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Progress on F p with the KLOE experiment (untagged)

Progress on F p with the KLOE experiment (untagged). Federico Nguyen Università Roma TRE February 27 th 2006. Outline. Present situation Selection criteria: the “small angle” analysis Particle discrimination Preliminary estimates of the background processes Conclusions.

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Progress on F p with the KLOE experiment (untagged)

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  1. Progress on Fp with the KLOE experiment (untagged) Federico Nguyen Università Roma TRE February 27th 2006

  2. Outline • Present situation • Selection criteria: the “small angle” analysis • Particle discrimination • Preliminary estimates of the background processes • Conclusions

  3. Available KLOE data sets in 2001, the veto of cosmic events (hardware) caused nonnegligible inefficiency in ppg events and made the measurement of mmg events not feasible, from 2002 on, this effect is taken out

  4. KLOE: performances for the ppg analysis Electromagnetic Calorimeter Pb / Scintillating Fibres Endcap + Barrel = 98% (4p) Drift Chamber 4 m,3.3 mlength 90% He,10%i-C4H10 sE/E = 5.4%/E(GeV) e+ e- e+ e- sp/p = 0.4% (q > 45°) srf = 150 mm , sz = 2 mm svtx~ 3 mm, sMpp ~ 1 MeV the whole structure is surrounded by a superconducting coil B=0.52 T

  5. p + p - Fiducial volume • 1 and only 1 vertex ( |z| < 7 cm ) connected to 2 tracks • each track with 50o < qtrack < 130o • small angle g ( qpp < 15o ) no photon tagging: • high statistics for ISR (~ q-2 ) • low relative FSR contribution • suppressed  p+p-p0wrt the signal • the threshold region is not covered

  6. [%] Mpp2 (GeV2) Benefits of the selected region sFSR-LO / sQED sppp / sppg in the selected region LO-FSR, and f p+p-p0 yields are small, from which the published result is based on: KLOE result (140 pb-1 of 2001) : Phys. Lett., B606 (2005) 12

  7. ′ ′ ′ Normalization to mmg events benefits from normalizing to mmg events, in the limit of neglecting FSR effects: Luminosity: 0.5%theory  0.3%exp., Bhabha most of the theoretical systematic effects cancel out

  8. Statistical error qpp< 15o, 50o < qp,< 130o ,DMpp2 = 0.01 GeV2 L = 240 pb-1 , e = 50% flat in s′, in both channels contrary to the luminosity normalization, statistics is an issue, however it is a good cross check of the region intriguing because of the difference with t data estimate performed with PHOKHARA-4 H. Czyż et al., Eur.Phys.J.C39 (2005) 411

  9. Discrimination p vs. e: time and energy /eseparation is performed using a particle ID function based on time and quantity and shape of the energy released in the calorimeter pions deposit ~ 40 MeV in each plane electrons deposit mostly in the first plane and negligible amount in the rest time of flight: for low p valuesbpbe ~ 1

  10. Improvements wrt the published result mtrk, defined by 4-momentum conservation under the hypothesis of 2 equal mass tracks and a g • improved selection • enlarged mtrk acceptance, from 90 MeV to 80 MeV • only 1/1000 of events with mmiss > 120 MeV • more efficient reconstruction filter: from 95% to 98.5% mmiss, defined by the 4-momentum conservation under the hypothesis of e+e- p+p- X

  11. before particle ID after particle ID Discrimination efficiencies for ppg and mmg muons or pions electrons z = Log Lp/Le (per track) mtrk (MeV) 1) the procedure is tested 2) the event is selected if at least one of the 2 tracks is not identified to be an electron it leads to a rejection power ~ 97%for e+ e- e+ e-events while keeping a selection efficiency> 99.8%for e+ e- p+p-g, m+m-g events

  12. Mpp2 [0.37,0.42] GeV2 p+p-p0 p+ p-p0 (MC) no man’s land DATA mtrk (MeV) Definition of ppg and mmg events (I) 130 MeV < mtrkand inside the area, are ppg mtrk < 115 MeV are mmg ( z1+ z2 ) / 2

  13. Definition of ppg and mmg events (II) Mpp2 [0.57,0.62] GeV2 ( z1+ z2 ) / 2 Mpp2 [0.87,0.92] GeV2 ( z1+ z2 ) / 2 mtrk (MeV) eeg contamination @ high Mpp2 can be neglected to 1st order mtrk (MeV)

  14. Tracking efficiencies for ppg events the agreement is on the level of 0.5-0.6%, at maximum, preliminary evaluated from data samples of p+p- and p+p-p0 events, and from a MC sample of p+p-g events, and compared

  15. Background for the ppg selection background yields are estimated using MC distributions after the whole selection, normalized to the luminosity of the selected data sample for data and 2 background sources: data dsvis/dM2 (nb/GeV2) preliminary MC mmg MC p+p-p0 M2 (GeV2)

  16. The “raw” ppg spectrum • pion with 50o < qtrack < 130o • small angle g ( qpp < 15o ) • mtrk > 130 MeV and inside the area (mtrk vs Mpp) • at least 1 track not to be identified as an electron dN/dM2 (events/0.01 GeV2) preliminary DMpp2 = 0.01 GeV2, L = 242 pb-1 of data taken in 2002 M2 (GeV2)

  17. Background for the mmg selection background yields are estimated using MC distributions after the whole selection, normalized to the luminosity of the selected data sample for data and 2 background sources: data dsvis/dM2 (nb/GeV2) preliminary MC ppg MC p+p-p0 M2 (GeV2)

  18. The “raw” mmg spectrum • muon with 50o < qtrack < 130o • small angle g ( qpp < 15o ) • mtrk < 115 MeV • at least 1 track not to be identified as an electron dN/dM2 (events/0.01 GeV2) preliminary DMpp2 = 0.01 GeV2, L = 242 pb-1 of data taken in 2002 M2 (GeV2)

  19. Conclusions and perspectives • the extraction of Fp, from both the absolute measurement of ppg events and from the ratio of ppg to mmg events, is in an advanced state, • these methods have different systematics, • we are finalizing the estimate of the corrections and of the systematic uncertainties, • good control of p/m/e discrimination, • even on the theory side some improvements are expected Results will come soon… Please, stay tuned

  20. Comparison among available data sets SND: Achasov et al., hep-ex/0506076 < Dampp> = (380.4  2.1 )  10-10 CMD-2, c2 = 0.3 CMD-2 EPS (‘05), c2 = 0.3 c4 pts2/ndf = 2.5 / 3 P(c2 > c4 pts2 ) = 48% s / sKLOE - 1 SND, c2 = 1 interpolation of KLOE 60 data points from 0.35 to 0.95 GeV2 KLOE, c2 = 0.9 Dampp (10-10 ) Mpp2 (GeV2) • CMD-2 (‘04) and KLOE agree @ high Mpp • disagreement btw KLOE and CMD-2/SND • around the r peak • fair agreement btw CMD-2 (‘04) • and KLOE • difference at about 1s btw KLOE and SND due to the r peak and above

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