Little Higgs Searches with ATLAS
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Transcript of 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
ASI - LHC Studies PRAHA - July 10th 2003
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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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
|| < 2.5 (jets and leptons)
PT(Z) > 500 GeV PT(h) > 500 GeV b-tagging
120 GeV 120 GeV
ZH , WH , AH
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Little Higgs searches
Signal and background
b-tag: b = 40%, Ru = 100 Inside mass window:S = 15 SB = 8 B
= 5
b-tag: b = 50%, Ru = 100 Inside mass window:S = 195 SB = 16 B
= 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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Little Higgs searches
WH W h with h bb
hh
bb
bbWH
WW
1 TeV
Cuts
Background: W + jet , tt
|| < 2.5 (jets and leptons)
assume colinear to l for WH reconstructionPT(Z) > 250 GeVPT(h) > 250 GeVb-tagging
120 GeV
ZH , WH , AH
b-tag: b = 50%, Ru = 100 Inside mass window:S = 1499 SB = 471 B
= 69
l
±
±
±
± ±
MW = 1 TeVH
M(WH) (GeV)
Eve
nts
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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
++ 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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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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Little Higgs searches
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