Gluon Condensation as a Unifying Mechanism for Special Spectra of Cosmic Gamma Rays and Low-Momentum Pion Enhancement at the Large Hadron Collider

TL;DR

GC is proposed as a mechanism that unifies two seemingly disparate phenomena: the broken power-law gamma-ray spectra from ultra-high-energy proton collisions in astrophysical sources and the low-momentum pion enhancement observed in LHC heavy-ion collisions. The approach traces nonlinear QCD evolution from CGC to GC via the ZSR framework, producing a peaked gluon distribution that drives prolific, low-momentum pion production and yields observable consequences through a simplified energy-conservation, hadronization picture. The key results show that GC can reproduce the BPL gamma spectra across hundreds of sources and explain the ALICE low-pT signal without requiring Bose-Einstein condensation, while providing clear predictions for future high-energy colliders. These findings position GC as a testable, novel structure within the Standard Model, with broad implications for particle physics and high-energy astrophysics, and offer a framework to study matter under extreme conditions.

Abstract

Decoding the internal structure of the proton is a fundamental challenge in physics. Historically, any new discovery about the proton has fuelled advances in several scientific fields. We have reported that gluons inside the proton accumulate near the critical momentum due to chaotic phenomena, forming gluon condensation. Surprisingly, the pion distribution predicted by this gluon distribution for the production of high-energy proton collisions could answer two puzzles in astronomy and high-energy physics. We find that during ultrahigh-energy cosmic ray collisions, gluon condensation may abruptly produce a large number of low-momentum pions, whose electromagnetic decays have the typical breakout properties appearing in various cosmic gamma-ray spectra. On the other hand, the Large Hadron Collider (LHC), which is well below the cosmic ray energy scale, also shows weak but recognisable signs of gluon condensation, which had been mistaken for BEC pions. The connection between these two phenomena, which occur at different scales in the Universe, supports the existence of a new structure within the proton-gluon condensation.

Figures (5)

• Figure 1: The evolution of gluon distribution in a QCD evolution equation from a CGC model to GC, where gluons at $x<x_c$ are condensed at a critical momentum $(x_c,k_c)$. All coordinates are on the logarithmic scale. There are two characteristics of this distribution: a sharp peak at the critical momentum and no gluons present at $x<x_c$.
• Figure 2: Inclusive gluon rapidity distribution in the $A-A$ collisions using ZSR equation and input Figure \ref{['fig:1']} at different energy $\sqrt{s}$. The panels a–i illustrate different regimes of $\sqrt{s}$, ranging from $\sqrt{s_{GC}}$ up to $1000\sqrt{s_{GC}}$. The resulting blue curves show the large fluctuations are arisen by GC. The black broken curves indicate the results without the QCD evolution.Using astrophysical cases, we estimate that gluon condensation in heavy-nucleus collisions occurs at $\sqrt{s_{GC}} \approx 1.4$ TeVZhu2022. Thus, Figures \ref{['fig:2']}b and \ref{['fig:2']}c correspond to the LHC energy region, where hadronization via a fragmentation model reproduces the results of Begun and Florkowski. Beyond Figure \ref{['fig:2']}f, the processes involve ultra-high-energy hadronic collisions producing $\gamma$ rays. They indicate that condensed gluons generate a vast number of mini-jets, whose pion production nearly saturates the available collision energy, thereby forming the BPL structure in the $\gamma$-ray spectra.
• Figure 3: Similar to Figure \ref{['fig:2']} but for the $k_T$-distributions of the gluon mini-jets in the $A-A$ collisions. The panels a–i illustrate different regimes of $\sqrt{s}$, ranging from $\sqrt{s_{GC}}$ up to $1000\sqrt{s_{GC}}$.
• Figure 4: (a) The solid curve represents the pion multiplicity $N_{\pi}$ with pion condensation, while the dashed curve represents it without pion condensation. (b) The condensation-spectrum for the VHE gamma-ray spectrum; when the highest proton energy $E_p$ does not reach the condensation threshold $E_p^{max}$, the gamma spectrum decays exponentially from $E_{\pi}^{cut}<E_{\pi}^{max}$.
• Figure 5: Several GRB gamma spectra. (a, b) Comparisons of the GC spectrum (blue solid curves) fitting GRB 190114C with two leptonic scenarios (IC, dashed curves). (c) The GC spectrum fitting GRB 221009A. (d) An IC model fitting GRB 221009A. The fitting procedure was done using iminuit (https://scikit-hep.org/iminuit/index.html).