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Transverse Beam Spin Asymmetries Measured from Helium-4 and Hydrogen Targets. L. J. Kaufman University of Massachusetts on behalf of the HAPPEX collaboration. - PowerPoint PPT Presentation
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May 19, 2006 PAVI06
Transverse Beam Spin Asymmetries Measured from
Helium-4 and Hydrogen TargetsL. J. KaufmanUniversity of
Massachusetts
on behalf of 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
May 19, 2006 PAVI06
World Data near Q2 ~0.1 GeV2
Caution: the combined fit is approximate. Correlated errors and assumptions not taken into account
Preliminary
GMs = 0.28 +/- 0.20
GEs = -0.006 +/- 0.016
~3% +/- 2.3% of proton magnetic moment
~0.2 +/- 0.5% of Electric distribution
HAPPEX-only fit suggests something even smaller:
GMs = 0.12 +/- 0.24
GEs = -0.002 +/- 0.017
May 19, 2006 PAVI06
Transverse Beam Spin Asymmetries
Beam normal asymmetries in elastic electron scattering
Electron Beam is polarized transverse to the beam direction
Interference between one- and two-photon exchange
Effect suppressed by • • Lorentz boost• forward angle
610s
mA eT
What is interesting about AT?
“elastic” “inelastic”GE/GM is influenced by the real part of 2- amplitude – Speculation is that radiative corrections are missing from Rosenbluth data.
AT is generated from the imaginary part of the 2- amplitude.
JLab Polarization Data
SLAC Rosenbluth Data
Dominated by spectrum of hadronic intermediate states
Provides a clear and accessible window on the treatment of hadronic intermediate states in box diagrams.
Possible background to PV asymmetry
May 19, 2006 PAVI06
Parity-Violation Experiments
All PV experiments can, and do, measure these to control possible systematic errors
• SAMPLE (200 MeV, back angle)• A4 (570 MeV, 855 MeV, large angle)• HAPPEX (3 GeV, forward angle)• G0 (3 GeV, forward angles)• E158 (45 GeV, very forward angle)• future back-angle A4, G0
PV experiments are optimized for small asymmetries:• High luminosity, low noise• Careful control of false asymmetries• Rapid helicity flip to cancel drifts, reduce noise• Symmetric configurations to cancel beam asymmetriesMeasurements are (or will be soon) available sampling a wide
range of kinematics:
May 19, 2006 PAVI06
Polarized e-
SourceHall A
Target400 W transverse flow20 cm, LH220 cm, 200 psi 4He
MøllerPolarimeter
High Resolution SpectrometerS+QQDQ 5 mstr over 4o-8o
Jefferson Lab
Hall A
May 19, 2006 PAVI06
Hall A High Resolution Spectrometers
May 19, 2006 PAVI06
Focal Plane Detector
May 19, 2006 PAVI06
Vertical Polarization SetupL-R symmetry of Hall A requires out-of-plane transverse polarization -> Vertical polarization is not standard for Jefferson Lab
Setup beam properties in the same way as for the PV measurement
Achieved with Wien filter and unbalanced counter-wound solenoid
Polarization measured with Mott polarimeter
May 19, 2006 PAVI06
Vertical Polarization Measurement
Vertical polarization does not precess through the accelerator ->Møller provides measurement in Hall A to check against Mott.
Tilted foil allows for sensitivity in the vertical plane
Møller also provides a cross-check of the sign of the polarization
May 19, 2006 PAVI06
Hydrogen Preliminary Results
Q2 = 0.099 ± 0.0009 GeV2
Araw = -4.947 ppm 1.094 ppm (stat)
Raw Transverse Asymmetry
310 K pairs, total width ~610 ppm
Araw correction ~ 0.14 ppm
Beam Corrected Detector Asymmetry (ppm)
Helicity Window Pair Asymmetry
# Pairs = 310 K
RMS = 887
# Pairs = 310 K
RMS = 887
Slug #
Slug #
asym
metr
y (
pp
m)
asym
metr
y (
pp
m)
Left HRS
Right HRS
May 19, 2006 PAVI06
Helium Preliminary Results
# Pairs = 935 K
RMS = 1480
# Pairs = 935 K
RMS = 1480
Helicity Window Pair Asymmetry
Q2 = 0.0772 ± 0.0004 GeV2
Araw = -10.930 ppm 1.073 ppm (stat)
Raw Transverse Asymmetry
935 K pairs, total width ~1040 ppm
Araw correction ~ 0.11 ppm
asym
metr
y (
pp
m)
asym
metr
y (
pp
m)
Slug #
Slug #
Left HRS
Right HRS
Beam Corrected Detector Asymmetry (ppm)
May 19, 2006 PAVI06
HAPPEX 2004 Hydrogen Transverse
AT = -6.58 ppm ± 1.47 ppm (stat) ± 0.24 ppm (syst)
Afanasev
HAPPEX 2004 (preliminary)
Total corrections ~200 ppb
Dominant systematic errors:• Polarimetry (190 ppb)• Beam asymmetry (100 ppb)• Al background dilution (70 ppb, assumed AT
Al = 0)
Ee = 3 GeV, CM ~16o, Q2 = 0.099 GeV2
May 19, 2006 PAVI06
HAPPEX 2005 Helium Transverse
AT = -13.51 ppm ± 1.34 ppm (stat) ± 0.37 ppm (syst)
Afanasev
HAPPEX 2005 (preliminary)
Dominant systematic errors:• Polarimetry (300 ppb)• Linearity (140 ppb)• Beam asymmetry (100 ppb)• Al background dilution (120 ppb)
Ee = 2.75 GeV, lab ~6o, Q2 = 0.077 GeV2
Curve for Eb =3 GeV
Without inelastic states, 10-9
May 19, 2006 PAVI06
Conclusion
Measurement of AT from the proton
First measurement of AT from a nucleus
Asymmetries are 3-4 orders of magnitude larger than original predictions => hadronic intermediate states matter for the proton and nuclei
AT for nuclei is non-negligible
=> AT will be an important measurement for upcoming experiments like PREX
Helium: AT = -13.51 ppm ± 1.34 ppm (stat) ± 0.37 ppm (syst)
Hydrogen: AT = -6.58 ppm ± 1.47 ppm (stat) ± 0.24 ppm (syst)