IMO _the_ resource on search UI design is http://searchuserinterfaces.com/ - very well researched booked, although getting a little dated (was written before the mobile app boom took off) but for example detailed coverage of the topic at hand - the design of the search box - http://searchuserinterfaces.com/book/sui_ch4_query_specifica... (the whole book is free to read online) e.g.
"Some interfaces allow the searcher to cut-and-paste long swaths of text into the search box, whereas others present short entry forms and limit the number of terms that the system will accept for processing. Researchers have speculated that short query forms lead to short queries. To test this hypothesis, [Franzen and Karlgren, 2000] designed two different query entry form boxes. The first showed one empty line and only 18 visible characters (but would accept up to 200 characters) and the second showed 6 lines of 80 characters each, which allowed arbitrarily long queries to be entered. The authors asked 19 linguistics students to use one of the two interfaces and to find relevant documents for three queries. There was a statistically significant difference between the two conditions, with those using the short box using 2.81 words on average, versus 3.43 for those using the larger box."
[Franzen and Karlgren, 2000]
K. Franzen and J. Karlgren. Verbosity and interface design. Technical report, Technical Report T2000, 2000.
"Some interfaces allow the searcher to cut-and-paste long swaths of text into the search box, whereas others present short entry forms and limit the number of terms that the system will accept for processing. Researchers have speculated that short query forms lead to short queries. To test this hypothesis, [Franzen and Karlgren, 2000] designed two different query entry form boxes. The first showed one empty line and only 18 visible characters (but would accept up to 200 characters) and the second showed 6 lines of 80 characters each, which allowed arbitrarily long queries to be entered. The authors asked 19 linguistics students to use one of the two interfaces and to find relevant documents for three queries. There was a statistically significant difference between the two conditions, with those using the short box using 2.81 words on average, versus 3.43 for those using the larger box."
[Franzen and Karlgren, 2000] K. Franzen and J. Karlgren. Verbosity and interface design. Technical report, Technical Report T2000, 2000.