Parity-violating Electron Scattering and Strangeness in the Nucleon: - PowerPoint PPT Presentation

Parity-violating Electron Scattering and Strangeness in the Nucleon: Results from HAPPEX-II …with apologies: this is a repeat …with apologies: this is a repeat of my Physics seminar, without of my Physics seminar, without particular focus on accelerator issues particular focus on accelerator issues Kent Paschke University of Massachusetts, Amherst For the HAPPEX Collaboration Thomas Jefferson National Accelerator Facility – Argonne National Laboratory – CSU, Los Angeles -William and Mary – Duke – DSM/DAPNIA/SPhN CEA Saclay - FIU – Harvard - INFN, Rome - INFN, Bari – IAE, Beijing – IPT Kharkov - Jozef Stefan Institute – Kent State - MIT – NPIRAS, St. Petersburg – ODU – Rutgers - Smith College – Syracuse – Temple – U. Blaise Pascal – U. of Illinois Urbana-Champaign – UMass, Amherst – U. of Kentucky – U. of Virginia – UST, Heifei

Strange Quarks in the Nucleon Strange Sea measured in ν N scattering Strange sea is well-known, but contributions to nucleon matrix elements are somewhat unsettled Spin polarized DIS γ μ γ 5 N s s N Inclusive: Δ s = -0.10 ± 0.06 uncertainties from SU(3), extrapolation Semi-inclusive: Δ s = 0.03 ± 0.03 fragmentation function Strange mass N s s N π N scattering: 0-30% μ Strange vector FF γ N s s N Kent Paschke – University of Massachusetts April 27, 2006

PV Electron Scattering to Measure Weak NC Amplitudes [ ] πα G 4 = λ μ + λ μ μ = λ NC 5 NC NC EM EM F M g J g J M Q J l μ μ μ PV A V 5 2 2 2 Q Interference with EM amplitude makes NC amplitude accessible γ Z 0 NC σ − σ M 2 Q PV = R L ~ ~ A ~ ( ) γ σ + σ PV 2 2 EM M M R L Z Kent Paschke – University of Massachusetts April 27, 2006

Flavor Separation of Nucleon Form Factors ∑ Γ G ~ N e q q N 2 1 1 μ γ = − − i i i , p u , p d , p s , p G G G G i E M E M E M E M / / / / 3 3 3 (assumes heavy quarks are negligible) , , p G γ γ Measuring n , cannot separate all three flavors G Adding in a measurement of Z p , G ⎞ ⎛ − ⎞ ⎛ − ⎞ ⎛ − 8 4 4 = θ − θ − θ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ Z 2 u 2 d 2 s G 1 sin G 1 sin G 1 sin G E M W E M W E M W E M / / / / ⎝ ⎠ ⎝ ⎠ ⎝ ⎠ 3 3 3 = u , p d , n G G and assuming charge symmetry = d , p u , n G G = s , p s , n G G ( ) γ = − θ − u 2 , p Z , p G 3 4 sin G G E , M W E , M E , M ( ) then we can write = − θ γ + γ − d 2 , p , n Z , p G 2 4 sin G G G E , M W E , M E , M E , M ( ) γ γ = − θ − − s 2 , p , n Z , p G 1 4 sin G G G E , M W E , M E , M E , M Kent Paschke – University of Massachusetts April 27, 2006

Parity-violating electron scattering For a proton: ⎡− ⎤ + + 2 G Q A A A ~ few parts per million = F E M A ⎢ ⎥ A σ πα ⎣ ⎦ 4 2 p ( ) = ε = τ = − − θ ε p Z p Z 2 ' p e A G G , A G G , A 1 4 sin G G E E E M M M A W M A Backward angle Forward angle = − θ + − + − Z 2 p p n n s G ( 1 4 sin )( 1 R ) G ( 1 R ) G G E , M W V E , M V E , M E , M = − + Δ + η + e e G G s F R A A A s alone (but For 4 He: G E For deuterium: e sensitivity only available at low Q 2 ) enhanced G A ⎡ ⎤ 2 s G Q G = θ + 2 F E ⎢ ⎥ A sin + PV πα W p n ⎣ ⎦ 2 ( G G ) 2 E E Kent Paschke – University of Massachusetts April 27, 2006

March 25, 2005: 2004 HAPPEX-II Results G s E = -0.039 ± 0.041 (stat) ± 0.010 (syst) ± 0.004 (FF) G s E + 0.08 G s M = 0.032 ± 0.026 (stat) ± 0.007 (syst) ± 0.011 (FF) Kent Paschke – University of Massachusetts March 25, 2005 April 27, 2006

World Data at Q 2 ~ 0.1 GeV 2 Extrapolated from G0 Q 2 =[0.12,0.16] GeV 2 Note: excellent agreement of world data set s = -0.12 ± 0.29 G E Δχ 2 = 1 s = 0.62 ± 0.32 G M Would imply that 7% of nucleon magnetic moment is Strange 95% c.l. Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account EINN ’05 Milos September 25, 2005 Kent Paschke – University of Massachusetts April 27, 2006

Summary (Sept 2005) • Suggested large values at Q 2 ~0.1 GeV 2 • HAPPEX-II, H and He running now! • Large possible cancellation at Q 2 ~0.2 GeV 2 G0 backward • G 0 backangle, conditionally approved for Summer ’06 HAPPEX-III • A4 backangle? G E s • Possible large values at Q 2 >0.4 GeV 2 • G 0 backangle, approved for Spring ’06 • HAPPEX-III, conditionally approved - 2007? 0.6 GeV 2 • A4 backangle? G M s Kent Paschke – University of Massachusetts EINN ’05 Milos September 25, 2005 April 27, 2006

HAPPEX (second generation) E=3 GeV θ =6 deg Q 2 =0.1 (GeV/c) 2 • Hydrogen : G s E + α G s M • 4 He : Pure G s E : sensitivity target A PV Stat. Syst. Error Error G s = 0 (ppm) (ppm) (ppm) 1 H -1.4 0.08 0.04 δ (G s E +0.08G s M ) = 0.010 (5.7%) (2.9%) 4 He +7.8 0.18 0.18 δ (G s E ) = 0.015 (2.2%) (2.1%) Kent Paschke – University of Massachusetts April 27, 2006

Measurement of P-V Asymmetries σ − σ 5% Statistical Precision on 1 ppm = ≈ 10 − 6 R L A -> requires 4x10 14 counts σ + σ LR R L Rapid Helicity Flip: Measure the asymmetry at few 10 -4 level, 30 million times − N N = R L A + LR N N R L •Analog integration of rates ~100 MHz •High luminosity: thick targets, high beam current •Control noise (target, electronics) •Polarized source uses optical pumping of strained photocathode: high polarization and rapid flip Statistics: high rate, low noise Systematics: beam asymmetries, backgrounds, Helicity correlated DAQ Normalization: Polarization, Linearity, Background Kent Paschke – University of Massachusetts April 27, 2006

Apparatus Upgrade HAPPEX-I precision: HAPPEX-H accuracy ~ 50 ppb ~ 1 ppm, 15% HAPPEX-He accuracy ~ 2% • High Luminosity => High I and P e (superlattice), thick new targets, rad-hard integrating det., improved DAQ. • Small forward angle => new Septum magnets • Accurate Normalization => improved polarimetry, new focal plane profile scanner • High systematic accuracy => improved polarized source, close attention to beam optics, luminosity monitor. Kent Paschke – University of Massachusetts April 27, 2006

HAPPEX-II HAPPEX-He June 2004 • about 3M pairs at 1300 ppm => δ A stat ~ 0.74 ppm HAPPEX-H June – July 2004 • about 9M pairs at 620 ppm => δ A stat ~ 0.2 ppm HAPPEX-He July-Sept 2005 • about 35M pairs at 1130 ppm => δ A stat ~ 0.19 ppm HAPPEX-H Oct – Nov 2005 • about 25M pairs at 540 ppm => δ A stat ~ 0.105 ppm Kent Paschke – University of Massachusetts April 27, 2006

2004 Results 4 He “slug” averages Parity-Violating Asymmetry 4 He pairs 4 He 3.3 M pairs, total width ~1300 ppm A raw correction < 0.2 ppm K.A.Aniol et al., Phys. Rev. Lett. 96 , 022003 (2006). A(G s =0) = +7.51 ppm ± 0.08 ppm “blinded” analysis used A PV = 6.72 ppm ± 0.84 (stat) ppm ± 0.21 (syst) ppm to eliminate human bias H pairs 1 H H “slug” averages 9.5 M pairs, total width ~620 ppm A raw correction < 0.06 ppm K.A.Aniol et al., Phys. Lett. B 635 (2006) 275. A(G s =0) = -1.44 ppm ± 0.11 ppm A PV = -1.14 ppm ± 0.24 (stat) ppm ± 0.06 (stat) ppm Kent Paschke – University of Massachusetts April 27, 2006

Hall A Polarimeters Compton Møller 1.5-2% syst 2-3% syst Continuous High Resolution Spectrometer Target S+QQDQ 5 mstr over 4 o -8 o 400 W transverse flow 20 cm, LH2 20 cm, 200 psi 4 He Kent Paschke – University of Massachusetts April 27, 2006

High Resolution Spectrometers Overlap the elastic line above the Very clean separation of � focal plane and integrate the flux elastic events by HRS optics Elastic Rate: PMT 1 H: 120 MHz 100 x 600 mm 4 He: 12 MHz Cherenkov cones 12 m dispersion sweeps away PMT inelastic events Large dispersion and heavy shielding reduce backgrounds at the focal plane Kent Paschke – University of Massachusetts April 27, 2006

Focal Plane Detectors PMT Brass-Quartz Integrating Cerenkov Shower Calorimeter • Insensitive to background • Directional sensitivity Cherenkov • High-resolution cones • Rad hard PMT Two segment “L”-shape covers hydrogen elastic peak Smaller 4 He elastic peak requires only ½ single- segment detector Kent Paschke – University of Massachusetts April 27, 2006

Septum Magnets Electrons scattered at 6 deg sent to the HRS at 12.5 deg. • Superconducting magnets with low cooling power: sensitive to scattered flux from the target! • Sweeper Magnet, located inside the scattering chamber, used in 2005 to reduce the flux of low energy Moller electrons Kent Paschke – University of Massachusetts April 27, 2006

High-Power Cryogenic Target New "race track" design – 20 cm (transverse cryogen flow) 20 cm 1.8% R.L. LH 2 20 cm 2.2% R.L. 4 He gas cell – Cold (6.6K), dense (230 psi) Al wall thickness – 4 mils (H) – 10 mils (He) Kent Paschke – University of Massachusetts April 27, 2006