Heavy fermion bound states for diphoton excess at 750 GeV — collider and cosmological constraints

Abstract

A colored heavy particle with sufficiently small width may form non-relativistic bound states when they are produced at the large hadron collider (LHC), and they can annihilate into a diphoton final state. The invariant mass of the diphoton would be around twice of the colored particle mass. In this paper, we study if such bound state can be responsible for the 750 GeV diphoton excess reported by ATLAS and CMS. We found that the best-fit signal cross section is obtained for the SU(2) L singlet colored fermion X with Y X = 4/3. Having such an exotic hypercharge, the particle is expected to decay through some higher dimensional operators, consistent with the small width assumption. The decay of X may involve a stable particle χ, if both X and χ are odd under some conserved Z 2 symmetry. In that case, the particle X suffers from the constraints of jets + missing E T searches by ATLAS and CMS at 8 TeV and 13 TeV. We found that such a scenario still survives if the mass difference between X and χ is above ∼ 30 GeV for m X ∼ 375 GeV. Even assuming pair annihilation of χ is small, the relic density of χ is small enough if the mass difference between X and χ is smaller than ∼ 40 GeV.

Diphoton signals from colorless hidden quarkonia

“…Thus, we take the η X constituents X to carry hypercharge only, but no standard model (SM) SU(3) c or SU(2) L quantum numbers. This is in contrast to similar recent work which featured bound states with colored constituents [10][11][12][13][14][15][16][17][18][19]. While the production cross section is controlled by the hypercharge of the constituents, Y X , and is proportional to Y 4 X , bound-state formation is controlled by the new strong force.…”

Resonances from QCD bound states and the 750 GeV diphoton excess

“…Note added: On the day this paper was submitted to the arXiv, the paper[32] appeared, which studies the fermion scenario and has some overlap with our results for that case.…”

Colorful Twisted Top Partners and Partnerium at the LHC

“…[90], and more recently in Refs. [91][92][93]. Via gauge interactions alone, spin-0 S-wave bound states of such particles can be produced from gluon fusion and annihilate to gg, γγ, γZ, ZZ, and W + W − (if the particles are charged under SU(2) L ).…”

“…Importantly, the studies in Refs. [90][91][92][93] assumed the particle couplings to the Higgs to be negligible relative to their couplings to gluons. For top partners, though, this assumption is not satisfied since y t ∼ g s .…”