Observation of Anomalous Internal Pair Creation in $^8$Be: A Possible Signature of a Light, Neutral Boson (1504.01527v1)

Abstract: Electron-positron angular correlations were measured for the isovector magnetic dipole 17.6 MeV state ($J^\pi=1^+$, $T=1$) $\rightarrow$ ground state ($J^\pi=0^+$, $T=0$) and the isoscalar magnetic dipole 18.15 MeV ($J^\pi=1^+$, $T=0$) state $\rightarrow$ ground state transitions in $^{8}$Be. Significant deviation from the internal pair creation was observed at large angles in the angular correlation for the isoscalar transition with a confidence level of $> 5\sigma$. This observation might indicate that, in an intermediate step, a neutral isoscalar particle with a mass of 16.70$\pm0.35 $ (stat)$\pm 0.5 $ (sys) MeV$/c^2$ and $J^\pi = 1^+$ was created.

• The paper identifies a significant deviation in the 18.15 MeV M1 transition from standard internal pair creation, suggesting the formation of a new light boson.
• Researchers employed proton-induced reactions and GEANT simulations to model electron-positron angular correlations with high precision.
• The observed boson, with a mass of approximately 16.7 MeV/c² and spin-parity 1+, offers promising implications for dark matter and related gauge theories.

Observation of Anomalous Internal Pair Creation in $^8$Be: A Possible Signature of a Light, Neutral Boson

The paper investigates an anomaly observed in the internal pair creation of $^8$Be, potentially indicating the presence of a light, neutral boson. The researchers center their investigation on electron-positron angular correlations originating from the decay of specific excited states of $^8$Be. Notably, the paper focuses on the isovector magnetic dipole (M1) transition at 17.6 MeV and the isoscalar M1 transition at 18.15 MeV. The results indicate a significant deviation from standard internal pair creation in the 18.15 MeV transition, suggesting the possible formation of a neutral isoscalar particle with a measured mass of 16.70 ± 0.35 (stat) ± 0.5 (sys) MeV/c² and spin-parity $J^\pi = 1^+$.

The methodology included populating $1^+$ states in $^8$Be via the $^7$Li(p,γ)$^8$Be reaction at specific proton energy resonances. Advanced detection systems and calibration methods were employed to achieve accuracy, while simulations using GEANT were utilized to model detector response and background interactions.

Significant findings were established by extending angular correlation measurements above the typical range used in previous studies. For the 18.15 MeV transition, the researchers observed a deviation from expected results consistent with M1 and E1 mixing, suggesting potential new physics. The angular correlation in this transition did not align with predictions assuming internal pair creation alone, instead displaying characteristics that could arise from the decay of a yet unidentified boson.

This paper's implications are manifold, particularly in its potential association with theoretical models proposing light bosons as components of dark matter. Such a boson could serve as a U(1)$_d$ gauge boson or perform within scenarios implicating secluded WIMP dark matter and dark Z bosons relevant to muon $g-2$ anomaly explanations. The experimental lifetime of the hypothetical boson aligns with theoretical predictions, enabling future verification through targeted resonance studies. Ongoing investigations could potentially extend or refute these conclusions via refined experimental setups or additional data from similar nuclear reactions.

This discovery bridges several domains within particle physics and opens investigative paths concerning dark matter interactions, fundamental forces, and the structural dynamics of light bosons in established nuclear frameworks. The high confidence level observed for the deviation, combined with a solid theoretical basis, sets a foundational stage for successive explorations into light, neutral mediators.

The continued exploration and validation of this anomaly may lead to significant advancements in our understanding of particle interactions and the subatomic field's underlying physical laws. Such findings might necessitate revisions of phenomenological models that interlink dark sector entities and observable nuclear phenomena, propelling both theoretical and practical aspects of high-energy physics into new territories.