How do I talk my mom into letting me go to a concert?

My brother is working a Dropkick Murphy's concert next week and told me I could go with him since they are one of my favorite bands. I want to ask my mom, but really don't know how because a few years ago, I went to a Green Day concert with him and she got really mad that I went with JUST him because she finds him irresponsible(but since he's WORKING the concert, he CAN'T be irresponsible at it)so, how do I ask her?