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02-06-2003 Simone Gennai SNS, INFN-Pisa
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Radion searches in CMS
A first look to hh
G. Dewhirst, L. Fano, S. Gennai, S. Nikitenko
02-06-2003 Simone Gennai SNS, INFN-Pisa
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Br of radion depends on m, mh, (scale), (-h) mixing
02-06-2003 Simone Gennai SNS, INFN-Pisa
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This final state is common also to other scenarios, like MSSM or little Higgs,
in the ED case the cross sections areenanched for some model parameters.
(M=300 GeV, Mh=125 GeV)
Possible backgrounds:tt, W+jj, Z+jj
p p
b
b
jet
l
hh bb+l+bb+
02-06-2003 Simone Gennai SNS, INFN-Pisa
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Few words about tt bkg tt is the most dangerous Atlas has considered:
ttWWbb l++jj+bb, xBR=180 pb Probably we should consider also:
ttWW+bb l+++bb l++jet+bb, xBR=18 pb
considering the -tagging efficiency and bkg rejection this channel could also contribute.
02-06-2003 Simone Gennai SNS, INFN-Pisa
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Trigger and basic selections
e/+ -jet trigger will be used At least 3 jets + 1 e/ to be reconstructed -jet identification (HLT + off line) At least 1 jet b-tagged (off line) ET missing based selection (to suppress
W+jj) Invariant mass of bb and +lepton Invariant mass ot 2 reconstructed Higgs
02-06-2003 Simone Gennai SNS, INFN-Pisa
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Where to find Real tau:When electron is collinear to 1st L1 Tau:
• 30% Real Tau is the 2nd Tau jet
• 38% Real Tau is the 1st Central jet
• 20% Real Tau is the 2nd Central jet
• 8% Real Tau is the 3rd Central jet
•.....
•Tau Tagging efficiency = 35%
• limiting to first 3 highest energy jets: Eff. = 30%
Tau isolation parameters:
PtLT>10 GeV
RM=0.1
RSIG=0.07
RISO=0.4
1.OR.3 Tracks inside Signal cone.
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B tagging Efficiency Tagging efficiency : # of events with tagged jet / #
matched events Total Efficiency : Eff. Match X Eff. Tagging
Btagging = Tk>2, ip >2
As efficiency for 1st and 2nd Jet are different, we can relax selection but requiring 2 tagged jets instead of at least 1.
B-jet
Eff. 1st Jet.66+-.01
Eff. 2nd Jet.52+-.01
Eff. 1 || 2 Jet.73+-.01
Tot Eff. 1st Jet.55+-.01
Tot Eff. 2nd Jet.22+-.01
Tot Eff. 1 || 2 Jet
.66+-.01
02-06-2003 Simone Gennai SNS, INFN-Pisa
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Signal invariant mass distributions
No big discrepancy between full and
fast simulation for the signal!
FAST
FULL
Vs
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Signal PT distributions
FAST
FULL
Vs
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Preliminary results
Ev. tt = 107
Ev. W+jj = 0
Ev. Z+jj = 33
Ev. Bkg = 140
Ev Sig = 43
S/sqrt(B+S) = 3.2
Efficiency parametrization
has been performed in order
to have the same number of signal events in
both Full and Fast simulation
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3-5 Sigma regionsReally PRELIMINARY
Theoretically excludedTheoretically excluded
3 sigma
5 sigma
CMS, 30 fb-
1
hhbbhh bb
GeV
hGeV
(GeV
)
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same point: m = 300 GeV, mh = 125 GeV
Generation Simulation Reconstruction events
signal Pythia ORCA 6 ORCA 6 4500
4b QCDPT>0(*)
Gr@ppa ORCA 6 ORCA 6 3500
4b QCDPT>100(*)
Gr@ppa ORCA 6 ORCA 6 1000
(*) at least one parton in the final state
-> hh -> bbbb – First View
02-06-2003 Simone Gennai SNS, INFN-Pisa
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Selection Efficiency - Energetic Threshold
Eff
Eff Eff
Jet ETJet ET
Jet ET
1 Jet2 Jet3 Jet4 Jet
Signal
4b QCD – no cut 4b QCD – PT > 100 GeV
4 Jet ET > 50 GeV :
10% signal1% QCD (PT>100 GeV)
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Selection Efficiency Energetic threshold + btag
Eff
Eff Eff
Jet ET
Jet ET Jet ET
1 leading Jet2 leading tagged Jet 3 leading and next-to-leading tagged Jets
Signal
4b QCD – no cut4b QCD – PT > 100 GeV
b-tag: 2 tracks with Sip2D>1.5
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Signal Kinematics
<jet> = 4.6 <b jet> = 2.5
Eta and PT distribution - 4 leading Jets
Eta PT
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Signal Reconstruction
Mbb 124 39 GeV
Mbbbb 304 64 GeV
Best jets combination is chosen minimizing the difference between all possible reconstructed mass M(i,j) – M(k,l)
Jets are preselected in the barrelrequiring ET>35 GeV
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Cuts and Selection Criteria
1 Jet ET > 177 GeV OR3 Jets ET > 86 GeV OR4 Jets ET > 70 GeV
Invariant reconstructed mass:124 - 1.5 < Mbb < 124 + 1.5 304 - 1.5 < Mbbbb < 304 + 1.5
AND
Signal: 58 pb BR(->hh) 0.33BR(h->bb) 0.9Eff 5%
4b QCD (PT>100 GeV):(qq,gg->bbbb) 930 pb Eff 3%
22.5*103 events 837*103 events
30 fb-1
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What is missing?
- Considering all QCD background sources- Considering resonant backgroud- Check other trigger strategy (using b-tag)
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