Is it possible to buy a ticket from Pingya to Chengdu and stop in Xian?

We would like to see the terracotta army, but we do not want to stay in XA. So is it possible to buy a ticket to Chengdu, get off the train in XA and travel further that same day with that same ticket? Or do we have to buy 2 tickets (Pingyao - XY and XY- Chengdu)?