Dynamical Dark Matter Search

Overview

The search for dynamical dark matter is based on the following publication:

Keith R. Dienes, Shufang Su, Brooks Thomas: Distinguishing Dynamical Dark Matter at the LHC: https://arxiv.org/abs/1204.4183

Signal samples

Privately produced signal samples by Peter with pair production of Ψ -> jj Χ with m(Ψ) = 1500 GeV and m(Χ) = 100 GeV can be found on the UofA Tier3:

/export/home/lochp/data2/DDM-1500-100-*

EVNT files with the pair-production of Ψ with different masses in the same event are currently being prepared by the theorists.

Background samples

Multijet samples:

mc15_13TeV:mc15_13TeV.361020.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ0W.evgen.EVNT.e4397
mc15_13TeV:mc15_13TeV.361021.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ1W.evgen.EVNT.e4397
mc15_13TeV:mc15_13TeV.361022.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ2W.evgen.EVNT.e4397
mc15_13TeV:mc15_13TeV.361023.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ3W.evgen.EVNT.e5622
mc15_13TeV:mc15_13TeV.361024.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ4W.evgen.EVNT.e5622
mc15_13TeV:mc15_13TeV.361025.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ5W.evgen.EVNT.e5622
mc15_13TeV:mc15_13TeV.361026.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ6W.evgen.EVNT.e5622
mc15_13TeV:mc15_13TeV.361027.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ7W.evgen.EVNT.e5622
mc15_13TeV:mc15_13TeV.361028.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ8W.evgen.EVNT.e5622
mc15_13TeV:mc15_13TeV.361029.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ9W.evgen.EVNT.e3569
mc15_13TeV:mc15_13TeV.361030.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ10W.evgen.EVNT.e3569
mc15_13TeV:mc15_13TeV.361031.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ11W.evgen.EVNT.e3569
mc15_13TeV:mc15_13TeV.361032.Pythia8EvtGen_A14NNPDF23LO_jetjet_JZ12W.evgen.EVNT.e3668

V + jets (V -> qq)

mc15_13TeV:mc15_13TeV.304307.Sherpa_CT10_Wqq_Pt280_500.evgen.EVNT.e4692
mc15_13TeV:mc15_13TeV.304308.Sherpa_CT10_Wqq_Pt500_1000.evgen.EVNT.e4692
mc15_13TeV:mc15_13TeV.304309.Sherpa_CT10_Wqq_Pt1000.evgen.EVNT.e4692

mc15_13TeV:mc15_13TeV.304707.Sherpa_CT10_Zqq_Pt280_500.evgen.EVNT.e4692
mc15_13TeV:mc15_13TeV.304708.Sherpa_CT10_Zqq_Pt500_1000.evgen.EVNT.e4692
mc15_13TeV:mc15_13TeV.304709.Sherpa_CT10_Zqq_Pt1000.evgen.EVNT.e4692

ttbar

mc15_13TeV:mc15_13TeV.410000.PowhegPythiaEvtGen_P2012_ttbar_hdamp172p5_nonallhad.evgen.EVNT.e4398
mc15_13TeV:mc15_13TeV.410007.PowhegPythiaEvtGen_P2012_ttbar_hdamp172p5_allhad.evgen.EVNT.e4398

all-hadronic split in different invariant ttbar mass ranges:

mc15_13TeV:mc15_13TeV.303722.PowhegPythiaEvtGen_P2012_ttbar_hdamp172p5_allhad_mtt_1.evgen.EVNT.e4321
mc15_13TeV:mc15_13TeV.303723.PowhegPythiaEvtGen_P2012_ttbar_hdamp172p5_allhad_mtt_2.evgen.EVNT.e4321
mc15_13TeV:mc15_13TeV.303724.PowhegPythiaEvtGen_P2012_ttbar_hdamp172p5_allhad_mtt_3.evgen.EVNT.e4321
mc15_13TeV:mc15_13TeV.303725.PowhegPythiaEvtGen_P2012_ttbar_hdamp172p5_allhad_mtt_4.evgen.EVNT.e4321
mc15_13TeV:mc15_13TeV.303726.PowhegPythiaEvtGen_P2012_ttbar_hdamp172p5_allhad_mtt_5.evgen.EVNT.e4321

single top

mc15_13TeV:mc15_13TeV.410013.PowhegPythiaEvtGen_P2012_Wt_inclusive_top.evgen.EVNT.e3753
mc15_13TeV:mc15_13TeV.410014.PowhegPythiaEvtGen_P2012_Wt_inclusive_antitop.evgen.EVNT.e3753

(s-channel and t-channel to be added, found only leptonic decays so far)

dibosons

Cross-section probably negligible with respect to other backgrounds.

EVNT -> DAOD_TRUTH4

The EVNT files are converted in DAOD_TRUTH4 format which saves the full parton information. Details on the procedure can be found here:

https://twiki.cern.ch/twiki/bin/view/AtlasProtected/TruthDAODTutorial

https://twiki.cern.ch/twiki/bin/viewauth/AtlasProtected/TruthDAOD

Truth-jet - quark matching

Matching jets to quarks using truth

1) Calculate dR of hardest parton to all jets.

2) The closest jet within a threshold value (<0.4) is accepted as a match.

3) Matched jet is removed from jet pool.

4) Repeat step 1) with next hardest parton.

Matching algorithms

The main challenge of this analysis arises due to the possibility of grouping the incorrect pair of final-state jets together. Several algorithms are being studied to yield the highest signal reconstruction efficiency.

1) Minimum mass algorithm

Jets are grouped together such that the invariant mass difference of the two pairs is minimal. Out of XXX events, the minimum mass algorithms pairs the jets correctly for YYY events, corresponding to an efficiency of ZZZ.

2) Maximum mass algorithm

3) Random

The efficiency of randomly pairing jets together corresponds to 33%.

4) pT pairing

The 1st hardest pT jet is automatically paired with the 4th hardest. The 2nd and 3rd form the remaining pair.

5) Minimise ΔR

Searches with four jets in the final state (https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2016-084/) used a distance criteria to get the "correct" jet pairing, the following quantity needs to be minimized

ΔR_min = Σ | Δ R_i - X|

where the sum i runs over the two jet pairs and X = 1.0 was optimized for the search. The value of X gives basically the boost of the system and tells you how close the jets should be. Might be a bit trickier for a three-body decay.

6) The Hemisphere method

The idea is that the parent particles give a large boost to their separate decay chains and thus the daughter particles are captured in a cone or hemisphere. Seems to provide good performance for off-shell decay chains. The procedure is described in https://arxiv.org/abs/1009.2751

7) The pT vs M method (https://arxiv.org/abs/1009.2751)

Look for correlations in high transverse momentum pairs with low invariant mass. Better performance than hemisphere method for on-shell production

Variables to consider for event selection

The following variables should be checked in order to discriminate between traditional dark matter models and DDM models or to differentiate between DDM signal and background processes:

• ΔΦ (j1j2) and ΔΦ (j3j4) (j1 and j2 does not necessarily mean leading and subleading jet here, just the jets that are matched to together)
• ΔR (j1,j2) and ΔR (j3,j4)
• m_T2 (inspired by SUSY searches)
• Scalar sum H_T of the transverse momenta of the jets
• Scalar sum H_T of the transverse momenta of the jets and Etmiss
• Rapidity difference (signal more central, t-channel production of QCD jets)
• Average mass m_avg = 0.5 * (m_jj1 + m_jj2) where m_jj1 and m_jj2 are the invariant masses of the combination of two jets (maybe not really discriminating between signal and background as we actually have a three body decay)
• Transverse component of the vectorial sum of the jet momenta of each pair, i.e. (vec(p_j1) + vec(p_j2))_T and as well for the second pair