Probing SUSY Dark Matter at the LHC

Transcription

1 Probing SUSY Dark Matter at the LHC Kechen Wang Mitchell Institute for Fundamental Physics and Astronomy Texas A&M University Preliminary Examination, Feb, 24

2 OUTLINE Supersymmetry dark matter (DM) Relic density & DM composition LHC search status DM search using Stop decay Stop decay & DM composition Light slepton case Heavy slepton case DM search using Vector Boson Fusing (VBF) processes VBF signature Search strategy Results Conclusion Kechen Wang Probing SUSY Dark Matter at the LHC / 25

3 Supersymmetric Dark Matter squark gaugino (a) Fermion Boson (b) R parity conserving SUSY, lightest neutralino cold dark matter candidate χ After EW symmetry breaking, χ W H d H u ( B,,, ) χ ( W, H u ) W H d χ (, ) Higgsino slepton (Planck, 23) 2 2 Kechen Wang Probing SUSY Dark Matter at the LHC 2 / 25

4 DM thermal relic density After EW symmetry breaking, χ W H d H u ( B,,, ) χ ( W, H u ) W H d χ (, ) Composition Bino To satisfy relic density 2 - GeV, depending on a slepton mass σ ann Generic case Relic density Possible mechanism small large Non-thermal, resonance, coannihilation, Comments Dominant: t channel slepton exchange Wino ~ 2.4 TeV large small Non-thermal, multi-component, Higgsino ~ TeV large small Strong bound from direct well-tempering production mixture, etc. Stop search: χ H ( B, ) VBF DM search: W, H,( B H ) χ Kechen Wang Probing SUSY Dark Matter at the LHC 3 / 25

5 LHC status of SUSY DM searches Challenge: small production cross section of EW sector. CMS ATLAS 4 Kechen Wang Probing SUSY Dark Matter at the LHC 4 / 25

6 OUTLINE Supersymmetry dark matter (DM) Relic density & DM composition LHC search status DM search using Stop decay Stop decay & DM composition Light slepton case Heavy slepton case DM search using Vector Boson Fusing (VBF) processes VBF signature Search strategy Results Conclusion Kechen Wang Probing SUSY Dark Matter at the LHC 5 / 25 5

7 DM search using Stop decay B. Dutta, T. Kamon, N. Kolev, K. Sinha, K. Wang and S. Wu, Phys. Rev. D87 (23) 957 [hep-ph/32.323]. ATLAS and CMS 8-TeV If mg mq, >.5 TeV [arxiv:28.949], [arxiv:26.76], [arxiv:27.898] Goal: t decay in a scenario: dark matter sector χ (B + H) Motivation: χ (B + H) Light t Correct relic density Naturalness 6 Kechen Wang Probing SUSY Dark Matter at the LHC 6 / 25

8 Why Stop can be light? Hierarchy Problem, naturalness SUSY solution 2 2 In SM enormous corrections to mh : m ΛUV from top quark. 2 In SUSY Stop loop cancels Λ UV term, and give a finite correction. Light stops (~TeV) needed for natural (not fine-tuned) solution to hierarchy problem. 7 Kechen Wang Probing SUSY Dark Matter at the LHC 7 / 25

9 Stop mixing m see for example, M. Badziak et. al., [hep/ph25.675] h 25GeV requires : Small mixing both stops in the multi-tev scale OR Large mixing Two stops close in mass, in the several hundred GeV scale. Large mixing Very large splitting between the two stops: one is very light (-2 GeV) 8 Kechen Wang Probing SUSY Dark Matter at the LHC 8 / 25

10 Stop decay Stop decay Stop mixing & neutralino/chargino composition (From Claudio Campagnari s talk) lighter stop heavier stop Classic scenario χ χ t B,; W ; t t R 2 χ + t (%) Our scenario χ (B + H), χ2,3 H ; t t R ; ± t χ + t (39%) ; χ χ + l + l (via l or Z) 3,2 3,2 9 Kechen Wang Probing SUSY Dark Matter at the LHC 9 / 25

11 χ (GeV) 25 2,3 H almost degenerate. q, g t χ + t 3,2 3,2 Light slepton case (39%) χ χ + l ± + l (%, via e ± or µ ± ) M M = m m edge ll χ 2 χ 5 t t Opposite-Sign Same Flavor dilepton χ l ± l ± l t b χ 3, % l χ 3,2 l ± l ± 8 % χ l ± ν χ ± p Kechen Wang Probing SUSY Dark Matter at the LHC / 25 ν l χ χ t b t t p

12 Final State: 2 l b + large MET MET > 5 GeV H T > GeV Dilepton mass distribution Dominant SM BG: tt + ets 3 fb - luminosity, 8 TeV OSSF (e ± e µ ± + µ ) tt and tt + ( 4) ets ± ± OSDF (e µ + µ e ) tt and tt + ( 4) ets OSSF OSDF A clear edge around M = m m = 63 GeV χ 2 χ BG data simulation: MadGraph + PYTHIA + PGS4 Signal data simulation: ISAJET + PYTHIA + PGS4 Kechen Wang Probing SUSY Dark Matter at the LHC / 25

13 The edge shifts with 3 fb - luminosity, 8 TeV Dilepton mass distribution M = m m χ χ 2 3,2 (%, or ) χ χ + l ± + l via e ± µ ± 2 Kechen Wang Probing SUSY Dark Matter at the LHC 2 / 25

14 Significance 3 fb - luminosity, 8 TeV 3 fb - luminosity, 8 TeV 2 GeV < M < 7 GeV ll s = N N S S + N B distinguishable edge, for m 55 GeV. significance 3σ, for m = 5 GeV. t t 3 Kechen Wang Probing SUSY Dark Matter at the LHC 3 / 25

15 Heavy slepton case (GeV) q, g t χ + t (3%) χ 3,2 ± χ + l + l 3,2 t (7%, via Z boson) 2 GeV < M < 7 GeV ll 3 fb - luminosity, 8 TeV s = N N S S + N B t t b 75 χ 3,2 7 % 64 χ ± 44 Small value of Z ll smaller significance. branch ratio causes ± ll l ± ν 2 χ 4 Kechen Wang Probing SUSY Dark Matter at the LHC 4 / 25

16 ( B + H ) Dark Matter m = 3 GeV M = m m 2 χ χ χ χ χ B (a),need coannihilation. a low p T lepton small significance. χ + ( B H) (b) and light, edge around M. χ + ( B H) l (c) and heavy, Z ll small significance. l l 5 Kechen Wang Probing SUSY Dark Matter at the LHC 5 / 25

17 OUTLINE Supersymmetry dark matter (DM) Relic density & DM composition LHC search status DM search using Stop decay Stop decay & DM composition Light slepton case Heavy slepton case DM search using Vector Boson Fusing (VBF) processes VBF signature Search strategy Results Conclusion Kechen Wang Probing SUSY Dark Matter at the LHC 6 / 25 6

18 VBF DM search Vector Boson Fusion production B. Dutta, A. Gurrola, T. Kamon, K. Sinha, K. Wang and S. Wu et al., Phys. Rev. Lett. (23) 68 [hep-ph/ ]. B. Dutta, A. Gurrola, T. Kamon, K. Sinha, K. Wang and S. Wu et al., [hep-ph/38.355]. Z Z χ χ χ W W χ ± χ χ ZW, h χ ZW, χ W Z χ W χ m χ Cross section ~ & composition of χ and χ ±. Depending on whether χ is Bino, Wino, Higgsino (and χ ± Wino/Higgsino), or mixture, it will enhance/suppress these diagrams to dominate the cross-section. For example, χ =Wino, χ ± =Wino WW diagrams dominate W luminosity is largest expect Wino + Wino case to give us largest x-section 7 Kechen Wang Probing SUSY Dark Matter at the LHC 7 / 25 7

19 VBF signature VBF tagged ets (2 energetic ets: large m, forward region, opposite hemispheres) ET ET VBF DM production topology Transverse plane Advantages of VBF DM search: (a) VBF tagging ets (b) Broad enhancements in MET (c) Compressed scenarios (d) Free from trigger bias (e) Direct probing EW sector, complementary agnostic about colored sector 8 Kechen Wang Probing SUSY Dark Matter at the LHC 8 / 25

20 Search strategy pp χχ + E,2 T BG: () Z νν : irreducible, mimic topology (2) W lν : veto leptons (3) tt + ets : veto b et, leptons, veto central ets W W χ ± χ χ Pre-selection: (a)met > 5 GeV (b)p T (,2 ) > 3 GeV (c) η(, ) > 4.2, ηη < 2 2 Final selection: (d) p T (,2 ) > 5 GeV Data simulation: (e) m(, 2) > 5 GeV MadGraph + PYTHIA + PGS4 (f) veto leptons (e, mu, tau) (g) veto b ets (7% efficiency,.5% fake rate) (h) veto central et with p T > 5 GeV (i) MET > 2 GeV (45 GeV) for m GeV (TeV) = χ 9 Kechen Wang Probing SUSY Dark Matter at the LHC 9 / 25

21 VBF production cross section After η(, 2) > 4.2 ± ± ± ± χ W or H : pp χ χ, χ χ, χ χ, χ χ (inclusive), since m ± m χ ( B + H ): pp χχ χ χ 2 Kechen Wang Probing SUSY Dark Matter at the LHC 2 / 25

22 Invariant mass distribution of VBF tagged ets After pre-selection cuts & p T (,2 ) > 5 GeV 2 Kechen Wang Probing SUSY Dark Matter at the LHC 2 / 25

23 MET distribution After all selection cuts, except E/ T cut. 22 Kechen Wang Probing SUSY Dark Matter at the LHC 22 / 25

24 Significance curve 5σ 3σ 23 Kechen Wang Probing SUSY Dark Matter at the LHC 23 / 25

25 DM mass & relic density VBF cross section, MET shape neutralino mass, composition DM relic density benchmark: m χ = GeV 24 Kechen Wang Probing SUSY Dark Matter at the LHC 24 / 25

26 Conclusion DM using decay: ( B + H ) 2 l (OSSF) b+ ET Two Cases: Light l : Sensitivity up to 6 GeV 3 fb -, 8TeV. Heavy l : Small significance. Relic density t DM using VBF: W, H, ( B + H ) 2 + ET Z χ Signature χ VBF tagging ets (large m, big rapidity gap ) χ Z Broad enhancements in MET Expected reach For W, 6 GeV fb - 5σ, 4 TeV. Relic density uncertainty: 2% (4%) for GeV W 5 fb -, 4 TeV. Further work: t TeV Heavier stop: small cross section, threshold (et, lepton), pile up large luminosity neutralino mass and composition DM relic density VBF DM Optimization, other kinematic distributions best significance 25 Kechen Wang Probing SUSY Dark Matter at the LHC 25 / 25

27 Status of Stop searches ATLAS Backup Slide CMS 26