V + jets / t t + jets background estimation for stop quark searches - - PowerPoint PPT Presentation

V + jets/t¯ t + jets background estimation for stop quark searches

Thierry Caebergs, Gr´ egory Hammad

Mons University

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V+jets and tt+jets estimation

Analysis code ported to common framework successfully Macro reading from AnaTree ready Started to test performances

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Performances

Previous studies have shown that stable results can be achieved with only one fixed parameter : ǫ′

mistag, mis-tagging for v-like events.

Once full analysis on tracks, should study if uncert. on estimated b-tagging eff. smaller than the one provided by BTV-11-003. Otherwise, use ǫbtag as fixed parameter. For testing purposes ;

ǫ′

mistag used as fixed parameter

value set to 0.179 (derived from MC simulations)

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Performances for 5000 pb−1

For n = 4 jets, using t¯ t + jets and W + jets only ; Constant Par. Value

• euds

1.7900e-01 Floating Par. InitialValue FinalValue (+HiError,-LoError)

• Ntt

2.4509e+04 2.4681e+04 (+3.65e+02,-3.61e+02) Nv 2.3431e+04 2.2822e+04 (+3.60e+02,-3.62e+02) eb 8.0000e-01 7.9570e-01 (+8.90e-03,-9.10e-03) eudsc 2.0000e-01 1.8046e-01 (+3.97e-03,-3.84e-03) Estimated b-tagging eff. compatible with value derived from data using t¯ t + jets events (BTV-11-003) : ǫbtag = 0.79 Input values for Nt¯

t-like and NV-like are taken from MC (fit stability

already studied).

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Future dev.

Mis-tagging efficiency :

Derived from DD methods : BTV-11-004 Needs to determine average jet pt :

from MC simulations ? from a control sample with no b-tagged jet (V-like enriched)?

Errors will be incorporated in MLE via gaussian constraint

Bias on estimations :

Use pseudo-exp. Code already in place.

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