1 / 55

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 !.

rosina
Download Presentation

Lead ( P b) R adius Ex periment : PREX

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related