Same-Sign Diletpon Signatures of Vector-like Quarks Chuan-Ren Chen (NTNU) 11/03/2015, CYCU HEP seminar In collaboration with H.-C. Cheng and I. Low, 1511.***** Main Goal of LHC: Higgs Boson New Physics Beyond the SM CRC (NTNU)3 preprint 31 Jul 2012 preprint 31 Aug 2012 July , both CMS and ATLAS announced discovery of new particle > 5 standard deviations Mass: GeV (CMS) (ATLAS) Main channel: , ZZ (4 leptons) CRC (NTNU)4 large cross section + low SM background current status at LHC: possible evidence of NP? ~ 2 TeV resonance in WW (2.6 ), WZ (3.6 ), ZZ (2.9 ) by ATLAS Others? Same-Sign Dilepton! CRC (NTNU)5 6 7 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, CRC (NTNU)8 Fermion CRC, Cheng, Low, 1511.***** Realistic model: T-odd heavy b in Littlest Higgs model with T-parity Dark Matter Other possibilities? exotic X 5/3 which decays into t and W a vector-like b with odd quantum number wrt SM pair production, less constrained Littlest Higgs Model CRC (NTNU)9 Cancellation CRC (NTNU)10 Little Higgs Model CRC (NTNU)11 Little Higgs Model w/ T-parity CRC (NTNU)12 Yukawa Sector CRC (NTNU)13 Dirac mass term with particle spectrum CRC (NTNU)14 SM T-parity EvenT-parity Odd * parameters: f, k q, k l, 1, m h * The lightest T-odd particle is stable dark matter candidate CRC (NTNU)15 production cross section of b at the LHC largest channel: Simplified Model: Realistic model: LHT CRC (NTNU)16 Constraints?? collider signatures of b are similar to stop/sbottom in SUSY current limit on stop/sbottom from RUN I ATLAS, CERN-PH-EP CRC (NTNU)17 Constraints?? collider signatures of b are similar to stop/sbottom in SUSY current limit on sbottom CMS, PAS SUS CRC (NTNU)18 current limit on stop ATLAS, CERN-PH-EP CRC (NTNU)19 translating current limit of sbottom to limit of b (simplified model) CRC (NTNU)20 comparing simplified model with Littlest Higgs with T-parity CRC (NTNU)21 translating current limit of stop to limit of t (simplified model) CRC (NTNU)22 comparing simplified model with Littlest Higgs with T-parity CRC (NTNU)23 Fitting CMS tth data production cross section is about 34 fb at 8 TeV LHC CRC (NTNU)24 Fitting CMS tth data exactly two same-sign leptons, Njet 4, Nbjet = 2 NOTE: for simplified model, i,.e. CRC (NTNU)25 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 !! CRC (NTNU)26 * 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. CRC (NTNU)27 CRC (NTNU)28 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. CRC (NTNU)29 b contributes about 3.7 events stop contributes about 3.1 events. CRC (NTNU)30 b contributes about 2.3 events stop contributes about 1.8 events. CRC (NTNU)31 CRC (NTNU)32 CRC (NTNU)33