Exploring dark Z_d-boson in future large hadron-electron collider

Abstract

The interaction between the dark U(1)_d sector with the visible Standard Model (SM) sector takes place through the kinetic mixing between the dark photon U(1)_d field Z_d^mu and the SM U(1)_Y gauge field B_mu . After the electroweak and U(1)_d symmetry breaking, the dark photon Z_d^mu acquires a mass and mixes with the SM neutral vector boson Z_mu . This mixing leads to parity-violating coupling between the Z_d^mu and SM. The coupling between the dark photon and SM can be explored in low energy phenomenology as well as in collider experiments. The Lorentz structure of dark photon interaction with SM fermions is explored in the proposed high energy future Large Hadron-electron collider, which would provide efficient energy and a clean environment using cross-section and asymmetries associated with polarisation observable of the dark photon in leptons decay. A chi ^2-analysis is performed to compare the strength of various variables for both the charge- and neutral-current processes. Based on this analysis, 90% confidence level (C.L.) contours in the varepsilon -m_{Z_d} and varepsilon -g_V plane are obtained to put limits on the Z_d^mu mass up to 100 GeV, coupling strength varepsilon and on the Lorentz structure of dark photon coupling with the SM fermions (g_V) at sqrt{s} approx 1.3 TeV.