$\tau$-lepton pair spin in proton-proton LHC collisions for anomalous dipole moments

Abstract

The spin correlations in the pair of $\tau$ leptons produced in the high-energy proton-proton collisions are studied. The invariant mass of the $\tau$-lepton pair is chosen close to $Z$-boson mass, in these conditions $Z$-boson exchange gives the dominant contribution to the Drell-Yan mechanism. The interaction of $Z$ boson with $\tau$ lepton, in addition to the Standard Model couplings, can include weak anomalous magnetic and electric dipole moments (or form-factors) of the $\tau$ lepton. Dependence of elements of the $pp$ spin-correlation matrix on the weak anomalous moments is determined for various regions of the rapidity of the $\tau$-lepton pair. Based on this calculation, we construct a semi-realistic observable built on the momenta of pions in the ${\tau }^{\mp }\to {\pi }^{\mp }{\nu }_{\tau }$ and ${\tau }^{\pm }\to {\rho }^{\pm }{\nu }_{\tau }\to {\pi }^{\pm }{\pi }^0{\nu }_{\tau }$ decay channels, and show that this observable can be sensitive to the weak anomalous dipole moments.

Comments: 10 pages, 6 figures, revtex4; v2: minor misprints corrected