Properties of Charm Particles in the Nuclear Medium

1. Properties of Charm Particles in the Nuclear Medium • Reminder about chiral symmetry breaking • Hadrons in the nuclear medium • Examples with Pions and Kaons • Charm production in antiproton-A reactions • Open charm production • Charmonium production, dilepton decay • Charmonium absorption • A couple words about hypernuclei • Summary / Conclusions J.Ritman Uni-Giessen

2. Origin of Hadron Masses 2Mu + Md ~ 15 MeV/c2 Explicit breaking of CS Mp = 938 MeV/c2 no low mass hadrons (except p, K, h) spontaneously broken chiral symmetry (P.Kienle)

3. Spontaneous Breaking of Chiral Symmetry Although the QCD Lagrangian is symmetric, the ground state need not be. Example:

4. The QCD vacuum is not empty Hadron masses are generated by the strong interaction with <qq> Quark Condensate The density of the quark condensate will change as a function of temperature and density in nuclei. This should lead to modifications of the hadron’s spectral properties.

5. u u u u u u d d d d d d d d d d d d Hadron Production in the Nuclear Medium Mass of particles may change in dense matter  Quark atom _ D+ d c attractive _ d c D- repulsive

6. Deeply Bound Pionic Atoms Pionic capture is possible with the appropriate choice of kinematics: d+n  3He + p- These results indicate a mass shift of ~25 MeV for pions at normal nuclear matter density.

7. Kaons in Nuclear Matter Kaon and anti-kaon masses should no longer be degenerate in nuclear matter. Expected signal: increased K- production compared to K+. J.Schaffner-Bielich et al., Nucl. Phys. A (1997) 325.

8. Measured K- Cross Section Comparison of proton-proton data with heavy ion data[2]: dramatic enhancement of the K- production probability KaoS [1] A.Sibirtsev et al., Z.Phys. A358 (1997) 101. [2] F.Laue et al., Phys.Rev. Lett. 82 (1999) 1640. [3] C.Quentmeier et al., Phys Lett B 515 (2001) 276.

9. What Can Antiproton Beams Contribute to this Discussion? Much lower momentum for heavy producedparticles (2 GeV for “free”)(Effects are smaller at high momentum) Open charm mass region (H atom of QCD) @HESR (single light quark) Well defined nuclear environment (T and r)

10. Open Charm in Nuclei Signal: strong enhancement of the D meson cross section near threshold p+A is complimentary to A+A, but the density is known and T ~ 0 !

11. Dilepton Measurements The spectral function of the charmonium state in the nuclear medium can be measured directly with dileptons.

12. cc Production in Nuclear Matter The mass of charmonium states is not expected to change much. However, a drop of the DD mass leads to a widening of the cc states. Y’ will have too high momentum, most decay outside.  but wider tails

13. Charmonium in Nuclei Due to the increased width, the dileptons from charmonium states below the free DD threshold are strongly suppressed. Golubeva et al. Eur.Phys.J. A17 (2003) 275-284

14. J/Y Absorption in Nuclei J/Y absorption cross section in nuclear matter p + A  J/Y + (A-1)

15. _ X 3 GeV/c X- Strange Baryons in Nuclear Fields Hypernuclei open a 3rd dimension (strangeness) in the nuclear chart • New Era: high resolution g-spectroscopy • Double-hypernuclei: very little data • Baryon-baryon interactions:L-N only short ranged (no 1p exchange due to isospin) L-L impossible in scattering reactions K+K Trigger p secondary target • X-(dss)p(uud)L(uds)L(uds)

17. Summary • Hadron masses are mostly due to their interaction with the QCD vacuum. • There is evidence for partial restoration of chiral symmetry for pions and kaons. • Antiproton – Nucleus interactions allow the charm region to be studied at relatively low momentum. • There is a wide program to measure open charm and dilepton spectroscopy of charmonium states. • Measurements of absorption cross sections possible. • (Double hypernuclei)