\documentclass[12pt]{article}
\addtolength{\hoffset}{-.25in}
\addtolength{\textwidth}{0.5in}
\addtolength{\voffset}{-0.5in}
\addtolength{\textheight}{1.0in}
\def\mtiny{\vrule width 0pt}
\def\mrm#1{\mathrm{#1}}
\def\DZ{\relax\ifmmode{D^0}\else{$\mrm{D}^{\mrm{0}}$}\fi}
\def\DZZ{\relax\ifmmode{D^\circ}\else{$\mrm{D}^{\mrm{\circ}}$}\fi}
\def\DZY{\relax\ifmmode{D^o}\else{$\mrm{D}^{\mrm{o}}$}\fi}
\def\DZB{\relax\ifmmode{\overline{D\mtiny^0}}
	\else{$\overline{\mrm{D}\mtiny^{\mrm{0}}}$}\fi}
\def\DZC{\relax\ifmmode{\overline{D}\mtiny^0}
	\else{$\overline{\mrm{D}}\mtiny^{\mrm{0}}$}\fi}
\def\DZD{\relax\ifmmode{{\bar D}\mtiny^0}
	\else{${\bar{\mrm{D}}}\mtiny^{\mrm{0}}$}\fi}
%-----------------------------------
\title{\underline{\textbf{\DZ, \DZB, \DZC, \DZD, \DZZ, \DZY}}}
\author{\textbf{Harry Nelson}}
\begin{document}
\maketitle
  \DZ, \DZB, \DZC, \DZD, \DZZ, \DZY\newline
 $\DZ$, $\DZB$ , $\DZC$ , $\DZD$, $\DZZ$ , $\DZY$ \newline

Looks to me like the RPP uses \DZ-\DZC\ mixing.
\end{document}