Elasticsearch-6.x norms false not working

[1a8e272e90cd3e11c4cb (runtime)]

That is what I have Done:
First:
curl -X PUT "localhost:9200/log_20180419"

Second

curl -X PUT "localhost:9200/log_20180419/_mapping/_doc" -H 'Content-Type: application/json' -d'
    {
      "properties": {    
        "title": {
          "type": "text",
          "norms": false
        }
      }
    }
    '

Third

    #I insert data with python client : elastisearch-py
    from elastisearch import Elastisearch
    es_conn = Elastisearch()
    content_tmp = "acxzcasiuchxzuicbhasuicgzyugas%s"
    for i in range(10000):
        result = content_tmp % i
        es_conn.index(index="log_20180419", body = {"title":result}, doc_type="_doc")

Forth
I Query It

curl -X GET "localhost:9200/log_20180419/_search?pretty" -H 'Content-Type: application/json' -d'
{
    "query": { 
        "match":{
  
  
  
  "title":"dasuioczxuivcaduciqanbcaiushcauinhauincsaincdjkxzcbyquiwbjkfcznkajsbcjkzxhcuiasbcjkzxchjdsfasckjbjak9999"
        }
    }
}
'

Result is

{
  "took" : 1,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : 1,
    "max_score" : 7.2293553,
    "hits" : [
      {
        "_index" : "log_20180419",
        "_type" : "_doc",
        "_id" : "oDR99mIBBZEcRu0i7LlO",
        "_score" : 7.2293553,
        "_source" : {
          "title" : "dasuioczxuivcaduciqanbcaiushcauinhauincsaincdjkxzcbyquiwbjkfcznkajsbcjkzxhcuiasbcjkzxchjdsfasckjbjak9999"
        }
      }
    ]
  }
}

You can see, it still has _score file in result, I get Confuse with it ?
The Doc is here norms | Elasticsearch Guide [8.11] | Elastic