Exploring a low-mass H dibaryon in light of the LZ event: A QCD sum rule study

Abstract: The LUX-ZEPLIN (LZ) Collaboration recently reported a candidate event consistent with a high-energy nuclear recoil, motivating a possible interpretation by Lee, Takahashi, and Tsai involving the production of an invisible baryon-number-two scalar with a mass near $1.85$ GeV. Motivated by this hypothetical scenario, we investigate the $J<sup>P=0<sup>+$ $uuddss$ hexaquark system using QCD sum rules. We consider five local diquark-diquark-diquark interpolating currents with different scalar and axial-vector diquark combinations, together with a baryon-baryon current constructed from two $Λ$-type baryon currents. The operator product expansions are calculated up to dimension sixteen, and their numerical behaviors are examined under different OPE truncations. Among the currents considered, only the $SU(3)<em>{\rm flavor}$-singlet current $J</em>{SSS}$, consisting of three scalar color-$\bar{\mathbf{3}}<em>C$ diquarks, yields a low-mass solution at $D=12$, with $M</em>{SSS}=1.85<sup>{+0.19}_{-0.20}$ GeV. Interestingly, scalar color-$\bar{\mathbf{3}}_C$ diquarks belong to the flavor $\bar{\mathbf{3}}_F$ representation, and their local color-singlet construction has a unique nonvanishing flavor structure, $[ud][ds][su]$, corresponding to $uuddss$. Analogous all-scalar-diquark currents vanish for other flavor configurations, such as $uuuddd$ and $uuudds$. Together with our QCD sum-rule results, this property highlights the special role of the all-scalar-diquark configuration, $[ud][ds][su]$, as a possible deeply bound structure. However, the higher-dimensional OPE contributions exhibit significant truncation dependence, and the low-mass solution remains conditional on the adopted OPE truncation rather than constituting a fully controlled mass prediction.