The GINGER project and status of the GINGERino prototype at LNGS

GINGER (Gyroscopes IN GEneral Relativity) is a proposal for measuring in a ground-based laboratory the Lense-Thirring eect, known also as inertial frame dragging, that is predicted by General Relativity, and is induced by the rotation of a massive source. GINGER will consist in an array of at least three square ring lasers, mutually orthogonal, with about 6-10 m side, and located in a deep underground site, possibly the INFN { National Laboratories of Gran Sasso. The tri-axial design will provide a complete estimation of the laboratory frame angular velocity, to be compared with the Earths rotation estimate provided by IERS with respect the xed stars frame. Large-size ring lasers have already reached a very high sensitivity, allowing for relevant geodetic measurements. The accuracy required for Lense-Thirring eect measurement is higher than 1014 rad/s and therefore Earth angular velocity must be measured within one part in 109. A 3:6 m side, square ring laser, called GINGERino, has been recently installed inside the Gran Sasso underground laboratories in order to qualify the site for a future installation of GINGER. We discuss the current status of the experimental work, and in particular of the GINGERino prototype.