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Measurements of the Electromagnetic Form Factor of the Proton at BES

Part 1. Measurements of the Electromagnetic Form Factor of the Proton at BES. Hui-hong LI (Beijing) for the BES Collaboration. XXXXth Rencontres de Moriond March 12th ~19th, 2005 (La Thuile, Italy). Introduction. ▪ Four form factors : , , ,

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Measurements of the Electromagnetic Form Factor of the Proton at BES

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  1. Part 1 Measurements of the Electromagnetic Form Factor of the Proton at BES Hui-hong LI (Beijing) for the BES Collaboration XXXXth Rencontres de Moriond March 12th ~19th, 2005 (La Thuile, Italy)

  2. Introduction ▪ Four form factors : , , , ▪ In the time-like region : and Study status of the proton form factor in the time-like region from other experiments

  3. Introduction ▪ At BES: measure the cross section of with data taken at center-of-mass energy 2.00--3.07GeV to extract the proton form factor.

  4. Event selection ▪ Two opposited charged tracks in the MDC ▪ mfit=2 ( track with good helix fit) ▪ Vertex: |Vr| ≤0.02m |Vz|≤0.15m ▪ |cosθ| ≤0.80 ▪ Acol ≤100 (Ecm=2.0GeV) Acol ≤30 (other data) ▪ Momentum: pmeas<pexp+3σp ▪ SCengp/pp<0.6 ▪ PID: dE/dx (Ecm=2.0 and 2.2GeV) TOF (other data)

  5. Background

  6. Summary of the results BES Preliminary !

  7. Form factors BES Preliminary !

  8. Part 2 Recent BES Results from ’Decays 1. Inclusive e+e-spectrum to measure the cJ mass and width from ’ cJ(J=0, 1, 2) 2. Final states with KsKs in’ decays 3. ’ 3 (π+π-) and J/ 2 (π+π-) from ’ decay

  9. Inclusive e+e- spectrum BESII ECAL: σE/E=22%/E charged tracking:σp/p=1.7%/1+p2 ▪Photons from ’ cJ have energies of 261, 171 and 128MeV for the c0 , c1 and c2 ▪ Momentum resolution of 1.6 to 4.1MeV can be obtained for low momentum electrons from 60 to 250MeV ▪use e+e- to achieve better resolution Conversion point Measure cJ mass and width

  10. Inclusive e+e- spectrum data BES Preliminary ! c1 Bkg subtract c0 c2 ’ cJ (J=0, 1, 2)

  11. Inclusive e+e- spectrum BES Preliminary ! hep-ex/0502031 M(c.o.g)= 3524.85±0.32±0.30 MeV Hope BESIII can do better!

  12. Final states with Ks Ks in’ decays ▪ The importance of the Color Octet Mechanism (COM) in radiative decays has been studied for many years. ▪ Experimental data of two- and four-body exclusive decays of P-wave charmonia with improved precision are of considerable interest in testing the new QCD approach with the effect of the COM.

  13. Final states with Ks Ks in’ decays ’  K0sK0s ’  h+h- K0sK0s BES Preliminary ! ’  π+π- K0sK0s ’  K+K-K0sK0s Invariant mass squared of the two remaining charged particles after K0sK0s selection

  14. Final states with Ks Ks in’ decays BES Preliminary ! hep-ex/0410028 Many channelsare observed for the first time !

  15. ’ 3 (π+ π-) and J/ 2 (π+ π-) from ’ decay B(’  3 (π+ π-) ) = (4.67±0.29±0.64)10-4 B(J/ 2 (π+ π-)) = (3.45±0.12±0.24) 10-3 Consistent with “12% rule” Form factor of 3 (π+ π-) |F(s=3.6502)|=0.21 ±0.02 |F(s=3.6862)|=0.20 ±0.01 BES Preliminary !

  16. Summary 1. Measurements of the electromagnetic form factor of the proton by at Ecm=2.0~3.07GeV. 2. Recent BES Results from ’ Decays * Inclusive e+e-spectrum to measure the cJ mass and width from ’ cJ (J=0, 1, 2) * Final states with KsKs in’ decays * ’ 3 (π+π-) and J/ 2 (π+π-) from ’ decay End Thank you !

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