Lepton Flavour Violation at ATLAS & CMS

Transcription

1 Lepton Flavour Violation at ATLAS & CMS Shikma Bressler on behalf of the ATLAS & CMS collaborations H τμ/τe/μe Z τμ/τe/μe Heavy X τμ/τe/μe Others 1

2 LHC results Library Higgs decays Experiment Process s [TeV] L [fb -1 ] CMS H τµ 8 20 CMS H eµ H eτ 8 20 CMS PAS HIG H τµ ATLAS H τµ 8 20 ATLAS H τµ H τe April

3 LHC results Library Z decays Experiment Process s [TeV] L [fb -1 ] CMS PAS EXO Z µe 8 20 ATLAS Z µe 8 20 ATLAS Z τµ 8 20 Heavy resonances & others Experiment Process s [TeV] L [fb -1 ] CMS X µe 8 20 ATLAS X τµ X τe 8 20 X µe ATLAS X τµ X τe X µe ATLAS τ 3µ April

4 In general. Theory Lepton Flavour is an accidental symmetry of the standard model Broken by neutrino oscillations implies also breaking i.e at Higgs decays but at a very low rate (< ) Many models predict LFV decays of Higgs and/or Z and/or other massive resonances Experiment Complementary efforts are made by both collaborations Different methods are being employed stringent cross checks different systematic uncertainties Detector performance plays a leading role Steep lepton reconstruction turn-on curves High lepton pt resolution Misidentified lepton rate the lower the better 21 April

5 H/Z decays Executive summary - April 2017 Process CMS ATLAS H τµ BR<1.20% BR<1.40% H τe BR<0.69% BR<1.04% H eµ BR<0.048% - Z τµ - BR< Z τe - - Z eµ BR< BR< April

6 H/Z decays Executive summary - April 2017 Background model strategy Process CMS ATLAS The symmetry method H τµ BR<1.20% BR<1.40% H τe BR<0.69% BR<1.04% H eµ BR<0.048% - Z τµ Z τe - - Z eµ BR< BR< Data driven MC based Due to the excellent mass resolutions The choice of method dictates the uncertainties and hence the sensitivity 21 April

7 H/Z decays Executive summary - April 2017 Misidentified lepton estimation strategy Process CMS ATLAS H τµ BR<1.20% BR<1.40% H τe BR<0.69% BR<1.04% H eµ BR<0.048% - Z τµ Z τe - - Z eµ BR< BR< Reversed isolation criteria τhad - Estimation in same-sign region τlep - Estimation using the Matrix Method 21 April

8 Higgs decays CMS H τµ CMS April

9 Higgs decays CMS H τµ Two search channels H µτhad H µτe Three jet categories 0-jets targeting ggf production 1-jet targeting ggf production 2-jets targeting VBF production Background CMS Z ττ Embedding (simulated τ response is embedded in Z μμ data sample) Misidentified leptons (W+jets, QCD) Based on reverse isolation criteria Validated in a same-sign region Mass estimator Collinear mass Other (ttbar, H ττ, WW, ZZ ) From simulation 21 April

10 Higgs decays CMS H τµ CMS H µτhad H µτe 10

11 Higgs decays CMS H τµ CMS H µτhad H µτe Yτµ - Off diagonal Yukawa coupling 21 April

12 Higgs decays ATLAS H τhadµ ATLAS April

13 Higgs decays ATLAS H τhadµ One search channel H µτhad Background ATLAS Two signal regions Mass estimator - MMC Missing Mass Calculator Exploiting the τ decay topology Use the τ mass a a constraint Z ττ Embedding (simulated τ response is embedded in Z μμ data sample) Misidentified leptons (W+jets, QCD) By rqcd Other (ttbar, H ττ, WW, ZZ ) From simulation 21 April

14 Higgs decays ATLAS H τhadµ ATLAS SR1 SR2 SR1+SR2 21 April

15 Higgs decays ATLAS H τµ/τe ATLAS April

16 Higgs decays ATLAS H τµ/τe Two searches & search channels H eτhad H µτe & H eτµ H eτhad Similar to H µτhad Similar SRs and methodologies SR1 ATLAS SR2 Mass estimator MMC Background estimation H τhade SR1+SR2 21 April

17 Higgs decays ATLAS H τµ/τe H τeµ & H τµe Mass estimator Collinear mass Two signal regions SRnoJets SRjets Background - the symmetry assumption Comparing eμ and μe events SM events are symmetric to the replacement of prompt electron with prompt muons Signal events break this symmetry Correction for asymmetric componenets Fake and non prompt leptons pt dependent effects Uncertainties governed by statistics Room for significant improvement when more data is available ATLAS

18 Higgs decays ATLAS H τµ/τe ATLAS April

19 Higgs decays CMS H τe/eµ CMS April

20 Higgs decays CMS H τe/eµ Two searches H eτ H eµ CMS H eτ Similar to H µτ Collinear mass NJet-based categories Background Z ττ - embedded sample Misidentified leptons scaling from sample with reversed isolation Other - MC 21 April

21 Higgs decays CMS H τe/eµ H eµ CMS categories Motivated by detector performance Signal mass resolution varied with lepton region Background composition dictated by the number of jets Inclusive jet categories VBF categories Background Functional fit All categories combined 21 April

22 13 TeV Higgs decays CMS H τµ PAS HIG April

23 13 TeV Higgs decays CMS H τµ Analysis similar to run-1 One exception - Z ττ model also from MC Deficit in the H mass window PAS HIG CMS Yτµ 21 April

24 Z decays CMS Z µe CMS-PAS-EXO April

25 Z decays CMS Z µe Background estimation CMS-PAS-EXO MC-based multi-jet region Mass estimator Invariant mass (no MET) 21 April

26 Z decays ATLAS Z µe ATLAS April

27 Z decays ATLAS Z µe Event selection High pt e and μ Little jet activity Little MET ATLAS Background estimation Side-band fit Possible due to the good mass resolution and the narrow mass range Third order polynomial Shape studied in MC Mass estimator Invariant mass (no MET) 21 April

28 Z decays ATLAS Z τµ ATLAS April

29 Z decays ATLAS Z τµ One search channels Z µτhad ATLAS Methodology Similar to the one employed in the corresponding Higgs search Cut values are lowered to match the kinematics of Z decays Larger background contribution from W+jets Estimated in more bins 21 April

30 Heavy resonances CMS X µe CMS April

31 Heavy resonances CMS X µe Motivations τ sneutrino in RPV SUSY Z and γ Quantum black holes (non resonant) Within a specific model Background estimation Irreducible - MC based Reducible - combination CMS April

32 13 TeV Heavy resonances ATLAS X τμ/τe/µe ATLAS April

33 13 TeV Heavy resonances ATLAS X τμ/τe/µe Motivations Z Assumes SM coupling to quarks Only one LFV decay is allowed τ sneutrino in RPV SUSY Quantum black holes (non resonant) Within two specific models ATLAS Background estimation Irreducible - MC based With some extrapolation when the MC statistics is limited Reducible - combination 21 April

34 Others ATLAS τ 3µ ATLAS April

35 Others ATLAS τ 3µ Search channel W τν ; τ 3μ Main discriminators 3 nearby muons. τ lifetime muons originating from a secondary vertex m3μ ~ mτ Strategy Step 1: event selection based on the discriminators Step 2: BDT - with loose selections To ensure enough statistics 16 input variables ATLAS ATLAS Yτµ Step 3: tight cuts on the BDT output score Step 4: optimize selection based on estimation in the sideband region Background Main source: Heavy Flavour decays Extrapolated from the sideband region 21 April

36 Others ATLAS τ 3µ ATLAS τ H µ µ µ Observed (expected) 21 April

37 Next steps Analyses are being repeated now with more data Optimization and improvements are done in parallel Multivariate analysis techniques are being exploited to further improve the sensitivity of the analyses Clear view of which paths are available for searching for LFV decays The track is pretty well defined Not all fronts are covered Are we missing anything? 21 April