Few activities in Statistics: Higgs + Exotics Samir FERRAG University of Glasgow

Introduction Very useful Stat Workshop at CERN last week Interacted and triggered some projects: –Alex Read (Shape analysis for ttH, Saverio) –Kyle (Stat Framework for ATLAS based on Roofit) – Feasibility of ttH –Extract the constraints on the background uncertainty –If feasible: define the priorities on real data: PDF, Background, ttH… –Counting experiment constraints to be extended to shape analysis

Theoretical uncertainties on ttbb ttbb production via gluon-gluon and quark-antiquark fusions ttbb cross section from AlgGen:  ttbb = 2.55 pb Theoretical uncertainties: +/- 6% +/- 6% from PDFs (classical recipe) +/- 55% +/- 55% from factorisation and renormalisation scales 1/2   <  <2   PDF uncetainties: can be irreducible and constitutes a serious source to constraint the analysis Relative uncertainty (%) PDF number Quadratic summation High-x gluons are not the main Source of uncertainties ~3%

constraint on ttH By extracting the relation between S/B and , we obtain the constraint relation: For a relative systematic uncertainty  on the background, the significance is:

Constraint on ttH for 10fb -1 55 44 33 22 6% of PDF uncertainties (on ttbb+ttjj) S/B systematic uncertainty on B (%) Requested S/B For 3  significane For 6% PDF uncertainty Need 1 to 2 % of accuracy On background to reach 2  significance Higgs mass=120GeV S/B=0.14 From Markus analysis (ATLFAST)

Constraint on ttH for 100fb -1 6% of PDF uncertainties S/B systematic uncertainty on B (%) Requested S/B For 3  significane For 6% PDF uncertainty 55 44 33 22 Need 4% of accuracy On background to reach 3  significance S/B=0.14 From Markus analysis (ATLFAST) Higgs mass=120GeV

Variation with the Higgs mass Higgs mass=120GeV Higgs mass=130GeV 10 fb fb -1      ATLFAST analysis ATLFAST analysis

Conclusion: Counting experiment…! Is ttH feasible ? << 6% –Reduce the PDF uncertainties to << 6% if not: PDF uncertainties are enough to cancel the discovery power < 5% –Background (ttbb+ttjj) measurement accuracy at < 5% Including PDF uncertainties above (?) Systematic uncertainties from Luminosity (?) Reconstruction and performance tools… (?) If Likelihood, Probability Density Function parameterisation (?) … 5% –For 100fb -1 (in 2011) and Background accuracy of 5% : S/B=30% for a 5  discovery (m Higgs =120 GeV) S/B=16% for a 3  evidence (m Higgs =120 GeV)

Extend to Shape Analysis Counting Experiment Shape (PDF) From the Statistic workshop at CERN: Alex Read Saverio ? Chris

First Steps in Roofit Roofit part of the package ROOT 5-02 Compiled and installed on my Laptop Goal: use it and develop the framework for: Compute limits (Exotics) Research of bumps (Higgs) Very nice Topic for Glasgow/UK collaboration