We present a feasibility study of $\rho_{T}$ and $a_{T}$ production using the $\rho_T/a_{T} \rightarrow WZ \rightarrow lll \nu$ final state. Such a signature is found in low scale walking Technicolor models. We perform this study using CMS fast simulation samples and conclude that it is possible to observe $\rho_T$ with masses up to 500~GeV in data samples ranging from 2-10~fb$^{-1}$ of integrated luminosity. We also find that the $a_T \rightarrow WZ$ process may be seen under the assumptions that $M_{a_T} \simeq 1.1 M_{\rho_T}$ (for $M_{\rho_T}=500$ GeV) and that the MET resolution from data will be in reasonable agreement with the simulation

Bose, T

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Available on CMS information server CMS CR-2008/004The Compact Muon Solenoid ExperimentMailing address: CMS CERN, CH-1211 GENEVA 23, SwitzerlandConference Report14 February 2008A search for Technicolor in the tri-lepton finalstateT. BoseAbstractWe present a feasibility study of ρT and aT production using the ρT /aT → WZ → lllν final state.Such a signature is found in low scale walking Technicolor models. We perform this study using CMSfast simulation samples and conclude that it is possible to observe ρT with masses up to 500 GeVin data samples ranging from 2-10 fb−1 of integrated luminosity. We also find that the aT → WZprocess may be seen under the assumptions that MaT ' 1.1MρT (for MρT = 500 GeV) and that theMET resolution from data will be in reasonable agreement with the simulation.Presented at Physics at TeV Colliders,11-29 June, 2007,Les Houches,France1 IntroductionTechnicolor (TC) is a strongly interacting gauge theory which allows for the dynamical breakdown of electroweaksymmetry [1, 2]. Recent versions with a slowly-running or walking gauge coupling enable extended technicolor(ETC) to generate realistic masses for fermions and techni-pions and also to evade the unwanted avor changingneutral current interactions [3]. An additional consequence is that the walking tends to make the technicolor scalelower than previously expected, and the spectrum of this low-scale technicolor (LSTC) [4] thereby becomes moreaccessible at the LHC center-of-mass energy,√s = 14 TeV. The lightest ρT and ωT are expected to have massesbelow≈ 500 GeV, and their decays channels (for eg. ρT → WZ) have distinctive signatures with narrow resonantpeaks.A long standing problem with walking technicolor has been a very large value for the precision-electroweak S-parameter [5]. Recent models incorporate the idea that the S-parameter can be naturally suppressed if the lightestρT and its axial-vector partner, aT , are nearly degenerate. The phenomenology of these techni-hadrons is describedin the Technicolor Straw-Man Model (TCSM) [6].This study was initiated during the Les Houches 2007 workshop and considers the tri-lepton nal state resultingfrom the ρT and aT decay via a WZ pair (ρT /aT → WZ → lllν). The major sources of background are WZdi-boson production, ZZ di-boson production, tt¯, and Z+jet production.2 Event Samples and SimulationFor this study we concentrated on three TCSM mass points not excluded by other experiments and that covera range accessible with early LHC data ( <≈ 10 fb−1 of integrated luminosity). These masses along with thesignal cross sections are listed in Table 1. These signal samples were generated using an updated version ofPYTHIA [7]. This updated version includes both the vector and axial-vector resonances, ρT and aT , respectively,with MaT = 1.1MρT . This helps to naturally suppress the electroweak parameter S since the rst set of vectorresonances (ρT ) and the rst set of axial-vector resonances (aT ) are nearly degenerate. In addition, the Technicolorparameters, MV (for techni-vectors) and MA (for aT ) were set to be equal to MρT and MωT . Furthermore, newdecay modes for aT were incorporated in this version of PYTHIA in order to fully model its behavior. Thisimplementation of aT has been studied for the rst time in a CMS analysis - an older analysis [8] used the previousmodeling of TCSM to study the ρT → WZ channel i.e. aT → WZ was not included1).Parameter Set mρT = mωT (GeV) maT (GeV ) mpiT (GeV) MV = MA (GeV) σ× BR (fb)A 300 330 175 300 112B 400 440 225 400 37C 500 550 275 500 16Table 1: Parameter sets for the signal samples used in the study. BR refers to the branching ratios of the W and Zto electrons and muons. Cross-sections quoted are computed by PYTHIA to leading-order(LO).Figure 1 shows the invariant mass of the WZ pair for parameter set C (from Table 1). The larger resonant peakcomes from the ρT while the smaller peak to its right denotes the aT resonance. The generator level sampleswere then processed using CMS Fast Simulation2). Background samples were also generated using PYTHIA andleading-order (LO) cross-sections were used for normalization.3 Event SelectionThe nal state signature consists of three charged leptons and a neutrino. The following selection criteria wereimposed in order to enhance the signal to background ratio:• Three isolated charged leptons (electrons or muons), with pT > 15 GeV and |η| < 2.5. Tracker-basedisolation is used for both electrons and muons with the isolation for electrons being dened as:1) The current analysis also employs somewhat different selection criteria in order to preserve the ability to study the decayangular distributions that could be used to differentiate between the vector and axial-vector resonances.2) This analysis uses release CMSSW 1 6 7 and the following tags: V00-07-09 FastSimulation/Configuration; V03-03-03FastSimulation/EventProducer2WZ invariant mass (GeV)300 400 500 600 700010002000300040005000Figure 1: Generator-level WZ invariant mass distribution for Parameter Set C. The resonance at 500 GeV corre-sponds to the degenerate ρT while the smaller resonance to its right corresponds to aT .∑track(ptrackTpeleT)2 < 0.02where all tracks with ptrackT > 1.5 GeV, within an η−φ annular isolation cone centered on the reconstructedelectron, are summed, and the cone has limits, 0.02 < ∆R < 0.6 where ∆R =√(∆η)2 + (∆φ)2 andpeleT is the momentum of the reconstructed electron. For muon isolation the sum of pT of tracks in a cone ofradius ∆R = 0.3 is required to be less than 3.0.• Missing transverse energy, MET > 40 GeV.• Leptonic HT, dened as the scalar sum of the transverse momentum of the three leptons, is required to begreater than 150 GeV.While the requirement of three high pT leptons reduces the contribution from background processes in general, therequirement of large missing transverse energy helps to reduce the Z+jet and ZZ background considerably. TheMET distribution for signal and background events is shown in Fig. 2. The other kinematic variable, leptonic HT,also serves as a good discriminating variable for distinguishing signal from background and is shown in Fig. 3.MET (GeV)0 100 200 30000.050.10.150.20.25:500Tρ:400Tρ:300TρttWZZZZ+jetsFigure 2: MET distributions for signal and background samples. The distributions are normalized to unit area.3Leptonic HT (GeV)0 100 200 300 400 50000.050.10.15 :500Tρ:400Tρ:300TρttWZZZZ+jetsFigure 3: Leptonic HT distributions for signal and background samples. The distributions are normalized to unitarea.4 Event ReconstructionAfter the above selection, the WZ invariant mass is reconstructed using the following procedure:• Reconstructing the Z boson:– If two of the charged leptons have the same avor, then they are used to reconstruct the Z boson. If allthree have the same avor, the lepton pair with an invariant mass closest to the Z boson mass (within12.5 GeV) is assigned to the Z candidate. In either case, the third lepton in the event is assigned to theW candidate. (In the case of more than three leptons, the highest pT lepton not assigned to the Z bosonis used to reconstruct the W candidate.)– The transverse momentum of the reconstructed Z boson is required to be greater than 65 GeV.• Reconstructing the W boson:– The unassigned (third) lepton and neutrino are assumed to have come from the W boson. The Winvariant mass constraint is used along with the MET vector to reconstruct the nal state.– The transverse momentum of the reconstructed W boson is required to be greater than 65 GeV.The Z pT and W pT distributions are shown in Figs. 4 and 5. The reconstructed WZ invariant mass plot correspond-ing to the generator-level parameter set (in Fig. 1) is shown in Fig. 6. The ρT and aT resonances are no longer asdegenerate as in the generator level case owing to MET resolution effects incorporated in the detector simulation.However, both ρT and aT can still be seen as shown by the red and blue curves, respectively, in Fig. 6. The nalevent selection efciencies for the signal samples are 0.20, 0.29 and 0.34 for parameter sets corresponding to ρTmasses 300 GeV, 400 GeV and 500 GeV, respectively.5 Discovery PotentialFig. 7 shows the WZ invariant mass distributions for both signal (Parameter Set C) and background events afterevent selection and reconstruction. The distributions are stacked on top of each other and a clear signal peak isvisible around 500 GeV. A simple event counting technique based on S/√(S + B) was then used to estimate thesignal and background yield under the mass peak. A mass window of 1.4 σ was chosen around the ρT mass peakand the discovery potential was evaluated for different luminosity settings. The results are shown in Fig. 8. Thenumber of signal and background events used in the computation are listed in Table 2. No systematic uncertaintieshave been applied yet. The plot indicates that for the mass range in consideration, a discovery could be made with2-10 fb−1 of integrated luminosity.4 (GeV)TZ p0 100 200 300 400 50000.050.10.150.2:500Tρ:400Tρ:300TρttWZZZZ+jetsFigure 4: Z pT distributions for signal and background samples. The distributions are normalized to unit area. (GeV)TW p0 100 200 300 400 50000.050.10.150.2:500Tρ:400Tρ:300TρttWZZZZ+jetsFigure 5: W pT distributions for signal and background samples. The distributions are normalized to unit area.2 Mass(WZ) GeV/c0 100 200 300 400 500 600 700 800 900 1000)2 Events / (4000.0 MeV/c020406080100120140160180200220240Figure 6: The reconstructed WZ invariant mass distribution for Parameter Set C. The resonance corresponds to theρT and aT combination. The distribution is tted to show the ρT component in red and the aT component in bluewhile the green curve corresponds to the total. Background contributions are not shown in this plot.5Parameter Set mρT Signal Events Background Events Lumi (fb)A 300 36 15 2.4B 400 36 16 4.9C 500 34 12 9.5Table 2: Total number of signal and background events in the signal mass window for the three parameter sets.These numbers correspond to the 5σ discovery points. The column on the extreme right denotes the integratedluminosity needed for discovery.WZ Invariant Mass (GeV)0 200 400 600 800 1000Events/5 GeV0246Events/5 GeV T, aTρttWZZZZ+jetsFigure 7: Stacked WZ invariant mass distributions for signal and background samples. The distributions arenormalized to an integrated luminosity of 10 fb−1.6 ConclusionWe have performed a feasibility study to search for technihadrons - ρT and aT - using nal state WZ invariantmass distributions. We nd that is is possible to observe ρT up to masses of about 500 GeV during the early phaseof LHC data-taking using between 2-10 fb−1 of integrated luminosity. Additionally we nd that the aT → WZprocess may also be seen under the assumption that MaT ' 1.1MρT and with MρT = 500 GeV. This also assumesthat the MET resolution from data will be in reasonable agreement with the current simulation.We should note that this is a feasibility study using fast simulation samples and hence should be considered a workin progress. More detailed studies using samples with pileup are underway. Additional analysis improvements arealso planned: full detector simulations of the signal and background samples, better lepton identication and fakeremoval. These should further enhance the sensitivity. This updated version of the analysis will also include adetailed study of systematic uncertainties.7 AcknowledgmentWe thank K. Lane, A. Martin and K. Black for useful discussions and collaboration on this work during the LesHouches workshop. We also thank Albert De Roeck, Sarah Eno, and Meenakshi Narain for helpful comments andsuggestions.References[1] S.Weinberg, Phys. Rev.D19 (1979) 1277-1280.[2] L.Susskind, Phys. Rev. D20 (1979) 2619-2625.[3] B. Holdom, Phys.Rev. D24 (1981) 1441.[4] E.Eichten and K.D.Lane, Phys.Lett. B388 (1996) 803-807.6 mass (GeV)Tρ300 350 400 450 500)-1Integrated Luminosity (fb246810CMS PreliminaryFigure 8: Integrated luminosity needed to reach 5σ signicance as a function of ρT mass.[5] M.E.Peskin and T.Takeuchi, Phys.Rev.Lett. 65 (1990) 964-967.[6] K.Lane and S.Mrenna, Phys. Rev. D67 (2003) 115011.[7] http://projects.hepforge.org/pythia6/[8] P. Kreuzer, Search for Technicolor at CMS in the ρTc → W + Z Channel, CMS Note 2006/135.7

A search for Technicolor in the tri-lepton final state

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