1. b-tagging efficiency in L+jets at 7TeV
Hongbo Liao
LPC, Clermont-Ferrand

2. Tag counting method
The number of events with n btag jets N_i depends on b tagging eb , non-b jet mistag rate e nonb and Fij, the fraction of number of events having i jets matching b quark and j jets not matching
Fit eb and Ntot, enonb and Fij fixed
Pre-selection :
Exactly 1 isolated lepton Pt>20GeV (e or µ)
At least 4 jets. 3jets Pt>40GeV+ 1 jet Pt>30GeV
Missing Et >20GeV
Cut SV0 > 8
eb = 50.2 ± 0.7%
enon b = 1.9 ± 0.1%

3. b tagging weight of SV0, JetProb, TrackCounting and SV1+IP3D
Thanks Nabil and Diane

4. b tagging efficiency
One can estimate weight cut to get such as expected 50% tagging efficiency

5. Light jet rejection

6. Light jet rejection vs btag efficiency
At same btag efficiency, SV1+IP3D has higher light jet rejection

7. Fit results (without bkg)
Track>2.5
SV0>8
JetPtob<0.001
SV1+IP3D>6
Expected :
eb = 48.9 ± 0.7%
Fit :
eb = 49.1 ± 7.3%
Expected :
eb = 46.6 ± 0.7%
Fit :
eb = 47.0 ± 7.0%
Expected : eb = 50.2 ± 0.7% N = 30.1 ± 5.5 Fit : eb = 50.3 ± 7.1% N = 30.4 ± 5.5
Expected :
eb = 49.4 ± 0.7%
Fit :
eb = 49.4 ± 7.2%
with bkg and more checks

8. combinational method for Top mass
Full-Hadronic
Semi-leptonic

9. Semi-leptonic (7TeV)
Idea: find the best combination by the minimum (no fit) to define Ttbar events
Here : the mean values and sigma come from the reconstructed objets which matched the thruth. Additional chooses: normal method; Pt dependence; fit?
Sample: 7TeV Ttbar, W+jets and Single Top samples
After reconstruction: Missing Et > 20 GeV; exactly one lepton Pt>20GeV; at least 4 jets, 3jets Pt>40GeV+1jets Pt>30GeV

10. + chi2<30
+ weight of 1 bjet >6
Pre_selection
S/B :

11. Full-Hadronic (10TeV)
Idea: find the best combination by the minimum (no fit) to define Ttbar events
Smaples : full-hadronic ttbar ;
QCD Multijet ( , , );
W+jets ( , , )
Multi-jet Triggers : 6j35_5j45_4j50_3j60, 4j35_3j45_2j50_j60, 4j45_j60, 5j45_2j60_j100,
5j45_4j60_j100,4j60_2j100_j170