Peaky blinders: searches for t t resonances James Ferrando - - PowerPoint PPT Presentation

SLIDE 1

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

Peaky blinders: searches for t¯ t resonances

James Ferrando

University of Glasgow

Elementary Particle Physics Group Seminar University of Birmingham 11th December 2013

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SLIDE 2

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

Outline

Why search for t¯ t resonances? Review of t¯ t resonance searches Looking towards the future Will focus on the details of ATLAS searches but also show the best results from the competition

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SLIDE 3

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

The Standard Model

The Standard Model (SM) of particle physics: Fermionic matter:

Three generations of quarks Three generations of leptons

Gauge Bosons:

Four Force carriers : γ(EM), W ±, Z (Weak), g (strong) The Higgs Boson to give mass

”Was she pretty?” asked the bigger of the small

• girls. ”Not as pretty as any of you,” said the

bachelor, ”but she was horribly good.” The storyteller - H. H. Munro (Saki)

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SLIDE 4

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

SM Problems

So what’s wrong with the Standard Model? No Dark Matter candidates Not enough CP violation to explain the

• bserved matter-antimatter imbalance

The Higgs boson has still not been observed No gravity Particle masses are not understood Is there physics beyond the Standard Model?

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SLIDE 5

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

The LHC

Where to look for answers? The Large Hadron Collider at CERN 27 km circumference ring Currently collides protons at centre-of-mass energy 8 TeV Four detectors installed around the ring An excellent environment to test the Standard Model and search for new Physics Triviality/Unitarity constraints

• n some SM cross sections

imply a Higgs Boson or something else at an energy scale < 800 GeV

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SLIDE 6

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

LHC Detectors

What equipment to use? A Toroidal Large ApparatuS (ATLAS) 4 Detectors:

2 General Purpose

ATLAS CMS

Two Specialised

ALICE - Heavy ion LHCb - CP violation

ATLAS with full solid angle coverage, excellent charged particle tracking, particle ID and energy measurement is well-suited for TeV-Scale physics (and so is CMS of course)

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SLIDE 7

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

Introducing: The Top Quark

The top quark was discovered at TeVatron in 1995 Extremely heavy for a fundamental particle:

Similar mass to a gold atom ∼ 35 times heavier than the next heaviest quark (the bottom quark)

Usually produced in a t¯ t pair with its partner the anti-top Could it provide a gateway to new physics?

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SLIDE 8

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

Top and BSM Physics

Many BSM scenarios on the market Large top mass (mt ≈ 173 GeV) → top

• ften plays a special role in BSM theories

BSM physics often has consequences for the third generation quarks Some examples: Add new heavy quarks: Often decay to tops or look like heavy tops Incorporate Gravity using Extra Dimensions: Many models predict new states with strong coupling to the top Exotic Higgs Bosons: large coupling to the top SUSY: naturalness prefers top-partners not too far from mt

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SLIDE 9

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

Hints of New Physics?

Extra motivation: TeVatron p¯ p data At¯

t = N(yt¯ t t

> 0) − N(yt¯

t t

< 0) N(yt¯

t t

> 0) + N(yt¯

t t

< 0) Tevatron collides p and ¯ p producing t¯ t At¯

t a measure of how much the

t prefers the p direction p-value of such a large slope 0.00646 (CDF) “Strengthens the case that new physics plays a role in t¯ t production”

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SLIDE 10

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

A Top Factory

Measurements of top properties at TeVatron statistically limited The LHC t¯ t production cross-section is much larger In effect the LHC is a top quark factory TeVatron: < 8 × 104 (10 fb−1) top pairs per experiment ∼10 years running LHC: > 6 × 106 top pairs per experiment in 2011-12 At the LHC many top quark studies are possible that were not feasible at TeVatron

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SLIDE 11

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

Top Signatures

t t t t t t t t q q q q g g g g g g t

In the SM, top decays approximately 100% t → Wb Classified according to the W decays

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SLIDE 12

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

New Physics with Tops

Broadly speaking can study new physics in t¯ t in three different ways Look for anomalous production of tops Look for unexpected behaviour in top quark decays Directly search for new particles decaying to tops (and possibly something else) This talk focuses on the latter, searching for a peak in the mt¯

t

distribution from production of new particles that decay to t¯ t pairs

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SLIDE 13

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

t¯ t resonances I

A wealth of peaky new physics signals from different scenarios: Extra dimensions (Bulk RS): Excitations of gluon (gKK)/ graviton (GKK) preferentially decay to t¯ t Topcolor-assisted Technicolor: Strong EWSB model via a top condensate - expect top-π (H-like) and top-ρ (Z ′-like ) the latter heavy enough to decay to t¯ t Composite Higgs scenarios: Usually require (naturalness) extra heavy-fermions, and commonly heavy “gluons” that decay to tR or new heavy fermions depending on the masses BSM Higgs: New heavy pseudoscalar Higgs-like particles in, e.g. the MSSM, would also have a large t¯ t branching ratio

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SLIDE 14

Introduction Recent Searches The Future Summary Outline The Standard Model What’s wrong with the SM? Why Top quarks? Signatures and Models

t¯ t resonances II

Searches so far have focused on two benchmark scenarios: Topcolor-assisted technicolor (TC2) Z ′

TC2 → t¯

t

Spin-1 Color singlet Narrow width (1.2%) modelled with SSM Z ′ (3%) width hep-ph/9911288,

• Eur. Phys. J. C (2012) 72 2072

RS Kaluza-Klein Gluon gKK → t¯ t

Spin-1 color octet wide (10-15%) BR(gKK → t¯ t) ∼ 92.5% JHEP 0709 (2007) 074

q q t t

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 ) [TeV]

TC2

m(Z’ Branching Ratio

Branching Ratios

TC2

LO Z’

=0.0

2

=1.0, f

1

hep-ph/9911288 - Harris et. al, Model IV, f Including correction from Ferrando and Frandsen used in

• Eur. Phys. J. C (2012) 72, 2072 - Harris and Jain

u u t t d d b b

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SLIDE 15

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Selecting t¯ t

First t¯ t resonance search at the LHC selected tops in a familar way (ATLAS - Eur.Phys.J. C72 (2012) 2083) dilepton channel Two isolated leptons ll = ee, eµ, µµ ee or µµ: Mll outside MZ window eµ : Require large HT Mll > 10 GeV E miss

T

2 or more jets l+jets channel Isolated electron or muon Missing Transverse momentum (E miss

T

) 4 or more jets (inclusive Anti-KT, R = 0.4) or, 3 jets and one jet has mass > 60 GeV At least 1 b-tagged jet HT is the scalar sum of PT of all hard objects in event.

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SLIDE 16

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

t¯ t resonances

Use kinematic distributions to search for background l+jets reconstruct mt¯

t

Solve quadratic for E miss

T

to reconstruct neutrino using mlν = mW constraint exclude jets if ∆R > 2.5 − 0.0015 × mj iteratively until none fail, or there are only three jets take 4 (or 3) highest pT remaining jets reconstruct the mass of the 4 jet, lepton + neutrino system

dilepton: use HT

mass [GeV] t Reconstructed t

500 1000 1500 2000

Event Fraction

0.05 0.1 0.15 0.2

=500 GeV

Z'

m =700 GeV

Z'

m =1000 GeV

Z'

m =1300 GeV

KK

m

ATLAS =7 TeV s Simulation James Ferrando Searches for t¯ t resonances 16/ 65

SLIDE 17

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Backgrounds

Estimation of backgrounds: top-pair: (irreducible) taken from Monte Carlo (MC) W+jets: taken from MC and then normalised using data control regions (l+jet channel) Z+jets: taken from MC and then normalised using data control regions (dilepton channel) single-top: taken from MC Massive di-boson: taken from MC non-top multijet: estimated directly from data

James Ferrando Searches for t¯ t resonances 17/ 65

SLIDE 18

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

t¯ t resonances

l+jets search for bumps in Mt¯

t

:

mass [GeV] t t 500 1000 1500 2000 2500 3000 Events / GeV

• 3

10

• 2

10

• 1

10 1 10

2

10 mass [GeV] t t 500 1000 1500 2000 2500 3000 Events / GeV

• 3

10

• 2

10

• 1

10 1 10

2

10

data t t W+jets Other Backgrounds Uncertainties Z' (800 GeV) (1300 GeV)

KK

g

ATLAS

• 1

Ldt=2.05 fb

∫

=7TeV s

dileptons Use HT + E miss

T

:

[GeV]

miss T

+E

T

H 200 400 600 800 1000 1200 Events / GeV

• 3

10

• 2

10

• 1

10 1 10

2

10 [GeV]

miss T

+E

T

H 200 400 600 800 1000 1200 Events / GeV

• 3

10

• 2

10

• 1

10 1 10

2

10

data t t Z+jets Other Backgrounds Uncertainties (1100 GeV)

KK

g

ATLAS

=7TeV s

• 1

Ldt=2.05 fb

∫

[GeV]

miss T

+E

T

H 200 400 600 800 1000 1200 Events / GeV

• 3

10

• 2

10

• 1

10 1 10

2

10

No evidence for new physics signals

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SLIDE 19

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

t¯ t resonances

l+jets

Z' mass [GeV] 600 800 1000 1200 1400 1600 1800 2000 ) [pb] t t → BR(Z' × σ

• 1

10 1 10

2

10

Lepton + jets

• Obs. 95% CL upper limit
• Exp. 95% CL upper limit

uncertainty σ

• Exp. 1

uncertainty σ

• Exp. 2

Leptophobic Z' Lepton + jets

• Obs. 95% CL upper limit
• Exp. 95% CL upper limit

uncertainty σ

• Exp. 1

uncertainty σ

• Exp. 2

Leptophobic Z'

ATLAS

• 1

= 2.05 fb dt L

∫

= 7 TeV s

mass [GeV]

KK

g 600 800 1000 1200 1400 1600 1800 ) [pb] t t →

KK

BR(g × σ

• 1

10 1 10

2

10

Lepton + jets

• Obs. 95% CL upper limit
• Exp. 95% CL upper limit

uncertainty σ

• Exp. 1

uncertainty σ

• Exp. 2

Kaluza-Klein gluon Lepton + jets

• Obs. 95% CL upper limit
• Exp. 95% CL upper limit

uncertainty σ

• Exp. 1

uncertainty σ

• Exp. 2

Kaluza-Klein gluon

ATLAS

• 1

= 2.05 fb dt L

∫

= 7 TeV s

l+jets: Limits set on narrow Z ′-like resonances: Exclude 500 < MZ ′ < 880 GeV for benchmark (Topcolor-assisted technicolor) Z’ model.

James Ferrando Searches for t¯ t resonances 19/ 65

SLIDE 20

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

t¯ t resonances

dileptons

mass [GeV]

KK

g 600 800 1000 1200 1400 1600 1800 ) [pb] t t →

KK

BR(g × σ

• 1

10 1 10

2

10

Lepton + jets

• Obs. 95% CL upper limit
• Exp. 95% CL upper limit

uncertainty σ

• Exp. 1

uncertainty σ

• Exp. 2

Kaluza-Klein gluon Lepton + jets

• Obs. 95% CL upper limit
• Exp. 95% CL upper limit

uncertainty σ

• Exp. 1

uncertainty σ

• Exp. 2

Kaluza-Klein gluon

ATLAS

• 1

= 2.05 fb dt L

∫

= 7 TeV s

mass [GeV]

KK

g 600 800 1000 1200 1400 1600 1800 ) [pb] t t →

KK

BR(g × σ

• 1

10 1 10

2

10

Dilepton

• Obs. 95% CL upper limit
• Exp. 95% CL upper limit

uncertainty σ

• Exp. 1

uncertainty σ

• Exp. 2

Kaluza-Klein gluon = 7 TeV s

• 1

= 2.05 fb dt L

∫ ATLAS

dileptons: Limits set on broader gKK-like resonances. Benchmark scenario: MgKK < 1025 TeV excluded. (l+jets excludes 500 < MgKK < 1130 for the main benchmark scenario)

James Ferrando Searches for t¯ t resonances 19/ 65

SLIDE 21

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Going Boosted

On the previous slides, expected limits flatten at higher mt¯

t

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SLIDE 22

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

t¯ t

When pushing to higher energies, new factors come into play: Low-energy tops t → bW , W → qq′ gives three distinct “jets”: High-energy tops top decay system is highly boosted and reconstructed as only one jet: Need new techniques to identify these boosted objects

James Ferrando Searches for t¯ t resonances 21/ 65

SLIDE 23

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Parton Merging

Merging of some description occurs for SM t¯ t production: Effect must be taken into account for SM measurements at higher Pt

T or Mt¯ t

James Ferrando Searches for t¯ t resonances 22/ 65

SLIDE 24

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Top Tagging

Hadronic top decays give the simplest case: Use the mass of the jet and exploit features of the KT algorithm:

Start with standard Anti-KT jets and run exclusive KT algorithm on the constituents. KT effectively undoes the QCD showering Objects merged at each step have smallest dij = min(k2

T,i, k2 T,j) (∆R)2 R

So the last objects merged have the largest dij (e.g. come from the highest scale splitting) We force KT to give us n jets and ask what the last dij was

James Ferrando Searches for t¯ t resonances 23/ 65

SLIDE 25

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Substructure Measurement

50 100 150 200 250 300 GeV 1 d m σ d σ 1 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02

ATLAS

• 1

L = 35 pb

∫

2010 Data, Statistical unc. Total unc. Pythia Herwig++

= 1, |y| < 2

PV

N R=1.0

t

anti-k < 500 GeV

T

400 < p

Jet mass [GeV] 50 100 150 200 250 300 MC/Data

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 10 20 30 40 50 60 70 80 90 100 GeV 1

12

d d σ d σ 1 0.01 0.02 0.03 0.04 0.05 0.06 0.07

ATLAS

• 1

L = 35 pb

∫

2010 Data, Statistical unc. Total unc. Pythia Herwig++

= 1, |y| < 2

PV

N R=1.0

t

anti-k < 500 GeV

T

400 < p

[GeV]

12

d

10 20 30 40 50 60 70 80 90 100 MC/Data

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

Jet substructure (including mass and splitting scales) was measured in ATLAS - JHEP 1205 (2012) 128 Calibration and uncertainties of simple splitting variables and jet mass already understood at ATLAS

James Ferrando Searches for t¯ t resonances 24/ 65

SLIDE 26

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

t¯ t

Put into practice in: ATLAS - JHEP 1209 (2012) 041 Same lepton selection as previous analysis (l+jets) No b-tag Look for boosted t → bqq:

Large-R (1.0) anti-kT jet Require large jet mass and first kT splitting scale (d12)

Reconstruct mt¯

t from

hadronic top cand +lepton, E miss

T

and nearest anti-kT (R=0.4) jet

James Ferrando Searches for t¯ t resonances 25/ 65

SLIDE 27

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Candidate

fat jet mass [GeV] 100 120 140 160 180 200 220 240 260 280 300 events / 10 GeV 10 20 30 40 50 60 ATLAS

= 7 TeV s

• 1

Ldt=2.05 fb

∫

Background subtracted Data t t Uncertainty

James Ferrando Searches for t¯ t resonances 26/ 65

SLIDE 28

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

t¯ t

Extract limits on narrow (<3%) or Wide (∼10%) resonance → t¯ t: comfortably outperforming the conventional analysis at high mt¯

t

James Ferrando Searches for t¯ t resonances 27/ 65

SLIDE 29

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

ATLAS l+jets 7 TeV

The first search to fully combine boosted and resolved approaches:

• Phys. Rev. D 88, 012004 (2013)

Boosted:

lepton E miss

T

≥ 1 large-R jet with pT > 350 GeV and large jet-mass ≥ 1 b-jet

Resolved

Fails boosted selection lepton E miss

T

≥ 4 jets or ≥ 3 jets and one jet has a mass > 60 GeV ≥ 1 b-jet

included also several improvements compared to previous iterations

James Ferrando Searches for t¯ t resonances 28/ 65

SLIDE 30

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

We can make it better

Building a better search: Resolved: Improve t¯ t reconstruction Boosted: Add b-tagging (reduce large W +jets background), Both: Improve isolation definition,

James Ferrando Searches for t¯ t resonances 29/ 65

SLIDE 31

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

t¯ t Reconstruction

Adopted a χ2 method for choosing jets to use in calculation of the t¯ t mass: χ2 = mjj − mW σW 2 + mjjb − mjj − mth−W σth−W 2 + mjℓν − mtℓ σtℓ 2 + (pT,jjb − pT,jℓν) − (pT,th − pT,tℓ) σdiffpT 2

James Ferrando Searches for t¯ t resonances 30/ 65

SLIDE 32

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Lepton Isolation

Conventional lepton isolation is also a problem for boosted tops: Standard isolation requirements: Require lepton and nearest jet well separated ( ∆R(l, j) > 0.4 ) require pT within a small cone around the lepton track is less than some value Solution: Adopt mini-isolation (JHEP 1103 (2011) 059) Size of isolation cone shrinks with pT , ∆R = k/pl

T (in the

case of ATLAS k = 10 GeV is used) Require pT is less than some value (in the case of ATLAS < pl

T/20.0 )

... and relax requirement on ∆R(l, j) in the µ channel.

James Ferrando Searches for t¯ t resonances 31/ 65

SLIDE 33

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Lepton Isolation

QCD background false-identification rate [%] 1 2 3 4 5 6 Signal efficiency [%] 20 40 60 80 100

T

p /

mini

I

mini

I

T

p Ptcone30 / Ptcone30

T

p Etcone20 / Etcone20 Preliminary ATLAS

• 1

= 14.2 fb L dt

∫

= 8 TeV s

QCD background false-identification rate [%] 1 2 3 4 5 6 Signal efficiency [%] 20 40 60 80 100

T

p /

mini

I

mini

I

T

p Ptcone30 / Ptcone30

T

p Etcone20 / Etcone20 Preliminary ATLAS

• 1

= 14.2 fb L dt

∫

= 8 TeV s

Performance of mini-isolation is very good and stable for different Z ′ masses (1.0 TeV (left) and 2 TeV (right))

James Ferrando Searches for t¯ t resonances 32/ 65

SLIDE 34

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Selection Efficiency

Muon channel efficiency now rises with mt¯

t

Fall-off at high masses for electrons because ∆R(l, j) cut could not be relaxed

James Ferrando Searches for t¯ t resonances 33/ 65

SLIDE 35

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Selection efficiency

Overall signal efficiency is high (this value is relative to all t¯ t)

James Ferrando Searches for t¯ t resonances 34/ 65

SLIDE 36

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

mt¯

t

James Ferrando Searches for t¯ t resonances 35/ 65

SLIDE 37

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

mt¯

t

James Ferrando Searches for t¯ t resonances 36/ 65

SLIDE 38

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

mt¯

t

benchmark models excluded up to 1.75 TeV (Z ′) and 2.1 TeV (gKK)

James Ferrando Searches for t¯ t resonances 37/ 65

SLIDE 39

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Going to 8 TeV

First ATLAS search using partial 8 TeV dataset: Improvements:

Introduced Trimming of large-R jet to mitigate pile-up

Disadvantages:

large-R jet triggers not available at this time (large hit im muon channel efficiency)

James Ferrando Searches for t¯ t resonances 38/ 65

SLIDE 40

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Trimming: Concepts

Performance of Trimming discussed in detail in: ATLAS - JHEP 1309 (2013) 076 Works by: running a small-R (0.3) kT algorithm on large-R jet constituents to make subjets keeping only subjets with pT greater than a certain fraction (0.05) of the large-R-jet This “trims” away soft activity in the jet

James Ferrando Searches for t¯ t resonances 39/ 65

SLIDE 41

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Trimming: Performance

)

PV

Reconstructed vertex multiplicity (N 2 4 6 8 10 12 14 [GeV] 〉

jet

m 〈 20 40 60 80 100 120 140 160 ATLAS

= 7 TeV s ,

• 1

Ldt = 1 fb

∫

Data 2011 LCW jets with R=1.0

t

anti-k | < 0.8 η < 300 GeV, |

T jet

p ≤ 200 No jet grooming =0.3

sub

=0.01, R

cut

f =0.3

sub

=0.03, R

cut

f =0.3

sub

=0.05, R

cut

f =0.2

sub

=0.01, R

cut

f =0.2

sub

=0.03, R

cut

f =0.2

sub

=0.05, R

cut

f

Jet mass [GeV] 50 100 150 200 250 300 Arbitrary units 0.02 0.04 0.06 0.08 0.1 0.12 0.14

t t → Ungroomed Z' Ungroomed Dijets t t → Trimmed Z' Trimmed Dijets

Simulation ATLAS

< 800 GeV

jet T

p ≤ LCW jets, 600

t

anti-k

Trimming makes jet substructure quantities robust against pile-up

James Ferrando Searches for t¯ t resonances 40/ 65

SLIDE 42

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

Selection Efficiency

Electron channel loss - due to trimming Muon channel loss - trimming and trigger Partly mitigated by some other gains in reconstruction

James Ferrando Searches for t¯ t resonances 41/ 65

SLIDE 43

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

mt¯

t

James Ferrando Searches for t¯ t resonances 42/ 65

SLIDE 44

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

mt¯

t

Events / TeV

1 10

2

10

3

10

4

10

5

10

6

10

Data t t Multi-jets W+jets Other Backgrounds 0.5 1 1.5 2 2.5 3 3.5

ATLAS Preliminary

= 8 TeV s

• 1

L dt = 14.3 fb

∫

e + jets boosted

[TeV]

reco t t

m Data/Bkg 0.5 1 1.5 0.5 1 1.5 2 2.5 3 3.5

Events / TeV

1 10

2

10

3

10

4

10

5

10

6

10

Data t t Multi-jets W+jets Other Backgrounds 0.5 1 1.5 2 2.5 3 3.5

ATLAS Preliminary

= 8 TeV s

• 1

L dt = 14.2 fb

∫

+ jets µ boosted

[TeV]

reco t t

m Data/Bkg 0.5 1 1.5 0.5 1 1.5 2 2.5 3 3.5 James Ferrando Searches for t¯ t resonances 43/ 65

SLIDE 45

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

mt¯

t

Z’ mass [TeV]

0.5 1 1.5 2 2.5 3

) [pb] t t → BR(Z’ ×

Z’

σ

• 2

10

• 1

10 1 10

2

10

3

10

• Obs. 95% CL upper limit
• Exp. 95% CL upper limit

uncertainty σ

• Exp. 1

uncertainty σ

• Exp. 2

Leptophobic Z’ (LO x 1.3)

• Obs. 95% CL upper limit
• Exp. 95% CL upper limit

uncertainty σ

• Exp. 1

uncertainty σ

• Exp. 2

Leptophobic Z’ (LO x 1.3)

ATLAS Preliminary

• 1

= 14.3 fb dt L

∫

= 8 TeV s

mass [TeV]

KK

g

0.5 1 1.5 2 2.5

) [pb] t t →

KK

BR(g ×

KK

g

σ

• 2

10

• 1

10 1 10

2

10

3

10

• Obs. 95% CL upper limit
• Exp. 95% CL upper limit

uncertainty σ

• Exp. 1

uncertainty σ

• Exp. 2

Kaluza-Klein gluon (LO)

• Obs. 95% CL upper limit
• Exp. 95% CL upper limit

uncertainty σ

• Exp. 1

uncertainty σ

• Exp. 2

Kaluza-Klein gluon (LO)

ATLAS Preliminary

• 1

= 14.3 fb dt L

∫

= 8 TeV s

benchmark models excluded up to 1.8 TeV (Z ′) and 2.0 TeV (gKK)

James Ferrando Searches for t¯ t resonances 44/ 65

SLIDE 46

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

CMS 8 TeV Search

New CMS search CMS - Phys. Rev. Lett. 111 (2013) 211804 Combines all-hadronic (boosted) and l+jets (resolved and boosted), channels Boosted l+jets:

Separated into separate channels by b-tag no isolation required for leptons require at least two jets Build t¯ t combination via a chi2, cut on the chi2 to reduce backgrounds

[GeV]

t t

M

500 1000 1500 2000 2500 3000 3500

Events / 100 GeV

• 1

10 1 10

2

10

3

10

4

10

Data t t

• thers

Z' 2 TeV

= 8 TeV s ,

• 1

CMS, 19.7 fb

= 0

b-tag

N µ e+ (a)

James Ferrando Searches for t¯ t resonances 45/ 65

SLIDE 47

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

CMS 8 TeV Search

New CMS search CMS - Phys. Rev. Lett. 111 (2013) 211804 Combines all-hadronic (boosted) and l+jets (resolved and boosted), channels Boosted l+jets:

Separated into separate channels by b-tag no isolation required for leptons require at least two jets Build t¯ t combination via a chi2, cut on the chi2 to reduce backgrounds

[GeV]

t t

M

500 1000 1500 2000 2500 3000 3500

Events / 100 GeV

• 1

10 1 10

2

10

3

10

4

10

Data t t

• thers

Z' 2 TeV

= 8 TeV s ,

• 1

CMS, 19.7 fb

1 ≥

b-tag

N µ e+ (b)

James Ferrando Searches for t¯ t resonances 45/ 65

SLIDE 48

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

CMS 8 TeV Search

New CMS search CMS - Phys. Rev. Lett. 111 (2013) 211804 Combines all-hadronic (boosted) and l+jets (resolved and boosted), channels All-hadronic:

Requires two high-pT large-R jets - that are “top-tagged” with a sophsiticated tagger two leading back-to-back b-tagged small-R jets

[GeV]

t t

M

1000 1500 2000 2500 3000 3500

Events / 100 GeV

• 1

10 1 10

2

10

3

10

4

10

Data t t NTMJ Z' 2 TeV

= 8 TeV s ,

• 1

CMS, 19.7 fb

all-hadronic (c)

James Ferrando Searches for t¯ t resonances 46/ 65

SLIDE 49

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

CMS 8 TeV Search

New CMS search CMS - Phys. Rev. Lett. 111 (2013) 211804 Combines all-hadronic (boosted) and l+jets (resolved and boosted), channels Resolved l + jets:

require at least four jets separate into b-tag categories build a χ2 and cut on it Fit a smoothyl falling pdf to the SM background

[GeV]

t t

(d) M

600 800 1000 1200 1400 1600 1800 2000

Events / 50 GeV

2

10

3

10

4

10

5

10 1 ≥

b-tag

, N µ e+

= 8 TeV s ,

• 1

CMS, 19.7 fb

Data Background Z' 750 GeV

James Ferrando Searches for t¯ t resonances 47/ 65

SLIDE 50

Introduction Recent Searches The Future Summary Early ATLAS searches @ 7 TeV ATLAS searches with the Full 7 TeV data ATLAS and CMS searches with 8 TeV data

CMS 8 TeV Search

[TeV]

Z'

M 0.5 1 1.5 2 2.5 3 ) [pb] t t → B(Z' ×

Z'

σ Upper limit on

• 3

10

• 2

10

• 1

10 1 10

2

10

Expected (95% CL) Observed (95% CL) Z' 1.2% width Expected σ 1 ± Expected σ 2 ±

= 8 TeV s ,

• 1

CMS, 19.7 fb

All-hadronic combined with the separate resolved and boosted l+jets results in different kinematc regimes.

James Ferrando Searches for t¯ t resonances 48/ 65

SLIDE 51

Introduction Recent Searches The Future Summary Towards Run II LHC upgrade Upgrade Schedule

Proud history bright future?

Boost 2012 report - arXiv:1311.2708 What’s next? Towards LHC run-II Prospects with the upgraded LHC

James Ferrando Searches for t¯ t resonances 49/ 65

SLIDE 52

Introduction Recent Searches The Future Summary Towards Run II LHC upgrade Upgrade Schedule

Towards Run II

How much luminosity is neeed at 13 TeV to be competitive with current data?

500 1000 1500 2000 2500 3000 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

@ 8 TeV

• 1

@ 13 TeV vs 20fb

• 1

1 fb (13 TeV)/(8 TeV) b s/ (GeV)

t t

m

(13 TeV) t t → Z' Current Observed Limit Current Expected Limit 500 1000 1500 2000 2500 3000 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

@ 8 TeV

• 1

@ 13 TeV vs 20fb

• 1

5 fb (13 TeV)/(8 TeV) b s/ (GeV)

t t

m

(13 TeV) t t → Z' Current Observed Limit Current Expected Limit

(simple extrapolation using cross sections for Z ′ and NLO t¯ t in appropriate mt¯

t range)

James Ferrando Searches for t¯ t resonances 50/ 65

SLIDE 53

Introduction Recent Searches The Future Summary Towards Run II LHC upgrade Upgrade Schedule

Towards Run II

500 1000 1500 2000 2500 3000 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

@ 8 TeV

• 1

@ 13 TeV vs 20fb

• 1

6 fb (13 TeV)/(8 TeV) b s/ (GeV)

t t

m

(13 TeV) t t → Z' Current Observed Limit Current Expected Limit 500 1000 1500 2000 2500 3000 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

@ 8 TeV

• 1

@ 13 TeV vs 20fb

• 1

7 fb (13 TeV)/(8 TeV) b s/ (GeV)

t t

m

(13 TeV) t t → Z' Current Observed Limit Current Expected Limit

Reach should start to increase as we approach 6-7 fb−1

James Ferrando Searches for t¯ t resonances 51/ 65

SLIDE 54

Introduction Recent Searches The Future Summary Towards Run II LHC upgrade Upgrade Schedule

Upgrades

James Ferrando Searches for t¯ t resonances 52/ 65

SLIDE 55

Introduction Recent Searches The Future Summary Towards Run II LHC upgrade Upgrade Schedule

Upgrade Schedule

Example, ATLAS upgrade schedule: Phase I Installation Date: 2018-19 Detector upgrades: µ-trigger, L1 Calo-trigger, FTK, new Small wheel for muons , new forward detectors . Various readout

• improvements. (Maintain

performance at higher luminosity) Lumi 2.2 × 1034 cm−2s−1, 300-400 fb−1 by 2022, µ = 55-80 Phase II Installation Date: 2022-24 Detector upgrades: Split L0/L1 trigger, numerous trigger and readout upgrades, improved HLT, RPC precision upgrade, complete tracker replacement. ( Maintain/improve performance at higher µ, improve resistance to radiation damage) Lumi 5 × 1034 cm−2s−1, up to 3000 fb−1, µ = 140-200

James Ferrando Searches for t¯ t resonances 53/ 65

SLIDE 56

Introduction Recent Searches The Future Summary Towards Run II LHC upgrade Upgrade Schedule

Upgrade studies

ATLAS upgrade performance and physics prospects have been studied in: Phase-I LOI: CERN-LHCC-2011-012 Phase-II LOI: CERN-LHCC-2012-022 t¯ t resonance search: ATL-PHYS-PUB-2013-003 Studies of t¯ t resonance searches done with a parametrisation of detector response, not at the full-simulation level.

James Ferrando Searches for t¯ t resonances 54/ 65

SLIDE 57

Introduction Recent Searches The Future Summary Towards Run II LHC upgrade Upgrade Schedule

Upgrade Studes

t¯ t in simplified l+jets (boosted) and dilepton selections

James Ferrando Searches for t¯ t resonances 55/ 65

SLIDE 58

Introduction Recent Searches The Future Summary Towards Run II LHC upgrade Upgrade Schedule

Upgrade Studes

t¯ t in simplified l+jets (boosted) and dilepton selections

James Ferrando Searches for t¯ t resonances 56/ 65

SLIDE 59

Introduction Recent Searches The Future Summary Towards Run II LHC upgrade Upgrade Schedule

Upgrade Studes

t¯ t in simplified l+jets (boosted) and dilepton selections

James Ferrando Searches for t¯ t resonances 57/ 65

SLIDE 60

Introduction Recent Searches The Future Summary Towards Run II LHC upgrade Upgrade Schedule

Upgrade Studes

t¯ t in simplified l+jets (boosted) and dilepton selections Exclusion reach for benchmarks could extend as far as 5-6 TeV after the phase=II upgrade Of course we hope for a discovery before then

James Ferrando Searches for t¯ t resonances 58/ 65

SLIDE 61

Introduction Recent Searches The Future Summary

Summary

ATLAS + CMS have performed several searches for new particles decaying to t¯ t Deployed new techniques for the identification of heavy boosted objects No evidence for new particles → t¯ t yet Need to look carefully at the data for all kinds of new physics, it may not contain what we expect...

James Ferrando Searches for t¯ t resonances 59/ 65

SLIDE 62

ATLAS All-hadronic More on l+jets Top Tagging

Back-up

James Ferrando Searches for t¯ t resonances 60/ 65

SLIDE 63

ATLAS All-hadronic More on l+jets Top Tagging

All-hadronic

Initial jet C/A C/A mj1/mjet < µfrac mj2/mj∗

2 < µfrac

James Ferrando Searches for t¯ t resonances 61/ 65

SLIDE 64

ATLAS All-hadronic More on l+jets Top Tagging

All-hadronic

Make exactly three jets Top candidate

mab = mW (1 ± 0.15)

(a, b = j1, j2, j3)

James Ferrando Searches for t¯ t resonances 62/ 65

SLIDE 65

ATLAS All-hadronic More on l+jets Top Tagging

l+jets Backgrounds

James Ferrando Searches for t¯ t resonances 63/ 65

SLIDE 66

ATLAS All-hadronic More on l+jets Top Tagging

l+jets Backgrounds

James Ferrando Searches for t¯ t resonances 64/ 65

SLIDE 67

ATLAS All-hadronic More on l+jets Top Tagging

top-tagging

Progress in top tagging: ATLAS-CONF-2013-084

James Ferrando Searches for t¯ t resonances 65/ 65