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Charmonium Spectroscopy in Proton-Antiproton Annihilation

This study presents recent results from FNAL E835 on the study of charmonium states in proton-antiproton annihilation. The experiment focuses on charmonium spectroscopy in annihilation, including e+e- annihilation and gg fusion. The experimental technique, event selection, and background measurements are discussed, along with the measurement of resonance parameters and branching ratios. The study provides insights into the mass, width, and properties of charmonium states.

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Charmonium Spectroscopy in Proton-Antiproton Annihilation

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  1. Recent results from FNAL E835 on the study of charmonium states in proton-antiproton annihilation Matteo Negrini Università degli Studi di Ferrara - INFN Photon 2003 – Frascati, 07-11 April 2003 Photon 2003

  2. Charmonium spectroscopy in annihilation • e+e- annihilation  only JPC=1–- states directly formed (J/y and y’) • gg fusion  all C=+ (J1) states directly accessible • B factory • annihilation  all the states directly formed through 2 or 3 gluons intermediate states • Large hadronic background • Detection of electromagnetic final states Photon 2003

  3. Antiproton beam and target • TARGET: • Hydrogen gas-jet target • Hydrogen clusters density: • 1 – 4·1014 atoms/cm3 • The H2 target density can be tuned to obtain constant luminosity: • L INST~ 2·1031 cm-2s-1 • Target dimension  7 mm • BEAM: • Antiprotons are accumulated until the desired current is reach. Then they are stochastically cooled and decelerated to the desired energy (continuous beam) • The total CM energy can be determined directly from the antiproton beam parameter • sE400keV - sE /E10-4 • Beam dimension  5 mm Photon 2003

  4. Detector Threshold Čerenkov counters (Separation of high energy e± from the hadronic background) Electromagnetic calorimeter (12°<q<68°) Luminosity monitor (Solid state detector. Counter of elastic interactions at 90°) Charged tracking system (15°<q<60°) Photon 2003

  5. Experimental technique • The beam energy is moved to scan the resonance (precision sE250 keV) • The number of events N at energy E is obtained as: • L = instantaneous luminosity • G(E) = beam energy distribution (gaussian) • e = detection efficiency • The resonance cross section is obtained by deconvolution of the measured rate with the beam profile Photon 2003

  6. Event selection where final state includes e+e- • Selection of electron / positron candidates: • high energy deposition in calorimeter • signal in the hodoscopes • signal in Čerenkov • Electron Weight (EW): • Maximum likelihood method for the single electron selection based on calorimeter cluster shape and pulse height inČerenkov and hodoscopes. EW1·EW2>1.5 Background • Kinematic fit Photon 2003

  7. c0 mass and width Luminosity: ~33 pb-1 (~20 pb-1 on resonance) on 17 energy points Selected channel: radiative decay to J/y N. Selected events: ~400 Electron Weight Kinematic Fit Photon 2003

  8. c0 mass and width Photon 2003

  9. gg final state selection • Exactly 2 “on-time” clusters in the central calorimeter with high energy deposit and invariant mass within 20% of ECM • No “undetermined-time” extra clusters with invariant mass within 35 MeV of the p0 mass • 4C kinematic fit to gg • |cos(q*)|cut to improve signal to background ratio Photon 2003

  10. gg background (feeddown) • Background mainly from: • where one or more photons are missing because of acceptance or calorimeter energy thresholds • Measurement of the cross section for the background processes and Monte Carlo determination of the background contribution • Comparison with measured gg cross section for off-resonance points Photon 2003

  11. c0gg Preliminary Taking from the PDG: Photon 2003

  12. hcgg Preliminary • 18.9 pb-1of data • All the resonance parameters are measured in the gg channel: Photon 2003

  13. Interference between c0p0p0 and the continuum Preliminary Measurement of the cross section for the process in the c0 energy region Interfering (helicity 0) Non-Interfering (helicity 1) Resonant ~500000 p0p0 candidates Photon 2003

  14. c0branching ratios Preliminary Using the PDG value: To be compared with the PDG: Using the result: To be compared with the PDG: Photon 2003

  15. Electric dipole trasition (PS+g) The value obtained for G(c0J/yg), using the new total width and the BR measurements, is consistent with the theory of electric dipole transition Photon 2003

  16. e+e- final states selection at the y’ • y’ and J/y detected through their e+e- decay • All the exclusive channels are selected with kinematic fits • 14.3 pb-1of datain they’ energy region collected in year 2000 • 12.4 pb-1onresonance  32862 events • 1.9 pb-1 offresonance  66 events Preliminary Photon 2003

  17. y’ branching ratios Preliminary J/yh J/yp0p0 J/yp+p- e+e- Photon 2003

  18. Conclusions • Charmonium states are studied in proton – antiproton annihilation detecting electromagnetic final states • Extensive study of the cc0 ... • Mass and total width • gg width • Interference in p0p0 decay • ... and of the hc • Mass and total width • gg width • New measurement of BR(y’J/y X) and BR(y’e+e-) Photon 2003

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