escaping forward slashes in elasticsearch

Use this query as example:

{
  "query": {
    "query_string": {
      "fields": [
        "account_number.keyword"
      ],
      "query": "AC\\/1234\\/A01",
      "analyzer": "keyword"
    }
  }
}

You should get what you want without escaping anything simply by specifying a keyword analyzer for the query string, like this:

{
  "query" : { 
     "query_string" : {
        "query" : "AC\\/1234\\/A01",
        "analyzer": "keyword"         <---- add this line
     } 
  }
}

If you don't do this, the standard analyzer is used (and will tokenize your query string) whatever the type of your field is or whether it is not_analyzed or not.