Slide 1

t/u-channel dark matterCoEPP / The University of Melbourne11 April 2013

Amelia Brennan, Kenji Hamano1The model2Model proposed by Bell et al, emailed round last week (arxiv.org/abs/1209.0231) is gauge-singlet Majorana fermion

is a scalar field, transforms as (3,2,1/3), ie charged under SU(3)C

Need to have all three diagrams to have a gauge invariant result3Used FeynRules and MadGraph5 to produce LHE files for 6 mass points:

Dont use m_eta < 700GeV, as this model is very similar to a SUSY model where m_eta is equivalent to a squark, and we know the squark mass is constrained around this region (though these constraints havent been examined in great detail)

Modelled the parton shower using Pythia8

m_ = 700GeVm_ = 1000GeVm_ = 10GeV(10, 700)(10, 1000)m_ = 100GeV(100, 700)(100, 1000)m_ = 200GeV(200, 700)(200, 1000)4We chose to compare our mass point (200, 700) with the effective operator samples, as this should be far enough away from the regime where the EFT technique is valid

Downloaded following samples to compare:MC12.158939.MadGraphPythia8_AU2MSTW2008LO_WimpPair_D1_DM200MC12.158939.MadGraphPythia8_AU2MSTW2008LO_WimpPair_D5_DM200MC12.158939.MadGraphPythia8_AU2MSTW2008LO_WimpPair_D9_DM200MC12.158939.MadGraphPythia8_AU2MSTW2008LO_WimpPair_ZZxx_DM200

Selections5Use mc_pt, mc_eta, mc_phi, mc_m and mc_charge variables, where first we require mc_pgdId==+/-13 or +/-11 (ie muon or electron)These variables should be truth levelFill histograms with mc_pt, mc_eta and mc_phiSelect the leading and subleading leptons, and reconstruct the di-lepton invariant massLepton pT6

Generally lower pT for leptons in the Ma model

(Problems with examining the lepton pt of ZZxx sample, so not shown here)Lepton phi7

Lepton eta8

More broadly distributed etaInvariant mass of leading lepton pair9More sharply peaked at Z mass maybe would change using original LHE files?

10A better comparison would be using the original EFT operator LHE files and showering with Pythia8 the same way we have showered our own samplesWe downloaded these from Chases afs public directory, but Pythia doesnt recognise the anti-particle ID number any suggestions?11We plan to request official MC productionAll mass points FastSim2 mass points FullSim also for comparisonMass pointNumber of eventsm_ = 10 GeVm_ = 700 GeV10,000m_ = 10 GeVm_ = 1000 GeV10,000m_ = 100 GeVm_ = 700 GeV10,000m_ = 100 GeVm_ = 1000 GeV10,000m_ = 200 GeVm_ = 700 GeV10,000m_ = 200 GeVm_ = 1000 GeV10,000