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Lead ( P b) R adius Ex periment : PREX

Lead ( P b) R adius Ex periment : PREX. 208. Elastic Scattering Parity Violating Asymmetry. E = 1 GeV , electrons on lead. Spokespersons Paul Souder Krishna Kumar Guido Urciuoli Robert Michaels. 208 Pb. Run in March 2010 !.

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Lead ( P b) R adius Ex periment : PREX

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

  2. Idea behind PREX 0 Z 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) :

  3. Measured Asymmetry PREX Physics Output Correct for Coulomb Distortions 2 Weak Density at one Q Mean Field Small Corrections for s n & Other G MEC G Atomic Parity Violation E E Models 2 Neutron Density at one Q Assume Surface Thickness Good to 25% (MFT) Neutron Stars Slide adapted from C. Horowitz R n

  4. Fundamental Nuclear Physics:What is the size of a nucleus ? Neutrons are thought to determine the size of heavy nuclei like 208Pb. Can theory predict it ?

  5. Reminder: Electromagnetic Scattering determines (charge distribution) 208 Pb 1 2 3

  6. Z of weak interaction : sees the neutrons 0 Analysis is clean, like electromagnetic scattering: 1. Probes the entire nuclear volume 2. Perturbation theory applies

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

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

  9. 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 • Adding R from Pb will eliminate the dispersion in plot. 208 N

  10. Thanks, Alex Brown PREX Workshop 2008 Skx-s15 E/N

  11. Thanks, Alex Brown PREX Workshop 2008 Skx-s20

  12. Thanks, Alex Brown PREX Workshop 2008 Skx-s25

  13. Interpretation of PREX Acceptance

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

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

  16. pressure density 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.

  17. PREX & Neutron Stars ( C.J. Horowitz, J. Piekarewicz ) R calibrates EOS of Neutron Rich Matter N Crust Thickness Explain Glitches in Pulsar Frequency ? Combine PREX R with Obs. Neutron Star Radii N Phase Transition to “Exotic” Core ? Strange star ?Quark Star ? Some Neutron Stars seem too Cold Cooling by neutrino emission (URCA) 0.2 fm URCA probable, else not Crab Pulsar

  18. Pol. Source Hall A CEBAF PREX Design Spectometers Lead Foil Target

  19. Polarized e- Source Hall A Hall A at Jefferson Lab

  20. 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

  21. 50 Septum magnet augments the High Resolution Spectrometers Increased Figure of Merit HRS-L HRS-R collimator Septum Magnet collimator target L / R HRS control vertical A_T. What about horizontal ?

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

  23. 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 McNulty Krishna Kumar Paul Souder

  24. Measure θ from Nuclear Recoil δE=Energy loss E=Beam energy MA=Nuclear mass θ=Scattering angle Scattered Electron Energy (GeV) Recoil is large for H, small for nuclei (3X better accuracy than survey)

  25. P I T AEffect Important Systematic : Polarization Induced Transport Asymmetry Intensity Asymmetry Laser at Pol. Source where Transport Asymmetry drifts, but slope is ~ stable. Feedback on See talk by Gordon Cates

  26. Double Wien Filter (NEW for PREX) 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 B2). • Flips spin without moving the beam ! Electron Beam SPIN See talk by Riad Suleiman

  27. Beam Asymmetries Araw = Adet - AQ + E+ ixi • natural beam jitter (regression) • beam modulation (dithering) Slopes from

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

  29. X Angle BPM Final Beam Position Corrections(HAPPEX-H) Beam Asymmetry Results Energy: -0.25 ppb X Target: 1 nm X Angle: 2 nm Y Target : 1 nm Y Angle: <1 nm micron Corrected and Raw, Left spectrometer arm alone, Superimposed! Total correction for beam position asymmetry on Left, Right, or ALL detector:10 ppb ppm Spectacular results from HAPPEX-H show we can do PREX.

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

  31. PREX Integrating Detectors UMass / Smith DETECTORS

  32. Lead Target (2 x I in proposal) 208 Pb Liquid Helium Coolant 12 beam C Diamond Backing: • High Thermal Conductivity • Negligible Systematics Beam, rastered 4 x 4 mm

  33. Target Assembly

  34. Lead Target Tests 208 Pb Elastic Low Rate at E = 1.1 GeV Detector Num. events 1st Excited State (2.6 MeV) • Check rates • Backgrounds (HRS is clean) • Sensitivity to beam parameters • Width of asymmetry • HRS resolution • Detector resolution Momentum (MeV) Num. events Y (m) X (dispersive coord) (m)

  35. 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. . (HAPPEX data) Test: Use the “Luminosity Monitor” to demonstrate noise (next slide)

  36. Luminosity Monitor • A source of extremely high rate • Established noise floor of 50 ppm

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

  38. Extra Slides

  39. “What if ’’ Scenarios Assuming other systematics are negligible

  40. Optimum Kinematics for Lead Parity: E = 1 GeV if <A> = 0.5 ppm. Accuracy in Asy 3% Fig. of merit Min. error in R maximize: n 1 month run 1% in R n (2 months x 100 uA  0.5% if no systematics) 5

  41. Hydrogen: 86.7% ± 2% Helium: 84.0% ± 2.5% PolarimetryAccuracy :1% from 2 methods Møller (New High-field design ) Compton HAPPEX Compton Polarimety Measuremens

  42. (slide from C. Horowitz) Pb Radius vs Neutron Star Radius • 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…

  43. Asymmetries in Lumi Monitors after beam noise subtraction ~ 50 ppm noise per pulse  milestone for electronics ( need << 120 ppm) Jan 2008 Data

  44. Liquid FP Solid TM1 Liquid/Solid Transition Density Neutron Star Crust vs Pb Neutron Skin • Thicker neutron skin in Pb means energy rises rapidly with density  Quickly favors uniform phase. • Thick skin in Pb  low transition density in star. C.J. Horowitz, J. Piekarawicz Neutron Star 208Pb

  45. PREX: pins down the symmetry energy (1 parameter) energy cost for unequal # protons & neutrons PREX error bar ( R.J. Furnstahl ) Actually, it’s the density dependence of a4 that we pin down. 208 Pb PREX

  46. (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. Rn-Rp in 208Pb If Yp > red line NS cools quickly via direct URCA reaction n p+e+

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

  48. Hall A Polarimeters Cherenkov cones Compton Moller PMT Target Spectro: SQQDQ

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

  50. At 50the new Optimal FOM is at 1.05 GeV (+/- 0.05) (when accounting for collimating small angle, not shown) 1% @ ~1 GeV

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