Index not used on DATE col when a range of days are passed in the query

Hello All,

can someone please help me understand why INDEX (which is on SCANNED and datatype is Date) is not used when i am .range of days?

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select out_value,count(*) as freq from tws_rav_prd.st_iws_fields where (application,batch)

in(select application,batch from tws_rav_prd.st_iws_summary where application = 'xxxx' and scanned between sysdate - 60 and sysdate )

and field_name in ('ClassificationTitle','ClassificationFormat')

and op_setvalue = 1

group by out_value;

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Indexes are as below:

IDX_FEILD_ID ST_IWS_FIELDS

IDX_PAGE_ID ST_IWS_FIELDS

IDX_ST_IWS_FIELDS ST_IWS_FIELDS