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Debora Leone Institut für Experimetelle Kernphysik Universität Karlsruhe

Debora Leone Institut für Experimetelle Kernphysik Universität Karlsruhe on behalf of KLOE collaboration. Tau04 Nara 14-17/09/2004. Measurement of the hadronic cross section at KLOE. a m theory vs. experiment. e + e - and t data differ for p + p -

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Debora Leone Institut für Experimetelle Kernphysik Universität Karlsruhe

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  1. Debora Leone Institut für Experimetelle Kernphysik Universität Karlsruhe on behalf of KLOE collaboration Tau04 Nara 14-17/09/2004 Measurement of the hadronic cross section at KLOE

  2. am theory vs. experiment e+e- and t data differ for p+p- channel in a specific energy window above 0.6 GeV2 (above the r peak) Dispersion integral for hadronic contribution to am evaluated for: a) CMD-2 (Novosibirsk/VEPP-2M) p+ p- channel with 0.6% precision < 1 GeV b) t-Data from ALEPH /OPAL/CLEO THEORY ‘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 ’02/‘04 am-11659000(10-10) Status up to July ’04 Hadronic cross section @ KLOE D. Leone

  3. The Radiative Return Mhadr ds(e+ e- hadrons + g) dMhadrons s(e+ e- hadrons) H(Mhadr ) The standard method to measure s(e+e- hadrons) is the energy scan, i.e. the syst. variation of c.m. energy of the machine. Since at DAFNE the collision energy is fixed, we use a complementary approach: looking for e+e- p+p-g events, where the photon is emitted in the initial state (ISR), we have a continuous variation of sp, the invariant mass of the hadronic system 4mp2< sp < mf2 Precise knowledge of ISR process Radiator function H(Q2,g,M2F) MC generator: Phokhara H. Czyz, A. Grzelinska, J.H. Kühn, G. Rodrigo Hadronic cross section @ KLOE D. Leone

  4. p+p-g selection e- e+ EM calorimeter Pion Tracks at large angles 50o < qp< 130o Drift chamber Photons at small angles qg< 15oandqg> 165o are masked by quadrupoles near the I.P. (no photon tagging) • High statistics for ISR Photons • Low relative contribution of FSR • Reduced background contamination Hadronic cross section @ KLOE D. Leone

  5. p+p-g cross section 141 pb-1 50000 40000 30000 dN(p+p-g)/dMpp2 [nb-1/GeV2] 20000 10000 Mpp2 [GeV2] No acceptance at threshold region dN(p+p-g)/dMpp2 after acceptance cuts Event analysis: Efficiencies and background Normalize to Luminosity Differential cross section d(p+p-g)/dMpp2 Divide by Radiator Function Radiative Corrections Cross section (e+e-  p+p-) Hadronic cross section @ KLOE D. Leone

  6. Background Rejection 1/2 Step 1: e+e-g are separated from p+p-g by means of a Likelihood method (signature of EmC-clusters and TOF of particle tracks) p+p-p0 Mtrk [MeV] p+p-gg tail signal region mp m+m-g + e+e-g mm Step 2: fp+p-p0 and e+e-m+m-g rejected by means “Trackmass ” Mpp2 [GeV2] mr2 Hadronic cross section @ KLOE D. Leone

  7. Background Rejection 2/2 Step 3: fit data trackmass distributions with MC ones (signal + background) with free normalization parameters Mpp2 [0.32,0.37] GeV2 Mtrk [MeV] Mtrk [MeV] Hadronic cross section @ KLOE D. Leone

  8. data • MC 55o 125o Polar Angle [°] Luminosity Measurement KLOE uses large angle Bhabha events for the luminosity evaluation: • Theory precision (radiative corr.) • BABAYAGA event generator • (Pavia group) • syst. comparison among other • generators (Bhagenf, BHWIDE, • VEPP-2M ); max. D = 0.7 % • uncertainty 0.5% =BABAYAGA error N = events with 55<<125 Experimental precision Excellent agreement data-MC Hadronic cross section @ KLOE D. Leone

  9. Analysis (e+e-p+p-g) 140 pb-1 of 2001 data 1.5 millions events ds(e+e-p+p-g)/dMpp2 [nb/GeV2] r-w Interference Mpp2 [GeV2] • EFFICIENCIES: • Trigger + Cosmic Veto • Tracking + Vertexing • p/e separation • Reconstruction filter • Trackmass cut • Unfolding procedure • Acceptance • BACKGROUND • e+e- e+e-g • e+e- m+m-g • f  p+p-p0 • LUMINOSITY • Bhabha at large angles 0.9 % 0.3 % 0.6 % Hadronic cross section @ KLOE D. Leone

  10. FSR Contribution Two kinds of FSR There is no initial state radiation and the e+ and the e- collide at the energy M  the virtual ghas Q2 =M2  Background Simultaneous presence of a initial and final photon The cross section e+e-p+p- has to be inclusive with respect to NLO FSR events: Hadronic cross section @ KLOE D. Leone

  11. FSR Treatment p+ } e+ sp s e- p- Invariant mass of the system p+p-, sp invariant mass of the virtual photon s Correction for unshifting Radiator H “FSRInclusive” approach N(e+e- p+ p- gISRgFSR) add back missing FSR Event analysis Phokhara ISR+FSR Luminosity s(e+e-  p+ p- gISRgFSR ) s(e+e- p+ p- gFSR ) Hadronic cross section @ KLOE D. Leone

  12. FSR uncertainty 1.05 Rel. difference inclusive - 1.04 exclusive approach 1.03 subtract FSR contribution estimated by MC 1.02 1.01 1. 1 0.99 0.98 0.97 D = 0.2% ± 0.1% 0.96 The 2 methods are in excellent agreement Higher order FSR corrections negligible Proof of Factorization Ansatz Radiator H 0.95 gFSR 0.8 .. 0.9% Schwinger ‘90 0.8 0.9 0.5 0.6 0.7 0.4 “FSRExclusive” approach N(e+e- p+ p- gISRgFSR) Event analysis Phokhara ISR Luminosity s(e+e- p+ p- gISR) s(e+e- p+ p-) • FSR systematic = 0.3%, coming from 2 contributions • 0.2% difference incl-excl correction • upper limit of 20% for scalar QED model • (point-like pions): 20%  1% = 0.2% Hadronic cross section @ KLOE D. Leone

  13. Cross Section (e+e-p+p-) spp[GeV2] Final spectrum: after the correction for vacuum polarization Dahad(s) from F. Jegerlehner, July 2003 Total error = 1.3 % Hadronic cross section @ KLOE D. Leone

  14. 2p contribution to amhadr |Fp(s)| • We have evaluated the dispersion • integral for 2p channel in the energy • range 0.35 <spp<0.95 GeV2 • CMD-2 • KLOE ampp = (388.7  0.8stat  3.5syst  3.5theo) 10-10 • Comparison with CMD-2 in the • energy range 0.37<spp<0.97 GeV2 sp [GeV2] KLOE (375.6  0.8stat  4.8syst+theo) 1.3% Error CMD-2 (378.6  2.7stat  2.3 syst+theo) 0.9% Error At large values of sp (>mr2) we are consistent with CMD-2 and we confirm the deviation from t-data. Hadronic cross section @ KLOE D. Leone

  15. Conclusion • KLOE has proven the feasibility to use initial state radiation to • measure hadronic cross section (hep-ex 0407048) • We expect to reduce the systematic error below 1% by repeating • the analysis with 2002 data. Improvements from theory are also • expected. • The analysis at large photon angle to study the region near the • threshold is going on. • Evaluation of ratio R – the analysis has already begun Hadronic cross section @ KLOE D. Leone

  16. Outlook preliminary Asymmetry = data = MC Polar angle [] qp+ qp- qp [] • Large angle photon analysis to explore the threshold region • tagged measurement • Test of sQED model: • at large photons angles the amount • of FSR is large. Here it is possible • to study the charge asymmetry. • It comes out from the interference • between ISR (C-odd) and • FSR (C-even) Integrating asymmetry we get a difference data-MC of (8.5  1.2)% Hadronic cross section @ KLOE D. Leone

  17. Backup slices Hadronic cross section @ KLOE D. Leone

  18. Unfolding the Mass Revolution sp (obs) [GeV2] sp (true) [GeV2] Trackmass [MeV] The smearing matrix “almost” diagonal Inversion of smearing matrix possible A more sophisticated unfolding technique is obtained by means of the unfolding package GURU (A. Höcker et.al./ALEPH). Issues: - Reliability of MC simulation  - Correct choice of the regularization parameter Systematics studied by varying meaningful values of the regularization parameter: Due to nature of the dispersion integral the effect on am is almost negligible Hadronic cross section @ KLOE D. Leone

  19. Terms not included in Phokhara Unshifting correction Hadronic cross section @ KLOE D. Leone

  20. Relative contribution of LO-FSR Relative contribution of NLO-FSR Hadronic cross section @ KLOE D. Leone

  21. e e Radiator Function before cutting on particle ID Fp=1 s (ppg) with Fp=1    after cutting on particle ID p+ p-p0 sp (GeV2) mp m+ m- g MTRK Likelihood effect on Mtrk distribution Hadronic cross section @ KLOE D. Leone

  22. Hadronic cross section @ KLOE D. Leone

  23. reconstructed kine Mpp2 [GeV2] Mpp2 [GeV2] Hadronic cross section @ KLOE D. Leone

  24. KLOE & DAFNE pb-1 • e+e-collider @ S = M = 1019.4 MeV • achieved peak Luminosity: 8  1031cm-2 s-1 • 2000-2002 data set: 500 pb-1 KLOE detector designed for CP violation studies  good time resolution s t= 57 ps /E(GeV)  54 ps in calorimeter and high resolution drift chamber (p/p is 0.4% for  > 45°), ideal for the measurement of M. Hadronic cross section @ KLOE D. Leone

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