searches for a light higgs boson in association with a photon and two forward jets
DESCRIPTION
Searches for a light Higgs boson in association with a photon and two forward jets. Emidio Gabrielli Helsinki Institute of Physics. work made in coll. with F.Maltoni, B. Mele, M.Moretti, F.Piccinini, R.Pittau (preliminary). - PowerPoint PPT PresentationTRANSCRIPT
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Searches for a light Higgs boson in association with a photon and two forward
jets
Emidio Gabrielli
Helsinki Institute of Physics
work made in coll. with F.Maltoni, B. Mele, M.Moretti, F.Piccinini, R.Pittau (preliminary)
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Higgs decay in bb(bar)
not a discovery channel, but…relevant for measuring the Hbb coupling
up to now the processes Htt(bar) and HW + 2 forward JETS have been considered
bckg can be reduced approximatively at the level of the signal
resulting x-sections after optimized cuts are of
the order of few fb.
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inclusive cross sections of HW in fb
Rainwater (2001)HW allows to measure Hbb coupling for mH=120 GeV with an uncertainty of 50%
13.9 11.2 8.6 5.1 2.5
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a b c
a
b
c
mH = 120 GeV
S/B 1/10 1/7 1/5
Rainwater (2001)
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Htt(bar) and H bb(bar)
extremely exclusive signature suitable for low Higgs mass, disfavored by low x-section
3 final states considered: fully leptonic, semileptonic, fully hadronic
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many jets in the eventmajor bckg from ttbb , Ztt, tt+Njets and QCD multijetsmajor problem, normalization of the bckg from datamany sources of uncertainties: MC predictions, Jet energy scaleall these systematics might Kill the signal !
main problems
Htt(bar) L=30/fb mH=115 GeVDrollinger, Muller, Denegri (2001)
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pp H + j j
E.G., F.Maltoni, B. Mele, M.Moretti, F.Piccinini, R.Pittau (preliminary)
same mechanism of H production by WW fusion + emission of a
bb(bar)
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main advantages
trigger on gamma
the bckg is less active than Hjj when a central photon is required
large x-section
provide a new independent test of Hbb(bar) and HWW couplings
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Higgs production in WW fusion
characteristic signal is the presence of two forwardJets with a typical transverse momentum
GeV 4030pT
large x-section, BUT it is difficult to measure due to the huge bckg with respect to signal
emission of a photon provide a trigger and also allows to reduce the bckg with respect to the signal
the mechanism: the angular cuts on gamma play a crucial role
Mangano, Moretti, Piccinini, Pittau, Polosa (2003)
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gauge invar. contribs.destr. interferencefor gamma at large angles
gauge invariant contr. comparable with others
bckg is less active by requiring a central photon
main bckg to pp H + j j
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different angular photon distribution with respect to bckg
sensitive to HWW and WWg couplings
no destructive interference at large angle, due to the charged gauge boson
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)(b),R(
signal bckg same normalization
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GeV 160 )m(H,GeV 12)(120 )b,m(b GeV 12)-(120
4 |)b()b(|GeV 800 )j,m(j
GeV 60 )b(p , )j(p2.5 |b)(|
0.7 R AllGeV 03 (j)p
21
21
21
1T1T
T
optimized cuts to enhance S/B
mH = 120 GeVBR = 69%L=100/fb
N(B)N(S)signf N(S)=LS)BR x (b)(b)(bb)
N(B)=L(B) x (bbb)(b) = 50% eff. b-tag(bb) = 80% eff. bb reconstr.
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signal (fb) bckg (fb)6.6 x BR pT(g) > 20 GeV
54.1 pT(g) > 20 GeV
4.9 x BRpT(g) > 30 GeV
41.6 pT(g) > 30 GeV
S/B signf 1/8 2.4
1/9 2.1
signal no rad (pb)
bckg no rad (pb)
0.472 103.8S/B=1/220
pp H + j j
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ConclusionsThe measure of Hbb coupling is challenging at the LHCknown promising channels are HW and Httwe propose an alternative channel
pp H jj + (WW fusion )main advantages with respect to Hjj
- less active bckg after requiring a central photon - trigger on photon
after suitable cuts signf = 2.4viable channel to measure Hbb, HWW couplings