SUSY Discovery Potential SUSY Discovery Potential in Trilepton in Trilepton Final States Final States at ATLAS: at ATLAS: the Strive for Lepton Purity the Strive for Lepton Purity – in collaboration in collaboration with ith ATLAS CSC 7 / 5 ATLAS CSC 7 / 5 Oleg Brandt Oleg Brandt supervisors: Pa Pawe wel Brückma l Brückman Ala Alan B Barr rr Ton Tony W Weidberg idberg
Today‘s menu Today‘s menu � Short overview of lepton preselection � Lepton isolation: � Track isolation � Calorimeter isolation � OSSF lepton selection: � First thoughts on measuring the isolated lepton rate from b-jets � Conclusion � Outlook SUSY SUSY discovery potential in trilep discovery potential in trilepton final states: Technical Aspects ton final states: Technical Aspects 2
Leading lepton Pt for Leading lepton Pt for SU2 U2 10 fb -1 SUSY Signal 10 fb -1 Need high lepton purity! Need high lepton purity! SUSY SUSY discovery potential in trilep discovery potential in trilepton final states: Technical Aspects ton final states: Technical Aspects 3
Preselection outlined Preselection outlined � Preselection (ATLAS SUSY WG cuts in blue): � Muons: � MuID � | η | < 2.5 � Calorimeter isolation in ∆ R = 0.2 cone: < 10 GeV � bestMatch(), isCombinedMuon() � chi²/NDF for track < 5, track match: < 20 � Jet isolation: no jets in ∆ R = 0.4 cone (against b) � Isolation w/r/t each other in: ∆ R = 0.1 (against J/Psi & Y) � Pt > 10 GeV � Electrons: � | η | < 2.5 � (isEM() & 0x3FF) == 0 � reconstructed by eGamma algorithm � Isolation w/r/t each other in: ∆ R = 0.1 � Pt > 15 GeV SUSY discovery potential in trilep SUSY discovery potential in trilepton final states: Technical Aspects ton final states: Technical Aspects 4
Track isolation: Track isolation: after after 3rd lepton requirement rd lepton requirement Define track isolation as: (inspired by H->4l) where µ e 1 1 o o t t d d e e s s i i l l a a m m r r o o n n SUSY discovery potential in trilep SUSY discovery potential in trilepton final states: Technical Aspects ton final states: Technical Aspects 5
Calorimeter isolation: Calorimeter isolation: after 3rd lepton requirement after 3rd lepton requirement µ „Conventional“ ATLAS calorimeter isolation from AOD, rel. 12.0.7 1 o t d e s i l a m r o n e 1 o t d e s i l a m Additional discrimination power? r o n SUSY discovery potential in trilep SUSY discovery potential in trilepton final states: Technical Aspects ton final states: Technical Aspects 6
Track vs. Calorimeter isolation Track vs. Calorimeter isolation µ � not 100% correlated :) � for tight track isolation calo isolation not efficient :( . t a e t s C M l l u f � Calo isolation potentially easier to understand . t a t s � Use the discrimination C M l l u f variable first understood! SUSY discovery potential in trilep SUSY discovery potential in trilepton final states: Technical Aspects ton final states: Technical Aspects 7
Study fake isolated leptons Study fake isolated leptons from from b-jets in ttbar events b-jets in ttbar events Study isolated lepton fake rate from b-jets: � Need a reasonably pure sample of b-jets: � - bb � - tt � - bb: � difficult due to high QCD backgrounds, e.g. W+j � not realistic � - tt: � Several handles to tag ttbar events � without using one of the b-jets - Use semileptonic tt channel � Orthogonal sample � approx. 10x more statistics � SUSY discovery potential in trilep SUSY discovery potential in trilepton final states: Technical Aspects ton final states: Technical Aspects 8
Study fake isolated leptons Study fake isolated leptons from from b-jets in ttbar events: Ansatz b-jets in ttbar events: Ansatz opposite sign SUSY SUSY discovery potential in trilep discovery potential in trilepton final states: Technical Aspects ton final states: Technical Aspects 9
Study fake isolated leptons Study fake isolated leptons from from b-jets in ttbar events: Ansatz b-jets in ttbar events: Ansatz ! ! s s y y a a c c e e e e l l d d b b i i r r s s a a a a b b e e t t f f t t t t c c o o i i N N n n o o t t p p e e l l i i d d o o t t e e u u d d SUSY discovery potential in trilept SUSY discovery potential in trilepton final states: Technical Aspects on final states: Technical Aspects 10
Study fake isolated leptons Study fake isolated leptons from from b-jets in ttbar events: Ansatz b-jets in ttbar events: Ansatz same sign! SUSY SUSY discovery potential in trilept discovery potential in trilepton final states: Technical Aspects on final states: Technical Aspects 11
Study fake isolated leptons Study fake isolated leptons from from b-jets in ttbar events: Ansatz b-jets in ttbar events: Ansatz full top decay chain same sign! Tags Tags dijet mass = m_W SUSY SUSY discovery potential in trilept discovery potential in trilepton final states: Technical Aspects on final states: Technical Aspects 12
Study fake isolated leptons Study fake isolated leptons from b-jets in ttbar events from b-jets in ttbar events Possible backgrounds (probably in order of importance): � - Dileptonic tt � lepton charge mismeasurement � Single top � associated W+t production: � hadronic W: contribution to the desired „signal“ sample � leptonic W: with additional contribution to „background“ � - most of other single top (t+bb ...): � contribution to the „signal“ � Z + QCD � - lepton charge mismeasurement + additional jets to mimic tt � - bb + jets � semileptonic b-decays with oscillaton / consecutive c-decays � W + QCD � 1 true lepton and one from QCD + additional jets � WZ, ZZ � � leptons from W / Z + additional jets ... Ideas? � SUSY SUSY discovery potential in trilept discovery potential in trilepton final states: Technical Aspects on final states: Technical Aspects 13
Conclusion Conclusion Studied lepton isolation: � Calorimeter isolation � Probably easier to understand � Track isolation � More powerful � Correlation � Resulting table of statistical significancies for SUx: 10 fb -1 SUSY SUSY discovery potential in trilept discovery potential in trilepton final states: Technical Aspects on final states: Technical Aspects 14
Outlook Outlook � Proceed with writing up CSC 7 / CSC 5 notes! � Study triggers for : � look at new trigger menu version in 13.0.30 � Identify optimal handles to adjust trigger rate � Study isolated lepton fake rate from b-jets: � Identify relevant backgrounds � First steps towards a way to measure this rate in data ... � Do more studies: � background � systematics SUSY discovery potential in trilept SUSY discovery potential in trilepton final states: Technical Aspects on final states: Technical Aspects 15
Backup & further discussion Backup & further discussion Backup slides following SUSY SUSY discovery potential in trilept discovery potential in trilepton final states: Technical Aspects on final states: Technical Aspects 16
Lepton trigger study Lepton trigger study � First running will be at � Focus on the „Worst Case“ scenario � the most critical SUSY analysis � cannot trigger on jets � triggering on MEt dodgy � need lepton triggers � rather low-Pt leptons � Lepton triggers for start-up: � efficient � unprescaled � failsafe: � no „risky“ cuts � rate adjustment � simple to understand SUSY discovery potential in trilept SUSY discovery potential in trilepton final states: Technical Aspects on final states: Technical Aspects 17
Lepton triggers analysed: Lepton triggers analysed: selection 10,2 fb -1 with jet veto Full SU2 s SUSY SUSY discovery potential in trilept discovery potential in trilepton final states: Technical Aspects on final states: Technical Aspects 18
Lepton triggers: Summary Lepton triggers: Summary SU2 „ χ ± χ 0 “ SU2 inclusive SU2 inclusive jet veto NO jet trigger fired all of SU2 to be updated with updated selection to be updated with updated selection SUSY SUSY discovery potential in trilept discovery potential in trilepton final states: Technical Aspects on final states: Technical Aspects 19
SUSY SU2 in Trilepton Channel SUSY SU2 in Trilepton Channel � MSSM: 105 paramers � SUSY spontaneously broken -> SUGRA � Mass unification at GUT scale -> mSUGRA � ATLAS mSUGRA benchmark points: � SU2: very hard to detect � SU3: „generic“ � SU4: light SUSY � „flat“ search performance in multilepton final states SUSY SUSY discovery potential in trilept discovery potential in trilepton final states: Technical Aspects on final states: Technical Aspects 20
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