The Tibet AS+MD Project; status report 2017

We built a large (approximately 4,000 m**2) water　Cherenkov- type muondetector array under the existing Tibet air showerarray at 4,300 m above sea level, to observe 10-1000 TeV gamma raysfrom cosmic-rayaccelerators in our Galaxy with wide field of view at very low background level. A gamma-rayinduced air showerhas significantly less muonscompared with a cosmic-rayinduced one. Therefore, we can effectively discriminate between primary gamma raysand cosmic-raybackground events by means of counting number of muonsin an air showerevent by the muondetector array. We make a status report on the experiment.