Try:
systemctl status PID
You should see something like this:
$ systemctl status 16736
salt-master.service - The Salt Master Server
Loaded: loaded (/lib/systemd/system/salt-master.service; disabled; vendor preset: enabled)
Active: active (running) since Thu 2015-09-10 05:11:21 MSK; 1min 8s ago
Main PID: 16736 (salt-master)
CGroup: /system.slice/salt-master.service
16736 /usr/bin/python /usr/local/bin/salt-master
16744 /usr/bin/python /usr/local/bin/salt-master
16751 /usr/bin/python /usr/local/bin/salt-master
systemctl(1) says:
> status [PATTERN...|PID...]]
>
> Show terse runtime status information about one or more units, followed by most recent log data from the journal. If a PID is passed, show information about the unit the process belongs to.