The shad measurement at DAFNE collider DAFNE: e+e- collider on f - mass  s = 1.02 GeV 61% of ahad is covered by the r - resonance region: 0.5 GeV < s < 0.9 GeV DAFNE can contribute with the s(e+e-  hadrons) measurement from the threshold up to the f mass Anna Ferrari - KAON 2001, June 12-17 2001

The radiative return method Standard way: energy scan of the beams Alternative Approach: e+e- hadrons + g at s=Mf where g is emitted in the initial state (ISR) the invariant mass of the hadronic system: M2had = Mf2-2 MfEg changes continuously in 4mp2 < M2had < Mf2 Anna Ferrari - KAON 2001, June 12-17 2001

Radiative return vs Energy scan Radiative return: a direct, pure QED, alternative method to measure s (e+e-  hadrons) errors on luminosity and on the center of mass energy of e+e- are the same for the full energy range by-product of the standard research program of KLOE BUT: accurate knowledge of the photon emission including radiative corrections is needed In practice, since there are regions with ISR strongly enhanced: - use a description of e+e-  hadrons + n g (all radiative corrections included) - fold with the detector description - fit the experimental data The most precise way is the inclusive approach define acceptance cuts use a description with 1 radiative photon: e + e -  p + p - g Anna Ferrari - KAON 2001, June 12-17 2001

+ = Radiation description: ISR and FSR EVA * Montecarlo generator qg * S. Binner, J.H. Kühn, K. Melnikov Phys. Lett. B 459 (1999) Eg (MeV) qg FSR (background): enhanced at small energies follows pion angular distribution ISR (signal): enhanced by the -resonance Cut in Eg-qg-plane : Eg >10 MeV + peaked at small angle 5°< gCM<21° 55°< p <125° (pT>200 MeV) = ISR/(ISR+FSR)>99% Anna Ferrari - KAON 2001, June 12-17 2001

Comparison Data/MC looks good Test of FSR/ISR simulation An efficient test of the MC model of FSR is the check of the charge asymmetry of pion pairs: 20° < qg <40° Comparison Data/MC looks good EVA -MC describes FSR on the some % - level 60° < qg <120° Anna Ferrari - KAON 2001, June 12-17 2001

The background f  f0 g  p + p - g The ‘direct’ decay   +  -  affects the region: M2had > 0.8 GeV2 Problem: the parameters of the f0 -meson through which the decay proceeds:  f0  +  -  are poorly known. constructive or destructive interference with FSR? Solution: study interference from 0 0  decay: study the charged decay experimentally at large photon angle: complementary analysis to hadronic cross section BR(f0  p0p0 )Exp = (0.80.090.06)•10-4 KLOE coll 1999 data 60° < qg <120° Contribution in that region at the few % level* *K. Melnikov, F. Nguyen, B. Valeriani, G. Venanzoni 2000 Anna Ferrari - KAON 2001, June 12-17 2001

The shad measurement at KLOE Superconducting Coil B=0.6 T I. The KLOE detector Iron Yoke Electromagnetic Calorimeter Pb / Scintillating Fibres (4880 PMTs) Endcap - Barrel - Modules sE /E = 5.7% /E(GeV) s t= 57 ps /E(GeV)  50 ps Cylindrical Drift Chamber 4 m , 3.3 m Length 90% Helium, 10% Isobutane 12582 / 52140 sense / total wires all stereo wires Be beam pipe (0.5 mm thickness) permanent Quad’s instru- mentation (32 PMTs) sp / p < 0.4% sz = 2 mm Anna Ferrari - KAON 2001, June 12-17 2001

e+ e -  e+ e -  (radiative Bhabha) e+ e -  m+ m -  II. The strategy e+ e -  p+ p -  - the acceptance efficiency eacc is evaluated from MC - the global selection efficiency esel is evaluated from DATA+MC - the trigger efficiency etrig is evaluated from DATA the experimental Backgrounds come from: e+ e -  e+ e -  (radiative Bhabha) e+ e -  m+ m -  e+ e -  f  p+ p - p 0 (BR = 15.5 %) the Luminosity is measured using Bhabha scattering at large angles Anna Ferrari - KAON 2001, June 12-17 2001

III. The event selection 1 charged vertex close to IR with 2 connected tracks + acceptance cuts: Likelihood method for p/e discrimination kinematical cuts for residual background suppression Event Display DIDONE p+ p- g (x2vtx +y2vtx ) < 8 cm |zvtx | < 15 cm 5° < gCM < 21° 55° < p < 125° ( pT>200 MeV) - Use drift chamber for p tracks detection and vertex reconstruction - Use calorimeter for p identification no explicit g detection needed ! Anna Ferrari - KAON 2001, June 12-17 2001

IV. Bhabha rejection elik - A Likelihood method based on: - ToF of ‘charged ’ clusters in EmC - shape and energy deposition of the charged cluster - +  - 0 are used for Pion information - e+ e - g are used for Electron information - We use two data samples: - A relative likelihood function is defined for different bins in momentum e |p| [MeV] elik  98% Log(rL) cut: Log(rL) = 0 for each bin Anna Ferrari - KAON 2001, June 12-17 2001

V. The residual backgrounds p+ p-g Before Likelihood ( Rad. Bhabhas ) Mtrk is defined by: After Likelihood Mtrack (MeV) V. The residual backgrounds e+e-g p+ p-g cut: 2s around the ppg peak m+ m-g p+ p-po Mtrack (MeV) Anna Ferrari - KAON 2001, June 12-17 2001

VI. f  p + p - p 0 rejection p+ p- p0 These events are separated at the streaming level by applying a cut in the ( Mtrack , Mpp ) plane we look at the events that fall in the ppg selection cut p+ p- g 6.5 pb-1 60°<Qg<120° 5°<Qg<21° p+ p- p0 Background in p+ p- p0 is dominating the very low Mpp2 - region p+ p- p0 background is almost negligible 21°<Qg<60° Mtrack (MeV) vs M2pp (GeV2) Anna Ferrari - KAON 2001, June 12-17 2001

VII. The measurement of the luminosity Use Large Angle Bhabhas ( seff = 425nb ): 55° < q + - < 125 ° Acoll. < 9 ° E+ -  400 MeV * Data BABAYAGA* - Berends/Drago/Venanzoni Track - Energy (MeV) LAB - Candidates (Systemat., Accept.) Background (gg, ppg, ...) Theoret. Generators with rad. corrections Track - Polar angle Berends/Drago/Venanzoni BABAYAGA* Luminosity- Measurement on % Level agreement with independent gg-Counter < 1% * C.M.C. Calame et.al. Nucl. Phys., B 584 (2000) Anna Ferrari - KAON 2001, June 12-17 2001

Preliminary results I. ds/dM2pp spectrum 16.4 pb-1 of Nov./Dec. 2000 Data dspp/dM2pp (nb/GeV2) M2pp (GeV2) Acceptance cuts: 5° < gCM < 21° 55° < p < 125° ( pT>200 MeV) data: 3.72 ± 0.14 (stat.) nb MC: 3.55 ± 0.07 (stat.) nb systematic  2% Anna Ferrari - KAON 2001, June 12-17 2001

|Fpp |2 II. The pion form factor s (MeV) theoretical function (superimposed) from Gounaris-Sakurai parametrization  with: mr = 770 MeV mw = 782 Mev Gr = 150 MeV Gw = 8.5 MeV s (MeV) Anna Ferrari - KAON 2001, June 12-17 2001

Conclusions and Outlook A method for the hadronic cross section measurement using the radiative return coming from ISR, has been tested at KLOE with 16.4 pb-1. The agreement with the EVA MC prediction (Kühn et.al.) is good (at the level of few %) Efficiencies, Systematics effects, Background and Luminosity are under control at the level of few % future: - refine the evaluation of all the effects, from data - work out the possibility to perform an inclusive measurement - measure shad at the level of 1% with an integrated Lumi. of 200pb-1 Input from theory: NLO generator from Kühn et.al.  increases statistics and reduces systematics, going down to qg=0 Anna Ferrari - KAON 2001, June 12-17 2001