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C. Di Donato and Ilaria Villella I.N.F.N. and Universita’ di Napoli

f Radiative decay meeting April 17th 2003. fhgp + p - gg. C. Di Donato and Ilaria Villella I.N.F.N. and Universita’ di Napoli. Why h  p + p - g. PDG’02: BR( h  p + p - g ) = (4.68±0.11)x10 -2 KLOE: 500pb -1  5x10 5 events ( e selection ~50%) BR measurement  error: 0.2x10 -4

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C. Di Donato and Ilaria Villella I.N.F.N. and Universita’ di Napoli

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  1. f Radiativedecay meeting April 17th 2003 fhgp+p-gg C. Di Donato and Ilaria Villella I.N.F.N. and Universita’ di Napoli

  2. Why hp+p-g • PDG’02: BR(h p+p-g) = (4.68±0.11)x10-2 • KLOE: 500pb-1 5x105 events (eselection~50%) • BRmeasurement  error: 0.2x10-4 • Study of |M|2 (Gormley et al. P.R.D2(1970),501 7250 events): ¤ simple gauge-invariant matrix element |M|2~q2k2sin2q; ¤different theoretical model include the effect of a pp final-state interaction assuming that the dipion phase shift is dominated by the r meson; April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  3. Signal and Background • s(mb) • Signal decay • fhgp+p-gg1.84 x10-3 • Background decay S/B • f p+p-p0p+p-gg 0.44 4 x 10-3 • e+e-wp0p+p-gg 7.66x10-6 240 • fhgp+p-p0g 8.717x10-3 0.2 April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  4. Signal: hp+p-g Final State: p+ p- g g MC Signal Production: 5x104 events Topological cut: • 2 prompt photons |tcl-lcl/c| < 5 st; • 1 charged vertex with two associated tracks • The Vertex must be inside the following region: rxy < 4 cm; |z|< 8 cm. Filfo EVCL(RADstream) topological cut Total eselection: 99% 54%86% 46 % April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  5. RPI stream efficiency eRPIstre eRPI= 11.50% Eg(Mev) RAD stream efficiency eRADstream Eg(Mev) gh energy Eg(Mev) April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  6. Invariant mass of two photons MCtrue MC true RAD Stream MC true RPI Stream Mgg (MeV) April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  7. RAD+RPI Stream Efficiency Average e = 66% Eg(Mev) Eg(Mev) April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  8. (Ep++Ep-)h(MeV) (Eg)h(Mev) Ep++Ep- (MeV) RPI Stream cuts SIGNAL h rest frame • f rest frame: (Egrad)f =363 Mev; ph = pf–pg • ph in lab. Frame • Boost p+ p- gh in h rest frame April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  9. RPI Stream cuts Background (Ep++Ep-)h(MeV) Ep++Ep- (MeV) (Eg)h(Mev) • Signal Background • =Ncuts/NRPI 80.7%17.8% (S/B)RPI =3x10-3 April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  10. RAD+RPI stream S S+B S/B=2x10-2 Egh (MeV) April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  11. Cuts • Both stream: • 356 MeV<Egrad<368MeV • S/B =0.14 April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  12. Strong cuts • Only RAD stream • P(c2)>10-4 • 356MeV<Egrad<368MeV • Track mass > 200 MeV • S/B =163 April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  13. Angular distribution Expected angular distribution  dN/d(cosq)~sin2q cosq Corrected MC generator is now in geanfi April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  14. A first look at data RAD stream 1 pb-1 Mtrack Mppg(MeV) Mppg(MeV) April 17th 2003 - Phi Radiative Decay Meeting- Frascati

  15. Conclusions and Outlook • Clear signal on data • Reasonable background for events in radiative stream • (but more careful evaluation is in progress) • Events in rpi stream are vital to fit the g spectrum; • a strategy to recover events is in development, but • will be necessary only if we improve S/B in that • kinematical region • Angular variables can help April 17th 2003 - Phi Radiative Decay Meeting- Frascati

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