Validation Regions for non-prompt background estimation in same charged \(W^{\pm}W^{\pm}\) scattering

(Status report)

Sebastian Ordoñez

jsordonezs@unal.edu.co

                                      23rd of March 2021                                             

Background Estimation

Typically for data-driven background estimation models reliying on statistically independent control (CR), validation (VR) and signal (SR) regions are employed.

• CR: enriched in non-prompt background and extrapolated to SR using a fake factor (FF) -> Max Dilepton CR

VR

SR

CR

FF apply

FF test

• SR: phase space that is defined through selections on kinematic variables, enriched in potential signal of interest -> ssWW

• VR: regions in phase space bet CR and SR where extrapolation is verified->My work

1. Validation Region for muons ​
2. Validation Region for electrons

Data-driven Matrix Method

We introduce the following four categories for our analysis. In truth level we define:

• Prompt leptons: originated from \(W^{\pm}\) or \(Z\) decay.
• Non-prompt leptons: coming from other sources e.g. hadron decays faking a signal lepton.

In reco level we have:

• Ana leptons: quite likely to be prompt. Tight kinematic and qualitative criteria, signal leptons in SR.
• Non-Ana leptons: kinematically close to Ana leptons but more likely to be non-promt, i.e. looser object quality selection.

Validation Region

1. Statistical significance: good statistics, i.e. large number of total events and high purity in non-promt events.

2. Composition of the non-promt leptons: in order to guarantee the assumption of FF being the same in both regions.

3. Orthogonality to the signal region.

4. Data modeling: Data in VR sufficiently well modeled by MC.

• The validation region consists of Ana and Non-Ana leptons and it should be dominated by non-promt events.

• In order to evaluate the validation region, the following criteria must to be taken into account:

Three lepton muon VR

• As final state we have one electron and two muons
  • Electron Ana selected and at least one muon Ana selected.
  • We expect the electron to be prompt and one muon to be prompt too.                       

• Non Prompt Muons in the SR are a motivation to define \(t\bar{t}\) validation regions for muons

Three lepton muon VR

•  We are using now the full Run 2.
• The current cutflow is composed by:

1. Three leptons

2. Lepton type

3. Ana electron

4. Same charged muons

Conclusions

• We have proven that most non-prompt muons come from b-hadron decay, which is in agreement with to our ssWW Signal Region.
• We have found that data modelling is good.
• The low statistics is being a big problem!

Next steps

• Since low statistics is our main issue, we have to look for alternatives in our cutflow
  • Adjust the same charge cut (Next slide): 
    • ​There are some good options to consider, e.g.  the opposite sign cut used by Heng and Joany.
    • We can employ a "merged cut​" between opposite sign and same charged.
• Study the composition and the data modelling for these new cuts.
• Adjust everything to apply the fake factors.

Next steps

https://indico.cern.ch/event/1017867/contributions/4271556/attachments/2209597/3739291/EstimationPLIVTightssWW_heng_20200316.pdf

Thank you!