Analysis of d(e,e’p)n in BLAST

1. Analysis of d(e,e’p)n in BLAST Aaron Maschinot Massachusetts Institute of Technology Spin 2004 Conference Trieste, Italy

2. + L=0 + L=2 Deuteron Electro-disintegration • Loosely-bound deuterium readily breaks up electromagnetically into two nucleons • e + d  e’ + p + n • Most generally, the d(e,e’N)N cross section can be written as: • In the Born approximation, • Additionally, vanishes in the L = 0 model for the deuteron (i.e. no L = 2 admixture) • is a good measure of L = 2 component • Also, is also a good measure of L = 2 as well as subnuclear degrees of freedom (e.g. MEC, IC, RC) SPIN 2004 Trieste, Italy

3. The BLAST Program • Bates Large Acceptance Spectrometer Toroid • Located at the MIT-Bates Linear Accelerator Facility in Massachusetts, USA • Utilizes polarized beam and polarized targets • 0.850GeV longitudinally polarized electron beam • polarized internal atomic beam source (ABS) target • Large acceptance, left-right symmetric spectrometer detector • simultaneous parallel/perpendicular, in-plane/out-of-plane asymmetry measurements • Toroidal magnetic field • Ideally suited for a comprehensive analysis of the spin-dependent electromagnetic response of few-body nuclei at momentum transfers up to 1GeV2 SPIN 2004 Trieste, Italy

4. Polarized Beam at Bates • 1GeV longitudinally polarized electron beam • 0.5GeV linear accelerator with recirculator • Polarized beam fills South Hall storage ring • location of BLAST experiment • Longitudinal polarization maintained by Siberian snakes • 25 minute lifetime @ 175mA ring current SPIN 2004 Trieste, Italy

5. Beam Polarization Measurements • Beam polarization measured via a Compton polarimeter • polarization ~ amount of back-scattered photons • nondestructive measurement of polarization • Long-term beam polarization stability • average beam polarization = 65% ± 4% PRELIMINARY SPIN 2004 Trieste, Italy

6. The BLAST Targets • Internal Atomic Beam Source (ABS) target • Hydrogen and Deuterium gas targets • Can quickly switch between polarization states • Hydrogen polarization in two-state mode • Vector : +Pz -Pz • Deuterium polarization in tri-state mode • (Vector, Tensor) : (-Pz, +Pzz) ( +Pz, +Pzz) (0, -2Pzz) • Flow = 2.2  1016 atoms/s, Density = 6.0  1013 atoms/cm2, Luminosity = 4.0  1031 /cm2/s @ 140mA • Actual polarization magnitudes from data analysis • 3He target ready for future running SPIN 2004 Trieste, Italy

7. The BLAST Spectrometer • Left-right symmetric detector • simultaneous parallel and perpendicular asymmetry determination • Large acceptance • covers 0.1GeV2 ≤ Q2 ≤ 1GeV2 • out-of-plane measurements • DRIFT CHAMBERS • momentum determination, particle identification • CERENKOV COUNTERS • electron/pion discrimination • SCINTILLATORS • TOF, particle identification • NEUTRON COUNTERS • neutron determination • MAGNETIC COILS • 4.5kG toroidal field BEAM DRIFT CHAMBERS TARGET CERENKOV COUNTERS BEAM NEUTRON COUNTERS SCINTILLATORS SPIN 2004 Trieste, Italy

8. Drift Chambers • Three wire chambers on either side • Two superlayers of cells per chamber • Three sense wires per cell • 3  2  3 = 18 hit wires for ionizing particle • 954 total sense wires, 9888 total wires • Large acceptance • 20° ≤  ≤ 80° , • -17° ≤  ≤ 17° • 1sr total solid angle • Each wire 98% efficient SPIN 2004 Trieste, Italy

9. Event Reconstruction • C++ OOP reconstruction library using ROOT • Resolutions are a “work in progress” • much progress has been made in the last six months . SPIN 2004 Trieste, Italy

10. Missing Mass and Momentum • Only the e- and p+ are measured • actually measure d(e,e’p)X • need cuts to ensure that X = n • Define “missing” energy, momentum, and mass: • Demanding that mM = mn helps ensure that X = n SPIN 2004 Trieste, Italy

11. Monte Carlo d(e,e’p)n Asymmetries • Using theoretical model from H. Arenhövel • Data take into account detector acceptance • Target polarization vector, ,set at 32º on the left side • can access different asymmetry components SPIN 2004 Trieste, Italy

12. Background Contributions • Empty target runs provide a measure of background • Negligible contribution at small pM • Larger contribution at high pM due to scattering off of Aluminum target Perpendicular Parallel SPIN 2004 Trieste, Italy

13. Beam-Vector Asymmetry Results • 200kC of data analyzed so far • 450kC projected total data • Vector polarization determined from fitting asymmetry below pM = 0.15GeV • Visible correlation with full subnuclear-effects model SPIN 2004 Trieste, Italy

14. Tensor Asymmetry Results • Tensor polarization from independent T20 fit • L=2 “dips” reproducible in the data • Still working on systematic checks; results are preliminary SPIN 2004 Trieste, Italy

15. Determining the Vector Polarization • In the quasi-elastic (QE) limit, d(e,e’p)n is well understood: • reduces to p(e,e’p) with spectator n • <1% model uncertainty in • Large asymmetry, high detector efficiency  small statistical uncertainty • QE d(e,e’p)n  pM pN = 0 • small uncertainty up to pM = 0.15GeV SPIN 2004 Trieste, Italy

16. Conclusions • Both the d(e,e’p)n beam-vector and tensor asymmetries are good measures of the L = 2 deuterium component. • The d(e,e’p)n beam-vector asymmetry is a good measure of subnuclear effects (and relativistic corrections). • Both asymmetries are being measured in BLAST • Final asymmetry results with 450kC expected within six months • Results will offer much discerning power between models SPIN 2004 Trieste, Italy