# Presentation: 667841

## Strategy for single top analysisin the e + jets  channel

- B.Andrieu, E. Busato (LPNHE, Paris)
- + special thanks to M. Kado (LAL, Orsay)

## Signal vs background
Low cross section signal (handful of events)  Maximize selection efficiency
High cross section background  After e + jets  preselection,  first use most efficient selection criteria (b-quark  jet tagging) before topological cuts
Background not precisely predicted by theory and Monte Carlo simulation Avoid restricting phase space too early in order to keep handle on background
Selection of b-quark  jets
No 100 % efficient, background-free, b-quark jet tagging method  Use (as many as possible) different subchannels (tagging methods, number of tags, ...)
But these different subchannels are based on the same sample  Use exclusive samples to be able to combine independent limits in the most efficient and simple way

- Low cross section signal (handful of events) ****** Maximize selection efficiency**
- High cross section background ****** After *****e + jets*****  preselection,  first use most efficient selection criteria (*****b-quark*****  jet tagging) before topological cuts**
- Background not precisely predicted by theory and Monte Carlo simulation****** Avoid restricting phase space too early in order to keep handle on background**
- Selection of *b-quark*  jets
- No 100 % efficient, background-free, *b-quark* jet tagging method ****** Use (as many as possible) different subchannels (tagging methods, number of tags, ...)**
**But **these different subchannels are based on the same sample ****** Use exclusive samples to be able to combine independent limits in the most efficient and simple way**

- General remarks

## FIRST use Soft Muon Tagging  Select events with >= 1 SMT jet
Well-established, simple and robust b-quark  tagging method
Experience from first-pass p13 analysis
Possible gain on trigger efficiency using e-mu  trigger jointly withe + jets  trigger
If possible, separate again according to 2nd jet tagging:
>= 2 SMT jets
Exactly 1 SMT jet + >= 1 JLIP-tagged jet
Exactly 1 SMT jet + 0 JLIP-tagged jet
THEN use a second tagger (JLIP)  Select events with >= 1 JLIP jet + SMT veto
Use only e + jets  trigger for this channel
If possible, separate again according to 2nd jet tagging (JLIP)

- Well-established, simple and robust *b-quark*  tagging method
- Experience from first-pass p13 analysis
- Possible gain on trigger efficiency using *e-mu*  trigger jointly with*e + jets*  trigger
- If possible, separate again according to 2nd jet tagging:
- >= 2 SMT jets
- Exactly 1 SMT jet + >= 1 JLIP-tagged jet
- Exactly 1 SMT jet + 0 JLIP-tagged jet
- THEN use a second tagger (JLIP) ****** **Select events with >= 1 JLIP jet + SMT veto
- Use only *e + jets*  trigger for this channel
- If possible, separate again according to 2nd jet tagging (JLIP)

- Strategy for *b-quark*  jet tagging

## Topological cuts?
Optimize cuts to obtain the best limit: in each channel separately or use the same cuts for all channels?
Combine statistically independent limits from different channels
Knowing the efficiencies of topological cuts on signal and background,is it possible to use a “Matrix Method” to estimate the contribution of signal and background for each channel? 
OR Combine the variables with the highest signal vs background separating power into a likelihood ratio?
Estimate a limit for each channel and combine these statisticallyindependent limits?
OR combine all channels using the likelihood-ratio distribution andderive a single limit for the e + jets  channel? 

- Optimize cuts to obtain the best limit: in each channel separately or use the same cuts for all channels?
- Combine statistically independent limits from different channels
- Knowing the efficiencies of topological cuts on signal and background,is it possible to use a “Matrix Method” to estimate the contribution of signal and background for each channel?
- OR Combine the variables with the highest signal vs background separating power into a likelihood ratio?
- Estimate a limit for each channel and combine these statisticallyindependent limits?
**OR** combine all channels using the likelihood-ratio distribution andderive a single limit for the *e + jets*  channel?

- Final selection?

## First attempt to define a strategy for e + jets  analysis
Combination of different tagging methods relatively clear
Strategy for final selection and result still to be discussed
Eventually, plans with evolve as analysis progresses and time schedule becomes tighter!

- Combination of different tagging methods relatively clear
- Strategy for final selection and result still to be discussed
- Eventually, plans with evolve as analysis progresses and time schedule becomes tighter!

- Summary