I got solution to track campaigns experiment status with one extra
ExperimentService.get call,hope it will help others.
$experimentService = $user->GetService('ExperimentService', ADWORDS_VERSION);
// Create selector.
$selector = new Selector();
$selector->fields = array('ServingStatus');
$campaignId = array("878745484","96587412"); //campaigns ids for tracking experiments
// Create predicates.
$selector->predicates[] = new Predicate('CampaignId', 'IN', $campaignId);
$selector->predicates[] = new Predicate('Status', 'EQUALS', 'ENABLED');
$result=$experimentService->get($selector);
print '<pre>';
print_r($result);