Tetraquark-Jet Systems at the High-Luminosity LHC

Abstract

We investigate the high-energy production of tetraquark-jet systems at the LHC and its forthcoming High-Luminosity upgrade. In this review, we examine the leading-power fragmentation of fully heavy tetraquarks ($T_{4Q}$) in hadronic collisions, highlighting their relevance as novel probes of multiquark dynamics in QCD. Our analysis relies on the hadron-structure-oriented TQ4Q1.1 fragmentation functions, built within a nonrelativistic QCD framework that incorporates both gluon- and heavy-quark-initiated channels. Threshold-consistent DGLAP evolution is performed through the HF-NRevo scheme, enabling a unified treatment of mass thresholds and scale variations. We also provide a systematic discussion of uncertainties arising from color-composite long-distance matrix elements (LDMEs) and from perturbative hard- and fragmentation-scale inputs (H- and F-MHOUs). Phenomenological predictions are obtained using the (sym)Jethad framework at NLL/NLO$^+$ accuracy for semi-inclusive tetraquark-jet production at the LHC and beyond. This review connects the emerging spectroscopy of fully heavy exotics with modern fragmentation-based approaches to hadron structure and high-energy QCD.

Figures (10)

• Figure 1: LO diagrams illustrating the collinear fragmentation of a gluon (left) and a heavy quark (right) into a fully heavy $S$-wave tetraquark in a color-singlet state. The partonic interactions shown on the left of each panel represent the perturbative SDCs, whereas the orange blobs on the right denote the nonperturbative LDMEs responsible for the hadronization into the physical tetraquark.
• Figure 2: $z$-profiles of the TQ4Q1.1 FFs for scalar tetraquarks $T_{4c}(0^{++})$ (left) and $T_{4b}(0^{++})$ (right) at various scales. Upper (lower) panels correspond to heavy-quark (gluon) channels. Main-panel bands combine F-MHOU and LDME uncertainties; lower panels display, respectively, F-MHOUs as replica envelopes and LDME effects as ratios to the central curve.
• Figure 3: $z$-profiles of the TQ4Q1.1 FFs for axial-vector tetraquarks $T_{4c}(1^{+-})$ (left) and $T_{4b}(1^{+-})$ (right) at various scales. Upper (lower) panels correspond to heavy-quark (gluon) channels. Main-panel bands combine F-MHOU and LDME uncertainties; lower panels display, respectively, F-MHOUs as replica envelopes and LDME effects as ratios to the central curve.
• Figure 4: $z$-profiles of the TQ4Q1.1 FFs for tensor tetraquarks $T_{4c}(2^{++})$ (left) and $T_{4b}(2^{++})$ (right) at various scales. Upper (lower) panels correspond to heavy-quark (gluon) channels. Main-panel bands combine F-MHOU and LDME uncertainties; lower panels display, respectively, F-MHOUs as replica envelopes and LDME effects as ratios to the central curve.
• Figure 5: Sketch of the semi-inclusive hadroproduction of a tetraquark-jet system within ${\rm NLL/NLO^+}$ factorization (diagram generated with JaxoDraw 2.0Binosi:2008ig). Collinear PDFs are represented by red ovals, while the off-shell emission vertex associated with the tetraquark (jet) is shown as a green (violet) blob. Tetraquark emissions are indicated by orange arrows. The central blue oval denotes the BFKL Green's function.