Higgs Searches Higgs Searches using using

Vector Boson FusionVector Boson Fusion

2Why a “Low Mass” Higgs (1)

MH<251 GeV (95% C.L.)

3

s = 206.7 GeV

B-tag probab.0.99 0.990.14 0.01

ZZ Hypothesis:MZ=91.7GeVMZ=100.2GeV

s/b = 4.7

CHECK lepCONCLUSIONS

2.2 fluctuation(3.4% Prob.)

MH>114.1GeV

Why a “Low Mass” Higgs (2)

4

ATLAS-SN-2003-024EPJ Direct, C: 32 Suppl. 2 (2004) pp.19-54

-- Detector Effects, Pile-up studies

-- Channel-by-channel discussion

5General 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

6Forward Jet DistributionHWW 2l 2ν

7Jet Reconstruction Efficiency

Probability to find a jet in a Cone of r=0.2 around a parton

Note the calorimeter structureAnd the end of the detector

8The effect of Pile-upEnergy released in the calorimeters from Minimum biasinteractions

Low luminosity = 1033 cm-2s-1

High luminosity = 1034 cm-2s-1

9Fake Veto from Pile-up

Events can be vetoed becauseOf a Jet from Minimum Bias

Low luminosity = 1033 cm-2s-1

High luminosity = 1034 cm-2s-1

10Fakes from Pile-up

11Comments 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 PT 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

12Higgs Decays

LEP

WW and tau tau decaysare the alternatives

Tau can be searched in 2 lepton final state, andOne lepton and one hadron

13HWW2 lep. decay

• Main Backgrounds– Top production– WW (electroweak production can be very similar to

signal)– Drell-Yan

• Selection– Forward tagging– Jet Veto– Mll < 75GeV, ETmiss > 30GeV– Tau rejection (Ztau tau)– Lepton Symmetry– Transverse mass

14Transverse Mass MT

160 GeV e/ Channel

MT before the angular cut on the leptons

Define: MT<175GeV Signal region MT>175GeV Background region

15Lepton Angular CorrelationSignal Region Background Region

16Higgs Mass Reconstruction

S=1.02fb B=2.28fb S=8.24fb B=2.44fb

17HττDefine x1 and x2 as the visible energy of the tau decay products

Use collinear approximation and assume all decay products (including) neutrino in the same direction

Mtt=mll/(x1x2)1/2

18Mass Reconstruction in the Tau Channel for 30 fb-1

Di-Lepton Tau Decays Lepton-Hadron Tau decays

19Discovery Potentials

20Comments

• 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