the \xNN notation is used to express hexadecimal like in Javascript(Hexadecimal escape sequences).
The provided forms are the same to represent the value of :0xaca7da
Difference :
\x could be used to express a special hex(initial form) value within a string e.g : "aca7\xd4"
which is in asci will be converted to hex 0x61636137da
so 'da' keeps its form(not considered as a string).However, hex"" will consider the whole string in the hex form.