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Charmonium Production with Antiproton - Gas Jet Interactions at FNAL

Explore the precise methods and historical significance of charmonium production using antiproton-gas jet interactions at Fermilab. Learn about the experimental techniques, spectrum observations, and detector specifications.

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Charmonium Production with Antiproton - Gas Jet Interactions at FNAL

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  1. Charmonium Production with Antiproton - Gas Jet Interactions at FNAL Matteo Negrini University of Ferrara - INFN for the E835 collaboration: Fermilab, Ferrara, Genova, Northwestern, Minnesota, Irvine, Torino ISMD-2003, Krakow, September 5-11, 2003

  2. Why ? • 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 EM final states ISMD-2003, Krakow, September 5-11, 2003

  3. FNAL Antiproton Accumulator ISMD-2003, Krakow, September 5-11, 2003

  4. FNAL Antiproton Accumulator • Antiprotons are accumulated until the desired current (~50 mA) is reach. Then they are stochastically cooled and decelerated to the desired energy (continuous beam) • Energy determined from the orbit lengthL and the revolution frequency f • L from reference orbit (LREF) measured at the y’: DL/L ~ 210-6 • f measured with precision: Df/f~ 10-7 • The error on the beam energy measurement is sE50-150 keV • Energy spread after stochastic cooling: sE400 keV. At the charmonium mass scale: ISMD-2003, Krakow, September 5-11, 2003

  5. Hydrogen Gas-Jet Target • Jet of clusterized H2 molecules • Density up to 1-4·1014 atoms/cm3 • Instantaneous luminosity up to 3·1031 cm-2s-1 • Luminosity is measured from elastic at 90° with 3% precision • Interaction region: 557 mm3 ISMD-2003, Krakow, September 5-11, 2003

  6. Experimental technique • Charmonium is formed in the complete annihilation of so the ECM is determined from the beam parameters • The beam energy is moved to scan the resonance • The number of events N of a given final state 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 ISMD-2003, Krakow, September 5-11, 2003

  7. Charmonium spectrum • hc' observed by Crystal Ball with mass 3594 MeV, later observed by Belle with larger mass (3654 MeV) • hc (observed by E760 at M=3526.2 MeV) needs confirmation ISMD-2003, Krakow, September 5-11, 2003

  8. Historical review - 1 • R704 at CERN (1984) • pioneered the technique and proved the feasibility • 3 pb-1 collected on J/y and c1,2 • E760 at Fermilab (1990-1991) - 30 pb-1 • First observation of 1P1 resonance • Precision measurement of cc1 and cc2masses and widths • First direct observation of hc in annihilations and mass measurement • Search for hc’ • Coupling to of J/y, y’ and c1,2 • Proton form factor in the time like region ISMD-2003, Krakow, September 5-11, 2003

  9. Historical review - 2 • E835 at Fermilab (1996-1997) -143 pb-1 • Measurement of c0 mass and width • Measurement of c0,2 • cc1 and cc2 angular distributions measurement • Proton form factor in the time like region • Precise measurement of thehcparameters • Extensive search of theh’cstate • Improved y’branching ratios measurements • Study of the fffinal state ISMD-2003, Krakow, September 5-11, 2003

  10. Historical review - 3 • E835-II at Fermilab (2000) -113 pb-1 • Extensive study of c0state • Data taken in the 1P1 energy region to confirm resonance • cc1 and cc2 mass and width measurement • Measurement of y’ branching ratios • Proton form factor in the time like region ISMD-2003, Krakow, September 5-11, 2003

  11. The E835-II 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°) ISMD-2003, Krakow, September 5-11, 2003

  12. Detector acceptance and resolution • The detector has cylindrical symmetry around the beam axis with 2p azimuthal coverage • Central calorimeter: • Acceptance: 11° < q < 70° • Energy resol.: • Angular resol.:sq6mrad, sf11mrad • Forward calorimeter: • Acceptance: 2° < q < 11° • Position resol.: sx5cm • Inner tracking • Acceptance: 15° < q < 55° • Angular resol.: sq4mrad, sf8mrad ISMD-2003, Krakow, September 5-11, 2003

  13. Selection of J/y,y'e+e- final states • Selection of high invariant mass e+e-candidates from y'e+e- or J/yXe+e-X: • 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 in Čerenkov and hodoscopes. • Decay products reconstructed in the detector and final state classified with kinematic fit EW1·EW2>1.5 Background ISMD-2003, Krakow, September 5-11, 2003

  14. Example of y’yp+p- event Charged tracking + Čerenkov + calorimeter f view Charged tracking q view ISMD-2003, Krakow, September 5-11, 2003

  15. c0 mass and width measurement (E835-II) • 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 ISMD-2003, Krakow, September 5-11, 2003

  16. c0 mass and width measurement (E835-II) S. Bagnasco et al., Phys. Lett. B533 (2002) 237 ISMD-2003, Krakow, September 5-11, 2003

  17. c1 and c2 scan (E835-II) Preliminary • New measurement of mass and width of the c1 and c2 • Luminosity: ~6 pb-1 (c1) - ~1 pb-1 (c2) - ~11 pb-1 (bkg) ISMD-2003, Krakow, September 5-11, 2003

  18. Results for  ccJ J/yg e+e-g T. A. Armstrong et al., Nucl. Phys. B 373 (1992) 35 M. Ambrogiani et al., Phys. Rev. Lett. 83 (1999) 2902 ISMD-2003, Krakow, September 5-11, 2003

  19. Electric dipole trasition (PS+g) • The value obtained for G(c0J/yg), anomalously large in the past, is now consistent with the theory of electric dipole transitions ISMD-2003, Krakow, September 5-11, 2003

  20. Angular distribution  y' e+e- Preliminary E835-I (2579 events) E835-II (4822 events) Combining the two data set: Measurement of the helicity 0 and 1amplitudes for the interaction ISMD-2003, Krakow, September 5-11, 2003

  21. y' branching ratios Preliminary • y’ and J/y detected through their e+e- decay. The observed channels are: • All the exclusive channels are fully reconstructed and selected with kinematic fits • 14.3 pb-1of datain they’ energy region collected in year 2000 • 12.4 pb-1onresonance  ~32000 events • 1.9 pb-1offresonance  ~60 events ISMD-2003, Krakow, September 5-11, 2003

  22. y' branching ratios Preliminary T. A. Armstrong et al., Phys. Rev. D 55 (1997) 1153 M. Ambrogiani et al., Phys. Rev. D 62 (2000) 032004 ISMD-2003, Krakow, September 5-11, 2003

  23. y' branching ratios Preliminary J/yh J/yp0p0 J/yp+p- e+e- ISMD-2003, Krakow, September 5-11, 2003

  24. Proton form factor in the time-like region • Measurement of non resonant cross section for the process • First order QED prediction: • At threshold: |GE|=|GM| (uniform angular distribution) • At high s: |GE| contribution negligible • QCD asymptotic behavior: C and L free parameters Upper limits at 90% C.L. M. Andreotti et al., Phys. Lett. B 559 (2003) 20 ISMD-2003, Krakow, September 5-11, 2003

  25. 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 ISMD-2003, Krakow, September 5-11, 2003

  26. 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 ISMD-2003, Krakow, September 5-11, 2003

  27. hcgg • 18.9 pb-1of data • All the resonance parameters are measured in the gg channel: M. Ambrogiani et al., Phys. Lett. B 566 (2003) 45 ISMD-2003, Krakow, September 5-11, 2003

  28. hc’ search • E760: hc’ search in the CBAL energy region (3594 MeV) • E835-I: scan on a wider energy range c2 T. A. Armstrong et al., Phys. Rev. D 52 (1995) 4839 M. Ambrogiani et al., Phys. Rev. D 64 (2001) 052003 ISMD-2003, Krakow, September 5-11, 2003

  29. c0gg(E835-II) Preliminary Interference No Interference Taking from the PDG: ISMD-2003, Krakow, September 5-11, 2003

  30. p0p0 and hh event selection • p0 and h detected through their gg decay • 4g neutral events • Search for p0 and h candidates cutting on invariant mass and opening angle of the photon pairs • 4-C kinematic fit to ISMD-2003, Krakow, September 5-11, 2003

  31. Study of p0p0 in the c0 region • Interference between resonant and non resonant process enhancing the resonance signal Interfering (helicity 0) Non-Interfering (helicity 1) Resonant M. Andreotti et al., hep-ex/0308055, to be published on PRL ISMD-2003, Krakow, September 5-11, 2003

  32. Study of  hh in the c0 region Preliminary ISMD-2003, Krakow, September 5-11, 2003

  33. Conclusions Charmonium states have been investigated at FNAL in proton antiproton annihilation obtaining... • Precision measurement of mass and width of the charmonium states • Measurement of branching ratios • Study of radiative decays: • Search for states that need confirmation • Interference between resonant and non-resonant multihadron production • Proton form factor in the time-like region at s=10-15GeV2 ISMD-2003, Krakow, September 5-11, 2003

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