Transcript Little Higgs Searches with ATLAS

XXXIXth Rencontres de Moriond
on behalf of ATLAS Collaboration
presented by: Jose E. Garcia (IFIC-Valencia)
Particle Spectrum
2
Littlest Higgs model
M
0,+,++
T
WH , ZH
1 TeV
AH
Z ,W
h
scalar
sector
v’
SM Higgs
Arkani-Hamed et al., JHEP 207 (2002) 34
t

Phenomenology
• Han et al., Phys. Rev. D67 (2003) 95004
gauge sector
top
sector

1/2
’
SU(5)  SO(5)
Gauge sector  [SU2U1]2
• Burdman et al., hep-ph/0212228
new couplings (+ scale f)
J. E. Garcia
Little Higgs searches at LHC
Rencontres de Moriond – March 04
Strategies at LHC
q
++
VH
T
q’
q
W
b
Wb fusion
q1
q2
q’1
W+
++
W+
q’2
qq annihilation
  (1)2
1/ 2  1 suppressed
by b-quark PDF.
T  bW, tZ, th
J. E. Garcia
VH
q’
T
3
  (cot)2
Wide range in cot 
possible.
ZH e+e- & WH l 
VH  V h (V is Z or W)
Little Higgs searches at LHC
VBF mechanism
  (v’)2
v’ should be small
++  W+W+
Rencontres de Moriond – March 04
heavy top T
4
• Production mechanism = Wb fusion
q
q’
W
b
T
(T) (fb)
 (
1 2
)
2
1/2 = 1
T
TT
BR
T
bW
50 %
T
tZ
25 %
T
th
25 %
1 , 2 Yukawa couplings of T and t

1

2%
M 16
J. E. Garcia
Little Higgs searches at LHC
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T  Wb
5
T  Wb  b-jet + lepton + ET
L = 3·105 pb-1
1/2=1
Cuts:
- pT(jet) > 200 GeV
- pT(lepton) > 100 GeV
- ET > 100 GeV
1 b-tag required
Backgrounds: tt, t, Wbb
Signal with 5 for MT < 2000 GeV
J. E. Garcia
Little Higgs searches at LHC
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T  Zt and T  ht
Signature:
3 leptons
+ 1 b-jet
+ ETmiss
T
1 TeV
l+
l
Z
t
-
l
W
Signature:
3 b-jets
+ 1 lepton
+ ETmiss
T
1 TeV

6
b
b
h
t
b
b
BKG
tbZ, tZ,WZ
clear peak but poor statistics
J. E. Garcia
l

W
BKG
tt, Wbb
Not distinguishable peak
Little Higgs searches at LHC
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T  Zt signal
MT= 1 TeV
7
T  tZ  3 leptons + b-jet + ET
L = 3·105 pb-1
1/2=1
Cuts:
- 3 isolated leptons
(2 of them with Ml l = MZ)
+ -
- 1 b –jet
- ET > 100 GeV
Signal with 5 for MT < 1050 GeV
J. E. Garcia
Little Higgs searches at LHC
Rencontres de Moriond – March 04
T  ht signal
MT= 1 TeV
8
T  ht  3 b-jets + lepton + ET
L = 3·105 pb-1
1/2=1
Cuts:
Bkg
MT= 1.0
- pT(3-jets) > 130 GeV
- pT(lepton) > 100 GeV
- 110 < Mh < 130 GeV
At least 1 b-tag
M(T) (GeV)
J. E. Garcia
Little Higgs searches at LHC
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Gauge Boson ZH
12%
e+e- + +- + +ZH
BR
(ZH) (fb)
  (cot ) 2
q
9
Zh
q
cot  = 1
cot 
Once a mass is given, the
only free parameter in
the model is, .
J. E. Garcia
(ll) ~ (cot ) 2
(Zh) ~ (cot 2) 2
Little Higgs searches at LHC
Rencontres de Moriond – March 04
Search for ZH
qq
ZH
e+eslight improvement is reached
using also +-
10
M(ZH) = 2 TeV
cot  = 1.0
L = 3·105 pb-1
S  5000
B  20
• 2 isolated electrons with
pT > 20 GeV and || < 2.5
• minimum invariant mass
equal to 800 GeV
N(e+e-) bkg subtracted
Selection cuts:
cot  = 0.2
S  100
B8
Background:
Drell-Yan (qq  Z/  e+e- )
M(e+e-) (GeV)
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Little Higgs searches at LHC
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Discovery region for ZH
L = 3·105 pb-1
11
• (ZH) decreases as M increases
cot 
• (ZH)  (cot )2
BR(ZH
e+e-) drops for cot   0
• If ZH is found, cot  can be
S >5
B
extracted from (ZH) and (ZH)

= [ 3.4 (cot )2 +0.071 (cot 2)2] %
M
2
4
6
MZH (TeV)
J. E. Garcia
Little Higgs searches at LHC
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ZH  Zh
q
12
Z
ZH
  (cot  cot 2) 2
q
h
cot 2
cot 
(cot )
mh = 120 GeV
BR(h
bb) = 66 %
BR(h
) = 0.2 %
Ratio
(cot  = 0.5)
mh = 200 GeV
J. E. Garcia
BR(h
W+W-) = 74 %
BR(h
ZZ) = 26 %
0.5
Little Higgs searches at LHC
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ZH  Zh with h  bb
13
l+
ZH
1 TeV
l+
l-
Z
b
ZH
2 TeV
h
Z
l-
h
b
b
b
Cuts
Cuts
|| < 2.5 (jets and leptons)
PT(Z) > 250 GeV
PT(h) > 250 GeV
b-tagging
|| < 2.5 (jets and leptons)
PT(Z) > 500 GeV
PT(h) > 500 GeV
b-tagging
Background: Z + jets
J. E. Garcia
Little Higgs searches at LHC
Rencontres de Moriond – March 04
ZH  Zh signal
MZ H= 1 TeV
14
MZ H= 2 TeV
L = 3·105 pb-1
L = 3·105 pb-1
cot  = 0.5
Events
Events
cot  = 0.5
M(ZH) (GeV)
M(ZH) (GeV)
b-tag: b = 50%, Ru = 100
b-tag: b = 40%, Ru = 100
S = 195
B = 16
S = 15
B=8
Inside mass window:
J. E. Garcia
S
B
= 50
Inside mass window:
Little Higgs searches at LHC
S
B
=5
Rencontres de Moriond – March 04
WH / ZH  W/Z h
with
h  
15
MZH= MW = 1 TeV
H
j
L = 3·105 pb-1
cot  = 0.5
j
WH + ZH

1 TeV
h

WH
ZH
Bkg
Cuts
|()| < 2.5
PT() > 25 GeV
PT(h) > 400 GeV
-tagging, () = 80%
J. E. Garcia
S(WH  Wh) = 64
S(ZH  Zh) = 33
97
B(h inclusive) = 8
B( inclusive) = 5
13
Little Higgs searches at LHC
S
= 27
B
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Discovery region for VH
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VH to leptons
L = 3·105 pb-1
S/B > 5
N > 10
Z H  l+ l WH  l 
h(120)  bb
ZH  Zh  l+ l- bb
WH  Wh  l  bb
h(120)  
ZH  Zh  jets 
WH  Wh  jets 
M(VH) (TeV)
J. E. Garcia
Little Higgs searches at LHC
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New Higgs
• Production: VBF mechanism
q’
W+W+  ++  W+W+
1
W+
M() = 1.5 TeV
++
W+
q’2
Decay: ++  W+W+
v’ = 25 GeV
  (v’)2
Decay of ++ to leptons is
suppressed in this model
J. E. Garcia
M() = 2 TeV
Events
q2
17
L = 3·105 pb-1
(vector boson fusion)
q1
++
Little Higgs searches at LHC
SM
Rencontres de Moriond – March 04
++  W+W+
18
++  W+W+  l+l+
L = 3·105 pb-1
Bkg:
WWqq, WZ
WZqq, Wtt
Main cuts:
•
•
•
•
•
2 forward jets (E > 100 GeV)
2 leptons (charge +)
PT(lepton 1) > 150 GeV
PT(lepton 2) > 20 GeV
ET > 50 GeV
• mT > 500 GeV
mT () (GeV)
mT = (E(l1) + E(l2) + |pT|)2 + (p(l1) + p(l2) + pT)2
J. E. Garcia
Little Higgs searches at LHC
Rencontres de Moriond – March 04
Outlook and Summary
19
• Searches for the new particles predicted by Littlest Higgs model at
LHC have been performed. Heavy Top and new Gauge boson sector are
observable over a large range of parameter.
• “Toy” model used for the study severely constrained by electro-weak
measurements
• Little
Higgs
idea
is
realized
in
several
different
models:
SU(5)/SO(5),SU(6)/SP(6), Minimal moose SU(3)2/SU(3) and general mooses
SU(3)n/SU(3)k, etc. They have similar particle content and are less
constrained.
• More detailed information on the ATLAS searches can be found
in G. Azuelos et al., hep-ph/0402037
J. E. Garcia
Little Higgs searches at LHC
Rencontres de Moriond – March 04
XXXIXth Rencontres de Moriond
on behalf of ATLAS Collaboration
presented by: Jose E. Garcia (IFIC-Valencia)
The Littlest Higgs model
broken at scale   1 TeV
SU(5)
21
S0(5)
dim 24
dim 10
10 GB
24 - 10 = 14 massless
6 GB
Goldstone bosons
4 GB used
to give mass
to ZH, WH, AH
contains
0 , + , ++
mass through
radiative
corrections
4 GB used
to give mass

to Z,W, and h
U(1)
SU(2)U(1)
2
[SU(2)U(1)]
broken at scale
  1 TeV
J. E. Garcia
Standard model
broken at scale
  244 GeV
Little Higgs searches at LHC
QED
Rencontres de Moriond – March 04
The Littlest Higgs model
• Motivation :
electroweak
hierarchy and
fine-tuning problems
• Quadratic divergences :
SUSY :
Little Higgs :
22
bosons
gauge bosons
cancellations
quarks
Planck
fermions
new gauge bosons
new quarks
• Higgs fields :
electroweak
pseudo-Goldstone bosons
"light" mass
J. E. Garcia
Planck
symmetry
breaking
Little Higgs searches at LHC
Goldstone bosons
massless
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Corrections
2
mh =
3
2
8  2 2
2
2
2
23
2
(4mt – 2Mw – 4Mz – mh )
t
t
t
Minimum needed to cancel all loops
T
WH, ZH

J. E. Garcia
heavy top
new EW singlet
heavy gauge bosons
new SU(2)U(1) symmetry
heavy higgs bosons
many new Goldstone bosons
EW triplet (0 , + , ++)
Little Higgs searches at LHC
Rencontres de Moriond – March 04
Mass Range
Upper limits:
to avoid fine tuning scale
T
mh = 120 GeV
M < 0.2 TeV
mh = 200 GeV
M < 2 TeV
W± ,
H

J. E. Garcia
ZH, AH
mh = 120 GeV
M < 2.2 TeV
mh = 200 GeV
M < 6 TeV
24
f <
 mh 

1 TeV· 
200
GeV


2
2
M<2
TeV·  mh 
 200GeV 
2
M<6
 mh 
TeV· 

200
GeV


M < 10 TeV
Little Higgs searches at LHC
Rencontres de Moriond – March 04
Top quark sector
25
Little Higgs t and  will mix  standard top t, heavy top T
v = electroweak scale = 244 GeV
 = heavy scale  1 TeV
1, 2 = Yukawa couplings O(1)
2 can be eliminated using SM top mass
 = 1 TeV
 2 new free parameters, , 1
 > 1 TeV
(EW data!)
but if MT is too large  fine tuning
J. E. Garcia
Little Higgs searches at LHC
Rencontres de Moriond – March 04
Littlest Higgs: particle content and couplings
new particles
New constants:
weakness of
the model
J. E. Garcia
couplings
scale  and 1,
26
mass
, ’, ’
- No relations between these new constants
- AH couplings not fixed by the model
- EW data  ƒ  fine tuning
2 TeV < ƒ < 4 TeV
Little Higgs searches at LHC
Rencontres de Moriond – March 04
Expectations for ZH
M(ZH)  mW (f/v) [cot  + 1/cot ]
27
f = scale for new physics
v = Fermi scale (244 GeV)
Avoid fine tuning  M < 2.2 TeV
(assuming mh = 120 GeV)
M expected in 1-2 TeV
region with wide range
of cot  parameter.
Agree with EW data  f > 2 TeV
J. E. Garcia
Little Higgs searches at LHC
Rencontres de Moriond – March 04
b-tagging
MZ H= 1 TeV
< pT (b)> = 220 GeV
115
MZ H= 2 TeV
< pT (bb)> = 800 GeV
~ 100
0.5
J. E. Garcia
28
0.4
Little Higgs searches at LHC
Rencontres de Moriond – March 04
W ±h with h
WH±
l
±
WH
1 TeV
bb
29
MWH= 1 TeV
±

W±
b
h
120 GeV
b
Cuts
|| < 2.5
(jets and leptons)
assume  colinear to l for WH reconstruction
PT(Z) > 250 GeV
PT(h) > 250 GeV
b-tagging
Inside mass window:
Background: W + jet , tt
J. E. Garcia
b-tag: b = 50%, Ru = 100
S = 1499
B = 471
Little Higgs searches at LHC
S
B
= 69
Rencontres de Moriond – March 04
Deductions for AH
30
• theorical uncertainties (strong model-dependency) for AH
• can deduce limits on .BR(AH  Z h) from results for ZH (same decays)
• hypothesis : favorable cases where M(WH/ZH) and M(AH) are distant
for each M(AH) (resolution of M(WH/ZH) being 45  80 GeV)
 WH/ZH not background for AH
fb
.BR(AH  Z h) min.
region excluded
at 95 % CL
if we see nothing
• deduced only from study
ZH  Z h
with
h  
• can combine other studies
M(AH) (GeV)
J. E. Garcia
Little Higgs searches at LHC
Rencontres de Moriond – March 04