A system with the transfer function $\frac{Y(s)}{X(s)}=\frac{s}{s+p}$ has an output $y(t)=\cos \left(2 t-\frac{\pi}{3}\right)$ for the input signal $x(t)=p \cos \left(2 t-\frac{\pi}{2}\right)$. Then, the system parameter $’p’$ is
- $\sqrt{3}$
- $\frac{2}{\sqrt{3}}$
- $1$
- $\frac{\sqrt{3}}{2}$