Charm and Beauty in Charged Current events

In charged current processes, $e^\pm p \rightarrow \stackrel{{\small (-)}}{\nu} X$, the charge of the exchanged $W$-boson provides sensitivity to the charges of the quarks and anti-quarks in the proton. Charm final states in charged current events are dominantly produced from the strange-quark distribution in the proton, $s W^+ \rightarrow c$, as the contribution from $d W^+ \rightarrow c$ processes is Cabibbo-suppressed: $d^2 \sigma(e^+p\rightarrow cX)/dxdQ^2 \propto (1-y)^2 (d(x)\vert V_{cd}\vert^2 + s(x)\vert V_{cs}\vert^2)$.

The production of charm in charged current processes has been used at fixed target experiments [243]. At HERA-I, first attempts to measure charm final states in charged current events have been made, but the statistical precision is yet too limited for the measurement to be performed. With the HERA-II statistics and refined methods of charm tagging, the measurement of charm production in charged current processes should become possible.