Yes they are. See the fields of psychiatry, neurology, physiological psychology, artificial intellegence and so on.
"No scientific experiment has ever or can ever confirm or disconfirm the existence of persons"
any idiot can make this observation and be scientific about it!
"or the nature of personhood"
Wrong. See the subject matter in the above fields. Note the self, or person is the subject matter of personality disorders.
"Personhood belongs entirely to the domain of philosophy."
Science will study whatever can be observed.
Cite one scientific experiment demonstrating what a person is. You can't because there is no such experiment and can never be.
Not all knowledge is obtainable or verifiable by the scientific method.
-A8