The most common and most likely answer to this crossword clue is the 6 letter word LEPTON
I've seen this crossword clue in The Daily Telegraph
L
E
P
T
O
N
More clues leading to the result LEPTON
- Particle quietly splitting gave the game away
- Parking permit outside – that’s feasible!
- Divulged information about origin of physics particle
- Greek currency soared, we hear, subject to …
- Greek money earlier showed purchasing power
- Was very keen, say, to get Greek money
- A bit spent in Athens once? Show you know about origin of Parthenon
Buddy explains!

The straight part
We know that "particle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case particle = lepton.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 LEPTON mean?
LEPTON noun- A coin used since ancient times in Greece, serving in modern times as one hundredth of a phoenix, a drachma, and a euro (as the Greek form of the Eurocent).
- A small, bronze Judean coin from the 1st century B.C.E., considered by some to be the widow's mite.
- An elementary particle that has a spin of 1/2 (i.e., is a fermion) and does not interact via the strong nuclear force; examples include the electron, the muon, the neutrino and the tauon.