It is not possible to close any process. However you have an option to request the android OS to kill a background application.
To do so,
ActivityManager activityManager = (ActivityManager)ApplicationActivity.this.getSystemService(Context.ACTIVITY_SERVICE);
List<ActivityManager.RunningAppProcessInfo> listOfProcesses = activityManager.getRunningAppProcesses(); // Returns all the running processes.
To request andriod to kill a process, you have to compare processName with the what you want to close then call,
android.os.Process.killProcess(process.pid);
android.os.Process.sendSignal(process.pid, android.os.Process.SIGNAL_KILL);
activityManager.killBackgroundProcesses(process.processName);
Note: this doesn't guarantee the close of the application. It is upto the android to do that.
Make sure you add these permissions,
<uses-permission android:name="android.permission.KILL_BACKGROUND_PROCESSES" />
<uses-permission android:name="android.permission.GET_TASKS" />
Hope this helps.