1. Search for Dark Matter in Jets plus MET final state for Non-therma Dark Matter model Using Data From Proton-Proton Collisions at √s = 13TeV Sonaina Undleeb (On Behalf of CMS Collaboration), Department of Physics, Texas Tech University
Signal  For μ+ μ+
Motivation
Dark matter (DM) outweighs visible matter roughly six to one, making up about 27% of the universe.
There are several theories to predict its nature – i.e. DM could contain “supersymmetric particles”… etc
Experiments at the Large Hadron Collider may provide more direct clues assuming that DM would be light enough to be produced at the LHC, escapes through the detector unnoticed while carries away energy and momentum so that its existence can be inferred through the “missing” information.
We are interested in dark matter pair production along with a single energetic jet (from ISR).
Results of the search are interpreted in terms of simplified dark matter signal models whose parameters are couplings and masses of mediator and dark matter particles.
A pair of dark matter particles couple to either a scalar, pseudo-scalar, vector or axial mediator.
Abstract
We will present a search for dark matter in events with one or more jets and large missing transverse energy using proton-proton collisions at center-of-mass energy of 13 TeV. The data was collected in 2016 by the CMS detector at the LHC corresponding to an integrated luminosity of 35.9 fb-1. The results are interpreted in terms of non-thermal dark matter model which explains presence of dark matter in the universe and justifies baryon asymmetry as well.
Non-thermal DM Limit Scan
95% CL expected (black thick line) and observed (red line) upper limits on
μ = σ/σth for a non-thermal DM particle for mediator masses MX1of 1 and 2 TeV,
in the λ1 − λ2 plane.
Generator Level Studies
Missing Transverse Energy Distribution in (λ1 ,λ2) Parameter Space
Mediator Mass Distribution in (λ1 ,λ2) Parameter Space
Event Selection
The data is 35.9 fb−1 with √s=13 TeV
Baseline Selection:
Etmiss >250 GeV (consistent with trigger turn-on).
Leading Jet (AK4) pT > 100 GeV with |η| < 2.5
min∆φ(Etmiss, jets) > 0.5
|Etmisscalo - EtmissPF |/Etmisscalo < 0.5
Signal NO
Leptons
b-jets
Photons
2 jets + MET channel dominance
YES
Control Region
Background Estimation
Leading electroweak backgrounds are estimated using combined maximum likelihood fit of five Control Regions.
Transfer factors are used to translate yields from control regions to signal region.
Monojet channel dominance
Dijet channel dominance
Z νν
W lν
Z(μμ)
Z(ee) Z
(γ+jets)
W(μν)
W(eν)
2 jets + MET channel dominance
Light Non-thermal Dark Matter Model
Simplified Model –
Predicts “light” dark matter (MDM ≈ MProton).
Mediator is heavy scalar color triplet(s) (~TeV)
Large missing energy associated with an energetic jet whose transverse momentum distribution shows jacobian-like shape.
Parameters of the model are: λ1 ,λ2 (couplings) , MX , MDM(Masses) and Width of mediator.
Explains baryongenesis.
Model Independent Limit
95% C.L. observed and expected upper limits on production cross-section for resonance process are shown where the mediator decays to light quark jet and light weakly interacting particle. The expected limit is model independent and holds for [λ1 –λ2]= [ ].
Results
Observed MET distribution in the signal regions compared with the post-fit background expectations for various SM processes.
The last bin includes all events with MET > 1250 GeV
Monojet channel dominance
Dijet channel dominance
Work In Progress
For λ1 =[ ] & λ2=[ ] mediator width is less than about 30% of its mass .
Backgrounds
Dominant Backgrounds:
Z(νν)+Jets
W(lν)+Jets
Together make up about 95% of total.
Subdominant Backgrounds:
Z(ll)+Jets
γ+ Jets (Serves as Control Region for background estimation)
Top
Diboson (WW, WZ, ZZ)
QCD
References:
B. Dutta, Y. Gao, and T. Kamon, “Probing Light Nonthermal Dark Matter at the LHC”, Phys. Rev. D 89 (2014) , doi: /PhysRevD , arXiv:
N. Daci et al., “Search for dark matter produced with an energetic jet, or a hadronically decayingW or Z boson, at √s = 13 TeV with the full 2016 dataset”, Technical Report, CERN, CMS Analysis Note : AN
Monojet
Dijet
ISGS
Pair Production of X