Barnes & Noble is not participating in Microsoft’s big announcement this afternoon in Los Angeles, we’ve been able to confirm — verifying a report this morning by Dow Jones Newswires, as noted by Business Insider.

At least for today, this appears to throw cold water on the theory that the bookseller will be teaming up with Microsoft on a tablet to rival the Kindle Fire or iPad.

Of course, it’s still possible that Microsoft will be coming out with its own tablet. But the absence of Barnes & Noble from the event takes away one of the more intriguing potential angles. The companies announced a partnership a while back that includes a $300 million investment by Microsoft in Barnes & Noble’s Nook unit.

TechCrunch had reported over the weekend that Microsoft would announce “a tablet/e-reader built in conjunction with Barnes & Noble.”

Bottom line, there’s no official word yet on what Microsoft will be announcing, and all of the reports we’ve seen so far are unconfirmed. Who knows, Microsoft could be announcing its intention to enter the commercial space race.

But the company has at least succeeded in stirring up a media frenzy, with its promise of “major” news that we wouldn’t want to miss. I’ve been getting calls all weekend and into the morning from TV and radio stations wanting to talk about the upcoming event. That translates into high expectations that could be tough for Microsoft to meet.

I’m on a plane right now en route to Los Angeles and will be reporting from the event later today.

Previously: All hail Xpad? How Microsoft could make a winning tablet

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