Learn French: L'historien, totalement absorbé, a perdu la notion du temps. - The historian, totally absorbed, lost track of time.

You can use the connector to link his absorption (the cause) to him losing track of time (the consequence). For example: L'historien était totalement absorbé, au point qu'il a perdu la notion du temps. Remember that au point que triggers the indicative, so we keep the regular passé composé a perdu rather than using the subjunctive.

Is perdre la notion du temps the standard way to say to lose track of time?

Yes, this is the most common and idiomatic translation. Literally, it means to lose the notion of time. You might also hear ne pas voir le temps passer (to not see the time pass), but perdre la notion du temps is the exact equivalent of losing track of time.

Why does absorbé stand alone without an auxiliary verb here?

The past participle absorbé is functioning directly as an adjective modifying L'historien. Because L'historien is masculine singular, absorbé takes the default masculine singular ending. If the subject were female (L'historienne), it would be spelled totalement absorbée.

Could I place the adverb totalement after absorbé instead?