Recent results from BLAST detector

Nucleon05Oct. 12-14, 2005

Evgeni TsentalovichMIT

Recent results from BLAST detector



Bates Linear Accelerator center

• • 850 MeV cw polarized electron beam• Beam polarization longitudinal at target • Storage ring filled to 225 mA; helicity flipped each fill• Lifetime 25 to 30 minutes• Automated synchronization of ring fill, detector HV ramp, data taking, ring dump using the EPICS control system

SiberianSnake



Electron beam polarization

• Compton polarimeter provides online control of stored beam polarization

• Laser beam helicity flipped with a Pockels cell (~10Hz)

• Backscattered photons are detected with CsI crystal

• Electron beam polarization flipped every new fill

• Average beam polarization 67%

Compton polarimeter



• ABS (Atomic Beam Source) produces flux of Hydrogen or Deuterium atoms

• ABS intensity ~• Dri-film coated T-shaped storage

cell.• Target thickness ~• Hydrogen polarization Pz78%• Deuterium polarization Pz72%,

Pzz 68%• Target polarization flipped every 5

min

213 cm/at10*5

Polarized Internal Target

sec/at10*2 16



BLAST • Toroidal field 3.8 kG• 2 instrumented sectors in the

horizontal plane - Drift chambers

- Cerenkov detectors

- Time of Flight scintillators

- Neutron detectors

BLAST DATA:

2004, Hydrogen - Pz78%, 81 pb-1

2004, Deuterium - Pz84%, 130 pb-1

Pzz68%2005, Deuterium - Pz72%, 180

pb-1

Pzz56%

BEAM

BEAM TARGET



Kinematics for spin-dependent electron scattering

ElectronLeft

ElectronRight

q

q

B

Electron scattering into left sector : q vector ~ perpendicular to target spin (perpendicular kinematics)

Electron scattering into right sector : q vector ~ parallel to target spin (parallel kinematics)

e

e’

q

p

*

*



BLAST physics program

H

Pol

Vect.-Pol D

Tens.-Pol D@

)'e,e(p

)p'e,e(p

n)'e,e(p

0)p'e,e(p

)n'e,e(p

)'e,e(d

)p'e,e(d

)n'e,e(d

)d'e,e(d

)d'e,e(d@

)p'e,e(d@ -production



)n'e,e(d

Measurements of neutron form factor n

EG

)}APAPA(hAPAP1{SddEd

d Tedzz

Vedze

Tdzz

Vdz0

CMee

**nM

nE*

2nM

2nE

**nM

nE

*2nMV

ed cossinG

Gbcosa

GcG

cossinGbGcosaGA

Product of beam and target polarizations (hPz) is determined from 2H(e,e’p)n reaction and verified with 2H(e,e’n)p in parallel kinematics

The Form Factors ratio is measured in perpendicular kinematics



)n'e,e(d

Preliminary results

Small systematic errors:

•The largest contribution (5%)– from the uncertainty in the target polarization angle (~12 % per degree)

•Uncertainty in hPz 2.5%

•Uncertainty in magnetic Form Factor 1.5 %

•Model dependency < 3%

•Radiative effects <1%



Measurements of deuteron form factors

)d'e,e(d@



Preliminary results)d'e,e(d@

The largest systematic error(~5%) – from the normalization on low-q points



)}APAPA(hAPAP1{SddEd

d Tedzz

Vedze

Tdzz

Vdz0

CMee

In the Born approximation

)p'e,e(d

)p'e,e(d@

,

0AAA Tede

Vd

TdA vanishes in the L=0 model for deuteron (no L=2 admixture)

TdA=> is a good measure of L=2 component

VedA is a good measure of L=2 component and reaction

mechanisms : MEC, IC, RC



Vector Asymmetry )p'e,e(d



Tensor Asymmetry )p'e,e(d@



)p'e,e(p

Separation of charge and magnetic proton

form factors

Existing data: 1.Rosenbluth separation

2.Polarization transfer measurements (scattering of polarized electrons on Hydrogen target and measuring a polarization of recoil protons)



)p'e,e(p

World Data



Super ratio

)p'e,e(p Scattering of polarized electrons on

polarized protons



Preliminary Results from BLAST

BLAST Left Sector BLAST Right Sector

)p'e,e(p



Preliminary Results from BLAST)p'e,e(p



Preliminary Results from BLAST with World Data)p'e,e(p



Preliminary results from BLASTquasi-elastic d(en) ( )

elastic d(ed) (T20) quasi-elastic d(ep)

elastic p(ep) ( )

Factor of two more data to analyze

Also analyzing data on production, resonance, T10/T11,inclusive….

More results to come !

Conclusion

pM

pE G/G

nEG

Recent results from BLAST detector

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