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Thomas Jefferson National Accelerator Facility

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1 Thomas Jefferson National Accelerator Facility
Parity Violation at Jefferson Lab PREX, MOLLER, & PVDIS Experiments Robert Michaels Hall A 1/16 Thomas Jefferson National Accelerator Facility

2 Parity Violating Asymmetry
2 + APV from interference 208Pb 208Pb Applications of APV at Jefferson Lab Nucleon Structure Test of Standard Model of Electroweak Nuclear Structure (neutron density) Strangeness s s in proton (HAPPEX, G0 expts) e – e (MOLLER) , e – q (PVDIS) elastic e – p at low Q2 (QWEAK) This talk PREX e Pb 2/16

3 How to do a Parity Experiment
(integrating method) Flux Integration Technique: HAPPEX: 2 MHz PREX: MHz Example : HAPPEX 3/16

4 Small beam-related Systematics -- thanks to Jlab beam quality
Parity Violating Asymmetry Offline asymmetries nearly identical to online. Corrections tiny (here, 3 ppb) Errors are statistical only Asymmetry (ppm) Slug HAPPEX-II data D. Lhuillier, K. Kumar spokespersons (~1 day) Araw = ppm  (stat)  0.04 (syst) HAPPEX-II data (HWP = optical element used to flip beam helicity, helps suppress some systematics) 4/16

5 Araw = Adet - AQ +  E+ i xi
Parity Quality Beam : Unique Strength of JLab Helicity – Correlated Position Differences Plotted below Araw = Adet - AQ +  E+ i xi Measured separately Points: Not sign-corrected nm diffs. with pol. source setup & feedback Sign flips using ½ wave plate & Wien filter This BPM, Average = nm Sign flips provide further suppression : Average with signs = what experiment feels achieved < 5 nm Units: microns PREX data Slug # ( ~ 1 day) 5/16

6 PREX : Z0 of weak interaction : sees the neutrons
T.W. Donnelly, J. Dubach, I. Sick proton neutron Electric charge 1 Weak charge 0.08 Nucl. Phys. A 503, 589, 1989 C. J. Horowitz, S. J. Pollock, P. A. Souder, R. Michaels Phys. Rev. C 63, , 2001 Neutron form factor C.J. Horowitz Parity Violating Asymmetry 6/16

7 PREX & Neutron Stars C.J. Horowitz, J. Piekarewicz RN calibrates equation of state (pressure vs density) of Neutron Rich Matter Combine PREX RN with Observed Neutron Star Radii Phase Transition to “Exotic” Core ? Strange star ? Quark Star ? Some Neutron Stars seem too cold Explained by Cooling by neutrino emission (URCA process) ? 0.2 fm URCA probable, else not 7/16 Crab Pulsar

8 PREX Hall A JLAB CEBAF Pol. Source Results Statistics limited ( 9% )
PRL 108 (2012) HRS + septum Physics Asymmetry Pb target Statistics limited ( 9% ) Systematic error goal achieved ! (2%) HRS Septum Magnet Pb target 50 8/16

9 Asymmetry leads to RN Neutron Skin = RN - RP = 0.33 + 0.16 - 0.18 fm
Establishing a neutron skin at ~95 % CL Neutron Skin = RN - RP = fm published proposed Spokespersons K. Kumar R. Michaels K. Paschke P. A. Souder G. Urciuoli Also considering a new 48Ca proposal 9/16

10 GeV Parity Program MOLLER (e-e scattering) PVDIS (e-q scattering)
Fundamental tests of electroweak theory 10/16

11 MOLLER Credit: Krishna Kumar Moller (e-e) Scattering: Search for New Physics at the TeV Scale + 11 GeV Beam LH2 5-10 mrad APV = 35.6 ppb best contact interaction reach for leptons at low OR high energy δ(QeW) = ± 2.1 % (stat.) ± 1.0 % (syst.) Luminosity: 3x1039 cm2/s! To do better for a 4-lepton contact interaction would require: Giga-Z factory, linear collider, neutrino factory or muon collider Ebeam = 11 GeV 75 μA 80% polarized δ(APV) = 0.73 parts per billion 11/16

12 SOLID Spectrometer for PVDIS
Credit: Paul Souder Standard Model test in the e – quark couplings. Novel window on QCD using a broad kinematic scan to unfold hadronic effects (CSV, higher twist) Project is still at an early planning stage Error bar σA/A (%) at bins in Q2, x Q2 (GeV2) 12/16

13 Interplay with LHC: New Physics
Assume either SUSY or Z’ discovered at LHC Does Supersymmetry provide a candidate for dark matter? MSSM Not if Nature lies in RPV SUSY space rather than MSSM space RPV SUSY Ramsey-Musolf and Su, Phys. Rep. 456 (2008) Virtually all GUT models predict new Z’s LHC reach ~ 5 TeV, but.... For ‘light’ 1-2 TeV, Z’ properties can be extracted Suppose a 1 to 2 TeV heavy Z’ is discovered at the LHC Can we point to an underlying GUT model? J. Erler and E. Rojas / TeV-Scale Z 13/16

14 Interplay with LHC: EW Physics
mW and sin2ϴW are powerful indirect probes of the mH use standard model electroweak radiative corrections to evolve best measurements to Q ~ MZ MOLLER projected δ(sin2θW) = ± (stat.) ± (syst.) precise enough to affect the central value of the world average 14/16

15 MOLLER Status ~ 20M$ project funding sought 3-4 years construction
Director’s Review chaired by C. Prescott: positive endorsement MOLLER Collaboration ~ 100 authors, ~ 30 institutions Expertise from SAMPLE A4, HAPPEX, G0, PREX, Qweak, E158 4th generation JLab parity experiment Technical Challenges ~ 150 GHz scattered electron rate Idea is to flip Pockels cell ~ 2 kHz 80 ppm pulse-to-pulse statistical fluctuations 1 nm control of beam centroid on target Improved methods of “slow helicity reversal” > 10 gm/cm2 liquid hydrogen target 1.5 m: ~ 5 85 μA Full Azimuthal acceptance with ~ 5 mrad novel two-toroid spectrometer radiation hard, highly segmented integrating detectors Robust and Redundant 0.4% beam polarimetry Compton and Moller Polarimeters ~ 20M$ project funding sought 3-4 years construction 2-3 years running 15/16 thanks, Krishna Kumar

16 Thomas Jefferson National Accelerator Facility
Conclusions : Parity-Violation at Jefferson Lab Robert Michaels Hall A Jefferson Lab is a great place to do parity-violation Leverages the strengths of the polarized source and superconducting RF accelerator. Parity experiments provide Unique information about structure of nucleon ( strangeness content ) nuclei ( neutrons ) PREX Precision Frontier of Standard Electroweak Model complementary to LHC. not discussed MOLLER, SOLID-PVDIS Thomas Jefferson National Accelerator Facility

17 appendix

18 MOLLER Spectrometer Design Progress
Magnet Concepts : increased the size of the water cooling hole simplified layout with slightly larger conductor current density fine with sufficient water flow water-cooling achievable weight and magnetic forces modest still need work on support structure and water/electrical connections Ongoing studies (students/postdocs) : optimize the optics position sensitivity studies magnetic forces for asymmetric coils Property Upstream Moller Concept 2 Qweak Field Integral (Tm) 0.15 1.1 0.89 Total Power (kW) 40 765 1340 Current per wire (A) 298 384 9500 Voltage per coil (V) 19 285 18 Current Density (A/cm2) 1200 1550 500 Wire cross section (ID: water hole) (in) 0.229x0.229 (0.128) 2.3x1.5 (0.8) Weight of a coil (lbs) 44 555 7600 Magnetic Forces (lbs) 100 3000 27000 The spectrometer consists of two resistive toroidal magnets. The upstream magnet provides pre-bending in order to enable the hybrid torus to more effectively separate the Moller electrons from the ep-elastic scattered electrons. The hybrid torus has several features which make it stand out. There are multiple current returns in order to focus a large range of Moller electrons angles and energies (5.5 to 17 mrads and 8.25 down to 2.75 GeV, respectively). There is a negative bend at the downstream end to reduce the amount of integral Bdl seen by the lowest energy (highest angle) Mollers. The magnet is relatively long, which allows it to achieve the necessary integral Bdl while still allowing full azimuthal acceptance. There are an odd number of coils so that the fact of identical particle scattering can be exploited to achieve full azimuthal acceptance, with opposite sectors blocked to avoid double-counting.

19 SoLID PVDIS Progress CLEO-II magnet fulfills requirements of SoLID PVDIS and SoLID SIDIS. Preliminary discussions about procuring magnet from Cornell have been started. Baffles: workable concept has been developed for the baffle assembly. GEM prototyping on going at UVa and several Chinese institutions (USTC, CIAE, Tsinghua U, Lanzhou U,IMP). Cherenkov conceptual design with two readout options (PMT/GEM). Shashlyk type EM Calorimeter R&D ongoing by user institutions, collaboration with IHEP from Russia. A Geant4 simulation framework, GEMC, is successfully applied. Analysis Software: Tracking framework and calibration methods being developed Aiming for a Director’s Review in Fall 2012

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

21 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 significantly reduce the dispersion in plot. 208 N

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

23 Thanks, Alex Brown PREX Workshop 2008 Skx-s20 E/N

24 Thanks, Alex Brown PREX Workshop 2008 Skx-s25 E/N

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

26 Performance of Lead / Diamond Targets
melted melted Targets with thin diamond backing (4.5 % background) degraded fastest. Thick diamond (8%) ran well and did not melt at 70 uA. NOT melted Last 4 days at 70 uA Solution: Run with 10 targets.

27 PREX-I Result Statistics limited ( 9% )
Systematic Errors Error Source Absolute (ppm) Relative ( % ) Polarization (1) 0.0083 1.3 Beam Asymmetries (2) 0.0072 1.1 Detector Linearity 0.0076 1.2 BCM Linearity 0.0010 0.2 Rescattering 0.0001 Transverse Polarization 0.0012 Q2 (1) 0.0028 0.4 Target Thickness 0.0005 0.1 12C Asymmetry (2) 0.0025 Inelastic States TOTAL 0.0140 2.1 Physics Asymmetry Statistics limited ( 9% ) Systematic error goal achieved ! (2%) A physics letter was recently accepted by PRL. (1) Normalization Correction applied PRL 108 (2012) (2) Nonzero correction (the rest assumed zero)

28 Septum Magnet Improvements for PREX-II Tungsten Collimator & Shielding
Region downstream of target Tungsten Collimator & Shielding HRS-L Q1 Septum Magnet target HRS-R Q1 Location of ill-fated O-Ring which failed & caused significant time loss during PREX-I  PREX-II to use all-metal seals Collimators

29 Geant 4 Radiation Calculations PREX-II shielding strategies
scattering chamber shielding Number of Neutrons per incident Electron MeV beamline Energy (MeV) PREX-I PREX-II, no shield PREX-II, shielded MeV Strategy Tungsten ( W ) plug Shield the W x 10 reduction in 0.2 to 10 MeV neutrons Energy (MeV) MeV Energy (MeV) 49

30 Polarized Electron Source
Laser GaAs Crystal Pockel Cell flips helicity Gun Halfwave plate (retractable, reverses helicity) - e beam Based on Photoemission from GaAs Crystal Polarized electrons from polarized laser Need : Rapid, random helicity reversal Electrical isolation from the rest of the lab Feedback on Intensity Asymmetry

31 P I T A Effect Intensity Asymmetry
Important Systematic : Polarization Induced Transport Asymmetry Intensity Asymmetry Laser at Pol. Source where Transport Asymmetry drifts, but slope is ~ stable Feedback on 28/53

32 Methods to Reduce Systematics
A simplified picture: asymmetry=0 corresponds to minimized DoLP at analyzer Perfect DoCP Intensity Asymmetry (ppm) Pockels cell voltage D offset (V) Scanning the Pockels Cell voltage = scanning the residual linear polarization (DoLP) A rotatable l/2 waveplate downstream of the P.C. allows arbitrary orientation of the ellipse from DoLP

33 Pull Plot (example) PREX Data

34 Corrections to the Asymmetry are Mostly Negligible
Coulomb Distortions ~20% = the biggest correction. Transverse Asymmetry (to be measured) Strangeness Electric Form Factor of Neutron Parity Admixtures Dispersion Corrections Meson Exchange Currents Shape Dependence Isospin Corrections Radiative Corrections Excited States Target Impurities Horowitz, PRC

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