A Search For Technicolor with the ATLAS Detector

1. A Search For Technicolor with the ATLAS Detector Jeremy Love

2. Jeremy Love - ANL ATLAS Group Outline • Preamble • Title slide, Outline • Theory • Standard Model • Technicolor • LSTC • Search Strategy • Experimental Apparatus • ATLAS • Muon Spectrometer • Transition Chambers • Performance • Dimuon mass resolution • Experimental Techniques • Datasets • Data, MC • Selection criteria • Event display • Invariant Mass Spectrum • Systematics • Statistical Methods • Signal Eff Comparison • Results • 1-D LSTC Limit • Combined and single lepton • 2-D combined LSTC Limit • Conclusions

3. Jeremy Love - ANL ATLAS Group Motivation • Though investigated for many decades the Standard Model mechanism of Electroweak Symmetry Breaking has not yet been observed • The Standard Model provides an accurate description of all experimental data to date • To directly test the Standard Model at the TeV scale must produce interactions at that energy • In the past dilepton final states have uncovered unexpected physics, and led to early discoveries at new accelerators • Famous examples include the J/ψ, Υ, and Z

4. Jeremy Love - ANL ATLAS Group Standard Model • Describes the interactions of matter fermions and force carrying bosons • Fermions grouped in two categories with three generations • Leptons – Electroweak • Quarks – Electroweak and Quantum Chromo Dynamics • Bosons • Confirmed– γ, W±, Z, gluons • Unconfirmed – Higgs • Mechanism for Electroweak symmetry breaking (EWSB) has not been observed

5. Jeremy Love - ANL ATLAS Group Standard Model • In the Standard Model the coupling of W± and Z to the scalar Higgs give them masses which break Electroweak Symmetry • Fermions get masses through the same coupling to the Higgs field • Using experimental measurements to fit for the Higgs mass gives a preferred mass of 89 GeV • Ruled out by direct search • What is at 125 GeV?

6. Jeremy Love - ANL ATLAS Group Technicolor Theories • Technicolor models predict a new strong QCD like force responsible for EWSB • Techniquarks and technigluons form colorless technihadrons in analogy with the QCD spectrum • The lightest are the scalar πT0,± and the vector ωT0 and ρT0,± • The πT now give masses to the W and Z breaking EWS • With no Higgs boson the π of QCD breaks EWS • This correctly predicts the ratio of MW/MZ • Mass of MW and MZ low by 103 • Gives EWSB with no fundamental scalar • What if the scale of QCD was 1000 GeV instead of 1 GeV?

7. Jeremy Love - ANL ATLAS Group Technicolor Phenomenology • The lightest states can be produced at colliders with sufficient energy • Produced through quark anti-quark annihilation • The vector mesons decay into πT[γ,W±,Z], and fermion pairs such as μμ and ee • Dominant background Drell-Yan process • Technihadrons do not directly couple to SM fermions

8. Jeremy Love - ANL ATLAS Group Low-Scale Technicolor • LSTC is a baseline technicolor model which describes the phenomenology of the light technihadrons • Implemented in PYTHIA at Leading Order • Previously tested by D0, CDF, CMS • Techni-isospin symmetry is valid making ρT/ωT resonances degenerate in mass, they have an intrinsic width of order 1 GeV • Observed line shape is dominated by detector resolution • The ρT/ωT preferentially decay to multiple πT and πT plus SM gauge bosons if allowed • The difference of ρT/ωT to πT mass changes the available decay modes • m(πT) = m(ρT/ωT) – 90 GeV allows for decays to πT/[W,Z] • In LSTC nothing keeps m(πT) light so it is expected to be greater than half the m(ρT/ωT ) • For the benchmark parameter choice we take m(πT) = m(ρT/ωT ) – 100 GeV to allow for ρT/ωTto decay to πT/SM gauge boson

9. Jeremy Love - ANL ATLAS Group LSTC Cross Sections • Cross section times branching fraction of ρT/ωT to dimuons • Also shown is the cross section times branching fraction dependence of ρT/ωT on πT mass • In LSTC m(πT) is expected to be close to m(ρT/ωT)

10. Jeremy Love - ANL ATLAS Group Search Strategy • MC normalized to number of data events in the Z peak • Search for new resonance every 40 GeV above 130 GeV • Search for new narrow resonances in the dilepton invariant mass spectrum • Using the ee and μμ final state • Combine measurements for increased sensitivity • Look for bump in smoothly falling spectrum • If no resonance observed set limits on cross section and mass of ρT/ωT • Most interesting region m(ρT/ωT ) = 200 – 600 GeV • Similar to SSM Z’ search • Quantify differences

11. Jeremy Love - ANL ATLAS Group ATLAS • Tracking Detectors – reconstruct particle momentum by measuring deflection in a magnetic field • Muon Spetrometer – enclosed in toroidal field with ~4Tm bending power • Precision chambers measure curvature of track to determine pT • Fast chambers provide trigger and aid in reconstruction • Inner Tracker – in a 2T solenoid field • Orthogonal momentum measurement to MS • Close to beam pipe good vertex information • Track based isolation • Calorimeters – measure energy of showeringparticles • Measure e, γ, hadrons • Minimum ionizing particle

12. Jeremy Love - ANL ATLAS Group Muon Spectrometer • The ATLAS Muon Spectrometer uses four distinct detector technologies to provide the performance required • Designed to achieve a resolution of 10% on 1TeV pT muon track • Arranged in three stations each with a cylindrical barrel portion and two disk shaped end caps • Precision technologies Monitored Drift Tubes and Cathode Strip Chambers • Fast response chambers Restive Plate Chambers and Thin Gap Chambers

13. Jeremy Love - ANL ATLAS Group Transition Region MDTs • MDTs in the transition region are necessary to increase acceptance and measure point of inflection for tracks with low B dl or where three stations not otherwise crossed • Passing inside coils and then outside the return • MDT BEE chambers mounted on End Cap Toroid present unique challenges • Grounding and shielding issues, coherent noise, magnetic field dependent noise, long services, no optical alignment… • BEE commissioning able to reduce noise rate by ~103 and achieve high efficiency • Track based alignment hasimproved • End cap orientation have optical alignment and are stillbeing installed • Currently 36 out of 62

14. Jeremy Love - ANL ATLAS Group Dimuon Mass Resolution • Use resolution function to smear MC muons • Fitted smearing values from Z peak region, using alignment constraint • Barrel, Transition, End Cap • Dominant term is S2 the intrinsic curvature resolution • S0 is negligible • Smeared MC shows good agreement with data • Used in all ATLAS muon analyses • Impact on resolution estimated by shifting parameters • Impact on 1.5 TeV SSM Z’ sensitivity is 5%

15. Jeremy Love - ANL ATLAS Group Dataset and MC Samples • Data from 2011 periods B-I • Use standard E/γ and Muon Good Runs Lists • Electrons – 1.08 fb-1 • Muons – 1.21 fb-1 • Background Samples • Drell-Yan • Pythia with LO* PDFs • Diboson (WW, WZ, ZZ) • Herwig with LO* PDFs • W+jets • ALPGEN with LO* PDFs • Top • MC@NLO with NLO PDFs • Technicolor ρTC/ωTC Signal • Pythia, with LO* PDFs • K-factor corrected to NNLO • Drell-Yan both EW and QCD • Technicolor signal to NLO • Same as SSM Z’

16. Jeremy Love - ANL ATLAS Group Electron Channel • Event Selection • Medium Electron Trigger 20 GeV threshold • E/gamma Good Runs List • Primary Vertex with 3 tracks • Electron Object Selection • |η| < 2.47 & ET > 25 GeV • Medium electron • If expected 1 Blayer hit • Etcone 20 < 7 GeV • Final event selection • Total efficiency of 67% • Normalize between 70 GeV < Mee < 110 GeV • Search region Mee > 130 GeV

17. Jeremy Love - ANL ATLAS Group Dielectron Event Display mee = 993 GeV

18. Jeremy Love - ANL ATLAS Group Mee Spectrum

19. Jeremy Love - ANL ATLAS Group Muon Selection Criteria • Event selection • 22 GeV Muon trigger • Primary vertex with 3 tracks • Muon object selection • MS and ID combined track • Muon pT > 25 GeV • Hit requirements for ID • MS require hits in 3 stations with no transition or overlap hits • Impact parameter selection • Isolation • Opposite charge • Final Event selection • Total efficiency 42% • Normalize70 GeV < Mμμ < 110 GeV • Search Mμμ > 130 GeV

20. Jeremy Love - ANL ATLAS Group Dimuon Event Display mμμ = 959 GeV

21. Jeremy Love - ANL ATLAS Group Dimuon Invariant Mass Distribution

22. Jeremy Love - ANL ATLAS Group Signal Comparison • Compare generator level distributions to determine difference in acceptance • Show good level of agreement in regions of interest • For fully simulated signals • Fit the LSTC efficiency with the SSM Z’ efficiency function plus a constant • Fit gives good agreement and efficiencies are consistent within uncertainties

23. Jeremy Love - ANL ATLAS Group Systematic Uncertainties • Normalize sum of MC backgrounds to the Z region 70–110 GeV • Removes mass independent systematics such as luminosity • Dominant systematic uncertainty comes from the PDF • For SSM Z’ and ρT/ωT it was shown that differences in acceptance are within the 1.5% and 4.5% efficiency systematics • Same limits can be used for both models

24. Jeremy Love - ANL ATLAS Group Statistical Methods • Search invariant mass spectrum above 130 GeV using signal templates • SSM Z’ every 40 GeV • A scan of mass versus cross section is performed • The most probable signal is determined • By means of a likelihood • Then the consistency of this signal with the background only hypothesis is determined • Dimuon – 24% • Dielectron – 54% • Using a Bayesian approach 95% Confidence Level limits are set • Limits on signal cross section times branching ratio normalized to Z cross section • Systematics are taken as nuisance parameters and marginalized • To combine channels the likelihood function is multiplied bin by bin • Dielectron and Dimuon

25. Jeremy Love - ANL ATLAS Group Dielectron & Dimuon – 95% CL Limits • Excluded ranges of ρT/ωT mass at 95% CL from the dielectron and dimuon channels

26. Jeremy Love - ANL ATLAS Group Dilepton – 95% CL Limits • Excluded ranges of ρT/ωT mass at 95% CL from the dilepton combined channel

27. Jeremy Love - ANL ATLAS Group Combined 2D Exclusion • Interpreting the 1D 95% CL on ρT/ωT vs πT cross section plane • Simulated cross section at 833 points in plane with less than 25 GeV spacing • For each ρT/ωT mass determine the πT mass where the production cross section intersects the 95% CL excluded cross section using a linear interpolation • LSTC ρT/ωT masses are excluded between130 – 480 GeV • For m(πT) between 50 – 480 GeV

28. Jeremy Love - ANL ATLAS Group Status of ATLAS Exotics Searches This Analysis

29. Jeremy Love - ANL ATLAS Group Conclusions • Using over 1 fb-1 of 7 TeV proton proton collisions taken with the ATLAS detector we exclude m(ρT/ωT) between 130 – 480 GeV for m(πT) between 50 – 480 GeV at 95% CL • This represented the worlds best limit on the Low-scale technicolor model • For the parameter choice of m(πT) = m(ρT/ωT) – 100 GeV masses of the ρT/ωT are excluded below 470 GeV at 95% CL • In the dimuon channel masses of ρT/ωT are excluded below 280 GeV and between 304 and 376 GeV at 95% CL • In the dielectron channel masses of ρT/ωT are excluded below 323 GeV and between 386 and 445 GeV at 95% CL • Analysis of the full 2011 run with 5 fb-1 nearing completion • Updated muon object selection • Minimal Walking Technicolor as well as Low-scale Technicolor • Including technicolor axial vector in addition to the ρT/ωT • Dedicated technicolor templates in limit setting framework • Thank you.

30. Additional Material

31. Jeremy Love - ANL ATLAS Group Electron QCD Estimation • Reverse identification • Loose 2 γ trigger – 20 GeV • Require 2 loose electrons • Failing strip hit requirement • Lead electron isolated • Fit spectrum with dijet function: • Fit to data with function and sum of MC backgrounds • Good agreement • Cross checks • Isolation Fit Method • Fake Rate Method

32. Jeremy Love - ANL ATLAS Group Dielectron Event Yields Per Mass Bin

33. Jeremy Love - ANL ATLAS Group Dimuon Event Yields Per Mass Bin

34. Jeremy Love - ANL ATLAS Group Electron 2-D Posterior Probability

35. Jeremy Love - ANL ATLAS Group Muon 2-D Posterior Probability