Can we give user access to one help center en not the others ?

Can we give user access to one help center en not the others ?

Hello,

Concerning Help Centers and user access : there is any possibility to separate users rights ?
In my company, we manage many help centers (1 help center = 1 company). When I create user and I given "final user" rights to this user and so to be abble to loggin into his help center... I can't say "this user can loggin to this help center an not the others".
Today, my final users can acccess to all my help center. 

Thanks,