* Live Nation to pay $400 mln in stock for Ticketmaster

* New York senator slams deal

* Shares of both companies fall on antitrust concerns

* Companies expect deal close in second half of 2009 (Adds executive comments, analyst reaction)

By Yinka Adegoke

NEW YORK, Feb 10 (Reuters) - The world's largest concert promoter, Live Nation Inc (LYV.N: Quote, Profile, Research), plans to buy Ticketmaster Entertainment Inc (TKTM.O: Quote, Profile, Research) for about $400 million in stock, aiming to create a company with dominant holdings in concert promotion and ticket sales.

But shares of both Live Nation and Ticketmaster fell on Tuesday, amid concerns the acquisition would be blocked by U.S. antitrust regulators under the new Obama administration.

U.S. Senator Charles Schumer slammed the deal ahead of its formal announcement, calling for a federal probe into Ticketmaster, the top U.S. ticket vendor.

"This merger would give a giant, new entity unrivaled power over concert-goers and the prices they pay to see their favorite artists and bands," the Democrat senator from New York said in a statement.