Searches for New Physics with Tau Leptons at the ATLAS Detector. Katharine Leney University of the Witwatersrand

Transcription

1 Searches for New Physics with Tau Leptons at the ATLAS Detector Katharine Leney University of the Witwatersrand

2 Overview Introduction: ATLAS and the LHC The Standard Model and beyond Tau leptons ATLAS searches for new physics with taus in the final state: Heavy particles (e.g. Z boson) decaying to τ + τ - 3rd generation leptoquarks decaying to b-jet and τ. Lepton flavour violating resonances. Supersymmetry Higgs boson(s?) Summary and outlook Katharine Leney 2

3 CERN and the LHC 27km long tunnel, 0m underground. Two beams of protons circulating in opposite directions, traveling at 99.99% of the speed of light. Katharine Leney 3

4 CERN and the LHC Beam is controlled by 1800 superconducting magnets (8T) operating at 1.9 K `bunches of protons per beam. 200 billion protons per bunch. Katharine Leney 4

5 The ATLAS Detector Diameter = 25m Length = 40m Weight = 7000 tonnes Katharine Leney 5

6 The ATLAS Detector Katharine Leney 6

7 ATLAS Data Events Z µµ event + 24 other p-p interactions Katharine Leney 7

8 The ATLAS Collaboration 3000 physicists 38 countries 175 institutes Katharine Leney 8

9 ATLAS in South Africa UJ Wits UKZN UCT Katharine Leney 9

10 The Standard Model & Beyond Dark Matter? Hierarchy problem? Gravity? Baryogenesis? Unification of electroweak and strong forces? Higgs mass fine tuning? Katharine Leney

11 Tau Decay Characteristics Hadronic τ-decay ID: Well collimated, low multiplicity jet. Deposits in both hadronic and EM calorimeters. One or three tracks (1p or 3p) in cone ΔR < 0.2 matching the calorimeter deposition. Identify using a boosted decision tree (BDT). τ-decay Modes & & & ;PG& ;PG& IOG& & & BG& =G&!! 201!! /01! ;BG& & τ-τ Decay Channels Di-Lepton Lepton-Hadron Hadron-Hadron 41.9% 45.8% 12.4% Katharine Leney 11

12 Why Use Taus? Many models predict preferential coupling to 3rd generation. New gauge bosons. Higgs bosons in supersymmetry theories. Flavour sector observed increased rates in B-meson decays to taus. 3.4σ deviation observed by the BaBar experiment. Can we find something to explain the discrepancy? And they re good fun! Challenging to reconstruct hadronic taus. Multiple decay channels per analysis. ATLAS Tau Workshop 2013, Corfu Katharine Leney 12

13 Interpreting Limit Plots Katharine Leney 13

14 Search for Z ττ Motivation New heavy gauge bosons predicted by many beyond the Standard Model theories (extended gauge sectors, string theory, KK etc). Enhanced coupling to 3rd generation predicted by several models (extended weak or hypercharge gauge groups). Use Sequential Standard Model (SSM) as benchmark model (same couplings as Standard Model). Existing Limits SSM Z ee/µµ excluded M Z < 2.6 (2.5) TeV by CMS (ATLAS). Z bosons with non-universal flavour-couplings excluded (indirectly) M Z < 1.1 TeV (LEP). Sub-Channels Considered Z τ τ e + µ + 4ν Z τ τ e/µ + τ had + 3ν Z τ τ τ had + τ had + 2ν (2011) 4.7 fb -1 data s = 7 TeV Katharine Leney 14

15 Z ττ eµ e/µ τ h τ h τ h One e, p T > 25 GeV One e (µ) p T > 25 (30) GeV Two τ had, p T > 50 GeV One µ, p T > 35 GeV One 1-p τ had, p T > 35 GeV # jets 1 Opposite-sign charge Visible tau decay products back-to-back Δφ (lead lepton, E miss T ) > Signal Region Z typically has narrow width (~3% mass) but mass resolution degraded due to missing E T from neutrinos in tau decays. Count events with high transverse mass (between visible tau decay products and missing E T ). Main Backgrounds Z ττ Z ll W+jets Multi-Jet Top Di-Boson M T (τ 1,τ 2, MET) = Katharine Leney 15

16 Events / 50 GeV 4 (a) ATLAS Data L dt = 4.6 fb Multijet s = 7 TeV Z/ * τhad-τhad Channel W Others Z (1250) tot miss m T ( had-vis, had-vis, E T ) [GeV] Z ττ (pp Z ) BR(Z ) [pb] (b) ATLAS ATLAS -1 L dt = 4.6 fb s = 7 TeV Channels combined Expected limit Expected ± 1 Expected ± 2 Exclude Z τ τ decays for M Z < 1.4 TeV arxiv: Published in PLB Observed limit Z SSM Z SSM th. uncert m Z [GeV] e + µ µ + τ had e + τ had τ had + τ had # Expected Background 3.6 ± ± ± ± 0.3 # Expected Signal 6.7 ± 0.3 (M Z = 750 GeV) 5.5 ± 0.7 (M Z = 00 GeV) 5.0 ± 0.5 (M Z = 00 GeV) 6.3 ± 1.1 (M Z = 1250 GeV) # Observed Katharine Leney 16

17 Search for 3rd Generation Leptoquarks Leptoquarks (LQs) provide link between quark and lepton sectors (explanation for many similarities of mass hierarchy, charge cancellation etc) Appear in a wide range of theories, including SU(5) grand unification, superstrings, SU(4) PatiSalam, and compositeness models. Good candidate to explain anomalies in the flavour sector, such as the BaBar observation of increased rates of B-meson decays to taus (PhysRevLett ). g! g! g! LQ! LQ! τe -! u! b _ b e +! τ + u! Search for pair produced, scalar, third generation leptoquarks in τb channel. LQ 3 LQ 3 τ b τ b e/µ b τ had b + 3ν Assume LQs couple exclusively to quarks and leptons of the same generation 3 generations of leptoquarks. Katharine Leney (2011) 4.7 fb -1 data s = 7 TeV 17

18 3rd Generation Leptoquarks One e (µ) p T > 25 (20) GeV One τ had, p T > 35 GeV Opposite-sign charge (lepton-tau) Missing E T > 20 GeV N Jets 2 (lead jet p T > 50 GeV) Leading or sub-leading jet is b-jet M (τ - closest-jet) > 90 GeV Angular requirements (e/µ, τ had, E miss T ) Main Backgrounds Top W+jets Z ττ Multi-Jet Use S T distribution to test for existence of leptoquarks. S T = p T (e/µ) + p T (τ had ) + p T (jet 1 ) + p T (jet 2 ) + missing E T Fit background distribution in high S T region. 18

19 3rd Generation Leptoquarks Combined arxiv: Submitted to JHEP Exclude LQ3LQ3 τb τb decays for M LQ < 534 GeV Katharine Leney 19

20 Supersymmetry (SUSY) Popular candidate for source of dark matter. ~ Charginos: χ ± ~ Neutralinos: χ 0 Solution for the hierarchy problem. Katharine Leney 20

21 Electroweak SUSY Production Search for chargino and neutralino decays to (s)taus: χ ± 1 χ0 2 τ Lν(τ ν) τ L τ τν χ 0 1 ττ χ0 1 χ ± ± 1 χ 1 2 τν( ντ) 2 τν χ0 1 ; ± τ ± τ 2 τ χ 0 1 At least two τ had, p T > 20 GeV At least one τ had - τ had pair with opposite-sign charge Light lepton veto Z-veto (71 GeV < M τ τ < 91 GeV) Zero jets M T2 > 90 GeV E T miss > 40 GeV No b-jets M T2 > 0 GeV (2012) 20.7 fb -1 data s = 8 TeV M T2 = stransverse mass = transverse mass between two hadronic taus and E T miss. Katharine Leney 21

22 Electroweak SUSY Production Main Backgrounds Multi-Jet W+jets Top-pair (+ W/Z) Single top Z/γ* + jets Diboson Exclude charginos (neutralinos) up to 350 (0) GeV. (ATL-CONF ) Chargino-neutralino production with mass: s( χ ± 1, χ 0 1) = (250, 0) GeV; ± Chargino-chargino production with mass: ( χ ± 1, χ 0 1) = (150, 50) GeV. SM process SR OS m T2 SR OS m T2 -nobjet top 0.2 ± 0.5 ± ± 0.8 ± 1.2 Z+jets 0.28 ± 0.26 ± ± 0.3 ± 0.3 diboson 2.2 ± 0.5 ± ± 0.5 ± 0.9 multi-jet & W+jets 8.4 ± 2.6 ± ± 3 ± 3 SM total 11.0 ± 2.7 ± ± 4 ± 3 data 6 14 SUSY Ref. point ± ± 1.2 SUSY Ref. point ± ± 0.7 Katharine Leney 22

23 Lepton Flavour Violating Resonances In some SUSY models, R-parity (lepton and baryon numbers) are no longer conserved. sneutrino decays to leptons (dd - ~ ν ll ). Extra gauge bosons (e.g. Z ) could also have lepton flavour violating decays. Z ll decays. Search for resonance in pairs of different flavour, opposite-sign leptons: eµ eτ µτ (2011) 4.7 fb -1 data s = 7 TeV Exactly two different flavour, opposite-sign leptons e : p T > 25 GeV µ : p T > 25 GeV τ : p T > 20 GeV Δφ (ll ) > 2.7 eτ and µτ events: Assume E miss T comes solely from neutrinos from τ-decay and correct τ p T for neutrino momentum narrower ll mass peak for signal. Katharine Leney 23

24 Lepton Flavour Violating Resonances Search for resonance in ll invariant mass spectrum Main Backgrounds Top Z ττ Di-Boson Multi-Jet Katharine Leney 24

25 Lepton Flavour Violating Resonances Set limits on sneutrino mass (using - dd ~ ν τ coupling (λ 311 ) = 0.05 as benchmark point). Exclude M~ ν < 1.61 TeV (eµ channel) M~ ν < 1.11 TeV (eτ channel) M~ ν < 1. TeV (µτ channel) arxiv: Submitted to Physics Letters B Katharine Leney 25

26 Standard Model Higgs ττ Searches Essential to establish whether or not recently discovered Higgs boson decays to fermions. Only direct fermion decays are to two b-quarks or to two τ s. bb has much larger branching ratio than ττ, but b-quark decays generally produce jets or low pt leptons. All sub-channels considered: H τ τ ee / eµ / µµ + 4ν H τ τ e/µ + τ had + 3ν H τ τ τ had + τ had + 2ν mh / GeV ( partial 2012) 4.7 fb -1 data at s = 7 TeV fb -1 data at s = 8 TeV Katharine Leney 26

27 Standard Model Higgs ττ Searches Event selection tuned for: Decay mode of tau-pair. 7 TeV or 8 TeV data. p T (e) : GeV p T (µ) : -25 GeV p T (τ had ) : GeV τ lep τ lep τ lep τ had τ had τ had Exactly two of e/µ Exactly one e/µ Exactly one τ had Opposite-sign charge between e/µ/τ had pair. Exactly two τ had 30 < Mll M < 75(0) GeV for Di-lepton veto Veto additional leptons ee/µµ (e/µ) channel M T (l,e miss T ) < 30 GeV - Also categorise depending on number and kinematic properties of reconstructed jets: Vector Boson Fusion (VBF) : Two forward jets Boosted Higgs : High p T jet, or Higgs has high p T. 0-jet 1-jet End up with s of different sub-channels! Main Backgrounds Z ττ Z ll W+jets Multi-Jet Top Di-Boson Katharine Leney 27

28 Standard Model Higgs ττ Searches ATL-CONF Limit on cross-section times branching ratio for SM H τ + τ observed (expected) to be 1.9 (1.2) times the SM prediction (m H =125 GeV) Katharine Leney 28

29 SUSY Higgs Searches SUSY requires two Higgs doublets: 5 observable Higgs bosons: 3 neutral (h/a/h) 2 charged (H ± ) Use Minimally Supersymmetric Standard Model (MSSM) as a benchmark model. MSSM Higgs not ruled out by recent Higgs discovery. May be just the lightest of the 3 neutrals... Decays into 3rd generation fermions strongly enhanced for large regions of phase space. Decays into pair of tau leptons important channel. Search for neutral Higgs follows similar analysis strategy (event selection, backgrounds etc) as SM analysis. (2011) MSSM neutral Higgs produced in association with 0, 1 or 2 b-jets. 4.7 fb Separate event categories for b-jet requirement and b- jet veto. -1 data s = 7 TeV Katharine Leney 29

30 MSSM Neutral Higgs ττ Searches Set limits in m A -tan β plane. tan β = ratio of v.e.v s of Higgs doublets Exclude large region of MSSM phase space. ATLAS-CONF Katharine Leney 30

31 MSSM Charged Higgs τν Searches Produced in top decays. Largest branching ratio is to τν. Sub-channels considered: τ+l: tt bbwh bb (lv) (τ had v) τ+jets: tt bbwh bb (qq) (τ had v) l+jets: tt bbwh bb (qq) (τ lep vv) (2011) 4.7 fb -1 data s = 7 TeV l+jets τ+jets τ+l One e (µ), p T > 25 (20) GeV Two jets tagged as b-jets One τ had, p T > 40 GeV At least 4 jets, pt > 20 GeV A least one jet tagged as b-jet Missing E T and topological cuts. One e (µ), p T > 25 (20) GeV One τ had, p T > 20 GeV Katharine Leney 31

32 MSSM Charged Higgs τν Searches Set limits on branching fraction of top quark decay to bh +. B(t bh + ) < 5% (m H+ = 90 GeV) B(t bh + ) < 1% (m H+ = 160 GeV) ATLAS-CONF Exclude large region of MSSM phase space. 32

33 Summary Comprehensive tau physics program at ATLAS covering wide range of topics. Set competitive limits on new physics processes using 2011 and 2012 data. Model Mass reach / sensitivity Dataset SSM Z τ τ M Z < 1.4 TeV 4.7 fb -1, 7 TeV LQ 3 LQ 3 τb τb M LQ < 538 GeV 4.7 fb -1, 7 TeV EW SUSY (2τ + E miss T ) ~ χ ± < 350 GeV, ~ χ 0 < 0 GeV 20.7 fb -1, 8 TeV LFV Resonances M ν < 1.61 TeV 4.7 fb -1, 7 TeV ~ SM H τ τ Exclude 1.9 x SM σ 4.7 fb fb -1, 7/8 TeV MSSM H τ τ MSSM H ± τ ν Exclude large regions of MSSM parameter space. 4.7 fb -1, 7 TeV 4.7 fb -1, 7 TeV Katharine Leney 33

34 Outlook LHC now in long shutdown for maintenance and upgrades. Resume running again in early Increased data-taking rate: proton-proton interactions per bunch crossing in Higher centre of mass collision energy ( s) 14 TeV - Production cross-section for most exotic processes increases with s. - Large improvements to analysis sensitivity. ATLAS will use this period to: Finish analysing 2012 data. - Develop sophisticated analysis techniques, e.g. using multivariate methods. Detector maintenance and upgrades. - e.g. insert extra layer of silicon pixel detectors between existing detector and new smaller beampipe allows for better vertex reconstruction. Develop analysis strategies (including coping with increased pile-up) for 2015 Katharine Leney 34

35 Back-Up Katharine Leney 35

36 The ATLAS Detector Katharine Leney 36

37 How much is an ev? A single electron accelerated by a potential difference of 1 volt will have a discreet amount of energy, E=qV joules, where q is the charge on the electron in coulombs and V is the potential difference in volts. 1 ev = (1.602 x 19 C) x (1 V) = x 19 J. 3 k (kilo) 6 M (mega) 9 G (giga) 12 T (tera) Katharine Leney 37

38 ABCD Methods Choose two uncorrelated variables (in this example E T miss and lepton isolation) ET miss D (Signal) C N D = N A N B N C A B Lepton isolation Katharine Leney 38

39 e + µ Channel Z ττ Background Estimation Data-driven methods used to estimate contributions of main background processes. Multi-Jet: Shown to be negligible (using data-driven methods). EW, top, di-boson: Estimated from MC and checked in high-purity control regions. e/µ + τ had Channel Multi-Jet and W+jets: Use fake-factors measured in control regions to weight events that fail muon isolation (multi-jet) or tau ID (W+jets). Others: Estimated from MC τ had + τ had Channel Multi-Jet: Extract shape from fit to same-charge τ had events. Normalise in low M T sideband. Others: Estimated from MC Normalised event rate / GeV OC / SC Opposite Charge (OC) Same Charge (SC) ATLAS L dt = 4.6 fb s = 7 TeV tot miss m T ( had-vis, had-vis, E T ) [GeV] Katharine Leney 39-1

40 Z ττ Observables τhad-τhad Channel µ-τhad Channel Events / 50 GeV 4 (a) ATLAS Data L dt = 4.6 fb Multijet s = 7 TeV Z/ * W Others Z (1250) Events / 50 GeV 4 (b) ATLAS Data L dt = 4.6 fb Z/ * s = 7 TeV W +jets Multijet Z µµ tt Diboson Single top Z (00) tot miss m T ( had-vis, had-vis, E T ) [GeV] tot miss m T (µ, had-vis, E T ) [GeV] e + µ µ + τ had e + τ had τ had + τ had # Expected Background 3.6 ± ± ± ± 0.3 # Expected Signal 6.7 ± 0.3 (M Z = 750 GeV) 5.5 ± 0.7 (M Z = 00 GeV) 5.0 ± 0.5 (M Z = 00 GeV) 6.3 ± 1.1 (M Z = 1250 GeV) # Observed Katharine Leney 40

41 Z ττ Observables e-τhad Channel eµ Channel Events / 50 GeV 4 (c) ATLAS Data L dt = 4.6 fb Z/ * s = 7 TeV W /Z+jets Multijet Z ee tt Diboson Single top Z (00) Events / 50 GeV 4 ATLAS (d) Data L dt = 4.6 fb Z/ * s = 7 TeV Diboson Z µµ tt W+jets Z (750) tot miss m T (e, had-vis, E T ) [GeV] tot miss m T (e, µ, E T ) [GeV] Katharine Leney 41

42 Z ττ Limits (pp Z ) BR(Z ) [pb] (a) Observed limits Expected limits Z SSM Z SSM th. uncert. ATLAS -1 L dt = 4.6 fb s = 7 TeV arxiv: Published in PLB m Z e µ e had / µ had had had comb. [GeV] (pp Z ) BR(Z ) [pb] (b) ATLAS -1 L dt = 4.6 fb s = 7 TeV Channels combined Expected limit Expected ± 1 Expected ± 2 Observed limit Z SSM Z SSM th. uncert e + µ µ + τ had e + τ had τ had + τ had COMBINED Expected TeV Observed TeV m Z [GeV] Katharine Leney 42

43 Z ττ Systematics Uncertainty [%] Signal Background hh µh eh eµ hh µh eh eµ Stat. uncertainty Eff. andfakerate Energy scale and res Theory cross section Luminosity Data-driven methods Table 2: Uncertainties on the estimated signal and total background contributions in percent for each channel. The following signal masses, chosen to be close to the region where the limits are set, are used: 1250 GeV for τ had τ had (hh); 00 GeV for τ µ τ had (µh) and τ e τ had (eh); and 750 GeV for τ e τ µ (eµ). A dash denotes that the uncertainty is not applicable. The statistical uncertainty corresponds to the uncertainty due to limited sample size in the MC and control regions. Katharine Leney 43

44 Z τ had τ had Candidate Event Katharine Leney 44

45 LQ 3 Analysis NLO LQ pair-production cross-sections at s = 7 TeV Leptoquark Mass / GeV 7 TeV Cross- Section / pb x x x x -3 LQ 3 decay modes Decay Mode Allowed Charge bτ 2/3, 4/3 bν τ 1/3 tτ 1/3, 5/3 tν τ 2/3 Katharine Leney 45

46 M τ-closest jet 43% of reconstructed taus in selected ttbar events are fake. 62% of these fakes come from W qq decays. Quark jets are narrower than gluon induced ones and therefore have a higher chance to fake taus. Calculate the visible mass between the reconstructed hadronic tau and the nearest jet with p T > 40 GeV. Cut is % more efficient at cutting events with fake taus than real taus. Cutting on M τ-jet > 90 GeV has 38% ttbar efficiency. Signal efficiency is mass dependent: M LQ = 200 GeV 85% M LQ = 500 GeV Events / 7 GeV Katharine Leney ATLAS Preliminary Simulation Ldt = 4.7 fb s = 7 TeV Top -1 LQ(m=300 GeV) m( had-vis, jet) [GeV] 46

47 3rd Generation Leptoquarks One e (µ) p T > 25 (20) GeV One τ had, p T > 35 GeV Opposite-sign charge (lepton-tau) Missing E T > 20 GeV N Jets 2 (lead jet p T > 50 GeV) Leading or sub-leading jet is b-jet M (τ - closest-jet) > 90 GeV Angular requirements LQ 3 Top Main Backgrounds Top W+jets Z ττ Multi-Jet 47

48 LQ 3 Background Estimation Data-driven methods used to estimate contributions of main background processes. Muon Channel Multi-Jet: ABCD method using lepton-tau charge product and lepton isolation. EW & Top: Define background enriched control regions in data and fit to get normalisation factor. Shape from simulation. Events / 50 GeV ATLAS Preliminary Ldt = 4.7 fb s = 7 TeV Top CR -1 Data 2011 Top Di-Boson Z Z µµ W Multi-Jet Electron Channel Multi-Jet: Define QCD-rich control region in data and fit to get normalisation. Shape from data. EW & Top: Define background enriched control regions in data. Calculate normalisation factor based on number of simulation and data events S T [GeV] Katharine Leney 48

49 3rd Generation Leptoquarks Perform shape analysis of S T distribution to test for existence of leptoquarks. S T = p T (e/µ) + p T (τ had ) + p T (jet 1 ) + p T (jet 2 ) + missing E T Fit background distribution in high S T region. Katharine Leney 49

50 LQ 3 Observable (Muon Channel) Katharine Leney 50

51 LQ 3 Systematics Muon Channel Background LQ(m=500 GeV) Luminosity 3.9 Theory Scale factor 9.3 Trigger efficiency MMS Muon reconstruction efficiency < TES Tau ID efficiency JES (NP dependent) < 0.2 JER b-tagging efficiency Electron Channel Background LQ(m=500 GeV) Luminosity 3.9 Theory Scale factor +16/ 19 Trigger efficiency EES Electron reconstruction efficiency TES Tau ID efficiency JES (NP dependent) < 0.2 JER b-tagging efficiency Katharine Leney 51

52 Supersymmetry (SUSY) Katharine Leney 52

53 Electroweak SUSY Production Background Estimation Multi-jet and W+jets: Taus are predominantly fake. Use ABCD method using taus which pass loose tau ID, but fail tight ID vs. tight taus, and M T2 < 40 GeV vs. M T2 > 90 (0) GeV. Others: Mix of real and fake taus. Use tag-and-probe methods to correct for differences in tau ID and trigger efficiency between data and simulation for both contributions. Real taus: Z ττ µτ had ; Fake taus: W µν Main Backgrounds Multi-Jet W+jets Top-pair (+ W/Z) Single top Z/γ* + jets Diboson Katharine Leney 53

54 Electroweak SUSY Production Chargino-neutralino production with mass: s( χ ± 1, χ 0 1) = (250, 0) GeV; ± Chargino-chargino production with mass: ( χ ± 1, χ 0 1) = (150, 50) GeV. SM process SR OS m T2 SR OS m T2 -nobjet top 0.2 ± 0.5 ± ± 0.8 ± 1.2 Z+jets 0.28 ± 0.26 ± ± 0.3 ± 0.3 diboson 2.2 ± 0.5 ± ± 0.5 ± 0.9 multi-jet & W+jets 8.4 ± 2.6 ± ± 3 ± 3 SM total 11.0 ± 2.7 ± ± 4 ± 3 data 6 14 SUSY Ref. point ± ± 1.2 SUSY Ref. point ± ± 0.7 Exclude charginos (neutralinos) up to 350 (0) GeV. (ATL-CONF ) Katharine Leney 54

55 Lepton Flavour Violating Resonances Direct lepton backgrounds: Estimate from MC and validate in Mll < 200 GeV control region. Fake lepton backgrounds: Use same-sign control region to estimate jet-lepton fake rate. Search for resonance in ll invariant mass spectrum Main Backgrounds Top Z ττ Di-Boson Multi-Jet Katharine Leney 55

56 Standard Model Higgs ττ Searches Main background from Z ττ : Z-mass close to Higgs mass (125 GeV). Two real taus with similar p T etc. Produced at much higher rates than Higgs. Irreducible, so need excellent prediction of its contribution. Embedding technique used to estimate directly from data: Select clean sample of Z µµ events in data. Remove muon tracks and associated calorimeter deposits. Replace with simulated taus which have the same momentum as the original muon. Re-reconstruct the event (to get missing E T etc) Rest of the event (incl. pileup) comes from data. Main Backgrounds Z ττ Z ll W+jets Multi-Jet Top Di-Boson Other backgrounds estimated from data where possible (e.g. using OS-SS ratios). Katharine Leney 56

57 MSSM Charged Higgs τν Searches Main background from top-quark pair production : t Wb, W e/µ/τ + ν or to jets. Sub-contributions from: - True τ s. - Jets faking τ s. - Electrons faking τ s. - Mis-identified leptons. Use data to calculate fake rates for leptons and taus and apply to MC simulations. Use embedding method using tt-like µ +jets events (replace muons with taus) to estimate true tau contribution. Multi-jets background (τ+jets channel) estimated by defining multi-jets enriched control region in data and fitting to ETmiss distribution to get normalisation. 57

58 MSSM Neutral Higgs ττ Searches Methods to estimate backgrounds similar to SM search (embedding for Z ττ etc). Use missing mass calculator (MMC) to resolve neutrinos and better reconstruct invariant mass of τ-pair. Use M ττ MMC as observable. Katharine Leney 58

59 MSSM Neutral Higgs ττ Searches Set limits in m A -tan β plane. tan β = ratio of v.e.v s of Higgs doublets Exclude large region of MSSM phase space. ATLAS-CONF Katharine Leney 59

60 MSSM Charged Higgs τν Searches Set limits on branching fraction of top quark decay to bh +. B(t bh + ) < 5% (m H+ = 90 GeV) B(t bh + ) < 1% (m H+ = 160 GeV) ATLAS-CONF Exclude large region of MSSM phase space. 60

61 MSSM Charged Higgs τν Searches Main background from top-quark pair production : t Wb, W e/µ/τ + ν or to jets. Sub-contributions from: - True τ s. - Jets faking τ s. - Electrons faking τ s. - Mis-identified leptons. Use data to calculate fake rates for leptons and taus and apply to MC simulations. Use embedding method using tt-like µ +jets events (replace muons with taus) to estimate true tau contribution. Multi-jets background (τ+jets channel) estimated by defining multi-jets enriched control region in data and fitting to ETmiss distribution to get normalisation. 61