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Lead ( P b) R adius Ex periment : PREX

First Results from. 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. Graduate Students

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Lead ( P b) R adius Ex periment : PREX

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  1. First Results from 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 Graduate Students Ahmed Zafar, Chun Min Jen, Abdurahim Rakham (Syracuse) Jon Wexler (UMass) Kiadtisak Saenboonruang (UVa) 208Pb Ran March – June 2010 in Hall A

  2. Standard Electroweak Model Symmetries  Lagrangian Gauge bosons Left –handed fermion fields (quarks and leptons) = doublets under SU(2) Right-handed fields = singlets under SU(2) Also 3 fermion families + single complex Higgs doublet Spontaneous symmetry breaking of the Lagrangian. and i = 1,2,3 Parity Violation

  3. A piece of the weak interaction violates parity(mirror symmetry)which allows to isolate it. Incident electron S Target (spin) Positive longitudinal spin P (momentum) Parity Transformation 208 Pb Negativelongitudinalspin

  4. Parity Violating Asymmetry 2 + Applications of PV at Jefferson Lab Applications of PV at Jefferson Lab • Nucleon Structure (strangeness) -- HAPPEX / G0 • Standard Model Tests -- Qweak, Moller • Nuclear Structure (neutron density):PREX

  5. Idea behind PREX 0 Z of Weak Interaction : Clean Probe Couples Mainly to Neutrons ( T.W. Donnelly, J. Dubach, I Sick 1989 ) In PWIA (to illustrate) : w/ Coulomb distortions (C. J. Horowitz) : 5

  6. 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

  7. 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 ?

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

  9. Z of weak interaction : sees the neutrons 0 Analysis is clean, like electromagnetic scattering: 1. Probes the entire nuclear volume 2. Perturbation theory applies 10

  10. 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

  11. 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

  12. PREX: 2 Measurement at one Q is sufficient to measure R N ( R.J. Furnstahl ) Why only one parameter ? (next slide…) proposed error

  13. 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

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

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

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

  17. 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 17

  18. 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)

  19. 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. 19

  20. 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

  21. Pol. Source Hall A CEBAF PREX: The entire lab is the experiment Spectometers Lead Foil Target 21

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

  23. Flux Integration Technique: HAPPEX: 2 MHz PREX: 500 MHz How to do a Parity Experiment (integrating method) Example : HAPPEX

  24. Pull Plot (example) PREX Data

  25. Polarized Electron Source Laser GaAs Crystal Pockel Cell flips helicity Halfwave plate (retractable, reverses helicity) Gun - e beam • Rapid, random helicity reversal • Electrical isolation from rest of lab • Feedback on Intensity Asymmetry

  26. 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

  27. Intensity Feedback Adjustments for small phase shifts to make close to circular polarization Low jitter and high accuracy allows sub-ppm cumulative charge asymmetry in ~ 1 hour ~ 2 hours 27

  28. Perfect DoCP A simplified picture: asymmetry=0 corresponds to minimized DoLP at analyzer Intensity Asymmetry (ppm) Pockels cell voltage D offset (V) Methods to Reduce Systematics Scanning the Pockels Cell voltage = scanning the retardation phase = scanning residual DoLP Voltage change of 58 Volts, added to both the + and - voltages, would zero the asymmetry. A rotatable l/2 waveplate downstream of the P.C. allows arbitrary orientation of DoLP

  29. 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 Joe Grames, et. al.

  30. “Spin Flipper” Joe Grames et.al. MFG1I04B = -45° or +45° MFG1I04A = -45° or +45° V-Wien = +90°

  31. Beam Asymmetries Araw = Adet - AQ + E+ ixi • natural beam jitter (regression) • beam modulation (dithering) Slopes from 31

  32. Charge Asymmetry 0.087 +/- 0.151 ppm ppm Slug # ( ~ 1 day)

  33. Parity Quality Beam ! Helicity – Correlated Position Differences < ~ 3 nm Wien Flips helped ! Points: Not sign corrected Average with signs = what exp’t feels Units: microns Slug # ( ~ 1 day)

  34. Araw = Adet - AQ + E+ ixi Detector slopes measured during run

  35. Hall A Compton Upgrade with Green Laser Sirish Nanda, et. al. • 1 % Polarimetry • at 1 GeV

  36. PREX Compton Polarimeter Results

  37. Magnet and Target Hall A Moller Upgrade Superconducting Magnet from Hall C Saturated Iron Foil Targets 1 % Polarimetry Sasha Glamazdin, et.al. DAQ Upgrade (FADC)

  38. Moller Results Example : Comparing old and new DAQ Thanks, Zafar Ahmed 38

  39. 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

  40. 50 Septum magnet augments the High Resolution Spectrometers Increased Figure of Merit HRS-L HRS-R collimator Septum Magnet collimator target

  41. Collimators inside Q1 Symmetry in all dimensions to 1 mm

  42. PREX Region After Target Top view HRS-L Q1 Septum Magnet target HRS-R Q1 O-Rings which failed and caused significant time loss Collimators

  43. Water Cell : Measure (agrees with survey) Nilanga Liyanage, Seamus Riordan, Kiadtisak Saenboonruang

  44. Q2 Measurements Use constructed position at target for precise correction of beam position 44

  45. Detector Package in HRS PREX Integrating Detectors UMass / Smith DETECTORS

  46. High Resolution Spectrometers 12C 4.4 MeV Momentum (GeV/c)

  47. Pure, Thin 208PbTarget Lead 5- State 2.6 MeV Momentum (GeV/c)

  48. Momentum (GeV/c) Detector integrates the elastic peak. Backgrounds from inelastics are suppressed.

  49. Backgrounds that might re-scatter into the detector ? Detector cutoff Run magnets down: measure inelastic region Run magnets up : measure probability to rescatter No inelastics observed on top of radiative tail. Small systematic for tail.

  50. Lead / Diamond Target Diamond LEAD • Three bays • Lead (0.5 mm) sandwiched by diamond (0.15 mm) • Liquid He cooling (30 Watts) 50

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