Fully charmed tetraquark production in forward rapidity $pp$ collisions at LHC and FCC energies

TL;DR

This paper addresses the forward-production of a fully charmed tetraquark $T_{4c}$ in $pp$ collisions by integrating the Color Glass Condensate (CGC) framework with hybrid factorization and the rcBK evolution. It treats both gluon-initiated and charm-initiated fragmentation channels, incorporating an intrinsic charm component in the projectile, and uses the TQ4Q1.1 fragmentation functions for the three lowest Fock states $(J^{PC}=0^{++}, 1^{+-}, 2^{++})$ to predict the $p_T$ distributions at LHC ($er s=13$ TeV) and FCC ($er s=100$ TeV) energies in forward rapidity. The results show that the tensor state $T_{4c}(2^{++})$ is predominantly GI-driven and yields cross sections of order a few nb at the LHC, increasing at the FCC, while the axial-vector $T_{4c}(1^{+-})$ is highly sensitive to intrinsic charm and mainly CI-driven. These findings suggest that forward measurements at current and future colliders could probe intrinsic charm and non-linear QCD dynamics through exotic heavy hadron production, with the IC effect more pronounced at lower energies and high rapidities.

Abstract

In this paper, we investigate the production of a fully charmed tetraquark state $T_{4c}$ in $pp$ collisions at forward rapidities through the fragmentation mechanism considering the Color Glass Condensate (CGC) formalism and the solution of the running coupling Balitsky-Kovchegov (BK) equation. The contributions of gluon - and charm - initiated processes are taken into account, and the impact of an intrinsic charm component in the proton's wave function is estimated. Predictions for the transverse momentum distribution of the $T_{4c}$ state are presented assuming different rapidities, distinct quantum numbers of the state and center-of-mass energies. Our results indicate that the higher cross-section is associated with the production of a tensor state $T_{4c}(2^{++})$, which is dominated by the gluon-initiated process. In contrast, the production of the axial-vector state $T_{4c}(1^{+-})$ is dominated by the charm-initiated process and is very sensitive to the presence (or not) of an intrinsic charm.

Figures (7)

• Figure 1: Gluon (left) and charm (right) - initiated contribution for the production of a $T_{4c}$ state with transverse momentum $p_T$ and rapidity $y$ in $pp$ collisions.
• Figure 2: Predictions of the different intrinsic charm models for the $x$ - dependence of the charm (lower blue curves) and gluon (upper red curves) distributions, as obtained by the CT18 (left panel) and NNPDF (right panel) parametrizations Hou:2019qauGuzzi:2022rca.
• Figure 3: Dependence on $z$ of the TQ4Q1.1 functions describing the gluon (left panels) and charm (right panels) fragmentation channels into scalar tetraquarks $T_{4c}(0^{++})$ (upper panels), axial-vector tetraquarks $T_{4c}(1^{+-})$ (middle panels) and tensor tetraquarks $T_{4c}(2^{++})$ (lower panels), calculated at various factorization scales $\mu_F$. Filled bands represent the uncertainties associated with LDMEs.
• Figure 4: Dependence of the transverse momentum distribution on the quantum numbers assumed for the $T_{4c}$ state. Results for the $T_{4c}$ production in $pp$ collisions at the LHC (left panel) and FCC (right panel) energies and fixed rapidity ($y = 5.0$).
• Figure 5: Contributions of the GI and CI processes for the transverse momentum distribution associated with the $T_{4c}(2^{++})$ production in $pp$ collisions at the LHC (left panel) and FCC (right panel) energies and fixed rapidity ($y = 5.0$). Results derived considering the solution of the rcBK equation and distinct PDFs.