Discovery of a standard model Higgs boson using

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

Higgs production Events for 10 fb-1 105 104 103 Leading order 10 Standard channels MH<2 MZ: tt. H lbb+X, H H ZZ* 4 l, H WW(*) l l MH>2 MZ: H ZZ 4 l qq. H ZZ ll , lljj qq. H WW l jj

VBF Signal (H WW l l ) Cross section ~20% of ggproduction BUT clear signature • forward tagging jets • correlated leptons Tagging jet W Z/W H W Tagging jet • 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 5 fb-1 at LHC in the mass range 130 -200 Ge. V

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), CTEQ 5 L 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 p. T in each hemisphere Fake jet rate in the central region has been studied. 20 Ge. V threshold at low luminosity Must be raised at higher luminosity. Comparison of jet construction with ATLFAST and full-simulation

Analysis of e channel • Two isolated leptons • p. T 1 >20 Ge. V, p. T 2 >15 Ge. V | | 2. 5 • leptons observed in the rapidity gap spanned by the tag jets • Two tag jets • p. Tj 1 40 Ge. V; p. Tj 2 20 Ge. V • tags 3. 8 • Reject tag jets identified as b-jets | | 2. 5 • Lepton cuts • ll 1. 05 • cosqll 0. 2 • Rll 1. 8 • Mll 85 Ge. V • p. T(l 1, l 2) 120 Ge. V p. T e

+jets • Real tau rejection • x 1, x 2 0. 0 for real s • MZ-25 M MZ+25 Ge. V • Mjj > 550 Ge. V • Transverse momentum balance: |PT| < 30 Ge. V PT=p. Tl 1+p. Tl 2+p. Tmiss+p. Tj 1+p. Tj 2 • Jet veto: no jets with p. T>20 Ge. V in the region | | 3. 2 • Z/ * rejection: m. T(ll )>30 Ge. V signal

Results Lepton p. T +tag jets Lepton angular MH=160 Ge. V Tau rejection, PT, Jet veto Drell-Yan rejection

Results MT bound For 5 fb-1, >5σ for 155<MH<180 Ge. V in e channel alone For 30 fb-1, >5σ for 125<MH<190 Ge. V in e +ee/ channels (σ in fb) PYTHIA and ME background calculations have been compared, ME~2. 1 x. PYTHIA 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+p. T-miss and lhad+p. T-miss channels • Similar analysis to WW(*) channel • ll+p. T-miss, e final state analysis – Two isolated leptons with p. T(e)>15 Ge. V, p. T( )>10 Ge. V, | l|<2. 5 – 2 tag jets with p. Tj 1 50 Ge. V; p. Tj 2 20 Ge. V (| | 5. 0 R < 0. 7)---? ? ? tags 4. 4, leptons are found in the rapidity gap between the tag jets – p. T-miss > 50 Ge. V – Invariant mass of tag jets, Mjj > 700 Ge. V – Central jet veto, no jets with p. T>20 Ge. V in the region tagmin j tagmax – Azimuthal separation between tag jet jj<2. 2 – reduces Zjj background – Re < 2. 6 – Real tau reconstruction: x 1, x 2 > 0, x 12+x 22 < 1 – Mass window around Higgs boson mass: m. H-10 Ge. V<m <m. H+15 Ge. V

Tau results for 30 fb-1 5σ discovery in the region 110<MH<135 Ge. V For 30 fb-1

Significance

Summary • A light Higgs can be discovered with ≥ 5σ significance in the VBF channels: – qq. H WW(*) ll+p. T-miss: 10 fb-1, 135 Ge. V<MH<190 Ge. V – qq. H ll+p. T-miss and lhad+p. T-miss: 30 fb-1, 110 Ge. V<MH<135 Ge. V • Combined with other channels ATLAS can discover a Higgs with 5σ significance with 10 fb-1 of data in the mass range: 120 Ge. V<MH<190 Ge. V • The measurement in VBF of WW and decays allows a measurement of: in the mass range 120 -150 Ge. V at level of ~10%