Analysis

What are we looking for?

• We look for new physics in multi-jets.


• Typical searches for new physics require either leptons and/or missing Et.
• They could miss new physics with strong couplings!


• Therefore we decided to look for a 3-jet signature in multi-jet (6 or more) events.


• ppbar -> QQ -> 3j+3j (final state has 6 or more jets)


• Q could be anything that decays hadronically into 3 jets


• Challenging:
• Huge QCD backgrounds


• Magnitude of multi-jet backgrounds from higher order processes is difficult to calculate a priori


• But new physics may be hidden in multi-jets.




• Standard Model example is the all-hadronic decay channel of ttbar which we use as a test region for our analysis

How does the analysis work?

• We look at all possible combinations in an multijet (6 or more jets) event.


• For each event we have an "ensemble" of 20 or more triplets.


• When we plot the invariant mass of the triplet versus the scalar sum pt we see that the real combinations will populate a horizontal line around the expected mass (red ellipse). The wrong triplets will lie along or above the diagonal line (blue ellipse).




• We require:


• 6 or more jets with pt>13 GeV/c
  
  
• SumPt of the 6 jets has to be greater than 250 Gev/c


• We use the statistically independent exclusive 5-jet sample to model the QCD background.