pronunciation - Are there other words in American English that use the same vowel sound as the "as" in "Pasta"?

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)

calm
father

bother
mop
lost
on

fast
pasta

(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).

Answer

Most American speakers use more-or-less the vowel of RP (Received Pronunciation, the most common or standard "reference" British English accent) "grass", "fast" and "arm" in all of pasta, father, mop, don. But not lost; that has a different vowel in "GA" ("General American," the "standard" reference American accent). "Lost" and "mop" have different vowels in "General American" English due to a vowel change similar to the one that is responsible for the different vowels of "last" and "lap" in RP British English. "Pasta" and "father" have the same vowel as "mop," but not the same vowel as "lost" in GA.

The vowel in the word "father" is typically written /ɑː/ when transcribing British English, with a vowl length marker (ː) because British English is often analyzed as having phonological vowel length.

Vowel length is less important (or at least, less obvious) in the phonological system of American English, so usually it is just written /ɑ/ when transcribing American speech.

Of course, as with all IPA vowel symbols, this is a simplified representation of a variable set of actual vowel sounds.

Distribution of /ɑ/ in a typical American English accent

You can see some explanation in the Wikipedia article Pronunciation of English ⟨a⟩. Basically, /ɑ/ is usual in rhotic American English accents for father, before /r/ (also analyzed as a unitary rhotic vowel /ɑ˞/), and for the majority of speakers, in some words that historically had a "short o" such as lot. The exception is words like cloth and lost where "short o" ended up being changed to the "aw" vowel of thought.

Words like palm also historically had /ɑ/, but the common restoration of /l/ has caused some speakers to change the vowel to the thought vowel (/ɔ/).