Hidden Light Scalars in Heavy-Ion Collisions: A Phenomenological Resolution to High-$p_T$ Quarkonium Anomalies

Abstract: The suppression of heavy quarkonia in heavy-ion collisions is a well-established signature of Quark-Gluon Plasma (QGP) formation. However, recent LHC measurements of the $Υ(1S)$ state exhibit an anomalous high-$p_T$ plateau in the nuclear modification factor ($R_{AA}$) and a vanishing elliptic flow ($v_2$), challenging standard QCD transport models. We propose a viable mechanism to account for these observations by introducing a minimal dark scalar $φ$ situated within a strict kinematic merging window ($m_φ\approx 9.40$~GeV). We demonstrate that the shared $p_T<sup>{-4}$ asymptotic fragmentation scaling between the hard-scattered dark scalar and Non-Relativistic QCD (NRQCD) color-octet production provides a constant theoretical dark fraction at high momenta. By extracting this fraction ($C_φ\approx 13.8\%$) from the anomalous $R_{AA}$ plateau, we establish a consistent phenomenological correlation: a single parameter addresses the $R_{AA}$ flattening, dilutes the inclusive $v_2$ toward zero, mitigates the long-standing quarkonium polarization puzzle, and naturally evades historical low-$p_T$ dimuon searches via a dynamic detector resolution threshold. We emphasize that future high-precision measurements of the dimuon mass lineshape at extreme transverse momenta are crucial for testing this paradigm.