top mass from tt +1jet: impact of scale uncertainties on the ̅ measurement
IFIC-DESY meeting on scale uncertainty
Katerina Lipka, Sebastian Wuchterl
DESY
26 February 2021
Motivation
Top quark mass from tt +1jet ̅
● use tt+1jet events for precision measurement ̅ of mt
● ingredients:
A) ℛ from fixed order NLO theory prediction
－ using pole-mass scheme
－ predictions for different mass hypothesis
B) ℛ from measurement based on data unfolded to parton level
● χ2 fit and comparison between A) and B)
■ 1+2 times (nominal + scale variations)
with ρ = 2m0
mtt+1jet¯ ,m0 = 170GeV
ℛ(mt, ρ) = 1 σtt+1jet¯
dσtt¯+1jet dρ
theory paper: arXiv:1303.6415
8 TeV
8 TeV
General procedure and estimates
Top quark mass extraction
0.05 0.1
a.u. 0.15 mt=166GeV mt=170GeV
=174GeV
mt mt=178GeV
=172GeV mt
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/172
0.05 0.1 0.15
a.u. =166GeVtm =170GeVtm
=174GeV
mt mt=178GeV
=172GeV mt
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/172
0.05 0.1 0.15
a.u. =166GeVtm =170GeVtm
=174GeV
mt mt=178GeV
=172GeV mt
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/172
μR=μF=0.5 μR=μF=1 μR=μF=2
165 170 175
top mass [GeV]
50 100 150 200
2 Χ
Data Fit
Work in Progress
CMS
fit result:
0.54 GeV 173.34 ±
165 170 175
top mass [GeV]
0 50 100
2 Χ
Data Fit
Work in Progress
CMS
fit result:
(Scale) GeV 0.01
+1.28
0.57 172.06 ±
165 170 175
top mass [GeV]
50 100
2 Χ
Data Fit
Work in Progress
CMS
fit result:
0.57 GeV 172.0 ±
➔ mt=172 GeV ± 𝒪(0.5 GeV, exp.). GeV(theory/scale)
mt=172.00 ± Δexp GeV mt=172.06 ± Δexp GeV
mt=173.34 ± Δexp GeV
+1.28
−0.06
● 2 point renormalisation and factorisation scale variation:
■ 0.5 and 2 times mt
■ extremely large and asymmetric scale variation
－ at small ρ: mass sensitivity due to crossing/normalisation
－ large scale uncertainty on extracted top quark mass
● after discussion with Adrian:
need to reduce pT cut to keep uncertainty under control Scale uncertainty
NLO fixed order predictions
0.05 0.1
xsec 0.15 Nominal Scale UP
Scale Down
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/Nominal
30 40 50 60 70 80 90 100
-cut [GeV]
pT
−5
−4
−3
−2
−1 0
1 2 3 4 5 [GeV] t MΔ
Symmetrized error Mt
=2× µ
t/2 µ=M
a.u. normalised to unity
from Adrian & Peter
from Adrian & Peter
● using prediction in finest binning received from Adrian:
■ 20 bins of size 0.05
■ rebin to mitigate scale variation effect at low ρ
－ first bin needs to include at least the crossing point Scale uncertainty
NLO fixed order predictions
0.5 1
xsec Nominal Scale UP
Scale Down
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/Nominal
0.1 0.2 0.3
xsec 0.4 Nominal Scale UP
Scale Down
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/Nominal
0.05 0.1 0.15
0.2
xsec Nominal Scale UP
Scale Down
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/Nominal
aggregate bins
a.u. a.u. a.u.normalised to unity normalised to unity normalised to unity
from Adrian & Peter from Adrian & Peter from Adrian & Peter
● general good agreement between fixed order NLO prediction and Powheg LHE level distributions
● some shape deviations from Parton shower (Pythia)
General comparison
FO NLO vs. Powheg (+Pythia)
0.05 0.1
a.u. 0.15 tt+j LHE
tt+j +Pythia
tt+j LHE (ATLAS) NLO fixed order
0 0.2 0.4 0.6 0.8 1
ρ 0.7
1 1.3
X/NLO
Normalised to unity
from Adrian & Peter from Esteban
FO NLO vs. Powheg (+Pythia)
FO NLO Powheg LHE Powheg + Pythia
0.05 0.1 a.u. 0.15
rho_jet_bin24
Nominal NLO
F=2
=2 µ µr
F=0.5
=0.5 µ µr
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1
X/Nominal
rho_jet_bin24
Normalised to unity
rho_jet_bin24 rho_jet_bin24
0.05 0.1
a.u. 0.15 Nominal NLO
F=2
=2 µ µr
F=0.5
=0.5 µ µr
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1
X/Nominal
Normalised to unity
crosscheck from ATLAS (Esteban)
0.05 0.1
a.u. 0.15 Nominal tt+j LHE
F=2
=2 µ µr
F=0.5
=0.5 µ µr
F=2 µ
F=0.5 µ
r=2 µ
r=0.5 µ
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1
X/Nominal
Normalised to unity
0.05 0.1
a.u. 0.15 Nominal tt+j +Pythia
F=2
=2 µ µr
F=0.5
=0.5 µ µr
F=2 µ
F=0.5 µ
r=2 µ
r=0.5 µ
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1
X/Nominal
Normalised to unity
● scale uncertainties vary by ~factor 2 between powheg and fixed order
NLO prediction
● mainly from variations of μR
Scale uncertainty comparison
from Adrian & Peter
Backup
For different PDF sets
NLO fixed order predictions
0.05 0.1 0.15
a.u. =166GeVtm =170GeVtm
=174GeV
mt mt=178GeV
=172GeV mt
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/172
0.05 0.1
a.u. 0.15 mt=166GeV mt=170GeV
=174GeV
mt mt=178GeV
=172GeV mt
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/172
0.05 0.1
a.u. 0.15 mt=166GeV mt=170GeV
=174GeV
mt mt=178GeV
=172GeV mt
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/172
ABMP16_5_nlo CT18NLO MMHT2014nlo68cl
normalised to unity normalised to unity normalised to unity
from Adrian & Peter from Adrian & Peter from Adrian & Peter
For different PDF sets
NLO fixed order predictions
0.05 0.1
a.u. 0.15 CT18NLO ABMP16_5_nlo
MMHT2014nlo68cl
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/CT18NLO
0.05 0.1
a.u. 0.15 CT18NLO ABMP16_5_nlo
MMHT2014nlo68cl
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/CT18NLO
0.05 0.1
a.u. 0.15 CT18NLO ABMP16_5_nlo
MMHT2014nlo68cl
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/CT18NLO
166 GeV 172 GeV 178 GeV
normalised to unity normalised to unity normalised to unity
from Adrian & Peter from Adrian & Peter from Adrian & Peter
Scale uncertainty
NLO fixed order predictions
0.05 0.1
a.u. 0.15 Nominal Scale UP
Scale Down
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/Nominal
0.05 0.1 0.15
a.u. Nominal Scale UP
Scale Down
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/Nominal
0.05 0.1
a.u. 0.15 Nominal Scale UP
Scale Down
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/Nominal
0.05 0.1
a.u. 0.15 Nominal Scale UP
Scale Down
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/Nominal
0.05 0.1
a.u. 0.15 Nominal Scale UP
Scale Down
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/Nominal
0.05 0.1
a.u. 0.15 Nominal Scale UP
Scale Down
0 0.2 0.4 0.6 0.8 1
ρ 0.5
1 1.5
Var/Nominal
166 GeV 166 GeV
172 GeV
172 GeV 178 GeV
178 GeV
ABMP16_5_nlo
CT18NLO
from Adrian & Peter from Adrian & Peter from Adrian & Peter
from Adrian & Peter from Adrian & Peter from Adrian & Peter
