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Fit of the Pion Form factor at small angle from p + p - g and first results from 2001 data A. Denig, S. Di Falco, M. Incagli, W. Kluge, S. Mueller, F. Nguyen, B. Valeriani, G. Venanzoni 2nd KLOE Physics Workshop @Otranto June 11th, 2002. Outline. Filtering of 2001 data

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  1. Fit of the Pion Form factor at small angle from p+ p-gand first results from 2001 dataA. Denig, S. Di Falco, M. Incagli, W. Kluge, S. Mueller, F. Nguyen, B. Valeriani, G. Venanzoni2nd KLOE Physics Workshop @OtrantoJune 11th, 2002

  2. Outline • Filtering of 2001 data • Extraction of |Fp|2 from p+ p-g events: • Fit of |Fp|2 with 73 pb-1 data • Comparison with CMD2 • Conclusions 2nd KLOE P.W., Otranto, June 11th, 2002

  3. Filtering of 2001 data: • 108 pb-1 of the version 13 have been filtered starting from the RAD stream • filtering time: 2 pb-1 /4h (total filtering time ~10days); • DST dimensions: ~450MB/2pb-1, raw banks are kept • cuts applied • - 35o < qp< 145o, pt > 200 MeV or |pz| > 90 MeV • - qg< 21o or qg> 169o • -track mass > 90 MeV • - Q2 < 1.02 GeV2 • the filtered events correspond to ~5%of RAD events • (~85000 events/2pb-1) 2nd KLOE P.W., Otranto, June 11th, 2002

  4. KLOE 2001 data: results on 73 pb-1 1083834 events after all the selection cuts (~50% of filtered events) ppg spectrum after selection cuts Ni TOTAL SELECTION EFFICIENCY ~15000/pb-1 Geometrical acceptance not included qg<15o (qg>165o), 40o<qp<140o Q2(GeV) Q2(GeV) 2nd KLOE P.W., Otranto, June 11th, 2002

  5. How to extract (and fit) |Fp|2 from ppg spectrum? • The Pion Form Factor is the main ingredient for am calculation. • Differently from e+e- p+ p- ,the extraction of |Fp|2 from ppg spectrum is mainly complicated by two factors: • calculation of ISR next to leading corrections, since ppg is already O(a) w.r.t. pp process; • interference between ISR and FSR; • To our knowledge (up to now) there is no analytical formulation for ds/dQ2ppgat a2 order with a cut on hard photon phase space. 2nd KLOE P.W., Otranto, June 11th, 2002

  6. p+ e+ ~Fp(s) e- p- How to extract (and fit) |Fp|2 from ppg data? • However, neglecting FSR interference (as in our case, at small angle): |Fp(Q2)|2 For single bin of Q2 = p+ e+ ~1 e- p- H(s) neglecting smearing effects! can be computed with MC Hi is the single bin integrated cross section for ppg assuming poitlike pions, Fp=1 2nd KLOE P.W., Otranto, June 11th, 2002

  7. Compute Hi with PHOKHARA Hi was computed with 2*106 events of Monte Carlo (PHOKHARA), (Fp=1), with the acceptance cuts of the analysis: qg<15o (qg>165o), 40o<qp<140o Hi spectrum MC MC s=(24.430.01) nb s=(2.5380.001) nb 2nd KLOE P.W., Otranto, June 11th, 2002

  8. Systematic effects on Hi has been checked by comparing the ratio for single point of dsi/Hi (points) with the corresponding analytical parametrization (line) |Fp|2 |Fp|2 = dsi/Hi =anal. param. Phokhara MC Q2(GeV) 0.4 GeV2 0.8 GeV2 2nd KLOE P.W., Otranto, June 11th, 2002

  9. 1083834 events after all the selection analysis cuts from MC: only ISR from VLAB:73753nb-1 TRG*FILFO*TRK* VTX*TCLO*LIKE* MTRK Main formula: 2nd KLOE P.W., Otranto, June 11th, 2002

  10. Observed Pion Form Factor (Preliminary) (ds/s)i : 2% |Fp|2 73 pb-1 (ds/s)i : 3% as average (ds/s)i :2% (ds/s)i:from 10%to 5% An overall error on luminosity of 1% must be added in quadrature to each point Q2(GeV2) qg<15o (qg>165o), 40o<qp<140o 2nd KLOE P.W., Otranto, June 11th, 2002

  11. Contribution to am: The region from threshold to 0.2 GeV2 (5.4% of total) is not accessible at small angle 2nd KLOE P.W., Otranto, June 11th, 2002

  12. Fit of |Fp|2 (Preliminary) |Fp|2 • |Fp|2 extracted from data has been fitted with: (J.H.Kuehn and A. Santamaria, Zeit. F. Physik C48 (1990), 445) • mr, Gra, b are free parameter of the fit, while mw Gw mr’Gr’ are fixed to (CMD2), luminosity from VLAB: • mw=0.78278 GeV, Gw=8.68•10-3 GeV • mr’=1.46 GeV, Gr’=0.31 GeV c2=313/70 (all points) c2=161/56 (Q2>0.4) • We get: • mr=0.7726  0.0005 GeV, Gr=0.1437 0.0007 GeV • a=(1.48 0.12) •10-3, b=-0.1473  0.002 Q2p+ p-(GeV2) 2nd KLOE P.W., Otranto, June 11th, 2002

  13. Fit of |Fp|2 (Preliminary) |Fp|2 • |Fp|2 extracted from data has been fitted with: (J.H.Kuehn and A. Santamaria, Zeit. F. Physik C48 (1990), 445) • mr, Gra, b are free parameter of the fit, while mw Gw mr’Gr’ are fixed to (CMD2), luminosity from VLAB : • mw=0.78278 GeV, Gw=8.68•10-3 GeV • mr’=1.46 GeV, Gr’=0.31 GeV • We get: • mr=0.7726  0.0005 GeV, Gr=0.1437 0.0007 GeV • a=(1.48 0.12) •10-3, b=-0.1473  0.002 Q2p+ p-(GeV2) 2nd KLOE P.W., Otranto, June 11th, 2002

  14. Fit of |Fp|2: Comparison with CMD2 • CMD2 uses a slightly different parametrization (Gounari-Sakurai Model) (hep-ex/0112031, PLB…) • They found: • mr=776.09  0.81 MeV • Gr=144.46 1.55 MeV • |d|=(1.57 0.15) •10-3 • argd =12.6o3.7o • b=-0.0695  0.0053 • We get: • mr=0.7726  0.0005 GeV • Gr=0.1437 0.0007 GeV • a=(1.48 0.12) •10-3 • b=-0.1473  0.002 mw Gw mr’Gr’ are (essentially) fixed 2nd KLOE P.W., Otranto, June 11th, 2002

  15. =CMD2 =CMD2 =KLOE =KLOE Fit of |Fp|2: Comparison with CMD2 (analitical function for CMD2 courtesy of Sibidanov) |Fp|2 |Fp|2 s(p+ p-)(GeV2) s(p+ p-)(GeV2) 2nd KLOE P.W., Otranto, June 11th, 2002

  16. Comments on smearing: Fit • As it is well known, it is better to fold the “theory” with the experimental resolution, rather than to correct data • This can be done for the Pion Form factor by minimizing the following c2: instead of theory data (which was used in our case, since Mij was taken as diagonal) 2nd KLOE P.W., Otranto, June 11th, 2002

  17. Comments on smearing: am • In order to obtain am theorists normally integrate the experimental points (measured pion form factor); this means to unfold data with the measured efficiencies and resolution • If it is necessary to unfold data, we don’t expect a strong bin-to-bin correlation since we use the drift chamber to get the Q2 value (sQ2 2*10-3 GeV2 from MC) ; many packages (for example RUN) are widely used in the high energy community to unfold data (CMD2 has not this problem, since they know very accurately the beam energy: dE=140 KeV) 2nd KLOE P.W., Otranto, June 11th, 2002

  18. Conclusion • About 73 pb-1 of 108 pb-1 filtered events of 2001 data were used to extract |Fp|2 • The average error for single point is 2%. • |Fp|2 was preliminary fitted according to Kuehn-Santamaria parametrization. • mr, Grwere found to be very close of what was found by CMD2, with a slightly different parametrization (GS). • Still missing is the correction for resolution (smearing effects), even if we don’t expect a strong bin-to-bin correlation. This is the first measurement of the pion form factor with the radiative return method: let’s publish soon!!!! 2nd KLOE P.W., Otranto, June 11th, 2002

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