The temperature in Beijing end of March? Is there a one day tor from Beijing to Xian?

the temperature has been warm
there is a one-day Xian Tour: https://www.travelchinaguide.com/package/tour-xa03.htm

The temperature is 0 - 15 C.
no need to worry about the radiation fallout.
if you decide to visit the Terracotta Warriors only, it is possible to take a round-trip to Xian from Beijing by flight within one day. or you can take a train at night and arrive in Xian in early morning the next day, after a day's visit in Xian, take an overnight train back to Beijing.