precision measurement of g e p /g m p with blast
DESCRIPTION
Precision Measurement of G E p /G M p with BLAST. Chris Crawford MIT Laboratory for Nuclear Science Ricardo Alarcon, John Calarco, Ben Clasie, Haiyan Gao, Hauke Kolster, Jason Seely, Tim Smith, Vitaliy Ziskin, and the BLAST Collaboration. Outline. Introduction and Motivation - PowerPoint PPT PresentationTRANSCRIPT
Precision Measurement of GE
p/GMp with BLAST
Chris Crawford
MIT Laboratory for Nuclear Science
Ricardo Alarcon, John Calarco, Ben Clasie, Haiyan Gao, Hauke Kolster, Jason Seely, Tim Smith, Vitaliy Ziskin, and the BLAST Collaboration
Outline
Introduction and Motivation» Theoretical calculations
Existing Measurements» Rosenbluth technique » Recoil proton polarization (FPP)» Super Rosenbluth
BLAST Experiment» Asymmetry super-ratio method» Polarized beam, polarized targets, detectors» Projected Results
Introduction
GE,GM fundamental quantities describing charge/magnetization in the nucleon
Test of QCD based calculations and models
Provide basis for understanding more complex systems in terms of quarks and gluons
Rosenbluth Separation
Elastic e-p cross section
At fixed Q2, fit dσ/dΩ vs. tan2(θ/2)» Measurement of absolute cross section
» Dominated by either GE or GM
Polarization Transfer
Recoil proton polarization
Focal Plane Polarimeter» recoil proton scatters
off secondary 12C target» Pt, Pl measured from
φ distribution » Pb, and analyzing power
cancel out in ratio
World Data
Unpolarized Data Polarization Transfer
» Milbrath et al. (BATES) 1999
» Jones et al. (JLAB), 2000
» Dieterich et al. (MAMI), 2001
» Gayou et al. (JLAB), 2002
Super-Rosenbluth» JLab Hall A, preliminary
results expected soon
Theory†
Direct QCD calculations» pQCD scaling at high Q2
» Lattice QCDMeson Degrees of Freedom
» Vector Meson Dominance (VMD), Lomon 2002» Dispersion analysis, Höhler et al. 1976» VMD + Chiral Perturbation Theory, Mergel et al. 1996
QCD based quark models» CQM, Frank et al. 1996» Soliton Model, Holzwarth 1996» Cloudy bag, Lu et al. 1998
†Nucleon Electromagnetic Form Factors, Haiyan Gao, Int. J. of Mod. Phys. E, 12, No. 1, 1-40(Review) (2003)
QCD Calculations
Perturbative QCD» diverges at low Q2
» F2/F1 scaling
Lattice QCD» must extrapolate to
physical pion mass
» quenched calculations
Constituent Quark Models
Relativistic CQMSoliton ModelCloudy Bag Model
Models in closest agreement with recent JLab results:
Form Factor Ratio @ BATES
New technique: polarized beam and target» exploits unique features of BLAST» different systematics
» insensitive to Pb and Pt
Q2 = 0.07 – 0.9 (GeV/c) 2 » overlap with JLab data
and RpEX (future exp.at Bates to measure rp)
BLAST Collaboration
R. Alarcon, E. Geis, J. Prince, B. Tonguc, A. Young
Arizona State University
J. Althouse, C. D’Andrea, A. Goodhue, J. Pavel, T. Smith,
Dartmouth College
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, H. Kolster, A. Maschinot, J. Matthews, N. Meitanis,
R. Milner, R. Redwine, J. Seely, S.Sobczynski, C. Tschalaer, E. Tsentalovich,
W. Turchinetz, Y. Xiao, H. Xiang, C. Zhang, V. Ziskin, T. Zwart
Massachusetts Institute of TechnologyBates Linear Accelerator Center
D. Dutta, H. Gao, W. Xu
Duke University
J. Calarco, W. Hersman, M. Holtrop, O. Filoti, P. Karpius, A. Sindile, T. Lee
University of New Hampshire
J. Rapaport
Ohio University
K. McIlhany, A. Mosser
United States Naval Academy
J. F. J. van den Brand, H. J. Bulten, H. R. Poolman
Vrije Universitaet and NIKHEF
W. Haeberli, T. Wise
University of Wisconsin
Polarized Beam and Target
Stored electron beam (80 mA) Eb: 0.27–1.1 GeV Pb: 0.70
1H / 2D target (ABS) L: 1.0×1032/cm2 s Pt: 0.50
3He target L: 1.2×1033/cm2 s Pt: 0.50
Compton Polarimeter
Polarization about 0.70 typical Statistical precision of
measurements governed mostly by signal-to-background ratio. Typical precision of 1-2% per hour.
Systematic errors estimated at 5% level presently. Working on reducing these through improved analysis of energy spectrum.
Full photon energy spectrum measured as function of laser helicity and for background
Polarization measurements made at currents up to 130 mA. Signal to background ratio worsens at high currents but still tractable.
Atomic Beam Source
Standard technologyDissociator & nozzle2 sextupole systems3 RF transitions
1
3
2
4nozzle
6-pole
1
2MFT (2->3)
1
3
6-pole
1Spin State Selection:
ABS Specifications
Cell geometry: cylindrical 15mm × 400mmCell coating: DrifilmCell temperature: T=80KTarget thickness: t=4.4×1013 cm-2 (H) Polarization: Pz = 0.59 (H), 0.78 (D)
Holding field: B=3mT (H), 35mT (D)
Ion polarimeter
Ions produced by electron beam inside the storage cell
are extracted and accelerated by electrostatic lenses. The
spherical deflector directs ions into the polarimeter arm. The
Wien Filter provides mass separation, and nuclear
reaction with large analyzing power is used to measure
nuclear polarization.
Currently, the tritium target is not installed yet, and Ion
Polarimeter is used as a mass spectrometer.
Laser Driven Source (LDS)
Optical pumping& Spin Exchange
Spincell designTarget and
PolarimeterResults
LDS Performance
Current Status» Flux: 1.1×1018 atoms/s» Atomic fraction: 0.56» Polarization: 0.37
Improvements» Diamond coating instead of drifilm» Double dissociator» Electro-Optic Modulator (EOM)
Detector Package
BLAST TorroidTOF ScintillatorsČerenkov DetectorsWire ChambersNeutron Bars, LADSSoftware
Detector Requirements» definition of the momentum transfer vector
» optimize statistics
» polarized targets: Atomic Beam & Laser Driven Sources
» simultaneous A-measurements
» e/p/n/ separation
NeL
Large , beam current, luminosity, polarization
Coil shape 1 m diameter in target region BLAST field = 0 at targetB-gradients 50 mG/cm
Symmetric Detector
()e 2 , e mrad, z 1 cm
PID
Čerenkov Detectors
1 cm thick aerogel tiles Refractive index 1.02-1.03 White reflective paint 80-90 % efficiency
5" PMT's, sensitive to 0.5 Gauss Initial problems with B field Required additional shielding 50% efficiency without shielding
Software
BLASTmc – Monte Carlo using Geant321BlastLib2 – recon library based on ROOT
» integrated on-line display » and offline reconstruction
CODA – data acquisitionEPICS – slow controls
Reconstruction Steps
Scintillators» timing, calibration
Wire chamber» hits, stubs, segments
» link, track fit
PID, DST
Radiative Corrections
MASCARAD code» A. Afanasev et al., Phys.Rev.D 64,113009
» Covariant calculation with no cutoff parameter
» small corrections (<1%) to asymmetry
Projected Results
Statistics» A1, A2
Systematics
» θ*1, θ*
2
Δp, Δθ, Δβ
Errors are minimized as a function of β (target spin angle)