Higgs Searches using Vector Boson Fusion

2 Why a “Low Mass” Higgs (1) M H <251 GeV (95% C.L.)

3  s = GeV B-tag probab ZZ Hypothesis: M Z =91.7GeV M Z =100.2GeV s/b = 4.7 CHECK lep CONCLUSIONS 2.2  fluctuation (3.4% Prob.) M H >114.1GeV Why a “Low Mass” Higgs (2)

4 ATLAS-SN EPJ Direct, C: 32 Suppl. 2 (2004) pp Detector Effects, Pile-up studies -- Channel-by-channel discussion

5 General Properties   Forward jets Higgs Decay Two quarks emitted in the forward region No color flow in the central part of the detector Require two forward (Tagging) jets and Veto extra jet Activity in the central region

6 Forward Jet Distribution H  WW  2l 2ν

7 Jet Reconstruction Efficiency Probability to find a jet in a Cone of  r=0.2 around a parton Note the calorimeter structure And the end of the detector

8 The effect of Pile-up Energy released in the calorimeters from Minimum bias interactions Low luminosity = cm -2 s -1 High luminosity = cm -2 s -1

9 Fake Veto from Pile-up Events can be vetoed because Of a Jet from Minimum Bias Low luminosity = cm -2 s -1 High luminosity = cm -2 s -1

10 Fakes from Pile-up

11 Comments on the IVB Signature Clearly depends on the Tagging and Veto performances. Last evaluation rather old (Summer ’01) Can we Identify jets in the Forward Region? (low signal/noise ratio) How well can we reconstruct low P T jets in the central region? The studies I showed assume a model for Minimum Bias, as in Pythia 5.7, 4 years ago. Systematic can be >~ 2

12 Higgs Decays LEP WW and tau tau decays are the alternatives Tau can be searched in 2 lepton final state, and One lepton and one hadron

13 H  WW  2 lep. decay Main Backgrounds –Top production –WW (electroweak production can be very similar to signal) –Drell-Yan Selection –Forward tagging –Jet Veto –M ll 30GeV –Tau rejection (Z  tau tau) –Lepton Symmetry –Transverse mass

14 Transverse Mass M T 160 GeV e/  Channel M T before the angular cut on the leptons Define: MT<175GeV Signal region MT>175GeV Background region

15 Lepton Angular Correlation Signal RegionBackground Region

16 Higgs Mass Reconstruction S=1.02fb B=2.28fb S=8.24fb B=2.44fb

17 H  ττ Define x 1 and x 2 as the visible energy of the tau decay products Use collinear approximation and assume all decay products (including) neutrino in the same direction M tt =m ll /(x 1 x 2 ) 1/2

18 Mass Reconstruction in the Tau Channel for 30 fb -1 Di-Lepton Tau Decays Lepton-Hadron Tau decays

19 Discovery Potentials

20 Comments Finding the Higgs is a tough job… Possible with 10 fb-1? –Depend on several channels exploiting different detector characteristics –Still do not include NLO corrections –Systematic from the minimum bias model used –I didn’t show any neural network analysis The most “interesting” mass region is also the most difficult