Something happened...

I'm 15 and today in school (idk who) but somebody put their hand up my skirt and grabbed my ass!! I turned around shocked but the corridor was superrrr packed I have no idea who done it. I should of made a scene but I was in shock and Idk now i just feel kinda vulnerable about the fact somebody went up my skirt and grabbed my ass luckily I was wearing shorts! Is this sexual assault? I told my mum about it and she's going to call up and complain somebody comfort me please :(