$U\left(a,z\right)=\frac{e^{-\frac{1}{4}{z}^2}}{\Gamma \left(\frac{3}{4}+\frac{1}{2}a\right)}{\int }_0^{\infty }{t}^{\frac{1}{2}a-\frac{1}{4}}{e}^{-t}{\left(z^2+2t\right)}^{-\frac{1}{2}a-\frac{1}{4}}dt$