Stat

Document Sample
Stat Powered By Docstoc
					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
Relative uncertainty (%)




                                Quadratic summation

                                                      High-x gluons are not the main
                                                      Source of uncertainties ~3%




                                        PDF number


• ttbb production via gluon-gluon and quark-antiquark fusions
• ttbb cross section from AlgGen: sttbb= 2.55 pb
• Theoretical uncertainties:
          +/- 6%     from PDFs (classical recipe)
          +/- 55% from factorisation and renormalisation scales 1/2m0 <m<2m0
• PDF uncetainties: can be irreducible and constitutes a serious source to
    constraint the analysis
                      constraint on ttH
• For a relative systematic uncertainty  on the background, the significance is:

                                              S
                                  N
                                         (1   2 B) B



• By extracting the relation between S/B and , we obtain the constraint relation:


                                  1                      2
                                          1       2   4
                                    S         S            N
                      B       
                          S              2 2
              Constraint on ttH for 10fb-1
  • Higgs mass=120GeV
                     S/B



                                 5s



                                 4s
Requested S/B
For 3s significane
For 6% PDF uncertainty

                                 3s

S/B=0.14 From                    2s
Markus analysis
(ATLFAST)
                                                             systematic uncertainty on B (%)

                                                       6% of PDF uncertainties (on ttbb+ttjj)
                           Need 1 to 2 % of accuracy
                           On background to reach
                           2s significance
          Constraint on ttH for 100fb-1
 • Higgs mass=120GeV
                  S/B

                                                                     5s


                                                                     4s

                                                                     3s
Requested S/B
For 3s significane
For 6% PDF uncertainty                                               2s
S/B=0.14 From
Markus analysis
(ATLFAST)


                                                       systematic uncertainty on B (%)


                         Need 4% of accuracy 6%   of PDF uncertainties
                         On background to reach
                         3s significance
     Variation with the Higgs mass
             • Higgs mass=130GeV   • Higgs mass=120GeV

• 10 fb-1                                                   5s
                                                            4s
                                                            3s
                                                            2s
                                                            1s

                                                         ATLFAST
                                                         analysis



• 100 fb-1




                                                         ATLFAST
                                                         analysis
             Conclusion: Counting
                experiment…!
• Is ttH feasible ?
   – Reduce the PDF uncertainties to << 6%
      • if not:
      PDF uncertainties are enough to cancel the discovery power
   – 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 (?)
      •   …
   – For 100fb-1 (in 2011) and Background accuracy of 5% :
      • S/B=30% for a 5s discovery (mHiggs=120 GeV)
      • S/B=16% for a 3s evidence (mHiggs=120 GeV)
       Extend to Shape Analysis
From the Statistic workshop at CERN:




            Counting Experiment
                                       Shape (PDF)




    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

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:12
posted:2/26/2012
language:English
pages:10