discovery of a standard model higgs boson using vector boson fusion at the lhc craig buttar...
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Discovery of a standard model Higgs boson using vector boson fusion at the LHC
Craig ButtarUniversity of Sheffield
Collaborators: G.Azuelos, V.Cavasinni, D.Costanzo, R.Harper, K.Jakobs, M.Klute, R.Mazini, E.Richter-Was, I.Vivarelli
Higgs production
Leading order
105
104
103
10
Events for10 fb-1
B
S
Standard channelsMH<2MZ: ttHlbb+X, H
H ZZ* 4l, H WW(*) llMH>2MZ:H ZZ 4l
qqH ZZ ll, lljjqqHWW ljj
VBF Signal (HWWll)
Cross section ~20% of gg-production BUT clear signature
•forward tagging jets
•correlated leptons
• low hadronic activity in central region
•central Higgs production
Based on parton level study by Zeppenfeld and Rainwater hep-ph/9906218Conclusion: >5 observation with 5fb-1 at LHC in the mass range 130-200 GeV
Tagging jet
Tagging jet
H
W
WZ/WZ/W
Backgrounds
• tt+jets•tWb•jets produced centrally•Use tagging, b-veto, central-jet veto
•QCD WW+jets, +jets•Does not have lepton correlation•Reduced using central-jet veto•Low tag-jet invariant mass-veto
•EW WWjj+jj•Signal-like difficult to reduce
Analysis
• Signal, tt+jets and QCD backgrounds generated using PYTHIA 6.1 (with ISR, FSR, MI), CTEQ5L structure functions
• EW backgrounds generated using Zeppenfeld and Rainwater parton level and interfaced to PYTHIA for PS (with ISR and FSR) and hadronization
• tt-background, Z+jet and Z generated using ME and PYTHIA interface for comparison with PYTHIA tt-generation
• TAUOLA is used for tau-decays
• Detector simulation with ATLFAST
Jet tagging and reconstruction
Tag jets defined as jets with highest pT in each hemisphere
Comparison of jet construction with ATLFAST and full-simulation
Fake jet ratein the centralregion has beenstudied.20 GeV thresholdat low luminosityMust be raised at higher luminosity.
Analysis of e channel
• Two isolated leptons•pT
1 >20GeV, pT2 >15GeV || 2.5
•leptons observed in the rapidity gap spanned by the tag jets
• Two tag jets• pT
j1 40GeV; pTj2 20GeV
tags 3.8•Reject tag jets identifiedas b-jets || 2.5
•Lepton cuts• ll 1.05
•cosll 0.2Rll 1.8• Mll 85GeV•pT(l1,l2) 120GeV
e
pT
•Real tau rejection• x1, x2 0.0 for real s•MZ-25 M MZ+25GeV
• Mjj > 550GeV
+jets signal
• Transverse momentum balance: |PT| < 30GeVPT=pT
l1+pTl2+pTmiss+pT
j1+pTj2
• Jet veto: no jets with pT>20GeV in the region || 3.2
• Z/* rejection: mT(ll)>30GeV
Results
Lepton pT +tag jets Lepton angular
Tau rejection, PT,Jet veto
Drell-Yan rejection
MH=160GeV
22 )()(miss
T
e
TTllTT ppEEM
Results
MT bound MT bound
PYTHIA and ME background calculations have been compared, ME~2.1xPYTHIAUse ME and assign an additional systematic uncertainty of 10% Experimentally background can be measured using tt-events outside signal region
For 5fb-1, >5σ for 155<MH<180GeV in e channel aloneFor 30fb-1, >5σ for 125<MH<190GeV in e+ee/ channels
(σ in fb)
Tau analysis
• Look at ll+pT-miss and lhad+pT-miss channels• Similar analysis to WW(*) channel• ll+pT-miss, e final state analysis
– Two isolated leptons with pT(e)>15 GeV, pT()>10GeV, |l|<2.5– 2 tag jets with pT
j1 50GeV; pTj2 20GeV (|| 5.0 R < 0.7)---???
tags 4.4, leptons are found in the rapidity gap between the tag jets– pT-miss > 50GeV– Invariant mass of tag jets, Mjj > 700GeV– Central jet veto, no jets with pT>20GeV in the region tag
min j tagmax
– Azimuthal separation between tag jet jj<2.2 – reduces Zjj background Re < 2.6– Real tau reconstruction: x1, x2 > 0, x1
2+x22 < 1
– Mass window around Higgs boson mass: mH-10GeV<m <mH+15GeV
Tau results
for 30fb-1
5σ discovery in the region 110<MH<135GeVFor 30fb-1
Significance
Summary
• A light Higgs can be discovered with ≥5σ significance in the VBF channels:– qqH WW(*) ll+pT-miss: 10fb-1, 135GeV<MH<190GeV– qqH ll+pT-miss and lhad+pT-miss: 30fb-1, 110GeV<MH<135GeV
• Combined with other channels ATLAS can discover a Higgs with 5σ significance with 10fb-1 of data in the mass range: 120GeV<MH<190GeV
• The measurement in VBF of WW and decays allows a measurement of:
W in the mass range 120-150GeV at level of ~10%
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