Adrian Sindile University of New Hampshire

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Proton Form Factor Ratio Measurement with BLAST
Adrian Sindile - University of New Hampshire
Ph.D. Thesis Defense April 3, 2006
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Outline of Presentation
- Overview and Motivation - Introduction -
Existing Methods Data - Phenomenological
Fits - Theoretical Models - Experimental
Apparatus - Bates Linac - Polarized Target -
BLAST Detector - DAQ
- Data Analysis - Event Selection - Data
Quality - Monte Carlo
- Results - Asymmetries - µGEp/GMp -
Systematic errors
- Discussion and Outlook
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Introduction
- Matter is made of atoms - The heart of the
atom is the nucleus - Nuclei contain protons and
neutrons or collectively, nucleons
- Goals are to test theories of nuclear
structure - What is the nature of the NN
interaction?
- How do we describe nuclear structure?
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E M in the Nucleon

• Electricity and Magnetism in the Nucleon

• Form Factors 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
• Necessary for parity-violation experiments

• Proton is easiest to study

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Form Factors
- Form Factor definition
- Nucleon current
- Fourier Transforms in Breit Frame
1, for Q2 0
2.79, for Q2 0 t Q2/4M2
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Existing Methods Unpolarized X-Section
Rosenbluth Separation
- Mott cross section describes the scattering of
a spin ½ electron off a spinless, point-like
nucleon
- For Q2 gt 1 (GeV/c)2 the electric form factor
is difficult to measure - At low Q2, the
magnetic form factor becomes difficult to extract
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World Unpolarized Data - GEp
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World Unpolarized Data - GMp
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Existing Methods Polarization Transfer
- Polarization transfer measurements use a Focal
Plane Polarimeter (FPP) - Pt and Pl of the
scattered proton are measured simultaneously
(using 12C)
- GEp/GMp is measured directly
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GEp/GMp Unpolarized Data
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GEp/GMp Polarized Data
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Phenomenological Fits
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Pion Cloud
- Just like particles appear in vacuum
- Pion as a pair of quarks
pions pop up continuously at the nucleon surface
- Pion contribution can be revealed in e-N
scattering
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Two-Photon Exchange Contributions
- Guichon and Vanderhaegen (2003) although small
(few ) the 2-photon effect is accidentally
amplified in the Rosenbluth method!
- Blunden et al. (2003) did a first
model-dependent calculation of the 2-photon
effect and found small corrections with strong
angular dependence at fixed Q2 , proving
significant for the Rosenbluth method they
explained about half of the discrepancy!!
- Chen et al. (2004) related the 2-photon effect
to the GPD and resolved most of the discrepancy
between unpolarized and polarized data!!!
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Theoretical Calculations
- Direct QCD calculations - pQCD scaling at high
Q2 - Lattice QCD - Meson Degrees of
Freedom - Dispersion analysis, Höhler et al.
1976 - Vector Meson Dominance (VMD), Lomon
2002 - Soliton Model, Holzwarth 1996 - QCD
based constituent quark models (CQM) - LF
quark-diquark spectator, Ma 2002 - LFCQM CBM,
Miller 2002
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Theoretical Models
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BLAST - Underlying Idea
- Capitalize on the magnetism of the nucleus
- We can polarize a collection of nuclei
- Polarization observables will manifest
themselves!
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BLAST - Underlying Idea

• Goal of BLAST was to map GEp/GMp in the low Q2
  region of the pion cloud
• Systematics different from Polarization Transfer
  Method
• insensitive to Pb and Pt
• Q2 0.1 0.9 (GeV/c) 2
• input for P.V. experiments
• Exploits unique features of BLAST
• internal target low dilution, fast spin reversal
• large acceptance simultaneously measure all Q2
  points
• symmetric detector super-ratio measurement

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The Super Ratio Technique
- Differential cross section for longitudinally
polarized electrons scattered from a polarized
proton target
- Spin-Dependent Asymmetry
- Experimental Spin-Dependent Asymmetry
- Super Ratio
- Beam and target polarizations cancel out in the
super ratio !
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Experimental Setup - Polarized Beam

• Polarized Source
• Linac
• Recirculator
• South Hall Ring (SHR)
• Siberian Snakes
• BLAST detector in SHR
• ABS BLAST target embedded in the
• beamline

• Storage Ring
• E 850 MeV
• Imax225 mA
• Pb 0.65

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Experimental Setup - Atomic Beam Source

• Internal ABS Target
• 60 cm storage cell
• t 4.9?1013 cm-2
• Pt 0.80

- pure internal target - high polarization, fast
spin reversal - L 3.1 ? 1031 cm-2s-1
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Experimental Setup - Atomic Beam Source

• Standard technology
• Dissociator nozzle
• 2 sextupole systems

Spin State Selection
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BLAST Detector Package

• - Large Acceptance
• 20o lt ?e lt 120o
• - 22o lt fe lt 22o
• 0.1 (GeV/c)2 lt Q2 lt 0.9 (GeV/c)2
• - Wire Chamber Tracking
• ?pe /pe ? 3?
• ??e ? 0.?
• ?z ? 1 cm
• - BLAST Field
• Bmax 3.8 kG
• - Cerenkov Detectors for PID
• - Scintillators for Time-Of-Flight

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BLAST Time-of-Flight System
- scintillating material BC-408 (Bicron) -
dimensions (cm) - backward angle 180 - 26.10
- 2.54 - forward angle 120 - 17.8 - 2.54 -
light-guides BC-800 - optical adhesive OP-21G
(Dymax)
- 3 PMTs - 9822 (Electron Tubes) - active
(transistorized bases) - optical grease BC-630
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BLAST Time-of-Flight System

• - Fast Timing Information
• TDC 50 ps/ch
• important for BLAST trigger
• - Energy Information
• ADC 50 fC/ch
• - Performance
• efficiency gt 99
• dT lt 500 ps FWHM

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BLAST Trigger and DAQ
- NIM and CAMAC electronics - 16 bit Sector
MLUs - XMLU and Trigger Supervisor - Fastbust
TDCs and ADCs
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BLAST Relational Database
RUN
TRIGGER
SC_TDC_RUN
SC_ADC_RUN
CC_TDC_RUN
CC_ADC_RUN
CC_ADC
CC_TDC
SC_ADC
SC_TDC
SC_PMT
CC_PMT
SC_HV
CC
CC_HV
SC
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BLAST Reconstruction

• Scintillators
• - timing, calibration
• Wire chamber
• - hits, stubs, segments
• - link, track fit
• Data Summary Tape
• - ep_skim ROOT Tree

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Event Selection WC Region
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Event Selection WC Region
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Event Selection WC Region

• After WC misalignment fixed

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Event Selection WC Region
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Event Selection BAT Region
If outside WC
Timing Cuts Cerenkov Cuts!
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Event Selection BAT Region
TOF (LeftTOP LeftBOT)/2 - (RightTOP
RightBOT)/2
POS (LeftTOP - LeftBOT) (RightTOP -
RightBOT)
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Data Quality
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Results - Asymmetries
BLAST Left Sector BLAST Right
Sector
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Results Form Factor Ratio
µGEp/GMp compared to Hoehlers Parametrization
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Results Systematic Errors
- Super Ratio
Spin Angle Tracking Contributions to
Systematics
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Results Systematic Errors
Q2 Discrepancy Contributions to Systematics
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Results Systematic Errors
Major Contributions to Systematic Errors
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Results Form Factor Ratio
µGEp/GMp
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Results Form Factor Ratio
µGEp/GMp
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Results Form Factor Ratio
µGEp/GMp
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Summary

• 1st measurement of mGEp/GMp using a polarized
  beam and a polarized target
• improvement in precision of mGEp/GMp at Q2
  0.1 0.5 GeV2
• sensitive to the pion cloud
• narrow dip around Q20.2-0.3 GeV2 ?
• systematic errors are being reduced
• further reducing the statistical errors for the
  last data point is possible

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THANK YOU!
R. Alarcon, E. Geis, J. Prince, B. Tonguc, A.
Young Arizona State University  J. Althouse, C.
DAndrea, 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, M. Kohl, H. Kolster, A.
Maschinot, J. Matthews, N. Meitanis, R. Milner,
R. Redwine, J. Seely, A. Shinozaki,
S.Sobczynski, C. Tschalaer, E. Tsentalovich, W.
Turchinetz, Y. Xiao, H. Xiang, C. Zhang, V.
Ziskin, T. Zwart Massachusetts Institute of
Technology Bates Linear Accelerator Center
D. Dutta, H. Gao, W. Xu Duke University J.
Calarco, W. Hersman, M. Holtrop, T. Lee O.
Filoti, P. Karpius, A. Sindile 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
BLAST Collaboration
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Results Systematic Errors
Beam Asymmetry
Target Asymmetry
False Asymmetries Contributions to Systematics
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Results Systematic Errors
- background about 0.8 of the total event
number - it acts only as dilution, it cancels to
first order in super-ratio
- radiative effects
Background and Radiative Effects Contributions
to Systematics