Use the -i flag to perform a case-insensitive search with ack.

$ ack -i easter

ack/ack-bar.md
3:The [`ack`](https://beyondgrep.com/) utility has a fun Easter egg that dumps

postgres/configure-the-timezone.md
18:Eastern time.

If you are a Vim user, you may be familiar with smart-case. The --smart-case option is a related Ack feature worth checking out.

See man ack for more details.