Medium Modifications of Hadron Properties and Partonic Processes

Abstract

Chiral symmetry is one of the most fundamental symmetries in QCD. It is closely connected to hadron properties in the nuclear medium via the reduction of the quark condensate <bar{q}q>, manifesting the partial restoration of chiral symmetry. To better understand this important issue, a number of Jefferson Lab experiments over the past decade have focused on understanding properties of mesons and nucleons in the nuclear medium, often benefiting from the high polarization and luminosity of the CEBAF accelerator. In particular, a novel, accurate, polarization transfer measurement technique revealed for the first time a strong indication that the bound proton electromagnetic form factors in 4He may be modified compared to those in the vacuum. Second, the photoproduction of vector mesons on various nuclei has been measured via their decay to e+e- to study possible in-medium effects on the properties of the rho meson. In this experiment, no significant mass shift and some broadening consistent with expected collisional broadening for the rho meson has been observed, providing tight constraints on model calculations. Finally, processes involving in-medium parton propagation have been studied. The medium modifications of the quark fragmentation functions have been extracted with much higher statistical accuracy than previously possible.

to appear in J. Phys.: Conf. Proc. "New Insights into the Structure of Matter: The First Decade of Science at Jefferson Lab", eds. D. Higinbotham, W. Melnitchouk, A. Thomas; added references

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• Equation of state for neutron stars in SU(3) flavor symmetry
• Equation of state for neutron stars with hyperons and quarks in relativistic Hartree-Fock approximation
• EoS for massive neutron stars
• Pion structure in the nuclear medium
• Exclusive J/psi and Upsilon photoproduction and the low x gluon
• In-Medium Pion Valence Distributions in a Light-Front Model
• Transverse momentum broadening in semi-inclusive deep inelastic scattering at next-to-leading order
• Impact of medium modification of the nucleon weak and electromagnetic form factors on the neutrino mean free path in dense matter
• Octet baryon electromagnetic form factor double ratios $(G_E^{\ast }/G_M^{\ast })/(G_E/G_M)$ in a nuclear medium
• Study of the in-medium nucleon electromagnetic form factors using a light-front nucleon wave function combined with the quark-meson coupling model
• Rho-meson properties in medium
• Weak interaction axial form factors of the octet baryons in nuclear medium
• Probing of compact baryonic configurations in nuclei in $A(p,\bar{p})X$ reactions and antiproton formation length in nuclear matter
• Electroweak form factors of baryons in dense nuclear matter
• In-medium rho-meson properties in a light-front approach
• In-Medium Pion Valence Distribution Amplitude
• Analysis of ${\gamma }^{\ast }\Lambda \to {\Sigma }^0$ transition in QCD
• Time-like electromagnetic form factors of $\Lambda ,\Sigma$ and ${\Xi }^{+}$ in a light-front quark model