1. Same-Sign Diletpon Signatures of Vector-like Quarks Chuan-Ren Chen (NTNU) 12/10/2015, NCTS Annual Theory Meeting In collaboration with H.-C. Cheng and I. Low, 1511.01452

2. Main Goal of LHC: SM -- Higgs Boson New Physics Beyond the SM

3. CRC (NTNU)3

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5. 5 What we have: same-sign dilepton “excess” in various searches observed same-sign dilepton has best fit SUSY SM tth same-sign dilepton (SS2L) Huang, Ismail, Low, Wagner, 1507.01601 4 W + b b

6. CRC (NTNU)6 Fermion CRC, Cheng, Low, 1511.01452 Realistic model: T-odd heavy b’ in Littlest Higgs model with T-parity DM: Dark Matter Other possibilities? exotic X 5/3 a vector-like b’ with odd quantum number wrt SM (existence of new symmetry @ TeV) less constrained, pair production

7. CRC (NTNU)7 production cross section of b’ at the LHC Simplified Model:

8. CRC (NTNU)8 Constraints?? collider signatures of b’ are similar to stop/sbottom in SUSY current limit on stop/sbottom from RUN I ATLAS, CERN-PH-EP-2015-138

9. CRC (NTNU)9 Constraints?? collider signatures of b’ are similar to stop/sbottom in SUSY current limit on sbottom CMS, PAS SUS-13-008

10. CRC (NTNU)10 translating current limit of sbottom to limit of b’ (simplified model)

11. Littlest Higgs Model CRC (NTNU)11

12. particle spectrum CRC (NTNU)12 SM T-parity EvenT-parity Odd * parameters: f, k q, k l, λ 1, m h * The lightest T-odd particle is stable dark matter candidate

13. CRC (NTNU)13 production cross section of b’ at the LHC largest channel: Simplified Model: Realistic model: LHT

14. CRC (NTNU)14 Constraints?? collider signatures of b’ are similar to stop/sbottom in SUSY current limit on stop/sbottom from RUN I ATLAS, CERN-PH-EP-2015-138

15. CRC (NTNU)15 comparing simplified model with Littlest Higgs with T-parity

16. CRC (NTNU)16 current limit on stop ATLAS, CERN-PH-EP-2015-138

17. CRC (NTNU)17 translating current limit of stop to limit of t’ (simplified model)

18. CRC (NTNU)18 comparing simplified model with Littlest Higgs with T-parity

19. CRC (NTNU)19 Fitting CMS tth data production cross section is about 34 fb at 8 TeV LHC taking LHT

20. CRC (NTNU)20 Fitting CMS tth data exactly two same-sign leptons, Njet ≥ 4, Nbjet = 2 NOTE: for simplified model, i,.e.

21. CRC (NTNU)21 Projection on LHC RUN II with 13 TeV with the same cuts imposed in 8 TeV (compared with stop: ) enlarging b’ contribution large enhancement in production cross section most of same-sign events in the search of SM tth come from b’ !!

22. CRC (NTNU)22 b’ contributes about 0.4 (0.3) events in low (high) p T region, stop contributes about 3 (2.3) events in low (high) p T region.

23. CRC (NTNU)23 b’ contributes about 3.7 events stop contributes about 3.1 events.

24. CRC (NTNU)24 b’ contributes about 2.3 events stop contributes about 1.8 events.

25. CRC (NTNU)25 * A stop with ~550 GeV could fit the excess of SS2L in the search of tth. * “ Excesses “ in same-sign dilepton with b-jets signatures are seen in several searches both by CMS and ATLAS in LHC RUN I data. * A fermionic b’ with ~ 750 GeV in LHT (or 850 GeV in simplified model) explains the SS2L excess in tth search, too! * Large enhancement in b’ (stop) pair production at LHC RUN II, compared to SM tth. * Imposing harder kinematic could extract b’ signal in the search of tth at LHC RUN II.

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30. Cancellation CRC (NTNU)30

31. Little Higgs Model CRC (NTNU)31

32. Little Higgs Model w/ T-parity CRC (NTNU)32

33. Yukawa Sector CRC (NTNU)33 Dirac mass term with