Hidden Valley Higgs Decays in the ATLAS detector The ATLAS Collaboration

1. The Hidden Valley Hidden Valley: parameters of the model Is the ATLAS detector able to cope with “unexpected” long-lived neutral particles? Model parameter hv production and decay: M(hv)=140 GeV M( pv )=40 GeV ct=1500mm “Hidden Valley” models predict a new dynamic accessible (may be) at LHC energies Hidden Valley and SM communicate through a mediator communicator(Higgs, Z’,LSP) All v-particles are neutral under the SM The lightest v-particles (pv) are stable in the v-sector and decay (weakly) only in the SM pv decay in heavy quarks (heavy leptons) pairs (bb,tt) Hidden Valley models are a general class of models that predict neutral, long-lived particles Hidden Valley Monte Carlo simulation based on Pythia Simulated process: Higgs → pvpv Decay length choosen to provide pvdecays throughout the ATLAS detector pv decay probability M. Strassler and K. Zureck , Phys.Lett.B 661:263(2008) Phys.Lett.B 651:374(2007) pv proper c (mm) “Pythia” event display (no detector simulation) “Atlantis” ATLAS event display pv decaying in the calorimeter • Small energy deposit in Electromagnetic calorimeters • Large deposit in Hadronic calorimeters • No tracks associated in ID pv decaying in the Muon Spectrometer • Large multiplicity • Tracks not pointing to nominal interaction vertex • No tracks in ID • No energy in calorimeters HV Calorimetric trigger HV muon trigger Ratio of energy deposit in calorimeters Log(EHAD/EEM) vs pv decay distance Di-jet sample 70 < ET< 140 Gev 140 < ET< 280 Gev Mean number of Level-1 Muon Candidates vspv decay length Large Level-1 multiplicity <NCandidates> ~ 3 pv decaying in Hadronic Calorimeter Number of LVL-1 Muon Candidates in cluster with D R=0.4 around pv line of flight pv decaying in Inner Detector or in the EM calorimeter appears as “usual” jets Hidden Valley Higgs Decays in the ATLAS detectorThe ATLAS Collaboration L.Bodine, G.Ciapetti, A.Coccaro, D.Depedis, C.Dionisi, S.Giagu, H.Lubatti, F.Parodi, M.Rescigno, G.Salamanna, C.Schiavi, A.Sidoti, M.Strassler, D.Ventura, L.Zanello BUT Displaced high multiplicity neutral vertices  Unique topological signature No SM process can mimick those signatures, HV processes almost background free Displaced high multiplicity neutral vertices  Non-pointing tracks and no charged track in the Inner Detector Low efficiencies for “conventional” trigger selections (jet trigger, muon triggers, tracking algorithms in Inner Detector) and reconstruction algorithms NEED A SIGNATURE DRIVEN TRIGGER STRATEGY ATLAS “Hidden Valleys” TriggersImplemented Level-2 triggers specific for Hidden Valley decays selection Jet Log(EHAD/EEM): • Jet ET>35 GeV in | h |<2.5 • log(EHAD/EEM)>1 • no reconstructed tracks pT>1GeV/c Muon Cluster: • at least 3 Level-1 muon candidates pT>6GeV/c • contained in a cone of D R=0.4 • isolated (D R=0.7) from jets Trackless Jet with muon: • Jet ET>35 GeV in | h |<2.5 • 1 Level-1 muon candidate with pT>6GeV/c • No tracks with pT>1GeV/c contained within the jet cone (D R=0.4) Expected Level1&Level2 background trigger rate from HV triggers: ~3 Hz at L=1033 cm-2s-1 evaluated with minimum bias and dijet samples * * * Overlap removed