HTML form input pattern with space, small letter, capital letters and no Numeric Digits

Please help me to build a pattern in the text input field like that,

<input name="BusinessOwner" type="text" id="BusinessOwner" pattern="?">

But the rule is that this input field only allow English small letter and/or Capital letter(include/Exclude space) and no Numeric Digits. So according to the rule,

Adam Smith => valid
adam => valid
AB CD => valid
abcd12 => Invalid
abcd 12 => Invalid

Please help me to build the pattern.