Presentation on theme: "Dielectron Channel at CMS Cairo University November, 26 2006 Waled Emam Centre for Theoretical Physics at the British Univ. in Egypt."— Presentation transcript:
Dielectron Channel at CMS Cairo University November, 26 2006 Waled Emam Centre for Theoretical Physics at the British Univ. in Egypt
Outline Physics motivation Randall-Sundrum Gravitons Heavy Z’ Bosons Monte Carlo simulation
Extra Dimensions Scenarios Several models include extra dimensions have been introduced to solve hierarchy problem between M EW ~1TeV and M pl ~10 16 TeV Arkani-Hamed, Dvipoulos and Dvali (ADD) introduce large spatial extra dimensions observed 3D space is a 3D-brane embedded in a higher dimensional space extra spatial dimensions (the bulk) are orthogonal to 3D-brane Standard Model particles are stick to the 3D brane Graviton can travel in all dimensions Size of large extra dimension: M D = Fundamental Plank scale in 4+n dimensional space ~ TeV Kaluza-Klein gauge bosons fermions are localized on 3d brane gauge bosons propagate in additional small extra dimension compactified on a circle of radius R c ~TeV -1 ~10 -17 cm masses of these gauge boson modes are M c compactification scale, M c =1/R c
Extra Dimensions Scenarios (Cont.) The Randall-Sundrum(RS) model introduce one warped extra dimension 5D space-time with 2 branes of 4D: Metric: e -2kr|φ| η υμ dx υ dx μ + r c 2 dφ 2 Curvature: k (~M pl ) Compactification radius: r c New coordinate: φ (-π ≤ φ ≤π) Traditional 4D coordinates: x ν Gravity scale : Λ π =M Pl e -krπ kr c ≈11-12 => Λ π ~1 TeV => no hierarchy Only the graviton can propagate in 5D On the 4D branes, Kaluza-Klein excitations of the graviton can be observed.
Z’ Gauge Bosons Extra neutral heavy gauge bosons are predicted in models beyond Standard Model 4 models studied: Z SSM Sequential Standard Model Z psi, Z eta, Z exi arising in E6 & SO(10) GUT group They all differ by couplings to the SM fermions The interaction of the Z’ to SM fermions is Two mass eigenstates Z’’ is heavy and decouple from Z & Z’ Z’ light and couple to Z
Serach for ED & Z’ at CMS single photon+missing E T Search for ADD direct graviton emission Topology Single high p t photon in the central η region High missing pt back-to-back to the photon in the azimuthal plane with a similar p t distribution Backgrounds single lepton+missing E T Search for W’ Topology Single high p t muon Muon isolation: no additional track within a cone of certain size Backgrounds dilepton, dipthoton, dijet Search for Z’ (leptons, jets) RS model (leptons, photons, jets) TeV-1 model (electrons)
Dielectron Channel at CMS Look for heavy resonances of order few TeV decaying into an electron pair Observation of a resonance peak in the dielecton mass spectrum over background Such heavy resonance can be interpreted as: Randall-Sundrum graviton or heavy Z’ bosons Once a heavy resonance is discovered, its observables can be used to characterize the theoretical framework: angular distributions measurement forward-backward asymmetries
Signal and Background: Production of excited Gravitons according to the Randall-Sundrum (RS) model through qq and gg initial states Two parameters control the RS model: M 0 The mass of first Kaluza-Klein excitation C=K/M pl The coupling constant Universal decay modes: e + e -, mu + mu -, tau + tau - and gamma+gamma Background: Drell-Yan Z/gamma->l + l - Fake electron: Dijet, gamma-jet, e-jet. But negligible Monte Carlo Simulation Pythia is used to produce the signal and background processes CMSSW framework Model parameters: Mass (TeV): 0.75, 1.00, 1.25, 1.50, 1.75, 2.00, 2.50, 3.00, 3.50, 4.00 Coupling: 0.01, 0.02, 0.05, 0.1 Randall Sundrum Gravitons
Monte Carlo Simulation (Cont.) Pythia settings: maxEvents= 5x10 3 !# of events PMAS(347,1)= 750. !mass of G MSEL=0 !full user control MSUB(391) = 1 !ff -> G MSUB(392) = 1 !gg -> G MDCY(347,1) = 1 !allow G decay CKIN(13) = -2.5 !eta cut |eta|<2.5 PARP(50) = 0.054 !C model coupling constant MDME(4166,1)= 1 !e+ e- Results: Still in progress Cross-section (fb) & Mass (TeV C\M1.001.502.002.503.003.504.00 0.015.920.690.130.030.0090.0030.001 0.02242.790.530.130.0370.0120.004 0.0514817.63.360.820.2380.0760.025 0.105966913.33.320.9540.3050.102
Signal and Background: Production of Z’ boson according to the E6 models through qq initial state Two parameters control the Z’ production: M The mass of the Z’ The coupling constants to the SM quarks and leptons Universal decay modes: e + e -, mu + mu -, tau + tau - Background: Drell-Yan Z/gamma->l + l - Monte Carlo Simulation Pythia is used to produce the signal and background processes CMSSW framework Model Parameters: Mass (TeV): 1.00, 3.00, 5.00 Couplings: Heavy Z’ Bosons Z SSM ZψZψ ZηZη ZχZχ CVCV -0.080-0.783-0.479 CACA 0.505-0.7830.159
Monte Carlo Simulation (Cont.) Pythia settings: maxEvents= 5x10 3 !# of events PMAS(32,1)= 1000. !mass of G MSEL=0 !full user control MSUB(141) = 1 !ff -> gamma/Z/Z’ MSTP(44) = 3 !select the Z’ process, the Z or DY CKIN(1) = 400 !mass cutoff' CKIN(13) = -2.5 !eta cut |eta|<2.5 PARU(125) = -0.08 !C V coupling PARU(126) = -1 !C A coupling MDME(297,1)= 1 !e+ e- Results: Still in progress Cross-section (fb) & Mass (TeV) & Drell-Yan complete interference MassZ SSM ZψZψ ZηZη ZχZχ 1.00487279561249 3.002.521.682.871.42 5.000.0450.0340.0510.027
To Do List Fast simulation: PYTHIA – Detector - Data Event selection: E HCAL /E ECAL < 10%. Isolation cut: Track associated with E ECAL is required for neutral rejection Comparison with analysis from dimuon and diphoton channels
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