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Invisible Higgs in weak bosons associative production with heavy quarks at LHC
Sergei Demidov
Institute for Nuclear Research RAS

in collaboration with E. Boos (SINP MSU) and D. Gorbunov (INR RAS)

9 September, 2010

E. Boos, D. Gorbunov, S. Demidov (INR RAS)

Invisible Higgs

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Introduction

Standard Model. Problems.

Experimental problems
Neutrino oscillations Evidence for dark matter Dark energy

Theoretical problems
Naturalness -- large loop corrections to mH Gauge hierarchy problem mEW < MPl Baryon asymmetry, strong CP problem, fermion mass hierarchy Nature of electroweak symmetry breaking

Standard Model is incomplete!

E. Boos, D. Gorbunov, S. Demidov (INR RAS)

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Introduction

SM extensions with invisible Higgs boson
Singlet scalar field (e.g. Burgess, Pospelov, ter Veldhuis, 2001): L = LSM + m2 1 (µ S )2 - 0 S 2 - S 2 H H + ... 2 2
2 m0 + v 2 2 vEW 8 mH 2 EW

Decay H SS is allowed if mS (H SS ) = Other possibilities:

< 1 mH 2
2 4mS 2 mH

1-

Higgs decay into other new scalars, neutralinos, gravitinos ... Combined LEP bound on invisible Higgs: mH > 114.4 GeV at 95% C.L.

E. Boos, D. Gorbunov, S. Demidov (INR RAS)

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Introduction

Invisible Higgs: strategies at LHC

The main idea: missing pT signature. Main channels for LHC: Vector boson fusion pp qqH (Eboli, Zeppenfeld, 2000) pp t¯H (Gunion, 1994) t Questions:

Associated production pp ZH or WH (Godbole at al. 2003) Why does missing pT come from Higgs boson? Only mH can be measured. Can we say something about H ?

E. Boos, D. Gorbunov, S. Demidov (INR RAS)

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¯ pp q q VV
Higgs boson is needed massive gauge bosons cross sections of those ¯ We consider pp q q V heavy (t or b ) quarks. to restore unitarity in processes with and its contribution should change the processes. ¯ V via q q VV scattering where q is

Higgs mass range mH < 2MV , vir tual Higgs, probing the Higgs width H .

b ¯ b

Z Z

b ¯ b

H

Z Z

E. Boos, D. Gorbunov, S. Demidov (INR RAS)

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pp t¯ZZ : framework t
Assumptions and calculational framework Higgs boson production rate is as in Standard Model Par tonic analysis in LO using CompHEP 4.5 (Boos at al., 2009) Only the main subprocess gg t¯ZZ t No phase space cuts, s = 14 TeV, CTEQ5L1 Amplitudes with and without vir tual Higgs boson were taken into account. ¯ t
g Z Z g t
E. Boos, D. Gorbunov, S. Demidov (INR RAS) Invisible Higgs 9 September, 2010 6 / 15

¯ t g g t Z Z

H


pp t¯ZZ : results I t
Invariant mass m
ZZ

distribution and total cross section

0.08 140 GeV 0.07 150 GeV 160 GeV 0.06 170 GeV 0.05 180 GeV 0.04 0.03 0.02 0.01 0 180 190 200 210 220 230 240 250 mZZ, GeV

2.6 SM Higgs 2.4 2SM 2.2 4SM 2 8SM 16SM 1.8 1.6 1.4 1.2 1 140 145 150 155 160 165 170 175 180 mH, GeV

The shape of m

ZZ

invariant mass distribution is very sensitive to m
Invisible Higgs 9 September, 2010

cross section, fb

1/ d/dmZZ

H

E. Boos, D. Gorbunov, S. Demidov (INR RAS)

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pp t¯ZZ : results II t
Invariant mass m
mH = 170 GeV

ZZ

distribution for different masses
mH = 180 GeV

0.016 0.014 0.012 0.01 0.008 0.006 0.004 0.002 0 180 190 200 210 mZZ,

1/ d/dmZZ

1/ d/dmZZ

SM 2SM 4SM 8SM 16SM 32SM

220 230 240 250 GeV

0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 180 190 200 210 mZZ,

SM 2SM 4SM 8SM 16SM 32SM

220 230 240 250 GeV

The shape of invariant mass mZZ distribution is very sensitive to H only when mH 2mZ
E. Boos, D. Gorbunov, S. Demidov (INR RAS) Invisible Higgs 9 September, 2010 8 / 15


pp t¯W + W - : results t
Invariant mass m
WW

distribution and total cross section
8.4 cross section, fb SM Higgs 2SM 8SM 8 32SM 128SM 7.8 8.2 7.6 7.4 7.2 120 125 130 135 140 145 150 155 mH, GeV

H = S M

0.009 110 GeV 0.008 120 GeV 0.007 130 GeV 140 GeV 0.006 150 GeV 0.005 0.004 0.003 0.002 0.001 160 180 200 220 240 260 280 300 mWW, GeV

1/ d/dmWW

Clear dependence on mH and rather weak dependence on H
E. Boos, D. Gorbunov, S. Demidov (INR RAS) Invisible Higgs 9 September, 2010 9 / 15


QCD corrections: crude estimate
pp t¯ZZ : dependence on the renormalization scale Q t
7e-06 6e-06 arbitrary units 5e-06 4e-06 3e-06 2e-06 1e-06 0 180 190 200 210 220 230 240 250 mZZ, GeV

2

Q2=MZ2 Q =(MZ+Mt)2
2

Q2 2 MZ (MZ + Mt )2 2 f pT /4

0 0 0

, fb .43 .24 .32

Q2= pT2/4

E. Boos, D. Gorbunov, S. Demidov (INR RAS)

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¯ pp bb VV : framework

mt - 10t < mbW + , mbW - < mt + 10t , to exclude large par t of ¯ t cross section with t and/or ¯ production

Yukawa of b -quark is small -- contributions with Higgs boson are suppressed ¯ ¯ Modification L = Yb H bb AYb H bb , A = 50 (branching ratio ¯ is also changed compared to SM case, new Higgs boson H bb width 0 ) ¯ For process pp b bW + W - we introduce cuts

E. Boos, D. Gorbunov, S. Demidov (INR RAS)

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¯ pp bb ZZ : results I
H = 0
0.06 0.05 1/ d/dmZZ 0.04 0.03 0.02 0.01 0 180 190 200 210 220 230 240 250 mZZ, GeV 140 150 160 170 180 GeV GeV GeV GeV GeV 0.012 0.01 1/ d/dmZZ 0.008 0.006 0.004 0.002 150 160 170 180 GeV GeV GeV GeV

H = 8

0

0 180 190 200 210 220 230 240 250 mZZ, GeV

The shape is very sensitive to both mH and H

E. Boos, D. Gorbunov, S. Demidov (INR RAS)

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¯ pp bb ZZ : results II
mH = 180 GeV

0.06 0.05 1/ d/dmZZ 0.04 0.03 0.02 0.01

cross section, fb

0 20 40 80

4000 3000 2000

0 20 40 80

0 180 190 200 210 220 230 240 250 mZZ, GeV

140

150

160 170 mH, GeV

180

¯ The cross section of pp b bZZ is quite large. Interesting for LHC!!! ¯ The similar results for pp b bW + W
E. Boos, D. Gorbunov, S. Demidov (INR RAS) Invisible Higgs

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Conclusions

Conclusions

Channels pp t¯ZZ and pp t¯W + W - can in principle be used t t for measuring mass and width of invisibly decaying Higgs boson with mass around 120 - 180 GeV. ¯ ¯ Channels pp b bZZ and pp b bW + W - can be used for measuring mass and width of invisibly decaying Higgs boson in models with enchanced Yukawa of b -quarks. More involved analysis is needed (irreducible background, detector response, NLO corrections).

Thank you!

E. Boos, D. Gorbunov, S. Demidov (INR RAS)

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Conclusions

¯ pp bb W + W - : results
0.009 mH = 150GeV 110 GeV 0.008 120 GeV 0.007 130 GeV 140 GeV 0.006 150 GeV 0.005 0.004 0.003 0.002 0.001 160 180 200 220 240 260 280 300 mWW, GeV
12 11 SM Higgs 2SM 10 4SM 9 8SM 8 7 6 5 4 3 120 125 130 135 140 145 150 155 160 mH, GeV

E. Boos, D. Gorbunov, S. Demidov (INR RAS)

Invisible Higgs

cross section, pb

1/ d/dmWW

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