Aha I see now
Initially I searched for (as the author suggested)
without a space. That returns nothing. Zero results.
I was expecting it to. So I then looked at the advanced query syntax and posted above as in some of the documentation it said that ( and ) and a load of others were reserved characters and needed escaping. It seems they are not reversed cahracters.
Searching for just
(again no space) returns loads of relevant result in normal search.
(with a space)
Even with the normal searches.
It seems odd that () normal searches and \(\) for advanced returns nothing at all.
And actually that is what the problem the OP encountered. There must be something special with searching for ().