Searches for Heavy Resonances at the LHC Tetiana Berger-Hryn’ova (LAPP, CNRS-IN2P3) For the ATLAS and CMS collaborations Moriond QCD 2014
Higgs Discovery & Searches Following the discovery of a scalar boson Standard Model (SM) is complete (but for an axion) and self-consistent A lot of questions still need answers: – Why is Higgs light? – What is dark matter? – How to accommodate gravity? – Why are there three generations? –…–… – Is there a theory which answers all our questions? We are looking for something – we do not know what – neither where to look – nor if there is any chance of finding it… Does it remind you of something? 2T. Berger-Hryn'ova Moriond QCD 2014
How do we search Approach 1 Pick a Theory Pick a model Look at various production/decay modes of new states! (model-independently) Approach 2 Pick a final state & look (model-independently) Get lucky! It sounds like a quest Go there- I don’t know where, Bring that – I don’t know what 3T. Berger-Hryn'ova Moriond QCD 2014
Look for Signatures! Interesting Models: Extended Gauge Groups Compositeness Wraped Extra Dimentions Technicolor etc … Interesting Signatures: Dibosons /W/Z+jet(s) Di/Tri-jet Dileptons (ll, ) etc… Look for bumps on smooth SM backgrounds! 4T. Berger-Hryn'ova Moriond QCD 2014 Focus on selection of results Apologies if your favourite is left out All limits are quoted at either 95% Confidence Level or Credibility Level (CL)
Today’s menu Searches in +jet final state Dilepton searches Diboson searches Tri-jet resonant searches X HH bbbb T. Berger-Hryn'ova Moriond QCD 20145
Searches in +jet final state Selection CMS(ATLAS): p T j/ >175(125) GeV + iso; | |<1.44(1.37), | j |<3.0(2.8) | ,j |<2.0(1.6) No significant excess seen. Exclude m(q*)<3.5 95% CL T. Berger-Hryn'ova Moriond QCD Background fit function: ATLAS: PLB 728, 562 (2013)
+jet limits Limit behaviour quite similar for various models: (QBH/q*)~83-72/85-80% What happens at high mass? T. Berger-Hryn'ova Moriond QCD Quantum Black Hole (QBH) q*
Effect on limits from Signal Shapes T. Berger-Hryn'ova Moriond QCD Increased fraction of the off-shell production for the signal events (“parton-luminosity tail”) as the kinematic production limit is approached size increases with the resonance width. Noticeable impact of this tail on cross-section limit values when >5-10% of events in the tail This affects most of the limits (q*, Z’ etc)! Usual signal Breit-Wigner shape Parton distribution functions Parton-luminosity tail
Effect on limits from Signal Shapes T. Berger-Hryn'ova Moriond QCD For thresholds or resonances with suppressed low-mass contributions (Z*) “parton- luminosity tail” effect is not present It is also not present it the resonance shape is input “by hand”, e.g. assuming a Gaussian or Breit-Wigner of certain width, instead of using shape from simulation QBH Production is a threshold! M D =M TH Mass M D =fundamental scale of quantum gravity M TH =threshold for black hole production
+jet limits: width effects T. Berger-Hryn'ova Moriond QCD Width assumptions matter at low masses: smaller width = better limits Also parton luminosity tail is larger for wider resonances, which leads to worse limits
Dilepton Resonant Searches Data consistent with SM predictions T. Berger-Hryn'ova Moriond QCD CMS signal shape assumption: Breit-Wigner with Z’ width ( /M=0.5%) convoluted with Gaussian of signal resolution ATLAS signal shape assumption: Monte-Carlo based Z’ SSM shape (with width /M~3%)
Dilepton Resonant Search Results 95% CL are: M(Z’ SSM ) > 2.96 TeV (CMS) & 2.8 TeV (ATLAS) M(Z’ )>2.60 TeV (CMS) & 2.38 TeV (ATLAS) Those assumptions affect the final results, making limits not comparable directly: effects of parton luminosity tail visible T. Berger-Hryn'ova Moriond QCD
VV & Vq (V=W/Z) Resonant Search Jets Cambridge-Aachen R=0.8, W/Z-tag jet, isolated leptons, kinematic cuts No excess over SM backgrounds is seen xBR(X WW)>70 (3) 0.8(2.5) TeV; m(G* ZZ)>710 GeV for k/M Pl =0.5 Different channels to enhance sensitivity T. Berger-Hryn'ova Moriond QCD See also ATLAS-CONF (ZZ lljj) & ATLAS-CONF (WW lll ) k/M Pl =0.1
Search for X HH (bb)(bb) 14T. Berger-Hryn'ova Moriond QCD back-to-back boosted doubly btagged di-jet systems 4 b-jets (MV1, eff 70%) anti-kt 0.4 p T >40 GeV, R(2b) 200 GeV Hadronic ttbar veto Background: multijet (90%); ttbar (<10%); Z+jets No evidence of signal is found CL for k/M Pl = <M(G* RS )<710 GeV <1.6
XX (3j)(3j) Resonant Search 15 T. Berger-Hryn'ova Moriond QCD 2014 No excess over SM backgrounds is seen. Limits on m(gluino) of 650GeV at 95% CL is set for light flavour jets 835GeV at 95% CL for 2 light and 1 b-jets See also ATLAS-CONF , dijet: CMS PAS EXO 059, ATLAS-CONF
We should not give up! Perspectives/Conclusions Resonant searches are very powerful – Many final states have been explored But no new physics seen in 8 TeV data yet… 16T. Berger-Hryn'ova Moriond QCD 2014 LHC Run 2 will provide us with more luminosity to explore lower couplings & LHC energy increase to higher masses.
We should not give up! Perspectives/Conclusions Resonant searches are very powerful – Many final states have been explored But no new physics seen in 8 TeV data yet… 17T. Berger-Hryn'ova Moriond QCD 2014 LHC Run 2 will provide us with more luminosity to explore lower couplings & LHC energy increase to higher masses. Stay tuned to new exciting results in 2015!
Documentation c/PhysicsResultsEXO c/PhysicsResultsEXO ic/ExoticsPublicResults ic/ExoticsPublicResults T. Berger-Hryn'ova Moriond QCD
Backup slides T. Berger-Hryn'ova Moriond QCD
T. Berger-Hryn'ova Moriond QCD
T. Berger-Hryn'ova Moriond QCD
Dijet Search T. Berger-Hryn'ova Moriond QCD CMS PAS EXO 059, ATLAS-CONF
Z’ hadronic search Z’ hadhad (~42% of the BF) No excess over SM backgrounds seen. Excluded M(Z’ SSM 95%CL 23