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Searches for Hidden Sectors Using Lepton Signatures at CMS

Searches for Hidden Sectors Using Lepton Signatures at CMS. Alexei Safonov Texas A&M University for the CMS Collaboration. LHC Workshop, UChicago , November 2012. Why Searching for Hidden Sectors?. Dark matter is one big reason

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Searches for Hidden Sectors Using Lepton Signatures at CMS

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  1. Searches for Hidden Sectors Using Lepton Signatures at CMS Alexei Safonov Texas A&M University for the CMS Collaboration LHC Workshop, UChicago, November 2012

  2. Why Searching for Hidden Sectors? • Dark matter is one big reason • If satellite experiments excesses have something to do with the dark matter, these could signify presence of dark sectors • Higgs “problems”: • While SUSY can be the answer to the hierarchy problem, MSSM isn’t that great of a candidate • Fine tuning, the m-problem etc. • …and in all likelihood it’s wrong anyway  • NMSSM can help some of these problems • Yields a more complex higgs sector with new fields weakly coupling to SM particles • Finally, they just might be there… A. Safonov, LHC Workshop, UChicago, November 2012

  3. TeV Scale Dark Matter • Unknown pulsar? Cosmic rays interacting with giant molecular clouds? • Or heavy dark matter annihilation in the galactic halo with a large x-section: • Light dark photon: an attractive long-distance force between slow WIMPs • Sommerfeld enhancement • can weakly couple to SM via kinetic mixing with photon • As no antiproton excess observed, M(≲ O(1 GeV) • PAMELA and Fermi observe rising positron fraction towards higher energy: +, e+ X  -, e-  +, e+  X -, e- arXiv:1109.0521v1 A. Safonov, LHC Workshop, UChicago, November 2012

  4. NMMSM Phenomenology • Modified superpotential: • MSSM: • NMSSM: • NMSSM less fine tuning and solves m-problem: • m is generated by singlet field VEV and naturally has EW scale • More complex Higgs sector: • 3 CP-even higgses h1,2,3, 2 CP-odd higgses a1,2 • a1 is hidden as it is mostly singlet and weakly couples to SM particles except through h1 • Experimentally relevant decays: • (Branchings depend on mixing) • (standard higgs hierarchy) • Couplings are weak but it has to decay somewhere A. Safonov, LHC Workshop, UChicago, November 2012

  5. A “Long Living” Example • A separate hidden strongly interacting sector coupling to SM only through a heavy Z’ • Visible higgs(es) can naturally mix with the hidden higgs • One can have models with higgs-like decays too • Striking signatures, relatively easy to look at • If Z’ is heavy, “hidden pions” can easily have decay lengths O(0-100 cm) • Z-like decay hierarchy for new hidden bosons Strassler, Zurek, PLB 661 (2008) A. Safonov, LHC Workshop, UChicago, November 2012

  6. Hidden Sectors Search Strategies • Aim to produce something that links visible and hidden sectors and look for evidence of new hidden states: • In the dark SUSY the “stable” visible LSP has no choice but to decay to hidden states even if small couplings • If we can make the LSP either through squark/gluino production or Higgs, we can see its decay products • In the NMSSM new higgs states can have very weak coupling to SM, but appreciable coupling to the SM-like higgs due to mixing – look for exotic higgs decays • Similar story for the “long living” example model • Brute force: make hidden sector particles • Because of typically small couplings, need high luminosity and clean final states A. Safonov, LHC Workshop, UChicago, November 2012

  7. Dark Photons in SUSY Cascades • SUSY with squarks/gluinos accessible by LHC: • Dark photons decay as SM g Branching fraction of arxiv:1002.2952 • MSSM LSP is a neutralino decaying to dark neutralino and light gdark/hdark • MSSM LSP is a squark decaying to q and light dark fermion and gdark/hdark A. Safonov, LHC Workshop, UChicago, November 2012

  8. Selections • Data: • 35 pb-1 of 2010 LHC data • Inclusive muon trigger pT>15 GeV • Offline: • Require at least 1 muon with pT>15 GeV, |h|<0.9 • Identify all other muons with pT>5 GeV, |h|<2.4 • Reconstruct muon jets and categorize • No isolations, cluster using pairwise mass of muons • Assume new bosons produced on-shell: A. Safonov, LHC Workshop, UChicago, November 2012

  9. Topologies: Data and Backgrounds • No events with consistent masses of dimuons in higher order categories A. Safonov, LHC Workshop, UChicago, November 2012

  10. Model-Independent Interpretation • Use three simplest topologies to set “conservative” model independent limits: • Dimuon+X • Two-dimuon+X • Quadmuon+X • Limits of applicability: • Mean pT(m-jet)≤250GeV • Easy to apply to other models: • Follow analysis steps to calculate branching and acceptance for a specific final state assuming an ideal detector • Compare with the limit plot • Complex topologies can be reduced to one of these three A. Safonov, LHC Workshop, UChicago, November 2012

  11. Models with TeV Scale Dark Matter Model from JHEP 04 (2009) 014. • MSSM LSP is a squark decaying to a quark, light dark fermion and either gdark (left) or hdark (right) More details in CMS-EXO-11-013 and JHEP07 (2011) 098 A. Safonov, LHC Workshop, UChicago, November 2012

  12. Search for Displaced Lepton Pairs • Generic search for H0XX, using leptonic decays Xll, with X having substantial lifetime • 2011 data: L=4 fb-1 for l=e, L=5 fb-1 for l=m • Selections: • Displaced e/m candidate defined as a trackwithin |h|<2 with pT>41/33 GeV and d0/sd>3/2 • Require at least one X-candidate per event: • A common vertex with c2/ndf>4, displaced more than 8(5)svtx-fitfrom the beamline for e(m)channel • M(ee/mm)>15 GeV, DR(mm)>0.2, pT(e) from ECAL • Isolation: SpT <4 GeV counting tracks w/ pT>1 GeV in DR(trk,e/m)<0.4 around each lepton (but not counting the other lepton in the X-candidate) A. Safonov, LHC Workshop, UChicago, November 2012

  13. Search for Displaced Lepton Pairs • Avoid standard lepton ID: • Inefficient for displaced tracks • Efficiency driven by tracking reconstruction efficiency • Cross-checked with cosmic muon data • Backgrounds dominated by Drell-Yan events • Shape from simulation cross checked with data • Normalization from the fit of the vertex Lxy/s distribution • B= and for e/m channel A. Safonov, LHC Workshop, UChicago, November 2012

  14. Search for Displaced Lepton Pairs • Signal region (significant Lxy): no excess • N0 events with Xmm candidates • 4 events Xee candidates ) • Limits as a function of the new boson mass A. Safonov, LHC Workshop, UChicago, November 2012

  15. Search for Displaced Lepton Pairs • Limits vs lifetime for M(H)=200 GeV and 1 TeV • Reflect track reconstruction efficiency dependence on decay path length • More details in CMS-EXO-11-101 (public note) A. Safonov, LHC Workshop, UChicago, November 2012

  16. Light Dark Sectors and Higgs • NMSSM: • Dark SUSY with light dark photons: • Similar signature, but softer dimuons and missing energy • Either h1 or h2 (or both) can decay to a1a1, BR depends on the singlet component • Production cross-section for h and BR highly model dependent A. Safonov, LHC Workshop, UChicago, November 2012

  17. Light Dark Sector Higgs Limits Following Phys. Rev. D 81 (2010) 075021. • Spin-off of the 35 pb-1muon jet analysis • ~5fb-1 of 2011 data • Focus on the topology with two muon pairs of consistent mass • Di-muon trigger with pT>17 and pT>8 GeV • Same selections, but apply loose track-based isolation • High signal efficiency, strong suppression of bb backgrounds • Insensitive to pile-up • No pairs with consistent mass found • Expect ~ 1 event A. Safonov, LHC Workshop, UChicago, November 2012

  18. Exotic Higgs Limits • Express in terms of limits on production • NMSSM: pp h1 or h2a1a1 4m • Dark SUSY: pp h c1c1 gdgdc1c1  4m + MET • Plots use SM higgs production cross-section • Most of time not true, but convenient benchmarking A. Safonov, LHC Workshop, UChicago, November 2012

  19. NMSSM Parameter Space • To gauge what it does to the NMSSM parameter space, scan NMSSM parameter space • Focus on ma<2mt • Use actual NMSSM cross-sections • Not SM • See EXO-12-012 for details • Make deep inroads into the allowed space A. Safonov, LHC Workshop, UChicago, November 2012

  20. Search for Direct NMSSM a1 Production • Production via gluon fusion • Large cross-section if mixing with MSSM A is large • Suppressed as a1has to be highly singlet to abide experimental constraints (cos2qA<1) • Usual enhancement with tanb • Search for resonances in dimuon spectrum • 5.5<m<8.8 and 11.5<m<14 GeV • Avoid region dominated by large Upsilon backgrounds • Early 2011 data (1.3 fb-1) • Had a dedicated very low pT di-muon trigger (prescale = 2) cos2qA =1 A. Safonov, LHC Workshop, UChicago, November 2012

  21. Search for Direct NMSSM a1 Production • Analysis selections: • Muon pT>5.5 GeV and |h|<2.4 • Isolation (per muon): • In the two signal regions, fit for the sum of Crystal Ball (signal) and a 1st order polynomial (background) • Plus the radiative tail of Upsilon for the low mass region A. Safonov, LHC Workshop, UChicago, November 2012

  22. Search for Direct NMSSM a1 Production • No significant excesses in data • Limits vs m(a) on the production rate • Further interpretation in terms of cosqA and tanb • LHC limits start superseding those from BaBar A. Safonov, LHC Workshop, UChicago, November 2012

  23. Summary • Several CMS analyses aiming at searches for hidden sectors • Different scenarios for production mechanisms and the lifetime of the new hidden bosons • Electron channels starting gaining ground • When possible, results presented in a quasi model independent fashion to allow future interpretations • No discoveries, but the new ground in sensitivity • Important complementarity to the SM Higgs searches as the searches for exotic higgs decays can rule out many non-SM scenarios • The data keeps coming in, so stay tuned A. Safonov, LHC Workshop, UChicago, November 2012

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