Transcript Slide 1
Parity Violating Neutron Densities Z 0 of Weak Interaction : Clean Probe Couples Mainly to Neutrons ( T.W. Donnelly, J. Dubach, I Sick ) 2 Low Q elastic nucleus scattering In PWIA -- but must account for Coulomb distortions (C. J. Horowitz) GF Q 2 A 2 2 dA 3% A PN12 Workshop JLab, Nov 2004 2 F n (Q ) 2 1 4 sin W FP (Q 2 ) dRn 1% Rn R. Michaels Jefferson Lab Parity Violating Asymmetry APV R L R L 2 e + Z0 e Applications : • Nucleon Structure (strangeness) • Nuclear Structure (neutron density) • Standard Model tests ( sin2 W ) PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab 0 Z sees the neutrons proton neutron Electric charge 1 0 Weak charge 0.08 1 PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab PREX in Hall A at JLab Lead Foil Target Polarized eSource Hall A PN12 Workshop JLab, Nov 2004 Pol. Source Hall A CEBAF R. Michaels Jefferson Lab Physics Impact of Lead Parity Measured Asymmetry Correct for Coulomb Distortions Weak Density at one Q 2 Mean Field & Other Models Small Corrections for Atomic Parity Violation G n E s GE MEC 2 Neutron Density at one Q Assume Surface Thickness Good to 25% (MFT) Neutron Stars Rn PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab Lead Parity: pins down the symmetry energy (1 parameter) ( R.J. Furnstahl ) PN12 Workshop JLab, Nov 2004 energy cost for unequal # protons & neutrons R. Michaels Jefferson Lab Pb Parity : Neutron Stars ( C.J. Horowitz, J. Piekarweicz ) R n calibrates EOS of Neutron Rich Matter Crust Thickness Explain Obs. Glitches in Pulsar Frequency ? Combine R n with Neutron Star Radius Exotic Core ? (strange matter, quark star) Some Neutron Stars too Cold Cooling by neutrino emission (URCA) Crab Pulsar ( from hubblesite.org ) PN12 Workshop JLab, Nov 2004 Rn Rp 0.2 fm URCA probable, else not R. Michaels Jefferson Lab Optimum Kinematics for Lead Parity: <A> = 0.5 ppm. E = 850 MeV, Accuracy in Asy 3% 1 month run 1% in Rn PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab High Resolution Spectrometers Spectrometer Concept: Resolve Elastic Elastic detector Inelastic Quad target Dipole PN12 Workshop JLab, Nov 2004 Q Q R. Michaels Jefferson Lab Septum Magnets (INFN) •Superconducting magnets •Commissioned 2003-4 Electrons scattered at 6 deg sent to the HRS at 12.5 deg. PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab Integrating Detection • Integrate in 30 msec helicity period. • Deadtime free. • 18 bit ADC with < 10 • -4 But must separate backgrounds & inelastics ( HRS). Integrator Calorimeter (for lead, fits in palm of hand) PMT PN12 Workshop JLab, Nov 2004 nonlinearity. ADC R. Michaels Jefferson Lab Lead Target 208 Pb Successful ly tested at 80 A Liquid Helium Coolant 12 beam C Diamond Backing: • High Thermal Conductivity • Negligible Systematics PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab Polarized Electron Source Laser GaAs Crystal Gun Pockel Cell Halfwave plate flips helicity (retractable, reverses helicity) e - beam • Rapid, random helicity reversal • Electrical isolation from rest of lab • Feedback on Intensity Asymmetry PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab Beam Asymmetries Araw = Adet - AQ + E+ ixi Slopes from PN12 Workshop JLab, Nov 2004 •natural beam jitter (regression) •beam modulation (dithering) R. Michaels Jefferson Lab Helicity Correlated Differences: Position, Angle, Energy “Energy” BPM Scale +/- 100 nm BPM Y2 Position Diffs avg ~ 10 nm BPM Y1 Negligible Systematic Error BPM X1 BPM X2 PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab Polarimetry Møller: dPe/Pe ~ 3 % (foil polarization) Compton: 2% syst. At present 2 analyses based on either electron or photon detection Electron only Photon only Superlattice: Pe=86% ! PN12 Workshop JLab, Nov 2004 Preliminary: 2.5% syst ( only) R. Michaels Jefferson Lab Upgrade of Compton Polarimeter (Nanda, Lhuillier) To reach 1% accuracy: • Green Laser • Integrating Method PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab Summary -- Neutron Skin • R n is Fundamental to Nuclear Physics • HAPPEX program to demonstrate most technical aspects • Polarimetry Upgrade needed • Planned 2-day test run in 2005 PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab extra slides -- PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab Moller Polarimetry with Atomic Hydrogen Target ( E. Chudakov, V. Luppov) H atoms Ultra Cold Traps • Polarization ~ 100% • Density 3 1015 cm3 Solenoid 8T • Lifetime > 10 min Polarimetry beam Trap • 1% stat. err. in 30 min at 30 A • Low background • High beam currents allowed (100 A) • Goal: ~ 0.5 % systematic error PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab Polarized Source High Pe High Q.E. Low Apower •Optical pumping of solid-state photocathode •High Polarization controls effective analyzing power Intensity Attenuator PN12 Workshop JLab, Nov 2004 Slow helicity reversal Tune residual linear pol. • Pockels cell allows rapid helicity flip •Careful configuration to reduce beam asymmetries. •Slow helicity reversal to further cancel beam asymmetries R. Michaels Jefferson Lab Beam Modulation to Calibrate Sensitivity to Beam Systematics PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab PITA Effect Polarization Induced Transport Asymmetry Intensity Asymmetry AI sin( ) Tx Ty where Tx Ty Laser at Pol. Source Transport Asymmetry drifts, but slope is ~ stable. Feedback on PN12 Workshop JLab, Nov 2004 R. Michaels Jefferson Lab