Z cross-sectionwith simultaneous fitZ cross-sectionwith simultaneous fit

Luca Lista for:Annapaola De Cosa, Michele De Gruttola, Salvatore Di Guida, Francesco Fabozzi,

Pasquale Noli, Davide Piccolo (LNF)

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Analysis strategyAnalysis strategy

•Zµµ two global muons, both matched to HLT primitive•Zµµ two global muons, one matched to HLT primitive•Zµsa 1 global + 1 stand-alone muons, global mu matched to HLT•Zµtk 1 global muon + 1 track, muon matched to HLT•Zµµ non-iso two global muons, at least one non-isolated, at least one matched to HLT

• Define five independent samples:

Luca Lista, Gr-I 2008 3

Data-driven di-muon mass PDFData-driven di-muon mass PDF

Luca Lista, Gr-I 2008 4

MC SamplesMC Samples

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Global fit approachGlobal fit approach

• Negligible background on Zµµ sample• Assume identical di-muon peak shape for other

samples– Fully data-diven model (no MC input!)

– Except Zµsa, fitted with a gaussian, due to poorer resolution

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Global fit resultsGlobal fit results

Nµµ = 3818 ± 64

Parameter Fit (%) Mc truth(%)

ε HLT Fit = < ε HLT * ε sa>/ < ε sa >

Low statisticsat 10 pb-1 !

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Different luminosity scenariosDifferent luminosity scenarios

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Cross section stabilityCross section stability

Cross section estimateuncorrected for kinematic efficiency

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iso 1

2 ET

Ecal 1

2 ET

Hcal

1 pT

α = 0.75α = 0.75

Relevant calorimeters Relevant calorimeters contributioncontribution

Optimization of isolation selectionOptimization of isolation selection

Luca Lista, Gr-I 2008 10

iso 1

2 ET

Ecal 1

2 ET

Hcal

1 pT

β = -0.75β = -0.75

Hcal more relevant Hcal more relevant than Ecal than Ecal

Optimization of isolation selectionOptimization of isolation selection

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First look at real dataFirst look at real data

(Cosmics, of course…)

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Ongoing improvementsOngoing improvements

• Apply optimized isolation– Background reduction of ~30 50 %– Reduced statistical error on by ~6%

• Extract peak shape for Zsa from data– Use Z, suppress track on one leg

• Use Extended Unbinned Max. Likelihood fit on low statistics sample

• Validate fit performances using a Toy MC

• Prepare abstract for winter conferences!