Right bit for cutting brass

I wasn't sure where I should ask this question, so if I'm not in the right place please transfer me.

I need to cut 2 slots (1 each side) in a brass tube with my cnc router, but as I'm relatively new to cnc I'm not sure what bit to use.

The tube is half an inch in diameter and 8 ins long and 1.5mm wall thickness. the slot is 4mm wide and 6ins long.

Can this job be done in one go or will I have to turn the tube around to do the other side.

You can see now how new I am as up to now I've only cut a number of patterns out of 12mm ply and acrylic.

This is my first stab at metal and don't want to spend a lot on finding the right bit for a job like this.

Thanks a lot.