Jieun
Kim
( CMS Collaboration )
APCTP 2012
LHC Physics Workshop at Korea
(Aug. 7
-
9, 2012)
1
Contents
Theoretical Motivation
Search Strategy
Event Selections
Backgrounds
Sensitivity for SUSY models
Summary
2
Supersymmetrized
Standard
Model
between
Fermions
and
Bosons
with
unification
of
gauge
couplings
SUSY Dark Matter
Cosmologically
a
natural
dark
matter
(DM)
candidate
(
stable
neutralino
)
3
Supergravity
(
mSUGRA
or
C
MSSM) models,
the lightest
neutralino
is the stable LSP which escapes the
detector
0
1
~
stau
-
neutralino
co
-
annihilation processes may be sensitive to
the amount of dark matter relic density observed by the
Wilkinson Microwave Anisotropy Probe (WMAP)
4
SUSY signature
at the
LHC is involved with high
multiplicity of energetic
jets because
squark
and
gluino
pairs are dominant
at the
pp
collisions, a
large momentum
imbalance in the detector
(from LSP CDM candidate),
and the
Taus
in the
stau
-
neutralino
co
-
annihilation
region
SUSY
Signature
SUSY
Search @ LHC
Dark Matter Identity
5
In large tan beta,
Branch ratio to
taus
becoming dominant
~100%
pp
@√
s = 7TeV,
4.98
fb
-
1
of
data
6
Particle Flow Jets clustered from
identified particles reconstructed using
all detector components with Anti
-
Kt
(R=0.5) jet clustering algorithms
HT
=
scalar
sum of Jet
p
T
MHT
= negative
vector sum of Jet
p
T
Tau lepton
Reconstruction and Identification
Electromagnetic
strips with E
T
>1
GeV
for neutral
pions
combined with
PFJets
to
reconstruct the tau decay modes
Isolation: no charged hadrons with P
T
> 1.5
GeV
/
c
or photons with E
T
> 2.0
GeV
in
Δ
R
< 0.3
Muon
ID efficiency 72.8%, tau ID efficiency 64.1%
7
7
Single
Hadron + Zero Strips
Single Hadron + One (two) Strip
Single
Hadron + Two Strips
Three Hadrons
ρ
(770)
Z
→
τ
τ
→
μ
+
τ
h
(
one prong tau
)
μ
Pt
= 23.1
GeV
/c
η =
-
1.31
τ
Pt
= 36.8
GeV
/c
η = 0.03
Event Selections
8
Baseline Selections
:
2 Jets + MHT
•
≥1
PFJet
with
pT
> 30
GeV
/c
•
1st Leading Jet
pT
> 100
GeV
/c
and |η| < 3
•
2nd Leading Jet
pT
> 100
GeV
/c
and |η| < 3
•
MHT > 250
GeV
(with
plateau “HLT_PFMHT150”
)
Tau Selections
:
2
τ
h
•
≥ 2
τ
h
’s with
pT
> 15 GeV/c and |
η
| < 2.1
•
≥ 2
τ
h
’s
passing
the HPS ”tight”
μ
veto
•
≥ 2
τ
h
’s passing the HPS ”tight” e veto
•
≥ 2
τ
h
’s passing the HPS decay mode finding
•
≥ 2
τ
h
‘s passing the HPS ”very loose” isolation
Topological Selections:
•
1st Leading Jet separated from
th’s
(
Δ
R(j
1
,
τ
h
) > 0.3)
•
2nd Leading Jet separated from
th’s
(
Δ
R(j
2
,
τ
) > 0.3)
•
≥
1
t
h
t
h
pair with
Δ
R(
τ
h,1
,
τ
h,2
) >
0.3
•
Δφ
(j
2
, MHT) >
0.5
Backgrounds
9
Background Estimation
in data driven
D
efine
control samples which are selected with most of the
selections
similar
to those used in the main search but enriched with
events from the background
process
M
easure
selection efficiencies of
jet
-
>tau
mistag
rates in those
control
regions
E
xtrapolate
to the region where we expect to observe our signal.
Estimate following equation for each
background
(
ttbar
,
wjets
,
zjets
,
but except QCD) contribution
10
Probability
of
(0,1,2) jets faking
taus
Correction factor
Background
Control Samples
11
TTbar
12
T
wo types of events in
TTbar
control region:
1.
1 real
τ
h
+ 1 jet faking a
τ
2.
2 jets faking 2
τ
.
•
A
τ
+j
=
fraction
of
t
-
tbar
events
with 1 real
τ
h
and 1 jet.
•
A
j+j
=
fraction of t
-
tbar
events
with 2 jets
.
•
P(N) & P(M) are the probabilities to have N (M) jets that
can fake the
τ
in category (1) and (2).
•
f = “fake rate”
•
P(2b) = Probability of tagging 2
-
b
-
jets.
•
ε
τ
iso
=Tau isolation efficiency.
•
C(
N,n
) = N choose n.
WJets
13
Two types of events in
W+Jets
control
region:
1.
1
real
τ
h
+ 1 jet faking a
τ
.
2.
2
jets faking 2
taus
.
•
A
τ
+j
= fraction of
Wjet
events with 1 real
τ
h
and
1 jet faking
τ
•
A
j+j
= fraction of
Wjet
events with 2 jets faking
τ
’s
•
P(N) & P(M) are the probabilities to have N (M) jets
that
can fake the
τ
in category (1) and (2
)
•
f = “fake rate”
•
P(0b) = Probability of tagging zero jets as b
-
jets.
•
ε
τ
iso
=Tau isolation efficiency.
•
C(
N,n
) = N choose n.
Invisible Z + Jets
14
•
A
μ
=
μ
acceptance efficiency.
•
ɛ
μ
=
μ
ID efficiency.
•
B(Z
νν
) = branching ratio for Z
νν
•
B(Z
μμ
) = branching ratio for Z
μμ
•
ɛ
Trigger
MHT
= efficiency of
HLT_PFMHT150 (plateau)
•
ε
Trigger
μτ
= efficiency of
μτ
cross
-
trigger.
•
ɛ
MHT
= efficiency of MHT (>250)
•
P(N) is the probability to have N jets that can fake
the
τ
in category (1) and (2).
•
f = “fake rate”
•
C(
N,n
) = N choose n.
15
•
A
μ
=
μ
acceptance efficiency.
•
ɛ
μ
=
μ
ID efficiency.
•
B(Z
νν
) = branching ratio for Z
νν
•
B(Z
μμ
) = branching ratio for Z
μμ
•
B(
τ
τ
h
) = branching ratio for
hadronic
τ
decay
•
ɛ
Trigger
MHT
= efficiency of
HLT_PFMHT150 (plateau)
•
ε
Trigger
μτ
= efficiency of
μτ
cross
-
trigger.
•
ɛ
MHT
= efficiency of MHT (>250)
•
P(N) & P(M) are the probabilities to have N (or M) jets that can fake
τ
•
f = “fake rate”
•
C(
N,n
) = N choose n.
Z
-
>tau
tau
+ Jets
QCD
multijets
16
For
QCD contribution, obtain a data
-
MC scale factor (SF
QCD
)
Search for New Physics
17
)
540
(
1
J
)
424
(
2
J
)
21
(
2
)
117
(
1
)
72
(
3
J
)
68
(
4
J
)
540
(
1
J
)
424
(
2
J
)
72
(
3
J
)
68
(
4
J
)
117
(
1
The Highest H
T
Event
18
19
Sensitivity
in SUSY models
Supergravity
models (
mSUGRA
/CMSSM)
Simplified Model Scenarios (SMS)
Gauge Mediated
Supersymmetry
Breaking
Models (GMSB)
20
•
tan
β
= 40,
A
o
= 500
GeV
,
μ
> 0,
M
top
= 173.8
GeV
•
Gaugino
mass
of <
495
GeV
@
95%
C.L.
•
Gluino
mass
<
1.15
TeV
@
95%
C.L
.
CMSSM /
mSUGRA
21
W
ith Single Tau :
Better sensitivity in the case of very small ∆M (~5GeV) in
the co
-
annihilation region, the low energy tau can’t be eff
ectively detected and only the energetic tau from the dec
ay of the
neutralino
can be observed
CMSSM /
mSUGRA
22
SMS
23
Gluino
mass
< 775
GeV
@
95%
C.L.
for LSP mass
up to 325
GeV
GMSB
24
Gluino
mass < 900
GeV
@ 95% C.L.
Summary
SUSY (R
-
parity conserved) search results with up to
~
5
/
fb
of
data, observed no
significant excess.
SM
background estimations done with data driven methods.
Setting
the 95% exclusion
limits on
the constrained MSSM
models, SUSY Simplified model, and GMSB.
Limits on
Gluino
mass reach to ~
TeV
with the 2011 data of
pp
@√s =
7TeV
25
Systematic Uncertainty
26
27
The Highest H
T
Event
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