1 B-tagging meeting overview Li bo Shandong University

2 outline Purpose information on b-tagging studying information on b-tagging studying The b-tagging meetings mainly deal with Trigger studies for b jets Trigger studies for b jets The performance of b-tagging The performance of b-tagging B-tagging calibration B-tagging calibration The validation of software release The validation of software release

3 The trigger study for b-jets Correlation of b-jet trigger at L2/EF with offline b-tagging Correlation of b-jet trigger at L2/EF with offline b-tagging Various b-jet triggers Various b-jet triggers rate reduction rate reduction

4 Correlation with offline taggers Aims at offline Є b =60% Aims at offline Є b =60% The plot shows the working points of L2 and EF are ~78% and ~68% The plot shows the working points of L2 and EF are ~78% and ~68%

5 Rate reduction of different b-jet triggers The rate reduction is almost constant with different Pt The rate reduction is almost constant with different Pt

6 The b-tagging performance The b-tagging performance The b-tagging performance b-tagging efficiency b-tagging efficiency rejection of light/c/tau jet rejection of light/c/tau jet Study on b-tagging performance Study on b-tagging performance 1 Studies for the various jet algorithms 1 Studies for the various jet algorithms 2 Impact from vertex reconstruction 2 Impact from vertex reconstruction 3 Impact from tracking performance 3 Impact from tracking performance 4 Measurement of mistag-rate 4 Measurement of mistag-rate 5 Misalignment 5 Misalignment

7 1 Studies for the various jet algorithms Requirement that jet has more than one track makes b tagging procedure more robust against jet reconstruction algorithms

8 2 Impact from primary vertex reconstruction Sources of impacts: Sources of impacts: PV reconstruction efficiencies PV reconstruction efficiencies PV resolutions PV resolutions Pile up Pile up

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10 Source of impacts: Source of impacts: SV reconstruction efficiencies SV reconstruction efficiencies SV reconstruction fake rate SV reconstruction fake rate SV resolution SV resolution 2 Impact of Secondary vertex reconstruction on b-tagging 2 Impact from secondary vertex reconstruction

11 Impact on b-tagging

12 3 Impact from tracking performance Sources of impacts: Sources of impacts: impact parameter resolution impact parameter resolution tracking efficiency and fake rate tracking efficiency and fake rate

13 Impact on b-tagging performance

14 4 Mis-tagging rate Definition: Definition: the ratio between the number of light jets tagged as b-jet and the number of light jets the ratio between the number of light jets tagged as b-jet and the number of light jets Sources leading to mis-tagging : Sources leading to mis-tagging : finite resolution of the reconstructed track/vertex parameters finite resolution of the reconstructed track/vertex parameters Tracks/vertices from the long-live particles that decay in jets. Tracks/vertices from the long-live particles that decay in jets. 4 Mis-tagging rate

15 Measurement Method: Measurement Method: 1. taking negative weight of all jets 2. inverting to positive to reperesent positive weight distribution of light jets 3. measure the mis-tagging rate 4. with MC, correction for the long-live meson presence in the light jet and heavy flavor jet contribution. Other method: Other method: using templates

16 Result of mistag rate The measured mistag rate is almost close to the actual mistag rate

17 Misalignment sets: Misalignment sets: Random 10 Random 10 Random 5 Random 5 5 Mis-alignment

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21 Purpose: Purpose: develop methods to get b-tagging efficiency with data develop methods to get b-tagging efficiency with data Method: Method: using di-jet events using di-jet events Pt-rel Pt-rel System 8 System 8 using ttbar events using ttbar events Tag couting Tag couting Control sample Control sample The b-tagging calibration

22 Dijet event Pt-rel method Pt-rel method Muons in μ-jet have different Pt distributions w.r.t jet axis originating from different flavor q/g Muons in μ-jet have different Pt distributions w.r.t jet axis originating from different flavor q/g use templates for b, c and light jets to determine their relative fractions use templates for b, c and light jets to determine their relative fractions

23 Pt-rel method Fraction of b-jets can be extracted from fitting to templates, before tagging (Fb ->u) and atfer tagging (Ftag b->u) efficiency calculated as

24 System 8 method Two sample with different heavy flavor content Two sample with different heavy flavor content Two independent taggers Two independent taggers Apply taggers to both samples Apply taggers to both samples jets passing two taggers both jets passing two taggers both Write a system of 8 equations to solve the tagging efficiency Write a system of 8 equations to solve the tagging efficiency

25 System8 both methods have good result up to 80Gev(jet Pt ) both methods have good result up to 80Gev(jet Pt ) improvements to system 8 method: improvements to system 8 method: use different release like r13 : improvements to performance of taggers use different release like r13 : improvements to performance of taggers use different samples and taggers use different samples and taggers Pt-rel

26 Using ttbar event count number of events with 1,2,3 b-tags(lepton+jet) or 1,2 b-tags (delepton) likelihood fit gives b-tag efficiency

27 ttbar results

28 Methods for b-jet sample selection topological topological reconstruct all combinations, apply mass windows kinematic kinematic apply kinematic fit assuming m bjj and m blv =m top, and select combination with best fit x 2 likelihood likelihood use jet/lepton energy and angular information

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30 B-tagging validation

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32 Summary The studies for b-jet triggers The studies for b-tagging performance the impact of vertex and tracking on b-jet performance the measurement of mistagging rate misalignment and error scaling The studies of b-tagging calibration measurement of b-tagging efficiency with di-jet and ttbar event b-jet sample selection with three methods