search: word1 word2 word3 to use AND-ing instead of OR-ing

[tiborsimko]

Current behaviour

Search for cms event. You get 5040 hits including PHENIX record etc which are not what users would expect.

This is because searching for cms event is equivalent to searching for cms OR event, followed by appied ranking.

If you look for cms AND event, you get 1038 hits which are closer to what users expect. (I.e. no PHENIX record, etc).

Expected behaviour

When a user searches for word1 word2 word3, one would expect to do word1 AND word2 AND word3 query instead of current word1 OR word2 OR word3. The former is much more common in general search engines.

Let's change the behaviour to "silent AND" instead of "silent OR" for multi-word queries.