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Inclusive SUSY searches with ATLAS and CMS detectors at LHC

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Inclusive SUSY searches with ATLAS and CMS detectors at LHC. Renaud Bruneli re ... SUSY is one of the major BSM topics at LHC. it is an interesting extension of SM : ... – PowerPoint PPT presentation

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Title: Inclusive SUSY searches with ATLAS and CMS detectors at LHC


1
Inclusive SUSY searches with ATLAS and CMS
detectors at LHC
Renaud Brunelière Physikalisches Institut
Universität Freiburg On behalf of ATLAS and CMS
Collaborations
2
SUSY searches at LHC
  • SUSY is one of the major BSM topics at LHC
  • it is an interesting extension of SM
  • could be dark matter candidate
  • solves Higgs mass hierarchy problem
  • it can provide clear experimental signatures
  • TeV-scale new physics gt direct search
  • look for excess in tails high missing Et
    high Pt jets,
  • In this talk, restrict to direct searches
  • of models conserving R-parity
  • LSP is stable gt escape detection gt large
    missing Et
  • SUSY particles produced by pairs gt cascade
    decays
  • GMSB models covered by Mark Terwort
  • focus on early SUSY searches
  • integrated luminosity of 1 fb-1 (1 month at
    nominal LHC lumi)

3
SUSY production at LHC
  • Production at LHC dominated by squarks and
    gluinos
  • Cross-sections mainly depend on SUSY masses (But
    masses are model dependent)

Cross section pb
SUSY ?
prospino
Huge background to be suppressed
SUSY Particle mass GeV/c2
4
SUSY signatures for early searches
  • squark and gluino production ? cascade decay ?
    high Pt jets
  • LSP stable ? large missing Et
  • Possibly some leptons

Generic signature Large MET multi-jets
multi-leptons
  • Build mutually exclusive channels depending on
    number/type of objects
  • Rather general hypothesis gt signatures are quite
    model independent (mSUGRA, AMSB, NUHM,)
  • Try to rely on data-driven determination of
    backgrounds
  • Poor understanding of detector (missing Et tails,
    JES, ) with early data
  • Rather large theoretical uncertainties on
    backgrounds in this part of phase space

5
Jets MET 0-lepton signature
1
2
  • ATLAS selection cuts
  • 4 jets, Pt(Jet1) gt 100 GeV, Pt(Jet4) gt 50 GeV,
    MET gt 100 GeV
  • MET gt 0.2Meff
  • Transverse sphericity gt 0.2,
    ??(MET, jet1,2,3) gt 0.2,
    no isolated e or ? (Pt gt 20 GeV),
    J70_X70 combined trigger
  • Similar CMS cuts
  • MET gt 200 GeV,
  • 3 jets(ET gt 30 GeV, ?lt3),
  • ?(Jet1) lt 1.7

3
Meff MET ? PT(jet)
6
QCD background rejection/estimation
  • QCD jets mimic SUSY events in 0-lepton channel
    through
  • fake MET due to jet mis-measurement gt
    reducible with cuts gt ?? cut
  • real MET due to decays into neutrinos (heavy
    flavor, B hadrons,)

CMS QCD
CMS SUSY
  • To estimate remaining QCD background after
    cleaning, the following method can be used
  • Measure smearing function (non gaussian tails) in
    events with large MET associated to a single jet
  • Select seed events with low MET-significance and
    smear each jet
  • Normalize estimate to data

7
Z/W jets background determination
  • Z??? jets is an irreducible background in
    0-lepton channel
  • But can be estimated with Z?ll- jets
  • This method bring good estimate (15 ALTAS, 5
    CMS)
  • Main limiting factor is control sample
    statistics (Br(Z?ll-)/Br(Z???) 0.17)
  • A good tail description requires MC OR
    extrapolation methods
  • W jets background is due to W????hadrons (42)
    or W?e/?? with lepton out of acceptance (41) or
    W?e/?? with non-selected lepton (17)
  • it can be estimated from Z?ll- jets or W?l?
    jets control samples

8
Jets MET 0-lepton discovery reach
CMS Reach vs integrated luminosity
ATLAS Reach vs nJet criteria
Relative contributions of the different
backgrounds after selection
9
Jets MET 1-lepton
  • Requiring at least 1 isolated lepton provide
    clean signature as it reduce QCD background
  • Main background then is top pairs

MET
  • Top background can be estimated with many
    methods
  • like using an additional discriminating variable
    MT used to select control sample region.
  • Normalization obtained with B/A

Signal region
Control sample
A
B
MT
10
Search comparisons
Discovery reach vs channel
Discovery reach vs SUSY model
0-lepton channel
  • 0-lepton channel is most efficient channel but
    1-lepton channel is less sensitive to QCD
    background
  • in the lower part of the plane, there is a good
    redundancy between search channels gt useful
    discovery cross-check
  • discovery reach is rather independent of model
    considered scanning grid

11
Conclusion
  • Recent studies using full simulation (CMS PTDR,
    ATLAS CSC) show
  • ATLAS and CMS should discover R-parity
    conserving SUSY with gluino and squark masses lt
    O(1 TeV) after having accumulated and understood
    1 fb-1.
  • Many backgrounds can be estimated with
    data-driven techniques but these analysis are
    delicate
  • Next test with real data !

Many thanks to the DIS08 organizers
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