LHC DMWG public meeting on dark photons

4/S-030 (CERN)



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###Meeting agenda


###Short summary

Morning hands-on tutorials

#Darkcast (P. Ilten): 

DarkCast is a tool to recast dark photon searches to obtain constraints on any massive gauge boson with vector couplings to the fermions of the Standard Model. Its key feature is its mechanism to painlessly obtain all branching fractions to Standard Model final states, including hadronic resonances below 2 GeV. The authors also compile a comprehensive set of the experimental constraints that may be relevant. 

website and code, with reference papers: https://gitlab.com/philten/darkcast

#Micromegas (A. Phukhov, B. Zaldivar): 

MicrOMEGAs is a code to calculate the properties of stable massive particles (such as freeze-in and freeze-out relic density, rates for direct and indirect detection) in models with a discrete symmetry like R-parity. Some models are already implemented by the authors, but others can be implemented by users.  

website and code, with reference papers: https://lapth.cnrs.fr/micromegas/

Main meeting

Talks with summary of dark photon searches by experimental collaborations (LHCb by P. Ilten, CMS by A. Albert, ATLAS by S. Giagu) show many searches targeting a variety of models (dark SUSY, generic invisible decays, Higgs-mediated dark sectors e.g. FRVZ, hidden valleys) and some commonalities between models but no common benchmark yet for comparisons across searches for prompt/LLP. 

From the discussion, dark photons are generally dominated by invisible decays if there is an invisible coupling, so when looking for visible decays the invisible ones are turned off, making those kinds of benchmarks essentially independent from the relic density. 

Talk and discussion from Physics Beyond Colliders (PBC) community (G. Lanfranchi, M. Pospelov) highlights the need to fully specifying the model details for comparison, which can draw from past experience of DMWG with simplified models (http://inspirehep.net/record/1427412). There will be further collaboration between the DMWG and the PBC group, as the dark photon is one of the benchmarks and they are collecting sensitivity projections for a number of experiments (e.g. Belle II, miniBoone, LDMX, PADME, SHIP...). 

It is possible to recast Mono-X-like searches that interpret results using vector mediator simplified models and into an asymmetric dark matter model with a displaced vertex (talk by P. Harris), as done in the Mathusla whitepaper arxiv: 1806.07396 

The connection of models with a dark photon and invisible decays to cosmology through the relic density is a topic of interest. For freeze-in, these kind of models need to have couplings too small to be detected at the LHC, unless some assumptions are relaxed (talks by F. Kahlhoefer, B. Zaldivar, I. John). Work will proceed in the direction of understanding the consequence of and also by talking to the broader cosmology community, and testing dark photon models with existing relic density calculation tools. 

How to proceed

There is a consensus on starting to work with the dark photon model used by LHCb/Physics Beyond Colliders. 

The Pythia version will be put on git.

The Feynrules/UFO will be provided and advertised once available.

The members of the experimental collaborations / PBC community can start testing this model and compare results once available. The next steps will be to compare kinematic distributions and rates as a function of couplings with the vector models, in the invisible and visible channels separately. (initial list of interested people: P. Ilten, S. Giagu, A. Albert)

The cosmology community will be contacted to discuss variations on freeze-in that allow LHC sensitivity (initial list of interested people: B. Zaldivar, G. Belanger, A. Arbey)

We will proceed with further testing of tools for calculation of relic density and connection to cosmology (initial list of interested people: B. Zaldivar, G. Belanger, S. Pukhov, I. John)

There are minutes attached to this event. Show them.
    • 09:00 13:00
      Hands-on session on recasting and relic density calculation for dark photons: Hands-on session

      Optional hands-on session on running Micromegas to calculate the relic density in freeze-out and freeze-in scenarios (https://lapth.cnrs.fr/micromegas/) and on recasting dark photon limits (https://gitlab.com/philten/darkcast)

      • 09:00
        Darkcast hands-on 1h 30m
        Speaker: Philip Ilten (University of Birmingham (GB))

        Prerequisites to get darkcast to work on lxplus:

        needs logging in with a graphical session (conda will look for DISPLAY)
        when you ask to put the miniconda directory in your PATH say no
        export PATH=/afs/cern.ch/user/d/doglioni/Work/miniconda2/bin:$PATH
        conda create --name=darkcastenv python=2.7
        source activate darkcastenv
        conda install -c conda-forge matplotlib
        every time you log in:
        export PATH=/afs/cern.ch/user/d/doglioni/Work/miniconda2/bin:$PATH
        source activate darkcastenv

        How to install and run darkcast example:

        tar -xzvf darkcast-master.tar.gz
        mv darkcast-master darkcast
        cd darkcast/examples
        python invisible.py 
      • 10:30
        Micromegas hands-on 1h 30m
        Speaker: Alexander Pukhov (SINP, MSU)
    • 13:30 14:00
      Public meeting: Recasting dark photon signals to connect to existing searches
    • 14:00 15:35
      Public meeting: Overview of models used by LHC collaborations
    • 15:35 16:00
      Coffee break 25m
    • 16:00 16:30
      Public meeting: Comparison of existing searches for dark photon/LLP benchmarks
      • 16:00
        Connecting LLP searches to vector model searches 20m
        Speaker: Philip Coleman Harris (Massachusetts Inst. of Technology (US))
      • 16:20
        Discussion 10m
    • 16:30 18:00
      Public meeting: Discussion and tools for relic density on LHC plots
      • 16:30
        On the LHC sensitivity for non-thermalised hidden sectors 20m
        Speaker: Felix Kahlhoefer (RWTH Aachen)
      • 16:55
        Freeze-in dark matter at the LHC 15m
        Speaker: Mr Bryan Zaldivar (LAPTh, Annecy)
      • 17:15
        Tests of freeze-out and freeze-in for vector models 15m
        Speaker: Ms Isabelle John (Lund University)
      • 17:30
        Discussion and next steps 15m