We present ALMA observations of 106 G- , K- , and M-type stars in the Upper Scorpius OB Association hosting circumstellar disks .
With these data , we measure the 0.88 mm continuum and ^ { 12 } CO J = 3 - 2 line fluxes of disks around low-mass ( 0.14 - 1.66 M _ { \odot } ) stars at an age of 5-11 Myr .
Of the 75 primordial disks in the sample , 53 are detected in the dust continuum and 26 in CO. Of the 31 disks classified as debris/evolved transitional disks , 5 are detected in the continuum and none in CO .
The lack of CO emission in approximately half of the disks with detected continuum emission can be explained if CO is optically thick but has a compact emitting area ( \lesssim 40 au ) , or if the CO is heavily depleted by a factor of at least \sim 1000 relative to interstellar medium abundances and is optically thin .
The continuum measurements are used to estimate the dust mass of the disks .
We find a correlation between disk dust mass and stellar host mass consistent with a power-law relation of M _ { \mathrm { dust } } \propto M _ { * } ^ { 1.67 \pm 0.37 } .
Disk dust masses in Upper Sco are compared to those measured in the younger Taurus star-forming region to constrain the evolution of disk dust mass .
We find that the difference in the mean of \log ( M _ { \mathrm { dust } } / M _ { * } ) between Taurus and Upper Sco is 0.64 \pm 0.09 , such that M _ { \mathrm { dust } } / M _ { * } is lower in Upper Sco by a factor of \sim 4.5 .