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%