1. 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

2. Higgs production Leading order 10 5 10 4 10 3 10 Events for 10 fb -1 Standard channels M H <2M Z :ttH lbb+X, H H ZZ* 4l, H WW(*) l l M H >2M Z :H ZZ 4l qqH ZZ ll, lljj qqH WW l jj

3. 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 Tagging jet H W W Z/W

4. 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

5. 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

6. Jet tagging and reconstruction Tag jets defined as jets with highest p T in each hemisphere Comparison of jet construction with ATLFAST and full-simulation Fake jet rate in the central region has been studied. 20 GeV threshold at low luminosity Must be raised at higher luminosity.

7. Analysis of e channel Two isolated leptons p T 1 >20GeV, p T 2 >15GeV | | 2.5 leptons observed in the rapidity gap spanned by the tag jets Two tag jets p T j1 40GeV; p T j2 20GeV tags 3.8 Reject tag jets identified as b-jets | | 2.5 Lepton cuts ll 1.05 cos ll 0.2 R ll 1.8 M ll 85GeV p T (l 1,l 2 ) 120GeV e pTpT

8. Real tau rejection x 1, x 2 0.0 for real s M Z -25 M M Z +25GeV M jj > 550GeV +jets signal Transverse momentum balance: |P T | < 30GeV P T =p T l1 +p T l2 +p T miss+p T j1 +p T j2 Jet veto: no jets with p T >20GeV in the region | | 3.2 Z/ * rejection: m T (ll )>30GeV

9. Results Lepton p T +tag jetsLepton angular Tau rejection, P T, Jet veto Drell-Yan rejection M H =160GeV

10. Results M T bound 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 For 5fb -1, >5σ for 155<M H <180GeV in e channel alone For 30fb -1, >5σ for 125<M H <190GeV in e +ee/ channels (σ in fb)

11. 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 GeV, p T ( )>10GeV, | l |<2.5 –2 tag jets with p T j1 50GeV; p T j2 20GeV (| | 5.0 R < 0.7)---??? tags 4.4, leptons are found in the rapidity gap between the tag jets –p T -miss > 50GeV –Invariant mass of tag jets, Mjj > 700GeV –Central jet veto, no jets with pT>20GeV in the region tag min j tag max –Azimuthal separation between tag jet jj <2.2 – reduces Zjj background – R e < 2.6 –Real tau reconstruction: x 1, x 2 > 0, x 1 2 +x 2 2 < 1 –Mass window around Higgs boson mass: m H -10GeV<m <m H +15GeV

12. Tau results for 30fb -1 5σ discovery in the region 110<M H <135GeV For 30fb -1

13. Significance

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