pptx

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