Probing Chiral Dynamics with photons

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Probing Chiral Dynamics with photons

• Henry R. Weller
• Duke University and Triangle Universities
  Nuclear Laboratory
• HIgS PROGRAM

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A wide variety of physical processes can be used
to study Chiral Dynamics, guided mainly by the
results of ChPT, an expansion of the Lagrangian
for low energy QCD about the chiral limit,
mq0.I want to mention a few of these
today.ReferenceInternational Workshop on
Chiral Dynamics 2006Organizers H. Gao, B.
Holstein, HRWwww.tunl.duke.edu/events/cd2006/pro
ceeding.html
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Chiral Anomaly(from Yelena Prok for the PrimEx
Collaboration)
The p0 decay rate is a fundamental prediction of
confinement scale QCD.
Chiral Anomaly the closed-loop triangle diagram
results in axial vector current
non-conservation, even in the limit of vanishing
quark masses.
The anomaly leads to the reduced decay amplitude,
in leading order (chiral limit)
where Fp 92.42/-0.25 MeV is the pion decay
constant.
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Decay Width
The p0ggg decay width is related to the amplitude
is presently known to 10
The goal of the PrimEx Experiment is to measure
the decay width to an accuracy of 1.5. ChPT
calculations Including effects of md-mu being
non-zero Increase G by 4.5.
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Success of ChPT at pion-thresholdLinearly
Polarized Photon asymmetry for the gp?p0p
reaction at an average energy of 159.5 MeVMAINZ
2001
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Difficulties!e p ? e p p0 at low Q2
--MAINZ
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Precision Measurement of the Electroproduction of
p0 Near Threshold at JLAB A Test of Chiral QCD
Dynamics Co-spokespersons J. Annand, D.
Higinbotham, R. Lindgren, V. Nelyubin, and B.
Norum,
q
)
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Pion Electro-Production in the US ? BigBite
Collaboration

• Target
• 10 - 15 cm Liquid Hydrogen( LH2)
• 125 mm Al Foil

HRS Electron
Beam Dump
e
LH2
BigBite
p
Electron Beam 15 mA
MWDC(15 Planes)
Two Segmented Scintillator Arrays
HRS Luminosity Monitor

• Luminosity
• 3 - 5 x 1037 Hz/cm2

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This experiment (now E04-007) is scheduled to be
run in Nov 2007, but may be delayed until April
2008 due to budget problems.
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New measurements of sP sA for the proton and
neutron at LEGS using the (SPHICE) frozen-spin
solid HD target
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LEGS data for the neutron
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LEGS

• The LEGS group has now completed taking data for
  both polarized p and polarized d targets.
• They have used their recently commissioned TPC to
  measure the charged pion channels.
• This will provide very accurate results for the
  GDH and the forward-spin-polarizability integrals
  for both p and n. Measuring them simultaneously
  will provide accurate values of the GDH n-p
  difference, where the theoretical uncertainty is
  the smallest and the discrepancy with multipole
  analysis of pi-photo-production data the largest

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N/Delta Physics at Mainz (IASA (Athens), MIT,
Mainz,)
g p ? D ? p N
Detect e' p or e' p in coincidence
N
p
D
p
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C2/M1 vs. Q2 (p0p channel)
W1232 MeV
Lattice QCD Results
Dynamical Model without pion cloud
Dynamical Model with pion cloud
Effective Field Theory Calculations Gail/Hemmert P
ascalutsa/Vanderhaeghen
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HIgS A free-electron laser generated g-ray source
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Upgraded Facility
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Upgrade Schedule
Commissioning of Booster and Ring
with OK-4underway now! Nuclear Physics
Program beginsMarch, 2007 March 07 ? Aug 07
Linear Pol.- Below 65 MeV, gt2x108 g/s
Dec. 07 ? Circ. Pol. Up to 110
MeV, gt108 g/s These are TOTAL intensities.
Beam on target is TOTAL x 1.5 x resolution
(ex. 5 res. at 100 MeV 7.5 x 106 g/s) Expect
to have energies up to 160 MeV by Spring 09
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The GDH integrand for deuterium below pion
threshold _at_ HIgS
A 400 hour run will allow us to measure the
GDH integrand between 5 and 100 MeV to an overall
accuracy of about 3 or better, assuming a beam
of 1 x 107 g/s with 5 energy spread. An
experiment to measure the GDH integrand for 3He
below pion threshold is also being developed by
Haiyan Gao et al.
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The upgraded BLOWFISH array as of January, 2005.
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Compton_at_HIgS Collaboration (see
www.tunl.duke.edu/mep/higs/compton.pdf)

• Use the intense polarized beams at HIgS to obtain
  very precise values of the electric and magnetic
  polarizabilities of the proton and the neutron.
• Perform double polarization experiments to obtain
  precise values of the spin-polarizabilities of
  the proton and the neutron.

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The HINDA Array(HIgS NaI Detector Array)

• Recently NSF/MRI funded projecta high
  resolution-high acceptance gamma-ray spectrometer
  consisting of eight 10x12 NaI detectors in 3
  thick segmented NaI shields.
• The Compton_at_HIgS Collaboration

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Electric and Magnetic Polarizability of the
proton

• Recent results (B. Pasquini) of a free fit to
  data yield
• 11.52 /- 2.4 x 10-4 fm3
• b 3.42 /- 1.70 x 10-4 fm3
• (with Baldin sum rule value of 13.82?
• a11.0 /- 1.4 b 2.8 /-1.4 )
• A 50 error in b which will impact future
  measurements.

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100 Linearly polarized beams at HIgS can improve
this

• Simulation (Blaine Norum) assumed
• Eg 120 MeV
• Target 80 mg/cm2
• 107 g/s
• 280 hours

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Determination of the electric and magnetic
polarizabilities of the protonusing 100
linearly polarized gammas_at_HIgS a 300 hr
experiment will yield 5 errors on both a (
now20) and b (now50).
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Compton scattering of g rays from the deuteron at
LUNDG. Feldman, M. Kovash, A. Nathan, B.
Schroder, H.R. Weller et al.

• This will give us the so called isoscalar
  polarizabilities. Since the proton is known,
  this gives the values for the neutron.
• The following shows ChPT calculations O(p4) (from
  Phillips and Choudhury)

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Solid curve-gtaN 12 bN 3Dashed curve-gtaN
6 bN 9
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Presently, results from 55 and 66 MeV disagree
with those obtained from 94 MeV data. eg. 94 MeV
(SAL) data yield aN - bN 2.5 while we expect a
value of 10 if the proton and neutron have the
same values for this difference (as expected from
Chiral Symmetry).
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The LUND experiment will make 5 measurements at
five angles and 3 energies between 40 and 110
MeV. The goal is to obtain errors for the
isoscalar polarizabilities comparable to those
which exist for the proton. This experiment will
be run in 2007.
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Spin polarizabilities.

• Measuring these requires polarized beams and
  polarized targets. They are predicted (ChPT) to
  be different for the n and the p.
• There are four dipole spin polarizabilities
  g1,2,3,4 which can be written in terms of
  gE1E1, E1M2, M1E2, M1M1.
• g1 (gE1E1) and g4(gM1M1) are the largest.

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HIgS Proposal for measuring the proton
spin-polarizabilitiesSpokesperson Rory Miskimen

• A 200 hr. run at 120 MeV will give helicity
  dependent cross sections at the 3 level, which
  translates into 10 measurments of
  spin-polarizabilities using the HINDA array.
• Sensitivity estimates for all four
  spin-polarizabilities are based upon calculations
  of Hildebrandt, Griesshammer and Hemmert.

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Projection for double-polarized Compton
scattering from proton
100 hrs for each target spin orientation
Total beam time for proton measurement 450 hrs
R. Miskimen, theory curves Hildebrandt,
Griesshammer, Hemmert, Nucl-th/0308054
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Experiments are being developed by Dr. Haiyan Gao
at Duke/HIgS to measure the spin-polarizabilities
of the neutron.

• Haiyan Gao has built a high pressure
  spin-polarized 3He target. Target thickness will
  be about 1022 atoms/cm2 with a length of 40 cm.
  Polarizations of 40 have been achieved.
• Effect of the reduced target thickness is offset
  by the increased sensitivity in the observables.

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Proposed set-up using the NaI detector array
(HINDA) and the 88-neutron detector array for
quasi-elastic Compton scattering studies using
the polarized 3He target.
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Present proposed experiments

• New theoretical calculations by Choudhury, Nogga
  and Phillips make extraction of
  spin-polarizabilities possible from elastic
  scattering data from 3He.
• With a gamma intensity of 2 x 107/sec and the
  target and detector system just described, a 350
  hour experiment will give neutron spin
  polarizabilities with errors of about /- 0.5 x
  10-4 fm4.

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Estimate of the experimental uncertainties in the
individual spin polarizabilities

• For example, at 90o, the longitudinal cross
  section difference is sensitive to g1 , while the
  transverse polarization cross section difference
  is sensitive to g4.
• The value of g0 for the proton was fixed from the
  Mainz experiment with an error of /- 13.
• (Could improve the resutls by considering
  additional constraints (B. Pasquini))..

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• Projected HI?S measurement on Nucleon Spin
• Polarizabilities (quasifree) (all in 10-4 fm4)

Proton HI?S projected uncertainties Neutron HI?S projected uncertainties
?p11.1 ?0.25 ?n13.7 ?0.40
?p2-1.5 ?0.36 ?n2-0.1 ?0.50
?p30.2 ?0.24 ?n30.4 ?0.50
?p43.3 ?0.11 ?n42.3 ?0.35

• McGovern et al. NLO heavy baryon Chiral
  Perturbation Theory

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Threshold pion-photoproduction from the proton _at_
HIgSp(g,p0)pCo-spokesperson Aron Bernstein

• The first experiment
• A measurement of the Target analyzing power at
  Eg 158 MeV.

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These experiments will provide stringent tests of

• The predictions of Chiral Perturbation Theory
• Predictions of isospin breaking due to the mass
  differences of the up and down quarks.

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The Neutral Meson Spectrometer (NMS)

• 2 BGO Layers
• 2 Sets of MWPC

• 60 CsI Crystals

• 14 Plastic
• Scintillators

• Phase I
• Calorimetry Only

• All Phases
• Veto Scint.

• Phase II
• Tracking

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Motivation Isospin Symmetry Breaking

•  
• A measurement of the imaginary part of the s-wave
  production amplitude (E0) provides a
  determination of the charge exchange scattering
  length acex(pn?p0p).
• Requires measurement of the polarized target
  analyzing power T(q).

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Simulations (Bernstein et al.)

• The results indicate that we can measure ImE0
  with a statistical uncertainty of 3.7 in 200
  hours of actual data taking at 158 MeV.
• This gives us the value of acex (pn -gt p0p).
• Isospin conservation
  implies
• acex (pn -gt p0p) -acex
  (p-p -gt p0n).
• The latter is well known from the width of pionic
  hydrogen (0.1301 /- 0.0059) after a decade of
  work. Our result will give a comparable accuracy
  for acex (pn -gt p0p).

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Resources at HIgS

• Mirror development is the key to pion threshold
  Physics at HIgS.
• Present mirrrors take us up to 110 MeV.
• Although a development plan is in place for 165
  nm mirrors (140 MeV), additional resources are
  needed to assure that 160 MeV is reached (150 nm
  mirrors) with full flux in a timely manner.
• Funding presently limits operations to 1000
  hrs/yr. In order to execute this program we
  would like to increase this to 3000 hours per
  year. This requires significant additional
  upport.

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A wide variety of process can be used to study
Chiral Dynamics, guided mainly by the results of
CHPT, an expansion of the Lagrangian for low
energy QCD about the chiral limit, mq0.

• EXAMPLES
• 1. PrimEx at JLABa precision measurement
  of the p0 lifetime.
• Pion-electroproduction from the proton near
  threshold at Mainz and JLAB. ChPT at finite Q2.
• N/D Physics at Mainz the pion-cloud to
  quark-parton transition.
• Compton scattering from the deuteron at
  LUNDneutron polarizabilities.
• Precision measurements of the polarizabilities of
  the proton at HIgS.
• Obtain 5 measurements of ap and bp.
• Double-polarization measurements at LEGS using
  the HD target.
• 7. Spin-polarizability measurements for
  both p and n at HIgS using polarized p, d and 3He
  targets.
• Test ChPT and Lattice QCD results
• .
• 8. Pion-threshold measurements at HIgS using
  polarized beam and target.

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EXTRA SLIDES?

• HIgS A free electron laser generated g-ray source

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HIgSAnticipated Schedule for 2007

• Linearly polarized beams below 65 MeV will be
  available in early 2007.
• Measure Compton scattering from the deuteron at
  50 MeV using a scintillating target
  (unpolarized).
• Circularly polarized beams (OK-5) will be
  available in late 2007 up to 110 MeV.
• Measure GDH on the deuteron up to 50 MeV using
  Blowfish and the frozen-spin target.

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• Spin-exchange optical pumping

• Optical pumping of alkali atoms (Rubidium)
• Spin-exchange of 3He with Rubidium
• High pressure target (10 bar), 3He poln 40 to
  50
• Target will be 40 cm in length giving 1 x 1022
  atoms/cm2

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Schedule for FEL Cavity Mirror RD

• 190 nm mirrors have been proven to work in our
  environmentthese will produce 110 MeV gammas.
• 165 nm mirrors will produce 140 MeV beams once
  OK-5 is operating at 4kA.

Date Milestone
July 2006 Delivery of 1st mirror sets with coatings for 190, 180 and 165 nm
May 2007 Intracavity evaluation of 1st set of 190, 180 and 165 nm mirrors
Oct. 2007 Delivery of 2nd mirror sets with coatings for 180 and 165 nm
Nov. 2007 Intracavity evaluation of 2nd set of 180 and 165 nm mirrors
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Recent results from Choudhury, Nogga and Phillips
for elastic scattering from 3He
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Primakoff Effect

• The ?0 photoproduction from Coulomb field of the
  nucleus.
• Production (??!?0) and decay (?0!??) mechanisms
  imply the Primakoff cross section is proportional
  to the ?0 lifetime.

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?0 production on 208Pb
Events/0.04 deg
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Frozen Spin Polarized Deuterium Target
Butanol Polarization 80 Polarizing Field
2.5 T Holding Field 0.6 T 4 x 1023 d/cm2
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COMPTON ON d WITH A SCINTILLATING TARGETVertical
axis light output from target
detectorHorizontal axis Missing energy (binding
energy)Courtesy of Rory Miskimen
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• Our measurement will determine b to /- 0.10,
  where
• ImE0(gp -gt p0p) b pp/mp
• and b ReE0 (gp -gt pn) acex
  (pn -gt p0p)
• ReE0 (gp -gt pn) is well measured (28.06
  /- 0.27 /- 0.45), giving us
• acex (pn -gt p0p).
• Isospin conservation implies acex (pn -gt p0p)
  -acex (p-p -gt p0n).
• The latter is well known from the width of
  pionic hydrogen (-0.1301 /- 0.0059) after a
  decade of work. Our measurement will give a
  comparable accuracy for acex (pn -gt p0p).

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Recent (PRC C71, 044002 (2005)) HBChPT
calculations of Choudhury and Phillips indicate
appreciable sensitivity of Sx observed in Compton
scattering from the deuteron to g1n at 135 MeV.
Test for consistency!
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