Dark Matter models with 𝒕-channel mediators @ LHC (LHC DM WG public meeting)

40/S2-C01 - Salle Curie (CERN)

40/S2-C01 - Salle Curie


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Christian Ohm (KTH Royal Institute of Technology (SE)), Oleg Brandt (Ruprecht Karls Universitaet Heidelberg (DE)), Philip Coleman Harris (Massachusetts Inst. of Technology (US)), Tim M.P. Tait (University of California, Irvine), Ulrich Andreas Haisch (University of Oxford (GB)), Xabier Cid Vidal (Instituto Galego de Física de Altas Enerxías)


Workshop goals:

  • Consolidateing existing work:
    • Converge on a set of models, 
    • agree on well-motivated sets of coupling values
    • map final states to parameter space regions
  • Going Beyond:
    • Look for uncovered regions of parameter space
    • Can LHCb (+ b-factories) cover unique parts of parameter space using B-mesons as a probe?
    • B-oscillations to constrain DM?
    • Opportunities at ATLAS and CMS with Run 3 of the LHC?
  • Final goal:
    • White Paper of the LHC DM WG on DM models with t-channel mediators

Workshop Poster


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  • Adil Jueid
  • Alejandro Ibarra
  • Alexandre Arbey
  • Alison Elliot
  • Andreas Albert
  • Bhawna Gomber
  • Caterina Doglioni
  • Cedric Prieels
  • Chang-Seong Moon
  • Christian Ohm
  • Christoph Borschensky
  • Christopher Smith
  • Corinne Goy
  • Darren Price
  • David Yu
  • Dipan Sengupta
  • Giorgio Busoni
  • Giuliano Gustavino
  • Haipeng An
  • Henning Flaecher
  • Jack Lindon
  • James Frost
  • Jan Heisig
  • Jonas Lindert
  • Jonatan Piedra
  • Joshua Berger
  • Jyothsna Rani Komaragiri
  • Jérôme Vandecasteele
  • Kajari Mazumdar
  • Kayla McLean
  • Kenji Hamano
  • Kirtimaan Mohan
  • Laura Lopez Honorez
  • Liantao Wang
  • Luca Mantani
  • Marie-Helene Genest
  • Michael James Baker
  • Michael Kent Wilkinson
  • Michel Lefebvre
  • Michel Tytgat
  • Monika Blanke
  • Nazila Mahmoudi
  • Niki Saoulidou
  • Oleg Brandt
  • Pedro Schwaller
  • Pyungwon Ko
  • Raman Khurana
  • Spyridon Argyropoulos
  • Stanislava Sevova
  • Stefan Vogl
  • Steven Worm
  • Sunil Manohar Dogra
  • Susanne Westhoff
  • Sushil Chauhan
  • Tim M.P. Tait
  • Varun Sharma
  • Vasiliki Mitsou
  • Xabier Cid Vidal
  • Yalcin Guler
  • Yang Bai
  • Yanyan Gao
  • Yiming Abulaiti
Videoconference Rooms
Public meeting of the LHC Dark Matter WG on models with t-channel production of Dark Matter.
Christian Ohm
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26.04.2019 t-channel workshop


  • Q: question

  • A: answer

  • C: comment

  • AI: action item


  • intro (Christian)

  • History and overview of t-channel models (Tim)

    • Q/p14: what do you mean with the systematics of searches?

      • A: resonant vs non-resonant signatures interplay

  • t-channel interpretations at CMS (Andreas)

    • Q/p2: do you use t-channel simplified models to reinterpret SUSY searches?

      • A: no

    • Q/p2: which UFOs do you use? → add links afterwards?

      • A: the top UFO is linked from p9, the p2 UFO is not public and provided by authors by email

        • AI: follow up with authors and make UFO public, e.g. using LHC DM WG github

    • Q/p9: not exactly t-channel, it’s here because it’s a flavoured mediator?

      • A: yes, it is a special case

        • C: need to see whether this is within the scope of this workshop

    • Q/p9: a and b are arbitrary: if they are set to 0.1, you still have the same diagram -- are there any constraints applied to these a b parameters?

      • no special reason to choose a=b=0.2, we probably took it from the pheno paper

    • Q/p10: right plot, limits are totally flat after 1 TeV. Why is it totally flat?

      • A: the last overflow bin starts at 600 GeV

    • Q/p9: I’m confused by the color structure of the model, is phi color-neutral?

      • A: it is colored

        • Q: psi not colored? What is the color structure?

    • Q: psi particle with these properties, good DM candidate? Could do 3-body decay to SM particles (i.e. unstable DM), no?

      • A: psi should be stable, but will need to look this up

        • C: if psi lighter than t, then still decays through off-shell t quark possible; in this case psi has to be lighter than d, s, and t decay products

  • t-channel interpretations at ATLAS (Millie)

    • Q/p5: SCCq model couples to LH quarks, CMS only to RH u quarks, but otherwise free parameters the same gDM = 1, Dirac DM → should we use the same model? (Pheno very similar)

      • C: Very similar

      • C: W radiation not possible for RH, otherwise similar

    • Q/p7: SCCb model couples to RH bottom quarks, similar to CMS model except for couplings to u vs b quarks?

      • C: yes, seems similar

      • C: CMS not using such a model for bb+MET

    • C/p5: SCCt model: make consistent choices for couplings and

      • C: it is not necessarily a DM model

  • Signatures of Majorana dark matter with t-channel mediators (Stefan et al)

    • Q/p10: what is the jets+MET and jet+MET? What do you reinterpret?

      • A: jet+MET: mono-jet, jets+MET: squark SUSY search

    • Q/p10: what are the numbers in the HESS contours?

      • A: multiplication factors for enhancing the existing limits, which would be otherwise too weak to show up on the plot

  • Dark matter with t-channel mediator: a simple step beyond contact interaction (Haipeng et al)

    • C/p5: CMS MET > 250 GeV rather than 120 GeV

    • Q: which MG UFO did you use?

      • A: generated signal ourselves

      • C: the difference between Dirac and Majorana is a qualitative result

    • Q: mediator degenerate -- have you considered this? Could a disappearing-track signature become relevant for small mass splittings?

      • A: if we considered this, DM can be part of a larger multiplet, then yes, the disappearing-track signature could be relevant

  • Simplified DM models with the full SM gauge symmetry (Pyungwon et al)

    • Q/p7: what makes mono-W enhanced? is it through uL -> dL so that it can couple to QL (and ~dL down the line)?

      • A: yes

  • Direct Detection and LHC constraints on a t-Channel Simplified Model of Majorana Dark Matter at One Loop (Kirtimaan et al)

    • Q: how does this (with Majorana) compare to what Stefan Vogel presented? What about bremsstrahlung for indirect detection? Corners where radiative corrections can be important.

      • C: Someone did recently try to calculate this.

    • C: Jets+MET has stronger constraints for Majorana DM, it's in the paper, but not the talk.

    • Q: DD did you include expansion of tree-level exchange at higher orders?

      • A: strong impact considered

    • C: UFO will be available soon

  • Brief review on the vector-like portal to scalar dark matter (Jerome)

    • Q/p5: why high mS needs an additional gluon, but the intermediate range not?

      • A: … (did not catch answer fully)

  • Discussion on above analyses (All):

    • Q: what are the fundamental differences between Majorana and Dirac DM? Is it fair to say that (i) the uu vs ~uu production and the (ii) dijet+MET enhancement are the only major differences?

      • C: yes, that’s right, there is a mass dependence on the production and a different balance between jet+MET and dijet+MET signatures. Generally, Majorana DM will be able to probe higher mass scales due to higher u quark PDFs at high Q2, dijet+MET more prominent for Majorana case (additional u-channel diagram)
        C: Majorana DM even richer pheno in terms of complementarity to DD and ID

    • Q: how to reconcile the Majorana and Dirac DM with the scalar DM case discussed last?

      • C: they all provide the same signatures in principle, but their relative contributions are different, and it is how to compare with DD and ID which is different.

      • C: scalar DM is more similar to Majorana DM case and has more diagrams → richer phenomenology

    • C: not sure we need to take RD very seriously as we are discussing simplified model and there may be additional particle content (DOF that we are integrating out), OK as long as RD is not many orders of magnitude off

      • C: yes, agreed

    • Q: why RH quark couplings easier to deal with? easier to motivate MFV assumption?

      • C: in terms of signatures no fundamental differences, but for RH no need to deal with W bosons, just simpler

    • AI: come up with a über-UFO that allows to harmonise what ATLAS and CMS already do (see talks). Ideally, this über-UFO should be able to do (with switches):

      • Dirac DM case

      • Majorana DM case

      • [nice to have] Scalar DM case

      • [nice to have] LH vs. RH up-type vs. RH down-type couplings

      • [nice to have] enhanced couplings ot 3rd gen

→ Can we do that?

  • Flavored dark matter beyond Minimal Flavor Violation (Monika et al)

    • Q/p5: what is the ~b~b result? MET in final state or di-bjet search?

      • A: SUSY-like bb+MET search

    • Q/p5: why b DM preferred? Is it only the GCE that plays into that?

      • A: only 1 parameter for three flavours, get splitting from lambda coupling matrix → mass hierarchy in the dark sector; DD and LHC searches as long as massive mediator,

      • C: b easier than s due to PDF, also top-flavoured DM is a preferred case though, Z-penguin contribution helps!

    • Q/p5: is the xenon-phobic model also argon-phobic and CRESST-phobic?

      • A: get right p/n ratio for Xenon, works somewhat for Argon, does not work for CRESST since it has light elements like O that has p/n = 1

    • Q: were decays into DM particles considered?

      • A: for oscillations we did → structure of lambda; super-light DM such that would allow B → DMDM K not within scope of this work, but potentially interesting. See discussion session.

    • Q: you mentioned the possibility to extend to a scalar, any feeling how that would pan out?

      • A: we have not looked into this explicitly; expect qualitatively the same, quantitative differences expected though

    • Q: Does LH DMFV have any effect on bb mixing?

      • A: No, unless mediator has m<10 GeV → final state with DM is also possible. Avoided on purpose in this analysis → easier

  • A flavoured dark sector (Pedro et al)

    • Q/12: what is the dF = 2 constraint? From oscillations? dR = 1 is the left diagram?

      • A: yes.

    • Q/13: why not go even higher for mpiD that would give for instance tops?

      • A: no real restrictions, we stayed here because it provides nice complementarity; maybe through exotic top decays

    • Q: how do you get RD?

      • A: we are not imposing RD constraints, relic abundance would be very small, has to be set externally

    • Q/: from which Belle analysis is the limit from?

      • A: B → K inv

      • C: this is something that we are trying to do

    • Q: dark sector lightest particle dark pion can decay to SM, what is the DM candidate?

      • A: two possibilities: either residual symmetries protecting some dark pions, or (what is done here) baryonic final states,

  • Leptonic WIMP Coannihilation and the Current Dark Matter Search Strategy (Michael Baker)

    • Q: is there anything in this model coupling to neutrinos

      • A: we only do RH leptons

    • Q: why are RH leptons considers

      • A: UV complete, SU(2) singlets → natural to assume SU(2) singlets

    • C: ID comment: big boost from radiative corrections in scalar case (propaganda alert)

  • Dark Matter search with Belle II

  • Discussion / going beyond (lead by Christopher/Monika):

  • Discussion on Direct (à la semileptonic b-decays) DM searches in B-sector (Christopher)

    • C: General, if UFOs and specific predictions on BR are provided, LHCb or Belle could perform toy studies.

      • C: Which channels? These toy studies could be part of the white paper, short analysis for a MSc thesis?

    • C: For LHCb, compensate lack of MET reconstruction by using the “opposite-side tagging technique”, i.e. looking at heavier resonances decaying to other stuff + DM. Better if these resonances are narrow. Example proposed, phi->K+K-, with K+ decaying to DM.

      • C: was done by KLOE already?

        • C: KLOE was looking for KS+KL, we don't produce them at rest like they did there. Yield of phi within LHCb acceptance not clear

        • C: good idea for a MSc thesis or similar, not massive pressure to produce a paper but interesting to explore

    • C: Also if decay exists of the type LLP->SM+DM, possible to use kinematic constraints (aka "corrected mass") to remove some of the background at LHCb →  use knowledge where the primary and secondary decays are → line of flight of the B → assume no transverse momenta relative to that → see if the momenta add up to B mass or if missing mass

  • Discussion on indirect searches (Monika):

    • Question, could there be new observables, e.g., angular distributions?

      • A: The effective operators in these models are the same as in others, so effectively they are covered by the EFT analyses already performed. Long story short, the observables will be the same

There are minutes attached to this event. Show them.
    • 13:00 13:40
      • 13:00
        Welcome: the LHC DM WG & goals of this meeting 10m
        Speakers: Christian Ohm (KTH Royal Institute of Technology (SE)), Oleg Brandt (Ruprecht Karls Universitaet Heidelberg (DE)), Philip Coleman Harris (Massachusetts Inst. of Technology (US)), Tim M.P. Tait (University of California, Irvine), Xabier Cid Vidal (Instituto Galego de Física de Altas Enerxías)
      • 13:10
        History and overview of t-channel models 20m
        Speaker: Tim M.P. Tait (University of California, Irvine)
    • 13:40 15:15
      Consolidating Existing Work
      • 13:40
        t-channel interpretations @ CMS 10m
        Speaker: Andreas Albert (Rheinisch Westfaelische Tech. Hoch. (DE))
      • 13:55
        t-channel interpretations @ ATLAS 10m
        Speaker: Millie McDonald (University of Melbourne (AU))
      • 14:10
        Dark matter with t-channel mediator: a simple step beyond contact interaction 10m
        Speakers: Mr HAO ZHANG (Theoretical Division, Institute of High Energy Physics, Chinese Academy of Sciences), Haipeng An (Perimeter Institute), Dr Haipeng An (Caltech), Haipeng An (University of Maryland), LianTao Wang (University of Chicago), Liantao Wang (University of Chicago (US)), Liantao Wang (Princeton University)
      • 14:25
        Signatures of Majorana dark matter with t-channel mediators 10m
        Speakers: Stefan Vogl (Max Planck Institute for Nuclear Physics), Stefan Vogl (Max Planck Institute for Nuclear Physics), et al
      • 14:40
        Simplified DM models with the full SM gauge symmetry 10m
        Speaker: pyungwon ko (Korea Inst. for Advanced Study (KIAS))
      • 14:55
        Direct Detection and LHC constraints on a t-Channel Simplified Model of Majorana Dark Matter at One Loop 10m
        Speakers: Kirtimaan Mohan (Michigan State University), et al
    • 15:15 15:45
      Rest your brains! 30m
    • 15:45 16:45
      Consolidating Existing Work
      • 15:45
        Brief review on the vector-like portal to scalar dark matter 10m
        Speakers: Jerome Vandecasteele, Michel Tytgat (Université Libre de Bruxelles)
      • 16:00
        Flavored dark matter beyond Minimal Flavor Violation 10m
        Speakers: Monika Blanke, Monika Blanke (Karlsruhe Institute of Technology), Monika Blanke
      • 16:15
        A flavoured dark sector 10m
        Speakers: Pedro Klaus Schwaller (Mainz University), Sophie Renner (University of Mainz), Sophie Renner (CERN)
      • 16:30
        Leptonic WIMP Coannihilation and the Current Dark Matter Search Strategy 10m
        Speakers: Michael Baker (Universitaet Zuerich (CH)), Michael James Baker (Universitaet Zuerich (CH))
    • 16:45 18:00
      Going Beyond
      • 16:45
        The scope of this session 5m
      • 16:50
        Direct (à la semileptonic b-decays) DM searches in B-sector [topic we'd like to discuss] 1m
        Speaker: Christopher Smith (LPSC)
      • 16:50
        Indirect (e.g. B0 - ~B0 oscillations) DM searches in B-sector [topic we'd like to discuss] 1m
        Speakers: Monika Blanke (Technucal University Munich), Monika Blanke (Karlsruhe Institute of Technology), Monika Blanke, Monika Blanke
      • 16:50
        What can we do at B-factories that we can't at the LHC in terms of DM searches? 15m
        Speakers: Enrico Graziani (INFN - National Institute for Nuclear Physics), Enrico Graziani (Universita e INFN Roma Tre (IT))
      • 16:50
        Your new ideas! 1m