A Search For Technicolor with the ATLAS Detector Jeremy Love

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 4/26/12Jeremy Love - ANL ATLAS Group2

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 4/26/12Jeremy Love - ANL ATLAS Group3

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 4/26/124Jeremy 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? 4/26/12Jeremy Love - ANL ATLAS Group5

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 π T 0,± and the vector ω T 0 and ρ T 0,±  The π T 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 M W /M Z  Mass of M W and M Z low by 10 3  Gives EWSB with no fundamental scalar  What if the scale of QCD was 1000 GeV instead of 1 GeV? 4/26/126Jeremy 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 π T [γ,W ±,Z], and fermion pairs such as μμ and ee  Dominant background Drell-Yan process  Technihadrons do not directly couple to SM fermions 4/26/12Jeremy Love - ANL ATLAS Group7

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 ρ T /ω T resonances degenerate in mass, they have an intrinsic width of order 1 GeV  Observed line shape is dominated by detector resolution  The ρ T /ω T preferentially decay to multiple π T and π T plus SM gauge bosons if allowed  The difference of ρ T /ω T to π T mass changes the available decay modes  m(π T ) = m(ρ T/ ω T ) – 90 GeV allows for decays to π T /[W,Z]  In LSTC nothing keeps m(π T ) light so it is expected to be greater than half the m(ρ T /ω T )  For the benchmark parameter choice we take m(π T ) = m(ρ T /ω T ) – 100 GeV to allow for ρ T /ω T to decay to π T /SM gauge boson 4/26/128Jeremy Love - ANL ATLAS Group

LSTC Cross Sections  Cross section times branching fraction of ρ T /ω T to dimuons  Also shown is the cross section times branching fraction dependence of ρ T /ω T on π T mass  In LSTC m(π T ) is expected to be close to m(ρ T /ω T ) Jeremy Love - ANL ATLAS Group94/26/12

 MC normalized to number of data events in the Z peak  Search for new resonance every 40 GeV above 130 GeV Search Strategy  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 ρ T/ ω T  Most interesting region m(ρ T /ω T ) = 200 – 600 GeV  Similar to SSM Z’ search  Quantify differences 4/26/12Jeremy Love - ANL ATLAS Group10

ATLAS 4/26/1211Jeremy Love - ANL ATLAS Group  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 p T  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 showering particles  Measure e, γ, hadrons  Minimum ionizing particle

 The ATLAS Muon Spectrometer uses four distinct detector technologies to provide the performance required  Designed to achieve a resolution of 10% on 1TeV p T 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 Muon Spectrometer 4/26/1212Jeremy 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 ~10 3 and achieve high efficiency  Track based alignment has improved  End cap orientation have optical alignment and are still being installed  Currently 36 out of 62 4/26/12Jeremy Love - ANL ATLAS Group13

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 S 2 the intrinsic curvature resolution  S 0 is negligible  Smeared MC shows good agreement with data  Used in all ATLAS muon analyses 4/26/1214Jeremy Love - ANL ATLAS Group  Impact on resolution estimated by shifting parameters  Impact on 1.5 TeV SSM Z’ sensitivity is 5%

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  with NLO PDFs  Technicolor ρ TC /ω TC Signal  Pythia, with LO* PDFs  K-factor corrected to NNLO  Drell-Yan both EW and QCD  Technicolor signal to NLO  Same as SSM Z’ 4/26/1215Jeremy 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| 25 GeV  Medium electron  If expected 1 Blayer hit  Etcone 20 < 7 GeV  Final event selection  Total efficiency of 67%  Normalize between 70 GeV < M ee < 110 GeV  Search region M ee > 130 GeV 4/26/1216Jeremy Love - ANL ATLAS Group

Dielectron Event Display 4/26/1217Jeremy Love - ANL ATLAS Group m ee = 993 GeV

M ee Spectrum 4/26/1218Jeremy 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 p T > 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%  Normalize 70 GeV < M μμ < 110 GeV  Search M μμ > 130 GeV 4/26/1219Jeremy Love - ANL ATLAS Group

Dimuon Event Display 4/26/1220Jeremy Love - ANL ATLAS Group m μμ = 959 GeV

Dimuon Invariant Mass Distribution 4/26/12Jeremy Love - ANL ATLAS Group21

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 4/26/12Jeremy Love - ANL ATLAS Group22

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 ρ T /ω T 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 4/26/1223Jeremy 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 4/26/12Jeremy Love - ANL ATLAS Group24

 Excluded ranges of ρ T /ω T mass at 95% CL from the dielectron and dimuon channels Dielectron & Dimuon – 95% CL Limits 4/26/1225Jeremy Love - ANL ATLAS Group

Dilepton – 95% CL Limits  Excluded ranges of ρ T /ω T mass at 95% CL from the dilepton combined channel 4/26/1226Jeremy Love - ANL ATLAS Group

Combined 2D Exclusion  Interpreting the 1D 95% CL on ρ T /ω T vs π T cross section plane  Simulated cross section at 833 points in plane with less than 25 GeV spacing  For each ρ T /ω T mass determine the π T mass where the production cross section intersects the 95% CL excluded cross section using a linear interpolation  LSTC ρ T /ω T masses are excluded between 130 – 480 GeV  For m(π T ) between 50 – 480 GeV 4/26/1227Jeremy Love - ANL ATLAS Group

Status of ATLAS Exotics Searches 4/26/12Jeremy Love - ANL ATLAS Group28 This Analysis

Conclusions  Using over 1 fb -1 of 7 TeV proton proton collisions taken with the ATLAS detector we exclude m(ρ T /ω T ) between 130 – 480 GeV for m(π T ) 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(π T ) = m(ρ T /ω T ) – 100 GeV masses of the ρ T /ω T are excluded below 470 GeV at 95% CL  In the dimuon channel masses of ρ T /ω T are excluded below 280 GeV and between 304 and 376 GeV at 95% CL  In the dielectron channel masses of ρ T /ω T 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 ρ T /ω T  Dedicated technicolor templates in limit setting framework  Thank you. 4/26/12Jeremy Love - ANL ATLAS Group29

Additional Material

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 4/26/1231Jeremy Love - ANL ATLAS Group

Dielectron Event Yields Per Mass Bin 4/26/12Jeremy Love - ANL ATLAS Group32

Dimuon Event Yields Per Mass Bin 4/26/12Jeremy Love - ANL ATLAS Group33

Electron 2-D Posterior Probability 4/26/12Jeremy Love - ANL ATLAS Group34

Muon 2-D Posterior Probability 4/26/12Jeremy Love - ANL ATLAS Group35