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[GeV] HM100 200 300 400 500 1000
H+X
) [pb
]
A(p
p m
-210
-110
1
10= 7 TeVs
LHC
HIG
GS
XS W
G 2
010
H (NNLO+NNLL QCD + NLO EW)
App
qqH (NNLO QCD + NLO EW)
App
WH (NNLO QCD + NLO EW)
App
ZH (NNLO QCD +NLO EW)
App
ttH (NLO QCD)
App
Signature
Search Window
Event Selection
Background Estimation
[GeV]H m200 250 300 350 400 450 500 550 600
SMm/
m 9
5% C
.L. l
imit
on
0
5
10
15
20
25ObservedExpected
m 1±m 2±
ATLAS Preliminary
=7TeVs, -1Ldt=1.04fb0llqqAZZAH
H→ZZ→llqqone lepton pair + 2 jets
Main Background:Z+jets productionttbar/di-boson ‣ non-negligible in “tagged” case
200 GeV ≤ mH ≤ 600 GeV ‣ Optimized: high/low mass sub-region(mH≥300GeV) ‣ Binned: “tagged” (2 b-tags) & “un-tagged” (0/1 b-tags)
Same-flavour pair of isolated high pT leptons: ‣ pT > 20 GeV, 76 GeV < mll < 106 GeVVeto on 3rd lepton.At least 2 jets: ‣ pT > 25GeV, |η|<2.5, with 70< mjj <105 GeVMET<50 GeV“High-mass”: pT(jets) > 50 GeV, Δφll<π/2, Δφjj<π/2Final discriminant:lljj invariant mass (mjj scaled to mZ)
Normalize Z+jets using the sidebands of mjj: ‣ uncertainty <10% for un-tagged ‣ uncertainty ~20% for tagged
Verify top expectation using sidebands of mll: ‣ uncertainty 10% from theory
Di-boson backgrounds from MC: ‣ uncertainty ~10%
Data-Driven QCD background: ‣ small contributions ‣ ee : QCD background templates ‣ μμ: 2D sideband using isolation and invariant mass of the pair
Good sensitivity in a wide mass range.Expected limit:
2.7 - 9 ×σSM.Observed Limit :
1.7 x σSM at mH = 360 GeV.
un-tagged
tagged
Sidebands of mjj(40,70 GeV) & (105, 150 GeV)
Sidebands of mll(60,76 GeV) & (106, 150 GeV)
Background Control Region: Signature
Search Window
Event Selection
Background Estimation
H→ZZ→llννone lepton pair + MET
Main backgrounds:top and di-boson productionSignal contributions from H→WW→lvlvOrthogonal to H→WW→lvlv search
200 GeV ≤ mH ≤ 600 GeV
Same-flavour opposite-sign pair of isolated high pT leptons.Veto on 3rd lepton & b-jet.MET > 66 GeV (“High-mass” MET > 82 GeV)Δφ(Leading Jet,MET)>0.3, for “High-mass” also Δφ(Z,MET)>1→1<Δφll<2.64 (“High-mass” Δφll<2.25).Final discriminant is the transverse mass:
Di-boson backgrounds from MC ‣ uncertainty ~10%
Top background ‣ MC expectation verified with data
Data-driven W+jets background ‣ taken for same-sign lepton pairs
Data-driven QCD background ‣ generally small contributions
m2T ⌘
qm2
Z + |~P llT |2 +
qm2
Z + |~PmissT |2
�2�h~P llT + ~Pmiss
T
i2 Sensitive in a wide mass range.Expected limit :
1.2 - 7 ×σSMExclude SM Higgs :
340 < mH< 460 GeV
Standard Model H→ZZ(*)→llqq,llνν,llll Searches with ATLAS at LHCRyan R. Rios, Southern Methodist University .
on behalf of the ATLAS CollaborationOverview:The latest results on the direct experimental search for a Standard Model Higgs boson decaying to a pair of Z bosons are presented.Three distinct final state modes are considered: H→ZZ(*)→llll, H→ZZ→llνν, and H→ZZ→llqq, where l=e,μ. These modes are characterized by low branching ratios with small background contributions. Additionally, the presence of at least one on-shell Z boson ensures clean final states.A dataset of more than 1fb-1 of pp collisions at √s=7 TeV collected by the ATLAS detector at the CERN LHC during the on-going 2011 run is used.
Signature
Search Window
Event Selection
Background Estimation
H→ZZ(*)→lllltwo leptons pairs
Main Backgrounds:ZZ→4lZ+jets/ttbar ‣ suppressed with isolation/impact parameter
110 GeV ≤ mH ≤ 600 GeV
Two same-flavour/opposite-sign isolated lepton (e/μ) pairs.Lepton pair mass cuts : |m12-mZ| < 15 GeV, m34 < 115GeV and m34>mThreshold[m4l].
For m4l < 190 GeV: ‣ additional impact parameter requirements.
Normalize ZZ production to MC expectation ‣ Including both qq/gq→ZZ and gg→ZZ ‣ Integrated luminosity uncertainty 3.7% ‣ Theory uncertainty 15%
Normalize top production to MC expectation ‣ Verified in control region ‣ Theory normalization uncertainty 10%
Normalize Z+jets production using control regions ‣ Z(→ll) + μμ/ee (no isolation/impact parameter requirements) → separate components (heavy flavour, fakes, electroweak) → extrapolated to signal region; uncertainties 20 - 40%
Sensitive for low and high masses.Expected limit :
≥1.05×σSMExclude SM Higgs :
192 < mH < 196 GeV214 < mH < 222 GeV
un-tagged
Candidate event with a Z decay to muon pairs,
recoiling against missing-ET. The muon candidates have transverse momenta of 50 and 126 GeV and a dimuon invariant mass of 94 GeV; the missing ET is measured to be 161 GeV.
Candidate event with 4μ.m12 : 90.6 GeVm34 : 47.5 GeVm4μ : 143.6 GeV
Summary: ‣ H→ZZ(*)→llll covers a large mass range from 110 to 600 GeV. ‣ H→ZZ →llνν and →llqq complement the H→ZZ(*)→llll channel by substantially improving the sensitivity in the high mass region above 200 GeV. ‣ The combined exclusion region of the 3 channels, H→ZZ(*)→llll, llqq and llνν, is:⇢192 < mH < 196 GeV, 214 < mH < 222 GeV, and 340 < mH < 460 GeV.
‣ H→ZZ(*) searches are supplemented by searches in the other decay channels such as H→WW, bb, ττ, γγ. When combined altogether, the excluded mass range extends to:⇢146 < mH < 232 GeV, 256 < mH < 282 GeV, and 296 < mH < 466 GeV.
Background Control Region:
[GeV]missTE
0 50 100 150 200 250 300
Even
ts /
20 G
eV
-110
1
10
210
310
410
510
[GeV]missTE
0 50 100 150 200 250 300
Even
ts /
20 G
eV
-110
1
10
210
310
410
510 -1 L dt=1.04 fb0Data Total BGTopZZ,WZ,WWZWMultijet
ATLAS Preliminary events µµ+µlike-sign ee+e
[GeV]missTE
0 50 100 150 200 250 300
Even
ts /
20 G
eV
-110
1
10
210
310
[GeV]missTE
0 50 100 150 200 250 300
Even
ts /
20 G
eV
-110
1
10
210
310
-1 L dt=1.04 fb0Data Total BGTopZZ,WZ,WWZWMultijet
ATLAS Preliminaryii llAH
[GeV]missTE
0 50 100 150 200 250 300
Even
ts /
20 G
eV
-110
1
10
210
310
410
[GeV]missTE
0 50 100 150 200 250 300
Even
ts /
20 G
eV
-110
1
10
210
310
410 -1 L dt=1.04 fb0Data Total BGTopZZ,WZ,WWZWMultijet
ATLAS Preliminary eventsµe
W+jets, same-sign lepton pairs (60, 150 GeV)
top eμ
top mll sidebands with b-tags(60, 150 GeV) not in mZ window
η distribution of the lepton candidates surviving selection criteria in data and MC.
pT distributions of the lepton candidates surviving selection criteria in data and MC.
Scatter plot of the invariant mass of leading and sub-leading di-lepton pair candidates (m12 and m34) surviving selection criteria in
data and MC.
4l invariant mass of candidates surviving selection criteria in data and MC.
[GeV]lljj m100 200 300 400 500 600 700 800 900
Eve
nts
/ 25
GeV
020406080
100120140160180200
[GeV]lljj m100 200 300 400 500 600 700 800 900
Eve
nts
/ 25
GeV
020406080
100120140160180200
[GeV]lljj m100 200 300 400 500 600 700 800 900
Eve
nts
/ 25
GeV
020406080
100120140160180200
-1 L dt=1.04 fb0data 20×Signal
=400 GeV)H
(mTotal BGZtopDiboson
ATLAS Preliminaryun-tagged
M4` [GeV] 120 130 140 150 160 165 180 190 >200M
threshold
[GeV] 15 20 25 30 30 35 40 50 60
tagged
tagged
lljj invariant mass of candidates surviving un-tagged (above) and tagged (below) selection criteria.
ll inv
arian
t mas
s fo
r eve
nts
with
≥ 2
b-
tagg
ed je
ts a
nd M
ET <
50
GeV
invar
iant m
ass
of s
elect
ed d
ijet p
airs
afte
r tag
ged
selec
tion
in da
ta a
nd M
C.
tagged
Di-lepton invariant mass for events with exactly two oppositely charged electrons or muons.
Δφll for events with exactly two oppositely charged electrons or muons and after mass window cut.
MET of events with exactly two oppositely charged electrons or muons.
Di-lepton invariant mass distribution of selected
candidates surviving selection criteria in data and MC.
[GeV]HM100 200 300 400 500
BR
[pb]
× m
-410
-310
-210
-110
1
10
LHC
HIG
GS
XS W
G 2
011
SM = 7TeVs
µl = e, oi,µi,ei = i
q = udscbbbi± lAWH
bb-l+ lAZH
-o+o AVBF H aa
qqi± lAWW
i-li+ lAWW
qq-l+ lAZZ
ii-l+ lAZZ
-l+l-l+ lAZZ
Relatively low branching ratios, especially for llll.H→ZZ final states: ‣ llqq ‣ llνν ‣ llll
Standard Model Higgs Production σ×BR
g
g
tH
Z *
Z
l
l
l/q/!
l/q/!
( )
•ggF - dominant contribution.•VBF - relatively small contribution
that increases with mH.
Standard Model Higgs Production Cross Sections
un-tagged
un-tagged
tagged
Day in 201102/03 31/03 29/04 28/05 26/06 25/07 24/08
]-1To
tal I
nteg
rate
d Lu
min
osity
[fb
0
0.5
1
1.5
2
2.5
3
3.5
Day in 201102/03 31/03 29/04 28/05 26/06 25/07 24/08
]-1To
tal I
nteg
rate
d Lu
min
osity
[fb
0
0.5
1
1.5
2
2.5
3
3.5 = 7 TeVs ATLAS Online Luminosity
LHC Delivered
ATLAS Recorded
-1Total Delivered: 2.68 fb-1Total Recorded: 2.55 fb
ATLAS - A Toroidal LHC ApparatusATLAS - A Toroidal LHC Apparatus
Tracking ‣ Pixel, Silicon detector, Transition Radiation Tracker; in a solenoidal magnetic field
Calorimetry‣ Liquid Argon + Scintillators
Muon Spectrometer‣ Cathode Strip Chambers, Monitored Drift Tubes, Resistive Plate Chambers, and Thin Gap Chambers; in a toroidal magnetic field
Trigger‣ A complex trigger system determines the events that are recorded, 3 levels. → Level 1 has a < 2.5 μs decision time
Magnets‣ 2T solenoid and 3 air-core toroids
More than 2.55fb-1 of data collected!Data taking efficiency: ~96%
Tracking ‣ Pixel, Silicon detector, Transition Radiation Tracker; in a solenoidal magnetic field
Calorimetry‣ Liquid Argon + Scintillators
Muon Spectrometer‣ Cathode Strip Chambers, Monitored Drift Tubes, Resistive Plate Chambers, and Thin Gap Chambers; in a toroidal magnetic field
Trigger‣ A complex trigger system determines the events that are recorded, 3 levels. → Level 1 has a < 2.5 μs decision time
Magnets‣ 2T solenoid and 3 air-core toroids