If you only had one sex partner during that time frame (say within two weeks), you can be reasonably confident that he's the father. Otherwise, if you're asking for paternity reasons, you'll need to do DNA testing. This can be done via amniocentesis but is much riskier and more expensive than waiting till after birth. An infant cheek swab and lab testing on the prospective father will cost about $500.
Sperm can survive in your body for up to 5-7 days. So it could've been anywhere up to a week before your conception date.
Also, you may not have conceived on the exact same day you ovulated. So it could also have been up to roughly a day or two after ovulation if you ovulated on the 23rd.