PREX 208 Pb Radius Experiment JLab Hall A
PREX : 208 Pb Radius Experiment JLab Hall A Collaboration Proposal to measure the RMS radius of the neutron distribution of lead through parity violating elastic scattering. R. Michaels (JLab), P. A. Souder (Syracuse), G. M. Urciuoli (INFN), C. J. Horowitz (Indiana) http: //hallaweb. jlab. org/parity/prex Low Q 2 elastic e - nucleus scattering E = 850 Me. V Z 0 Couples Mainly to Neutrons : (weak interaction) (T. W. Donnelly, J. Duback, I. Sick). L & R Polarized Electrons (C. J. Horowitz) Applications : • Crab Nebula Fundamental Check of Neutron Star Nuclear Theory • R N is necessary input to precision atomic tests of the Standard Electroweak Model. Pb (Horowitz, Piekarewicz, Carriere) 2 Liquid FP Meaurement at one Q constrains R N Solid Neutron Star Structure • 208 R N constrains pressure of neutron matter. Can predict radius of neutron star and other properties. Input to Atomic PV Expts • (neutron star) Neutron star has a solid crust over a liquid core. TM 1 Thick neutron skin in Pb Low transition density in neutron star. • Heavy nuclei have a neutron skin • Both neutron stars and neutron skins are made from neutron rich matter at similar densities. • Common unknown: Equation of state (EOS) at subnuclear densities. • Neutron radius measurement constrains URCA cooling of NS by determining the density dependence of the symmetry energy. Measurement of R N determines the symmetry energy and its density dependence. (R. J. Furnstahl) Choice of Kinematics Rn-Rp in 208 Pb Experimental Aspects • Spectrometer and Integrating DAQ of HAPPEX • Septum magnet at 6 to increase figure of merit. • New high power Lead Target Proton fraction YP in neutron star as constrained by R N - R P Lead Target 208 Successfully tested at 80 A Pb Liquid Helium Coolant 12 C Electron Beam Diamond Backing: • High Thermal Conductivity • Negligible Systematics Elec Bea n o r t m
- Slides: 1