Color-Singlet and Color-Octet Quark Matters

TL;DR

The work proposes that color-singlet $q\bar{q}$ quark matter, confined by a confining QED interaction, can form stable QED mesons with masses near $m_{I=0}^{QED}\approx 17.9$ MeV and $m_{I=1}^{QED}\approx 36.4$ MeV, offering a potential explanation for anomalous soft photons and the X17/E38 observations. It builds a theoretical framework using $3\otimes\bar{3}=1\oplus8$ to distinguish color-singlet and color-octet sectors, applies the Schwinger confinement mechanism in 1+1D to estimate QED and QCD meson masses, and connects predictions to experimental signals across ATOMKI, HUS, and Dubna. The paper also explores extensions to $qqq$ color-singlet matter, including a hypothesized QED neutron with mass around 44.5 MeV that could be a dark matter candidate, and even speculative QED neutron stars. If confirmed, these results would reveal a confining regime for QED and yield new phases of quark matter with broad implications for particle physics and astrophysics. The work calls for targeted experiments to confirm X17/E38 and to search for QED mesons in diverse environments.

Abstract

Quarks and antiquarks carry color and electric charges and belong to the color-triplet $3$ group and the color-antitriplet $\bar 3$ group respectively. The product groups of $3$ and $\bar 3$ consist of the color-singlet $1$ and the color-octet $8$ subgroups. Therefore, quarks and antiquarks combine to form color-singlet $[q \bar q]^1$ quark matter and color-octet $[q \bar q]^8$ quark matter. The color-octet quark matter corresponds to the $q\bar q$ quark matter as envisaged in the realm of present knowledge but the color-singlet quark matter is as yet unexplored and now submitted for exploration. The color-singlet quark matter with two flavors can be separated into charged and neutral color-singlet quark matters. In the neutral color-singlet quark matter, the quark and the antiquark interacting only in the QED interaction may form stable and confined colorless QED mesons non-perturbatively at about 17 MeV and 38 MeV (PRC81,064903(2010) and JHEP(2020(8),165). It is proposed that the possible existence of the QED mesons may be a signature of the neutral color-singlet quark matter at $T=0$. The observations of the anomalous soft photons at CERN, and the anomalous bosons with mass about 17 MeV at ATOMKI, DUBNA, and HUS, and mass about 38 MeV at DUBNA hold promising experimental evidence for the existence of such QED mesons, pending further confirmations.

Figures (7)

• Figure 1: The classification of the $q\bar{q}$ quark matter with two light flavors in color space, temperature $T$, and possible phases. The big question mark points to new and unexplored physics frontiers worthy of further exploration.
• Figure 2: The anomalous soft photon yield in the $e^+e^-$ annihilation at $Z^0$ energy in DELPHI measurements at CERN DEL10. In Fig. 2(a), (Yield$_1$) is the yield as a function of the number of neutral particles, $N_{\rm neu}$, inclusive of different number of charged particles, $N_{\rm ch}$. In Fig. 2(b), (Yield$_2$) is the yield as a function of $N_{\rm par}$=$N_{\rm neu}$+$N_{\rm ch}$, the total number of neutral and charged particles.
• Figure 3: The $e^+e^-$ opening angle distribution, $\sin( \theta_{e^+e^- })dP /d\Omega_{\theta_{e^+e^- }}$, for different proton $E_p^{\rm lab}$, different kinetic energies $K$ of the X17 boson, and different reaction initial participants and final compound nucleus states, for $m_{X17}$=16.7 MeV.
• Figure 4: The invariant mass distribution of the emitted $e^+$ and $e^-$ in the de-excitation of the compound nucleus $^4$He$^*$ state at 20.49 MeV in the $^3$H($p,e^+e^-){}^4$He$_{\rm gs}$ reaction at $E_p^{\rm lab}=$0.9 MeV as given in Kra19. Red data points are the data in the signal region, $19.5 < E_{e^+e^-}<$ 22.0 MeV, and black points are data in the background region, $5 < E_{e^+e^-}<$ 19.0 MeV .
• Figure 5: Comparison of the experimental data of the minimum opening angle $\theta_{e^+e^-}$(min) as a function of the X17 kinetic energy $K$ from ATOMKI Kra16Kra21Kra22Kra23 and HUS Tra24 for different collision energies, targets, and final states. The X17 emission model envisages the fusion of the incident proton $p$ with the target nucleus $B$ forming a compound nucleus $C^*$, which subsequently de-excites to the final state $C_{\rm f}$ with the simultaneous emission of the X17 particle. Subsequent decay of the X17 particle into $e^+$ and $e^-$ then gives the angle $\theta_{e^+e^-}$ between $e^+$ and $e^-$. The curves give the theoretical predictions of $\theta_{e^+e^-}$(min) as a function of the X17 kinetic energy $K$.