This document discusses adding a single top channel (Wt) analysis to simultaneous cross-section measurements of other channels using the AIDA technique at 8 TeV. The aim is to measure the Wt cross-section independently to reduce model dependencies and search for new physics. Preliminary plots of missing energy, invariant mass, and jet binning are shown using MC data with one electron and one muon. The motivation, significance studies comparing binning techniques, inclusion of normalization and important shape systematics, and conclusions are discussed.

1. Adding the Single Top to the
simultaneous cross-section
measurements using the AIDA
technique at 8 TeV
- Ruturaj Apte

2. Aim
● Adding the Single Top channel (Wt) to the analysis of the other 3
channels namely the ttbar, z/γ -> ττ and the WW channels using
the AIDA technique.
● The aim is to measure the cross-section of the Wt channel in an
inclusive manner so as to reduce the dependencies on models
and to search for any new physics.
● The plots shown on the subsequent slides have the requirement
of exactly one electron and one muon with opposite signs, with
no particular requirements on the number of b tagged jets.
● The plots only include MC data.

3. Motivation for measuring single top (Wt)
* CMS σ = 23.4 ± 5.4 pb June
2014 – first 5σ measurement
(http://arxiv.org/abs/1401.2942)
* ATLAS σ = 27.2 ± 5.8 pb Sep
2013
The top mass is very close to
the energy of the electroweak
symmetry breaking scale. It has
been speculated that the single
top plays an important role in
the symmetry breaking.
Any deviation from the
predicted rate will be a signal of
new physics.
CMS 8 TeV:
ATLAS 8 TeV:
σ

4. Missing Energy

5. Invariant Mass

6. Normal Jet binning- 2 bins

7. Normal Jet Binning- 6 bins

8. Jet Class
● Jet classes introduced to better resolve the
Wt events from the t-tbar events
Class 0 1 2 3 4
bjets 0 0 1 ≥1 others
Total Jets 0 1 1 2

9. Jet Class Binning

10. Fitting to Pseudodata with the
Jetclass binning – fitted yields for
single top channel

11. Fitting to Pseudodata with the
Jetclass binning – Pull distributions
for st channel

12. Test Statistic
● The test statistic used to test for the significance of the
signal is the
(-2) * ln( ratio of the likelihood functions)
In the numerator likelihood is maximised by fixing μ = 0.
Wheras in the denominator μ is fitted to the value that gives
the maximum likelihood.
● We checked the validity of the asymtotic limit formulae by
comparing them to the test statistic distributions generated
from pseudodata.
● They turned out to be in good agreement and hence we
used the asymtotic limits for our significance studies.

13. Significance Study Results
● We did significance studies for the 2bin, 6bin and
jet class binning using only statistical uncertainties.
● We found that the 2bin gives a much lower
significance ~ 3sigma than the other two types.
● Both jet class and 6 jet binnning give a
significance > 5 sigma.
● The significance of jet class binning was slightly
greater than that of the 6 jet bin case.

14. Including Systematics
● Next thing was to include 80 different sources of
systematic uncertainties related to electron,
muon and jet variables in the analysis.
● We first looked only at the normalization
uncertainties due to the systematics.

15. Normalization systematics
● These are the % differences in the event
acceptance from the nominal distrubution of the
four main rate systematics.
Jet Energy Resolution : 0.60 %
Electron Id SF : 2.35 %
Muon Id SF : 0.51 %
Jet Vertex Fraction : 1.18 %
● In the next slides we shall look at what these
four variables mean.

16. What they mean
● Jet Energy Resolution : It is measured using two
different techniques.
● The differences between the results of these two
methods is a source of a systematic uncertainty.
● To evaluate the impact, the jet energies in MC
simulations are randomly smeared by
adding/subtracting a range of one standard
deviation on jet energy resolution.
● This propagates to an acceptance change.

17. What they mean
● Electron and Muon Id SF : Various cuts are
applied on the tracks and energy
depositions in the detector before it is
identified as an electron or a muon.
● There is a scaling factor associated with
these cuts for the MC to match data.
● This scaling factor has an associated
systematic uncertainty.

18. What they mean
● Jet Vertex Fraction : In a given jet, JVF is
the fraction of tracks that come from the
primary vertex. We have a cut on 0.5 for
this.
● There is an uncertainty associated with the
cuts (+- 0.1) that we apply to the Jet Vertex
Fraction.
● This is another source of a systematic
uncertainty.

19. Jet Energy Resolution
red -> nominal blue-> shifted template
ratio-> nominal / shifted

20. Electron Id scaling factor
red -> nominal blue-> shifted template
ratio-> nominal / shifted

21. Muon Id Scaling Factor
red -> nominal blue-> shifted template
ratio-> nominal / shifted

22. Jet Vertex Fraction
red -> nominal blue-> shifted template
ratio-> nominal / shifted

23. Shape Systematics
● To determine the effect of a shape systematic we
first generated pseudodata from the particular
systematic.
● Then to this pseudodata we fitted the nominal
histograms.
● We then calculated the percentage difference
between the mean fit value of the Wt and the Wt
yield in the nominal case.
● Repeated the procedure for all the 80
systematics

24. Important shape syst.
● Following percentages are calculated as % difference
between the mean fit value to the fits done to
pseudodata generated from systematics by the nominal
channel and the nominal Wt yield.
Jet Energy Resolution : 2.75 %
Electron ID Scaling Factor : 2.82 %
B Tag Scaling Factor : 6.20 %
Jet Energy Scale : 5.94 %

25. Conclusions
● We have completed studying the systematic
uncertainties for the signal Wt channel.
● Without systematics, we found the significance of
jet class binning slightly better than 6 jet. But it
can be seen that there is a large systematic
uncertainty in the B Tag Scaling Factor.
● We need to extend the analysis of systematics for
all the rest of the signal and background channels.
● Finalize the binning based on significance studies
including all the systematics.

26. Backup Slides

27. Significance Testing using Asymtotic
Limits – test statistic obtained by
fitting to the background only

28. Test Statistic
● Next we calculate it for a pseudodata that has been generated
by adding the signal to the background templates.
● The median of this test statistic needs to be well resolved
from the previous distribution for us to obtain a good
significance.
● Here we have checked the validity of the asymptotic formulae
to approximate the behaviour of these two distributions.
● In the future we will only be using the asymptotic formulae
rather than generating a lot of pseudodata, since its validity
has been tested.

29. Significance Testing using Asymtotic
Limits - test statistic obtained by
fitting to the sig + backg

30. List of shape syst.

31. List of shape syst.

32. List of shape syst.

33. List of shape syst.