# Put angle symbol between segments

I'm not sure how to put the angle arc symbol between the segments 'pm' and 'pz' in this figure I'm making:

\documentclass[tikz, border=5mm]{standalone}
\usepackage[utf8]{inputenc}
\usepackage[brazilian]{babel}
\usepackage{amssymb}
\usepackage{tikz,tkz-euclide}
\usetkzobj{all}
\usepackage{xcolor}
\usetikzlibrary{shapes.geometric,intersections,arrows.meta}

\begin{document}
\begin{tikzpicture}[scale=3, mydot/.style={fill, circle, inner sep=1.5pt},every
node/.style={font=\Large},>={Latex[length=3mm]}, decoration={markings, mark=at position
0.6 with {\arrow{latex}}}]

\node[mydot] at (2.3,-2) {};

\tkzDefPoints{0/0/O, 5/0/M, 0/-1/A, 0/-2/B, 0/-3/C, 0/-4/D, 5/-1/S1, 5/-2/S2, 5/-3/S3}

\tkzLabelPoint[right](M){{\Large $M$}}
\tkzLabelPoint[right](S1){{\Large $S_{t_1}$}}
\tkzLabelPoint[right](S2){{\Large $S_{t}$}}
\tkzLabelPoint[right](S3){{\Large $S_{t_z}$}}

\draw[very thick,name path=Xp] (.3,-1.2) .. controls +(-3:1) and +(150:.2) .. (2.3,-2)
.. controls +(-45:1) and +(178:1) .. (4.7,-2.8);

\draw[very thick,-latex,postaction={decorate},shorten >= 3pt] (2.3,-2) .. controls +
(270:1) and +(90:1) .. (2.3,-2.9);
\draw[very thick,-latex,shorten >= 3pt] (2.3,-2) .. controls +(210:0) and +(20:0) ..
(1.7,-2.6);

\node at (2.34,-1.9) {$p$};
\node at (2.45,-2.9) {$m$};
\node at (2.45,-2.5) {$\partial_t$};
\node at (1.65,-2.6) {$z$};
\node at (4.7,-2.65) {$S$};
\end{tikzpicture}
\end{document}


Can anyone help me with this?

I've redrawn the non-tkz-euclide part of your picture to simplify things and to draw the angle.

\documentclass[tikz, border=5mm]{standalone}
\usepackage[utf8]{inputenc}
\usepackage[brazilian]{babel}
\usepackage{amssymb}
\usepackage{tikz,tkz-euclide}
\usetkzobj{all}
\usepackage{xcolor}
\usetikzlibrary{shapes.geometric,intersections,arrows.meta,angles,quotes}

\begin{document}
\begin{tikzpicture}[scale=3, mydot/.style={fill, circle, inner sep=1.5pt},every
node/.style={font=\Large},>={Latex[length=3mm]}, decoration={markings, mark=at position
0.6 with {\arrow{latex}}}]

\node[mydot] at (2.3,-2) {};

\tkzDefPoints{0/0/O, 5/0/M, 0/-1/A, 0/-2/B, 0/-3/C, 0/-4/D, 5/-1/S1, 5/-2/S2, 5/-3/S3}

\tkzLabelPoint[right](M){{\Large $M$}}
\tkzLabelPoint[right](S1){{\Large $S_{t_1}$}}
\tkzLabelPoint[right](S2){{\Large $S_{t}$}}
\tkzLabelPoint[right](S3){{\Large $S_{t_z}$}}

\draw[very thick,name path=Xp] (.3,-1.2) .. controls +(-3:1) and +(150:.2) .. (2.3,-2)
.. controls +(-45:1) and +(178:1) .. (4.7,-2.8) node[above]{$S$};
\path[name path=hori] (S2) -- ++ (-5,0);
\path[name intersections={of=Xp and hori,by=p}];

\draw[very thick,-latex,postaction={decorate},shorten >= 3pt] (p)
node[above]{$p$} -- node[midway,right] {$\partial_t$} ++ (0,-0.9)
coordinate[label={[yshift=-3pt]right:$m$}](m);
\draw[very thick,-latex,shorten >= 3pt] (p) -- ++(-0.6,-0.6)
coordinate[label={[yshift=-3pt]left:$z$}] (z);

\draw pic [fill=black!50] {angle = z--p--m};
\end{tikzpicture}
\end{document}


I am wondering how much you insist on using tkz-euclide here. Without it there would be no problem to also load the babel and quotes libraries, which will allow you to write an angle without pain. (You can do that with tkz-euclide, too, but there might be a point where it becomes impractical.)