Putting the symbol hat in math mode in LaTeX How to put the hat in the above symbol in LaTeX?

• Hat covers the whole expression. – Suman Nov 29 '13 at 7:48
• possible duplicate of Really wide hat symbol – Federico Nov 29 '13 at 7:55
• @Federico It is not a duplicate of the suggested question. OP wants hat after, not over the whole expression. – Przemysław Scherwentke Nov 29 '13 at 9:37
• @PrzemysławScherwentke that it is not what I understand from its comment above: "Hat covers the whole expression" – Federico Nov 29 '13 at 9:46
• Sorry @Federico. I wanted to mean after the whole expression. – Suman Nov 29 '13 at 14:08

I understand, that it is like some kind of Fourier transform of the whole expression. An alternative version added.

\documentclass{article}

\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}

\newcommand{\Sel}{\operatorname{Sel}}

$\Sel_{E}^{\Sigma_0}(\mathbb{Q}_\infty)_p{}\widehat{}$

But probably better

$(\Sel_{E}^{\Sigma_0}(\mathbb{Q}_\infty)_p)\,\widehat{}$

\end{document} If a really wide "hat" symbol that should cover the entire expression is what you're after, you may want to look into using the Mathtime Professional 2 (mtpro2) package. The full package isn't free of charge, but its "lite" subset, which is all that's needed to create a superwide hat symbol, is indeed free. \documentclass{article}
\usepackage{amsmath,amssymb}
\newcommand{\Sel}{\operatorname{Sel}}
\usepackage[lite]{mtpro2}
\begin{document}
\begin{equation*}
\widehat{\Sel_{\mathrm{E}}^{\Sigma_0}(\mathbb{Q}_\infty)_p}
\end{equation*}
\end{document}

you write

Hat covers the whole expression

Do you mean something like this?

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}

\newcommand{\Sel}{\operatorname{Sel}}

\begin{equation*}
\widehat{\Sel_{E}^{\Sigma_0}(\mathbb{Q}_\infty)_p{}}
\end{equation*}

\end{document}

also, you might want to check this question