Britney  Spears
will NOT be a judge on "X Factor" next season  -- and it's entirely her doing ... TMZ has learned.

We have  unimpeachable sources who tell us Britney loves the show but wants to focus on  her music ... which she is doing right now.  Britney is in the studio  recording her 8th album, with some help from Will.i.am and  producer Hit-Boy, the brains behind Kanye and Jay-Z's "N****s in Paris."

One of our sources tells us  ... "Britney loves Simon, she likes Demi Lovato but her thing  is music."

We're told after she completes the album, Britney is seriously  considering going on tour again.

Walking away from $15 mil ...Yeah, she's  that rich.