Top physics and the top mass
Lecture 3/3
2013 CERN-Fermilab HCP Summer School
Prof Dr Freya Blekman
Interuniversity Institute for High Energies
Vrije Universiteit Brussel, Belgium
(and this year also: LHC Physics Centre, Fermilab) Outline
•  Wednesday:
–  Lecture 1: Intro to top physics and its jargon. •  Thursday:
–  Lecture 2: SM top physics and the top mass
•  Friday:
–  Lecture 3: SM and top physics, the portal to physics searches
•  Measuring top properties
•  Searches for physics beyond the standard model using tops
2
Freya Blekman (IIHE-VUB)
Top quark and new physics
•  Precise SM measurements
–  Heaviest known elementary particle
(large Yukawa coupling)
•  Constraints on Higgs mass
•  Unique window on bare quarks due to
short lifetime
()
–  Probe for QCD at scale >gauge bosons
•  A window to new physics
–  New physics - many models couple
preferentially to top
–  New particles may decay to top –  Non-standard couplings
•  In many new physics scenarios (e.g.
SUSY) top is dominant BG
•  Great tool to calibrate detector
–  Jet energy scale, b-jet efficiency
Top pair production rate
Top mass
Single top production rate
B(t→Wb)
|Vtb|
W helicity
Top polarization
Anomalous couplings
Spin correlations
Rare decays
Top width
…
3
Freya Blekman (IIHE-VUB)
Properties of top pair production
Differential Cross Section
1/ σtt dσtt/dy
tt
• Enough data to
•  Very large LHC samples
data
NLO (MCFM)
make a large
1 ∫
ALPGEN
allow differential
cross
MC@NLO
set
of
differential
section measurements
cross-section
•  Most bins
limited by
measurements.
systematic
uncertainties
10
Top
•  Many
• differential
Vs. kinematics of
1.2
1
kinematics
examined
- tt̄ system
-3
-2
-1
0
1
2
3
y
• Study
additional
•  Active-interaction
top quark with
jets to test QCD
generator
and
pdf
- decay products
and MC generators.
community
• Good agreement
•  Improvement
of models • Extensive list of
with
generators
of great
benefit
to
quantities probed.
tested.
community
for next LHC
run •– particularly
for
→ ISR/FSR variations
Most bins are
searches
reduced.
ATLAS
L dt = 2.05 fb
-1
Theory/Data
-1
Pair Production in Associat
Eur.Phys.J. C (2013) 72:2043
CMS-PAS-TOP-12-041
ATL-P
ATLAS
tt
systematics
limited.
Eur. Phys. J. C (2013) 73:2261, CMS-PAS-TOP-12-027, CMS-PAS-TOP-12-028
S ARA S TRANDBERG , S TOCKHOLM U NIVERSITY
P. 7
4
EPSHEP 2013, S TOCKHOLM , J ULY 22, 2013
Freya Blekman (IIHE-VUB)
Top Pair Production in Association with Z, W and γ
SM production of ttbar+Z/photon/W
Phys. Rev. Lett. 110 (2013) 172002
Dilepton analysis tt̄V (V = W, Z)
Trilepton analysis tt̄Z
ATLAS-CONF-2012-126
3.0σ
a.u.
# γ / bin
3.3σ
-1
ATLAS Preliminary
40
tt̄γ
ATLAS-CONF-2011-153
e+jets
data
ttγ
non-tt bkg
bkg ttγ
electron fakes
hadron fakes
∫ L dt = 1.04 fb
50
7 TeV
30
2
7 TeV
background only
p-value = 0.71 %
2.7σ
1
20
∫ L dt = 1.04 fb
10
0
0
-1
ATLAS Preliminary
2
4
6
8
10
12
14
16
18
pcone20
T
20
0
0
50
100
[GeV]
σtt̄γ (pγT > 8 GeV) = 2.0 ± 0.5 (stat) ± 0.7 (syst) ± 0.08 (lumi) pb
150
200
250
number of observed events
SM prediction = 2.1 ± 0.4 pb (LO + LO→NLO k-factor)
S ARA S TRANDBERG , S TOCKHOLM U NIVERSITY
P. 9
EPSHEP 2013, S TOCKHOLM , J ULY 22, 2013
5
Freya Blekman (IIHE-VUB)
TOP
IONPRODUCTION
different PDF contribution
only virtual q in pp
PRODUCTION
Single top production
different PDF contribution
Tevatron
LHC
•  Single top in t-channel
•  Single top in tW-channel
single top production
Observatio
2.
SINGLE
TOP
PRODUCTION
First observation
2. SINGLE TOP PRODUCTION
t-channel Production
production:
tW-channel
t-channel
2
ATLAS-CONF-2012-056,
ATLAS-CONF-2012-132
t-channel
ion
V
tb
on and EWK top
σ [pb]
polarization and ATLAS
EWKPreliminary
top
t-channel single top
± 13 pb
n
8TeV
σt
mena:
top+antitop
=s-channel
95 ± 18 pb
data
t -channel
t t ,Wt,s-channel
W +heavy flavour
W +light jets
Z +jets, diboson
0.22 pb
LHC pp (7 TeV)
4.63 pb
64.6 pb
15.7 pb
LHC pp (8 TeV)
5.55 pb
LHC
87.1 pb
Tevatron pp (1.96 TeV)
pp22.2
(7100
TeV)
pb
LHC pp (8 TeV)
antitop
80
1
4
ATLAS
∫ L dt = 2.05
s = 7 Te
3
60
Dilepton 1
Moriond / EW , 2-9 Mar 2013, La Thuile, Valle 40
d'Aosta (Italy)
C. Battilana (CIEMAT)
Theory (approx. NNLO)
1.04 fb-1 arXiv:1205.3130
4.7 fb-1 ATLAS-CONF-2012-056
20
5.8 fb-1 ATLAS-CONF-2012-132
9
10
11
12
13
0-1
14
CM energy [TeV]
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etron:
methods
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ees,
matrix orelement
:
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multivariatemethod)
method
∫
Signal background discrimination:
or multivariate
method 0.22 pb
2.08 pb
L dt = 5.8 fb-1 s=8 TeV
2.08 pb
s-channel
Moriond
/ EW , 2-9 Mar 2013, La Thuile, Valle d'Aosta (Italy)
ds (neural networks, boosted
trix
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s Welement
tb couplings
mination:
ackground
discrimination:
5
6
7
8
variate method
TLAS Preliminary
jets SR
1.05 pb
top
2
10
SM phenomena:
C. Battilana (CIEMAT)
ation
plings
:
uplings
tW-channel
Tevatron pp (1.96 TeV)
Events / 0.03
top
of production:
single top
6.0 S.D. significance!
• First observation
of W t 23.4±5.5 pb
• Evidence
Cross
section:
s-channel
t-channel
tW-channel
sCollider
production
byσtbCMS. σtqb Collider
σtW
σ = 23.4+5.5
−5.4 pb
significance
Freya Blekman 6.0σ
(IIHE-VUB)
Tevatron: multivariate methods (neural networks, boostedCMS-PAS-TOP-12-040
-0.8 -0
σ = 16.8 ± 2
6
3.3σ
Phys. Le
Single top in s-channel
Observation of single top production:
Evidence for s-channel
Production tW-channe
2
t-channel
cross section Vtb
study top-polarization and EWK top
•  Tevatron legacy?
•interaction
First evidence of s-channel production by D0.
s
•  Cross section: 1.10+0.33-0.31 pb
+0.33
• σ(pp̄
→ tb 1.06±0.04
+ X)
= 1.10pb
−0.31 pb
Test
of
non-SM
phenomena:
•
(A)NNLO:
couplings
4th generation
•  →
Significance:
3.7 S.D.!!!
3.7σ significance.
Yield [Events/0.04]
FCNC couplings
W50, H
-1
(b)
DØ
9.7
fb
anomalous
Wtb couplings
Data
background
discrimination:
40
tb
tqb
W+jets
Z+jets/Diboson
tt
Multijets
s-channel
tqb cross section [pb]
henomena:
DØ 9.7 fb-1
(a)
C.5Battilana (CIEMAT)
1 SD
2 SD
3 SD
4
3
Tevatron: multivariate
methods (neural networks, boosted
30
decision trees, matrix element method)
2
20
Signal background discrimination:
LHC:
cut-based or multivariate method
on:
10
0
Moriond / EW , 2
Measurement
SM
Four generations
Top-flavor
Tevatron: multivariate 1methods (neural networks,
boosted
Top pion
decision trees, matrix element FCNC
method)
0
0.8 LHC:0.9
1
cut-based
or
method
0 multivariate
1
2
3
4
5
0.7
Ranked s-channel discriminant
1.05 pb
S ARA
S TRANDBERG
, S TOCKHOLM U NIVERSITY
ür Experimentelle
Kernphysik,
KIT
tb cross section [pb]
2.08 pb
0.22 pb
arXiv:1307.0731 [hep-ex], submitted to Phys. Lett. B
661.05
pb pb
Freya Blekman (IIHE-VUB)
P. 13
2.08 pb
7
EPSHEP 2013, SICHEP
TOCKHOLM
, J ULY
22, 2013
2012,
Melbourne
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ng the strength
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arXiv:1205.2484
and ±right-handed
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This paper describes measurements
and Aleft,
0.006 [4].
− = −0.841
of the W boson po
ons or the angular
asymmetries.
In the presence of anomalous
tb couplings14
the helicity
fractions
angular
asymmeL. Masetti - W
19/07/13
Intrinsic
top
quarkand
properties
in
ATLAS
R=0.0009
and
the
constraints
on
the
W tbFvertex
structure based on
This paper tries
describes
measurements
of
the
W
boson
polarization
in
top
quark
decays
depart from their Standard Model values [5, 10]. In effective field theories, dimensionATLAS
detector
between March and June 2011 and corre
the constraints
on
the
W
tb
vertex
structure
based
on
a
data
set
recorded
with
the
rangian:
six operators can be introduced which modify the W tb vertex [11–13]. −1
Coefficients con8
polar angle between the momentum vector of the charged lepton (or d, s
quark) and the negative momentum direction of the b quark.
The normalized angular functions wi (q ) (i = 0,
of the different helicity states:
, +) reflect the angular dependence
3
sin2 q ,
4
3
w (q ) =
(1 cos q )2 ,
8
3
w+ ( q ) =
(1 + cos q )2 .
8
w0 ( q ) =
(2.34)
(2.35)
(2.36)
By using the helicity fractions f i introduced previously, Eq. 2.33 can be rewritten in
the following form:
w (q ) =
3
(1
4
3
cos2 q ) f 0 + (1
8
3
cos q )2 f + (1 + cos q )2 f + .
8
(2.37)
The fraction of W bosons with longitudinal polarization, f 0 , is given by [23, 24, 25]:
minosity
of
1.04
fb
helicity fractions were measured
Freya
Blekman
(IIHE-VUB)
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the helicity
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)
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,
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o
, FR = 0.0017 ± 0.0001(1.2)
±
[4].
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arization
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angle
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R 10]. In the Standard Model, the NNLO values for these
Figureand
2.5: Definition
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h
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ang
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ractions
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polar±
angle
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and A− = −0.841
0.006
[4].
quark) and the negative momentum direction
of the b quark.
∗ > z)[6–8]
∗Tevatron,
complementary
quark,
both
boosted
into
the
W
boson
rest
frame
[5].
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angular
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laborations
at
the
are
in
agreement
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Standard
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predictions.
N
(cos
θ
−
N
(cos
θ
<
z)
r these asymmetries are A
=
0.537±0.004
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and
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channels,
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+
In the, presence of anomalous
W tb couplings the hel
(1.2)
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) FAL +
(110].
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as
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A
,
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∗
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cos θ asymme4
8
8
the
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3
owing the dependence six
on Foperators
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can
be
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modify
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W
L and FR to
w0 (q ) ∗= which
sin2 q ,
∗ >
N
(cos
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N
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θ
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previous
measurements
of
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helicity
fractions,
performed
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4
,to10].
In
effective
field
theories,
dimensionwith
z
=
±(1
−
,
A
=
3
±simple
the helicity fractions
by
a
system
of
equations
[9,
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S ARA S TRANDBERG , S TOCKHOLM U NIVERSITY
P. 35
EPSHEP 2013, S TOCKHOLM , J ULY 22, 2013 12
Freya Blekman (IIHE-VUB)
.,
Asymmetry at the LHC?
t. ,
syst.:
p
Tyler Dorland
15
7 / 25
13
Freya Blekman (IIHE-VUB)
17 SM parameters do not constrain creativity
•
SUSY in all it’s variations
–
–
•
•
GMSB
MSSM, CMSSM etc
New strong interactions?
–  Technicolor; excited quarks; compositeness;
new “contact” interactions
Exotica:
–  Weird stuff: leptoquarks?
–  New “forces”?
–  New resonances (W-Z-like)
–  More generations?
•
•
•
Fourth generation (b’/t’)
–  Gravity descending at the TeV scale?
–  New resonances; missing stuff; black holes;
SUSY-like signatures [Universal Extra
dimensions]
SUSY-inspired exotica:
–  Long-lived massive (new) particles?
Some true inspirations: “hidden valleys”?
src: H.Murayama 14
Freya Blekman (IIHE-VUB)
Little Hierarchy problem, Naturalness
t
Z
mHiggs
126 GeV
W
BSM?
15
Freya Blekman (IIHE-VUB)
Little Hierarchy problem, Naturalness
t
Z
Motivation
W
Motivation
mHiggs
126 GeV
The CMS and ATLAS collaborations have observed a new boson
with mass ~125 GeV
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their mass from other SM particles:
●
The CMS and ATLAS collaborations
have observed a new boson
with mass ~125 GeV
●
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their
● mass from other SM particles:
●
BSM?
Restricting fine tuning to the 10% level requires new physics which
cuts off these divergent contributions [1]:
●
David Sperka: Search for t+b resonances with the CMS experiment
3
Restricting fine tuning to the 10% level requires new physics which
cuts off these divergent contributions [1]:
●
Freya Blekman (IIHE-VUB)
16
Little Hierarchy problem, Naturalness
t
Z
Motivation
W
Motivation
mHiggs
126 GeV
The CMS and ATLAS collaborations have observed a new boson
with mass ~125 GeV
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their mass from other SM particles:
Motivation
●
The CMS and ATLAS collaborations
have observed a new boson
with mass ~125 GeV
●
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their
● mass from other SM particles:
●
BSM?
The CMS and ATLAS collaborations have observed a new boson
with mass ~125 GeV
●
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their mass from other SM particles:
●
Restricting fine tuning to the 10% level requires new physics which
cuts off these divergent contributions [1]:
●
?
?
David Sperka: Search for t+b resonances with the CMS experiment
3
Restricting fine tuning to the 10% level requires new physics which
cuts off these divergent contributions [1]:
Restricting fine tuning to the 10%●level requires new physics which
cuts off these divergent contributions [1]:
●
Freya Blekman (IIHE-VUB)
David Sperka: Search for t+b resonances with the CMS experiment
3
17
Little Hierarchy problem, Naturalness
t
Z
mHiggs
126 GeV
W
BSM?
If fine tuning <=10%:
Restrictions:
Λquarks ~< 2 TeV
Λgauge ~< 5 TeV
18
Freya Blekman (IIHE-VUB)
Little Hierarchy problem, Naturalness
t
Z
Motivation
W
Motivation
mHiggs
126 GeV
The CMS and ATLAS collaborations have observed a new boson
with mass ~125 GeV
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their mass from other SM particles:
Motivation
●
The CMS and ATLAS collaborations
have observed a new boson
with mass ~125 GeV
●
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their
● mass from other SM particles:
●
BSM?
The CMS and ATLAS collaborations have observed a new boson
with mass ~125 GeV
●
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their mass from other SM particles:
●
Restricting fine tuning to the 10% level requires new physics which
cuts off these divergent contributions [1]:
●
Susy
Susy
David Sperka: Search for t+b resonances with the CMS experiment
3
Restricting fine tuning to the 10% level requires new physics which
cuts off these divergent contributions [1]:
Restricting fine tuning to the 10%●level requires new physics which
cuts off these divergent contributions [1]:
●
Freya Blekman (IIHE-VUB)
David Sperka: Search for t+b resonances with the CMS experiment
3
19
Supersymmetry - in top sector?
What%does%SUSY%do%to%solve%ques@ons%beyond%the%SM?*
•  Solves hierarchy
problem,
• *Solves*the*hierarchy*problem*
GUT convergence and can
• *Convergence*of*the*coupling*constants*
add CP violation
• *Can*provide*more*CP*violaJon*
• *Plausible*Dark*MaXer*candidate*in**
•  Dark Matter candidates
*models*with*Rcparity*conservaJon*
available The*“Best”*candidate*for*dark*maXer*is*the*lightest*neutralino:**
•  Naturalness motivations can
be interpreted to favor light
stop SUSY*&*ExoJcs*
N˜ 1 ( χ˜10 )
€
HASCO*2012*
& many more
70*
–  ttbar+MET, ttbar+X+MET
signatures
20
Freya Blekman (IIHE-VUB)
Example stop search in l+jets+MET
•  ATLAS-CONF-2013-037
•  requires detailed understanding of
top quark pair production at high
missing ET –  Analysis works in many signal regions,
looking in boxes constrained by number
of b-tags, transverse mass, MET, etc
–  Sensitivity for stop depends on scenario
considered, each region has strengths/
weaknesses
–  Strong limits on stop mass
One signal
region
•  Can exclude direct stop production with
masses lower than 600 GeV (with some
caveats on neutralino mass, etc)
21
Freya Blekman (IIHE-VUB)
Little Hierarchy problem, Naturalness
t
Z
Motivation
W
Motivation
mHiggs
126 GeV
The CMS and ATLAS collaborations have observed a new boson
with mass ~125 GeV
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their mass from other SM particles:
Motivation
●
The CMS and ATLAS collaborations
have observed a new boson
with mass ~125 GeV
●
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their
● mass from other SM particles:
●
BSM?
The CMS and ATLAS collaborations have observed a new boson
with mass ~125 GeV
●
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their mass from other SM particles:
●
Restricting fine tuning to the 10% level requires new physics which
cuts off these divergent contributions [1]:
●
W’
Z’
David Sperka: Search for t+b resonances with the CMS experiment
3
Restricting fine tuning to the 10% level requires new physics which
cuts off these divergent contributions [1]:
Restricting fine tuning to the 10%●level requires new physics which
cuts off these divergent contributions [1]:
●
Freya Blekman (IIHE-VUB)
David Sperka: Search for t+b resonances with the CMS experiment
3
22
of
uction:
single top production:
t-channel
on Vtb2
WK
olarization
top
and EWK top
W
W’ to tb
tW-channel
t-channel
W’
s-channe
Colli
σtb
Collider
tW-channel
Tevatron pp (1.96 TeV)Tevatron
1.05 pp
pb
LHC pp (7 TeV)
LHC
4.63pp
pb
LHC pp (8 TeV)
LHC
5.55pp
pb
M phenomena:
•  analogue s-channel
to single top s- s-channel
tion
channel production
Moriond
La Thuile,
/ EW ,Valle
2-9 Mar
d'Aosta
2013,
(Italy)
La Thuile, Va
plings C. Battilana (CIEMAT) C. Battilana (CIEMAT) Moriond / EW , 2-9 Mar 2013,
•  Leptonic top decay:
–  Final state of lepton+MET+2 b
Wtb couplings jets
mination:
•  (neural
Mass
reconstruction
also
ral
methods
networks,
boosted
networks, boosted
used in SM top physics, using
ment
es, matrix
method)
element method)
W boson
mass to constrain
nd
ignal
discrimination:
background
discrimination:
or
method
multivariate
MET
method
•  Interpret in left and
right handed W’
scenarios
ultivariate
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methods
multivariate
(neural networks,
methods (neural
boosted
networks,
boosted
–  decision
With element
additional
top
mass element method)
ecision trees, matrix
trees,method)
matrix
constraint
ut-based
LHC:or multivariate
cut-based
method
or multivariate method
b.08 pb
2.08 pb
0.22 pb
0.22 pb
Freya Blekman (IIHE-VUB)
src: B2G-12-010 PAS
23
Motivation
Investigating ttbar invariant mass distribution
•  Differential cross sections now
Many new physics models which explain the light
available for 8 TeV sub-set ggs mass introduce new particles which cancel
•  Searches
tails
of distributions
e divergences
of the in
top,
gauge,
and self-coupling
ops
ongoing for 8 TeV full sample
W'
Z’
Our search focuses on a heavy new charged
uage boson, referred to as a W', which is predicted
y many theories, for example:
●
Little Higgs [1]
Extra Dimensions [2,3]
Extended Technicolor [4]
Left-Right Symmetry [5]
•  Z’ scenarios interwoven with
natural EXO solutions and AFB●
explaining models
●
•  Mttbar distribution sensitive to
We perform a model independent search for a W'
many new physics scenarios
●
oson which
decays toPAS
a top+bottom quark pair
src:toTOP-12-027
24
Freya Blekman (IIHE-VUB)
d Sperka: Search for t+b resonances with the CMS experiment
4
Introduction
Top resonaces physics motivation
site
LHC?
...
what kind of
e top is a
ome
er by some new
src: T. Tait
Weakly coupled
The Standard
Model (SM) predicts production of top-antitop pairs through
bare constituents?
•  Many new physics models predict extra
the exchange of gluons
●
exchange of massive particles in top quark
production
–  Would be observed in a peaked or general
excess/dip in the top-antitop invariant mass
some of its
70%
30%
spectrum
Higher
dimensional
o.
operators
–  Substantial number of theoretical models ● (like
esonances
But certain new models (beyond– SM)
also predict
theRandall-Sundrum/ADD
production of top-antitop
Z’,
colorons,
axigluons,
D). They are
Pseudo-scalar Higgs to ttbar
pairs through
a massive resonancegravitons,
Z'
.
Point-like SM particles
ouple strongly to
ple very very
Resonances?
•  And many more
only
•  Searches presented can beIllustration
interpreted
in any of these
–  For general comparison,“Topcolor-assisted
technicolor” model: hep-ph/991.1288: Hill, Parke, Harris Eg: “Topcolor-assisted technicolor” model which predicts a leptophobic Z'
25
with strong couplings to the third generation: hep-ph/9911288: Hill, Parke, Harris
●
Freya Blekman (IIHE-VUB)
April APS 2012
Supriya Jain
2
Event Select
analysis strategy
•  Searches in all available top decay
channels
proton
–  Dileptons
t t →   νν bb
–  Semileptonic ≡= lepton+jets
t t → ν qqbb
–  Hadronic ≡= alljets
t t → qqqqbb
− +
•  And in different regimes
?
Z'
proton
–  Close to 2x(top mass) threshold
•  Sensitive to shape of SM M(ttbar) distribution ●
•  Conventional top physics techniques may be We
used
●
choose “dileptons” decay mode (ee, mu
Selections:
–  More boosted
●
Leptons: two high-pT, isolated, opposite
•  Sensitive to more massive M(ttbar) BSM physics
- pseudorapidity |η| < 2.5
•  Dedicated reconstruction techniques may be
●
Missing transverse energy, MET > 30 Ge
necessary
●
m(ll) > 12 GeV; in ee and mumu channels,
●
N(jets) > =2, pT > 30 GeV, |η| < 2.5
●
At least one b-tag (based on secondary
26
Freya Blekman (IIHE-VUB)
All hadronic, boosted, 8 TeV
•  Using boosted objects and jet
pruning to identify substructure
–  Full merged topology
•  Cambridge-Aachen jets All-Hadronic Analysis
•
•
–  ‘top jets’
–  ‘W boson jets’
Fully merged, “type 1” : JHU top tagger
Partially merged, “type 2” : U of W jet pruning with BDRS mass drop as a “W tagger”
CMS-PAS-EXO-11-006
CMS-PAS-JME-11-013
W candidate
Top candidates
Top candidate
b candidate
src: CMS-B2G-12-005
• 2 jets, pT > 350 GeV
• Both jets are top tagged
•
•
•
•
Not type 1 + 1
Jet 1 pT > 350 GeV, top tagged
Freya Blekman (IIHE-VUB)
Jet 2 pT > 200 GeV, W tagged
Jet 3 pT > 30 GeV, form top
27
All hadronic, boosted, 8 TeV
•  Using boosted objects and jet
pruning to identify substructure
–  Full merged topology
•  Cambridge-Aachen jets All-Hadronic Analysis
•
•
–  ‘top jets’
–  ‘W boson jets’
Fully merged, “type 1” : JHU top tagger
Partially merged, “type 2” : U of W jet pruning with BDRS mass drop as a “W tagger”
CMS-PAS-EXO-11-006
CMS-PAS-JME-11-013
W candidate
Top candidates
Top candidate
b candidate
src: CMS-B2G-12-005
• 2 jets, pT > 350 GeV
• Both jets are top tagged
•
•
•
•
Not type 1 + 1
Jet 1 pT > 350 GeV, top tagged
Freya Blekman (IIHE-VUB)
Jet 2 pT > 200 GeV, W tagged
Jet 3 pT > 30 GeV, form top
28
All hadronic, boosted, 8 TeV
•
LLH fit to bumps in mass
spectrum
used
to
set
limits
src: CMS-B2G-12-005
29
Freya Blekman (IIHE-VUB)
All hadronic, boosted, 8 TeV
•  LLH fit to bumps in mass
spectrum
used
to
set
limits
•
•
•
Narrow (1.2%) Z’ limit: M(Z’) > 1.7 TeV
Wide (10%) Z’ limit:
M(Z’) > 2.35 TeV
RS Kaluza-Klein gravitons: M(KKG) > 1.8 TeV
•  95% CL upper limits on
increased cross section at high
mass:
σNP+SM < 1.79 σSM for masses above
1 TeV
src: CMS-B2G-12-005
30
Freya Blekman (IIHE-VUB)
Semileptonic, threshold
•  Require only one lepton, >= 4 jets and
split in b-tag multiplicity
•  χ2 sorting used to select best jet combination •  Using data-driven estimates for falling
distribution of top pair mass spectrum above
500 GeV/c2
•  Systematic uncertainties take into
account rate and shape changes for
signal and background model
src: CMS PAS B2G-12-006
31
Freya Blekman (IIHE-VUB)
Semileptonic, boosted
•  Resolved topologies –  use standard lepton+jets selection
(lepton, MET, 4 jets, b-tag) –  with χ2 sorting –  and constraints from top and W boson
mass (including pT balance of tops)
•  Boosted topologies –  uses wide jet (r=1) as top candidate
•  With selection on substructure to optimise
for top quarks
–  other side ‘normal’ ak5 jet, lepton,
missing ET
src: ATLAS-CONF-2013-052
32
Freya Blekman (IIHE-VUB)
Semileptonic, non-isolated
•  Multiple scenarios considered
–  Worlds best limit on production of resonant
ttbar:
•
•
•
•
Z’ (width 1.2%): m > 2.10 TeV
Z’ (width 10%): m > 2.68 TeV
KK gluons: m > 2.69 TeV
Resonances in low-mass region:
excluded with xsec > 1-2 pb!!
src: CMS PAS B2G-12-006
33
Freya Blekman (IIHE-VUB)
Vector like quarks intro
•  Non- SM fourth generation
–  Can enhance CP violation
–  Heavy neutrino as DM candidate
•  Vector-like fermions (nonchiral fermions):
•  Models benchmark for new
physics decaying top-like:
–  Extremely rich phenomenology
with final states with multiple
gauge bosons, b and t quarks:
–  Typical: exotic 4th generation
top/bottom partner
•  2HDM models
•  Little Higgs models •  Warped extra dimensions
–  Not excluded by Higgs mass
constraints/branching ratios
–  Current searches mostly pair
production
34
Freya Blekman (IIHE-VUB)
Little Hierarchy problem, Naturalness
t
Z
Motivation
W
Motivation
mHiggs
126 GeV
The CMS and ATLAS collaborations have observed a new boson
with mass ~125 GeV
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their mass from other SM particles:
Motivation
●
The CMS and ATLAS collaborations
have observed a new boson
with mass ~125 GeV
●
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their
● mass from other SM particles:
●
BSM?
The CMS and ATLAS collaborations have observed a new boson
with mass ~125 GeV
●
Fundamental scalar particles such as the Standard Model Higgs
receive divergent corrections to their mass from other SM particles:
●
Restricting fine tuning to the 10% level requires new physics which
cuts off these divergent contributions [1]:
●
t’/b’
David Sperka: Search for t+b resonances with the CMS experiment
3
Restricting fine tuning to the 10% level requires new physics which
cuts off these divergent contributions [1]:
Restricting fine tuning to the 10%●level requires new physics which
cuts off these divergent contributions [1]:
●
Freya Blekman (IIHE-VUB)
David Sperka: Search for t+b resonances with the CMS experiment
3
35
Vector-like quark partners
•  CMS: 1,2,3 lepton channels combined •
–  1-lepton top quark partner analysis
includes tagging of hadronic W bosons
ATLAS: 4 separate channels including Z+b,
multileptons and T to bW 1-lepton+jets with
high b jet multiplicity (incl W tagging) CMS PAS B2G-12-015
ATLAS-CONF-2013-060/018/051/056
Freya Blekman (IIHE-VUB)
36
Vector-like quark partners
•  CMS and ATLAS set limits in
same space – presentation
different but same message
•  ATLAS also sets limit on
bottom partners
•  For full LHC 8 TeV dataset
•  typical 95% CL exclusion for
masses are 650-800 GeV,
depending on the decay channel
CMS PAS B2G-12-015
ATLAS-CONF-2013-060/018/051
Freya Blekman (IIHE-VUB)
37
General search multi-leptons
•  Full ATLAS 8 TeV dataset
examined in 3-lepton final states –  On- and off-Z boson regions
–  Maximally one hadronic tau
–  Several kinematic variables
examined
–  split by number of b tagged jets
•  No excess above SM predictions
Limits on fourth
generation, doubly
charged Higgs (including
Higgs triplets), various
exotic neutrino models
ATLAS CONF-2013-070
Freya Blekman (IIHE-VUB)
38
Baryon Number Conservation
•  Baryon number conserved in Standard Model
–  Small violation possible from non-perturbative effects
•  Supersymmetry, Grand Unified Theories and
black-hole physics naturally allow Baryon Number
violation (BNV).
–  stringent limits from precision measurements in
nucleon, tau, HF mesons and Z bosons
–  Top decay (small BR) of type t to μbc not excluded
Freya Blekman (IIHE-VUB)
39
Search for BNV in tops
•  Idea: should be visible as
subtle increase of top
events in lepton+jets with
very low missing
transverse energy
•  Experimentally extremely
challenging regime –  Lepton
–  5 jets
–  No MET
src: CMS PAS B2G-12-023
Freya Blekman (IIHE-VUB)
40
Search for BNV tops
•  Construct chi2 requirement on hadronic top system and
make tight cut on chi2 (<20) and MET (<20) Constrain low
MET, low chi2 region from bulk •  Fit to BR and selection efficiency instead of event counts
CMS PAS B2G-12-023
Freya Blekman (IIHE-VUB)
41
Search for BNV tops
6
5
( T | B)
Signal search strategy
( T | B)
discussed above) in the tight selection, and ett̄
(etW ) is the efficiency for tt (tW) events to
pass the tight selection once the basic selection is passed.
All the quantities in the square brackets of Eq. 3 are functions of BR and can be expressed
in terms of the tt and tW cross sections (stt and stW , respectively), integrated luminosity, and
efficiencies for passing the basic and tight selections. If these variables are introduced, Eq. 3
becomes:
2
3
⇣
⌘
T ( BR )
etTt̄ ( BR)
etW
1
1
6
7
T
B
B
T
Nexp = Nobs Nbck 4
⇥
+
⇥
+ Nbck
(4)
5
B
B
B
B
stW etW ( BR)
stt̄ ett̄ ( BR)
e
(
BR
)
e
(
BR
)
tW
1 + s eB ( BR)
tt̄
1 + s eB ( BR)
tt̄ tt̄
tW tW
In Eq. 4, ettB (ettT ) indicates the efficiency of the basic (tight) selection for tt events. Similarly,
B (e T ) indicates the efficiency of the basic (tight) selection for tW events. Each of these four
etW
tW
CMS PAS B2G-12-023
efficiency values is a function of BR and of three (for tt events) or two (for tW events) efficiency
42
Freya Blekman (IIHE-VUB)
values, which correspond to the different decay modes:
Search for BNV tops
•  Modeling of QCD multijet
background derived in Z+jets
events
•  Fit to efficiencies and BR •  Even in challenging e+jets
channel decent data-MC
agreement
•  Limits on in µ (e) channels:
•  BF< 0.016 (0.017) •  First limit ever on BNV in top
sector!
43
Freya Blekman (IIHE-VUB)
End of lecture three – questions?
44
Freya Blekman (IIHE-VUB)
MSSM vs SUSY
SUSY
N=1
MSSM
Dirac
gauginos
pMSSM
NMSSM
singlinos
CMSSM
U(1)’
16
45
Freya Blekman (IIHE-VUB)
Lepton Forward-Backward Asymmetry
• AtFt̄B measurement requires full reconstruction of tt̄ system.
• Alternative method based on y of
lepton from leptonic W decay.
A!F B =
N (q! y! > 0) − N (q! y! < 0)
N (q! y! > 0) + N (q! y! < 0)
• A!F B ≈ 0.5·AtFt̄B if no t polarization.
CDF Note 10975
• Can also use events with jets out
of acceptance (3-jet bin).
Forward-Backward Lepton Asymmetry, %
CDF: A!F B = 0.094+0.032
−0.029
DØ preliminary, 9.7 f b-1
Production Level
3 jets, 1 b tag
D0: A!F B = 0.047 ± 0.023(stat)+0.011
−0.014 (syst)
3 jets, ≥2 b tags
• CDF result approximately 2σ
above SM prediction.
≥4 jets, 1 b tag
≥4 jets, ≥2 b tags
• D0 measurement consistent with
SM (and CDF) within errors.
inclusive
χ2/ N.D.F.: 8.2 / 3
(with syst.)
S. Frixione and B.R. Webber,
JHEP 06, 029 (2002)
-10
0
10
20
D0 note 6394-CONF
S ARA S TRANDBERG , S TOCKHOLM U NIVERSITY
P. 20
EPSHEP 2013, S TOCKHOLM , J ULY 22, 2013
Freya Blekman (IIHE-VUB)
46
Top Forward-Backward and Charge Asymmetries
• New physics in top sector can alter angular distributions.
• Study forward-backward and charge asymmetries.
N (∆y > 0) − N (∆y < 0)
N (∆y > 0) + N (∆y < 0)
with ∆y = yt − yt̄
AtFt̄B =
N (∆|y| > 0) − N (∆|y| < 0)
N (∆|y| > 0) + N (∆|y| < 0)
with ∆|y| = |yt | − |yt̄ |
AC
AtCt̄ =
Unfolded
SM
Axigluon m=300 GeV
Axigluon m=7000 GeV
0.2
0.15
ATLAS Preliminary
s= 7 TeV
∫ L dt = 4.7 fb
-1
0.1
0.05
0
-0.05
-0.1
0
100
200
300
400
500
600
700
800
900
mtt [GeV]
Phys. Rev. D 87 092002 (2013)
Phys. Lett. B 717, 129 (2012)
ATLAS-CONF-2013-078
• Tevatron AtFt̄B measurements in tension with SM at ∼ 2.5σ.
• LHC AtCt̄ measurements consistent with SM.
S ARA S TRANDBERG , S TOCKHOLM U NIVERSITY
P. 19
EPSHEP 2013, S TOCKHOLM , J ULY 22, 2013
Freya Blekman (IIHE-VUB)
47