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)