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Study of charmonium states formed in  pp annihilations: results from Fermilab E835

Study of charmonium states formed in  pp annihilations: results from Fermilab E835. Diego Bettoni INFN - Sezione di Ferrara for the E835 Collaboration Fermilab University and INFN Ferrara University and INFN Genova University of California at Irvine Northwestern University

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Study of charmonium states formed in  pp annihilations: results from Fermilab E835

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  1. Study of charmonium states formed inpp annihilations: results from FermilabE835 Diego Bettoni INFN - Sezione di Ferrara for the E835 Collaboration Fermilab University and INFN Ferrara University and INFN Genova University of California at Irvine Northwestern University University and INFN Torino

  2. OUTLINE • Introduction. • Experimental Method. • Results: • pp  0  J/  e+e- • pp  c  + • pp  2  + • pp  0  + • search forpp  c’ + • proton e.m. form factors (time-like) • pp  c    4K • Summary and outlook.

  3. Introduction E835 studies the direct formation ofcc states in pp annihilations. It is a fixed target experiment, in which the antiproton beam circulating in the Fermilab accumulator intersects a hydrogen gas jet target. The charmonium system has often been called the hydrogen atom of strong interactions. Non relativistic potential models + relativistic corrections + Perturbative QCD make it possible to calculate masses, widths and branching ratios to be compared with experiment.

  4. Why pp ? In e+e- annihilations only states with the quantum number of the photon JPC = 1-- can be formed directly via the process e+e- * cc. States with JPC  1-- are usually studied from radiative decays, e.g. e+e- ’   +  In this case the measurement accuracy ( for masses and widths ) is limited by the detector. In pp annihilations all quantum numbers are directly accessible. The resonance parameters are determined from the beam parameters and do not depend on the detector energy and momentum resolution.

  5. CHARMONIUM SPECTRUM

  6. E835 DETECTOR

  7. pp0J/+e+e-+PRELIMINARY

  8. c(11S0)   PRELIMINARY

  9. E835 has improved the measurement of the partial width to two photons of the state:

  10. cc0 The cc0 state has also been studied through the two photons decay Analysis of the data is in progress

  11. search • E835 searched for the state in the region: • No evidence has been found Cristal ball

  12. h’csearch • We fit the data (maximum likelihood) with hypothesis of a spin 0 resonance plus a power law background, for three values of the total width • According to our result we can set the upper limits:

  13. hc’ search in other channels

  14. Determination of s(mc)

  15. Proton e.m. form factorsin the time-like region The proton electromagnetic form factors in the timelike region can be extracted from the measurement of the cross section for the process: pp  e+e- First order QED predicts: Background from 00, 0, and +- has been carefully evaluated and is negligible. The form factors are extracted from the data under two separate hypotheses: • |GE| = |GM|. • Neglecting the term containing GE. The data are well fitted by the PQCD predicted functional form:

  16. Proton Magnetic Form Factor The dashed line is the PQCD fit. The dot-dashed line represents the dipole behaviour of the form factor in the spacelike region for the same values of |q|2.

  17. c    4K • This channel has a peculiar kinematics, so we can extract it in the huge hadronic background. • Special trigger ( using hodoscopes and SciFi detector): 4 tracks with the right kinematics. • Event selection: • 4 charged tracks • cuts on Dj, Dq opening angle (<250) • cuts on calculated invariant mass • kinematic fit probability > 60%

  18. Conclusions and outlook A lot of progress has been made in our knowledge of the charmonium spectrum. , ’, 1, 2very well measured. 0, cwell measured. Nonetheless there is stilla lot to be done: 1P1needsfurther investigation. new decay modes. Stillmissing:c’, D states. The hadronic decay channels look promising.

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