I have no personal experience of this but I do know that my SD did it to her mums little boy, not out of malice she just didnt know how to interact with him, mum praised her being good and gentle and moved her away with not so much as telling off as a comment on not making baby sad when she did it and SD stopped not long after
Praise the good and re-direct the anger/jealousy. I think all too often we tell our children 'No, you must not hit', when they may be feeling things that they cannot express verbally, but need to get out.
You can always say 'I see you feel angry, it's not okay to hit your brother, but you can hit a cushion or the sofa'.
Personally I have a six foot punchbag, somedays it comes in very handy