Father has Mass with band of musicians (3,5)

I believe the answer is:

pop group

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'band of musicians' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'father has mass' is the wordplay.
'father' becomes 'pop' (pop is a kind of father).
'has mass' becomes 'group' (I can't explain this - if you can you should believe this answer much more).
'pop'+'group'='POP GROUP'

'with' is the link.

Can you help me to learn more?

(Another definition for pop group that I've seen is " One Direction or Westlife, say".)

I've seen this clue in the Irish Times and the Irish Times (Crosaire).

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