Presentation on theme: "Thomas Jefferson National Accelerator Facility"— Presentation transcript:
1 Thomas Jefferson National Accelerator Facility Lead (208Pb) Radius Experiment : PREXElastic Scattering Parity Violating AsymmetryE = 1 GeV, electrons on leadPAVI – 11ConferenceSpokespersonsKent Paschke, Paul Souder, Krishna Kumar,Guido Urciuoli, Robert Michaels (presenting)PREX-I Results RunApproved PREX-II ProposalFuture : PREX-N ? (N = III, IV, V …)Thomas Jefferson National Accelerator Facility
2 Z0 of weak interaction : sees the neutrons T.W. Donnelly, J. Dubach, I. SickprotonneutronElectric charge1Weak charge0.08Nucl. Phys. A 503, 589, 1989C. J. Horowitz, S. J. Pollock, P. A. Souder, R. MichaelsPhys. Rev. C 63, , 2001Neutron form factorC.J. HorowitzParity Violating Asymmetry
4 PREX Physics Output Mean Field & Other Atomic Parity Violation Models Measured AsymmetryPhysics OutputCorrect for CoulombDistortionsWeak Density at one Q2Mean FieldSmall Corrections forns& OtherAtomic Parity ViolationGGMECEEModels2Neutron Density at one QAssume Surface Thickness Good to 25% (MFT)NeutronStarsSlide adapted from C. HorowitzRn
5 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 ofratio proton/neutronsn.m. densitySlope unconstrained by dataAdding R from Pb will eliminate the dispersion in plot.208N5
9 APV Application: Atomic Parity Violation Low Q test of Standard Model Needs RN (or APV measures RN )2Isotope Chain Experiments e.g. Berkeley YbAPV9
10 PREX & Neutron StarsC.J. Horowitz, J. PiekarewiczRN calibrates equation of state (pressure vs density) of Neutron Rich MatterCombine PREX RN with Observed Neutron Star RadiiFig from: Dany Page J.M. Lattimer & M. Prakash, Science 304 (2004) 536.Phase Transition to “Exotic” Core ?Strange star ? Quark Star ?Some Neutron Stars seem too coldExplained by Cooling by neutrino emission (URCA process) ?0.2 fm URCA probable, else notCrab Pulsar
11 PREX Overview Spectometers Lead Foil Target Hall A JLAB CEBAF Parity: “The entire lab is the experiment”CEBAFHall AJLABPol. SourceSpectometersLead Foil Target
12 Parity Quality Beam ! < ~ 3 nm ( why we love Jlab ! ) Helicity – Correlated Position Differences< ~ 3 nmPoints: Not sign correctedAverage with signs = what exp’t feelsUnits: micronsSlug # ( ~ 1 day)
13 Flips spin without moving the beam ! Double Wien Filter(NEW for PREX)Crossed E & B fields to rotate the spinTwo Wien Spin Manipulators in seriesSolenoid rotates spin +/-90 degrees (spin rotation as B but focus as B2).Flips spin without moving the beam !Electron BeamSPINJoe Grames, et. al.13
14 Hall A Compton Upgrade 1 % Polarimetry at 1 GeV with Green Laser Sirish Nanda, et. al. (Megan Friend’s talk)1 % Polarimetryat GeV
15 Hall A Moller Upgrade < 1 % Polarimetry Magnet and Target Superconducting Magnet from Hall CSaturated Iron Foil Targets< 1 % PolarimetrySasha Glamazdin, et.al. (talk Thurs)DAQ Upgrade (FADC)
16 Hall A High Resolution Spectrometers Resolve Elastic ScatteringDiscriminate Excited StatesElasticdetectorInelasticPure, Thin Pb Target2.6 MeVtargetDipoleDETECTOR footprintQuadsScattered Electron’s Momentum (GeV/c)16
17 Lead / Diamond Target Diamond LEAD Three bays Lead (0.5 mm) sandwiched by diamond (0.15 mm)Liquid He cooling (30 Watts)
18 Performance of Lead / Diamond Targets meltedmeltedTargets with thin diamond backing (4.5 % background) degraded fastest.Thick diamond (8%) ran well and did not melt at 70 uA.NOT meltedLast 4 days at 70 uASolution: Run with 10 targets.
19 + - Beam-Normal Asymmetry in elastic electron scattering i.e. spin transverse to scattering planeyzx+-AT > 0 meansPossible systematic if small transverse spin componentNew results PREXPreliminary !Publication in preparationSmall AT for 208Pb is a big (but pleasant) surprise.AT for 12C qualitatively consistent with 4He and available calculations (1) Afanasev ; (2) Gorchtein & Horowitz19
22 * * Asymmetry leads to RN Establishing a neutron skin at ~90 % CL*Neutron Skin = RN - RP = fmfig from C.J. HorowitzPREX data*Preliminary: Awaiting the “final” acceptance function:
23 PREX-I Result, cont. Neutron Skin = RN - RP = 0.31 + 0.15 - 0.17 fm DATArN - rP (fm)theory: P. RingrN = rPAtomic Number, ADATAPreliminary: Awaiting the “final” acceptance functionA physics letter is in preparation for publication.23
24 PREX-II Approved by PAC (Aug 2011) “A” Rating days run in 2013 / 2014
25 Septum Magnet PREX Region After Target Tungsten Collimator & Shielding Improvements for PREX-IITungsten Collimator & ShieldingHRS-LQ1Septum MagnettargetHRS-RQ1Former O-Ring location which failed & causedtime loss during PREX-I PREX-II to use all-metal sealsCollimators
26 Geant 4 Radiation Calculations PREX-II shielding strategiesJ. Mammei, L. Zanascattering chambershieldingNumber of Neutrons per incident ElectronMeVbeamlineEnergy (MeV)PREX-IPREX-II, no shieldPREX-II, shieldedMeVStrategyTungsten ( W ) plugShield the Wx 10 reduction in0.2 to 10 MeV neutronsEnergy (MeV)MeVEnergy (MeV)26
27 Other Nuclei ? RN Surface thickness RN Surface thickness Shape Dependence ?Surface thicknessParity Violating Electron Scattering Measurements of Neutron DensitiesShufang Ban, C.J. Horowitz, R. MichaelsRNSurface thicknessarXiv: [nucl-th]
28 Possible Future PREX Program ? Each point 30 days stat. error onlyNucleusE (GeV)dRN / RNcomment208Pb11 %PREX-II (approved)48Ca2.2 (1-pass)0.4 %natural 12 GeV exp’t2.62 %surface thickness40Ca0.6 %basic check of theorytin isotope1.8apply to heavy ion1.6 %Not yet proposed.Just a “what if ?”Shufang Ban, C.J. Horowitz, R. MichaelsarXiv: [nucl-th]
29 Future in Hall A at JLab PREX – II ? Early Experiments g2p/GEp 12 mo. Shutdownno promised beamCommissioningSuperBigbite$Beam 1st to Hall AMoller$$$SOLID$$$$PREX – II ?20112012201320142015201620172018
30 PREX : Summary Fundamental Nuclear Physics with many applications PREX-I achieved a 9% stat. error in Asymmetry (original goal : 3 %)Systematic Error Goals Achieved !!Significant time-losses due to O-Ring problem and radiation damagePREX-II approved (runs in or we hope )
32 How to Measure Neutron Distributions, Symmetry Energy Proton-Nucleus ElasticPion, alpha, d ScatteringPion PhotoproductionHeavy ion collisionsRare Isotopes (dripline)Magnetic scatteringPREX (weak interaction)TheoryInvolve strong probesMost spins couple to zero.MFT fit mostly by data other than neutron densities
33 Parity Violating Asymmetry Electron - Nucleus Potentialelectromagneticaxialis small, best observed by parity violation208Pb is spin 0neutron weak charge >> proton weak chargeProton form factorNeutron form factorParity Violating Asymmetry
34 Corrections to the Asymmetry are Mostly Negligible Coulomb Distortions ~20% = the biggest correction.Transverse Asymmetry (to be measured)StrangenessElectric Form Factor of NeutronParity AdmixturesDispersion CorrectionsMeson Exchange CurrentsShape DependenceIsospin CorrectionsRadiative CorrectionsExcited StatesTarget ImpuritiesHorowitz, et.al. PRC
35 Optimum Kinematics for Lead Parity: E = 1 GeV if <A> = 0.5 ppm. Accuracy in Asy 3%Fig. of meritMin. error in Rmaximize:n1 month run1% in Rn(2 months x uA 0.5% if no systematics)5PAVI 09
37 Liquid/Solid Transition Density Neutron Star Crust vs Pb Neutron SkinFPTM1SolidLiquidC.J. Horowitz, J. PiekarawiczNeutron Star208PbThicker neutron skin in Pb means energy rises rapidly with density Quickly favors uniform phase.Thick skin in Pb low transition density in star.
38 Backgrounds that might re-scatter into the detector ? Detector cutoffRun magnets down: measure inelastic regionRun magnets up : measure probability to rescatterNo inelastics observed on top of radiative tail. Small systematic for tail.
39 Pb PREX: pins down the symmetry energy (1 parameter) PREX error bar energy cost for unequal # protons & neutronsPREX error bar( R.J. Furnstahl )Actually, it’s the density dependence of a4 that we pin down.208PbPREX
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