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Neutral Current Deep Inelastic Scattering in ZEUS

Neutral Current Deep Inelastic Scattering in ZEUS. Ricardo Gonçalo Imperial College. The HERA collider NC Deep Inelastic Scattering at HERA The ZEUS detector Neutral current cross section measurement Some ZEUS structure functions results Conclusions and outlook.

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Neutral Current Deep Inelastic Scattering in ZEUS

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  1. Neutral Current Deep Inelastic Scattering in ZEUS Ricardo Gonçalo Imperial College The HERA collider NC Deep Inelastic Scattering at HERA The ZEUS detector Neutral current cross section measurement Some ZEUS structure functions results Conclusions and outlook

  2. HERA and the ZEUS detector 1996-1997 running:  820 GeV protons  27.5 GeV positrons  Integrated luminosity 38.6 pb-1 1998-1999running:  920 GeV protons  27.5 GeV electrons  Integrated luminosity 16.6 pb-1 1999-2000running:  920 GeV protons  27.5 GeV positrons  Integrated luminosity 66.0 pb-1 Bunch crossings every 96ns Centre of mass energy: s = 318 GeV (98/00) 300 GeV (92/97) IoP HEPP Conference, Southampton, 3-5 April 2001

  3. Deep Inelastic Scattering at HERA Kinematic variables: Q² four momentum transfer x Bjorken scaling variable y inelasticity Only 2 independent variables: Q2 = x.y.s (s is the c.m. energy) e (k) e (k’) ,Z0 (Q2=-q2) X (P’) p (P) xF3parity violating FL negligible at high Q2 Leading order cross section: with: Our aim: to determine the proton structure through the measurement of the proton structure functions IoP HEPP Conference, Southampton, 3-5 April 2001

  4. HERA and the ZEUS detector Depleted uranium compensating calorimeter:  99.7% solid angle coverage  Timing resolution < 1ns (E>4.5 GeV)  Energy resolution (test beam) electrons protons Central Tracking Detector (CTD)  Angular acceptance 15o<<164o  r- resolution  230 m y Magnetic field of 1.43 T achieved with thin superconducting solenoid z x IoP HEPP Conference, Southampton, 3-5 April 2001

  5. Neutral current cross section measurement • Offline selection cuts: • Find the electron • Vertex within: -50 < Zvtx < 50 cm • Scattered electron cuts: • Electron energy: Ee > 10 GeV • Electron isolation • Within CTD acceptance: •  Electron track momentum > 5 GeV •  Track and cluster matching • Forward electrons: PT,e > 30 GeV • Total transverse momentum should be small: PT,tot < 4ET,tot • Background cut: 38 <  < 65 GeV, • with: IoP HEPP Conference, Southampton, 3-5 April 2001

  6. Neutral current cross section measurement Low Q2:  exchange  similar cross sections for e-p and e+p High Q2:  and Z0 exchange plus interference term  cross sections greater for e-p (d/dQ2 xF3) than for e+p (d/dQ2 -xF3) IoP HEPP Conference, Southampton, 3-5 April 2001

  7. Why measure F2?  F2 sensitive to valence and sea quarks  All flavors contribute to F2  Gluon density can be extracted from d F2 /dlnQ2 IoP HEPP Conference, Southampton, 3-5 April 2001

  8. How to measure F2em ? • Start by measuring Neutral Current reduced cross section • Cross section has contributions from  and Z0 exchange and their interference(at high Q2, reduced cross section falls for e+p data and rises for e-p data) • Apply corrections to get F2from R Reduced cross section: IoP HEPP Conference, Southampton, 3-5 April 2001

  9. Why measure xF3? xF3 sensitive to valence quarks only Sea quarks created in pairs => (quark-antiquark)=0 And How? IoP HEPP Conference, Southampton, 3-5 April 2001

  10. First xF3 measurement from ZEUS • First direct look at valence quarks at high Q2 • Yellow band is the calculated FLmultiplied by 10 • Measurement used e+p data from 1996-97 (c.m. energy of 300 GeV) and e-p data from 1998-99 (c.m. energy of 318 GeV) => corrections necessary IoP HEPP Conference, Southampton, 3-5 April 2001

  11. Conclusions and outlook  Present Neutral Current results from ZEUS are systematics limited up to Q2 800 GeVbut there is room for improvement for higher Q2 using the currently available data.  Neutral current cross sections will be measured at high Q2using data from 1998/99 (e-p) and 1999/00 (e+p)with s = 318 GeV.  Measurement of F2 and xF3 can be made with available data. Outlook • Lepton beam polarization after the 2000/2001 shutdown and high luminosity expected (1 fb-1 until 2006). • Improved tracking (new vertex detector and forward tracking) • This will allow: •  Setting limits for the mass of W-R, W+L, using Charged Current measurements, •  The direct measurement of weak couplings to quarks u and d. •  Possibility of lower systematic errors for lepton tagging in fwd region. •  Charm tagging. IoP HEPP Conference, Southampton, 3-5 April 2001

  12. My neutral current cross section measurement • Only d/dQ2 so far • Statistical errors only • Analysis of 1998/99 e-p data and 1999/00 e+p data going in parallel • Still a lot of work to be done... IoP HEPP Conference, Southampton, 3-5 April 2001

  13. Luminosity upgrade and polarisation Charged Current: cross section linear on polarisation. Limits or measurement of mass of W-R, W+L Neutral current: 4 different x-sections will allow measurement of couplings au, vu, ad, and vd (HERA sensitive to u & d; LEP sensitive to c & b) IoP HEPP Conference, Southampton, 3-5 April 2001

  14. xF3 from H1 Luminosity upgrade and polarisation With both lepton flavors and polarizations  4 different cross sections xF3 measurement from H1: different binning IoP HEPP Conference, Southampton, 3-5 April 2001

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