An experiment campaign does not copy previous metrics from the base campaign. It is instead treated as an entirely new campaign. During the experiment, metrics for the base campaign and the experiment campaign accrue separately; each one has its own impressions, clicks, etc. This does not change when either promoting or graduating the experiment. Metrics stay where they are and are never copied over to another campaign.
After promotion, the base campaign keeps all of its past metrics and goes forward with the new changes copied into it. The metrics from the experiment campaign are still associated with the experiment campaign after promotion.
After graduation, the base campaign and experiment campaign continue to exist as separate entities and each one keeps its own metrics for reporting.
You can report on experiment campaigns in all the same ways you could report on
regular campaigns. You can differentiate a experiment campaign and a base
campaign in your search query by selecting
EXPERIMENT to differentiate the type of campaign.