Transcript Slide 1
Lead ( 208 Pb) Radius Experiment : E = 850 MeV, 6 0 electrons on lead PREX Elastic Scattering Parity Violating Asymmetry 0 Z of Weak Interaction : Clean Probe Couples Mainly to Neutrons ( T.W. Donnelly, J. Dubach, I Sick ) In PWIA (to illustrate) : d d 2 F ( Q ) 2 n GF Q d R d L 2 A 1 4 sin W 2 F ( Q ) 2 2 d d P d R d L 0 208Pb w/ Coulomb distortions (C. J. Horowitz) : dA 3% A R. Michaels HE06 July 2006 dRn 1% Rn PREX at Parity Violating Asymmetry APV R L ~ 10 6 R L 2 + e Z0 e Applications of PV at Jefferson Lab • Nucleon Structure (strangeness) -- HAPPEX / G0 • Standard Model Tests ( sin 2 W ) -- e.g. Qweak • Nuclear Structure (neutron density) : PREX R. Michaels HE06 July 2006 PREX at 0 Z of weak interaction : sees the neutrons Analysis is clean, like electromagnetic scattering: 1. Probes the entire nuclear volume 2. Perturbation theory applies proton neutron Electric charge 1 0 Weak charge 0.08 1 R. Michaels HE06 July 2006 PREX at Reminder: Electromagnetic Scattering determines r (charge distribution) 208 Pb r d mb d str 1 R. Michaels HE06 July 2006 2 q fm1 3 PREX at Electron - Nucleus Potential Vˆ (r ) V (r ) 5 A(r ) axial electromagnetic / V (r ) d r Z (r ) | r r | 3 208 / / A(r ) d d | FP (Q 2 ) | 2 d d Mott FP (Q 2 ) 1 4 3 d r j0 (qr ) P (r ) 2 2 (1 4 sin 2 W ) Z P (r ) N N (r ) A(r ) is small, best observed by parity violation Pb is spin 0 Proton form factor GF 1 4 sin 2 W 1 neutron weak charge >> proton weak charge Neutron form factor FN (Q 2 ) 1 4 d 3 r j 0 (qr ) N (r ) Parity Violating Asymmetry d d GF Q 2 d R d L A 2 2 d d d R d L R. Michaels HE06 July 2006 FN (Q 2 ) 2 1 4 sin W FP (Q 2 ) 0 PREX at PREX: 2 Measurement at one Q is sufficient to measure R N ( R.J. Furnstahl ) Why only one parameter ? (next slide…) PREX error bar (1 ) R. Michaels HE06 July 2006 PREX at PREX: pins down the symmetry energy E N Z av a 4 A A ( R.J. Furnstahl ) 2 as / A 1/ 3 ... (1 parameter) energy cost for unequal # protons & neutrons PREX error bar (1 ) 208 Pb PREX R. Michaels HE06 July 2006 PREX at Nuclear Structure: Neutron density is a fundamental observable that remains elusive. Reflects poor understanding of symmetry energy of nuclear matter = the energy cost of N Z E (n, x) E (n, x 1 / 2) S (n) (1 2 x 2 ) x ratio proton/neutrons n n.m. density • Slope unconstrained by data 208 • Adding R N from Pb will eliminate the dispersion in plot. R. Michaels HE06 July 2006 PREX at PREX & Neutron Stars ( C.J. Horowitz, J. Piekarweicz ) R N calibrates EOS of Neutron Rich Matter Crust Thickness Explain Glitches in Pulsar Frequency ? Combine PREX R N with Obs. Neutron Star Radii Phase Transition to “Exotic” Core ? Strange star ? Quark Star ? Some Neutron Stars seem too Cold Cooling by neutrino emission (URCA) Crab Pulsar R. Michaels HE06 July 2006 Rn R p 0.2 fm PREX URCA probable, else not at Neutron EOS and Neutron Star Crust ( C.J. Horowitz, J. Piekarweicz ) Liquid/Solid Transition Density Liquid FP Solid Fig. from J.M. Lattimer & M. Prakash, Science 304 (2004) 536. R. Michaels HE06 July 2006 TM1 • Thicker neutron skin in Pb means energy rises rapidly with density Quickly favors uniform phase. • Thick skin in Pb low transition density in star. PREX at Pb Radius vs Neutron Star Radius ( C.J. Horowitz, J. Piekarweicz ) • The 208Pb radius constrains the pressure of neutron matter at subnuclear densities. • The NS radius depends on the pressure at nuclear density and above. • Most interested in density dependence of equation of state (EOS) from a possible phase transition. • Important to have both low density and high density measurements to constrain density dependence of EOS. – If Pb radius is relatively large: EOS at low density is stiff with high P. If NS radius is small than high density EOS soft. – This softening of EOS with density could strongly suggest a transition to an exotic high density phase such as quark matter, strange matter, color superconductor, kaon condensate… R. Michaels HE06 July 2006 PREX at PREX Constrains Rapid Direct URCA Cooling of Neutron Stars ( C.J. Horowitz, J. Piekarweicz ) • Proton fraction Yp for matter in beta equilibrium depends on symmetry energy S(n). • Rn in Pb determines density dependence of S(n). • The larger Rn in Pb the lower the threshold mass for direct URCA cooling. • If Rn-Rp<0.2 fm all EOS models do not have direct URCA in 1.4 M¯ stars. • If Rn-Rp>0.25 fm all models do have URCA in 1.4 M¯ stars. Rn-Rp in 208Pb If Yp > red line NS cools quickly via direct URCA reaction n p+e+ R. Michaels HE06 July 2006 PREX at Impact on Atomic Parity Violation 2 • Low Q test of Standard Model Isotope Chain Experiments e.g. Berkeley Yb • Needs R N to make further progress. H PNC N 2 GF 2 N (r ) Z (1 4 sin 2 W ) P (r ) e/ 5 e d 3 r 0 APV R. Michaels HE06 July 2006 PREX at Corrections to the Asymmetry are Mostly Negligible • Coulomb Distortions ~20% = the biggest correction. • Transverse Asymmetry (to be measured) • Strangeness • Electric Form Factor of Neutron • Parity Admixtures • Dispersion Corrections • Meson Exchange Currents • Shape Dependence Horowitz, et.al. PRC 63 025501 • Isospin Corrections • Radiative Corrections • Excited States • Target Impurities R. Michaels HE06 July 2006 PREX at PREX: Experimental Issues Spokespersons: P.A. Souder, G.M. Urciuoli, R. Michaels Hall A Collaboration Experiment R. Michaels HE06 July 2006 PREX at PREX in Hall A at JLab Spectometers Lead Foil Target Pol. Source Hall A CEBAF R. Michaels HE06 July 2006 PREX at Hall A at Jefferson Lab Polarized eSource R. Michaels HE06 July 2006 Hall A PREX at High Resolution Spectrometers Spectrometer Concept: Resolve Elastic 1st excited state Pb 2.6 MeV Elastic detector Inelastic Quad Left-Right symmetry to control transverse polarization systematic target Dipole Q Q R. Michaels HE06 July 2006 PREX at 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 R. Michaels HE06 July 2006 PREX at Important Systematic : 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 R. Michaels HE06 July 2006 PREX at Intensity Feedback Adjustments for small phase shifts to make close to circular polarization HAPPEX Low jitter and high accuracy allows sub-ppm Cumulative charge asymmetry in ~ 1 hour ~ 2 hours R. Michaels HE06 July 2006 In practice, aim for 0.1 ppm over duration of data-taking. PREX at Beam Position Corrections (HAPPEX) X Angle BPM Beam Asymmetry Results micron Energy: -0.25 ppb X Target: 1 nm X Angle: 2 nm Y Target : 1 nm Y Angle: <1 nm Corrected and Raw, Left spectrometer arm alone, Superimposed! ppm Total correction for beam position asymmetry on Left, Right, or ALL detector: 10 ppb Spectacular results from HAPPEX-H show we can do PREX. R. Michaels HE06 July 2006 PREX at Integrating Detection • Integrate in 30 msec helicity period. • Deadtime free. • 18 bit ADC with < 10 • -4 nonlinearity. But must separate backgrounds & inelastics ( Integrator Calorimeter (for lead, fits in palm of hand) ADC PMT R. Michaels HE06 July 2006 HRS). PREX at The Raw Asymmetry Flux Integration Technique: HAPPEX: 2 MHz PREX: 850 MHz R. Michaels HE06 July 2006 PREX at Application of Parity Violating Electron Scattering : HAPPEX & Strange Quarks Hall A Proton Parity Experiment Isolating the u, d, s quark structure in protons (and 4 He) Electromagnetic Scattering: GEp, M G n E,M 2 u GE , M 3 1 d 1 GE , M GEs , M 3 3 2 d 1 u 1 s GE , M GE , M GE , M 3 3 3 Parity Violation can Access: 0 1 1 1 Z G sin 2 W GEu , M sin 2 W GEd , M GEs , M p E,M R. Michaels HE06 July 2006 4 4 3 PREX at Preliminary 2006 Results Raw Parity Violating Asymmetry Araw correction ~11 ppb Asymmetry (ppm) 1H Helicity Window Pair Asymmetry Slug Q2 = 0.1089 ± 0.0011GeV2 Araw = -1.418 ppm 0.105 ppm (stat) R. Michaels HE06 July 2006 PREX at Strange FF near ~0.1 GeV2 GMs = 0.28 +/- 0.20 GEs = -0.006 +/- 0.016 ~3% +/- 2.3% of proton magnetic moment ~0.2 +/- 0.5% of electric distribution Preliminary R. Michaels HE06 July 2006 PREX at Polarimetry Accuracy : Hydrogen: 86.7% ± 2% 2 % required, 1% desired Preliminary Møller : dPe/Pe ~ 3 % (limit: foil polarization) (a high field target ala Hall C being considered) Helium: 84.0% ± 2.5% Compton 2% syst. Prelim. HAPPEX Results R. Michaels HE06 July 2006 PREX at e at present : Upgrade of Compton Polarimeter To reach 1% accuracy: • Green Laser (increased sensitivity at low E) laser on-hand, being tested • Integrating Method (removes some systematics of analyzing power) developed during HAPPEX & in 2006 • New Photon Detector R. Michaels HE06 July 2006 PREX at Optimum Kinematics for Lead Parity: <A> = 0.5 ppm. E = 850 MeV, Accuracy in Asy 3% Fig. of merit Min. error in Rn maximize: 1 month run 1% in R n R. Michaels HE06 July 2006 PREX at Lead Target 208 Pb Successful ly tested at 80 A Liquid Helium Coolant 12 beam C Diamond Backing: • High Thermal Conductivity • Negligible Systematics R. Michaels HE06 July 2006 PREX at PREX : Summary • Fundamental Nuclear Physics with many applications • HAPPEX & test runs have demonstrated technical aspects • Polarimetry Upgrade needed • Will run 1 month in 2008 R. Michaels HE06 July 2006 PREX at Extra Slides R. Michaels HE06 July 2006 PREX at PREX Physics Impact 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 Heavy Ions Stars Rn R. Michaels HE06 July 2006 PREX at 4He Raw Parity Violating Asymmetry Araw correction ~ 0.12 ppm Helicity Window Pair Asymmetry Asymmetry (ppm) Preliminary 2006 Results Slug Q2 = 0.07725 ± 0.0007 GeV2 Araw = 5.253 ppm 0.191 ppm (stat) R. Michaels HE06 July 2006 PREX at Optimization for Barium -- of possible direct use for Atomic PV 1 GeV optimum R. Michaels HE06 July 2006 PREX at Num. events 208 Pb Elastic Detector 1st Excited State (2.6 MeV) Momentum (MeV) Data taken Nov 2005 • Check rates • Backgrounds (HRS is clean) • Sensitivity to beam parameters • Width of asymmetry Num. events A 1 R. Michaels HE06 Lead Target Tests July 2006 • HRS resolution • Detector resolution PREX at I Neutron Skin and Heavy – Ion Collisions • Impact on Heavy - Ion physics: constraints and predictions • Imprint of the EOS left in the flow and fragmentation distribution. Danielewicz, Lacey, and Lynch, Science 298 (2002) 1592. R. Michaels HE06 July 2006 PREX at Example : Recent Pion Photoproduction B. Krusche arXiv:nucl-ex/0509003 Sept 2005 This paper obtains RP !! RN Proton – Nucleus Elastic: 0.083 RN RP 0.111 fm Mean Field Theory 0.05 RN RP 0.35 fm PREX accuracy d RN 0.05 fm R. Michaels HE06 July 2006 PREX at Transverse Polarization Part I: Left/Right Asymmetry Transverse Asymmetry AT AT0 PT sin Systematic Error for Parity Theory est. (Afanasev) A 5 1 ppm 0 T Transverse polarization PT P sin 3o HRS-Left P d A d AT0 PT “Error in” Left-right apparatus asymmetry Control w/ slow feedback on polarized source solenoids. d AT0 1 ppm HRS-Right Need measure in ~ 1 hr (+ 8 hr setup) PT << 10 3 10 3 correction R. Michaels HE06 July 2006 PREX syst. err. at Transverse Polarization Part II: Up/Down Asymmetry Vertical misalignment cos 0 Systematic Error for Parity d A d AT0 PT cos Horizontal polarization e.g. from (g-2) • Measured in situ using 2-piece detector. PT P sin up/down misalignment HRS-Left P • Wien angle feedback ( July 2006 ) Need HRS-Right PT cos << 10 3 10 3 R. Michaels HE06 • Study alignment with tracking & M.C. ( Note, beam width is very tiny PREX at ~ 100 m ) Noise • Need 100 ppm per window pair • Position noise already good enough • New 18-bit ADCs Will improve BCM noise. • Careful about cable runs, PMTs, grounds. Will improve detector noise. • Plan: Tests with Luminosity Monitor to demonstrate capability. R. Michaels HE06 July 2006 PREX at Warm Septum Existing superconducting septum won’t work at high L Warm low energy (1 GeV) magnet designed. Grant proposal in preparation (~100 k$) [Syracuse / Smith College] TOSCA design P resolution ok R. Michaels HE06 July 2006 PREX at 2 Measurement at one Q is sufficient to measure R N Pins down the symmetry energy (1 parameter) PREX accuracy PREX accuracy ( R.J. Furnstahl ) R. Michaels HE06 July 2006 PREX at