Charged Higgs search with top : example of single-top events in ATLAS

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Charged Higgs search with top example of
single-top events in ATLAS
Ketevi Assamagan (BNL) Arnaud Lucotte (LPSC
Grenoble)
Outline Motivation Single-top production
_at_ LHC Single-top cross-section measurements Events
selection Results and performance Charged Higgs
contribution measurements Cross-sections in
(mH,tan ?) Efficiency and event yields in
(mH,tan ?) Conclusion
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Single top Production _at_ LHC

• Production at the LHC
• 3 contributing mechanisms in SM

-

• sNLO(qb(g)?tb(g)) 1506 pb
• sNLO(qb(g)?tb(g)) 88.54 pb
• dominant at the LHC
• used for Vtb, ?t, FCNC

-
t-channel

• sLO(gb?tW) 6015 pb
• high level of bcgkd tt
• sensitive to extra W, H

-
Wt channel
-
sNLO(qq?tb) 6.10.3 pb sNLO(qq?tb) 3.80.2
pb - high level of bckgd tt, Wjets
-
s-channel
-
?stheo/s 4-8
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Single top Production _at_ LHC

• Production at the LHC
• 3 contributing mechanisms in SM Higgs in 2HDM

-

• sNLO(qb(g)?tb(g)) 1506 pb
• sNLO(qb(g)?tb(g)) 88.54 pb
• dominant at the LHC
• used for Vtb, ?t, FCNC

-
t-channel

• sLO(gb?tH) in (mH,tan?)
• Up to a few pb
• High level of tt t backgds

Wt channel
H
-
sLO(H?tb) in (mH,tan?) - Up to a few pb - High
level of t tt Wjets
H
s-channel
-
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W single top event selection

• Analysis Strategy
• Select and tag event
• 1 high-pT lepton (25 GeV/c)
• High missing ET (25 GeV/c)
• at least 2 high-pT central jets
• with at least 1 b-tagged jet
• Discriminate from non-W background
• Reconstruct the (leptonic) mWT
• Discriminate from top-pair background
• Veto of a 3rd high-pT jet
• Keep low total energy events (HT or MTOT)
• Discriminate from Wjets background
• Require a 2nd high-pT b-tagged jet
• Reconstruct a Top mass Mlvb
• Use event shape high

e,µ
b
b
v
q
s x BR (pb)
W ? (lv)b b 2.2
Wjets? lvjets 3,850
WQQ? lvQQ 66.7
WZ ?lvjets 3.4
WW ? lv jets 17.1
tt ? (lv)b (lv)b 38.2
tt ? (lv)b (jj)b 242.8
ljets final state
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W single top selection jet multiplicity

• Jet selection
• Jet mulitplicity
• At least two high-pT central jets
• ? useful against Wjets
• Veto of 3rd high-pT jet (difficult...but
  crucial)
• ? needed against top pair events

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W single top selection b-tagged jets

• Jet selection
• Jet mulitplicity
• At least two high-pT central jets
• ? useful against Wjets
• Veto of 3rd high-pT jet (difficult...but
  crucial)
• ? needed against top pair events

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W single top selection leptonic top mass

• Top mass reconstruction
• 1) Determination of longitudinal pZ(?)
• Interpret of mET as pT(?)
• Compute pz(?) using W-mass constraint
• ? 2-fold ambiguities for pz(?) choose best
  M(lvb)
• ? If no solution (MWT gt MW) take real part

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W single top selection total energy

• Total transverse energy HT
• HT Definition
• HT ?pT(jet) pT(lepton) mET
• Note can also use Mtot, Ptot
• Discriminating power
• Optimization of the window on HT

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W single top selection total energy

• Total transverse energy HT
• HT Definition
• HT ?pT(jet) pT(lepton) mET
• Note can also use Mtot, Ptot
• Discriminating power
• Optimization of the window on HT

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W single top selection event yields

• Performance
• Efficiency and rejection
• Efficiency e 1.7 and N(30fb-1) 600
  events
• Main backgrounds in 30 fb-1
• top pair 2,500 evts l?bjjb(60) llbb(30)
  ??b??b(10)
• WQQ, Wjets 1,400 evts
• Wg channel 1,100 evts

S/B 0.14 v(SB)/S 12
_
_
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W single top selection statistical precision

• Performance
• Efficiency and rejection
• Efficiency e 1.7 and N(30fb-1) 600
  events
• Main backgrounds in 30 fb-1
• top pair 2,500 evts l?bjjb(60) llbb(30)
  ??b??b(10)
• WQQ, Wjets 1,400 evts
• Wg channel 1,100 evts

S/B 0.14 v(SB)/S 12
_
_
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W single top selection main systematics

• Systematic uncertainties
• Main experimental biases
• Knowledge of b-tagging efficiency (rejection
  rate)
• ? important since double-tag evts
• ? consider 3 uncertainty in ?b
• Gluon Radiation Modeling
• ? ISRs affect the jet multiplicity
• ? FSRs affect the jet energy multiplicity

?s/s 6.6
?s/s 8.7
?s/s 5
?s/s 8
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W single top with 30 fb-1 where we talk about
H

• Charged Higgs single-top
• Production mode in 2 HDM
• 5 higgs 3 neutral (A,h,H) 2 charged (H)
• Mass spectrum predicted in MSSM
• ? (Htb) couplings depends on mH and tanß

Cross-section in pb
mH (GeV/c2)
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Charged Higgs sensitivity cross-section and
efficiency

• Performance in (mH,tan?) plane
• Strategy
• Use the very same analysis developed for the
  s-channel
• No specific analysis performed for a H
  search
• no use of spin-0 property of H
• no use of other H decays (tau..)
• ? Limited by the precision on s(single-top),
  s(top pair)..

Efficiency in
Cross-section in pb
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Charged Higgs sensitivity event yields(1)

• Performance in (mH,tan?) plane
• Selection efficiency
• Cross-section increases with tan?
• Cross-section decreases with mH
• Efficiency increases with mH
• Event yields mH220 GeV/c2 ,tan?50
• efficiency ? 0.3
• Event yield 14010 evts (after Mlvb and HT
  window cuts)

mH 220, tanß50 S/?B 1.3
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Charged Higgs sensitivity event yields(2)

• Performance in (mH,tan?) plane
• Selection efficiency
• Cross-section increases with tan?
• Cross-section decreases with mH
• Efficiency increases with mH
• Event yields mH250 GeV/c2 ,tan?50
• efficiency ? 1.9
• Event yield 28515 evts (after Mlvb and HT
  window cuts)

mH 250, tanß50 S/?B 5.7
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Charged Higgs sensitivity event yields(3)

• Performance in (mH,tan?) plane
• Selection efficiency
• Cross-section increases with tan?
• Cross-section decreases with mH
• Efficiency increases with mH
• Event yields mH300 GeV/c2 ,tan?50
• efficiency ? 2.02
• Event yield 19010 evts (after Mlvb and HT
  window cuts)

mH 300, tanß50 S/?B 3.9
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Charged Higgs sensitivity significance

• Performance in (mH,tan?) plane
• Significance
• A 5s-discovery can be reached in a (mH,tan?)
  region
• provided s(single-top), s(top pair) are well
  determined
• provided we can control experimental
  systematics
• Perspectives

Significance in Ns
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Charged Higgs sensitivity significance

• Performance in (mH,tan?) plane
• Significance
• A 5s-discovery can be reached in a (mH,tan?)
  region
• provided s(single-top), s(top pair) are well
  determined
• provided we can control experimental
  systematics
• Perspectives

ATL-PHYS-2001-017
tanß30, mH300 GeV
Significance in Ns
direct gb? H? tb search
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Conclusion perspectives

• Single-top cross-section measurements
• Event Selection
• S/B 12-15 and about 1,000 evts / 10 fb-1
• Significant level of background contamination
• ? top pair, Wjets events, QCDother single-top
• Performance
• Statistical precision of 7-12 for W channel
• Measurements dominated by systematics 10
• ? experimental b-tag, JES, ISR/FSR
• ? theoretical use of MC for backgrounds
• Charged Higgs with top events
• Indirect/direct measurements
• Low Higgs mass top-pair production
• disappearance of semi-leptonic e/ ? events
• appearance of extra tau contributions
• Low and High Higgs mass single top production
• deviation in s(Wt) measurement
• deviation from s(W) in (e,?) final state

All these measuremetns are Complementary to
other direct searches