LHC Dark Matter Working Group

Green led News

  • NEW Spring 2023 LHCDMWG meeting May 16 - agenda
  • NEW t-channel white-paper effort kicked off. In need of person-power, esp. from ATLAS. Interested people should get in touch with t-channel contacts!


Group organisers and contacts

LHC DM WG organisers Mail lhc-dmwg-admin Person Uli Haisch, Tim Tait (Theory), Spyros Argyropoulos (ATLAS), Matteo Cremonesi (CMS), Xabier Cid Vidal (LHCb)
ATLAS Common Dark Matter subgroup conveners Mail atlas-phys-gen-common-dark-matter-conveners Person Spyros Argyropoulos, Zirui Wang
CMS Dark matter subgroup conveners Mail Matteo Cremonesi Person Matteo Cremonesi
LHCb Dark matter subgroup conveners Mail Xabier Person Xabier Cid Vidal
t-channel contacts Mail lhc-dmwg-tchannel-contacts Person Benjamin Fuks (theory), Benedikt Maier, David Yu (CMS), Rute Pedro (ATLAS)


The LHCDMWG aims to hold general meetings 3 times per year, nominally January, May, September. Meetings related to ongoing projects (e.g. t-channel) happen more regularly. The list of previous meetings per category can be found below.

LHCDMWG meetings indico List of all previous meetings & contributions
t-channel meetings indico List of all previous meetings & contributions


General LHCDMWG mailing list List for meeting general announcments (only administrators can/should post) lhc-dmwg
General contributors List for technical discussions on all topics (everyone can post) lhc-dmwg-contributors
t-channel contributors For people contributing to t-channel WP (everyone can post) lhc-dmwg-contributors-tchannel
Mattermost channel Mattermost channel (under development) Subscribe

Model repository

A list of DM models can be found at https://github.com/LHC-DMWG/model-repository.

NB: to obtain access you need to subscribe to the lhc-dmwg-material e-group.

NB2: the repository above only serves as a place to collect models. For the official generation of events to be used by experimental collaborations, we invite the contributors to check with the respective conveners listed above.

Recommendations for benchmark models

SM Higgs portal

Work in progress, under construction Under construction

The limits on the branching ratio of Higgs to invisible can be converted into limits on the WIMP-nucleon cross-section, thus allowing to compare the results from the LHC searches for DM to direct detection experiments. We propose 3 comparisons:

  • WIMP-nucleon cross-section vs DM mass using EFT models
  • WIMP-nucleon cross-section vs DM mass using UV-complete models
  • Coupling vs DM mass (for EFT models)

The formulae to be used in order to translate the Higgs-to invisible branching ratio (denoted by BR in the following) are given below.

EFT models

The WIMP-nucleon cross-sections are given by the formulate below for scalar (1), Majorana (2) and vector (3) DM are given below:

  \begin{displaymath} \sigma_{SN}=8\frac{\mathrm{BR}}{1-\mathrm{BR}}\frac{\Gamma_h}{v^2}\frac{m_N^4f_N^2}{m_h^3(m_s+m_N)^2}\left(1-4\frac{m_s^2}{m_h^2}\right)^{-1/2} \end{displaymath} (1)

  \begin{displaymath} \sigma_{fN}=16\frac{\mathrm{BR}}{1-\mathrm{BR}}\frac{\Gamma_h}{v^2}\frac{m_N^4m_f^2f_N^2}{m_h^5(m_f+m_N)^2}\left(1-4\frac{m_f^2}{m_h^2}\right)^{-3/2} \end{displaymath} (2)

  \begin{displaymath} \sigma_{VN}=32\frac{\mathrm{BR}}{1-\mathrm{BR}}\frac{m_N^4m_V^4f_N^2}{v^2m_h^7(m_V+m_N)^2}\frac{\Gamma_h}{\sqrt{1-4\frac{m_V^2}{m_h^2}}\left(1-4\frac{m_V^2}{m_h^2}+12\frac{m_V^4}{m_h^4}\right)} \end{displaymath} (3)


  \begin{displaymath} \Gamma_h=\Gamma_h^{SM}=4.07\mathrm{\ MeV}, v=246\mathrm{\ GeV}, m_{N}=939\mathrm{\ MeV}, f_N=0.308. \end{displaymath} (4)

The latter quantity (fN) parametrises the Higgs-nucleon interaction and has been calculated using lattice QCD in 1708.02245. The above formulae are obtained from Djouadi et al, 1112.3299, with the difference that the Higgs vev is set to 246 GeV (instead of 246/sqrt(2) used in that paper).

Couplings EFT models

For scalar DM the coupling is given by

  \begin{displaymath} \lambda_{hSS}^2=128\pi\frac{\mathrm{BR}}{1-\mathrm{BR}}\frac{\Gamma_h}{v^2}\frac{m_h}{\sqrt{1-m_s^2/m_h^2}}. \end{displaymath} (5)

For Majorana DM, the coupling is given by

  \begin{displaymath} \frac{\lambda_{hff}^2}{\Lambda^2}=64\pi\frac{\mathrm{BR}}{1-\mathrm{BR}}\frac{\Gamma_h}{v^2}\frac{1}{m_h(1-m_s^2/m_h^2)^{3/2}} \end{displaymath} (6)

For vector DM, the coupling is given by

  \begin{displaymath} \lambda_{hVV}^2=512\pi\frac{\mathrm{BR}}{1-\mathrm{BR}}\frac{\Gamma_h}{v^2}\frac{m_V^4}{m_h^3\sqrt{1-m_V^2/m_h^2}\left(1-4\frac{m_V^2}{m_h^2}+12\frac{m_V^4}{m_h^4}\right)} \end{displaymath} (7)

Formulae for UV-complete models

Various UV complete models for vector dark matter have been proposed in the literature (see Bibliography section below). In these models an extra U(1)' symmetry is introduced, under which the DM is charged. An additional Higgs field h2 spontaneously breaks this U(1)' symmetry, thereby generating the DM mass. The additional Higgs boson associated to the breaking of the extra U(1)' symmetry (hereafter denoted by ) mixes with the SM Higgs boson, with a mixing angle .

The first model we recommend to show is the one from Arcadi et al, 2001.10750, for which the WIMP-nucleon cross-section can be expressed as

  \begin{displaymath} \sigma_{UV}=32\cos^4\theta\frac{\mathrm{BR}}{1-\mathrm{BR}}\frac{\Gamma_h}{v^2}\frac{m_V^4m_N^4f_N^2}{m_h^3(m_V^2+m_N^2)}\frac{1}{\sqrt{1-4\frac{m_V^2}{m_h^2}}\left(1-4\frac{m_V^2}{m_h^2}+12\frac{m_V^4}{m_h^4}\right)}\left(\frac{1}{m_2^2}-\frac{1}{m_h^2}\right)^2 \end{displaymath} (8)

Two mass of the additional Higgs boson should be varied in order to get a range of predictions. In Zaazoua et al, 2107.01252 it was found that correspond to the maximum and minimum WIMP-nucleon cross-sections for

Todo: Provide script for obtaining the curve for the radiative model

Recommendations at a glance

  • EFT curves to be shown: scalar, Majorana, vector EFT + UV complete vector DM model (Dirac not shown since it amounts to a rescaling of the Majorana curve)
  • For UV complete vector DM model show:
  • Besides the WIMP-nucleon cross-section vs mDM plots we recommend providing also the limits on the couplings as a function of mDM
  • While the LHC limits for a DM mass of 1 GeV could be extended down to massless DM, for very low DM masses the WIMP assumptions break down, therefore we do not recommend displaying masses much lower than 1 GeV.


Simplified s-channel models

Work in progress, under construction Update information with detailed instructions for MadGraph generation

Recommendations for the production of signatures in the simplified s-channel model have been provided in the white papers listed below. An improved (more accurate) prescription for the generation of certain signatures is being discussed. Details will be posted below, once the prescription is agreed upon.



4-top NEW

Coupling rescaling NEW

A tool for rescaling the s-channel limits for arbitrary values of the couplings have been developed and presented in Albert et al, 2203.12035. We recommend following the prescriptions there for the presentation of results with rescaled couplings.

Models with extended Higgs and gauge sectors


Detailed recommendations for the generation of 2HDMa signal samples for various signatures can be found in the relevant white paper listed below. More information about the model and the existing constraints can be found at the bibliography section.


2 Mediator DM model aka "Dark Higgs"

The 2MDM model, introducing a heavy Z' boson and an additional Higgs boson has recently started being explored by ATLAS and CMS.

Work in progress, under construction Recommendations for the harmonised presentation of results are in progress.


t-channel models


White papers produced or endorsed by the LHCDMWG

-- MichelangeloMangano - 2023-02-14

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Topic revision: r12 - 2023-05-16 - SpyridonArgyropoulos
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