Searches for new physics in the Top Sector at the LHC Davide Gerbaudo On behalf of the CMS and ATLAS collaborations Fermilab, April 2015
LHC: not only more tops... 2015 1995 2
but also boosted tops LHC searches entering the TeV-scale Boosted top quarks from BSM signals jiahang.zhong@cern.ch Efficient hadronic t-tag: large R jet as t-candidate, less combinatorics jet substructure can be exploited for powerful discriminants 3
Top Quark and New Physics Several reasons for which final states containing top quarks are an excellent mean to probe new physics: the top quark decays before hadronization direct studies of top-quark properties searches for NP with top-pairs the top quark is heavy in many NP models top is special to explain its mass its mass plays an important role in quantum corrections large BR(heavy particle t+x) (à la Z') tt resonances (à la W') tb resonances top quark Vector-likequarks Q t+x or Q Wb+X SUSY stop or Dark matter monotop 4
ATLAS: tt resonances in l+jets ATLAS-CONF-2015-009 new Resolved + boosted selections: Boosted: leptonic top = l+v+small R jet hadronic top = large R jet with high mass, hard substructure Resolved: tt with l+v+4 small R jets; choose kinematically best combination Wide mass range covered Resolution ~10% Narrow resonance excluded up to 1.8TeV 5
CMS: tt resonances in all final states CMS B2G-13-008 new Optimized for boosted tops, using jet substructure. Consider all three possible top-pair decays: 6
CMS: W' tb Single lepton (e/µ) final state Missing ET >2 jets (small-r), at least 1 b-tag top pt reweighting derived in control region Exclude W'R up to 2.03 TeV PAS B2G-12-010 JHEP 05 (2014) 108 All-hadronic final state Focus on di-jet topology, with one b-jet and one large-r t-jet (substructure) Exclude W'R up to 2.0 TeV Both studies use an effective Lagrangian to derive limits vs. al and ar PAS B2G-12-009 7
ATLAS: W' tb Single-lepton (e/µ) final state Missing ET 2 or 3 jets (small-r), 2 b-tags BDT as discriminant, inputs: m(tb), pt(t), etc. Exclude W'R (W'L)as heavy as 1.92 (1.80) TeV All hadronic final state, two jets with ΔR>2.0 Phys. Lett. B 743 (2015) 235 new One R=0.4 jet, with b-tag One R=1.0 jet, with t-tag Two categories based on b-tag of top candidate jet substructure N-subjettiness Unbinned lhood fit on m(tb) Bkg estimation from data Exclude W' up to 1.68 TeV L W' up to 1.76 TeV R hep-ex/1408-0886 8
CMS: all-hadronic monotop WIMP probe complementary to monojet and monophoton DM searches Large missing E T Three high-p jets T One b-tag Exclusion up to 350 GeV (scalar) 630 GeV (vector) New CMS B2G-12-022 hep-ex/1410.1149 9
ATLAS: ℓ+jets monotop t Wb (W ℓυ) + MET tt ( dilepton) is the main background mt(ℓ, MET) and ΔΦ(ℓ, b) are the main discriminating variables Eur. Phys. J. C (2015) 75 Interpretation: many theories predicting monotop use effectivel models: resonant production of spin-0 t f R 1/2 non-resonant production of spin-1 + t R 10
ATLAS: Dark Matter + HF Investigate the production of dark matter pair production with t or b: large missing E T at least one high-p jet T four selections targeting different production modes one or two b-jets two top quarks, both with hadronic decays or one hadronic and one leptonic optimized selection with several advanced variables: amt2, topness Eur. Phys. J. C (2015) 75 Strong limits in the low mass region, relevant to recent claims by DAMA/LIBRA, COGENT, CDMS 11
VLQ production and decay Pair Production Single Production tz 0 tz W b tz BR(T Wb) W bw b Rich signatures: top quarks b jets V jj/j had 1 H bb. 0 6-8 jets 2-6 b-tags 2-3 Vhad 0 Hbb 6 jets 4 b-tags 1 Vhad1 1 Hbb BR(T Wb) Njets l Nb-tags b U Σ B nph R ys >1 ic a Vh ad th W 1 8 jets 6 b-tags 1 Vhad 2 Hbb N BR(T th) th tz Possible decays: T Wb/Zt/Ht B Wt/Zb/Hb NH bb U ΣB nph R ys >1 ic al 1t H th Possible signatures for TT (l+jets) BR(T th) Possible final states for TT 4 jets 2 b-tags 1 Vhad 0 Hbb 1 12
ATLAS: VLQ ATLAS-CONF-2015-012 13
ATLAS: VLQ Preliminary result: Same-sign dilepton/trilepton (+ b-jets) Also look for four-top production 2.2σ 2.4σ 14
ATLAS: VLQ TT Z( ll)t + X >2 jets, several selections on leptons, b-jets, fw-jets JHEP 11 (2014) 104 15
ATLAS: VLQ ATLAS-CONF-2015-012 16
ATLAS: VLQ B in l+jets hep-ex/1503.05425 new Assuming allowable decay modes are: B Wt/Zb/Hb Consider subsets with 1 or more reconstructed hadronic boson Do not measure charge Whad also set limits on T5/3 Wt >840GeV 17
ATLAS: VLQ New: results also available for vector-like B searches. For more summary plots, see the ExoticsPublicResults 18
CMS: VLQ l+jets New CMS-PAS-B2G-12-017 Assume BR(T Wb)=BR(Q Wq)=100% For the hadronic W, consider both resolved decay boosted decay 19
CMS: VLQ all-had >2 high-pt CA jets (R=1.5) >1 top candidate (HEP top tagger) >1 Higgs candidate For the first time: tagging boosted Higgs with a combination of jet substructure and b-tagging. New hep-ex/1503.01952 20
CMS: VLQ Ht+X, H γγ One Higgs boson required to decay H γγ Low BR, high purity Hadronic (W qq) and leptonic (W lv) channels Loose kinematic selection (HT) CMS-PAS-B2G-14003 21
CMS: inclusive VLT & VLB Comprehensive searches for TT and BB in: Phys. Lett. B729 (2014) 149-171 Single lepton Multilepton Opposite-sign, on/off-z Same-sign Trilepton CMS-PAS-B2G-12-019 Single lepton >4 jets, >1 b-jet 0, 1, 2> V-tags 22
ATLAS: stop Three categories considered: fully resolved (6 jets) partially resolved (2 jets reclustered with R=1.2) five jets Most discriminating variable: missing ET Pair produced stop detected in all-hadronic top decays: JHEP 09 (2014) 015 Two decay modes considered: Pair produced stop detected Several signal regions in ℓ+jets top decays: accounting for different JHEP11(2014)118 mass hierarchies and decay modes Shape fits enhance sensitivity in challenging scenarios 23
Stop Searches hep-ex/1412.4742 Impressive coverage already reached last year Detailed tt measurements made it possible to probe the stealth stop region see yesterday's talk by Frederic Deliot 24
Outlook Top turns 20, and plays a central role in many searches for new physics at the LHC New tools, such as top tagging and reconstruction of boosted objects, are key in many of these searches Looking forward to the next 20 years of top physics; hopefully it will be served with new physics! 25
Thank you For their hard work: CMS and ATLAS colleagues For the inspiration and feedback with the slides' preparation: A.Lister, T.Golling, S.Majewski, S.Rappoccio, J.Erdmann, J.Boyd,... 26