higgs searches using vector boson fusion. 2 why a “low mass” higgs (1) m h
TRANSCRIPT
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
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
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
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
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