The number of beams produced in the Stern-Gerlach experiment is related to the angular momentum quantum number $l$. The magnetic quantum number $m_l$ can take integer values ranging from $-l$ to $+l$ in steps of 1, so the total number of possible values for $m_l$ is $2l + 1$.
Given that the angular momentum is $\sqrt{12} \hbar$, we know that:
\[
l = \sqrt{12} ⇒ l = 2
\]
Thus, the number of possible values for $m_l$ is:
\[
2l + 1 = 2(2) + 1 = 5
\]
So, the beam splits into 7 distinct beams. Therefore, the correct answer is (B).