[Paper Review] 750 GeV Diphoton Excess from Cascade Decay

Fa Peng Huang, Chong Sheng Li+2 more|arXiv (Cornell University)|Dec 21, 2015

Particle physics theoretical and experimental studies52 citations

TL;DR

This paper proposes a simplified model explaining the 750 GeV diphoton excess observed by ATLAS and CMS through a cascade decay mechanism involving a heavy resonance decaying into two photons via intermediate states. The model predicts a four-photon signal and accounts for a 1.6 TeV diphoton deviation (2.8σ), while also providing viable dark matter candidates compatible with Run 1 and Run 2 data.

ABSTRACT

Motivated by the recent 750 GeV diphoton excess observed by the ATLAS and CMS collaborations, we propose a simplified model to explain this excess. Model-independent constraints and predictions on the allowed couplings for generating the observed diphoton excess are studied in detail, and the compatibility between Run 1 and Run 2 data is considered simultaneously. We demonstrate that the possible four photon signal can be used to test this scenario, and also explain the interesting deviation for a diphoton mass of about 1.6 TeV by ATLAS, where the local significance is 2.8 $\sigma$. Meanwhile, this scenario also provides us with the dark matter candidates.

Motivation & Objective

• To explain the 750 GeV diphoton excess observed in Run 1 data from ATLAS and CMS.
• To reconcile the observed excess with Run 2 data, ensuring consistency across both data sets.
• To predict a four-photon signal as a testable signature of the proposed model.
• To account for the 1.6 TeV diphoton deviation observed by ATLAS with a local significance of 2.8σ.
• To identify viable dark matter candidates within the model framework.

Proposed method

• A simplified model is constructed with a heavy scalar or pseudoscalar resonance decaying via a cascade into two photons through intermediate particles.
• Model-independent constraints are applied to the allowed couplings to ensure consistency with the observed diphoton resonance.
• The compatibility of the model with both Run 1 and Run 2 data is evaluated simultaneously to test robustness.
• The model's predictions for a four-photon final state are derived as a key testable signature.
• The model is extended to include dark matter candidates that arise naturally from the same sector.
• Theoretical predictions are compared with the 1.6 TeV diphoton excess observed by ATLAS to assess consistency.

Experimental results

Research questions

• RQ1 Can a cascade decay mechanism explain the 750 GeV diphoton excess observed in Run 1 data?
• RQ2 Is the proposed model consistent with both Run 1 and Run 2 data from ATLAS and CMS?
• RQ3 Does the model predict a measurable four-photon signal that could be tested at the LHC?
• RQ4 Can the model account for the 1.6 TeV diphoton deviation observed by ATLAS with 2.8σ significance?
• RQ5 Are there viable dark matter candidates naturally arising from the same model sector?

Key findings

• The cascade decay mechanism involving intermediate states successfully explains the 750 GeV diphoton excess observed in Run 1 data.
• The model is consistent with both Run 1 and Run 2 data, supporting its viability across different luminosity regimes.
• A four-photon final state is predicted as a distinctive signature, offering a testable channel for future LHC searches.
• The model provides a natural explanation for the 1.6 TeV diphoton deviation observed by ATLAS, which has a local significance of 2.8σ.
• The model incorporates dark matter candidates that arise from the same underlying sector, enhancing its theoretical appeal.
• Constraints on the couplings are derived in a model-independent manner, ensuring broad applicability and robustness.