Transcript Slide 1
Parity Violation at Jefferson Lab PREX, MOLLER, & PVDIS Experiments Robert Michaels Hall A 1/16 R. Michaels, Jlab DOE S&T 2012 Thomas Jefferson National Accelerator Facility Parity Violating Asymmetry APV R L ~ 104 Q 2 R L 2 e + 208Pb e Z0 APV from interference 208Pb Applications of APV at Jefferson Lab • Nucleon Structure Strangeness s s in proton (HAPPEX, G0 expts) • Test of Standard Model of Electroweak sin e–e This talk (MOLLER) , 2 W e – q (PVDIS) elastic e – p at low Q2 (QWEAK) • Nuclear Structure (neutron density) PREX e R. Michaels, Jlab DOE S&T 2012 208Pb 2/16 How to do a Parity Experiment (integrating method) Flux Integration Technique: Example : HAPPEX HAPPEX: 2 MHz PREX: 500 MHz R. Michaels, Jlab DOE S&T 2012 3/16 Small beam-related Systematics -- thanks to Jlab beam quality • Offline asymmetries nearly identical to online. Parity Violating Asymmetry • Errors are statistical only Asymmetry (ppm) • Corrections tiny (here, 3 ppb) HAPPEX-II data D. Lhuillier, K. Kumar spokespersons Slug (~1 day) Araw = -1.58 ppm 0.12 (stat) 0.04 (syst) HAPPEX-II data R. Michaels, Jlab DOE S&T 2012 (HWP = optical element used to flip beam helicity, helps suppress some systematics) 4/16 Parity Quality Beam : Unique Strength of JLab Helicity – Correlated Position Differences X R X L for helicity L, R Plotted below Araw = Adet - AQ + E+ i xi Sign flips provide further suppression : Average with signs = what experiment feels achieved < 5 nm R. Michaels, Jlab DOE S&T 2012 Units: microns Points: Not sign-corrected. 20-50 nm diffs. with pol. source setup & feedback Measured separately Sign flips using ½ wave plate & Wien filter ++ -+ +- -This BPM, Average = 2.4 3.1 nm PREX data Slug # ( ~ 1 day) 5/16 PREX : Z0 of weak interaction : sees the neutrons proton neutron Electric charge 1 0 Weak charge 0.08 1 Neutron form factor FN (Q 2 ) 1 4 T.W. Donnelly, J. Dubach, I. Sick Nucl. Phys. A 503, 589, 1989 C. J. Horowitz, S. J. Pollock, P. A. Souder, R. Michaels Phys. Rev. C 63, 025501, 2001 C.J. Horowitz 3 d r j0 (qr ) N (r ) Parity Violating Asymmetry GF Q 2 A 2 2 FN (Q 2 ) 2 1 4 sin W FP (Q 2 ) 0 R. Michaels, Jlab DOE S&T 2012 6/16 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) ? Rn Rp 0.2 fm R. Michaels, Jlab DOE S&T 2012Crab Pulsar URCA probable, else not 7/16 PREX HRS + septum Results PRL 108 (2012) 112502 Physics Asymmetry A 0.656 ppm Pb target Hall A JLAB 0.060( stat) 0.014(syst ) Pol. Source CEBAF Statistics limited ( 9% ) Systematic error goal achieved ! (2%) HRS Septum Magnet Pb target R. Michaels, Jlab DOE S&T 2012 50 8/16 Asymmetry leads to RN Establishing a neutron skin at ~95 % CL Neutron Skin = RN - RP = 0.33 + 0.16 - 0.18 fm published proposed Spokespersons K. Kumar R. Michaels K. Paschke P. A. Souder G. Urciuoli R. Michaels, Jlab DOE S&T 2012 Also considering a new 48Ca proposal 9/16 12 GeV R. Michaels, Jlab DOE S&T 2012 Parity Program • MOLLER (e-e scattering) • PVDIS • Fundamental tests of electroweak theory (e-q scattering) 10/16 MOLLER Credit: Krishna Kumar Moller (e-e) Scattering: Search for New Physics at the TeV Scale + 11 GeV Beam 5-10 mrad LH2 APV = 35.6 ppb best contact interaction δ(QeW) = ± 2.1 % (stat.) ± 1.0 % (syst.) reach for leptons at low OR high energy 39 2 Luminosity: 3x10 cm /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 R. Michaels, Jlab DOE S&T 2012 11 11/16 SOLID Spectrometer Credit: Paul Souder for PVDIS 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 Q2 (GeV2) Error bar σA/A (%) at bins in Q2, x R. Michaels, Jlab DOE S&T 2012 12/16 Interplay with LHC: New Physics Assume either SUSY or Z’ discovered at LHC Does Supersymmetry provide a candidate for dark matter? MSSM RPV SUSY Not if Nature lies in RPV SUSY space rather than MSSM space Ramsey-Musolf and Su, Phys. Rep. 456 (2008) J. Erler and E. Rojas TeV-Scale Z / •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? R. Michaels, Jlab DOE S&T 2012 13/1613 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) = ± 0.00026 (stat.) ± 0.00012 (syst.) precise enough to affect the central value of the world average R. Michaels, Jlab DOE S&T 2012 14/16 MOLLER Status Director’s Review chaired by C. Prescott: positive endorsement • MOLLER Collaboration Technical Challenges • ~ 150 GHz scattered electron rate – ~ 100 authors, ~ 30 institutions – Expertise from SAMPLE A4, HAPPEX, G0, PREX, Qweak, E158 – Idea is to flip Pockels cell ~ 2 kHz – 4th generation JLab parity experiment – 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 kW @ 85 μA • Full Azimuthal acceptance with lab~ 5 mrad – novel two-toroid spectrometer – radiation hard, highly segmented integrating detectors • Robust and Redundant 0.4% beam polarimetry – Compton and Moller Polarimeters R. Michaels, Jlab DOE S&T 2012 •~ 20M$ project funding sought • 3-4 years construction • 2-3 years running 15/16 thanks, Krishna 15 Kumar 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 ) not discussed nuclei ( neutrons ) PREX • Precision Frontier of Standard Electroweak Model MOLLER, SOLID-PVDIS complementary to LHC. R. Michaels, Jlab DOE S&T 2012 Thomas Jefferson National Accelerator Facility appendix R. Michaels, Jlab DOE S&T 2012 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 R. Michaels, Jlab DOE S&T 2012 Moller Property Upstream 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) 0.229x0.229 (0.128) 2.3x1.5 (0.8) Weight of a coil (lbs) 44 555 7600 Magnetic Forces (lbs) 100 3000 27000 Concept 2 Qweak 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 R. Michaels, Jlab DOE S&T 2012 PREX: 2 Measurement at one Q is sufficient to measure R N ( R.J. Furnstahl ) Why only one parameter ? (next slide…) proposed error R. Michaels, Jlab DOE S&T 2012 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 N Z E(n, x) E(n, x 1/ 2) S (n) (1 2 x 2 ) n n.m. density x ratio proton/neutrons • Slope unconstrained by data 208 • Adding R N from Pb will significantly reduce the dispersion in plot. R. Michaels, Jlab DOE S&T 2012 Thanks, Alex Brown Skx-s15 PREX Workshop 2008 E/N N R. Michaels, Jlab DOE S&T 2012 Thanks, Alex Brown Skx-s20 PREX Workshop 2008 E/N N R. Michaels, Jlab DOE S&T 2012 Thanks, Alex Brown Skx-s25 PREX Workshop 2008 E/N N R. Michaels, Jlab DOE S&T 2012 Lead / Diamond Target Diamond • Three bays • Lead (0.5 mm) sandwiched by diamond (0.15 mm) LiquidJlab He R. •Michaels, DOE S&T 2012 cooling (30 Watts) LEAD Performance of Lead / Diamond Targets melted NOT melted Last 4 days at 70 uA melted Targets with thin diamond backing (4.5 % background) degraded fastest. Thick diamond (8%) ran well and did not melt at 70 uA. Solution: Run with 10 targets. R. Michaels, Jlab DOE S&T 2012 PREX-I Result Systematic Errors Error Source Absolute (ppm) Relative ( %) Physics Asymmetry Polarization (1) 0.0083 1.3 A 0.656 ppm Beam Asymmetries (2) 0.0072 1.1 Detector Linearity 0.0076 1.2 BCM Linearity 0.0010 0.2 Rescattering 0.0001 0 Transverse Polarization 0.0012 0.2 Q2 (1) 0.0028 0.4 Target Thickness 0.0005 0.1 12C 0.0025 0.4 Inelastic States 0 0 TOTAL 0.0140 2.1 Asymmetry (2) (1) Normalization Correction applied (2) Nonzero correction (the rest assumed zero) R. Michaels, Jlab DOE S&T 2012 0.060( stat) 0.014(syst ) Statistics limited ( 9% ) Systematic error goal achieved ! (2%) A physics letter was recently accepted by PRL. PRL 108 (2012) 112502 Improvements for PREX-II Region downstream of target Tungsten Collimator & Shielding HRS-L Septum Magnet Q1 target HRS-R Q1 Location of ill-fated O-Ring which failed & caused significant time loss during PREX-I Jlab PREX-II R. Michaels, DOE S&T 2012 to use all-metal seals Collimators Geant 4 Radiation Calculations scattering chamber PREX-II shielding strategies shielding Number of Neutrons per incident Electron 0 - 1 MeV beamline Energy (MeV) 1 - 10 MeV Strategy ------- PREX-I PREX-II, no shield PREX-II, shielded • Tungsten ( W ) plug Energy (MeV) 0.7 3 0 0 10 - 1200 MeV • Shield the W • x 10 reduction in 0.2 to 10 MeV neutrons R. Michaels, Jlab DOE S&T 2012 Energy (MeV) 49 Polarized Electron Source GaAs Crystal Gun Laser Pockel Cell flips helicity 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 R. Michaels, Jlab DOE S&T 2012 Important Systematic : P I T A Effect Polarization Induced Transport Asymmetry Intensity Asymmetry where Tx Ty AI sin( ) Laser at Pol. Source Tx Ty Transport Asymmetry drifts, but slope is ~ stable. Feedback on R. Michaels, Jlab DOE S&T 2012 28/53 Methods to Reduce Systematics Intensity Asymmetry (ppm) Perfect DoCP Scanning the Pockels Cell voltage = scanning the residual linear polarization (DoLP) Pockels cell voltage offset (V) A rotatable l/2 waveplate downstream of the P.C. allows arbitrary orientation of the ellipse from DoLP R. Michaels, Jlab DOE S&T 2012 A simplified picture: asymmetry=0 corresponds to minimized DoLP at analyzer Pull Plot (example) R. Michaels, Jlab DOE S&T 2012 PREX Data ( A A)/ 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 R. Michaels, Jlab DOE S&T 2012 Horowitz, et.al. PRC 63 025501