Top Quark Mass - IN2P3moriond.in2p3.fr/QCD/2016/SundayAfternoon/McCarthy.pdfT.G.McCarthy - Top Quark Mass @ ATLAS & CMS Rencontres de Moriond QCD Session, March 20, 2016 1 Rencontres

T.G.McCarthy - Top Quark Mass @ ATLAS & CMS Rencontres de Moriond QCD Session, March 20, 2016 1

Rencontres de Moriond QCD 2016 La Thuile, Aosta Valley, Italy

Measurements @ ATLAS & CMS

Sunday, March 20th, 2016

Top Quark Mass

Thomas McCarthy1on behalf of the ATLAS & CMS Collaborations

1Max-Planck-Institut für Physik, München


General Overview

1 Overview & Highlights of LHC Run 1 mtop Measurements (√s = 7 & 8 TeV)

2 LHC Combinations from Run 1

3 Summary & Outlook

https://twiki.cern.ch/twiki/bin/view/AtlasPublic/TopPublicResultsLink to ATLAS Top Quark Public Results

Link to CMS Top Quark Public Resultshttps://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsTOP

A nice summary of LHC mtop

measurements @ Run 1…G. Cortiana (MPI Munich) Submitted to Reviews in Physics

“Top-quark mass measurements: review and perspectives”

http://arxiv.org/abs/1510.04483

pp

Direct measurements from kinematics & event reconstructionAlternative measurements (e.g. from σtt)-

Focus today on a select number of analyses (many more results available, see backup or below)

mtop a fundamental parameter of the Standard Model Short lifetime O(10-25) ➙ no bound hadronic states formed Direct access to top quark properties via its decay products Better knowledge of mtop ➙ better performance in analyses with top backgrounds

Top Quark{

https://twiki.cern.ch/twiki/bin/view/AtlasPublic/TopPublicResults

https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsTOP







































http://www.apple.com

T.G.McCarthy - Top Quark Mass @ ATLAS & CMS Rencontres de Moriond QCD Session, March 20, 2016

tW +

bW

proton

proton

b

+

q q

3

Measurements of mtop @ the LHC: An Overview

t

W +

bb_

W

t_

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proton

q

q

q

qproton

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gg

g

7 TeV8 TeV

7 TeV8 TeV

Eur.Phys.J.C. (2015) 75:158

Combined Channels (7&8 TeV)

All-Hadronic (All-Jets) tt Channel

Single-Top Enriched Events

8 TeV

t

W +

b

b_

W

t_

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proton

qq

proton_

gg

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+

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tt + 1-Jet Channel

7 TeV

-

t

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bb_

W

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proton

proton

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7 TeV8 TeV

7 TeV8 TeV

Eur.Phys.J.C. (2015) 75:330


Dileptonic tt Channel--

Top Mass from tt Cross-Section

7/8 TeV

7/8 TeV

-

t

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bb_

W

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proton

q

qproton

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gg

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7 TeV8 TeV

7 TeV8 TeV

Eur.Phys.J.C. (2015) 75:330


Semileptonic tt Channel-

ATLAS-CONF-2014-055 ATLAS-CONF-2014-053Eur.Phys.J. C74 (2014) 3109

CMS-PAS-TOP-13-004 *Only most precise measurements in each channel summarized on this page. See links to additional analyses in overviews on later slides.

*

CERN-PH-EP-2015-234 CERN-PH-EP-2015-234 CERN-PH-EP-2015-234

arXiv:1603.02303

arXiv:1509.04044 arXiv:1509.04044arXiv:1509.04044

CMS-PAS-TOP-15-0018 TeV




https://cds.cern.ch/record/1951323




https://cds.cern.ch/record/2053213?ln=en









Eur.Phys.J.C. (2015) 75:158

arXiv:1509.04044

Updated & Combined Channels:

t

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bb_

W

t_

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proton

q

q

q

qproton

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All-Hadronic (All-Jets) tt Channel- Direct mtop MeasurementsThe All-Hadronic tt Channel

Advantages:Largest branching ratio Full event reconstruction possible (no neutrinos in W decays)

Combinatorics: large number of jet-parton associations Tight cuts required due to very large multi-jet background

Disadvantages:

-

7 TeV

7 TeV

1D template method

2D template method

= Covered in this Talk= See Backup

2D template method8 TeV

Eur.Phys. J.C. 74 (2014) 2758

(1) W Branching Ratios from: K.A. Olive et al. (Particle Data Group), Chin. Phys. C, 38, 090001 (2014) and 2015 update

tt BR ~ 45%-(1)

CERN-PH-EP-2015-234






MC Mass

Pole MassCERN-PH-EP-2015-234Updated/Combined

Channels (7/8 TeV)√s = 7 TeV

√s = 8 TeVAll-Hadronic Channel @ 8 TeV

(∆mtop = 0.29 GeV) [0.2%] (∆mtop = 0.25 GeV) [0.1%] (∆mtop = 0.20 GeV) [0.1%] (∆mtop = 0.19 GeV) [0.1%]

Dominant Sources of Uncertainty (hybrid)

Measured (Improved!) Result:

7 TeV Result:

2D Template Method mtop extracted together with global JSF (compared w/ 1D)

Updated since Moriond 2015!

b-Dependent JEC Data Statistics Backgrounds In-Situ JEC

Jet energies modified by constraints from kinematic fits using known W boson mass Multi-jet background is modelled using an event-mixing technique (able to get fsig ~ 78%!) Likelihood built from S & B shapes, splitting signal into correct or wrong (from simulation)

arXiv:1509.04044




Direct mtop Measurements

Advantages:Good balance: large BR and modest cuts required Leptonic top identifies event (via lepton) Hadronic top can then be fully reconstructed

Combinatorics remains an issue (typically ≥ 4 jets)

Disadvantages:

t

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Eur.Phys.J.C. (2015) 75:330

Semileptonic tt Channel-

The Semileptonic tt Channel-

7 TeV

7 TeV

3D template method

2D template method


1D µ+jets with BEST8 TeV CMS-PAS-TOP-14-011

JHEP 12 (2012) 105

Updated & Combined Channels:2D template method8 TeV

tt BR ~ 34%-(1)

(1) W Branching Ratios from: K.A. Olive et al. (Particle Data Group), Chin. Phys. C, 38, 090001 (2014) and 2015 update (Value quoted includes all lepton types: e/µ/𝜏 except hadronic 𝜏 decays)

J/𝜓 (l+jets / dileptonic)8 TeV CMS-PAS-TOP-15-014

(Would be ~44% including hadronic tau decays)

e + jets µ + jets

e + jets µ + jets

e + jets µ + jets

e µ + jets

e/µ + J/𝜓 + jets

CERN-PH-EP-2015-234 BR ~ 0.032%arXiv:1509.04044

e/µ + hadrons + jets8 TeV lepton / secondary verticesJust Released}CMS-PAS-TOP-12-030









MC Mass

Pole Mass

√s = 7 TeV

√s = 8 TeV+ Jets Channel @ 8 TeV Updated/Combined Channels

(∆mtop = 0.35 GeV) [0.2%] (∆mtop = 0.16 GeV) [0.1%] (∆mtop = 0.16 GeV) [0.1%]

Dominant Sources of Uncertainty (hybrid)

b-Dependent JEC Semileptonic B-decay modelling Data Statistics

Left: large reduction in (mostly combinatorial) background by applying goodness-of-fit (Pgof) weighting Above: Also evaluate mt separately in different bins of kinematic variables sensitive to top quark production & decay

Final measured result (1D vs hybrid compared):

CERN-PH-EP-2015-234

Precision of ~0.3%!

Best-precision measurement in a single channel at CMS

Analysis strategy similar to 7 TeV and 7/8 TeV all-hadronic

Fitted jet energies used to reconstruct final observable




MC Mass

Pole Mass

Physics Analysis Summary (PAS)

√s = 7 TeV

√s = 8 TeVLepton(s) + J/𝜓 Events @ 8 TeV

Measured Result:

Very small BR, but sensitivity to mtop w/o using jets to build observable (avoid JES/bJES)

Variation on semileptonic / dileptonic channels, requiring at least one of the top quarks have a final leptonic state For the main leptonic top quark decay, aim to identify cases where b-quark decays via (b ➙J/𝜓 + X ➙ µ+µ- + X)

Remains statistically limited for now

Top Quark pT ME-PS Matching Threshold Renormalization Scale

(∆mtop = -0.64 GeV) [0.4%] (∆mtop = +0.58 GeV)[0.3%] (∆mtop = +0.46 GeV)[0.3%]

Dominant Sources of Uncertainty

BR ~ 0.032%

CMS-PAS-TOP-15-014

New Result!



MC Mass

Pole Mass

Will supersede previous result

√s = 7 TeV

√s = 8 TeVSecondary Vertices + Lepton(s)

Sensitivity to mtop primarily from leptons (e/µ) and via decay lengths of charged hadrons (from b-quark decay) Target signal events in both semileptonic and dileptonic channels:

e + jets µ + jets

ee µµ eµDileptonic tt Channel:

Semileptonic tt Channel:

--

Reconstruct charged hadrons (left: J/𝜓, but also D0, D*) resulting from b-quark decays Allows one to retain a stronger sensitivity to mtop without inclusion of jets (where related systematics would otherwise dominate) Ultimately select msvl (invariant mass of lepton / secondary vertex) as mtop-sensitive observable Inclusion of b-quark fragmentation studies (leading systematic)

More generalized version of J/𝜓 analysis

Measured Result:

Dominant systematics: top quark pT & b-quark fragmentation

CMS-PAS-TOP-12-030

New Result!




Advantages:Extremely low backgrounds (typically a few percent) Two lepton/b-jet permutations (combinatorics simplified)

Two neutrinos ➙ full event reconstruction not possible Loss of sensitivity to mtop ➙ energy taken by neutrinos

Disadvantages:

The Dileptonic tt Channel

t

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proton

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Dileptonic tt Channel-

-

Eur.Phys.J.C. (2015) 75:3307 TeV

7 TeV

1D template with mlb

kinematic endpoints = Covered in this Talk= See Backuptemplate AMWT7 TeV Eur.Phys. J.C. 72 (2012) 2202

Eur.Phys. J.C. 73 (2013) 2494

template AMWT8 TeV

eµ b-jet energy peak8 TeV CMS-PAS-TOP-15-002

Updated & Combined Channels:

tt BR ~ 6%-(1)



ee µµ eµ

ee µµ eµ

ee µµ eµ

ee µµ eµ

ee µµ eµ

CERN-PH-EP-2015-234

CMS-PAS-TOP-14-0148 TeV mlb with forward folding ee µµ eµ

arXiv:1509.04044



http://arxiv.org/abs/1304.5783v2






√s = 7 TeV

√s = 8 TeV

MC Mass

Pole Mass Eur.Phys.J.C. (2015) 75:330

One/two b-tagged jets required in event selection

Small amount of background in Nb-tag=1 events (~3%) (predominantly cases of fake leptons)

Invariant mass mlb formed by considering both lepton/b-jet permutations (two such pairings / event)

Select pairing with minimum average mlb (motivated by performance in simulation)

Dilepton Channel @ 7 TeV

t b

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t b

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1D template method employing simulated MC datasets with varying values of mtop

Measured Result:



Jet Energy Scale (JES) bJet Energy Scale (bJES) Data Statistics Hadronization Modelling



MC Mass

Pole Mass

√s = 7 TeV

√s = 8 TeVPhysics Analysis Summary (PAS) CMS-PAS-TOP-15-002Dilepton Channel @ 8 TeV

New since Moriond 2015!

Measured Result:



t b

W + +

Specifically target the sensitivity of the peak of the b-jet energy spectrum to mtop

pT ≥ 17 GeV (1st lepton) [Offline: 20 GeV]

pT ≥ 8 TeV (2nd lepton) [Offline: 20 GeV]

Measured peak position re-calibrated to correct for observed bias (from simulation) [lower left]

eµ channel, trigger two oppositely charged leptons:

Generator Modelling Top pT Reweighting Jet Energy Scale (JES) Data Statistics


T.G.McCarthy - Top Quark Mass @ ATLAS & CMS Rencontres de Moriond QCD Session, March 20, 2016

tW +

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Advantages:Access to mtop through EW production of top quarks Orthogonal datasets w.r.t. other channels ➙ combinations

Lower cross-sections and higher backgrounds

Disadvantages:

Single-Top Enriched Channel

Single-Top Enriched Events

ATLAS-CONF-2014-0558 TeV 1D template m(lb) & NN

tt BR ~ 25%-(1)

(1) W Branching Ratios from: K.A. Olive et al. (Particle Data Group), Chin. Phys. C, 38, 090001 (2014) and 2015 update (Value quoted is for single top quarks and includes all lepton types: e/µ/𝜏 except hadronic 𝜏 decays)


e + jets µ + jets

e µ + jetst-channel with µ + jets8 TeV CMS-PAS-TOP-15-001





MC Mass

Pole Mass

√s = 7 TeV

√s = 8 TeVATLAS-CONF-2014-055Single Top Enhanced (t-Channel) @ 8 TeV

Jet Energy Scale (JES) t-Channel Hadronization Data Statistics W+jets Normalization



Measured Result:

build control region for W+jets background by loosening b-tagging requirement

Left: Following neural net, m(lb) observable selected for mtop sensitivity (1D template method)

tW +

bW

proton

proton

b

+

qq}}e/µ

2 jets (1 b-tag)

https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2014-055/


MC Mass

Pole Mass

√s = 7 TeV

√s = 8 TeVSingle-Top Enriched with µ + Jets Physics Analysis Summary (PAS)

CMS-PAS-TOP-15-001

LO (5-flavour scheme) NLO (4-flavour scheme)

Single-Top t-Channel Productiont

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bW

proton

proton

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qq }}µ

2 jets (1 b-tag)

Require 1 high-pT, isolated reconstructed muon Require 2 reconstructed jets w/ 1 b-tag (signal region)

Zero b-tag events characterize the W+jets background

Invariant mass of reconstructed top (mlνb) is selected as the mtop-sensitive observable

In final extended unbinned likelihood fit, the signal (single-top) normalization + shape parameters left to float

Extraction of mtop comes from mean parameter of Crystal Ball (used to parameterize signal shape)

JES systematic uncertainty dominates (∆mtop ~ 0.68 GeV)

Result shown at QCD EW Session last week (link to agenda)

Measured Result:

New Result!


https://indico.in2p3.fr/event/12279/other-view?view=standard


Indirect Measurements

Advantages:Access to top quark pole mass directly

Compounded combinatorics

Disadvantages:

Pole Mass in tt + 1-jet Channelt

W +

b

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proton_

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tt + 1-Jet Channel-

-

ATLAS-CONF-2014-0537 TeV pole mass in tt+1-jet = Covered in this Talk

tt BR ~ 34%-(1)



e + jets µ + jetsJHEP 10 (2015) 121

One leptonically decaying top quark ➙ keeps background low

where difference between MC & pole mass O(1 GeV)(A. Hoang: arXiv:1412.3649v1)





Pole Mass

MC Mass

JHEP 10 (2015) 121Pole Mass from tt+1-jet events @ 7 TeV-


Measured Result:


(∆mtop = 1.5 GeV) [0.9%] (∆mtop = 0.94 GeV) [0.5%] (∆mtop= +0.93/-0.44 GeV)[+0.5/-0.3 %] (∆mtop = 0.72 GeV) [0.4%]

arXiv:1303.6415Motivated by theory:

where:

Clean channel w/ ~6% background !

Very promising pole mass result

Statistical uncertainty quite large (but √s = 7 TeV dataset)

(m0 = 170 GeV)

(largest: single top)

Extract top quark pole mass directly using differential tt+1-jet cross-section-

√s = 7 TeV

√s = 8 TeV

Data Statistics JES & bJES Scale Variations ISR/FSR

ATLAS-CONF-2014-053





Indirect Measurements

Advantages:Access to top quark pole mass directly Can take advantage of low backgrounds of eµ channel

Sensitivity not as strong as in direct measurements Systematic uncertainties typically larger

Disadvantages:

mtop from Production Cross-Section

Top Mass from tt Cross-Section-

Phys.Lett.B. 738 (2014) 526

7/8 TeV

7 TeV

pole mass eµ channel

first mass from XS


pole mass eµ channel7 TeV

JHEP 07 (2011) 049

Eur.Phys.J. C74 (2014) 3109 ee µµ eµ

ee µµ eµ

ee µµ eµ

ee µµ eµ7/8 TeV pole mass eµ channel CMS-PAS-TOP-13-004






Pole Mass √s = 8 TeV

MC Mass √s = 7 TeVEur.Phys.J. C74 (2014) 3109Pole Mass from Cross-Section at √s = 7 & 8 TeV

Measured Result:

MC Mass


√s = 7 TeV

Great improvement over previous measurement:

Pole Mass from Cross-Section at √s = 7 & 8 TeV

Measurement relies on a given choice of PDF sets and 𝛼s (quoted result uses NNPDF3.0, 𝛼s = 0.118 ± 0.001)

Consistent results using CT14 and MMHT2014, and also comparing √s = 7 & 8 TeV separately Left: √s = 7 & 8 TeV measured values & prediction vs. mtop

Measurement of σtt together with NNLO theoretical prediction allows for extraction of the pole mass (mt)

Luminosity

Dominant Uncertainties

PDFs & 𝛼s

Considered PDF sets: MSTW2008, CT10, and NNPDF2.3Ultimately quoted value comes from maximizing a product of likelihoods based on √s = 7 & 8 TeV

Final result reflects combination of 7 & 8 TeV datasets (as above)

Submitted to JHEP

arXiv:1603.02303




Combinations of ATLAS & CMS Results

ATLAS/CMS mtop Combinations



Link to ATLAS Top Quark Public Results

Link to CMS Top Quark Public Resultshttps://twiki.cern.ch/twiki/bin/view/

CMSPublic/PhysicsResultsTOP

ATLAS-CONF-2013-102

LHC / Tevatron (World) Combination

LHC Combination (√s = 7 TeV)

CMS-PAS-TOP-13-014

ATLAS-CONF-2014-008

CDF Note 11071

D0 Note 6416

CMS-PAS-TOP-13-005

Precision of ~0.3%!


https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsTOP








Summary & Outlook

https://twiki.cern.ch/twiki/bin/view/LHCPhysics/SingleTopRefXsechttps://twiki.cern.ch/twiki/bin/view/LHCPhysics/TtbarNNLO

were produced during 2012 data-taking!

At peak instantaneous luminosities @ ATLAS & CMS:

~2 top pairs/sec~1 single top/sec

~4M top quarks produced in 2011 (√s = 7 TeV)



Era of Precision Top Quark Measurements

(per experiment)

Overall from both experiments combined:

Cross-section values taken from:

pp

√s = 13 TeV

Increasing 𝛾top = Etop/mtop

qq_

b

tq

q

_

t b

W +

Planned measurements of mtop @ √s = 13 TeV Higher √s ➙ greater % of boosted top quarks As always, trade off between with stats / syst Avoiding jets ➙ avoid (b)JES systematics…but b-quark fragmentation / top pT systematics increase New methods should aim to strike optimal balance (see nice LHC talk in EW session last week) [link]

Great success by ATLAS & CMS in making precision mtop measurements during Run 1! Several novel approaches with a variety of final-state signatures (& differing backgrounds)

Thanks for your attention.

Looking Ahead to Run II…

https://indico.in2p3.fr/event/12279/other-view?view=standard


Backup Material



CMS-TOP-14-0027 & 8 TeV

CMS mtop Combinations

A variety of analyses in all main channels

Many analyses employ orthogonal datasets (greater impact on combination)

Dominant contribution from √s = 8 TeV lepton plus jets channel measurement (72.5% BLUE combination coefficient)

Individual per-systematic correlation values used for performing combination are itemized (by decay channel / year)

There remains some tension with results of the Tevatron combination (2014)


Run 1 Comb CMS-PAS-TOP-14-015


https://cds.cern.ch/record/1951019?ln=de



CMS-TOP-14-0027 & 8 TeV

CMS mtop Combinations

Run 1 Comb CMS-PAS-TOP-14-015

New Summary March 2016

CMS-PAS-TOP-15-001

CMS-PAS-TOP-15-014

arXiv:1603.02303

CMS-PAS-TOP-12-030

Eur. Phys. J. C 73 (2013) 2494

CMS-PAS-TOP-15-002


https://cds.cern.ch/record/1951019?ln=de









ATLAS-CONF-2013-102

LHC / Tevatron (World) Combination

LHC Combination (√s = 7 TeV)

CMS-PAS-TOP-13-014

ATLAS-CONF-2014-008

CDF Note 11071

D0 Note 6416

CMS-PAS-TOP-13-005

Summary Plots

ATLAS mtop Combinations

Current combinations include only results using √s = 7 TeV dataset

Expect increased precision at √s = 8 TeVATLAS Sumary PlotsSemi-/di-leptonic (7 TeV) Eur.Phys.J.C. (2015) 75:330

As with CMS, greatest sensitivity in the semileptonic (lepton+jets) channel

In addition several analyses of pole mass performed

Also see:







https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CombinedSummaryPlots/TOP/



Top Quark Production Cross-Sections (Top Quark Pairs)


Top Quark Production Cross-Sections (Single Top)


Top Quark Pole Mass Measurements

https://twiki.cern.ch/twiki/bin/view/AtlasPublic/TopPublicResultsLink to ATLAS Top Quark Public Results



Top Quark Mass World (LHC + Tevatron) CombinationLHC / Tevatron (World) Combination

CMS-PAS-TOP-13-014

ATLAS-CONF-2014-008

CDF Note 11071

D0 Note 6416






(Some!) Observables Sensitive to mtop in Template Measurements

Sensitivity to

mtop

Invariant mass of the lepton/b-jet pair

t b

W +

t b

W -

-_

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+

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Peak of the b-jet energy spectrum

Invariant triple-jet mass

Ratio of reconstructed top-to-W masses (‘R’ or ‘R3/2’)

Advantages:No full kinematic event reconstruction required

Avoids to some extent ambiguity from MET (2 neutrinos)

Lost sensitivity to mtop from neutrinoDisadvantages:

Advantages:Reconstructed top quark most sensical observable to probe true top quark properties

Linearity with generator mtop is likely the most intuitive

t b

W +

Very large susceptibility to fluctuations in JES

Full event reconstruction required (hadronic side)

Combinatorics (jet-parton assignment difficult)

Disadvantages:

q

q

_

t b

W + +

t b

W + q

q

_

}}}

}}Full event reconstruction required (hadronic side)

Susceptibility to bJES uncertainty persists

Disadvantages:

Advantages:Similar sensitivity as mjjj

Less susceptibility to JES ➙ mitigated by similar sensitivity to JES in denominator

Also avoids loss of stats in 2D (/3D) template method

No longer have leptons or neutrinos as probes to top

Increased JES and top quark pT modelling systematics

Disadvantages:

Advantages:No full kinematic event reconstruction required

Presence of leptons + b-tagged jets enough to trigger event (very low backgrounds in dilepton channel)

Technically possible in any channel

Combinatorics not an issue

Eb-jet


√s = 7 TeV

√s = 8 TeV

MC Mass

Pole Mass

Kinematic likelihood employed for event reconstruction

1D template method with R3/2 = mjjj/mjj as mtop-sensitive observable

R3/2 observable: suppress the contribution from JES systematic uncertainty Data-driven ‘ABCD’ method employed for multi-jet background estimation

In final fit two parameters are left to float: top mass (mt)& the fraction of bkgd events (fbkg)

Eur.Phys.J.C. (2015) 75:158All-Hadronic Channel @ 7 TeV

Data Statistics bJet Energy Scale (bJES) Hadronization Modelling Jet Energy Scale (JES)


(∆mtop =1.4 GeV) [0.8%] (∆mtop = 0.62 GeV) [0.4%] (∆mtop = 0.50 GeV) [0.3%] (∆mtop = 0.51 GeV) [0.3%]



√s = 7 TeV

√s = 8 TeV

MC Mass

Pole Mass

Employs ideogram method Investigated precision of 1D or 2D method (2D method simultaneously extracts global JES) Likelihood variable based on S & B parameterizations:

Updated/Combined Channels (7&8 TeV)

Particular Analysis Eur.Phys. J.C. 74 (2014) 2758All-Hadronic Channel @ 7 TeV

1D Method

2D Method together with

global JES

Signal split into three permutation cases: (correct, incorrect, unmatched) from simulation Event weights lessen impact of incorrect jet-parton associations from kinematic fit (keeping total number of events unchanged)

Jet energies modified by constraints from kinematic fits Jet Energy Scale (JES)

Data Statistics Data Statistics


Dominant Sources of Uncertainty (1D)

CERN-PH-EP-2015-234




MC Mass

Pole Mass

Updated/Combined Channels (7&8 TeV)

√s = 7 TeV

√s = 8 TeVAll-Hadronic Channel @ 8 TeV CERN-PH-EP-2015-234

arXiv:1509.04044




√s = 7 TeV

√s = 8 TeV

MC Mass

Pole Mass Eur.Phys.J.C. (2015) 75:330+ Jets Channel @ 7 TeV

Targets three different observables, each sensitive to a particular key parameter Background also sensitive to JSF, bJSF

Build template parameterizations and perform a global 3D fit to extract all parameters simultaneously

Observable

Target sensitivity

Observable

Target sensitivity

Observable

Target sensitivity

Where

is defined differently for

events with 1 or ≥ 2 b-tagged jets{



√s = 7 TeV

√s = 8 TeV

MC Mass

Pole Mass Eur.Phys.J.C. (2015) 75:330

Background fraction from ~ 25% (1 b-tag events) to 3% (≥2 b-tag events)

+ Jets Channel @ 7 TeV

Dominant Sources of Uncertainty (3D)


Measured Results:

(mostly W+jets) (mostly single top)

1D Template Method

Use of 3D template method (over 1D) improves JES / bJES syst uncertainties

2D Template Method 3D Template Method

Also correlations between this and dilepton analysis reduced (useful for combinations)

Statistics (incl. JSF/bJSF cont.)

Jet Energy Scale (JES) b-Tagging ε / mistag ISR/FSR



MC Mass

Pole MassPhysics Analysis Summary (PAS)

√s = 7 TeV

√s = 8 TeVCMS-PAS-TOP-14-011+ Jets Channel @ 8 TeV

Alternate √s = 8 TeV analysis performed in µ+jets channel

Template method employing R observable (ratio of reconstructed top/W masses)

Bi-Event Subtraction Technique (BEST) used to estimate background shape

Note good agreement in both distributions:

(Left)

(Right)

Also note shapes differ

Crucially R is more resistant to shifts in JEC

{}

Reconstructed top (from event X)

Reconstructed W

1 2

Replace 1 non-tagged jet with

one from event Y

{} R = _________m( )m( )

Yields a distribution of R representative of combinatorial background

W-mixing with BEST (b-mixing similar)

Combinatorial W

Combinatorial top




MC Mass

Pole MassPhysics Analysis Summary (PAS)

√s = 7 TeV

√s = 8 TeVCMS-PAS-TOP-14-011+ Jets Channel @ 8 TeV

Measured Result:



Left: Good agreement in between signal and data-minus-background

Total systematic using R (∆mtop = 0.90 GeV)Total systematic using mbjj (∆mtop = 2.45 GeV)

Note this is an alternate analyses of the full √s = 8 TeV dataset in l+jets channel

Precision of ~0.3%!

The analysis covered in the main talk yields the following result:

Data Statistics Renorm/Factor. Scale Flavor-Dep. Hadronization b Fragment. + B had. BR




Particular Analysis √s = 7 TeV

√s = 8 TeV

MC Mass

Pole Mass

JHEP 12 (2012) 105+ Jets Channel @ 7 TeV

Build 2D likelihood function to extract simultaneously mtop and a global JES

Per-permutation weights applied to heighten contribution from correct jet-quark assignments

Left (upper): all permutations for reconstructed mtop prior to kinematic fit and Pgof weighting

Left (lower): following Pgof cut, weighting and kinematic fit

Dominant Systematics: Color Reconnection (0.54 GeV), bJES (0.61 GeV)

Build templates for all simulated signal{Here ‘correct’

permutations shown but done for all 3 categories

Strong sensitivity to generator mtop as expected

Measured Results:

CERN-PH-EP-2015-234




MC Mass

Pole Mass

√s = 7 TeV

√s = 8 TeV+ Jets Channel @ 8 TeV

Comparisons between 1D, 2D and hybrid template method Hybrid: incorporates prior knowledge about JSF using a Gaussian constraint Best precision obtained in hybrid case as in all-had channel


Updated/Combined Channels CERN-PH-EP-2015-234

arXiv:1509.04044




√s = 7 TeV

√s = 8 TeV

MC Mass

Pole Mass Eur.Phys.J.C. (2015) 75:330+ Jets + Dilepton Channel @ 7 TeV



√s = 7 TeV

√s = 8 TeV

MC Mass

Pole Mass Eur.Phys.J.C. (2015) 75:330+ Jets + Dilepton Channel @ 7 TeV




Particular Analysis √s = 7 TeV

√s = 8 TeV

MC Mass

Pole Mass

Eur.Phys. J.C. 73 (2013) 2494Dilepton Channel @ 7 TeV

Measured Result:

(∆mtop = +1.3/-1.8 GeV) [+0.7/-1.0%] !(∆mtop ~ ±0.6 GeV) [0.3%]


Analysis strategy ideally suited to scenarios when pairs of parent particles each decay to a partially invisible final state, e.g.

General approach allows for measurement of all three masses – mtop, mW and m𝜈 (or DM rather than neutrinos)

Alternatively constrain system using mW and m𝜈 for precision mtop measurement (as is done here)

t b

W + +

t

W -

-b_

_

-Key observable (MT2) based on the more familiar transverse mass variable (MT):

Sensitivity to kinematic endpoints in distributions

QCD Effects Background Shape Fit Range

Jet Energy Scale (JES)

CERN-PH-EP-2015-234

http://arxiv.org/abs/1304.5783v2



MC Mass

Pole Mass

√s = 7 TeV

√s = 8 TeVDilepton Channel @ 8 TeV

(Updated!) Measured Result:

Consider ee, µµ, eµ channels (modest background [~18%], largely D-Y) Employ an Analytic Matrix Weighting Technique (AMWT) Require ≥ 1 b-tagged jet (if < 2 also take non-tagged jet with leading pT)

mtop extracted from a likelihood fit based on templates constructed from simulation

Consider large number of possible neutrino momenta and weight solution accordingly via:

where:

7 TeV Result:


Renorm/Factor. Scales b Fragmentation JEC b Flavour Comp



Associated 7 TeV Result

Updated/Combined Channels

Eur.Phys. J.C. 72 (2012) 2202

CERN-PH-EP-2015-234




MC Mass

Pole Mass

√s = 7 TeV

√s = 8 TeVDilepton Channel @ 8 TeVAssociated 7 TeV Result

Updated/Combined Channels

Eur.Phys. J.C. 72 (2012) 2202

CERN-PH-EP-2015-234




MC Mass

Pole Mass

√s = 7 TeV

√s = 8 TeVDilepton Channel @ 8 TeV Physics Analysis Summary (PAS)

CMS-PAS-TOP-14-014

Separate analysis of dileptonic tt channel data @ 8 TeV 1D template method using mlb observable (defined below) to probe mtop:

-

Measured Result:

Top Quark pT b Fragmentation

(∆mtop = 0.66 GeV) [0.4%] (∆mtop = 0.62 GeV) [0.4%]


Base signal MC employs:MADGRAPH 5.1.5.11 for ME generator MADSPIN for heavy resonance decays Pythia 6.426 for PS and hadronization

Require two opposite-sign leptons (specifically eµ) Forward detector folding of theoretical prediction to allow for comparison with measured data

angle between lepton-bin W rest frame




MC Mass √s = 7 TeVEur.Phys.J. C74 (2014) 3109Pole Mass from Cross-Section at √s = 7 & 8 TeV

Measured Result:

Predominantly a high-precision cross-section calculation measurement Pole mass (mtop) can simultaneously be extracted from dependence on XS Work specifically in the eµ channel (oppositely charged leptons)

where

}Solve for&

Allows for solution of system of equations below Simultaneous measurements:

Look @ Number of Data Events with 1 or 2 b-tagged Jets (N1 & N2, respectively)

Inclusive cross-section ( ) Efficiency to reconstruct and tag a b-quark jet ( )

Luminosity Parton Distribution Functions (PDFs)

Dominant Uncertainties (Largely Theoretical):Uncertainties on 𝛼s



MC Mass

Pole MassPole Mass from Cross-Section at √s = 7 & 8 TeV

Measurements of σtt together with NNLO theoretical prediction allow for the extraction of the top quark pole mass (mt) Relies on a given choice of PDF sets and 𝛼s (quoted result uses NNPDF3.0, 𝛼s = 0.118 ± 0.001)

Consistent results using CT14 and MMHT2014 Parameterize functional dependence of σtt on mt as exponential function

Maximization of final likelihood yields measured value (after 7/8 TeV combination):

Submitted to JHEP

√s = 8 TeV

√s = 7 TeV

Precision cross-section measurements performed at √s = 7 & 8:

Great improvement previous measurement:

Above: Measured values (black markers) with the vertical bars indicating the total 1-σ uncertainty. The theoretical predictions are shown as the coloured bands.

Three points above correspond to different mt hypotheses(for which σtt fit is repeated) ∆mt/mt ~ 1%

Top quark pole mass precision of

arXiv:1603.02303



MC Mass

√s = 8 TeVPole Mass

√s = 7 TeVPhys.Lett.B. 738 (2014) 526Pole Mass from Cross-Section at √s = 7 TeV

Measured Result:

!Measured value taken from dileptonic (eµ) channel result (most precise) Result gives a Baysian contour interval on mtop under external constraint of 𝛼s

Baysian analysis to determine a value of mtop (pole mass) based on measured and theoretical σtt

Very good precision on 𝛼s:

Sensitivity to Uncertainty on 𝛼s

But even shifting by this amount greatly affects ∆mtop:



Alternate Measurements

Advantages:Can take advantage of ‘tag and probe’ method of lepton + jets channel (relatively low backgrounds) Complimentary to direct top quark mass measurements as there no distinction is made between top/anti-top

Very sensitive to detector’s b- vs. b-jet response Differences in W- / W+ production also significant systematic uncertainty

Disadvantages:

Top/Anti-top Quark Mass Difference

Top Quark Mass Difference

t W +

bb_

t_

W _

qq_

+mt-

mt

_

Phys. Lett. B. 728C (2014)

JHEP 06 (2012) I 09

7 TeV

7 TeV

semileptonic (e/µ) ∆mtop

semileptonic (e/µ) ∆mtop


e + jets µ + jets

e + jets µ + jets




√s = 7 TeVPhys. Lett. B. 728C (2014)Pole Mass √s = 8 TeV

MC MassTop/Anti-top Quark Mass Difference √s = 7 TeV

∆mtop = 0.67 GeV ± 0.61 (stat) ± 0.41 (syst) GeV

Measured Result:

Result Consistent with Standard Model

Predictions and CPT invariance

Require two b-tagged jets Event reconstruction: kinematic fit ∆mm calculated on per-event basis Maximum likelihood fit to final distribution

fit

}e/µ charge from

leptonic top quark decay

Semileptonic channel with 1 hadronically / 1 leptonically decaying top quark

∆m [GeV]fit

Choice of b fragmentation model ➙ Different Responses to b/b-Jets

Dominant Uncertainty:

_

Data statistics



√s = 7 TeV

√s = 8 TeV

MC Mass

Pole MassTop/Anti-top Quark Mass Difference √s = 7 TeV

Performed separately for e+jets and µ+jets channels Final likelihood-based fit performed separately for each distribution (as shown above) Results show ∆mt = |mtop - manti-top| consistent with 0 as required by CPT theorem

Average mt also consistent with other measurements

e+jets:µ+jets:

combined:

∆mt = -0.44 GeV ± 0.46 (stat)

± 0.27 (syst) GeV

Measured Result:

JHEP 06 (2012) I 09


Documents

Top Quark Mass - IN2P3moriond.in2p3.fr/QCD/2016/SundayAfternoon/McCarthy.pdfT.G.McCarthy - Top Quark Mass @ ATLAS & CMS Rencontres de Moriond QCD Session, March 20, 2016 1 Rencontres