -> 3 pi + nu(tau) in the threshold region is explored, with emphasis on the sensitivity to the size of the quark antiquark condensate <qq>.
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.
We perform a complete simulation of the process $ e^+ e^- \to τ^+ τ^- ν\barν$, where $ν$ can be an electron, muon or tau neutrino, in the context of a general Higgs coupling to $τ$ leptons. We analyse various kinematical distributions and obtain the sensitivity regions in the parameter space that can be explored at a future $e^+ e^-$ collider. In particular, inclusion of $W$ boson fusion enhances the sensitivity significantly.
We demonstrate that a measurement of the impact parameter in one-prong tau decay can be useful for the determination of the Higgs boson parity in the H/A --> tau tau; tau --> rho nu decay chain. We have estimated that for a detection set-up such as TESLA, use of the information from the tau impact parameter can improve the significance of the measurement of the parity of the Standard Model 120 GeV Higgs boson to 4.5 sigma, and in general by factor of about 1.5 with respect to the method where this information is not used. We also show that the variation in the assumption on the precision of th…
We propose to measure the Wess-Zumino anomaly contribution by considering angular distributions in the decays $τ\toν_τηπ^{-}π^{0}$, $τ\toν_τK^- π^{-} K^+ $ and $τ\toν_τK^- π^- π^+$. Radial excitations of the $K^*$, which cannot be seen in $e^++e^-$, should be observed in the $ K^- π^+ π^-$ decay channel.
Tau tau fusion to light h and heavy H,A Higgs bosons is investigated in the Minimal Supersymmetric Standard Model (MSSM) at a photon collider as a promising channel for measuring large values of tan(beta). For standard design parameters of a photon collider an error close to unity, uniform for tan(beta) above 10, may be expected, improving on complementary measurements at LHC and e+e- linear colliders.
We present a very promising method for a measurement of the Higgs boson parity using the H/A -> tau^+ tau^- --> rho^+ nu rho^- nu --> pi^+ pi^0 nu pi^- pi^0 nu decay chain. The method is both model independent and independent of the Higgs production mechanism. Angular distributions of the tau decay products which are sensitive to the Higgs boson parity are defined and are found to be measurable using typical properties of a future detector for an e^+ e^- linear collider. The prospects for the measurement of the parity of a Higgs boson with a mass of 120 GeV are quantified for the case of e^+ e…
Measurement of the tau lepton polarization in \eett\ is an important electro-weak measurement at ILC and other future electron-positron colliders. In this paper we discuss several methods to extract polarimeter information for \eett\ events at the nominal centre-of-mass energy, and develop a new method, based on charged particle impact parameter measurement, which can accurately reconstruct tau momenta even in events with significant Initial State Radiation. In future work we will extend the study to estimate the precision with which the tau polarization can be measured at ILC-250, both for hi…
We calculate the medium dilepton yield from a quark-gluon plasma which has a time-dependent local momentum-space anisotropy. A phenomenological model for the hard momentum scale, p_hard(tau), and plasma anisotropy parameter, xi(tau), is constructed which interpolates between free streaming behavior at early times (tau << tau_iso) and ideal hydrodynamic behavior at late times (tau >> tau_iso). We show that high-energy dilepton production is sensitive to the assumed plasma isotropization time, tau_iso, and can therefore be used to experimentally determine the time of onset for hydrodynamic expan…
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…
In the Standard Model, the Higgs boson is a CP even state with CP conserving couplings; any deviations from this would be a sign of new physics. These CP properties can be probed by measuring Higgs decays to tau lepton pairs: the transverse correlation between the tau spins depends on CP. This paper develops such an analysis, using full simulation of signal and background events in the International Large Detector concept for the International Linear Collider. We consider Higgs-strahlung events e+ e- -> Z H) in which the Z boson decays to electrons, muons, or hadrons, and the Higgs boson decay…
We compute the SUSY effective hamiltonian that describes the |ΔS|=1 semileptonic decays of tau leptons. We provide analytical expressions for supersymmetric contribution to tau --> u bar{s} nu_{tau} transition in mass insertion approximation. We show that SUSY contributions may enhance the CP asymmetry of tau --> K pi nu_{tau} decays by several orders of magnitude than the standard model expectations. However, the resulting asymmetry is still well below the current experimental limits obtained by CLEO collaborations. We emphasize that measuring CP rate asymmetry in this decay larger than 10^{-…
We propose a {\em unitarity method} for determining $τ$ neutrino appearance probability $P(ν_μ \rightarrow ν_τ)$ in long-baseline (LBL) accelerator experiments and atmospheric neutrino observations. When simultaneous in situ measurements of $P(ν_μ \rightarrow ν_μ)$ and $P(ν_μ \rightarrow ν_{e})$ proceed, as is typical in the LBL experiments, one can use unitarity to "measure" $P(ν_μ \rightarrow ν_τ)$. A theorists' toy analysis for the model-independent determination of $P(ν_μ \rightarrow ν_μ)$ and $P(ν_μ \rightarrow ν_{e})$ is presented by using the NOvA data. It is shown in our analysis that …
We investigate the LHC and Higgs Factory prospects for measuring the CP phase in the Higgs-tau-tau coupling. Currently this phase can be anywhere between 0 degrees (CP even) and 90 degrees (CP odd). A new, ideal observable is identified from an analytic calculation for the $τ^\pm \to ρ^\pmν\to π^\pm π^0 ν$ channel. It is demonstrated to have promising sensitivity at the LHC and superior sensitivity at the ILC compared to previous proposals. Our observable requires the reconstruction of the internal substructure of decaying taus but does not rely on measuring the impact parameter of tau decays.…
We show that the decay mode B -> D tau nu is competitive with and complementary to B -> tau nu in the search for charged-Higgs effects. Updating the relevant form factors, we find that the differential distribution in the decay chain B -> D nu tau[-> pi nu] excellently discriminates between Standard-Model and charged-Higgs contributions. By measuring the D and pi energies and the angle between the D and pi three-momenta one can determine the effective charged-Higgs coupling including a possible CP-violating phase.
The measurement of the trilinear couplings A in the part of the Lagrangian which breaks supersymmetry softly will be a difficult experimental task. In this report the heavy Higgs decays H,A -> stau_1 stau_2 to stau pairs are investigated for measuring the stau trilinear coupling A_tau. Based on detailed simulations of signal and backgrounds for a specific reference point in future high luminosity e+e- linear collider experiments, it is concluded that the parameter $_tau can be determined with a precision at the 10% level in the region of moderate to large tan(beta).
We study the prospects of measuring the CP property of the Higgs ($h$) coupling to tau leptons using the vector boson fusion (VBF) production mode at the high-luminosity LHC. Utilizing the previously proposed angle between the planes spanned by the momentum vectors of the $(π^+π^0)$ and $(π^- π^0)$ pairs originating in $τ^\pm$ decays as the CP-odd observable, we perform a detailed Monte Carlo analysis, taking into account the relevant standard model backgrounds, as well as detector resolution effects. We find that excluding a pure CP-odd coupling hypothesis requires $\mathcal{O}(400 {~\rm fb}^…
In many SUSY models the first SUSY signal in the proposed International Linear Collider is expected to come from the pair production of $\tildeτ_1$, followed by its decay into $τ$+LSP. We study a simple and robust method of measuring the polarization of this $τ$ in its 1-prong hadronic decay channel,and show how it can be used to discriminate between SUSY models and to determine SUSY parameters.
An accurate determination of the Higgs decay branching ratios to bb, cc, gg, WW* and tau tau pairs is important for the study of the Higgs couplings and for determining its SM or MSSM nature in the mass range 100 GeV/c2 < M_H < 140 GeV/c^2. This measurement also represents an important benchmark for the optimisation of the detector design. The accuracy on the determination of the Higgs decay branching ratio to fermions and WW* pairs has been studied using the simulation of the detector designed for the TESLA e+e- linear collider at c.m. energy of 350 GeV and 500 GeV. The results are discussed …
The doubly-charged scalar boson H^{--} is involved in several new physics models for generating neutrino masses. Depending on new physics models, H^{--} has the Yukawa interaction with a pair of left-handed charged leptons or a pair of right-handed ones. In this talk, we see that these two Yukawa interactions can be distinguished by measuring energy distributions of charged pions produced by decays of tau leptons if pair-produced H^{++} H^{--} can decay sufficiently into four charged leptons which involve one or two tau leptons. The information on the Yukawa interaction of H^{--} will help to …
We investigate the potential for measuring the relative couplings of a low-mass Higgs boson at the Large Hadron Collider using WH, ZH, and ttbarH production, where the Higgs boson decays to tau-lepton pairs. With 100/fb of sqrt(s) = 14 TeV pp collision data we find that these modes can improve sensitivity to coupling-ratio measurements of a Higgs boson with a mass of about 125 GeV/c^2.
If CP is violated in any decay process involving leptons it will signify the existense of a new force (called the X boson) responsible for CP violation that may be the key to understanding matter-antimatter asymmetry in the universe. We discuss the signatures of CP violation in (1) the decay of tau lepton, and (2) the semileptonic decay of $π$, K, D, B and t particles by measuring the polarization of the charged lepton in the decay. We discuss how the coupling constants and their phases of the coupling of the X boson to 9 quark vertices and 3 lepton vertices can be obtained through 12 decay pr…
There is growing evidence for deviation from the standard model predictions in the ratios between semi-tauonic and semi-leptonic $B$ decays, known as the $R(D^{(*)})$ puzzle. If the source of this non-universality is new physics, it is natural to assume that it also breaks CP symmetry. In this paper we study the possibility of measuring CP violation in semi-tauonic $B$ decays, exploiting interference between excited charm mesons. Given the current values of $R(D^{(*)})$, we find that our proposed CP-violation observable could be as large as about 10%. We discuss the experimental advantages of …
The doubly charged scalar boson (H^{\pm\pm}) is introduced in several models of the new physics beyond the standard model. The H^{\pm\pm} has Yukawa interactions with two left-handed charged leptons or two right-handed charged leptons depending on the models. We study kinematical properties of H^{\pm\pm} decay products through tau leptons in order to discriminate the chiral structures of the new Yukawa interaction. The chirality of tau leptons can be measured by the energy distributions of the tau decay products, and thus the chiral structure of the new Yukawa interaction can be traced in the …
A method for measuring the average longitudinal polarization of the electron beam at an electron-positron collider operating near the $J/ψ$ resonance is proposed. The method utilizes the differential cross-section of $J/ψ\to [Λ\to pπ^-][\barΛ\to\bar{p}π^+]$ decay. It can be used to measure the average longitudinal polarization of electrons with the statistical precision better than $10^{-3}$ at a Super Charm-Tau factory operating at the luminosity of $10^{35}~\mathrm{cm}{}^{-2}\mathrm{s}{}^{-1}$. The method is discussed in the context of the weak mixing angle measurement in the same experiment…
The experimental prospects for precise measurements of the leptonic decays B_u -> tau nu / mu nu, B_s -> mu+ mu-, D -> mu nu and D_s -> mu nu / tau nu are very promising. Double ratios involving four of these decays can be defined in which the dependence on the values of the decay constants is essentially eliminated, thus enabling complementary measurements of the CKM matrix element V_ub with a small theoretical error. We quantify the experimental error in a possible future measurement of |V_ub| using this approach, and show that it is competitive with the anticipated precision from the conven…
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…
In the present report, let us adress the issues related to simulation of decays for particle embodied in full production and decay chains of Monte Carlo programs set-up for experiments such as at LHC or LC. Both technical issues related to the way how the events may be stored in event records and issues related to physics (in particular non-factorizable correlations of the Einstein-Rosen-Podolsky type) will be reviewed on the basis of practical examples. We will limit our discussion to the case of tau lepton and W boson decays, but similar problems (and solutions) may arise also in case of sim…
We investigate flavour violating decays of the long-lived lightest slepton and the tau lepton in the coannihilation region of the Minimal Supersymmetric Standard Model with a Seesaw mechanism to generate neutrino masses. We consider a situation where the mass difference between the lightest neutralino, as the Lightest Supersymmetric particle (LSP), and the lightest slepton, as the Next-to-LSP, is smaller than the mass of tau lepton. In this situation, the lifetime of the lightest slepton is very long and it is determined by lepton flavour violating (LFV) couplings because the slepton mainly co…
Dark matter decaying or annihilating into mu+mu- or tau+tau- has been proposed as an explanation for the e+e- anomalies reported by PAMELA and Fermi. Recent analyses show that IceCube, supplemented by DeepCore, will be able to significantly constrain the parameter space of decays to mu+mu-, and rule out decays to tau+tau- and annihilations to mu+mu- in less than five years of running. These analyses rely on measuring track-like events in IceCube+DeepCore from down-going nu_mu. In this paper we show that by instead measuring cascade events, which are induced by all neutrino flavors, IceCube+Dee…
A method of indirect measurement of the light quark running mass $\hat{m} = (m_d + m_u)/2$ is elaborated in detail. It is based on measuring 1\%-level azimuthal angular asymmetries in the decay $τ\rightarrow ν_τ+ 3π$. The latter are then used in QCD sum rules to obtain experimental lower bounds for $\hat{m}$. For a sample of $2.5 \times 10^5$ $τ\rightarrow ν_τ+ 3π$ decays free of background, the resulting statistical error in the bound for $\hat{m}$ is estimated to be 1 MeV, i.e., comparable to the systematic error due to the use of QCD sum rules. Contribution to the Third Workshop on the $τ$ …
In this paper we discuss the possibility of measuring the anomalous magnetic and electric dipole moments of the $τ$ lepton. The method consists in studying the spin precession induced by the strong effective magnetic field inside channels of a bent crystal with a dedicated setup at the CERN Large Hadron Collider.
We discuss the test of CP and CPT violation in $τ$ decay without using the polarized electron beam by comparing partial fractions of $τ^-$ and $τ^+$ decay into channels with strong final state interactions. For example, $Γ(τ^-\rarrow π^-+π^0+ν) \ne Γ(τ^+\rarrow π^++π^0+ν)$ signifies violation of CP. The optimum energy to investigatge CP violation in $τ$ decay is discussed. We conclude that this energy is a few MeV below $ψ(2s)$ in order to avoid the charm contribution and over abundance of hadrons at the $ψ(2s)$ peak.
The phenomenon of neutrino flavor oscillations motivates searches for sterile neutrinos in a broad range of masses and mixing-parameter values. A sterile neutrino $N$ that mixes predominantly with the $τ$ neutrino is particularly challenging experimentally. To address this challenge, we propose a new method to search for a $ν_τ$-mixing with $N$ lighter than the $τ$ lepton. The method uses the large $e^+e^-\toτ^+τ^-$ samples collected at $B$-factory experiments to produce the $N$ in $τ$-lepton decays. We exploit the long lifetime of a sterile neutrino in this mass range to suppress background a…
We discuss lepton flavor violation (LFV) associated with tau leptons in the framework of the two-Higgs-doublet model. Current data for rare tau decays provide substantial upper limits on the LFV Yukawa couplings in the large $\tanβ$ region where $\tanβ$ is the ratio of vacuum expectation values of the two Higgs doublets. We show that measuring the LFV Higgs boson decays $h \to τ^\pm μ^\mp$ at future colliders can be useful to further constrain the LFV couplings especially in the relatively small $\tanβ$ region.
The tau-lepton plays an important role in the physics program at LHC. Its spin can be used for separation of signal from background or in measuring properties of New Particles decaying to tau leptons. The TauSpinner package represents a tool to modify tau spin effects in any sample containing tau leptons. Generated events, featuring taus produced from intermediate state W, Z, H bosons can be used as an input. The information on the polarization and spin correlations is reconstructed from the kinematics of the tau lepton(s) (nutau in case of W-mediated processes) and tau decay products. By weig…
Perturbative and nonperturbative QCD corrections to semileptonic B decay rates are calculated and given in analytical and numerical forms. We present the analytic expression for the double distribution in hadronic mass and electron energy in B to X(u) e nu_e decays through one loop order of QCD. We then study the leading twist corrections to that quantity within the formalism of HQET and employ it in a proposed method of measuring V_ub with an accuracy of 10%. Our other point of interest is the polarisation of the tau lepton in B to X(c) tau nu_tau processes. Analytic formulae are given for th…
We study measurement of the CP property of the Higgs boson at a photon linear collider. One method where we take advantage of interference between Higgs-production and background amplitudes is proposed. A broad peak of the photon energy spectrum is helpful in observing the energy dependence of the interference effects. Numerical results for the process $γγ\to t \bar{t}$ are shown as an example.
We investigate potential for measuring CP state of the Higgs boson in the H to tau tau$ decay with consecutive tau-lepton decays in channels: tau^+- to rho^+- nu_tau and tau^+- to a1^+- nu_tau combined. Subsequent decays rho^+- to pi^+- pi^0, a1^+- to rho^0 pi^+- and rho^0 to pi^+ pi^- are taken into account. We will explore extensions of the method, where acoplanarity angle for the planes build on the visible decay products, pi^+- pi^0 of tau^+- to pi^pm pi^0 nu_tau, was used. The angle is sensitive to transverse spin correlations, thus to parity. We show, that in the case of the cascade deca…
In this paper, we present a preliminary study of $CP$ violation effect of $K^{0}-\bar{K}^{0}$ system in $J/ψ$ decay. The $CP$ violation parameters $η_{+-}$ and $η_{00}$ as well as their corresponding phase $ϕ_{+-}$ and $ϕ_{00}$ can be determined by the difference of the time-dependent decay rates between $K^{0}$ and $\bar{K}^{0}$ produced from $J/ψ\rightarrow K^{-}π^{+}K^{0} + c.c.$ processes. We investigate the precisions of the measurements of the CP violation effect at the Super Tau-Charm facility(STCF), a $e^{+}e^{-}$ collider with a peak luminosity of $0.5\times10^{35}\ \rm{cm}^{-2}\rm{s}…
We study the prospects for the measurement of the stau - lightest neutralino mass difference (dM) and the gluino mass (Mg) in the supersymmetric co-annihilation region at the LHC using tau leptons. Recent WMAP measurements of the amount of cold dark matter and previous accelerator experiments indicate that the coannihilation region of mSUGRA is characterized by a small dM (5-15 GeV). Focusing on taus from N2 -> tau stau -> tau tau N1 decays in gluino and squark production, we consider inclusive 3 tau+jet+missing Et production, with two taus above a high Et threshold and a third tau above a low…
It is shown that the phase of phi-omega interference in the reaction e^+e^- -->pi^+ pi^- pi^0 at energies close to the phi(1020) peak can be calculated in a way that is practically independent of the model of phi-omega mixing. The magnitude of the presently measured interference phase, still of poor accuracy, is in agreement with the predictions based on extending the omega(782) resonance tail from the peak position to the phi mass upon assuming the omega -->rho pi -->3pi model. The calculated omega width at the phi mass is about 200 MeV.
