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Measurements of the top quark masswith the ATLAS detector
p ptb
b-jet
W+
ν�
�+
t
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b-jet
W−
�−ν�
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ATLAS-1=8 TeV, 20.2 fbs
ATLAS measurements of the top quark mass Richard Nisius (MPP Munchen) Venice, July 6, 2017 2 /2
EPS 2017 ConferenceVenice, July 7, 2017
Richard Nisius (MPP Munchen)for the ATLAS Collaboration
Introduction Indirect determination Direct measurements Combination Conclusions Backup
The plan of this presentation
fg/p
fg/p
σgg→tt
τ+τ 1%
τ+µ 2%
τ+e 2%
µ+µ 1%
µ+e 2%
e+e 1%
e+jets 15%
µ+jets 15%
τ+jets 15%
"jets" 46%
"lepton+jets""dilepton" Introduction
[GeV]µe
TDilepton p
0 50 100 150 200 250 300
pred
ictio
n / d
ata
0.7
0.8
0.9
1
1.1
1.2
1.3
ScalePDFAlphaS
Data uncertainty
MCFM+HERAPDF 1.5
ATLAS Preliminary-1 = 8 TeV, 20.2 fbs
Indirect determination of mpoletop
− Lepton differential distributions, ATLAS-CONF-2017-044
[GeV]recolbm
50 100 150
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topm167.5 GeV172.5 GeV177.5 GeV
ATLASSimulation
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11.21.4
Direct measurements of mtop
− All-jets channel, arXiv:1702.07546
− Lepton + jets channel, Eur. Phys. J. C75 (2015) 330
− Dilepton channel, Phys. Lett. B761 (2016) 350
[GeV]topm165 170 175 180 185
1
17
0.70± 172.84 Phys. Lett. B761 (2016) 350 ATLAS Comb. June 2016
-1 =4.6 fbintL
JHEP 10 (2015) 121+1-jet) t(tσ 2.1 2.3 ±173.7
-1 =4.6-20.3 fbintL
Eur. Phys. J. C74 (2014) 3109) dilepton t(tσ 2.6 2.5 ±172.9
-1 = 20.2 fbintLarXiv:1702.07546all jets 1.0 )± ( 0.6 1.2 ±173.7
-1 = 20.2 fbintL
Phys. Lett. B761 (2016) 350 dilepton → 0.7 )± ( 0.4 0.8 ±173.0
-1 = 4.7 fbintL
Eur. Phys. J. C75 (2015) 330 dilepton → 1.3 )± ( 0.5 1.4 ±173.8
-1 = 4.7 fbintL
Eur. Phys. J. C75 (2015) 330 l+jets → 1.0 )± 0.7 ± 0.2 ± ( 0.2 1.3 ±172.3
-1 =20.3 fbintLCONF-2014-055single top* 2.0 )± ( 0.7 2.1 ±172.2
-1 = 4.6 fbintL
Eur. Phys. J. C75 (2015) 158all jets 1.2 )± ( 1.4 1.8 ±175.1
-1 - 20.3 fb-1 = 4.6 fbint
summary - May 2017, Ltopm
syst.)± bJSF ± JSF ± tot. (stat. ± top m
σ 1 ±ATLAS Comb. stat. uncertainty
bJSF uncertainty⊕ JSF ⊕stat. total uncertainty
Input to comb.→Preliminary, *
ATLAS Preliminary
Combination of direct measurements
Conclusions
����H
HHH
Note: - I cannot discuss in detail all displayed content, however, the main result
figures have hyperlinks to the web page of the corresponding document.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 2 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
The lepton differential cross-sections from 8 TeV data
An example compared to simulation
[GeV]µe
TDilepton p
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-1 = 8 TeV, 20.2 fbs
Data 2012 Powheg+PY6tt
WtZ+jetsDibosonMis-ID lepton
Powheg+PY6MC@NLO+HWAlpgen+HW
[GeV]µe
TDilepton p
0 50 100 150 200 250
MC
/Dat
a
0.8
1
1.2 Stat. uncert.
− Measure a number of lepton differential distributions in tt→ eµ + X events.
The sensitivity of peµT to mtop
[GeV]µe
TDilepton p
0 50 100 150 200 250 300
ref
σ)/
ref
σ-σ
Nor
mal
ised
(
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
=172.5 GeVt
ref. fit Powheg+PY6 m=165 GeV
talt. fit Powheg+PY6 mdata stat. error
ATLAS Simulation Preliminary
− Correct to stable particle level (using Powheg+Pythia6+CT10), subtract the back-ground and convert into normalised lepton differential cross-sections 1
σxdσxdx .
− Clear sensitivity to mtop for x = p`T, peµT ,meµ, pe
T+pµT , Ee+Eµ, but not for |η`|, |yeµ|,∆Φeµ.
The lepton differential cross-sections can be used to determine mtop or mpoletop .
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 3 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
The mpoletop mass from lepton differential cross-sections
Comparison to a fixed order prediction
[GeV]µe
TDilepton p
0 50 100 150 200 250 300
pred
ictio
n / d
ata
0.7
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1
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ScalePDFAlphaS
Data uncertainty
MCFM+HERAPDF 1.5
ATLAS Preliminary-1 = 8 TeV, 20.2 fbs
bars = full data uncertainty
−Within the sizeable uncertainties, the fixed order prediction describes the data.
The fitted mpoletop values
TLepton p µe
TDilepton p
µeDilepton m µ
T+pe
TDilepton p
µ+EeDilepton E Comb. (8 dist)
[GeV
] t p
ole
m
160
165
170
175
180
185
CT14MMHTNNPDF 3.0HERAPDF 2.0ABM 11NNPDF nojet
ATLAS Preliminary-1 = 8 TeV, 20.2 fbs
total uncertainty statistical uncertaintyworld-average direct reconstruction
/2 t
=mµMCFM NLO fixed-order,
χ2Ndf =
64−7168
6
��@@
− The results in mpoletop are from fits to individual distributions, or to all distributions (including
|η`|, |yeµ|,∆Φeµ) while constraining the syst. uncertainties with nuisance parameters.− The spread in the individual results is about 6 GeV. The combined result is:
mpoletop = 173.2± 0.9 (stat.)± 0.8 (syst.)± 1.2 (theo.) GeV = 173.2± 1.6 GeV. The theo. un-
certainty is from PDF (0.3 GeV) and fixed vs. dynamic (e.g. ET2 ) scale variations (1.1. GeV).
The first measurement of mpoletop using this method results in an uncertainty of 1.6 GeV.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 4 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
The uncertainty in the jet energy scale (JES)
g
g
b - Jet
W
Neutrino
Lepton
b - Jet
Wq - Jet
q - Jet
t
t
t
tt → (b e ν) (b q q), M(qq) = mW, M(bqq) = mtop
νe
b-jet
e
jet
jet
b-jet
− Precise calibrations of the energy scale of inclusive jets(JES) and the relative b-to-light-jet energy scale (bJES)are vital for precise measurements of mtop.
ref
T/pjet
Tp
0 0.5 1 1.5 2 2.5
Eve
nts
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20
40
60
80
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140
< 80 GeVref
T60 < p
ATLAS Preliminary-1
Ldt=20.3 fb∫=8 TeV, s
R = 0.4, LCW+JEStanti-k
)-jet - Dataµµ ee/→(Z
Jet Z → e+e−µ+µ−
pT,Jet = pT,Z
Calibration via pT - balance
ATL
AS
-CO
NF-
2015
-057
[GeV]jetT
p20 30 40 210 210×2 310 310×2
Frac
tiona
l JES
unc
erta
inty
0
0.02
0.04
0.06
0.08
0.1
ATLAS Preliminary correctionin situ = 0.4, LCW+JES + R tanti-k
= 8 TeVsData 2012, = 0.0η
Total uncertainty JESin situAbsolute JESin situRelative
Flav. composition, inclusive jetsFlav. response, inclusive jetsPileup, average 2012 conditionsPunch-through, average 2012 conditions
ATLAS-CONF-2015-037
JES uncertainty versus Jet - pT
-
0.01 · mtop ≈ 1.7 GeV!− For high precision in mtop the possibility of in-situ cali-
brations of the mean JES and bJES are extremely helpful.
A small JES-induced uncertainty in mtop is indispensible.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 5 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
Measurement in the all-jets channel from 8 TeV datap p
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QCD Multi-jet (Data-Driven)
Syst. Uncertainty⊕Stat.
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The mjj distribution
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QCD Multi-jet (Data-Driven)
Syst. Uncertainty⊕Stat.
jj/mjjj = m3/2R1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4
Dat
a / P
redi
ctio
n
0.5
1
1.5
The R32 distribution Some analysis details
− The number of b-tagged jets amongstthe six leading jets and 〈∆Φ(b,W )〉 inthe signal and three control regionsare used to determine the shape of thebackground distributions from data.
�����− Chosing the R32 =
mjjjmjj
=mbqqmqq
distri-bution (with an ATLAS Exp. expected’peak’ at 172.84
80.37 = 2.15) stabilises mtop
against a global JES uncertainty.
jj/mjjj = m3/2R
1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4
Ent
ries
/ 0.0
4
0
200
400
600
800
1000
= 8 TeVsData Signal FitBackground FitTotal Fit
ATLAS-1 Ldt = 20.2 fb∫ -1 Ldt = 20.2 fb∫ -1 Ldt = 20.2 fb∫
/ndf = 72.3/48 = 1.512χ
The result from the fit to data
− mtop = 173.72 ± 0.55 (stat) ± 1.01 (syst) GeV− Most important systematic uncertainties: JES (0.60 GeV)
bJES (0.34 GeV) and hadronisation (0.64 GeV).− The summary so far:
Channel (√
s) Stat Model Background ExperimentalAll-jets (8) 0.55 0.70± 0.16 0.19 0.71± 0.04
An about 40% improvement compared to the 7 TeV analysis.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 6 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
Three-dimensional lepton + jets analysis from 7 TeV datap p
tb
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νℓ
ℓ+
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Single topW +jetsZ +jetsWW/WZ/ZZNP/fake lep.Uncertainty
[GeV]recotopm
130 140 150 160 170 180 190 200 210 220
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a/M
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ATLAS-1=7 TeV, 4.6 fbs
The analysis idea− (b)JSF = (b)Jet Scale Factor
to obtain scaled jets
p′t (q) = JSF · pt(q)
p′t (b) = JSF · bJSF · pt(b)
1. mrecotop = f(mtop, JSF, bJSF).
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ATLAS-1=7 TeV, 4.6 fbs
− Additional dimensions
2. mrecoW = 2E1E2(1− cosθ12)
∝ JSF2
2. mrecoW = f(JSF).
recobqR
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recobqR
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ATLAS-1=7 TeV, 4.6 fbs 3. Rreco
bq =
∑pt(b)∑pt(q)
∝ bJSF·JSFJSF = bJSF
3. Rrecobq = f(bJSF) with a weak mtop dependence.
− The 2D (mrecotop , mreco
W ) or 3D (+Rrecobq ) template fit redu-
ces the JES and bJES induced uncertainties in mtop.− Since the JSF and bJSF are global, but JES and
bJES are f(pt, η), residual uncertainties remain.
This is the first 3D mtop analysis worldwide.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 7 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
The list of systematic uncertaintiesDRAFT
tt ! lepton+jets tt ! dilepton Combinationm`+jets
top [GeV] JSF bJSF mdiltop [GeV] mcomb
top [GeV] ⇢
Results 172.33 1.019 1.003 173.79 172.99Statistics 0.75 0.003 0.008 0.54 0.48 0
– Stat. comp. (mtop) 0.23 n/a n/a 0.54– Stat. comp. (JSF) 0.25 0.003 n/a n/a– Stat. comp. (bJSF) 0.67 0.000 0.008 n/a
Method 0.11 ± 0.10 0.001 0.001 0.09 ± 0.07 0.07 0Signal MC 0.22 ± 0.21 0.004 0.002 0.26 ± 0.16 0.24 +1.00Hadronisation 0.18 ± 0.12 0.007 0.013 0.53 ± 0.09 0.34 +1.00ISR/FSR 0.32 ± 0.06 0.017 0.007 0.47 ± 0.05 0.04 �1.00Underlying event 0.15 ± 0.07 0.001 0.003 0.05 ± 0.05 0.06 �1.00Colour reconnection 0.11 ± 0.07 0.001 0.002 0.14 ± 0.05 0.01 �1.00PDF 0.25 ± 0.00 0.001 0.002 0.11 ± 0.00 0.17 +0.57W/Z+jets norm 0.02 ± 0.00 0.000 0.000 0.01 ± 0.00 0.02 +1.00W/Z+jets shape 0.29 ± 0.00 0.000 0.004 0.00 ± 0.00 0.16 0NP/fake-lepton norm. 0.10 ± 0.00 0.000 0.001 0.04 ± 0.00 0.07 +1.00NP/fake-lepton shape 0.05 ± 0.00 0.000 0.001 0.01 ± 0.00 0.03 +0.23Jet energy scale 0.58 ± 0.11 0.018 0.009 0.75 ± 0.08 0.41 �0.23b-Jet energy scale 0.06 ± 0.03 0.000 0.010 0.68 ± 0.02 0.34 +1.00Jet resolution 0.22 ± 0.11 0.007 0.001 0.19 ± 0.04 0.03 �1.00Jet e�ciency 0.12 ± 0.00 0.000 0.002 0.07 ± 0.00 0.10 +1.00Jet vertex fraction 0.01 ± 0.00 0.000 0.000 0.00 ± 0.00 0.00 �1.00b-Tagging 0.50 ± 0.00 0.001 0.007 0.07 ± 0.00 0.25 �0.77Emiss
T 0.15 ± 0.04 0.000 0.001 0.04 ± 0.03 0.08 �0.15Leptons 0.04 ± 0.00 0.001 0.001 0.13 ± 0.00 0.05 �0.34Pile-up 0.02 ± 0.01 0.000 0.000 0.01 ± 0.00 0.01 0Total 1.27 ± 0.33 0.027 0.024 1.41 ± 0.24 0.91 �0.07
Table 3: The measured values of mtop and the contributions of various sources to the uncertainty in the tt !lepton+jets and the tt ! dilepton analyses. The corresponding uncertainties in the measured values of the JSF andbJSF are also shown for the tt ! lepton+jets analysis. The statistical uncertainties associated with these valuesare typically 0.001 or smaller. The result of the mtop combination is shown in the rightmost columns, together withthe correlation (⇢) within each uncertainty group as described in Sect. 8. The symbol n/a stands for not applicable.Values quoted as 0.00 are smaller than 0.005. Finally, the last line refers to the sum in quadrature of the statisticaland systematic uncertainty components.
Pile-upThe residual systematic uncertainty due to pile-up was assessed by determining the dependence of thefitted top quark mass on the amount of pile-up activity, combined with uncertainties in modelling theamount of pile-up in the sample.
7.5. Summary
The resulting sizes of all uncertainties and their sum in quadrature are given in Table 3. The total un-certainties on m`+jets
top , JSF, bJSF and mdiltop, amount to 1.27 GeV, 0.027, 0.024 and 1.41 GeV, respectively.
Within uncertainties, the fitted values of JSF and bJSF are consistent with unity.
16th March 2015 – 15:41 25
Sta
tistic
sM
odel
Bac
kgr.
Exp
erim
enta
l
− The third dimensions reduces the bJES induceduncertainty in mtop from 0.88 to
√0.672 + 0.062
= 0.67, but now it is mostly statistical.− As a side effect a number of MC modelling uncer-
tainties are reduced as well. This is because adifferent bJSF better accounts for the MC diffe-rences than a different mtop.
− The uncertainty in mtop is back to being dominatedby the JES induced uncertainty.
− The summary so far:
Channel (√
s) Stat Model Background ExperimentalAll jets (8) 0.55 0.70± 0.16 0.19 0.71± 0.04
Lepton + jets (7) 0.75 0.53± 0.11 0.31± 0.00 0.82± 0.08
In this channel, the bJES induced uncertainty has finally lost its fright.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 8 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
Optimisation in the dilepton channel from 8 TeV datap p
tb
b-jet
W+
νℓ
ℓ+
t
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top, mtt
Uncertainty Single top
NP/fake leptons Z+jetsWW/WZ/ZZ
ATLAS-1=8 TeV, 20.2 fbs
[GeV]T,lb
p0 50 100 150 200 250 300 350 400
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a/M
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1.2
The pT ,`b distribution
− The variable pT ,`b denotes the mean pT of the two lepton–b-jet pairs.− The data-to-MC difference in pT ,`b is covered by the hadronisation uncertainty (backup).
requirement [GeV]T,lb
p0 40 70 80 90 100 110 120 130 140 150 160
Tot
al u
ncer
tain
ties
[GeV
]
0
0.2
0.4
0.6
0.8
1
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1.4
1.6
Total Total syst. Stat.
Total theor. Total exp.
ATLAS
Uncertainty vs. pT ,`b
− Using pT ,`b > 120 GeV results in the smallest total uncertainty⇒ final selection.
�
The optimisation significantly reduces the total uncertainty.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 9 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
The result from 8 TeV data
[GeV]recolbm
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√s = 7 TeV
√s = 8 TeV Correlations Combinations
m`+jetstop [GeV] mdil
top [GeV] mdiltop [GeV] ρ01 ρ02 ρ12 m7 TeV
top [GeV] mdiltop [GeV] mall
top [GeV]
Results 172.33 173.79 172.99 172.99 173.04 172.84
Statistics 0.75 0.54 0.41 0 0 0 0.48 0.38 0.34Method 0.11 ± 0.10 0.09 ± 0.07 0.05 ± 0.07 0 0 0 0.07 0.05 0.05
Signal Monte Carlo generator 0.22 ± 0.21 0.26 ± 0.16 0.09 ± 0.15 +1.00 +1.00 +1.00 0.24 0.10 0.14Hadronisation 0.18 ± 0.12 0.53 ± 0.09 0.22 ± 0.09 +1.00 +1.00 +1.00 0.34 0.24 0.23Initial- and final-state QCD radiation 0.32 ± 0.06 0.47 ± 0.05 0.23 ± 0.07 −1.00 −1.00 +1.00 0.04 0.24 0.08Underlying event 0.15 ± 0.07 0.05 ± 0.05 0.10 ± 0.14 −1.00 −1.00 +1.00 0.06 0.10 0.02Colour reconnection 0.11 ± 0.07 0.14 ± 0.05 0.03 ± 0.14 −1.00 −1.00 +1.00 0.01 0.03 0.01Parton distribution function 0.25 ± 0.00 0.11 ± 0.00 0.05 ± 0.00 +0.57 −0.29 +0.03 0.17 0.04 0.08
Background normalisation 0.10 ± 0.00 0.04 ± 0.00 0.03 ± 0.00 +1.00 +0.23 +0.23 0.07 0.03 0.04W/Z+jets shape 0.29 ± 0.00 0.00 ± 0.00 0 0 0.16 0.00 0.09Fake leptons shape 0.05 ± 0.00 0.01 ± 0.00 0.08 ± 0.00 +0.23 +0.20 −0.08 0.03 0.07 0.05
Jet energy scale 0.58 ± 0.11 0.75 ± 0.08 0.54 ± 0.04 −0.23 +0.06 +0.35 0.41 0.52 0.41Relative b-to-light-jet energy scale 0.06 ± 0.03 0.68 ± 0.02 0.30 ± 0.01 +1.00 +1.00 +1.00 0.34 0.32 0.25Jet energy resolution 0.22 ± 0.11 0.19 ± 0.04 0.09 ± 0.05 −1.00 0 0 0.03 0.08 0.08Jet reconstruction efficiency 0.12 ± 0.00 0.07 ± 0.00 0.01 ± 0.00 +1.00 +1.00 +1.00 0.10 0.01 0.04Jet vertex fraction 0.01 ± 0.00 0.00 ± 0.00 0.02 ± 0.00 −1.00 +1.00 −1.00 0.00 0.02 0.02b-tagging 0.50 ± 0.00 0.07 ± 0.00 0.03 ± 0.02 −0.77 0 0 0.25 0.03 0.15Leptons 0.04 ± 0.00 0.13 ± 0.00 0.14 ± 0.01 −0.34 −0.52 +0.96 0.05 0.14 0.09Emiss
T 0.15 ± 0.04 0.04 ± 0.03 0.01 ± 0.01 −0.15 +0.25 −0.24 0.08 0.01 0.05Pile-up 0.02 ± 0.01 0.01 ± 0.00 0.05 ± 0.01 0 0 0 0.01 0.05 0.03
Total systematic uncertainty 1.03 ± 0.31 1.31 ± 0.23 0.74 ± 0.29 0.77 0.74 0.61
Total 1.27 ± 0.33 1.41 ± 0.24 0.84 ± 0.29 −0.07 0.00 0.51 0.91 0.84 0.70
− Largest experimental uncertaintiesstem from the jet energy scales.
− Largest modelling uncertainties aredue to Hadronisation and ISR/FSR.
− The summary: Channel (√
s) Value Stat Model Background Experimental TotalAll-jets (8) 173.72 0.55 0.70± 0.16 0.19 0.71± 0.04 1.15 (0.66 %)
Lepton + jets (7) 172.33 0.75 0.53± 0.11 0.31± 0.00 0.82± 0.08 1.27 (0.74 %)Dilepton (8) 172.99 0.41 0.35± 0.09 0.08± 0.01 0.64± 0.04 0.85 (0.49 %)
− The correlations of the estimatorsfor all sources of systematic uncer-tainty are evaluated rather thanassigned (as is commonly done).
����
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Look at these lines on next slide
This is the most precise ATLAS measurement and the most precise result in this channel.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 10 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
The correlations of the estimators for individual sources
(7 TeV) [GeV]diltopm∆
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
(8
TeV
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m∆
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0
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1+ = ρ 1− = ρ
ATLAS
Dilepton 7 vs. dilepton 8 TeV
(7 TeV) [GeV]l+jetstopm∆
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
(8
TeV
) [G
eV]
dil
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m∆
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-0.2
0
0.2
0.4
0.6
0.8
1+ = ρ 1− = ρ
ATLAS
Lepton + jets, 7 vs. dilepton 8 TeV
− ∆m = shift in mass from pairs of samples using 500 pseudo-experiments of the data size.− Each point corresponds to a single (sub-) component, with ρ = +1 or ρ = −1.
h h
bJES: 0.30 ± 0.01 (dil, 8), 0.68 ± 0.02 (dil, 7, ρ = +1), 0.06 ± 0.03 (`+jets, 7, ρ = +1).
i i
ISR/FSR: 0.23 ± 0.07 (dil, 8), 0.47 ± 0.05 (dil, 7, ρ = +1), 0.32 ± 0.06 (`+jets, 7, ρ = −1).
By construction, the correlations to the three-dimensional lepton + jets analysis are small.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 11 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
The ATLAS measurements of mtop and mpoletop
[GeV]topm165 170 175 180 185
1
17
0.70± 172.84 Phys. Lett. B761 (2016) 350 ATLAS Comb. June 2016
-1 =4.6 fbintL
JHEP 10 (2015) 121+1-jet) t(tσ 2.1 2.3 ±173.7
-1 =4.6-20.3 fbintL
Eur. Phys. J. C74 (2014) 3109) dilepton t(tσ 2.6 2.5 ±172.9
-1 = 20.2 fbintLarXiv:1702.07546all jets 1.0 )± ( 0.6 1.2 ±173.7
-1 = 20.2 fbintL
Phys. Lett. B761 (2016) 350 dilepton → 0.7 )± ( 0.4 0.8 ±173.0
-1 = 4.7 fbintL
Eur. Phys. J. C75 (2015) 330 dilepton → 1.3 )± ( 0.5 1.4 ±173.8
-1 = 4.7 fbintL
Eur. Phys. J. C75 (2015) 330 l+jets → 1.0 )± 0.7 ± 0.2 ± ( 0.2 1.3 ±172.3
-1 =20.3 fbintLCONF-2014-055single top* 2.0 )± ( 0.7 2.1 ±172.2
-1 = 4.6 fbintL
Eur. Phys. J. C75 (2015) 158all jets 1.2 )± ( 1.4 1.8 ±175.1
-1 - 20.3 fb-1 = 4.6 fbint
summary - May 2017, Ltopm
syst.)± bJSF ± JSF ± tot. (stat. ± top m
σ 1 ±ATLAS Comb. stat. uncertainty
bJSF uncertainty⊕ JSF ⊕stat. total uncertainty
Input to comb.→Preliminary, *
ATLAS Preliminary
? = new since EPS2015
??
? Normalised differential lepton distributions 173.2± 1.6
− The combination of three ATLAS measurements results in:mtop = 172.84 ± 0.34 (stat) ± 0.61 (syst) GeV = 172.84 ± 0.70 GeV (0.40%).
The direct measurements are superior in determining mtop.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 12 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
Conclusions
− ATLAS has performed various mpoletop measurements based on novel methods,
e.g. by using tt + 1-jet events and differential distributions of leptonic variables .
− Compared to direct measurements of mtop, these mpoletop determinations are performed
in a well-defined renormalisation scheme, but suffer from larger uncertainties.
− The top quark mtop mass was directly measured in all tt decay channels.
− The dilepton result: mtop = 172.99 ± 0.41 (stat) ± 0.74 (syst) GeV = 172.99 ± 0.84 GeV,
is the most precise ATLAS measurement and the most precise in this channel to date.
− The largest experimental uncertainties stem from the calibration of the jet energy scales.
− The largest modelling uncertainties are due to Hadronisation and ISR/FSR radiation.
− For the combination of this result with other measurements the correlations of the estima-
tors for all sources of systematic uncertainty are evaluated rather than assigned.
− The result is: mtop = 172.84 ± 0.34 (stat) ± 0.61 (syst) GeV = 172.84 ± 0.70 GeV.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 13 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
Backup - Transparencies
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 14 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
Production and decay of top-quark pairs
Production processes
fq/p
fq/p
σqq→tt
Quark-induced,O(10%)
fg/p
fg/p
σgg→tt
Gluon-induced,O(90%)
− For mtop = 172.5 GeV and√
s = 8 TeV, the cross-section is σ(tt) = 253+13
−15 pb, resulting in 250k events per 1/fb.
Decay channels (Vtb ≈ 1)
Decay channels
p ptb
W+
t
bW−
p ptb
b-jet
W+
q
q
jet
jet
t
b
b-jet
W−
jetjet
All-jets channel
All-jets: highest rateO(46%), but largest background.
p ptb
b-jet
W+
νℓ
ℓ+
t
b
b-jet
W−
jetjet
Lepton + jets channel
Lepton + jets: medium rateO(30%), lepton ’tag’, good compromise.
p ptb
b-jet
W+
νℓ
ℓ+
t
b
b-jet
W−
ℓ−νℓ
Dilepton channel
Dilepton: lowest rateO(4%), high purity, incomplete kinematics.
τ+τ 1%
τ+µ 2%
τ+e 2%
µ+µ 1%
µ+e 2%
e+e 1%
e+jets 15%
µ+jets 15%
τ+jets 15%
"jets" 46%
"lepton+jets""dilepton"
The LHC is a top quark factory. In all channels, the systematic uncertainties matter most.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 15 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
mpoletop from the normalised differential tt + 1-jet cross-section
even
ts /
0.1
0
100
200
300
400
500
600
700
800ATLAS
-1= 7 TeV, 4.6 fbs
Data
=172.5 GeVt
, mtt
Background
Uncertainty
sρ
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
data
/ pr
ed.
0
1
2
The data distribution
− Measure distribution of tt + 1-jet events in the lepton + jets channel in 7 TeV data.
ρs = 340 GeVmtt+1-jet
) sρ,po
le
tm(
R
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Data
=pole
t+1-jet at NLO+PS for mtt
170 GeV175 GeV180 GeV173.7 GeV (best fit)
ATLAS-1=7 TeV, 4.6 fbs
(parton level)s
ρ0 0.2 0.4 0.6 0.8 1
be
st fi
tR
/ R 0.7
1
1.3
The unfolded distribution
R(mpoletop , ρs) = 1
σtt+1-jet
dσtt+1-jetdρs
(mpoletop , ρs) -
− Unfold to parton level and compareR to the NLO+PS prediction as a function of mpoletop .
Larg
ests
ensi
tivity
iscl
ose
toth
resh
old
�
− Perform χ2 minimisation to get mpoletop that best describes the data.
− Result: mpoletop = 173.7± 1.5 (stat.)± 1.4 (syst.)+ 1.0
− 0.5 (theo.) GeV = 173.7+ 2.3− 2.1 GeV
The first measurement of mpoletop using this mehod, still with about 2.2 GeV uncertainty.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 16 /24
Introduction Indirect determination Direct measurements Combination Conclusions Backup
mpoletop mass from lepton differential cross-sections - additional info
0 200 400
[p
b]
T/d
pσ
d⋅ σ
1/
6−10
5−10
4−10
3−10
2−10
1−101
= 8 TeV; L = 20.3 fbs; t t→pp
ATLAS Data l+jets
uncorrelatedδ
totalδ
t = mR,F
µ
/2t = mR,F
µ
/4T = HR,F
µ
/2T = ER,F
µ
[GeV] t
T p
0 200 400
Theory
/Data
0.9
1
1.1
ATLAS Preliminary
The top quark pT spectrum
/2 t
=mµComb. (8 dist), /4T
=HµComb. (8 dist), /2T
_=EµComb. (8 dist),
[GeV
] t p
ole
m
166
168
170
172
174
176
178
CT14MMHTNNPDF 3.0HERAPDF 2.0ABM 11NNPDF nojet
ATLAS Preliminary-1 = 8 TeV, 20.2 fbs
total uncertainty statistical uncertaintyworld-average direct reconstruction
MCFM NLO fixed-order
mpoletop for different scale choices
[GeV]poletm
170 175 180
)t(tσD0 inclusive 3.3 GeV±172.8
)t(tσATLAS inclusive 2.6 GeV±172.9
)t(tσCMS inclusive 1.8 GeV±173.8
tt, mt
TD0 differential p 2.5 GeV±169.1
+1j)t(tσATLAS differential 2.2 GeV±173.7
ATLAS leptonic (8 dist.) 1.6 GeV±173.2
poletm
Stat. Uncertainty
Full Uncertainty
ATLASPreliminary
Comparison of measurements of mpoletop
The largest theoretical uncertainty stems from the choice of the QCD scale.
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Measurement in the all-jets channel from 8 TeV data
p ptb
b-jet
W+
q
q
jet
jet
t
b
b-jet
W−
jetjet
Numbers of events retained in the selection
Event yields (thousands)Cut Data tt all-hadronic (MC)
Initial 850450 2338 ± 1NPV>4 tracks
& no isolated e/µ 33476 308.7 ± 0.6Trigger: 5 jets with pT > 55 GeV & ≥ 6 good jets 16110 241.4 ± 0.5No 2 good jets (ji, jk) within ∆R(ji, jk) < 0.6 7646 142.9 ± 0.4≥ 5 good jets with pT > 60 GeV 3303 51.4 ± 0.2Emiss
T < 60 GeV 3021 46.3 ± 0.2∆φ(bi, bj) > 1.5 1737 30.9 ± 0.2χ2 < 11 645.8 22.3 ± 0.1Nbtag ≥ 2 21.9 6.61 ± 0.08〈∆φ(b,W )〉 < 2 12.9 4.40 ± 0.07
The list of uncertainties
Source of uncertainty ∆mtop [GeV ]
Monte Carlo generator 0.18 ± 0.21Hadronisation modelling 0.64 ± 0.15Parton distribution functions 0.04 ± 0.00Initial/final-state radiation 0.10 ± 0.28Underlying event 0.13 ± 0.16Colour reconnection 0.12 ± 0.16Bias in template method 0.06Signal and bkgd parameterisation 0.09Non all-hadronic tt contribution 0.06ABCD method vs. ABCDEF method 0.16Trigger efficiency 0.08 ± 0.01Lepton/Emiss
T calibration 0.02 ± 0.01Overall flavour-tagging 0.10 ± 0.00Jet energy scale (JES) 0.60 ± 0.05b-jet energy scale (bJES) 0.34 ± 0.02Jet energy resolution 0.10 ± 0.04Jet vertex fraction 0.03 ± 0.01
Total systematic uncertainty 1.01Total statistical uncertainty 0.55
Total uncertainty 1.15
− Results: 7 TeV: mtop = 175.1 ± 1.4 (stat) ± 1.2 (syst) GeV = 175.1 ± 1.8 GeV.8 TeV: mtop = 173.72 ± 0.55 (stat) ± 1.01 (syst) GeV = 173.72 ± 1.16 GeV.
An about 40% improvement compared to the 7 TeV analysis.
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The dilepton channel from 8 TeV data
p ptb
b-jet
W+
νℓ
ℓ+
t
b
b-jet
W−
ℓ−νℓ
Pre-selection of events in 8 TeV data
− Use W+W− → `+`−νν with ` = e, µ.− Quality requirements⇒ 20.2± 0.4 fb−1.− Trigger, good primary vertex≥ 5 tracks.− Electrons: ET > 25 GeV, |η| < 2.47.− Muons: pt > 25 GeV, |η| < 2.5.− ee, µµ channel: Emiss
T > 60 GeVm`` > 15 GeV, |m`` − MZ0 | > 10 GeV.
− eµ channel: HT > 130 GeV.− At least two jets with pt > 25 GeV
and |ηjet| < 2.5.− At least one b-tagged jet (εb = 70%).
− Single top quark production is treated as signal rendering an mtop independent background.
The pre-selection yields about 36k events with 1% background.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 19 /24
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The hadronisation uncertainty in 8 TeV data
p ptb
b-jet
W+
νℓ
ℓ+
t
b
b-jet
W−
ℓ−νℓ
[GeV]T,lb
p100 150 200 250 300 350 400
Eve
nts
/ 10
GeV
1
10
210
310
410
510
610Data =172.5 GeV
top, mtt
Uncertainty Powheg+Herwig
Single top NP/fake leptonsZ+jets WW/WZ/ZZ
ATLAS-1=8 TeV, 20.2 fbs
[GeV]T,lb
p100 150 200 250 300 350 400
Dat
a/M
C
0.81
1.2
− The difference between POWHEG+PYTHIA and POWHEG+HERWIG resultsin an hadronisation induced uncertainty in mtop of 0.22± 0.09 GeV.
For this distribution, the data description is better for the POWHEG+HERWIG event sample.
Measurements of the top quark mass with ATLAS Richard Nisius (MPP Munchen) Venice, July 7, 2017 20 /24
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Combination - dilepton and lepton + jets at 7 TeV
totalρ
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
tota
l unc
erta
inty
[GeV
]to
pm
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
) = 1.41 GeVdil
top(mσ
) = 1.27 GeVl+jets
top(mσ
) = 0.91 GeVcomb
top(mσ
totalρ) vs. comb
top(mσ
ATLAS-1=7 TeV, 4.6 fbs
The uncertainty in mtop
ρest=-0.07
ρass=+0.51
totalρ
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 [G
eV]
top
m
170.5
171
171.5
172
172.5
173
173.5
174
174.5
175
= 173.79 GeVdiltopm
= 172.33 GeVl+jetstopm
= 172.99 GeVcombtopm
totalρ vs. comb
topm
ATLAS-1=7 TeV, 4.6 fbs
The combined value of mtop
(1) mtop = 172.91 ± 0.50 (stat) ± 1.05 (syst) GeV (assigned ρass,i from world combination).(2) mtop = 172.99 ± 0.48 (stat) ± 0.78 (syst) GeV, (estimated ρest,i ).⇒ σ2
σ1= 0.91
1.16 = 0.78, i.e. a very significant improvement due to the estimated correlations.
The use of the three-dimensional versus the one-dimensional fit is paying off.
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Combination - dilepton at 8 TeV with lepton + jets at 7 TeV
totalρ
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
tota
l unc
erta
inty
[GeV
]to
pm
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
) (7 TeV) = 1.27 GeVl+jets
top(mσ
) (8 TeV) = 0.84 GeVdil
top(mσ
) = 0.70 GeVpair
top(mσ
totalρ) vs.
pair
top(mσ
ATLAS
The uncertainty in mtop
totalρ
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 [G
eV]
top
m170
170.5
171
171.5
172
172.5
173
173.5
174
174.5
175
(7 TeV) = 172.33 GeVl+jetstopm
(8 TeV) = 172.99 GeVdiltopm
= 172.79 GeVpairtopm
totalρ vs. pair
topm
ATLAS
The combined value of mtop
− Large improvement with respect to the more precise result, because the correlationis low, ρ = 0.00� 0.84
1.27 = 0.66⇔ the point of no improvement.
The use of the three-dimensional versus the one-dimensional fit is paying off.
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Introduction Indirect determination Direct measurements Combination Conclusions Backup
The various combinations
√s = 7 TeV
√s = 8 TeV Correlations Combinations
m`+jetstop [GeV] mdil
top [GeV] mdiltop [GeV] ρ01 ρ02 ρ12 m7 TeV
top [GeV] mdiltop [GeV] mall
top [GeV]
Results 172.33 173.79 172.99 172.99 173.04 172.84
Statistics 0.75 0.54 0.41 0 0 0 0.48 0.38 0.34Method 0.11 ± 0.10 0.09 ± 0.07 0.05 ± 0.07 0 0 0 0.07 0.05 0.05
Signal Monte Carlo generator 0.22 ± 0.21 0.26 ± 0.16 0.09 ± 0.15 +1.00 +1.00 +1.00 0.24 0.10 0.14Hadronisation 0.18 ± 0.12 0.53 ± 0.09 0.22 ± 0.09 +1.00 +1.00 +1.00 0.34 0.24 0.23Initial- and final-state QCD radiation 0.32 ± 0.06 0.47 ± 0.05 0.23 ± 0.07 −1.00 −1.00 +1.00 0.04 0.24 0.08Underlying event 0.15 ± 0.07 0.05 ± 0.05 0.10 ± 0.14 −1.00 −1.00 +1.00 0.06 0.10 0.02Colour reconnection 0.11 ± 0.07 0.14 ± 0.05 0.03 ± 0.14 −1.00 −1.00 +1.00 0.01 0.03 0.01Parton distribution function 0.25 ± 0.00 0.11 ± 0.00 0.05 ± 0.00 +0.57 −0.29 +0.03 0.17 0.04 0.08
Background normalisation 0.10 ± 0.00 0.04 ± 0.00 0.03 ± 0.00 +1.00 +0.23 +0.23 0.07 0.03 0.04W/Z+jets shape 0.29 ± 0.00 0.00 ± 0.00 0 0 0.16 0.00 0.09Fake leptons shape 0.05 ± 0.00 0.01 ± 0.00 0.08 ± 0.00 +0.23 +0.20 −0.08 0.03 0.07 0.05
Jet energy scale 0.58 ± 0.11 0.75 ± 0.08 0.54 ± 0.04 −0.23 +0.06 +0.35 0.41 0.52 0.41Relative b-to-light-jet energy scale 0.06 ± 0.03 0.68 ± 0.02 0.30 ± 0.01 +1.00 +1.00 +1.00 0.34 0.32 0.25Jet energy resolution 0.22 ± 0.11 0.19 ± 0.04 0.09 ± 0.05 −1.00 0 0 0.03 0.08 0.08Jet reconstruction efficiency 0.12 ± 0.00 0.07 ± 0.00 0.01 ± 0.00 +1.00 +1.00 +1.00 0.10 0.01 0.04Jet vertex fraction 0.01 ± 0.00 0.00 ± 0.00 0.02 ± 0.00 −1.00 +1.00 −1.00 0.00 0.02 0.02b-tagging 0.50 ± 0.00 0.07 ± 0.00 0.03 ± 0.02 −0.77 0 0 0.25 0.03 0.15Leptons 0.04 ± 0.00 0.13 ± 0.00 0.14 ± 0.01 −0.34 −0.52 +0.96 0.05 0.14 0.09Emiss
T 0.15 ± 0.04 0.04 ± 0.03 0.01 ± 0.01 −0.15 +0.25 −0.24 0.08 0.01 0.05Pile-up 0.02 ± 0.01 0.01 ± 0.00 0.05 ± 0.01 0 0 0 0.01 0.05 0.03
Total systematic uncertainty 1.03 ± 0.31 1.31 ± 0.23 0.74 ± 0.29 0.77 0.74 0.61
Total 1.27 ± 0.33 1.41 ± 0.24 0.84 ± 0.29 −0.07 0.00 0.51 0.91 0.84 0.70
− The combined result: mtop = 172.84 ± 0.34 (stat) ± 0.61 (syst) GeV = 172.84 ± 0.70 GeV.
This combination of only three results has a precision of 0.4%.
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Introduction Indirect determination Direct measurements Combination Conclusions Backup
Precision measurements and the Standard Model
[GeV]topm165 170 175 180 185
1
17
0.70± 172.84 Phys. Lett. B761 (2016) 350 ATLAS Comb. June 2016
-1 =4.6 fbintL
JHEP 10 (2015) 121+1-jet) t(tσ 2.1 2.3 ±173.7
-1 =4.6-20.3 fbintL
Eur. Phys. J. C74 (2014) 3109) dilepton t(tσ 2.6 2.5 ±172.9
-1 = 20.2 fbintLarXiv:1702.07546all jets 1.0 )± ( 0.6 1.2 ±173.7
-1 = 20.2 fbintL
Phys. Lett. B761 (2016) 350 dilepton → 0.7 )± ( 0.4 0.8 ±173.0
-1 = 4.7 fbintL
Eur. Phys. J. C75 (2015) 330 dilepton → 1.3 )± ( 0.5 1.4 ±173.8
-1 = 4.7 fbintL
Eur. Phys. J. C75 (2015) 330 l+jets → 1.0 )± 0.7 ± 0.2 ± ( 0.2 1.3 ±172.3
-1 =20.3 fbintLCONF-2014-055single top* 2.0 )± ( 0.7 2.1 ±172.2
-1 = 4.6 fbintL
Eur. Phys. J. C75 (2015) 158all jets 1.2 )± ( 1.4 1.8 ±175.1
-1 - 20.3 fb-1 = 4.6 fbint
summary - May 2017, Ltopm
syst.)± bJSF ± JSF ± tot. (stat. ± top m
σ 1 ±ATLAS Comb. stat. uncertainty
bJSF uncertainty⊕ JSF ⊕stat. total uncertainty
Input to comb.→Preliminary, *
ATLAS Preliminary
The mtop combination
− The combination of three ATLAS measurements results in:mtop = 172.84 ± 0.34 (stat) ± 0.61 (syst) GeV = 172.84 ± 0.70 GeV (0.4%).
[GeV] tm165 170 175 180 185
[GeV
]W
m
80.25
80.3
80.35
80.4
80.45
80.5 ATLAS 0.019 GeV± = 80.370 Wm
0.70 GeV± = 172.84 tm
0.24 GeV± = 125.09 Hm
t and mW68/95% CL of m
68/95% CL of Electroweak
t and mW Fit w/o m (Eur. Phys. J. C 74 (2014) 3046)
Consistency of the Standard Model
− The good description of the precise measurements of mW with σ(mW) = 0.02%, mtop withσ(mtop) = 0.4% and MH with σ(MH) = 0.2% (from LHC) is another success of the SM.
The Standard Model has successfully passed another precisions test.
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