Lead 208 Pb Radius Experiment PREX Elastic Scattering

Lead ( 208 Pb) Radius Experiment : PREX Elastic Scattering Parity Violating Asymmetry E = 1 Ge. V, electrons on lead Spokespersons • Paul Souder • Krishna Kumar • Guido Urciuoli • Robert Michaels 208 Pb Run in March 2010 ! R. Michaels PAVI 09 PREX at

Idea behind Z 0 PREX of Weak Interaction : Clean Probe Couples Mainly to Neutrons ( T. W. Donnelly, J. Dubach, I Sick ) In PWIA (to illustrate) : w/ Coulomb distortions (C. J. Horowitz) : R. Michaels PAVI 09 PREX at

PREX Physics Output 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) Slide adapted from C. Horowitz R. Michaels PAVI 09 Neutron Stars Rn PREX at

Fundamental Nuclear Physics : What is the size of a nucleus ? Neutrons are thought to determine the size of heavy nuclei like 208 Pb. Can theory predict it ? R. Michaels PAVI 09 PREX at

Reminder: Electromagnetic Scattering determines (charge distribution) 208 1 R. Michaels PAVI 09 Pb 2 3 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 R. Michaels PAVI 09 proton neutron Electric charge 1 0 Weak charge 0. 08 1 PREX at

Electron - Nucleus Potential electromagnetic 208 Pb is spin 0 axial is small, best observed by parity violation neutron weak charge >> proton weak charge Proton form factor Neutron form factor Parity Violating Asymmetry R. Michaels PAVI 09 PREX at

PREX: 2 Measurement at one Q is sufficient to measure R N ( R. J. Furnstahl ) Why only one parameter ? (next slide…) proposed error * R. Michaels PAVI 09 * 2/3 this error if 100 u. A, d. Pe/Pe = 1% PREX at

Slide adapted from J. Piekarewicz Nuclear Structure: Neutron density is a fundamental observable that remains elusive. Reflects poor understanding of symmetry energy of nuclear matter = the energy cost of ratio proton/neutrons n. m. density • Slope unconstrained by data 208 • Adding R N from Pb will eliminate the dispersion in plot. R. Michaels PAVI 09 PREX at

Thanks, Alex Brown PREX Workshop 2008 Skx-s 15 E/N R. Michaels PAVI 09 PREX at

Thanks, Alex Brown PREX Workshop 2008 R. Michaels PAVI 09 Skx-s 20 PREX at

Thanks, Alex Brown PREX Workshop 2008 R. Michaels PAVI 09 Skx-s 25 PREX at

Interpretation of PREX Acceptance R. Michaels PAVI 09 PREX at

Application: Atomic Parity Violation • Low Q 2 test of Standard Model • Needs RN (or APV measures RN ) Isotope Chain Experiments e. g. Berkeley Yb APV R. Michaels PAVI 09 PREX at

Application : Neutron Stars What is the nature of extremely dense matter ? Do collapsed stars form “exotic” phases of matter ? (strange stars, quark stars) Crab Nebula R. Michaels PAVI 09 (X-ray, visible, radio, infrared) PREX at

re ity su de ns es pr Inputs: Eq. of state (EOS) PREX helps here Hydrostatics (Gen. Rel. ) Astrophysics Observations Luminosity L Temp. T Mass M from pulsar timing (with corrections … ) Mass - Radius relationship Fig from: Dany Page. J. M. Lattimer & M. Prakash, Science 304 (2004) 536. R. Michaels PAVI 09 PREX at

PREX & Neutron Stars ( C. J. Horowitz, J. Piekarewicz ) 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 PAVI 09 0. 2 fm URCA probable, else not PREX at

PREX Design Spectometers Lead Foil Target Pol. Source Hall A CEBAF R. Michaels PAVI 09 PREX at

Hall A at Jefferson Lab Polarized e. Source R. Michaels PAVI 09 Hall A PREX at

High Resolution Spectrometers Spectrometer Concept: Resolve Elastic 1 st excited state Pb 2. 6 Me. V Elastic detector Inelastic Quad Left-Right symmetry to control transverse polarization systematic target Dipole Q Q R. Michaels PAVI 09 PREX at

50 Septum magnet augments the High Resolution Spectrometers HRS-L Increased Figure of Merit HRS-R Se collimator ptu m Ma collimator gn et target L / R HRS control vertical A_T. What about horizontal ? R. Michaels PAVI 09 PREX at

Collimator at entrance to spectrometer Suppressing A_T systematics Paul Souder A_T hole Be degrader Aligned in spectrometers to define identical Left / Right scattering angles as well as good up / down symmetry Insertable blocker to block Be R. Michaels PAVI 09 PREX at

Events from A_T hole (Be plug) Main detector A_T detector Measures horizontal A_T systematic. (Vertical is measured from Left/Right spectrometers) Thanks: Dustin Mc. Nulty Krishna Kumar Paul Souder R. Michaels PAVI 09 PREX at

Measure θ from Nuclear Recoil δE=Energy loss E=Beam energy MA=Nuclear mass θ=Scattering angle Scattered Electron Energy (Ge. V) Recoil is large for H, small for nuclei (3 X better accuracy than survey) R. Michaels PAVI 09 PREX at

Important Systematic : PITA Effect Polarization Induced Transport Asymmetry Intensity Asymmetry Laser at Pol. Source where Transport Asymmetry drifts, but slope is ~ stable. Feedback on R. Michaels PAVI 09 See talk by Gordon Cates PREX at

(NEW for PREX) Double Wien Filter Crossed E & B fields to rotate the spin • Two Wien Spin Manipulators in series • Solenoid rotates spin +/-90 degrees (spin rotation as B but focus as B 2). Flips spin without moving the beam ! Electron Beam SPIN R. Michaels PAVI 09 See talk by Riad Suleiman PREX at

Beam Asymmetries Araw = Adet - AQ + E+ i xi Slopes from R. Michaels PAVI 09 • natural beam jitter (regression) • beam modulation (dithering) PREX at

The Corrections Work ! X Angle BPM ppm With corrections micron Helicity-corr. Position diff Shown : period of data during HAPPEX (4 He) when beam had a helicity-correlated position due to a mistake * in electronics. Helicity signal to driver reversed Helicity signal to driver removed Raw ALL Asymetry * The mistake: Helicity signal deflecting the beam through electronics “pickup” R. Michaels PAVI 09 PREX at

Final Beam Position Corrections (HAPPEX-H) 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 PAVI 09 PREX at

Redundant position measurements at the ~1 nm level (i) Stripline monitors (2 pairs of wires) (ii) Resonant microwave cavities Y (cavity) X (stripline) R. Michaels PAVI 09 HAPPEX 2005 nm nm (Helicity – correlated differences averaged over ~1 day) nm Y (stripline) PREX at nm

PREX Integrating Detectors UMass / Smith DETECTORS R. Michaels PAVI 09 PREX at

Lead Target 208 (2 x I in proposal) Pb Liquid Helium Coolant 12 beam C Diamond Backing: • High Thermal Conductivity • Negligible Systematics m red e rast , m Bea R. Michaels PAVI 09 m 4 x 4 PREX at

Target Assembly R. Michaels PAVI 09 PREX at

Num. events 208 Lead Target Tests Pb Elastic Low Detector at Rate E = 1. 1 Ge. V 1 st Excited State (2. 6 Me. V) Num. events Momentum (Me. V) Y (m ) R. Michaels PAVI 09 X d) e coor v i s r e p (dis • Check rates • Backgrounds (HRS is clean) • Sensitivity to beam parameters • Width of asymmetry • HRS resolution • Detector resolution (m) PREX at

Noise (integrating at 30 Hz) • PREX: ~120 ppm Want only counting statistics noise, all others << 120 ppm • New 18 -bit ADCs • . improve beam noise. Careful about cable runs, PMTs, grounds loops. Test: (HAPPEX data) Use the “Luminosity Monitor” to demonstrate noise (next slide) R. Michaels PAVI 09 PREX at

Luminosity Monitor A source of extremely high rate Established noise floor of 50 ppm R. Michaels PAVI 09 PREX at

PREX : Summary • Fundamental Nuclear Physics with many applications • HAPPEX & test runs have demonstrated technical aspects • Polarimetry Upgrade critical • 2 month run starting March 2010 R. Michaels PAVI 09 PREX at

Extra Slides R. Michaels PAVI 09 PREX at

“What if ’’ Scenarios Assuming other systematics are negligible 50 u. A 30 days 100 u. A 60 days R. Michaels PAVI 09 d. Pe/Pe = 1% d. Pe/Pe = 2% 1% 1. 2 % 0. 6 0. 8 % d. RN/RN - % PREX at

Optimum Kinematics for Lead Parity: <A> = 0. 5 ppm. E = 1 Ge. V if Accuracy in Asy 3% Fig. of merit Min. error in R n maximize: 1 month run 1% in R (2 months x 100 u. A 0. 5% if no systematics) 5 R. Michaels PAVI 09 n PREX at

Polarimetry Accuracy : 1% from 2 methods Hydrogen: 86. 7% ± 2% Møller (New High-field design ) Compton Helium: 84. 0% ± 2. 5% HAPPEX Compton Polarimety Measuremens R. Michaels PAVI 09 PREX at

(slide from C. Horowitz) Pb Radius vs Neutron Star Radius • The 208 Pb 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 PAVI 09 PREX at

Asymmetries in Lumi Monitors after beam noise subtraction ~ 50 ppm noise per pulse milestone for electronics ( need << 120 ppm) Jan 2008 Data R. Michaels PAVI 09 PREX at

Neutron Star Crust vs Pb Neutron Skin Liquid/Solid Transition Density C. J. Horowitz, J. Piekarawicz Liquid FP Neutron Star 208 Pb Solid TM 1 • Thicker neutron skin in Pb means energy rises rapidly with density Quickly favors uniform phase. • Thick skin in Pb low transition density in star. R. Michaels PAVI 09 PREX at

PREX: pins down the symmetry energy (1 parameter) energy cost for unequal # protons & neutrons ( R. J. Furnstahl ) 208 PREX error bar Actually, it’s the density dependence of a 4 that we pin down. Pb PREX R. Michaels PAVI 09 PREX at

(slide from C. Horowitz) PREX Constrains Rapid Direct URCA Cooling of Neutron Stars • 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. R. Michaels PAVI 09 Rn-Rp in 208 Pb If Yp > red line NS cools quickly via direct URCA reaction n p+e+ PREX at

How to Measure Neutron Distributions, Symmetry Energy • • • Proton-Nucleus Elastic Pion, alpha, d Scattering Pion Photoproduction Heavy ion collisions Rare Isotopes (dripline) • Magnetic scattering • PREX • Theory R. Michaels PAVI 09 Involve strong probes Most spins couple to zero. (weak interaction) MFT fit mostly by data other than neutron densities PREX at

Hall A Cherenkov cones PMT Polarimeters Compton Moller Target R. Michaels PAVI 09 Spectro: SQQDQ PREX at

Heavy Ions (adapted from Betty Tsang, PREX Workshop) R. Michaels PAVI 09 Isospin Diffusion (NSCL) Probe the symmetry energy in 124 Sn + 112 Sn PREX at

At 50 the new Optimal FOM is at 1. 05 Ge. V (+/- 0. 05) (when accounting for collimating small angle, not shown) 1% @ ~1 Ge. V R. Michaels PAVI 09 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 PAVI 09 PREX at

Successful Results of beam tests Jan 2008 Good energy resolution R. Michaels PAVI 09 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 PAVI 09 In practice, aim for 0. 1 ppm over duration of data-taking. PREX at

Optimization for Barium -- of possible direct use for Atomic PV 1 Ge. V optimum R. Michaels PAVI 09 PREX at

Warm Septum Existing superconducting septum won’t work at high L Warm low energy (1 Ge. V) magnet designed. Grant proposal in preparation (~100 k$) [Syracuse / Smith College] TOSCA design P resolution ok R. Michaels PAVI 09 PREX at