The most common and most likely answer to this crossword clue is the 8 letter word WRANGLER
I've seen this crossword clue in The Guardian
W
R
A
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G
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More clues leading to the result WRANGLER
Buddy explains!

The straight part
We know that "Cambridge mathematician" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cambridge mathematician = wrangler.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WRANGLER mean?
WRANGLER noun- Someone who wrangles or corrals.
- A cowboy who takes care of saddle horses.
- A cowboy who takes care of tourists.
- An animal handler or trainer.
- (University of Cambridge) A student who has completed the third year of the mathematical tripos with first-class honours.
- A special education teacher.