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PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Lead ( Pb) Radius Experiment : PREX Z of Weak Interaction : Clean Probe Couples Mainly to Neutrons.

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Presentation on theme: "PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Lead ( Pb) Radius Experiment : PREX Z of Weak Interaction : Clean Probe Couples Mainly to Neutrons."— Presentation transcript:

1 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Lead ( Pb) Radius Experiment : PREX Z of Weak Interaction : Clean Probe Couples Mainly to Neutrons ( T.W. Donnelly, J. Dubach, I Sick ) 0 In PWIA (to illustrate) : w/ Coulomb distortions (C. J. Horowitz) : Pb E = 850 MeV, electrons on lead Elastic Scattering Parity Violating Asymmetry

2 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab A piece of the weak interaction violates parity (mirror symmetry) which allows to isolate it. Negative longitudinal spin Positive longitudinal spin Pb 208 P S (spin) (momentum) Incident electron Target

3 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Parity Violating Asymmetry + 2 Applications of PV : Nucleon Structure (strangeness) -- HAPPEX / G0 Standard Model Tests ( ) -- e.g. Qweak Nuclear Structure (neutron density) : PREX

4 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Measured Asymmetry Weak Density at one Q 2 Neutron Density at one Q 2 Correct for Coulomb Distortions Small Corrections for G n E G s E MEC Assume Surface Thickness Good to 25% (MFT) Atomic Parity Violation Mean Field & Other Models Neutron Stars R n PREX Physics Impact

5 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab PREX in Hall A at JLab CEBAF Hall A Pol. Source Lead Foil Target Spectometers

6 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Impact on Nuclear Physics : What is the size of a nucleus ? Is the size of a heavy nucleus determined by neutrons or by protons ?

7 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Reminder: Electromagnetic Scattering determines Pb 208 (charge distribution)

8 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Z of weak interaction : sees the neutrons 0 proton neutron Electric charge 1 0 Weak charge Analysis is clean, like electromagnetic scattering: 1. Probes the entire nuclear volume 2. Perturbation theory applies

9 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab neutron weak charge >> proton weak charge is small, best observed by parity violation Electron - Nucleus Potential electromagnetic axial Neutron form factor Parity Violating Asymmetry Proton form factor

10 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Neutron Densities Proton-Nucleus Elastic Pion, alpha, d Scattering Pion Photoproduction Magnetic scattering Theory Predictions Fit mostly by data other than neutron densities Involve strong probes Most spins couple to zero. Therefore, PREX is a powerful check of nuclear theory.

11 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab B. Krusche arXiv:nucl-ex/ Sept 2005 Example : Recent Pion Photoproduction This paper obtains Mean Field Theory PREX accuracy !! Proton – Nucleus Elastic:

12 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab ( R.J. Furnstahl ) Measurement at one Q is sufficient to measure R 2 N PREX error bar Why only one parameter ? (next slide…) PREX:

13 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab PREX: pins down the symmetry energy (1 parameter) ( R.J. Furnstahl ) energy cost for unequal # protons & neutrons PREX PREX error bar Pb 208

14 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Impact on Atomic Parity Measures atomic overlap with weak charge. Neutrons carry most weak charge

15 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Atomic Parity Violation Low Q test of Standard Model Needs R to make further progress. 2 N APV Isotope Chain Experiments e.g. Berkeley Yb

16 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Impact on Neutron Stars What is the nature of extremely dense matter ? Do collapsed stars form exotic phases of matter ?

17 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Fig. from J.M. Lattimer & M. Prakash, Science 304 (2004) 536. Inputs: Eq. of state (EOS) Hydrostatics (Gen. Rel.) Typ. Astro. Observations Luminosity L Temp. T Mass M from pulsar timing PREX constraint (with corrections … ) Mass - Radius relationship pressure density

18 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab PREX & Neutron Stars Crab Pulsar ( C.J. Horowitz, J. Piekarweicz ) R calibrates EOS of Neutron Rich Matter Combine PREX R with Obs. Neutron Star Radii Some Neutron Stars seem too Cold N N Crust Thickness Explain Glitches in Pulsar Frequency ? Strange star ? Quark Star ? Cooling by neutrino emission (URCA) 0.2 fm URCA probable, else not Phase Transition to Exotic Core ?

19 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab FP TM1 Solid Liquid Liquid/Solid Transition Density Thicker neutron skin in Pb means energy rises rapidly with density Quickly favors uniform phase. Thick skin in Pb low transition density in star. Neutron Star Crust vs Pb Neutron Skin PREX calibrates the EOS at subnuclear densities. 208 Pb Neutron Star

20 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab 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…

21 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab PREX Constrains Rapid Direct URCA Cooling of Neutron Stars Proton fraction Y p for matter in beta equilibrium depends on symmetry energy S(n). R n in Pb determines density dependence of S(n). The larger R n in Pb the lower the threshold mass for direct URCA cooling. If R n -R p <0.2 fm all EOS models do not have direct URCA in 1.4 M ¯ stars. If R n -R p >0.25 fm all models do have URCA in 1.4 M ¯ stars. R n -R p in 208 Pb If Y p > red line NS cools quickly via direct URCA reaction n p+e+

22 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab PREX: Experiment Design Spokespersons: P.A. Souder, G.M. Urciuoli, R. Michaels Hall A Collaboration Experiment

23 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Hall A at Jefferson Lab Polarized e - Source Hall A

24 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Target Spectro: SQQDQ Hall A Cherenkov cones PMT Compton Moller Polarimeters

25 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab High Resolution Spectrometers Elastic Inelastic detector Q Dipole Quad Spectrometer Concept: Resolve Elastic target

26 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Optimum Kinematics for Lead Parity: E = 850 MeV, = 0.5 ppm. Accuracy in Asy 3% n Fig. of merit Min. error in R maximize: 1 month run 1% in R n

27 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Corrections to the Asymmetry are Mostly Negligible Coulomb Distortions ~20% = the biggest correction. Strangeness Electric Form Factor of Neutron Parity Admixtures Dispersion Corrections Meson Exchange Currents Shape Dependence Isospin Corrections Radiative Corrections Excited States Target Impurities Horowitz, et.al. PRC

28 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Septum Magnets (INFN) Electrons scattered at 6 deg sent to the HRS at 12.5 deg. Superconducting magnets Commissioned

29 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Integrating Detection PMT Calorimeter (for lead, fits in palm of hand) ADC Integrator electrons Integrate in 30 msec helicity period. Deadtime free. 18 bit ADC with < 10 nonlinearity. But must separate backgrounds & inelastics ( HRS). - 4

30 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Lead Target Liquid Helium Coolant Pb C Diamond Backing: High Thermal Conductivity Negligible Systematics Beam, rastered 4 x 4 mm beam

31 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Halfwave plate (retractable, reverses helicity) Laser Pockel Cell flips helicity Gun GaAs Crystal e beam - Rapid, random helicity reversal Electrical isolation from rest of lab Feedback on Intensity Asymmetry Polarized Electron Source

32 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab P I T A Effect at Polarized Source Laser at Pol. Source Polarization I nduced Transport Asymmetry where Transport Asymmetry Intensity Asymmetry drifts, but slope is ~stable. Feedback on (G. D. Cates)

33 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Beam Asymmetries A raw = A det - A Q + E + i x i natural beam jitter (regression) beam modulation (dithering) Slopes from

34 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Energy BPM BPM Y2 BPM Y1 BPM X1 BPM X2 Scale +/- 10 nm Position Diffs avg ~ 1 nm Redundant Monitors Stripline Monitors Resonant Cavities Negligible Systematic Error Helicity Correlated Differences: Position, Angle, Energy slug slug = ~1 day running

35 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Polarimetry Electron only Photon only Preliminary: 2.5% syst ( only) Møller : P e /P e ~ 3 % (limit: foil polarization) Compton : 2% syst. at present 2 analyses based on either electron or photon detection Superlattice: P e =86% ! PREX: 1 % desirable 2 % required

36 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Upgrade of Compton Polarimeter (Nanda, Lhuillier) To reach 1% accuracy: Green Laser (increased sensitivity at low E) Integrating Method (removes some systematics of analyzing power) electrons

37 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab Moller Polarimetry with Atomic Hydrogen Target ( E. Chudakov, V. Luppov, D. Crabb) H atoms Solenoid 8T Trap beam Ultra Cold Traps Polarization ~ 100% Density Lifetime > 10 min Polarimetry 1% stat. err. in 30 min at 30 A Low background High beam currents allowed (100 A) Goal: ~ 0.5 % systematic error

38 PREX UVa Seminar, Nov 2005 R. Michaels Jefferson Lab PREX : Summary Fundamental Nuclear Physics HAPPEX to demonstrate most technical aspects Polarimetry Upgrade needed PREX test run Nov 2005 (this weekend !) Experiment Runs in 2007 ?


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