Probing Dark Matter at the LHC

Transcription

1 July 15, 2016 PPC2016 1

2 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 PPC Laser Kaplan 2

3 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

4 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 TeV data July 15, 2016 PPC2016 4

5 An Aside q q p g 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

6 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: July Kaplan 15, 2016 Laser 15 PPC

7 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: [hep-ex] photon JHEP06 (2016) 059 W/Z jj ATLAS-CONF H bb ATLAS-CONF H γγ ATLAS-CONF H 4 leptons ATLAS-CONF July 15, 2016 PPC2016 MET 7

8 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 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 miss ATLAS E T miss [GeV] Data 2015 Laser July Kaplan 15, 2016 PPC Standard Model -1 s = 13 TeV, 3.2 fb arxiv: Z( ν ν ) + jets W( τ ν ) + jets 8

9 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: Laser Kaplan 9

10 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: Laser Kaplan

11 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: Laser Kaplan 11

12 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 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 s=13 TeV, 3.2 fb 90% CL limits Axial-vector mediator Dirac DM, g =0.25, g =1 q DM XENON mono-jet 3 m χ 4 [GeV] mono-photon 2 LUX PICO-2L 3 m χ 4 [GeV] July 15, 2016 PPC

13 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: Laser Kaplan 13

14 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 Laser Kaplan 14

15 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 PPC Laser Kaplan 15

16 Mono-Higgs(bb) Search h bb is the dominant decay mode Events / 20 GeV 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 [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 Laser Kaplan 16

17 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 Laser Kaplan 17

18 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 Laser Kaplan 18

19 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 γ+dijet ATLAS-CONF 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 PPC

20 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 PPC

21 Low-mass Dijet Resonance Search Extend sensitivity to lower masses using data scouting analysis performed with trigger objects Extend sensitivity to mediator masses GeV jet g q M g q jet ATLAS-CONF July 15, 2016 PPC

22 Photon+Dijet Resonance Search Trigger on photon to avoid high jet trigger thresholds Extend sensitivity to mediator masses < 450 GeV ATLAS-CONF July 15, 2016 PPC

23 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 PPC

24 Mono-X and Mediator Searches July 15, 2016 PPC

25 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 PPC Laser Kaplan 25

26 Additional Material July 15, 2016 PPC

27 Dijet Search arxiv: ATLAS-CONF 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 PPC Laser Kaplan 27

28 Laser July Kaplan 15, 2016 PPC Summary of Previous Results

29 Back-up Laser July Kaplan 15, 2016 PPC

30 ATLAS vs Direct Detection Mono-jet Mono-photon July 15, 2016 PPC Laser Kaplan 30

31 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: July 15, 2016 PPC Laser Kaplan 31