Search for Charged Higgs at the LHC Ashfaq Ahmad (Stony Brook)

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Search for Charged Higgs at the LHCAshfaq Ahmad
(Stony Brook)
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Contents

• Introduction
• Charged Higgs studies in ATLAS and CMS
• Search for the light charged Higgs bosons with H
  -gt ?? in top quark decays
• Search for heavy charged Higgs bosons with
• H -gt ?? decay channel
• H -gt tb decay channel
• Discovery reach

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LHC experiments
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ATLAS and CMS Detectors
ATLAS as of July 2007
CMS as of Jan 2007
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Charged Higgs Boson

• MSSM, the minimal supersymmetric extension to SM
  requires two Higgs doublets
• Give masses to the up and down type quarks and
  leptons
• Corresponds to 8 degrees of freedom
• 3 of which are absorbed as Goldstone bosons to
  give mass and longitudinal components to the W
  and Z
• Leaves five physical states (Higgs particles)
• Two neutral scalars, h0, H0, a pseudo scalar A0
  and a pair of scalar charged Higgs H
• At tree level all masses and couplings can be
  expressed as a function of two parameters
• The pseudo scalar Higgs boson mass mA
• and tan ? the ratio of the vacuum expectation
  values of the two Higgs doublets

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Charged Higgs at the LHC

• Production modes for heavy charged Higgs
• Below top mass
• t?Hb
• LHC is a top factory, NLO ttbar cross section
  833pb ? over 8M ttbar pair in one year (10fb-1)
• Above top mass
• Via gluon fusion, gg?tbH
• And gb?tH
• Decay modes
• H???, H?tb, H?cs

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Search for Charged Higgs below Mtop (1)

• In MSSM charged Higgs may be produced in top
  decay if kinematically allowed via ttbar?WbH-b
• If MH lt (Mtop Mb) the decay t?Wb together
  with t?Hb saturates the top decay width in the
  MSSM
• BR is large at SMALL and LARGE tanß (for a given
  MH) but it has a pronounced minimum at tanß
  vmtop/mb 7.5
• BR(t?Hb)mtop2 cotan2ßmb2 tan2ß

LEP excludes 0.5 lt tan ? lt 2.4
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Search for Charged Higgs below Mtop (2)

• Assuming a heavy SUSY spectrum a charged Higgs
  will decay exclusively into SM particles and
  below Mtop the braching ratio H??? is100
• Main channels of interest

H Decay W Decay
??,??had qq
??,??had l?
??, ??lep qq
H decay BR. into different final states for tan
? 20
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ttbar ? H-bWbbar, H-? ?had?, W?qq (1)

• Exploited the difference between signal and ttbar
• mH gt mW so diff in pT and ET miss
• Spin (helicity effect) scalar H, vector W
• Event Selection
• TauMET ot JetMET trigger
• Tau jet pT gt 25 GeV
• 2 b jets, pTj1 gt35GeV, pTj2 gt20GeV
• isolated lepton veto
• ET miss gt 45 GeV
• W/top reco. in 20/40 GeV mass window
• ttbar event pattern cuts on ??? between two reco
  tops and the ratio between their pT(lt 2)
• pT?? /pTb gt 0.8
• transverse mass (MT) tau pT gt 30 GeV
• Main background
• ttbar, QCD

ATL-PHYS-2003-038
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ttbar ? H-bWbbar, H-? ?had?, W?qq (2)
Expected events _at_ 10fb-1, tan?? 30
Sig/bkg Standard cuts MT(H) gt80GeV pT (tau) gt3 0GeV
mH 85GeV 5100 -
mH 127GeV 4200 2000
mH 140GeV 2900 1700
mH 160GeV 410 240
ttbar 2300 350
QCD 20 0

• significant ttbar background with standard cuts
• Masses above 113 GeV are passed through a final
  event selection on the
• charged Higgs transverse mass, and tightening
  of the tau pT cut

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ttbar ? H-bWbbar, H-? ?had?, W?qq (3)

• The dip between tanß 5 and tanß 10 is covered
  by hadronic channel
• A high significance is obtainable for all tan?
  and mH lt 150

Results given here are from ATLAS fast
simulation. Full simulation studies are in
progress
Leptonic channel (W?l?) was studied long time
ago(ATL-PHYS-94-053). This channel features a
high Pt lepton for triggering, but the presence
of two neutrinoes exludes any mass extraction
possibilities. 5? line _at_30fb-1 is also shown.
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ttbar ? HbW-bbar, H? ?had?, W?l? (1)

• Enhanced tau-lepton rate in ttbar decays
• mass of H cannot be directly reconstructed
  because several neutrinos are produced in the
  final state
• Excellent ?-ID is a must!
• Measurement of significance of the event excess
  with an isolated ? with respect to rate foreseen
  by SM

BACKGROUNDS
SIGNAL
Due to fake taus
intrinsic
Wjets
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ttbar ? HbW-bbar, H? ?had?, W?l? (2)
CMS Note 2006/056

• Exploited difference between signal and ttbar
• mH gt mW, diff in pT and ET miss
• Spin scalar H, vector W
• Event Selection
• Triggered lepton
• 3 jets with ET gt 40GeV
• At least one b-tagged jet
• Q(l)Q(?)0
• Tau jet ET gt 40GeV
• Plead track/ E? gt 0.8, to exploit opposite
  helicity correlations in the taus coming from H
  and W
• ET miss gt 70GeV

Sig/bkg ?xBR(fb) Events _at_ 10fb-1
mH 140GeV 10700 510
mH 150GeV 5060 254
mH 160GeV 1830 92
tt ?l???bb 2.6x104 516
tt ?l?l?bb 4.0x104 293
tt ?l?qqbb 2.5x105 366
W3jets, W ?l? 8.4x105 107
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Discovery potential (3)

• 5? contour in mH , tan? plane for the light
  Charged Higgs with and without systematic
  uncertainties
• tan? gt 50, covered up to top mass
• Due to systematic uncertainties there is a
  decrease of 5-10GeV in the observable charged
  Higgs mass for tan? lt 50
• Charged Higgs mass of 170GeV observable at tan?
  100

CMS Note 2006/056
I am working on this channel for
ATLAS. Preliminary results expected in few weeks.
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Search for Charged Higgs above Mtop

• Above top mass
• Via gluon fusion, gg?tbH
• And gb?tH
• BR(H?tb)0.8-1
• H?tb results in complex final states
• Having 3 or 4 b jets
• Crucial to supress very large kinematically
  similar ttbarjets background

Channels of interest
?xBR (pb)
H Decay W Decay
??,??had qq
tb l? qq
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gb/gg ? t(b)H ? Wb(b) tb ? l?b (b) jjbb(1)
CMS Note 2006/109 SN-ATLAS-2004-042

• Event Selection
• Isolated muon, pT gt 20GeV
• At least 3(4) b jets
• At least 5(6) jets with pT gt 25GeV
• Kinematic fit imposing mass constraints on both
  W,s and top quarks
• LH to suppress combinatorial background
• 3(4)b-tags, with LH based secondary vertex
  algorithm
• Background
• ttbarb, ttbarjets
• High combinatorics

CMS S/B ratio after selection 1 for mH 300
GeV
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Discovery potenial (2)
CMS 4 b-tags
CMS 3 b-tags
30 fb-1
30 fb-1

• No sensitivity in MSSM space even with very low
  systematic
• uncertainties
• Similar conclusions from ATLAS FAST simulation
  studies

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gb/gg ? t(b)H ? qqb(b) ?had? (1)

• Event Selection
• One ?-jet, PT gt 100 GeV
• At least three non ?-jets(at least one b-tag)
• No more than one hard b-jet (? lt 2.0, PT gt 50
  GeV)
• Reconstruct W/top in 25 GeV mass window
• ET miss gt 100 GeV
• cut on the azimuthal opening angle (?f) between
  the ?-jet and missing Pt. Require ?f gt 1.1
• Veto on isolated leptons
• Plead track/ E? gt 0.8
• Main background
• ttbar, QCD, Wjets

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Discovery potenial (2)
ATLAS
CMS
with systematics
without systematics

• without systematics
• Background FAST simul.

• systematics included
• Background Full simul.

• promising channel for heavy charged Higgs

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CMS and ATLAS Discovery Potential
Full simulation
ATLAS
CMS
30 fb-1
300 fb-1

• Fast simulation
• ATLAS full simulation studies in progress.
  Results by
• the end of 2007
• Charged Higgs covered at LHC for mH lt mtop
• Heavy Charged Higgs sensitive at high tan?

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Conclusions

• Both ATLAS and CMS are sensitive to light charged
  Higgs below top mass
• Discovery potential _at_ 30fb-1
• Heavier charged Higgs would have to wait for the
  high luminosity mode
• Accessible at high tan?
• The intermediate tan? region in MSSM space is not
  covered by any SM decay
• H??? is the best H discovery channel at the LHC

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