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B-tagging meeting B-tagging meeting overviewoverview

Li boLi boShandong UniversityShandong University

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outlineoutline

Purpose Purpose information on b-tagging studyinginformation on b-tagging studying

The b-tagging meetings mainly deal withThe b-tagging meetings mainly deal with Trigger studies for b jetsTrigger studies for b jets The performance of b-taggingThe performance of b-tagging B-tagging calibrationB-tagging calibration The validation of software releaseThe validation of software release

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The trigger study for b-jetsThe trigger study for b-jets

Correlation of b-jet trigger at L2/EF Correlation of b-jet trigger at L2/EF with offline b-taggingwith offline b-tagging

Various b-jet triggers Various b-jet triggers rate reductionrate reduction

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Correlation with offline tagCorrelation with offline taggersgers

Aims at offline Aims at offline ЄЄbb =60%=60%

The plot shows thThe plot shows the working points e working points of L2 and EF are of L2 and EF are ~78% and ~68% ~78% and ~68%

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Rate reduction of different b-jet triggersRate reduction of different b-jet triggers

The rate reduction is almost constant with differThe rate reduction is almost constant with different Ptent Pt

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The b-tagging performanceThe b-tagging performance

The b-tagging performanceThe b-tagging performance b-tagging efficiency b-tagging efficiency

rejection of light/c/tau jetrejection of light/c/tau jet

Study on b-tagging performanceStudy 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 performance3 Impact from tracking performance 4 Measurement of mistag-rate 4 Measurement of mistag-rate 5 Misalignment5 Misalignment

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1 Studies for the various jet algorithms1 Studies for the various jet algorithms

Requirement that jet has more than one track makes b tagging procedure more robust against jet reconstruction algorithms

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2 Impact from primary vertex reconstruction2 Impact from primary vertex reconstruction

Sources of impacts:Sources of impacts: PV reconstruction efficiencies PV reconstruction efficiencies PV resolutions PV resolutions Pile upPile up

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Source of impacts: Source of impacts: SV reconstruction efficiencies SV reconstruction efficiencies SV reconstruction fake rateSV reconstruction fake rate SV resolutionSV resolution

2 Impact of Secondary vertex reconstruction on b-tagging2 Impact of Secondary vertex reconstruction on b-tagging

2 2 Impact from secondary vertex reconstructionImpact from secondary vertex reconstruction

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Impact on b-taggingImpact on b-tagging

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3 Impact from tracking performance3 Impact from tracking performance

Sources of impacts:Sources of impacts: impact parameter resolutionimpact parameter resolution tracking efficiency and fake ratetracking efficiency and fake rate

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Impact on b-tagging performanceImpact on b-tagging performance

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4 Mis-tagging rate4 Mis-tagging rate

Definition:Definition: the ratio between the number of light jets tthe ratio between the number of light jets t

agged as b-jet and the number of light jetsagged as b-jet and the number of light jets

Sources leading to mis-taggingSources leading to mis-tagging:: finite resolution of the reconstructed track/vfinite resolution of the reconstructed track/v

ertex parametersertex parameters Tracks/vertices from the long-live particles Tracks/vertices from the long-live particles

that decay in jets.that decay in jets.

4 Mis-tagging rate4 Mis-tagging rate

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Measurement Method:Measurement Method:1.1. taking taking negativenegative weight of weight of all jetsall jets2.2. inverting to inverting to positive positive to reperesent positive weigto reperesent positive weig

ht distribution of ht distribution of light jetslight jets3.3. measure the mis-tagging ratemeasure the mis-tagging rate4.4. with MC, correction for the long-live meson prewith MC, correction for the long-live meson pre

sence in the light jet and heavy flavor jet contribsence in the light jet and heavy flavor jet contribution.ution.

Other method: Other method: using templates

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Result of mistag rateResult of mistag rate

The measured mistag rate is almost close to the actual mistag rate

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Misalignment sets:Misalignment sets: Random 10Random 10 Random 5Random 5

5 Mis-alignment5 Mis-alignment

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Purpose:Purpose: developdevelop methods to get b-tagging efficiency with datamethods to get b-tagging efficiency with data

Method: Method: using using di-jet eventsdi-jet events

Pt-rel Pt-rel System 8 System 8

using using ttbar eventsttbar events Tag couting Tag couting Control sampleControl sample

The b-tagging calibrationThe b-tagging calibration

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Dijet eventDijet event

Pt-rel methodPt-rel method Muons in Muons in μμ-jet-jet have diff have diff

erent Pt distributions w.r.t erent Pt distributions w.r.t jet axis originating from difjet axis originating from different flavor q/g ferent flavor q/g

use templates for b, c ause templates for b, c a

nd light jets to determine thnd light jets to determine their relative fractionseir relative fractions

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Pt-rel methodPt-rel method

ubtagF

Fraction of b-jets can be extracted from fitting to templates, before tagging (Fb ->u) and atfer tagging (Ftag b->u)

efficiency calculated as

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System 8System 8 method method Two sample with different Two sample with different

heavy flavor contentheavy flavor content

Two independent taggersTwo independent taggers

Apply taggers to both samApply taggers to both samplesples

jets passing two taggers bjets passing two taggers bothoth

Write a system of 8 equaWrite a system of 8 equations to solve the tagging tions to solve the tagging efficiencyefficiency

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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 : use different release like r13 : improvements to performance improvements to performance of taggersof taggers

use different samples and taggers use different samples and taggers

Pt-relPt-rel

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Using ttbar eventUsing ttbar event

count number of events with 1count number of events with 1,2,3 b-tags(lepton+jet) or 1,2 b,2,3 b-tags(lepton+jet) or 1,2 b-tags (delepton)-tags (delepton)

likelihood fit gives b-tag likelihood fit gives b-tag efficiencyefficiency

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ttbar resultsttbar results

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Methods for b-jet sample Methods for b-jet sample selectionselection

topologicaltopologicalreconstruct all combinations, apply mass windowsreconstruct all combinations, apply mass windows

kinematickinematic

apply kinematic fit assuming mapply kinematic fit assuming mbjj bjj and mand mblvblv=m=mtoptop, and , and

select combination with beselect combination with best fit st fit xx2 2

likelihoodlikelihooduse jet/lepton energy and angular information use jet/lepton energy and angular information

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B-tagging validationB-tagging validation

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SummarySummary

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