编译 \align* 时出错

Question

我写了以下代码：

\section{Quantum Harmonic Oscillator}
 The quantum harmonic oscillator is the analogue of harmonic oscillator in classical mechanics scaled down to the quantum domain.
\subsection{One Dimensional Harmonic Oscillator}
\large{Hamiltonian and Eigenstates}
The Hamiltonian of the particle is : 

\begin{align*}
 \hat{H} $= \frac{hat{p^{2}}}{2m} + \frac{1}{2}mw^{2}\hat{x^{2}} \\
a $= b 
\end{align*}

编译时出现错误“扫描 \align* 时文件结束”。我该如何纠正这个问题？提前致谢。