July 15, 2016 PPC2016 1
Probing Dark Matter at the LHC SM SM DM DM Search for production of DM particles from interacting SM particles Models tested at ATLAS assume DM WIMP Infer DM production through large amounts of missing transverse momentum July 15, 2016 PPC2016 2 Laser Kaplan 2
The LHC and ATLAS LHCb ATLAS ALICE CMS This talk: results based on 3.2 fb-1 13 TeV data collected by ATLAS experiment at LHC in 2015 Feb 17, 2014 Wilson Fellowship Interview 3
Scope of Talk search for direct production of DM WIMPs (χ) search for mediators (M) decaying to SM particles X = jet,γ,w, Z, h χ jet g q M g DM g q M g q χ jet mono-x dijet resonance Showing only results with 2015 13 TeV data July 15, 2016 PPC2016 4
An Aside q q p g 01 01 g p q q All R-parity conserving SUSY searches are dark matter searches (and I am not going to cover any of them) See talk by A. Ventura for ATLAS SUSY results July 15, 2016 PPC2016 5
Interpreting Results of LHC DM Searches Run-I searches used effective-field-theory models 2 Valid only for q2<<mmed use simplified models Joint experimental-theoretical LHC Dark Matter Forum (DMF) established to defined benchmark simplified models, summarized in DMF report [1]: Dirac WIMP mediators: t- and s-channel exchange vector/axial-vector/scalar/pseudo-scalar (MFV) MET+heavy flavor, W, Z, and Higgs WIMP mediators: Results with many models presenteddiracfor 2015 data, t- and s-channel exchange more to come for 2016 results vector/axial-vector/scalar/pseudo-scalar (MFV) MET+heavy flavor, W, Z, and Higgs 15 [1] arxiv:1507.00966 July Kaplan 15, 2016 Laser 15 PPC2016 6 6
rching for Dark Matter Production Mono-X Searches (or: collider-stable weakly-interacting particles) X = jet, γ,w, Z, h gq M χ gdm X MET χ X References jet arxiv:1604.07773 [hep-ex] photon JHEP06 (2016) 059 W/Z jj ATLAS-CONF-2015-080 H bb ATLAS-CONF-2016-019 H γγ ATLAS-CONF-2016-011 H 4 leptons ATLAS-CONF-2015-059 July 15, 2016 PPC2016 MET 7
Mono-Jet Search Most powerful search channel at a hadron collider Signature is ISR jet recoiling off MET Model assumes axial-vector mediator A with coupling to quarks g q and DM g χ and Dirac fermion DM Dominant Z(νν)+jets background estimated using in W(μν)+jets control region Events / 50 GeV Data / SM / 50 GeV 6 5 4 3 2 1 1 1.5 1 0.5 ATLAS s = 13 TeV, 3.2 fb W( µν) Control Region miss p >250 GeV, E >250 GeV T T -1 Data 2015 Standard Model Z( ν ν ) + jets W( τ ν ) + jets W( µν) + jets W( eν) + jets Z( ll) + jets Dibosons tt + single top 400 600 800 00 1200 1400 miss ATLAS E T miss [GeV] Data 2015 Laser July Kaplan 15, 2016 PPC2016 5 Standard Model -1 s = 13 TeV, 3.2 fb arxiv:1604.07773 Z( ν ν ) + jets W( τ ν ) + jets 8
Mono-Jet Results jet + MET search region exclusion in m χ vs. m A plane No significance excess of events with large MET observed Limits set in 2D DM mass and mediator mass plane July 15, 2016 PPC2016 arxiv:1604.07773 9 Laser Kaplan 9
Mono-Photon Search Next most powerful final state is mono-photon, looking for either ISR photon from a simplified model or γγχχ EFT interaction Signature: high-p T, isolated photon with minimal extra jet activity and no charged leptons Dominant Z( νν)γ background estimated from Z(ee)γ and Z(μμ)γ control regions Data is consistent with expected background γ + MET search region E T miss [GeV] July 15, 2016 PPC2016 arxiv:1604.01306 Laser Kaplan
Mono-Photon Interpretations Limits set on simplified model mediator and DM mass, and EFT coupling scale Truncation is used to address EFT model validation July 15, 2016 PPC2016 arxiv:1604.01306 11 Laser Kaplan 11
Mono-X DM Interpretations Model-dependent translation to constraints in DM σ SD vs. m χ Valid only in context of this axial vector mediator model Assumes minimal mediator width, g q = ¼, and g χ = 1, Dirac fermion χ Most stringent constraints from mono-jet search: σ SD < ~ -42 for DM masses up to ~300 GeV ] 2 (χ-proton) [cm σ SD 30 33 36 39 ATLAS -1 s = 13 TeV, 3.2 fb 90% CL limits XENON0 LUX PICO-2L PICO-60 Axial Vector Mediator Dirac Fermion DM g = 0.25, g = 1.0 q χ ] 2 χ-proton cross section [cm 34 ATLAS 35 36 37 38 39 40 41-1 s=13 TeV, 3.2 fb 90% CL limits Axial-vector mediator Dirac DM, g =0.25, g =1 q DM XENON0 42 1 2 mono-jet 3 m χ 4 [GeV] 42 43 mono-photon 2 LUX PICO-2L 3 m χ 4 [GeV] July 15, 2016 PPC2016 12
Mono-V(jj) Search Search for hadronically-decaying W/Z boson recoiling against MET q Z Reconstruct W/Z fat jets : Z small-r jet q (a) W/Z boost large-r jet with 2 sub-jets W/Z(jj) + MET search region small-r jet Consider ISR W/Z and EFT ZZχχ EFT interaction Data consistent with background E T miss [GeV] July 15, 2016 PPC2016 arxiv:1604.01306 13 Laser Kaplan 13
Mono-W/Z( jj) Searches Set limits on simplified model signal strength in ma vs. mχ plane (left) and EFT mass scale vs. m χ (right) q Z Z q (a) July 15, 2016 PPC2016 ATLAS-CONF-2015-080 14 Laser Kaplan 14
Mono-Higgs Z vector model higgs λ q Higgs boson discovery provides unique method for probing dark matter at LHC Higgs ISR rate suppressed probe higgs-dm interaction directly Higgs can also serve as mediator for DM particles (higgs χχ) Z vector model with 2HDM pseudoscalar A July 15, 2016 PPC2016 15 Laser Kaplan 15
Mono-Higgs(bb) Search h bb is the dominant decay mode Events / 20 GeV 12 8 6 ATLAS Preliminary -1 s = 13 TeV Ldt = 3.2 fb Merged : 0 lepton miss E T > 500 GeV 2 b-tags Data Z+jets tt + Single top W+jets Diboson SM Vh Background Uncertainty Pre-fit Background mono-h Vector Mediator M Z = 2 TeV, M χ = 1 GeV σ Signal = 0.1 pb Analysis combines resolved jet region and boosted Higgs-jet region for wide MET range search Resolved: two small-r b-jets Boosted: one large-r jet with two b-tagged sub-jets Data/Pred 4 2 0 1.5 1 0.5 80 0 120 140 160 180 200 220 240 260 280 [GeV] m J Search for peak at m jj or m J ~ m h No excess observed set limits for three simplified models July 15, 2016 PPC2016 ATLAS-CONF-2016-019 16 Laser Kaplan 16
Mono-Higgs(γγ) Search h γγ has small BF (2e-3), but very clean final state Search for peak at m γγ ~ m h No excess set limits on σ(pp hχχ) July 15, 2016 PPC2016 ATLAS-CONF-2016-011 17 Laser Kaplan 17
Mono-Higgs(4l) Search Extremely clean four lepton channel but very low branching ratio Search for excess high MET events No excess set limits on σ(pp hχχ) July 15, 2016 PPC2016 ATLAS-CONF-2015-059 18 Laser Kaplan 18
Mediator Searches jet g q M g q dijet resonance jet Signature References high-mass dijet PLB 754 (2016) 302 low-mass dijet ATLAS-CONF-2016-030 γ+dijet ATLAS-CONF-2016-029 Pro: better sensitivity than mono-x over wide regions of m med Con: an observed excess wouldn t necessarily be linked to DM July 15, 2016 PPC2016 19
High-mass Dijet Resonance Search Select dijet events and search for bump in dijet mass Probe mediators with mass > 1.5 TeV Large rates high trigger thresholds new strategies needed for m < 1.5 TeV jet g q M g q jet PLB 754 (2016) 302 July 15, 2016 PPC2016 20
Low-mass Dijet Resonance Search Extend sensitivity to lower masses using data scouting analysis performed with trigger objects Extend sensitivity to mediator masses 450-950 GeV jet g q M g q jet ATLAS-CONF-2016-030 July 15, 2016 PPC2016 21
Photon+Dijet Resonance Search Trigger on photon to avoid high jet trigger thresholds Extend sensitivity to mediator masses < 450 GeV ATLAS-CONF-2016-029 July 15, 2016 PPC2016 22
Summary of Mediator Constraints γ+dijet high-mass dijet low-mass dijet Sensitivities at m jj<1 TeV will exceed 8 TeV searches with ~present dataset Use dijet searches to set limits on DM-quark coupling vs. mediator mass July 15, 2016 PPC2016 23
Mono-X and Mediator Searches July 15, 2016 PPC2016 24
Summary Many new results from ATLAS probe DM using mono-x and dijet resonance signatures No significant excess observed in any analysis limits set in simplified models and effective field theories Mono-jet and mono-photon provide best sensitivity at low mediator mass Dijet resonance provides best sensitivity at high mediator mass Stay tuned for more updates with 2016 data and beyond July 15, 2016 PPC2016 25 Laser Kaplan 25
Additional Material July 15, 2016 PPC2016 26
Dijet Search arxiv:1512.01530 ATLAS-CONF-2016-030 Various di-jet analyses have also released results in the same simplified model interpretanon as mono-jet and mono-photon Fully reconstructed analysis Search for pair of close-by jets, bump hunt over falling QCD background Trigger level analysis July 15, 2016 PPC2016 27 Laser Kaplan 27
Laser July Kaplan 15, 2016 PPC2016 28 28 Summary of Previous Results
Back-up Laser July Kaplan 15, 2016 PPC2016 29 29
ATLAS vs Direct Detection Mono-jet Mono-photon July 15, 2016 PPC2016 30 Laser Kaplan 30
Mono-Heavy Flavor (Run-1) Various EFT models with different final state b-jet mulnplicines Limits also set on b-fdm model No Run-2 update yet arxiv: 14.4031 July 15, 2016 PPC2016 31 Laser Kaplan 31