J/psi production in association with a charm-quark pair at the Tevatron

TL;DR

The paper computes the leading-order hadroproduction of J/psi in association with a ccbar pair at Tevatron energies within NRQCD, considering both color-singlet and color-octet transitions. It shows that gluon fusion dominates, with color-octet contributions becoming significant at moderate to high Pt and often controlling the high-Pt tail via gluon fragmentation, while color-singlet fragmentation is subdominant but non-negligible. The study compares full LO results to the fragmentation approximation, finding it unreliable for the Tevatron range—octet fragmentation overestimates at low Pt but aligns at high Pt, whereas charm fragmentation underestimates. The authors propose practical experimental signatures, including J/psi with charm mesons and Delta R distributions between J/psi and the softest charm, to distinguish production mechanisms and polarization patterns. A measurement of J/psi events with associated charmed mesons could illuminate the mechanisms behind inclusive heavy-quarkonium production.

Abstract

I study the direct hadroproduction of Jψassociated with a charm-quark pair at leading order in alpha_S and v in NRQCD. This process provides an interesting signature that could be studied at the Tevatron. I consider both colour-singlet and colour-octet transitions. I compare our results to the fragmentation approximation and discuss the associated experimental signatures.

Figures (6)

• Figure 1: Left-hand-side: differential cross section for the process $p\overline{p}\to J/\psi + c\overline{c}$ at the Tevatron, $\sqrt{s}=1.96$ TeV. Right-hand-side: polarisation parameter for the same process.
• Figure 2: Left-hand-side: typical Feynman diagram for the colour-octet $J/\psi$ production via the fragmentation of a gluon. Right-hand-side: typical Feynman diagram for the colour-singlet $J/\psi$ production via the fragmentation of a (anti-) charm quark.
• Figure 3: Comparison between the full LO cross section for $p\overline{p}\to J/\psi + c \overline{c}$ and the fragmentation approximation at $\sqrt{s}=1.96$ TeV, for $^3S_1$ colour-octet transition (left-hand-side plot) and for colour-singlet transition (right-hand-side plot). No cut on rapidity is applied.
• Figure 4: Angular separation between the $J/\psi$ and the $P_T$-softest charm quark, for the $^3S_1^{[8]}$ transition (left-hand-side plot) and for the $^3S_1^{[1]}$ transition (right-hand-side plot).
• Figure 5: Leading order Feynman diagrams for the c-quark initiated $J/\psi$ production process.