$heads =DB::table('heads');

->where('companies.company_id',$company)
        ->where('participants.dni',$dni)


public function search(Request $request){
        $company=request::get('cliente');//recuperodatosenvporgetopost.
        $dni=request::get('search')
        $heads =DB::table('heads')
        ->join('participants', 'heads.id','=','participants.head_id')
        ->join('companies','company.id','=','companies.id')
        ->select('companies.name as nom_com','participants.firstlastname as ape_pat','participants.secondlastname as ape_mat','participants.name
           as  nombre','companies.created_at as fec1','companies.updated_at as fec2')
        ->where('companies.company_id',$company)
        ->where('dni',$dni)
        ->get();
        return  Response::json('heads');
       }