Context : HD~141569 is a pre-main sequence star with a disc uniquely placed between protoplanetary and debris discs , similar to the older ‘ hybrid ’ type discs .

Aims : This work aims to place the mass and spatial structure of the disc midplane in the context of the debris , hybrid and protoplanetary discs .

Methods : We observed HD 141569 with ALMA in 1.3 mm continuum and ^ { 13 } CO ( 2-1 ) .
This is the first detection and image of the optically thin gas emission from the midplane of this disc .

Results : In continuum emission , we detect a combination of an unresolved central peak and a ring of millimetre emission at 220 \pm 10 au , slightly interior to one of the rings discovered in scattered light .
The minimum dust mass of the ring is 0.13 \pm 0.02 M _ { \oplus } while the unresolved millimetre peak at the stellar location is predominantly thermal emission due to a minimum of 1.2 \pm 0.2 M _ { \oplus } of dust . ^ { 13 } CO is distributed asymmetrically around the stellar position with a peak at 1 \aas@@fstack { \prime \prime } 1 distance and a P.A .
of -33 ^ { \circ } .
The gas is detected as far as 220 \pm 10 au , a radial separation the same as that of the mm ring .
Assuming optically thin emission and standard ISM abundances , we use our ^ { 13 } CO data to derive the gas mass in the disc of ( 6.0 \pm 0.9 ) \times 10 ^ { -4 } ~ { } M _ { \odot } .
Comparison to published ^ { 12 } CO data shows that ^ { 12 } CO is optically thick , explaining why estimates based on ^ { 12 } CO underestimated the gas mass .

Conclusions :