Hadronic production of $Ξ_{cc}$ at a fixed-target experiment at the LHC

TL;DR

The paper develops a NRQCD-based framework for hadronic production of doubly heavy baryons at the After@LHC fixed-target setup, incorporating both gluon-gluon fusion and extrinsic charm channels with multiple $(cc)$ diquark configurations. It provides quantitative predictions for $Ξ_{cc}$, $Ξ_{bc}$, and $Ξ_{bb}$ yields, showing that large $Ξ_{cc}$ and $Ξ_{bc}$ rates are feasible at After@LHC, with extrinsic charm dominating at small $p_t$ and PMC-scale setting reducing theoretical uncertainties. The results suggest After@LHC as a promising platform to study baryon properties, probe small-$x$ QCD dynamics, and potentially address the SELEX discrepancy, while highlighting the importance of small-$p_t$ measurements and diquark fragmentation assumptions. Overall, the work emphasizes the value of fixed-target hadroproduction in constraining heavy-baryon production mechanisms and QCD factorization details.

Abstract

In the paper, we present a detailed discussion on the $Ξ_{cc}$ production at a fixed target experiment at the LHC (After@LHC). The doubly charmed baryon $Ξ_{cc}$ is produced via the channel, ${\rm Proton} + {\rm Proton}\toΞ_{cc}+X$. In estimating its hadroproduction, we discuss three dominant subprocesses, e.g. $g+g\to Ξ_{cc} +\bar{c} +\bar{c}$, $g+c\to Ξ_{cc}+\bar{c}$ and $c+c\to Ξ_{cc}+g$. During the production, it shall first generate a binding diquark and then form the $Ξ_{cc}$ baryon by grabbing soft light-quarks or gluons. We observe that both the two diquark configurations $(cc)[^3S_1]_{\bf\bar 3}$ and $(cc)[^1S_0]_{\bf 6}$ can have sizable contributions to the $Ξ_{cc}$ production. Large number of $Ξ_{cc}$ events can be generated at the After@LHC, whose total production cross section is larger than that of the SELEX experiment by about thirty-five times. It may also possible to study the properties of $Ξ_{bc}$ at the After@LHC. More specifically, we shall have about $8.3 \times 10^6$ $Ξ_{cc}$ events/year and $1.8 \times 10^4$ $Ξ_{bc}$ events/year when its integrated luminosity approaches to $2$ fb$^{-1}$/year. Thus, in addition to SELEX and LHC, the After@LHC shall provide another useful platform for studying the baryon properties.

Figures (7)

• Figure 1: The schematic Feynman diagrams for the baryon production via the gluon-gluon fusion mechanism, $g(p_{1})+g(p_{2}) \to \Xi_{QQ'}(p_3) + \bar{Q}(p_{4})+\bar{Q'}(p_{5})$ with the diquark state $(QQ')[n]$, where $Q$ or $Q^{\prime}$ stands for $b$ or $c$ quark, respectively. The dashed boxes stand for the hard interaction kernel, each contains $36$ Feynman diagrams.
• Figure 2: Typical Feynman diagrams for the process $c(p_{1})+g(p_{2}) \to \Xi_{cc}(p_{3})+ \bar{c}(p_{4})$ via the diquark state $(cc)[n]$, where the intermediate $(cc)$-diquark is in $[^3S_1]_{\bar{\textbf{3}}}$ or $[^1S_0]_{\textbf{6}}$, respectively.
• Figure 3: Typical Feynman diagrams for the process $c(p_{1})+c(p_{2}) \to \Xi_{cc}(p_{3})+ \bar{c}(p_{4})$ via the diquark state $(cc)[n]$, where the intermediate $(cc)$-diquark is in $[^3S_1]_{\bar{\textbf{3}}}$ or $[^1S_0]_{\textbf{6}}$, respectively.
• Figure 4: The $\Xi_{cc}$, $\Xi_{bc}$, and $\Xi_{bb}$$p_t$-distributions for various intermediate diquark states at the After@LHC, in which no rapidity cut has been applied.
• Figure 5: The $\Xi_{cc}$, $\Xi_{bc}$, and $\Xi_{bb}$ rapidity distributions for various intermediate diquark states at the After@LHC, where the $p_t>0.2$ GeV is taken.