02-06-2003simone gennai sns, infn-pisa1 radion searches in cms a first look to hh g. dewhirst, l....

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


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Br of radion depends on m, mh, (scale), (-h) mixing


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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+


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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.


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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


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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


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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-

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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


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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)

02-06-2003simone gennai sns, infn-pisa1 radion searches in cms a first look to hh g. dewhirst, l....

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