Future Colliders

Abstract:

In this paper, a measurement of τ polarization in W → τν decays is presented. It is measured from the energies of the decay products in hadronic τ decays with a single final state charged particle. The data, corresponding to an integrated luminosity of 24 pb⁻¹, were collected by the ATLAS experiment at the Large Hadron Collider in 2010. The measured value of the τ polarization is Pτ = −1.06±0.04 (stat) ^+0.05−0.07 (syst), in agreement with the Standard Model prediction, and is consistent with a physically allowed 95 % CL interval [−1,−0.91]. Measurements of τ polarization have not previously been made at hadron colliders.

Abstract:

This letter reports on a search for hypothetical heavy neutrinos, N, and right-handed gauge bosons, W R , in events with high transverse momentum objects which include two reconstructed leptons and at least one hadronic jet. The results were obtained from data corresponding to an integrated luminosity of 2.1 fb −1 collected in proton–proton collisions at √ s = 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. No excess above the Standard Model background expectation is observed. Excluded mass regions for Majorana and Dirac neutrinos are presented using two approaches for interactions that violate lepton and lepton-flavor numbers. One approach uses an effective operator framework, the other approach is guided by the Left– Right Symmetric Model. The results described in this letter represent the most stringent limits to date on the masses of heavy neutrinos and W R bosons obtained in direct searches.