Top quark mass measurement using t¯ t + 1 jet events with the ATLAS detector
Esteban Fullana, Juan Fuster, Davide Melini, Adrian Irles, Luis Monsonis, Alberto Prades ∗ , Marcel Vos
October 14 th , 2019
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Contents
1 Intoduction
The ATLAS detector
Top quark pair decay channels
2 Observable definition with t t ¯ + 1-jet events Parton level
Detector level
3 Summary of 7 and 8 TeV measurements Uncertainties breakdown
4 Summary
Intoduction The ATLAS detector
The ATLAS detector
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Intoduction The ATLAS detector
ATLAS detector delivered Luminosity
Luminosity:
7 TeV → L ' 4.6fb −1
8 TeV → L ' 20.6fb −1
13 TeV → L ' 150fb −1
Intoduction Top quark pair decay channels
Top quark decay channels
The top quark decays before hadronizing due to its short lifetime (< τ had )
Each W boson can decay W → q q ¯ 0
W → lν l
Top quark pair decay Fully hadronic Semileptonic Dileptonic
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Observable definition witht¯t+ 1-jet events Parton level
t t ¯ + 1-jet event selection at parton level
p extrajet T > 50 GeV and |η| < 2.5
Observable definition witht¯t+ 1-jet events Detector level
t t ¯ + 1-jet event selection at detector level
one electron or muon n jets ≥ 5
two b-tagged jets
E T miss > 25 GeV p T lep > 25 GeV
extra jet p T > 50 GeV & |η| < 2.5
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Observable definition witht¯t+ 1-jet events Detector level
Observable definition with t ¯ t + 1-jet events
R(m pole t , ρ s ) = 1 σ t¯ t+1–jet
d σ t¯ t+1–jet
d ρ s (m pole t , ρ s ) , ρ s = 2m 0
√ s t¯ t+1–jet
7 TeV simulations
S (ρ
s) = |R(m
0+ ∆m, ρ
s) − R(m
0− ∆m, ρ
s)|
2∆mR(m
0, ρ
s) ,
∆R R
≈
m
tpoleS
×
∆m
poletm
tpoleSummary of 7 and 8 TeV measurements
Summary of 7 and 8 TeV measurements
7 TeV (4.6 fb
−1) 8 TeV (20.3 fb
−1)
The increase in statistics allow a smaller binning in the high sensitivity region which lead to a
greater sensitivity to m top
⇓
Decrease in statistic and systematic uncertainties
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Summary of 7 and 8 TeV measurements
Summary of 7 and 8 TeV results
R(m pole t , ρ s ) = 1 σ t t+1–jet ¯
d σ t t+1–jet ¯
d ρ s (m pole t , ρ s ) , ρ s = 2m 0
√ s t t+1–jet ¯
7 TeV results (JHEP 10 (2015) 121)
m pole t = 173.7 ± 1.5(stat.) ± 1.4(syst.) +1.0 −0.5 (theory) GeV
8 TeV results (Approved TOPQ-2017-09)
m t pole = 171.05 ± 0.43(stat.) ± 0.92(syst.) +0.66 −0.32 (theory) GeV
An improvement in statistic and systematic uncertainties,
with respect to the 7 TeV analysis, has been achieved at 8TeV,
thanks to a higher sensitivity and improved methodology.
Summary of 7 and 8 TeV measurements Uncertainties breakdown
Uncertainties breakdown
7 TeV (4.6 fb
−1) 8 TeV (20.3 fb
−1)
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Summary of 7 and 8 TeV measurements Uncertainties breakdown
Uncertainties breakdown
arXiv links: 1507.01769v2 & 1905.02302v2
Uncertainty breakdown (8 TeV) Main sources of
systematic uncertainties:
Modelling → Shower + Hadronization
→ Colour reconnection
→ Underlying event Detector Uncertainties
→ JES
The theoretical uncertainties of the
running mass are higher than in the
pole mass.
Summary of 7 and 8 TeV measurements Uncertainties breakdown
Uncertainties in the analysis
To reduce these uncertainties and the theoretical ones at 13 TeV:
We expect to use larger samples and full detector simulation for t t ¯ + 1-jet samples
→ reduce the statistical uncertainty of the systematical error
→ simplify the unfolding process
Use the dileptonic final state. Different systematic errors to be explored The JES and b-JES uncertainties can be reduce thanks to a better understanding of the detector response.
Main challenges:
Increase sensitivity region (this can also reduces systematics)
→ smaller bin size
→ closer to threshold region
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Summary
Summary
Prospects of m t measurements with t t ¯ + 1 jet at √ 13 TeV
The R observable has provided very competitive results for the top quark pole and running mass measurement at 7 / 8 TeV
For the 13 TeV measurement, our intention is to explore new
methodologies to improve even more aiming for a precision in top
quark pole mass of 0.5 − 1 GeV.
Summary
Back-up
Back-up
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Summary
Unfolding. From detector to parton level
Parton level Particle level
→
→
Parton shower Detector level
→ Pre-hadronization level →
Summary
Unfolding. From detector to parton level 8 TeV unfolding
8 TeV observable unfolded from particle to parton level
Unfolding matrix
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Summary
Multiple final states
Semileptonic
This final state is going to take advantage of the 7 and 8 TeV expertise
The same method followed in the 8 TeV measurement will be applied Try to improve the method applied at 8 TeV aiming 0.5 − 1 GeV uncertainty
Dileptonic
Top mass measurement using the Dileptonic final state For this final state there are new pure perturbative theoretical calculations at particle level ( JHEP 1803 (2018) 169 and other calculations).
Combinations of these two measurements could be possible
Summary
Top quark running mass
200 400 600 800 1000
145 150 155 160 165
μ [GeV]
m
— t( μ ) [ GeV ]
7 TeV measurement → m t (m t ) = 165.9 +2.4 −2.0 (total) GeV
(Eur.Phys.J. C77 (2017) no.11, 794 (2017-11-22))
8 TeV measurement → m t (m t ) = 162.9 +2.3 −1.6 (total) GeV
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