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Dark showers snowmass project meeting
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Description
Join Zoom Meeting: https://cern.zoom.us/j/99757610588?pwd=ZmNpcUFjSHRNRjFlVmJzSzVOaU9xQT09
Meeting ID: 997 5761 0588
Passcode: 771905
Dark showers meeting
(7 December 2020)
Indico (incl. recording): https://indico.cern.ch/event/979547/
Introduction (Suchita Kulkarni)
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Collection of models/generator cards started on github. Let us know if you have some you’d like to add
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Timescale of the whitepaper (pheno of LHC benchmarks, summary of ongoing work, connect to theory frontier, LLP whitepaper, individual member whitepapers...): first draft in April, if the timeline of snowmass doesn’t shift (see questionnaire)
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A python module to analyse kinematics being setup, will be on github - contributors welcome
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We should also decide on benchmarks for simulation (Delphes cards if used, smearing parameters…). Do we need a central BG samples?
Marie-Helene: particularly important for dijet, as none is foreseen to be produced centrally within the snowmass effort - we should request it if we want it.
Event-level observables for semivisible jet production with additional objects (Hugues Beauchesne)
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There might be event-level variables that are better to id dark jets (HT, MT2,...)
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Proof of principle with charged mediators decaying to lepton + semivisible jet (similar to LQ) - minimize lep-jet mass in pairing
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The ability to tag dark jets -> new event level variables possible (eg dphi(dj,met)); dark jets could also be produced in assoc. with other objects
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Goal of the project: identify such variables - which are the best? Mostly unexplored, can use UFO + HV model
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If interested in contributing, contact Hugues or Giovanni (see slides for mail)
Suchita: what about efficiencies from experimental side?
Hugues: not sure if to use Delphes yet
Suchita: it would be nice to agree on a strategy, evgen, smearing or delphes to have the possibility to make common plots, etc
Hugues: yes, MET with delphes might be tricky?
Kevin Pedro: MET in Delphes - real MET will be well modelled, but fake MET is more tricky. There is CMS open data 13 TeV dijet simulation, could eventually add some smearing to delphes to match more realistic bkg simulation. Could be a nice goal.
Hugues: BG might not need to be super precise for our studies though, it is interesting though, but might be slightly outside the scope of the project
Kevin: the comparison to BG will likely not be valid as not representative of the BG.
Suchita: could invite some Delphes authors at a meeting to understand what we could do; and initiate in parallel a discussion on the mailing list.
Collider constraints on dark mediators (Hanna Mies)
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New paper: 2011.13990
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QCD-like dark sector, hadronization to dark pions, mediator Xd. Changing param: m(Xd), m(pi_d), ctau(pi_d)
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Increasing decay length of pi_d: prompt 4j (ATLAS) -> emerging jets (CMS) -> met + 2 jets (CMS)
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Compute acceptance x xsec x lumi for each signal in each analysis => constraints shown in the plane of m(Xd) vs ctau for a given m(pi_d)
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Also adding more than one dark flavour (can have different ctau) and redo the analysis
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Also studies constraints from BBN and direct detection experiments: very large constraints from Xenon1T for k_0 coupling of 1.0, but if the coupling is lower, collider bounds become more important
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Flavoured constraints from non-collider experiments
Daniel Stolarski: for the prompt search, what were the requirements?
Hanna: requiring at least 2 tracks with pt > 400 MeV
Daniel: but if we have ‘bordeline’ lifetimes, does it affect acceptance? How prompt is prompt? How is it modelled?
Hanna: used cuts in pythia
Daniel: ok, so no effect on acceptance considered
Sean Mee: what are the DM candidates, the baryons?
Hanna: the DM candidates are not considered really here
Pedro: we did not focus on that, there is an unbroken U(1) dark baryon number (dark colour ensures dark baryons are stable)
Hugues: did you considered paired dijet resonances? They could be helpful probably.
Pedro: the main problem is that the available search is old
Hanna: but would be interesting
Suchita: are there ways to improve on the searches that were looked at?
Hanna: full run-2 data of emerging jets
Alex Perloff: there are many considerations to take into account, for ex slide 10, need a patch for pythia* to generate the multiple flavours, also some look like b-jets
* from Kevin: https://github.com/kpedro88/pythia8/tree/emg/230
Suchita: what makes them so similar?
Alex: for some mediator masses, ctau is not long enough that it looks different from a bjet; there could be 3 dark pion flavours that decay promptly and 1 displaced, making a 3:1 ratio - looking at more than diagonal/off diagonal
James Beacham: ATLAS search still ongoing, trying to be as model-independent as possible
Pedro: what we did for recasting is not necessarily optimal (MET analysis takes any decay outside detector, etc) - there is room for improvement. Also, for multiple flavours, if you veto on prompt tracks that might kill some signal,...
Long Wang: do you set any constraint on the dark pion mass itself?
Hanna: we looked for different dark pion masses, but limits don’t change much between 2 and 10 GeV (backup slide)
Pedro: if very light, the lifetime can become too long to be part of the emerging jet search. Maybe look at different benchmarks (20, 50 GeV?)
AOBs:
Pedro: can we have a regular meeting instead of doodling everytime?
Suchita: we will ask on the mailing list. There will be no other meeting in 2020.
Merry Christmas and happy new year in advance everyone!
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