Obviously, pasta is a loanword, but generally loanwords are pronounced with the closest vowels which already exist in the language.
In American English, the "a" in pasta is the same vowel that I hear in RP British English words like "grass", "fast" and "arm". Which is strange, because that isn't how Americans pronounce words with a long a sound in RP such as "fast", "last" and "bath".
In British English, "pasta" has a short A. In my dialect, there is no trap-bath split, so I pronounce "pasta" the same as I would words such as "past" and "cast".
I asked in the original question if pasta had the same vowel as "lost" and "mop". The answer seems to have been no, but that it is the same vowel as father.
This is a little confusing, and I understand that most American accents have a "father-bother" merger, so it's confusing to me that pasta does share a vowel with father, but not with lost
In order to narrow it down, in terms of their vowels, how does the following list fit together in the majority of American Accents (I've grouped them based on my accent)
(I've left out "caught" words, as I don't think it's relevant here, but if I'm wrong and should have chosen some different words, then please do correct me).