1. Dielectron Channel at CMS Cairo University November, 26 2006 Waled Emam Centre for Theoretical Physics at the British Univ. in Egypt

2. Outline Physics motivation  Randall-Sundrum Gravitons  Heavy Z’ Bosons Monte Carlo simulation

3. 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

4. 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.

5. 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

6. 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)

7. 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

8.  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

9.  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

10.  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

11.  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

12. 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