The global search index is configured in the above-mentioned configuration file (portal/WEB-INF/conf/jcr/repository-configuration.xml) in the tag "query-handler".

<query-handler class="org.exoplatform.services.jcr.impl.core.query.lucene.SearchIndex">

In fact, when using Lucene, you should always use the same analyzer for indexing and for querying, otherwise the results are unpredictable. You don't have to worry about this, eXo JCR does this for you automatically. If you don't like the StandardAnalyzer configured by default, just replace it by your own.

If you don't have a handy QueryHandler, you should learn how to create a customized Handler in 5 minutes.