An Overview of the Anomalous Soft Photons in Hadron Production

Abstract

Productions of soft photon with low transverse momenta in high-energy hadron-hadron collisions and e + -e − annihilations indicate that they are consistently produced in excess of what are predicted by electromagnetic bremsstrahlung when hadrons (mostly mesons) are produced, but they agree with electromagnetic bremsstrahlung predictions in the absence of hadron production. These excess soft photons are called anomalous soft photons. The occurrence of anomalous soft photons in association with hadron production reveals the presence of additional QED soft photon sources in QCD hadron production. Many different models have been proposed to explain the anomalous soft production. We shall examine specifically a quantum field theory of simultaneous meson and soft photon production in QCD×QED in which the meson production arises from the oscillation of color charge densities of the quarks of the underlying vacuum in a flux tube. As a quark carries both a color charge and an electric charge, the oscillation of the color charge densities will be accompanied by the oscillation of electric charge densities, which will in turn lead to the simultaneous production of anomalous soft photons during the meson production process.

Open string QED meson description of the X17 particle and dark matter

“…As a quark and an antiquark cannot be isolated and the intrinsic motion of a qq system in its lowest-energy states lies predominantly in 1+1 dimensions [62][63][64][65][66][67][68][69][70][71][72], an open string description in 1+1 dimensions can be applied to study the qq system in QCD and QED interactions. Such interactions lead to confined and bound physical QCD and QED meson states [34][35][36]. We show that the π 0 , η, and η can be adequately described as open string QCD mesons in 1+1 dimensions, when we properly take into account the relevant physical effects.…”

“…Many different models have been presented to describe the anomalous soft photons as arising from quantized bosons [34][35][36] or from a continuous spectrum [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]. We shall focus our attention on the quantized boson description of [34][35][36] which has the prospect of linking the anomalous soft photons with the X17 and E38 particles. We note that owing to the simultaneous and correlated production alongside with hadrons, a parent particle of the anomalous soft photons is likely to contain some elements of the hadron sector, such as a light quark and a light antiquark.…”

Soft-photon radiation in high-energy proton-proton collisions within the tensor-pomeron approach: bremsstrahlung

“…Experimental studies trying to verify Low's theorem [3][4][5][6][7][8][9][10][11][12][13][14] have, in many cases, found large deviations from the SPA calculations. For a review of the experimental and theoretical situations see [15]. Clearly, more experimental and theoretical work is needed in order to clarify this so called "soft photon problem".…”

Soft photon bremsstrahlung at next-to-leading power

“…In the rich physics program that would be enabled by this upgrade, the possibility to measure ultra soft photons at very low transverse momentum is particularly attractive. In fact, new measurements of the photon bremsstrahlung could shed light on a long-standing discrepancy between the theoretical predictions and the observed soft photon spectra emitted in hadronic decay channels [2][3][4][5][6][7][8][9][10][11]. In this program, it is crucial to have reliable and highly precise theoretical predictions.…”

“…Moreover, the logarithmic corrections are enhanced for very small photon energies. This might help to explain the observed discrepancies [2][3][4][5][6][7][8][9][10][11] in the production rates.…”