Discovery of a standard model higgs boson using vector boson fusion at the lhc
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Discovery of a standard model Higgs boson using vector boson fusion at the LHC. Craig Buttar University of Sheffield Collaborators: G.Azuelos, V.Cavasinni, D.Costanzo, R.Harper, K.Jakobs, M.Klute, R.Mazini, E.Richter-Was, I.Vivarelli. 10 5. 10 4. 10 3. Leading order. 10. Higgs production.

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Discovery of a standard model Higgs boson using vector boson fusion at the LHC

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Discovery of a standard model Higgs boson using vector boson fusion at the LHC

Craig Buttar

University of Sheffield

Collaborators: G.Azuelos, V.Cavasinni, D.Costanzo, R.Harper, K.Jakobs, M.Klute, R.Mazini, E.Richter-Was, I.Vivarelli


105

104

103

Leadingorder

10

Higgs production

Events for

10 fb-1

Standard channels

MH<2MZ:ttHlbb+X, H

H ZZ* 4l, H WW(*) ll

MH>2MZ:H ZZ 4l

qqH ZZ ll, lljj

qqHWW  ljj


Tagging jet

W

Z/W

H

Z/W

W

Tagging jet

VBF Signal (HWWll)

  • 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/9906218

Conclusion: >5 observation with 5fb-1 at LHC in the mass range 130-200 GeV


Backgrounds

  • tt+jets

    • tWb

    • 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

Fake jet rate

in the central

region has been

studied.

20 GeV threshold

at low luminosity

Must be raised at

higher luminosity.

Comparison of jet construction with

ATLFAST and full-simulation


Analysis of em channel

  • Two isolated leptons

    • pT1 >20GeV, pT2 >15GeV ||  2.5

    • leptons observed in the rapidity gap spanned by the tag jets

  • Two tag jets

    • pTj1  40GeV; pTj2  20GeV

    • tags  3.8

    • Reject tag jets identifiedas b-jets ||  2.5

  • Lepton cuts

    • ll  1.05

    • cosqll  0.2

    • Rll  1.8

    • Mll 85GeV

    • pT(l1,l2)  120GeV

e

pT


signal

+jets

  • Real tau rejection

    • xt1, xt2  0.0 for real s

    • MZ-25  Mtt  MZ+25GeV

  • Mjj > 550GeV

  • Transverse momentum balance: |PT| < 30GeV

    • PT=pTl1+pTl2+pTmiss+pTj1+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

MH=160GeV

Tau rejection, PT,

Jet veto

Drell-Yan rejection


Results

MT bound

MT bound

(σ in fb)

For 5fb-1, >5σ for 155<MH<180GeV in e channel alone

For 30fb-1, >5σ for 125<MH<190GeV in e+ee/ channels

PYTHIA and ME background calculations have been compared, ME~2.1xPYTHIA

Use ME and assign an additional systematic uncertainty of 10%

Experimentally background can be measured using tt-events outside signal region


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 pTj1  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 tagmin  j  tagmax

    • Azimuthal separation between tag jet jj<2.2 – reduces Zjj background

    • Re < 2.6

    • Real tau reconstruction: xt1, xt2 > 0, xt12+xt22 < 1

    • Mass window around Higgs boson mass: mH-10GeV<m <mH+15GeV


Tau results

for 30fb-1

5σ discovery in the region 110<MH<135GeV

For 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:

in the mass range 120-150GeV at level of ~10%


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