Little Higgs Searches with ATLAS

ASI - LHC Studies PRAHA - July 10th 2003

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Little Higgs searches

Little Higgs Searches with ATLAS

S. Asai, G. Azuelos, K. Benslama, D. Costanzo,

G. Couture, J. E. Garcia, F. Gianotti, I. Hinchliffe,

N. Kanaya, M. Lechowski, R. Mehdiyev,

G. Polesello, E. Ros, D. Rousseau

presented by: M. LECHOWSKIM. LECHOWSKI (LAL-Orsay)

The Little Higgs task force


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Little Higgs modelLittle Higgs model

• Motivation :Motivation :

• Quadratic Quadratic divergences :divergences :

• Higgs fields :Higgs fields :

electroweak Planck

hierarchy and fine-tuning problems

bosons fermionsgauge

bosons new quarks

new gauge bosonsquarks

cancellationsSUSY : Little Higgs :

electroweak Planck

Goldstone bosons

pseudo-Goldstone bosons

symmetry breaking

"light" mass

massless


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ParticlesParticles

We have to look for the following particles:We have to look for the following particles:

T heavy top

WH ZH AH

Higgs triplet 0 , + , ++

heavy W± heavy Z heavy

heavy Higgs bosons

±

arXiv:hep-ph/0301040 Phenomenology of the Little Higgs Model

described in :


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Mass Range

Upper limits:Upper limits: to avoid fine tuning scale f < 1 TeV·

• T M < 2 TeV·

mh = 120 GeV M < 0.2 TeV

mh = 200 GeV M < 2 TeV

• WH , ZH, AH M < 6 TeV·

mh = 120 GeV M < 2.2 TeV

mh = 200 GeV M < 6 TeV

M < 10 TeV

2

200

GeVmh

2

200

GeVmh

2

200

GeVmh±

M(WH) M(ZH)±


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Decays

T tZ, bWtZ, bW

thth

ZH, AH l l + + l l --, qq, …, qq, …

ZhZh

WH ll , qq’, …, qq’, …

WW±±hh

++ WW+ + WW++, , l l + + l l --, , ……

discovery discovery

channelchannel

test of the test of the

modelmodel

The modes th, Zh, W±h, … may be difficult to see but are necessary to test the model

±very heavy particlesvery heavy particles

very high pvery high pTT final state final state


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GenerationGeneration

We have used the following software for the analysis:We have used the following software for the analysis:

• Generation: Generation: Pythia 6.2Pythia 6.2

• new top:new top: 4 4thth generation quarks ( generation quarks (TT = = t’t’) ) MSUB(83)MSUB(83)

• new heavy bosons:new heavy bosons: generated via generated via MSUB(141), MSUB(141), MSUB(142)MSUB(142)

• new Higgs sector: new Higgs sector: generated via generated via MSUB(351)MSUB(351)

• Decays: Decays: modify Pythia decay tables to match Little modify Pythia decay tables to match Little Higgs modelHiggs model

• Analysis: Analysis: fast simulationfast simulation


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Heavy top T

q

W

b T

q’

(T

) (f

b)

T TT

1 = 2 1

• Production mechanism = Production mechanism = Wb fusionWb fusion

T bWbW 50 %50 %

T tZtZ 25 %25 %

T thth 25 %25 %

BRBR1 , 2 Yukawa couplings

11M 16M 16 2 %

1

2

( )2

T


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T searches

h

bb

bb

T

t1 TeV W

bb

t

TZ

1 TeV

bb

l +

l -

l

W

Signature:3 leptons+ 1 b-jet+ ETmiss

Signature:3 b-jets + 1 lepton+ ETmiss

l

T

120 GeV

Background: pp tZpp WZ

Background: pp ttpp Wbb


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T Zt signal

Cuts:- 3 isolated leptons, pT >30 GeV (2 of them with Ml l= MZ)

- 1 b –jet- ET > 100 GeV

MT= 1 TeV

1 = 2

S = 10 B = 11

T tZ 3 leptons + b-jet + ET

+ -

T

Signal

Bkg

Signal

Bkg

S/B > 5 (S 10) in the window mass discovery

L = 3·105 pb-1


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T ht signal

Cuts:- pT(3-jets) > 80 GeV- pT(lepton) > 70 GeV- in window mass of H

At least 1 b-tag

M(T) (GeV)

MT= 700, 1000, 1300 GeV T ht 3 b-jets + lepton + ET

MMTT= 700= 700

MMTT= 1000= 1000

MMTT= 1300= 1300

BkgBkgEve

nts

/ 30G

eV

using cross-sections to achieve3 observations :

T

MT (GeV)

MMTT= 700 = 700 atat 33 BRBRTht > > 525 525 fbfbMMTT= 1000= 1000 atat 33 BRBRTht > > 220 220 fbfbMMTT= 1300 = 1300 atat 33 BRBRTht > > 210 210 fbfb

L = 3·105 pb-1


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Gauge Boson ZH

Once a mass is given, the only free parameter in the model is .

(Z

H)

(fb

) (cot ) 2

cot = 1

q

q

ZH

(ll ) ~ (cot ) 2

(Zh) ~ (cot 2) 2

ZhZh

ee++ee- - + + ++- - + + ++--

12%12%

BR

cot

ZH , WH , AH

NB: (WH) = 2 (ZH) NB: (Wh) for WH = (Zh) for ZH


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Search for ZH

qq ZH ee++ee--

L = 3·105 pb-1

Selection cutsSelection cuts::

• 2 isolated electrons with 2 isolated electrons with ppTT > 20 GeV > 20 GeV and and ||| < 2.5| < 2.5 • minimum invariant mass minimum invariant mass equal to 800 GeVequal to 800 GeV

BackgroundBackground::

Drell-Yan (Drell-Yan (qq Z/ ee++ee- - )) other bkg’s are under evaluationother bkg’s are under evaluation

M(e+e-) (GeV)

N(e

+e- )

bkg

subt

ract

ed

cot = 1.0 S 5000B 20

cot = 0.2 S 100B 8

ZH , WH , AH

MZ = 2 TeVH


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low low .BR(Z.BR(ZH H ee++ee))

Discovery region for ZH

L = 3·105 pb-1

SB

> 5

2 4 6

cot

If ZIf ZHH is found, cot is found, cot can be can be

extracted from extracted from (Z(ZHH) and ) and (Z(ZHH))

MM

= [ 3.4= [ 3.4 (cot (cot ))22 +0.071 (cot 2 +0.071 (cot 2))22] %] %

MZ (TeV)H

low low (Z(ZHH))

ZH , WH , AH


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mh = 200 GeV

BR(h W+W-) = 74

%BR(h ZZ) = 26 %

ZH Zh

q

q

cot cot 2

(cot cot 2) 2

(cot )(cot = 0.5) mh = 120 GeV

BR(h bb) = 66 %BR(h ) = 0.2 %

ZH

hh

ZZ

Rat

io0.5

ZH , WH , AH


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ZH Zh with h bb

hh

ZH

ZZ

l +

l -

bbbb

2 TeVhh

bb

bbZH

ZZ

l +

l -

1 TeV

Cuts

Background: Z + jets

Cuts

|| < 2.5 (jets and leptons)

PT(Z) > 250 GeVPT(h) > 250 GeVb-tagging


PT(Z) > 500 GeV PT(h) > 500 GeV b-tagging

120 GeV 120 GeV

ZH , WH , AH


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Signal and background

b-tag: b = 40%, Ru = 100 Inside mass window:S = 15 SB = 8 B

= 5


= 50

M(ZH) (GeV)

MZ = 1 TeVH

M(ZH) (GeV)

MZ = 2 TeVH

L = 3·105 pb-1

cot = 0.5L = 3·105 pb-1

cot = 0.5

Eve

nts

Eve

nts

* *

* from full sim.

ZH , WH , AH


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WH W h with h bb

hh

bb

bbWH

WW

1 TeV

Cuts

Background: W + jet , tt


assume colinear to l for WH reconstructionPT(Z) > 250 GeVPT(h) > 250 GeVb-tagging

120 GeV

ZH , WH , AH


= 69

l

±

±

±

± ±

MW = 1 TeVH

M(WH) (GeV)

Eve

nts


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WH / ZH W/Z h with h

Cuts |()| < 2.5 PT() > 25 GeV m (h) 120 GeV PT(h) > 400 GeV -tagging, () = 80% PT(W/Z) > 200 GeV inside mass window

S(WH Wh) = 64 S(ZH Zh) = 33

B(h inclusive) = 8 B( inclusive) = 5

97

13

S

B= 27

WH

ZH

Bkg

L = 3·105 pb-1

cot = 0.5

Eve

nts

MZ = MW = 1 TeVHH

M(WH/ ZH) (GeV)

hh

WH +ZHW+ZW+Z

j

j

big jetor

1 TeV

120 GeV

* 23 without reconstructing W/Z

*

ZH , WH , AH

Background: h() inclusive inclusive


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Combined results

M(ZH/WH) (TeV)

cot

ZH l l bbWH l bb

ZH/WH j j

Regions with Regions with S/S/B > 5B > 5 and and S > 10S > 10

L = 3·105 pb-1

M < 2.2 TeV for mh = 120 GeV

ZH , WH , AH

exclu

ded


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Deductions for AH ZH , WH , AH

WWHH/Z/ZHH not background for A not background for AHH

M(AH) (GeV)

.BR(A.BR(AHH Z h) min. Z h) min.

fbregion excluded at 95 % CL if we see nothing

• deduced only from study deduced only from study ZH Z h with h • can combine other studiescan combine other studies

• theorical uncertainties (strong theorical uncertainties (strong model-dependencymodel-dependency) for A) for AHH

• can deduce can deduce limits on limits on .BR(A.BR(AHH Z h)Z h) from results for Z from results for ZHH (same decays)(same decays)

• hypothesis : favorable cases where M(Whypothesis : favorable cases where M(WHH/Z/ZHH) and M(A) and M(AHH) are distant ) are distant for each M(A for each M(AHH) ) (resolution of M(W(resolution of M(WHH/Z/ZHH) being 45 ) being 45 80 GeV) 80 GeV)


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q’

New Higgs ++

• Production: Production: VBF mechanismVBF mechanism(vector boson fusion)

++ WW++WW++

++ ++ ++, , ee++ee++, …, …DecaysDecays

Eve

nts

L = 3·105 pb-1

M() = 1.5 TeVM() = 2 TeV

W+W+ ++ W+W+

q1

W+

q2

q’

W+

1

2

++

might be suppressed

v’ = 25 GeV (v’)2

SM

++


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++ W+W+

Eve

nts

L = 3·105 pb-1

++ W+W+ l +l +

M(++) = 1.5 TeV

2 forward jets• PT(lepton 1) > 100 GeV• PT(lepton 2) > 50 GeV• ET > 50 GeV

• MT > 600 GeV

Main cuts:

Bkg

Signal (v’ = 25 GeV)

MT () (GeV)

S = 3.2B = 20

Parameter v’ > 67 GeVto achieve 5

++

PRELIMINARY

(theorical

uncertainties)

Background: WWqq, WZ

WZqq, Wtt


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Background: WWjj, tt

++ + +

++ ++ lepton + jet

Main cuts :

M(++) (GeV)

M(++) = 0.3 TeV

M(++) = 0.7 TeV

M(++) = 1.5 TeVEve

nts

(arb

itrar

y un

its)

( Couplings might be suppressed in the little Higgs model )

++

M(++) (GeV)

1) Forward jet tagPT(j1) > 40 GeV

PT(j2) > 20 GeV| | < 3.8 Mjj > 600 GeV

2) Central jet veto

3) selection cuts

4) Same charge for

-jet and lepton

Required .BR(++++) (fb) for 5 discovery :


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Summary

T tZtZ M=1 TeV :M=1 TeV : S/ S/B B >5 >5 ((1 1 = = 22))

th th M=0.7, 1M=0.7, 11.3 TeV :1.3 TeV : visible at 3 visible at 3

ZH e e ++e e -- easily visible easily visible for M for M < < 2TeV2TeV

ZhZh

WH WW±±hh

++ WW+ + WW+ + M=1.5 TeV :M=1.5 TeV : visible at 5visible at 5 for v' for v' > > 67GeV67GeV

+ + ++ M=0.7M=0.71.5 TeV :1.5 TeV : visible at 5 visible at 5

±M=1 (2) TeV :M=1 (2) TeV : S/ S/B=27 (5)B=27 (5)

ll ++ll

-- bbbb qqqq

M=1 (2) TeV :M=1 (2) TeV : S/ S/B=50 (5)B=50 (5)

qqqq L = 3·105 pb-1

l l ++l l ++

3b3b l l ++

33l l bb

3b3b l l

discovery discovery

channelchanneltest of the test of the

modelmodel

for for ..BRBR((++++++++)) >> 2fb 2fb

(cot(cot=0.5)=0.5)

(cot(cot=0.5)=0.5)

l l ±± bbbb

M=1 TeV :M=1 TeV : S/ S/B=69B=69 (cot(cot=0.5)=0.5)

for for ..BRBR((TTthth)) >> 525, 220 fb 525, 220 fb


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Conclusions

The search for particles The search for particles predicted by the Little Higgs predicted by the Little Higgs models using the ATLAS detector models using the ATLAS detector has started . has started .

A large part of parameter space A large part of parameter space will be covered .will be covered .

Work also done on following channels:Work also done on following channels: (but no time to show)(but no time to show)

• TT th th andand Z ZHH Zh Zh with with M(h) = 200 M(h) = 200 GeVGeV

• ++++ W W++WW++ ljj andand ++++ ee++ee++, , ++++


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Additionnal slides

• b-tagging for ZH Zh with h bb

• without reconstructing W/Z for WH / ZH W/Z h with h


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b-tagging

< pT (b)> = 220 GeV < pT (bb)> = 800 GeV

WH(400) from DC1 data

bbbb

115~ 100

Full simulation of double b-jets

0.5

MZ = 1 TeVH

MZ = 2 TeVH

0.4

ZH , WH , AH


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WH / ZH W/Z h with h

Cuts

|()| < 2.5 PT() > 25 GeV m (h) 120 GeV PT(h) > 400 GeV -tagging, () = 80%

S(WH Wh) = 107 S(ZH Zh) = 53

B(h inclusive) = 31 B( inclusive) = 17

160

48

S

B= 23

WH

ZH

BkgL = 3·105 pb-1

cot = 0.5

Eve

nts

MZ = MW = 1 TeVHH

pT(WH/ZH) (GeV)

hh

WH +ZHW+ZW+Z

X

1 TeV

120 GeV

ZH , WH , AH

Background: h() inclusive inclusive

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Little Higgs Searches with ATLAS

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