General Kinematics for Polarized e Scattering on Polarized Target

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BLAST A Detector for Internal Target Experiments

• Introduction
• Overview and status of the Program
• Present Results
• Outlook

John Calarco, UNH and UT U. Kentucky, 31 March
2005
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BLAST COLLABORATION   R. Alarcon, E. Geis, J.
Prince, B. Tonguc, A. Young Arizona State
University, Tempe, AZ 85287   J. Althouse, C.
DAndrea, A. Goodhue, J. Pavel, T. Smith,
Dartmouth College, Dartmouth, NH   D. Dutta, H.
Gao, W. Xu Duke University Durham, NC
27708-0305 H. Arenhövel, Johannes
Gutenberg-Universität, Mainz, Germany   T.
Akdogan, W. Bertozzi, T. Botto, M. Chtangeev, B.
Clasie, C. Crawford, A. Degrush, K. Dow, M.
Farkhondeh, W. Franklin, S. Gilad, D. Hasell, E.
Ilhoff, J. Kelsey, M. Kohl, H. Kolster, A.
Maschinot, J. Matthews, N. Meitanis, R. Milner,
R. Redwine, J. Seely, S. Sobczynski, C.
Tschalaer, E. Tsentalovich, W. Turchinetz, Y.
Xiao, C. Zhang, V. Ziskin, T. Zwart Massachusetts
Institute of Technology, Cambridge, MA 02139
and Bates Linear Accelerator Center, Middleton,
MA 01949   J. Calarco, W. Hersman, M. Holtrop, O.
Filoti, P. Karpius, A. Sindile, T. Lee University
of New Hampshire, Durham, NH 03824   J.
Rapaport Ohio University, Athens, OH 45701   K.
McIlhany, A. Mosser United States Naval Academy,
Annapolis, MD 21402   J. F. J. van den Brand, H.
J. Bulten, H. R. Poolman Vrije Universitaet and
NIKHEF, Amsterdam, The Netherlands   W. Haeberli,
T. Wise University of Wisconsin, Madison, WI
53706        
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• Approved BLAST Scientific Program
• Form Factor Measurements Q2 ?
  1.0 (GeV/c)2
• Proton Charge and Magnetism
• Elastic Scattering with Polarized Beam and H
  Target (01-01)
• Neutron Charge and Magnetism and Deuteron
  Electromagnetic Structure
• Quasi-elastic Scattering with Polarized Beam and
  D Target (89-12 and 91-09)
• Elastic scattering off Tensor and Vector
  Polarized Deuterium (00-03
• and 03-02)

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General Kinematics for Polarized e Scattering on
a Polarized Target
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Bates Linac
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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
• 3.8kG toroidal field

BEAM
DRIFT CHAMBERS
TARGET
CERENKOV COUNTERS
BEAM
NEUTRON COUNTERS
SCINTILLATORS
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BLAST Present Configuration
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Detector Performance

• All detectors operating at or near designed level
• Drift chambers 98 efficient per wire
• TOF resolution of 300ps
• Clean event selection
• Cerenkov counters 85 efficient in electron/pion
  discrimination
• Neutron counters 10 (25-30) efficient in left
  (right) sectors
• To be improved further
• Reconstruction resolutions good but still being
  improved

current goal
?p 3 2
?? 0.5 0.3
?? 0.5 0.5º
?z 1cm 1cm
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(No Transcript)
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ep Elastic Kinematic Correlation
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Asymmetries AL and AR
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mGE/GM from ep Elastic
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mGE/GM Comparison between BLAST and JLab
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Inclusive H(e,e) Cross Sections sTL , sTT from
MC
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Inclusive H(e,e) Cross Sections from Data
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Motivation I Why Deuteron

• N-N Interaction
• Deuteron as test-bed for N-N interaction models
• THE 2-nucleon bound state
• D-wave admixture Tensor force
• Model predictions vary from 4 to 7
• Deuteron as neutron target
• understand Deuteron structure

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Deuteron Electrodisintegration

• Loosely-bound deuterium readily breaks up
• electromagnetically into two nucleons
• e d ? e p n
• Most generally, the cross
  section
• can be written as
• In the Born approximation,
• vanishes in the L 0 model for the
  deuteron (i.e. no L 2 admixture)
• Measure of L 2 contribution and thus tensor NN
  component
• Reaction mechanism effects (MEC, IC, RC)
  convoluted with tensor contribution
• There is no direct measure of the tensor
  component. -- somebody
• provides a measure of reaction mechanisms
• Useful for extraction of Gne
• Beam-vector dilution (hPz) gotten from analysis

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Beam and Target Performance

• Beam fills to 175mA with 25min lifetime, average
  polarization 65 4
• 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 _at_ 140mA
• Target polarizations from data analysis Pz 88
  4, Pzz 65 2

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Motivation II Why T20
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e-d Elastic Event Selection

• Need clean e-d elastic sample
• e-d Elastic rate 3 of coincident rate by one
  positive and one negative charge scattered into
  either sector.

• Timing Cuts

• Coplanarity ??1o

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e-d Elastic Event Selection

• Mass timing tracking
• Blue everything
• Red after coplanary cut

• Kinematics
• ?pe24MeV ??d1o

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Preliminary T20 Result
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From Measurements of the Elastic Vector Asymmetry
AVed
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Deuterium Wave Functions

• The NN interaction conserves only total angular
  momentum
• Spin-1 nucleus lies in an L 0, 2 admixture
  ground state
• A tensor component must be present to allow ?L
  2
• Fourier transform into momentum space
• L 2 component becomes dominant at pM 0.3GeV

(Bonn Potential)
(Bonn Potential)
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Deuteron Density Functions

• Calculate the density functions
• One-to-one correspondence between md and the
  (PZ,PZZ) polarization states
• In the absence of a tensor NN component, these
  plots are spherical and identical
• Famous donut and dumbbell shapes

PZZ
(-1,1)
(1,1)
PZ
(0,-2)
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Missing Mass

• Only the e- and p are measured
• actually measure d(e,ep)X and thus need cuts to
  ensure that X n
• Define missing energy, momentum, and mass
• Demanding that mM mn helps ensure that X n
• Momentum magnitude corrections greatly improve mM
  spectra

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Missing Momentum
Left Sector Electron
Right Sector Electron

• Good MC agreement up to pM 0.5GeV/c

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Beam-Vector Asymmetry
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Beam-Vector Asymmetry (cont.)
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Tensor Asymmetry Results
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Tensor Asymmetry (cont.)
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Potential Dependence

• Monte Carlo for Bonn, Paris, and V18 potentials
  compared to BLAST data
• Potential dependence small compared to MEC and IC
  contributions

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Determination of hPz
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D(e,en) Kinematic Distribution
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Missing Mass from D(e,en) QES
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GE/GM for the Neutron from D(e,en) QES
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GnM
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GnE from D(e,en)
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Conclusions and Outlook

• World-class data for GpE/GpM , GnE/GnM , D(e,e)
  elastic T20 , D(e,ep) QES AVed and ATd,,
  Inclusive H(e,e)X and D(e,e)X
• Analysis still in progress
• Many other channels to be analyzed H(e,ep)p0 ,
  H(e,en)p , H(g,n)p , D(g,pn) , etc.
• Continuing to take data on D until June (?)
  expect to at least double data set (or more!)
• Shut down and decommission relocate detectors
  and remap BLAST field

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The BLASTers