1. A brief update on b-tagging of High P jets
8/4/2019
A brief update on b-tagging of High P jets
Data p14 and MC p14 based study
8/4/2019
Eugene Galyaev

2. Definition (simplified):
A brief reminder: 2D Decay Length Significance as a discriminating variable
Definition (simplified):
Two-dimensional Decay Length
Significance is
Two-dimensional Decay Length divided by its uncertainty s
It was decided to take log(DlSig2) to further bring out the shape differences and to alleviate future fitting procedure
Fit for b frac.
8/4/2019
Eugene Galyaev

3. Previous results and observations, MC vs. Data
Efficiency and Purity dependence on Pt (no cut applied):
b – vertex finding efficiency in MC is slowly decreasing with Pt
b – content in data seems to be in disagreement with the MC, especially
at low Pt
- The fitting procedure is
inefficient at low Pt?…
- Data IS different
8/4/2019
Eugene Galyaev

4. Check the fitting procedure’s consistency
Try to fit the templates to the inclusive QCD MC
Good “Simulation”
Yield >>perfect<< fits EVERY TIME!!!
Fitting is NICE with Monte Carlo!
So the DATA must be different……….
c2 = 0.75
At 100 GeV Pt bin !
37% Vs. 34%
MC ‘Truth’ purity
8/4/2019
Eugene Galyaev

5. Another look at the templates and Data shapes
Ways the b-template “finds its place”
Log(2D Dl Significance)
The extracted fractions inconsistency may come from
Wrong template position
Incorrect MC description (UNLIKELY)
MC Templates positions might be affected by the difference in the uncertainty between MC and Data
This will result in horizontal template(s) shift
8/4/2019
Eugene Galyaev

6. Can build Vertex Error Ellipses
Taking a detailed look at the 2D Decay Length Significance: Uncertainty s up close… q 2a 2b SV PV
2D Decay Length Significance is defined through the combined (PV+SV) covariance matrix elements
Variances
Can build Vertex Error Ellipses
Parameters ‘a’ and ‘b’ of the Error Ellipses as well as the orientation angle q are drawn for the PV and SV from their covariance matrix elements, respectively.
8/4/2019
Eugene Galyaev

7. Taking a detailed look at the 2D Decay Length Significance: Error ellipse on Event Display
Default Event display
A close-up view
SV Error Ellipse PV SV PV SV 2a !
The uncertainty associated with the PV was found do be small compared to the SV
By configuration of the PV and SV Error Ellipses it was found that only parameter ‘a’ of the Secondary Vertex is of the most importance to the MC vs. Data difference
8/4/2019
Eugene Galyaev

8. Exploring the Error Ellipsoids, parameter ‘a’ (major axis)
SV ‘a’ vs. Pt
MC and Data’s difference in parameter ‘a’ for the SV is visible both in the mean value profiles and the distribution shapes
The idea is to make MC and Data’s uncertainties agree better
Find a way to SCALE the MC to agree with the data
Ratio vs. Pt
Jet Pt
8/4/2019
Eugene Galyaev

9. Exploring the Error Ellipsoids, parameter ‘a’ , continued …
It might be possible to come up with the k-factor(s) to alter slightly the MC’s parameter ‘a’ thus affecting the Decay Length Significance
Might yield in better template positions
Better description of the Data and better agreement with the measured properties
Need universality of the effect on
b, c, and Light MC
Need to explore errors properties more…!
SV Parameter ‘a’ distributions shape difference
QCD MC, inclusive
Data
Scaled MC, trial
8/4/2019
Eugene Galyaev

10. Exploring the Error Ellipsoids, parameter ‘a’ , continued …
Sample plots…
Sample plots…
Sample plots…
Currently many variables are being looked at in b,c,light MC and Data in search of universal behavior of the parameter ‘a’ with respect to them in various Pt bins…
Among variables looked at were:
Decay Length
2VTX Mass
dR (2VTX, CalJet)
2 VTX Track Multiplicity…
8/4/2019
Eugene Galyaev

11. Work in progress…! Status and plans…
Yielded a better understanding of the Decay Length Significance
The nature of the variable is better understood, explicit formula driven
The major source of the difference in uncertainties in MC and Data have been found (The ‘a’ parameter of the 2VTX).
Have the tools to operate with the Error Ellipses, uncertainties for vertices
Active work is being done to emerge the agreement between MC and the Data
Search for the universal variable(s) in hope of the possibility to correct the MC with correct corresponding k-factors for b, c, udsg MC
Will allow to have more reliable templates
Promise for a better, more sound description of the Detector resulting a agreement of the experiment and theoretical prediction
Goals
Find a reliable way to correct MC
Make corrected MC templates in Decay Length Significance
Extract b-fraction in Data as well as we can!
Work in progress…!
8/4/2019
Eugene Galyaev