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Measurement of the Hadronic Cross Section at DA F NE with KLOE

Measurement of the Hadronic Cross Section at DA F NE with KLOE. 1. 4. 2004 La Thuile, Vall é e d’Aoste XXXIX th Rencontres de Moriond - QCD. Achim G. Denig for the KLOE Collaboration. Outline: Motivation & Radiative Return Analysis s hadr Results & Outlook.

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Measurement of the Hadronic Cross Section at DA F NE with KLOE

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  1. Measurement of the Hadronic Cross Section at DAFNE with KLOE 1. 4. 2004 La Thuile, Vallée d’Aoste XXXIXth Rencontres de Moriond - QCD Achim G. Denig for the KLOE Collaboration

  2. Outline: • Motivation & Radiative Return • Analysis shadr • Results & Outlook Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  3. HadronicVacuum Polarization 2nd largest contrib., cannot be calculated in pQCD Error of hadronic contribution is dominating total error ! Muon - Anomaly • Motivation: Determination of Hadronic Vacuum Polarization = High Precision Test of the Standard Model: • Anomalous magnetic moment of the muon am=(g-2)m • Running fine structure constant at Z0-mass aQED(MZ) Dirac-Theory: (g - 2 ) = 0 Quantum corrections: (g - 2 )  0due to corrections of: - electromagnetic interaction - weak interaction - strong interaction (and maybe NEW PHYSICS ???) Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  4. H 1 / s2 makes low energy contributions especially important: in the range < 1 GeV contributes to 70% ! Hadronic Cross Section Hadronic contribution to amcan be estimated by means of a dispersion integral: - K(s) = analytic kernel-function - above sufficiently high energy value, typically 2…5 GeV, use pQCD Input: a) hadronic electron-positron cross section data b) hadronic t- decays, which can be used with the help of the CVC-theorem and an isospin rotation (plus isospin breaking corrections) Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  5. Muon-Anomaly: Theory vs. Experiment ComparisonExperimental ValuewithTheory - Prediction New cross section data have recently lowered theory error: a) CMD-2 (Novosibirsk/VEPP-2M) p+ p- channel with 0.6% precision < 1 GeV b) t-Data from ALEPH /OPAL/CLEO Theoretical values taken from M. Davier, S. Eidelman, A. Höcker, Z. Zhang hep-ex/0308213 THEORY ’20/‘03 e+ e- - Data: 2.7s - Deviation t – Data: 1.4s - Deviation Experiment BNL-E821 Values for m+(2002) and m-(2004) in agreement with each other. Precision:0.5ppm Experiment ’20/‘04 am- 11 659 000 ∙ 10-10 Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  6. ISR ds(e+ e- p + p- g) dMpp MC- Generator PHOKHARA = NLO J. Kühn, H. Czyż, G. Rodrigo Radiator-Function H(s) H(s) Radiative Return • Standard methodfor cross section measurement is the energy scan, i.e. the • systematic variation of the c.m.s.-energy of the accelerator • DAFNE is a f - factory and therefore designed for a fixed c.m.s.-energy: • s = mf = 1.019 MeV; a variation of the energy is not foreseen in near future Complementary approach: Take events with Initial State Radiation (ISR) “Radiative Return” to r-resonance: e+ e- r + g  p+ p- + g r0 Cross section as a function of the 2-Pion invariant mass s’=Mpp2 s’ Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  7. Background Luminosity Signal Acceptance Selections-Efficiency Analysis p+p-g • Final state e+e- p+ p- grelatively easy signature, however cross • section measurement on percent level is a challenging task (normali- • zation, efficiencies, background) • KLOE Detector designed for CP – violation, we are having a high • resolution tracking chamber ideal for the measurement of Mpp ! Analysis- Items: Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  8. Selection p+p-g Drift Chamber EM Calorimeter Pion tracks at large angles 50o < qp< 130o Photons at small angles qg< 15oandqg > 165o are shadowed by quadrupoles near the I.P. 500<  < 1300  NO PHOTON TAGGING  > 1650  < 150  • • High statistics for ISR events • Reduced background contamination • Low relative contribution of FSR Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  9. Background p+p-g MTRK (MeV) • Rad. Bhabhase+e- e+e-g • Pion-Electron-Separation by means of a • Particle-ID algorithm using EmC-cluster- • signature of tracks and TOF p+p-p0 p+p-gg tail signal region • f p+ p- p0 • e+e- m+ m- g Kinematic Separation: „Trackmass“ mp Mpp – dependent MTRK-Cut mm m+m-g + e+e-g • Residual backgroundafter cuts Fit MC-Spectrum for signal und background with free normalization parameters mr2 Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  10. p>400MeV 55°<Q<125° Acoll.<9° MC Data Bhabhas Bhabhas Bhabhas Cut Cut Cut Polar Angle [°] Momentum [MeV] Acoll. [°] Luminosity L=NBhabhas /seffMC Experimental precision: Theoryprecision (radiative corrections): • Large Angle Bhabha Events > 55º • Excellent agreement Data – MC • Background-”free” ( 0.5% p+p- ) • Experimental uncertainty 0.3% • BABAYAGA event generator (Pavia group) • systematic comparison among other generators • (Berends, KKMC, VEPP-2M), max. D=0.7% • Theoretical uncertainty 0.5% (BABAYAGA) Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  11. Analysis s(e+e- p+p-g) • Efficiencies: • - Trigger & Cosmic veto • Tracking, Vertex • p- e- separation • Reconstruction filter • Trackmass-cut • Unfolding resolution • Acceptance Statistics:141pb-1 of 2001-Data 1.5 Million Events High Statistics! High Resolution! Errors: 1.0% • Background: • e+ e- e+ e-g • e+ e- m+ m- g • fp+ p- po 0.5% Luminosity: Bhabhas at large angles > 55°, seff = 430 nb, r-w Interference 0.3%exp 0.5%theo Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  12. Extraction s(e+e- p+p-) Radiator-Function (ISR): s(e+e- p+p-) • ISR-Process calculated at NLO-level • Generator PHOKHARA(Kühn et.al) • Comparison withKKMC(Jadach et.al.) • Precision: 0.5% Radiative Corrections: i) Bare Cross Section divide by Vacuum Polarisation ii) FSR - Corrections Cross section spp must be incl. for FSR Vacuum Polarization Cross Section Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  13. To be included ! Pion Formfactor after FSR corrections Suppressed by Acceptance cuts line = approach 1 + = approach 2 ratio = approach 1 / approach 2 Both methods in excellent agreement! For the error on the model dependence of FSR (scalar QED) we take 0.5% FSR Corrections • 2 approaches for FSR corrections: • Approach 1: “exclusive NLO-FSR“ • - Correcting measured sppg for FSR • - Use MC with pure ISR in analysis • - Add FSR-contrib. to spp (ca. 0.8%) by hand • Approach 2: “inclusive NLO-FSR“ • - Correct for „unshifting“, i.e. s‘ Mpp • - Use MC with ISR + FSR in analysis Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  14. Muon Anomaly • We have evaluated the dispersions integrals for the 2-Pion-Channel in the energy range 0.35 <Mpp2<0.95 GeV2 ampp = (389.2  0.8stat  4.7syst  3.7theo) 10-10 • Comparison with CMD-2 in energy range 0.37 <Mpp2<0.93 GeV2 (376.5  0.8stat  5.4syst+theo) 10-10 KLOE* (378.6  2.7stat  2.3syst+theo) 10-10 CMD2 * Error on model dependence FSR and VP not included! • Discrepancy of ca. 10% between e+e- - Dataund t – Data (ALEPH) for Mpp2 > 0.6 GeV2 KLOE – data confirms discrepancy with respect to t – data ! Explanation: m(r0)m(r) ??? Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  15. |Fp|2 — KLOE 40  CMD2 30 20 10 0 0 0.5 0.7 0.9 Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  16. Summary • We have proven the feasibility to use the Radiative Return to perform a high-precision measurement of the hadronic cross section at the f-factory DAFNE • Statistical Error is negligible • In the energy range Mpp2 > 0.6 GeV2we do reproduce the large deviation seen by t-data with respect to e+e- • Our evaluation of the hadronic contribution of the muon anomaly confirms the deviation btw. Theory and Experiment of about 3 sigma A draft for a paper is under collaboration-wide review! and in this sense data has still to be considered as PRELIMINARY Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  17. Asymmetry [%] 20 • Data • MC 10 0 -10 K L O E P R E L I M I N A R Y -20 50 70 90 110 130 Polar Angle [°] Outlook • Study events at large photon angles to access lower M2 region Photon tagging will be possible in this case • Use mmg events for normalization advantages from experimental and theoretical point of view • CheckFSR parametrization (scalar QED) by testing the Charge Asymmetry Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

  18. Work supported by: Emmy – Noether – Programm Achim G. Denig Radiative Return @ DAFNE Moriond -QCD 2004

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