θ² distributions of ON (blue circles) and OFF (black line) events above 0.2 TeV towards the centre of the head region (left) and that of the tail region (right). The region between zero and the vertical dashed line (at θ² = 0.0256 deg²) was used to estimate ON and OFF events. The OFF data represent the average of six regions rotated by 120 and 240 deg with respect to each wobble centre from the ON region.