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Radiative Corrections & Generators for Low Energy Hadronic Cross Section Measurement of DANE Luminosity with KLOE Exper

This presentation discusses the motivations, selection criteria, and main systematics of the experimental analysis for measuring the luminosity with the KLOE experiment at the DANE collider. It also explores improvements to the analysis and comparisons with theoretical predictions.

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Radiative Corrections & Generators for Low Energy Hadronic Cross Section Measurement of DANE Luminosity with KLOE Exper

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  1. Working Group on Radiative Corrections and Generators for Low Energy Hadronic Cross Section and Luminosity Measurement of the DANE Luminosity with the KLOE Experiment A. Denig, F. N. October 17th 2006 based on F. Ambrosino et al. [KLOE Collaboration], EPJC47 (2006) 589

  2. Outline • Motivations: the error on  • Selection criteria of large angle Bhabha events • Main systematics of the experimental analysis • Improvements? See previous talks…

  3. DANE,e+ e-collider at s ~ 1.019 GeV ~ M FINUDA e+ 510MeV e- KLOE 510MeV LINAC Damping Ring DANE VINEYARDS

  4. DANE,e+ e-collider at s ~ 1.019 GeV ~ M FINUDA e+ 510MeV e- KLOE 510MeV LINAC Damping Ring DANE VINEYARDS KLOE ISR analyses? statistics unlimited!

  5. KLOE Drift chamber(4 m   3.3 m)  Gas mixture: 90% He + 10% C4H10  12582 stereo–stereo sense wires  almost squared cells structure inserted in magnetic field (B = 0.52 T)

  6. KLOE Electromagnetic calorimeter  lead/scintillating fibers, 15 X0  4880 PMT’s  98% solid angle coverage structure inserted in magnetic field (B = 0.52 T)

  7. Resolutions in KLOE t = 57ps /E(GeV)  100ps e+ e- e+ e- EMC features: Drift Chamber features: E/E = 5.7%/E(GeV) p/p = 0.4% ( > 45°) r = 150 m , z = 2 mm vtx~ 3 mm

  8. Selection of large angle Bhabha = angle btw the 2 most energetic clusters counts the luminosity is given by Bhabha events divided for a  evaluated folding theory (QED rad. corrs.) with the detector simulation e+ e-  e+ e- 2 clusters with: 1)300 MeV < < 800 MeV 2)55o< 1,2 < 125o 3) = |1 + 2 - 180o| < 9o e+ e-   2 tracks with: 1) < 7.5 cm, |z| < 15 cm 2) p > 400 MeV 3) opposite curvature

  9. e+ e-  Bhabha event as seen by KLOE E 39 MeV for E = 510 MeV Cluster = Energy release in EmC p 1.3 MeV for E = 510 MeV Track in DC Cluster w/o associated track = Photon

  10. BHWIDEvs.BABAYAGA we compared the 2 MC codes applying our kinematic cuts E > 400 MeV 55o<  < 125o E > 400 MeV 55o<  < 125o = |1 + 2 - 180o| < 9o we tested the differential cross sections in acollinearity, , and lost energy, v =1-Mee2/s, no significant difference has been found in the shapes

  11. Momentum and  comparisons we checked that the MC code folded with the detector simulation reproduces the kinematic variables, especially at the borders p > 400 MeV • - MC • data dn/dp [(0.5 MeV)-1]  < 9 o • +Data • Babayaga (MC) • Bhagenf (MC) • perfect agreement in the acollinearity distributions • very good agreement near p ~ 400 MeV

  12. Polar angle systematics • global agreement is very good but the cut occurs in a steep region of the distributions  estimate of border mismatches • after normalizing MC to make it coincide with data in the region 65o <  < 115o, we estimate as a systematic error: ~ 0.25%

  13. DATA events/3 MeV A0 A1 MC events/3 MeV Background estimate (I) mtrk: 4-mom. conserv. under the hypothesis of 2 equal mass tracks and a  other than Bhabha, there are events with mtrk ~ 137 MeV, e+e- + - around mtrk ~ [100,170] MeV the exponential is subtracted from data

  14. Background estimate (II) a second method consists in discr. e/, at least one track identified as  an average background content of 0.6% and a systematic error of 0.1% are estimated +- pions deposit ~ 40 MeV in each plane E (last plane)(MeV) E (first plane)(MeV) electrons deposit mostly in the first plane and negligible amount in the rest E (last plane)(MeV) e+e- E (first plane)(MeV)

  15. Loss due to veto of cosmic events genuine cosmic event Bhabha event rejected because taken as cosmic at the trigger level, events are rejected because they have characteristics similar to cosmic rays (amount of energy released at the outer planes of the EMC) a fraction 0.4% of large angle Bhabha events are lost because of this

  16. Dependence on sqrt(s) since the cross section is evaluated at the nominal value of s1/2= 1019.5 MeV, we corrected for DANE variations of s1/2 in time L/L = -/ is parameterized as a function of s1/2, from Monte Carlo

  17. Systematics BABAYAGA: eff = ( 431.0 ± 0.3stat ) nb BHAGENF: eff = ( 430.7 ± 0.3stat ) nb both groups of authors claim 0.5% putting all together: 0.5 % (theory) 0.3 % (experiment) = 0.6 % (total error) summing in quadrature: 0.3 %

  18. Conclusions and perspectives • the measurement of the luminosity is performed using large angle Bhabha events, detected in KLOE in 2001 • the major source of uncertainty is (was?) from theory • we are going to use the improved version of BABAYAGA, but from the genuine exp. side, better than 0.1% is really tough • we gave a look at the process e+e- → , as an independent luminometer reaction, which is the precision of radiative corrections in this channel?

  19. LAB-GGL LAB LAB-GGL LAB Preliminary checks with e+e-  comparison btw counters: Large Angle Bhabha vs. Gamma Gamma Lumi [%] Mean Difference LAB – GGL = 0.3 % Run-Nr. [%]

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