Dielectron Channel at CMS

1. CENTER FOR THEORETICAL PHYSICS THE BRITISH UNIVERSITY IN EGYPT 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 MEW~1TeV and Mpl~1016 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: • MD = 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 Rc~TeV-1~10-17 cm • masses of these gauge boson modes are • Mc compactification scale, Mc=1/Rc

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| ηυμdxυ dxμ + rc2dφ2 • Curvature: k (~Mpl) • Compactification radius: rc • New coordinate: φ (-π ≤ φ ≤π) • Traditional 4D coordinates: xν • Gravity scale : • Λπ=MPl e-krπ • krc≈11-12 => Λπ~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: • ZSSM Sequential Standard Model • Zpsi, Zeta, Zexi 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 ET • Search for ADD direct graviton emission • Topology • Single high pt photon in the central ηregion • High missing pt back-to-back to the photon in the azimuthal plane with a similar pt distribution • Backgrounds • single lepton+missing ET • Search for W’ • Topology • Single high pt 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. Randall Sundrum Gravitons • 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: • M0The mass of first Kaluza-Klein excitation • C=K/Mpl 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

9. Monte Carlo Simulation (Cont.) • Pythia settings: • maxEvents= 5x103 !# 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

10. Heavy Z’ Bosons • Signal and Background: • Production of Z’ boson according to the E6 models through qq initial state • Two parameters control the Z’ production: • MThe 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:

11. Monte Carlo Simulation (Cont.) • Pythia settings: • maxEvents= 5x103 !# 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 !CVcoupling • PARU(126) = -1 !CA coupling • MDME(297,1)= 1 !e+ e- • Results: • Still in progress • Cross-section (fb) & Mass (TeV) & Drell-Yan complete interference

12. To Do List • Fast simulation: • PYTHIA – Detector - Data • Event selection: • EHCAL/EECAL<10%. • Isolation cut: • Track associated with EECAL is required for neutral rejection • Comparison with analysis from dimuon and diphoton channels