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Spring 2020 LHC DM WG meeting: DM models with 𝒕-channel mediators

→ Europe/Zurich
Oleg Brandt (Ruprecht Karls Universitaet Heidelberg (DE)), Philip Coleman Harris (Massachusetts Inst. of Technology (US)), Priscilla Pani (Deutsches Elektronen-Synchrotron Campus Zeuthen (DE)), 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)
Description

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Meeting goals:

  • Consolidating existing work/recent studies on t-channel models:
    • Converge on a set of models and quantum numbers of DM, 
    • finalise 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?
    • Explore the transition to LLP signatures
  • Final goal:
    • White Paper of the LHC DM WG on DM models with t-channel mediators
  • Defining future projects/priority of the LHC DM WG:
  • Wildcard session:

 

Logistics:

  • for subscription to the general LHC DM WG mailing list used for announcements go here
  • for subscription to the contributors mailing list used for discussions among LHC DM WG participants go here
  • for LHC DM WG web page go here

 

Registration
Participants
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Participants
  • Adil Jueid
  • Albert De Roeck
  • Alejandro Ibarra
  • Alexander Josef Grohsjean
  • Alexandre Arbey
  • Alicia Calderon Tazon
  • Alison Elliot
  • Amanda Steinhebel
  • Andreas Albert
  • Benjamin Fuks
  • Bhawna Gomber
  • Caterina Doglioni
  • Cedric Prieels
  • Chang-Seong Moon
  • Chiara Arina
  • Chiara Rizzi
  • Christian Ohm
  • Christoph Borschensky
  • Christoph Paus
  • Christopher Smith
  • Corinne Goy
  • Darren Price
  • David Yu
  • Deepak Kar
  • Dipan Sengupta
  • Disha Bhatia
  • Elias Bernreuther
  • Enrico Morgante
  • FEDERICA GIACCHINO
  • Federica Giacchino
  • Federica Piazza
  • Galo Rafael Gonzalvo Rodriguez
  • Gilly Elor
  • Giorgio Busoni
  • Giuliano Gustavino
  • Guglielmo Frattari
  • Haipeng An
  • Hanna Mies
  • Henning Flaecher
  • Jack Lindon
  • Jakub Salko
  • James Frost
  • Jan Heisig
  • Jan Henryk Kalinowski
  • Jannik Geisen
  • Jeanette Miriam Lorenz
  • Jesse Liu
  • Jonas Lindert
  • Jonatan Piedra
  • Jonathan Butterworth
  • Joshua Berger
  • José Francisco Zurita
  • Julia Harz
  • Jyothsna Rani Komaragiri
  • Jérôme Vandecasteele
  • Kajari Mazumdar
  • Kayla McLean
  • Kenji Hamano
  • Kirtimaan Mohan
  • Krisztian Peters
  • Laura Lopez Honorez
  • Liantao Wang
  • Luca Mantani
  • Luca Panizzi
  • Marcella Bona
  • Maria Jose Costa
  • Maria Moreno Llacer
  • Maria Savina
  • Marie-Helene Genest
  • Marvin Flores
  • Maura Barros
  • Michael James Baker
  • Michael Kent Wilkinson
  • Michael Krämer
  • Michel Lefebvre
  • Michel Tytgat
  • Miguel Escudero
  • Monika Blanke
  • Nazila Mahmoudi
  • Niki Saoulidou
  • Oleg Brandt
  • Ondrej Kovanda
  • Pedro Schwaller
  • Peiwen Wu
  • Pyungwon Ko
  • Raman Khurana
  • Reham Aly
  • Richard Teuscher
  • Rohini Godbole
  • Shaaban Khalil
  • Shankha Banerjee
  • Shin-Shan Yu
  • Silvia Resconi
  • Spyridon Argyropoulos
  • Stanislava Sevova
  • Stefan Vogl
  • Stefano Giagu
  • Steven Worm
  • Sukanya Sinha
  • Sunil Manohar Dogra
  • Susanne Westhoff
  • Sushil Chauhan
  • Suzan Basegmez Du Pree
  • Tania Robens
  • Tasnuva Chowdhury
  • Tim M.P. Tait
  • Varun Sharma
  • Vasiliki Mitsou
  • Xabier Cid Vidal
  • Yalcin Guler
  • Yang Bai
  • Yanyan Gao
  • Yiming Abulaiti
  • Zirui Wang
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  • Introduction

    • Welcome: the LHC DM WG & goals of this meeting (Xabier Cid Vidal)

    • DM results from ATLAS hot off the press (Amanda Steinhebel)

      • C: long-lived stops: 4-body stop decays may be displaced, but this does not always have to be the case, it depends on the exact scenario: mass splittings etc.

      • Q: do we expect any ATLAS dark photon minimal model result? 

        • A: Not as far as I know. Will follow up offline

      • Q/p11: pretty similar sensitivity to scalar and pseudoscalar case, where does this come from? Pseudoscalar xsec should be smaller, where does the sensitivity come from?

        • A: ps and s kinematics same, smaller ps masses allowed, but no specifics in ps case are targeted

    • CMS Dark Matter Results (Bhawna Gomber, Deborah Pinna)

      • Q/p13: which visible final states are actually targeted? tt + tt? How do you get same-sign leptons?

        • A: the Feynman diagrams are representative, we are looking for tt + tt, but also 3t final states

      • Q/p25: any appreciable difference to previous result? Any kinetic mass mixing interpretation planned?

        • A: don’t think the result have changed drastically, mostly on the interpretation.

        • A: this model assumes y_dark is massless, so it’s a different scenario from the vanilla y_dark model. Jacob will present vanilla y_dark results

      • Q: for the full Run 2 results, if we could have limits on absolute xsec, rather than signal strength

        • C: there is a lot of effort to provide more information, we are aware of this and will provide results in such format (e.g. through HEPdata)

        • C: same efforts on ATLAS

 

  • t-Recent t-channel studies

    • A universal framework for t-channel dark matter models (Luca Mantani)

      • Q: avoid double-counting, does this apply to all restrictions, is this a general feature

        • A: relevant for every model. In pair-production the interference is small if t-channel small due to small DM coupling

      • Q/p13-16: comparison LO vs NLO -- which PDF did you use for that? Did you use LO PDF for LO, and NLO PDF for NLO

        • A: use NLO for both because LO is a poor fit

          • Q: This comparison does not make sense, you have a normalisation shift? It’s not a fair comparison

            • A: If you have a LO PDF, there are large uncertainties. 

      • Q: how critical are the kinematic differences? Can we generate LO, and use constant NLO k-factors

        • A: the shape changes somewhat

          • Could we generate XX, XY, YY separately and calculate their 

      • Q/p12: “Simulate interference at LO and reweight by geometric mean of k-factors (QCD and t-channel) bin by bin” → is that happening automatically, or does one have to do it by hand?

      • Q/15: how do the k-factors btw NLO and LO look like generally in the phase space? (in a linear-scale ratio plot)? How flat in kinematic observables like e.g. MET?

      • Q: how to generate LO? Is any splitting into 5 different samples necessary?

        • A: LO can be generated in one go

      • Q/p9: excluded region in NLO, how large is the effect of the DD xsec?

        • Not included

          • C: in this case model couples to uR, we don’t expect large uncertainties from the form factor, for strange that would be different

            • C: uR is not very realistic, but was used for the studies

      • Q: technical Q, at NLO you use a trick to avoid double-counting, there are several ways to do this -- do the different methods give similar results, or do we have to take this into account?

        • A: not looked at in detail, but probably OK for uR

      • Q/p9: what are the stripes?

    • Discussion: t-channel studies for the White Paper in the spirit of the LHC DM WG (Oleg Brandt)

      • Discussion after next talk

    • Towards a white paper on t-channel models (Benedikt Maier, David Yu)

      • C: it would be easy to make a restriction for ATLAS

      • C: good to have timelines, but we try to do 2 things: a) comparable set of parameters, could converge on this quickly b) are there further questions, requiring thought and studies

        • Q: do you envisage two WPs, or just one?

          • A: overhead in work, one WP 

      • C: sounds reasonable

      • Q: how is mono-t fitting into that theory?

        • A: qq mediator interaction is not there, cannot exist in t-channel model, for mono-t no way out in t-channel. Current model would have to be extended in a not nice way (breaking Z2)

          • S-channel mediator

      • Q: scope of WP -- aim to have a document out that is citable, or something more ambitious? Repository of possible models and benchmarks? Do we want to restrict this to t-channel only?

        • A: a large and comprehensible body of work is possible with this particular model, see p8 of the talk, a snapshot of just a few things it can do

      • Meta-analysis of the points brought up:

        • 1) On a short timescale of couple of weeks:

          • Agree on parameter choices for first generation coupling scenario (mono-jet signatures), in time for the upcoming mono-jet results

        • 2) on a somewhat longer timescale of a couple of months:

          • More detailed studies about scalar/vector/Dirac/Majorana DM, 3rd gen couplings, more exotic signatures like LLP

    • Long-lived particle signatures of t-channel dark matter models (Jan Heisig)

      • C: 4-body decays and non-prompt in stops: on p17 the lambda_SUSY line is crossing the boundary between prompt and non-prompt, so one has both types of signatures

      • Q: what is freeze-in?

        • A: start with 0 or some fixed value of DM abundance, then small leakage of other particles that are in thermal bath into DM sector. Efficient if mother particle decaying into DM sufficiently abundant, once its abundance drops, freeze-in dies out

    • Baryogenesis and Dark Matter from B Mesons (Miguel Escudero)

      • Q: classification of models, same category as mono-t one. Mediator and DM are not Z2 odd. This would need a separate model

        • A: Agreed. Would need a qq~ mediator

      • Q/p14: Diagram: decay into 3 particles

        • A: see p19, psi -> phi+xi, where phi is DM

      • Q/p19: diagram violates flavour?

        • The coupling on itself not constrained intera

 

  • Wildcard session

    • Casting a ParticleNet to catch dark showers (Alexander Mueck, Elias Bernreuther, Felix Kahlhoefer, Michael Kramer)

      • Q/p8: which dark meson masses?

        • A: We are interested in the 1 GeV scale -- 5, 20, 50 GeV

      • Q: do you train a specific classifier for each point in the parameter space of your model?

        • A: Yes, otherwise discrimination is significantly worse

      • Q: what does it learn?

        • A: number of constituents, pT configuration

      • Q/p8: mono-jet, dphi cut would kill your signal -- did you exclude it?

        • A: we include it, one of the dark showers stays invisible

      • [Q: what kind of detector simulation used?]

      • [Q: what exactly enters the cloud of points? Each of the four coordinates of 4-momenta?]

    • Inert Doublet Model (Tania Natalie Robens)

      • Q: what is omega_c?

        • A: RD measure

 

  • Wildcard: future projects

    • The LLP WG and community (José Francisco Zurita)

      • C: good idea to have liasons of each group 

      • Q: Relationship between LLP WG and PBC?

        • A: PBC is more for light new physics, and beyond LHC. Sizeable overlap

    • Latest results on dark photons at the LHC (Jakob Salfeld-Nebgen)

      • C: strongest constraint on y_dark is the coupling to SM, coupling to DM smallest

      • Q: you mentioned you’ll go below 10 GeV, why not done already?

        • A: it’s only a question of timelines

      • Q: Why in intermediate mass region 10-20 GeV is LHCb better, despite better acceptance at CMS

        • A: CMS could improve sensitivity through better bgr rejection

        • A: Sliding mass window range had to be decreased because of the dip around 20 GeV on p9

      • C: Mass mechanism for y_dark, can couple to Higgs and dark Higgs. How much restrictions are there? ATLAS and CMS took very different interpretations

        • C: Diagram on p12 is not responsible for mass generation. Once the dark Higgs is considered, the phenomenology becomes richer

    • Exploring dark matter in dark sectors at the LHC (Caterina Doglioni)

      • C: many stimulating ideas in this talk, thanks!

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