b-jet energy scale determination method for top mass
DESCRIPTION
b-Jet Energy Scale Determination Method for Top Mass. Presentation for summer student program Mitsutoshi Ogino. Motivation. Systematic uncertainties of Mtop measurement by top mass template group. All-hadronic : ~45%. No missing objects. Many events come from All hadronic channel. - PowerPoint PPT PresentationTRANSCRIPT
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b-Jet Energy Scale Determination Method
for Top Mass
Presentation forsummer student program
Mitsutoshi Ogino
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Systematic uncertainties of Mtop measurementby top mass template group
This is excellent prescription, but we always want confirmation from data. 1
Many events come from All hadronic channel.
But, there are large background …(I did not consider the background at this study)
All-hadronic: ~45%No missing objects
Motivation
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Method
22yxT PPP E
PPP
PPE
zyx
yx
T 222
22
2
)(bpT
perpendicular parallel
x
y
)(bpT
)( bbpT)( qpT
)(bfpT
)(bfpT)()1()( bbpfbbE TT
To estimate Jet Energy Scale
Sum of energy is 0 on x-y plane fron Energy momentum conservation.
fbbEbbp
bbEjT
jT
jT
1)()(
)(
To estimate Jet Energy Scale (JES),We watch response:
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Method
3
Top Mass estimation
Estimation
Correction at All-hadronic (for check)
Likelihood (including product templates)
Identify b-quark with b-tagging and level 5 jet correction
Define as likelihood fitting function of b-jet energy scaling factor.
Estimate mean and sigma from fitting function of likelihood.
Check the effect of b-JES on parton, error bias and accuracy from plots.
Estimate top-quark mass and effect of error.
Match b-jet and 4 light quark jets. (dR < 0.4)
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Event selectionLv:5_Correction (Pre-Selection)
A) Number of tight lepton = 0B) |Zjvert| < 60 cmC) |Zjvert - Zpvert| < 5 cmD) N(vert_class12) 1≧E) MET_significance < 3F) 6 Njet 8 (jets with Et 15, |η| 2.0)≦ ≦ ≧ ≦G) DeltaRmin (dRmin) 0.5 between jets≧
4
Matching 6 jets each other at dR < 0.4 after pre-selection.
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[The method of least squares (LS)]
Likelihood
Nev
ii bJESxPbJesL
1
;)(
constbJesLbJES )(ln2)(2
bJES
truexxpull
[Likelihood function]
Estimate Mean, Mean’s Error, Sigma, and Sigma’s Error from χ2(bJES).
[pull]
Besides, to discuss accuracy …
5
)(ln2 bJESL
L(bJES) = “Gaussian”
bJES
χ2=-2lnL
bJES
L0
L0+1
1
1
σbJES
σbJES
If…
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Signal template
fbbEbbp
bbEjT
jT
jT
1)()(
)(
[response]
Make signal templates and View the shift of response.
After, search all fitting function at f=0.90~1.10separating 21 variation.
6
pro
ba
bil
ity
)()(/)( bbpbbEbbE TTT
f : Jet Energy Scale
We fit the histograms above to get the P(xi,bJES).
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Pseudo Experiment (practice)
7
Lln2 )()(/)( bbpbbEbbE TTT
1PE Example (f = 0.90)
fitting
Nev
t-2
ln(L
)
bJES
bJES = 0.917 +/- 0.016
To estimate statistical uncertainties,We performed pseudo experiments.
1. Get 191 events from template histogram
2. Performed likelihood fit to get the bJES and its error.
Repeat same procedure 10k times at each bJES
bJES
No
of
mea
n
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Results (practice)
8
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Problem (for practice result)
9
We didn’t consider acceptance effect due to bJES
Bad Fitting lead to slight bias & <1 pull width
We want to improve the uncertainties.
⊿(bJES) ~ 0.017 (Mtop) = 1.2GeV⊿
Try it again this analysis after introducing Top Specific Correction!!
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Top Specific Correction (TSC)
10
Matching
Fitting
Correct Jet Energy
Change parameter form dR<0.4 to dR<0.1
Jet energy separate to 20~30, 30~40, 40~50, 50~60, 60~70, 70~100, and 100~ [Gev] each ranges. (to examine for Jet Energy dependence)
Product distribution plots of JetEt – PartonEt at each ranges.
Estimate mean and sigma around peak after fitting with Gaussian.
Recipe for TSC in this study
Make templates from estimated value of mean and sigma
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Making template (TSC)
12
pro
ba
bil
ity
response
Example (f = 0.90)
original
corrected
Cannot improve top mass using this Top Specific Correction…
I abandoned to use this correcting method.
at f=0.90~1.10, corrected response approach 1-f,But no improve from original
Make template probability of response about f=0.90~1.10 cases.
To original response fit corrected…
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summary
13
Hereafter …
Top Specific Correction
Estimate Jet Energy Scale
Result for practice
There is still scope for improvement.Try to improve using other correcting method?But, summer student program is last 2days only…
⊿(bJES) ~ 0.017 (Mtop) = 1.2GeV⊿But, there are some problem.
We do not have improvement from Top Specific Crrection.
To examine JES, We research response.
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Back up
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Template fitting( practice)
15
Example (f = 0.90)
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Error result (for practice)Example (f = 0.90)
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Top specific correction( b-Jet)
16
Number of event
jetEt - partonEt
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Top specific correction (4 lq-Jet)
17
Number of event
jetEt - partonEt
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Template( TSC)
18
)()(/)(1 bbpbbEbbEf TTT
f = 1.00 f = 1.10
response
pro
bab
ilit
y
response:
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Top invariant mass(for practice)
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Mw constraint
response
Ne vt