Constraining the dipole moments of the top quark

Abstract

We investigate the direct and indirect bounds on dipole operators involving the top quark. A careful analysis shows that the experimental upper limit on the neutron electric dipole moment strongly constrains the chromo-electric dipole of the top. We improve previous bounds by two orders of magnitude. This has significant implications for new physics models and it also means that CP violation in top pair production mediated by dipole operators will not be accessible at the LHC. The CP conserving chromo-magnetic dipole moments are constrained by recent measurements of the t\bar t spectrum by the ATLAS collaboration. We also update the indirect constraints on electric and magnetic dipole moments from radiative b -> s transitions, finding that they can be considerably larger than their colored counterparts.

Figures (3)

• Figure 1: Diagrams generating the contribution to the Weinberg operator at the top threshold. The grey blob denotes the insertion of the chromo-electric dipole operator Braaten:1990gqChang:1991ryBoyd.
• Figure 2: Indirect constraints on the top EDM and MDM coming from radiative and rare semileptonic B decay observables (as defined in Ref. Altmannshofer:2012az): $Br(B\to X_s\gamma)$ (dashed $1\sigma$ contours), $A_{CP}(B\to X_s \gamma)$ (dotted $1\sigma$ contours), $\langle A_{FB}\rangle(B\to K^* \ell^+\ell^-)[1\,{\rm GeV}^2<q^2<6\,{\rm GeV}^2]$ (dot-dashed $1\sigma$ contours) and $\langle F_{L}\rangle(B\to K^* \ell^+\ell^-)[1\,{\rm GeV}^2<q^2<6\,{\rm GeV}^2]$ (double dot-dashed $1\sigma$ contours) . The combined allowed region is bounded by full line contours and shaded in lighter green ($68\%$C.L.) and darker red ($95\%$C.L.).
• Figure 3: Combined current LHC and Tevatron $95\%$ C.L. constraints on the top CMDM ($\tilde{\mu}_t$) and the CEDM ($\tilde{d}_t$) (shaded in yellow). Individual constraints come from the total cross-section and $m_{t\bar{t}}$ spectrum measurements at the Tevatron (dashed blue and doted red), as well as the LHC (shaded blue and red). The combination of only Tevatron constraints is drawn in black. Finally the CEDM indirect constraint is presented in green.