Dark matter annihilation decay at the LHC

Yuhsin Tsai, Lian-Tao Wang, and Yue Zhao

Phys. Rev. D 93, 035024 – Published 24 February 2016

Abstract

Collider experiments provide an opportunity to shed light on dark matter (DM) self-interactions. In this work, we study the possibility of generating DM bound states—the Darkonium—at the LHC and discuss how the annihilation decay of the Darkonium produces force carriers. We focus on two popular scenarios that contain large DM self-couplings: the Higgsinos in the $λ − SUSY$ model and the self-interacting DM (SIDM) framework. After forming bound states, the DM particles annihilate into force mediators, which decay into the standard model particles either through a prompt or displaced process. This generates interesting signals for the heavy resonance search. We calculate the production rate of bound states and study the projected future constraints from the existing heavy resonance searches.

Received 7 January 2016

DOI:https://doi.org/10.1103/PhysRevD.93.035024

Physics Subject Headings (PhySH)

Bound states Particle dark matter Particle production Supersymmetric models

Particles & Fields

Authors & Affiliations

Yuhsin Tsai¹, Lian-Tao Wang^2,3, and Yue Zhao⁴

¹Maryland Center for Fundamental Physics, Department of Physics, University of Maryland, College Park, Maryland 20742, USA
²Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
³Enrico Fermi Institute and Kavli Institute for Cosmological Physics, The University of Chicago, Chicago, Illinois 60637, USA
⁴Michigan Center for Theoretical Physics, University of Michigan, Ann Arbor, Michigan 48109, USA

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Vol. 93, Iss. 3 — 1 February 2016

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Figure 1
Higgsinonium production and decay at the LHC.
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Figure 2
Upper left: Higgsinonium production through $p p \to Z^{*} \to ({\tilde{h}}^{0} {\bar{\tilde{h}}}^{0})$ into $1^{-}$ bound state under different assumptions of the $λ$ coupling. The solid curves show production cross sections in which a nonvanishing mass window Eq. (9) of the singlet scalar exists. The dash-dotted extension of the curves has $m_{s} < m_{h} / 2$ , which violates the invisible Higgs decay constraint unless a tuned coupling or an extra singlet field is included. The purple dashed (dot-dashed) curves show the 13 TeV projection of the CMS resonance search $p p \to X \to h h \to 4 b$ [47] with $300 {fb}^{- 1}$ ( $3 {ab}^{- 1}$ ) of data. The bound gives an idea of the possible future reach if the singlet scalar has a similar mass and decay branching ratio to the SM Higgs. Upper right: the production $q \bar{q} \to W^{*} \to ({\tilde{h}}^{\pm} {\tilde{h}}^{0})$ into the $1^{-}$ state. The purple dashed (dotted) curve shows the 13 TeV projection of the ATLAS resonance search $p p \to V \to W h$ [48] with $300 {fb}^{- 1}$ ( $3 {ab}^{- 1}$ ) of data. The red dashed (dotted) curve shows the 13 TeV projection of the ATLAS search $p p \to W^{'} \to W Z$ [49] with $300 {fb}^{- 1}$ ( $3 {ab}^{- 1}$ ) of data, with the $Z$ branching ratio rescaled to the singlet scalar into $b \bar{b}$ . The $Z W$ bound can be used to compare with the scenario when the singlet mass similar to $Z$ , and the efficiency of the $Z \to jets$ tagging is similar for the singlet scalar decay. Lower plots: the same plots for a 100 TeV hadron collider. The dashed (dotted) curves correspond to projections for $1 {ab}^{- 1}$ ( $3 {ab}^{- 1}$ ) of data.
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Figure 3
Darkonium production and decay at the LHC.
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Figure 4
Left: the mediation scale $M_{*}$ for having a 1 fb $0^{-}$ bound state production through the pseudoscalar mediation at 13 TeV LHC. The red-shaded region shows the 95% C.L. exclusion bound from the 8 TeV ATLAS heavy $quark + MET$ search [59]. The dashed curve shows the 95% C.L. bound from the mono- $b$ search estimated in [60], assuming $300 {fb}^{- 1}$ of data at 14 TeV LHC. The purple-shaded region has the DM scattering $σ / m_{χ} < 0.5 cm / g^{2}$ at dwarf galaxies (assume $v = 1 0^{- 4}$ ), assuming $m_{med}$ matches the size of $(m_{χ}, α_{χ})$ that gives $\sin δ_{0} = 1$ in Eq. (18). The gray-shaded region corresponds to $α_{χ} > 1$ , for which the nonrelativistic calculation of the bound state production fails. Right: the 1 fb region of the $1^{-}$ state through the vector coupling. The red-shaded region corresponds to the 95% C.L. exclusion bound from the 8 TeV ATLAS monojet search [61]. The dashed curve shows the 95% C.L. bound from the monojet search estimated in [62], assuming $300 {fb}^{- 1}$ of data at 14 TeV LHC.
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Figure 5
Left: the mediation scale $M_{*}$ of the pseudoscalar operator for the $0^{-}$ bound state production. The $0^{-}$ decays into two dark photons, which have displaced decays into $e^{+} e^{-}$ and form displaced lepton jet (DLJ) signals. The light mediator mass is fixed to be $m_{med} = 100 MeV$ , and different curves correspond to different sizes of the mixing $ε_{γ^{'}} F_{μ ν} {F^{'}}^{μ ν}$ . We require 10 events containing two identified DLJ’s at the HCAL from the dark photon decay, assuming $300 {fb}^{- 1}$ of data at 13 TeV LHC. See details in the text for the assumed cuts and reconstruction efficiency. Right: the mediation scale $M_{*}$ of the axial-vector operator for the $1^{-}$ bound state production. The $1^{-}$ decays into two scalar mediators, which have displaced decays into $e^{+} e^{-}$ and give the DLJ signals. Different curves correspond to different sizes of the coupling $ε_{ϕ} ϕ \bar{e} e$ . The current and projected bounds from the missing energy searches are described in Fig. 4. Two remarks: first, compared to the bound state production rate in Fig. 4, the signal efficiency of our DLJ study is of order 0.1%–1%. A better searching strategy, such as including signals in the tracker and $μ$ chamber, may improve the result. Moreover, the $M_{*}$ bound from the mono- $b$ search is much lower than the typical center of mass energy at 14 TeV LHC. Therefore, simplified models with light mediators will give more accurate descriptions of collider signal, and the result will depend on the assumption of mediator coupling. Here, we include results from effective operators to show an estimated mediation scale that the missing energy searches can reach.
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