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

SPIN 2004 Trieste, Italy 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) Deuteron Electro-disintegration L=0 + L=2 +

SPIN 2004 Trieste, Italy 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 1GeV 2

SPIN 2004 Trieste, Italy 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 175mA ring current

SPIN 2004 Trieste, Italy 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 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 : +P z  -P z Deuterium polarization in tri-state mode  (Vector, Tensor) : (-P z, +P zz ) ( +P z, +P zz ) (0, -2P zz ) Flow = 2.2  atoms/s, Density = 6.0  atoms/cm 2, Luminosity = 4.0  /cm 2 140mA Actual polarization magnitudes from data analysis 3 He target ready for future running

SPIN 2004 Trieste, Italy The BLAST Spectrometer Left-right symmetric detector  simultaneous parallel and perpendicular asymmetry determination Large acceptance  covers 0.1GeV 2 ≤ Q 2 ≤ 1GeV 2  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 DRIFT CHAMBERS CERENKOV COUNTERS SCINTILLATORS NEUTRON COUNTERS TARGET BEAM

SPIN 2004 Trieste, Italy 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 Event Reconstruction C++ OOP reconstruction library using ROOT Resolutions are a “work in progress”  much progress has been made in the last six months currentgoal pp 3%2%  0.5°0.3°  0.5°0.5º zz 1cm.

SPIN 2004 Trieste, Italy 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 m M = m n helps ensure that X = n

SPIN 2004 Trieste, Italy 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 32 º on the left side  can access different asymmetry components electron side side asymmetry component leftrightperpendicular rightleftparallel

SPIN 2004 Trieste, Italy Background Contributions Empty target runs provide a measure of background Negligible contribution at small p M Larger contribution at high p M due to scattering off of Aluminum target PerpendicularParallel

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

SPIN 2004 Trieste, Italy Tensor Asymmetry Results Tensor polarization from independent T 20 fit L=2 “dips” reproducible in the data Still working on systematic checks; results are preliminary

SPIN 2004 Trieste, Italy 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  p M  p N = 0  small uncertainty up to p M = 0.15GeV perppara hP z 0.467± ±0.006 h0.65±0.04 PzPz 0.72± ±0.04

SPIN 2004 Trieste, Italy 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