Ashton Kutcher -- The Party's Over, Returns to LA

Ashton Kutcher finally touched down in LA -- two days after Demi Moore was rushed to the hospital -- looking far more concerned than he did earlier this week in Brazil.

Ashton was spotted partying hard at a Bruno Mars concert -- the day after Demi was hospitalized when she fell into convulsions at home. She was taken by ambulance to a nearby hospital ... where she's been getting treatment for substance abuse.

Demi announced her plans to divorce Ashton back in November.