Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userExcited tau lepton contribution to $W->tau nu(tau)$ decay at the one-loop level
94
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We evaluate the compositeness effects of tau lepton on the vertex W-tau-nu(tau) in the context of an effective Lagrangian approach. We consider that only the third family is composed and we get the corrections to the non universal lepton coupling g_(tau)/g_(e). As the experimental bounds on non universal lepton couplings in W decays are weak, we find that the excited particles contributions do not give realistic limits on the excited mass, since they lead to Lambda<m*.
rate research
Read More
In this paper, we present the one-loop radiative corrections to the electroweak precision observable $Delta rho$ coming from the $I_W=1$ multiplet excited leptons. We have calculated the couplings of the exotic lepton triplet to the vector bosons and ordinary leptons using effective Lagrangian approach. These couplings are then used to estimate the excited lepton triplet contribution to the $Delta rho$ parameter. The mass degenerate excited lepton contribution to $Delta rho $ is small and can be neglected. However, if the excited leptons are non-degenerate, their contribution can be large which can result in more stringent constraints on the excited fermion parameter space compared to the constraints from present experimental searches and perturbative unitarity condition.
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.
We report the first measurement of the $tau$ lepton polarization in the decay ${bar B} rightarrow D^* tau^- {bar u_{tau}}$ as well as a new measurement of the ratio of the branching fractions $R(D^{*}) = mathcal{B}({bar B} rightarrow D^* tau^- {bar u_{tau}}) / mathcal{B}({bar B} rightarrow D^* ell^- {bar u_{ell}})$, where $ell^-$ denotes an electron or a muon, with the decays $tau^- rightarrow pi^- u_{tau}$ and $tau^- rightarrow rho^- u_{tau}$. We use the full data sample of $772 times 10^6$ $B{bar B}$ pairs accumulated with the Belle detector at the KEKB electron-positron collider. Our preliminary results, $R(D^*) = 0.276 pm 0.034{rm (stat.)} ^{+0.029} _{-0.026}{rm (syst.)}$ and $P_{tau} = -0.44 pm 0.47 {rm (stat.)} ^{+0.20} _{-0.17} {rm (syst.)}$, are consistent with the theoretical predictions of the Standard Model within $0.6$ standard deviation.
Lepton-flavour violating tau-decays are predicted in many extensions of the Standard Model at a rate observable at future collider experiments. In this article we focus on the decay tau to mu mu antimu, which is a promising channel to observe lepton-flavour violation at the Large Hadron Collider LHC. We present analytic expressions for the differential decay width derived from a model-independent effective Lagrangian with general four-fermion operators, and estimate the experimental acceptance for detecting the decay tau to mu mu antimu at the LHC. Specific emphasis is given to decay angular distributions and how they can be used to discriminate new physics models. We provide specific predictions for various extensions of the Standard Model, including supersymmetric, little Higgs and technicolour models.
In phenomenological preparation for new measurements one searches for the carriers of quality signatures. Often, the first approach quantities may be difficult to measure or to provide sufficiently precise predictions for comparisons. Complexity of necessary details grow with precision. To achieve the goal one can not break the theory principles, and take into account effects which could be ignored earlier. Mixed approach where dominant effects are taken into account with intuitive even simplistic approach was developed. Non dominant corrections were controlled with the help of Monte Carlo simulations. Concept of Optimal Variables was successfully applied for many measurements. New techniques, like Machine Learning, offer solutions to exploit multidimensional signatures. Complementarity of these new and old approaches is studied for the example of Higgs Boson CP-parity measurements in H to tau^+tau^-, tau^pm to nu (3pi)^pm cascade decays.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
