Question: when did the beatles became popular in the us
[{'answer': 'February 1964', 'provenance': [{'wikipedia_id': '844475', 'title': 'Beatlemania', 'start_paragraph_id': 2, 'start_character': 3, 'end_paragraph_id': 2, 'end_character': 16, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]