Z^0 Decay into Charmonium via Charm Quark Fragmentation
Eric Braaten, Kingman Cheung, Tzu Chiang Yuan
TL;DR
The fragmentation functions describing the splitting of charm quarks into S-wave charmonium states to leading order in the QCD coupling constant are calculated and agree with the complete leading order calculation of the rate for Z 0 → ψcc.
Abstract
In decays of the $Z^0$, the dominant mechanism for the direct production of charmonium states is the decay of the $Z^0$ into a charm quark or antiquark followed by its fragmentation into the charmonium state. We calculate the fragmentation functions describing the splitting of charm quarks into S-wave charmonium states to leading order in the QCD coupling constant. Leading logarithms of $M_Z/m_c$ are summed up using Altarelli-Parisi evolution equations. Our analytic result agrees with the complete leading order calculation of the rate for $Z^0 \rightarrow ψc {\bar c}$. We also use our fragmentation functions to calculate the production rate of heavy quarkonium states in $W^\pm$, top quark, and Higgs decays.