R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 P b E = 1 GeV, electrons on lead 0 5 Elastic Scattering Parity Violating Asymmetry Spokespersons Paul Souder, Krishna Kumar Guido Urciuoli, Robert Michaels Ran March – June 2010 in Hall A Graduate Students Ahmed Zafar, Chun Min Jen, Abdurahim Rakham (Syracuse) Jon Wexler (UMass) Kiadtisak Saenboonruang (UVa)
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R. Michaels, Jlab UGM, June, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating Asymmetry.
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R. Michaels, Jlab UGM, June, 2011
Lead ( Pb) Radius Experiment : PREX208
208Pb
E = 1 GeV, electrons on lead
05
Elastic Scattering
Parity Violating Asymmetry
Spokespersons
Paul Souder, Krishna Kumar
Guido Urciuoli, Robert Michaels
Ran March – June 2010 in Hall A
Graduate Students
Ahmed Zafar, Chun Min Jen, Abdurahim Rakham (Syracuse)
Jon Wexler (UMass)
Kiadtisak Saenboonruang (UVa)
R. Michaels, Jlab UGM, June, 2011
)(
sin4122 2
22
QF
QG
dd
dd
dd
dd
AP
WF
LR
LR
)( 2QF n
%1%3 n
n
R
dR
A
dA
Idea behind PREX
Z of Weak Interaction :
Clean Probe Couples Mainly to Neutrons( T.W. Donnelly, J. Dubach, I Sick 1989 )
0
In PWIA (to illustrate) :
w/ Coulomb distortions (C. J. Horowitz) :
0
R. Michaels, Jlab UGM, June, 2011
Measured Asymmetry
Weak Density at one Q2
Neutron Density at one Q2
Correct for CoulombDistortions
Small Corrections forG
nE G
sE MEC
Assume Surface Thickness Good to 25% (MFT)
Atomic Parity Violation
Mean Field & Other
Models
Neutron
Stars
R n
PREX Physics Output
Slide adapted from C. Horowitz
R. Michaels, Jlab UGM, June, 2011
Fundamental Nuclear Physics :
What is the size of a nucleus ?
Neutrons are thought to determine the size of heavy nuclei like 208Pb.
Can theory predict it ?
R. Michaels, Jlab UGM, June, 2011
str
mb
d
d
1fmq
Reminder: Electromagnetic Scattering determines
r
rPb
208
(charge distribution)
1 2 3
d
d
R. Michaels, Jlab UGM, June, 2011
Z of weak interaction : sees the neutrons
proton neutron
Electric charge 1 0
Weak charge 0.08 1
0
Analysis is clean, like electromagnetic scattering:
1. Probes the entire nuclear volume
2. Perturbation theory applies
6
R. Michaels, Jlab UGM, June, 2011
)()()(ˆ5 rArVrV
)(
)(sin41
22 2
22
2
QF
QFQG
d
d
d
d
d
d
d
d
AP
NW
F
LR
LR
neutron weak charge >> proton weak charge
is small, best observed by parity violation
||)()(/
//3 rrrZrdrV )()()sin41(22
)( 2 rNrZG
rA NPWF
22 |)(| QFd
d
d
dP
Mott
)()(4
1)( 0
32 rqrjrdQF PP )()(
4
1)( 0
32 rqrjrdQF NN
Electron - Nucleus Potential
electromagnetic axial
Neutron form factor
Parity Violating Asymmetry
)(rA
1sin41 2 W
Proton form factor
0
Pb is spin 0208
R. Michaels, Jlab UGM, June, 2011
( R.J. Furnstahl )
Measurement at one Q is sufficient to measure R
2
N
proposed error
Why only one parameter ?
(next slide…)
PREX:
R. Michaels, Jlab UGM, June, 2011
ZN
Nuclear Structure: Neutron density is a fundamental observable that remains elusive.
Reflects poor understanding of symmetry energy of nuclear matter = the energy cost of
xn
)21()()2/1,(),( 2xnSxnExnE
n.m. density
ratio proton/neutrons
• Slope unconstrained by data
• Adding R from Pb will eliminate the
dispersion in plot.
N208
Slide adapted from J. Piekarewicz
R. Michaels, Jlab UGM, June, 2011
Skx-s15Thanks, Alex Brown
PREX Workshop 2008
E/N
N
R. Michaels, Jlab UGM, June, 2011
Skx-s20Thanks, Alex Brown
PREX Workshop 2008
R. Michaels, Jlab UGM, June, 2011
Skx-s25Thanks, Alex Brown
PREX Workshop 2008
R. Michaels, Jlab UGM, June, 2011
Application: Atomic Parity Violation• Low Q test of Standard Model
• Needs RN (or APV measures RN )
2
0
Isotope Chain Experiments e.g. Berkeley Yb
13
APV
rdrZrNG
H eePWNF
PNC35/2 )()sin41()(
22
R. Michaels, Jlab UGM, June, 2011
Neutron
StarsWhat is the nature of extremely dense matter ?
Do collapsed stars form “exotic” phases of matter ? (strange stars, quark stars)
Crab Nebula (X-ray, visible, radio, infrared)
Application :
R. Michaels, Jlab UGM, June, 2011
PREX & Neutron Stars
pn RRCrab Pulsar
( C.J. Horowitz, J. Piekarewicz )
R calibrates EOS of Neutron Rich Matter
Combine PREX R with Obs. Neutron Star Radii
Some Neutron Stars seem too Cold
N
N
Crust ThicknessExplain Glitches in Pulsar Frequency ?
Wien Flips helped !Average with signs = what exp’t feels
Points: Not sign corrected
R. Michaels, Jlab UGM, June, 2011
Hall A Compton Upgrade
with Green Laser
Sirish Nanda, et. al.
1 % Polarimetry
at 1 GeV
R. Michaels, Jlab UGM, June, 2011
Hall A Moller Upgrade
Superconducting Magnet from Hall C
Saturated Iron Foil Targets
1 % Polarimetry
Magnet and Target
DAQ Upgrade (FADC)
Sasha Glamazdin, et.al.
R. Michaels, Jlab UGM, June, 2011
High Resolution Spectrometers
Elastic
Inelastic
detector
Q Q
Dipole
Quad
Spectrometer Concept: Resolve Elastic
target
Left-Right symmetry to control transverse polarization systematic
1st excited state Pb 2.6 MeV
R. Michaels, Jlab UGM, June, 2011
Collimators
Septum Magnet
Top view
target
HRS-L
Q1
HRS-R
Q1
PREX Region After Target
Former O-Ring location which failed and caused significant time loss
Planned Tungsten Collimator and Shielding
R. Michaels, Jlab UGM, June, 2011
10 m
-1 m
Geant 4 Radiation Calculations
• benchmarking against LD2 (ran at 100 uA)
• exploring shielding strategies
J. Mammei, L. Zana
Number of Neutrons per incident Electron
Z (distance along beamline)
1 mLD2 tgtPb tgt
1 - 50 MeV
50 - 500 MeV
0 - 1 MeV
Strategy
• Tungsten ( W ) plug
• Shield the W
• x10 reduction in 0.2 to 10 MeV neutrons
(similar to LD2)
00 37.0
W
PREX-II proposal
PREX -I
PREX -II
R. Michaels, Jlab UGM, June, 2011
Pure, Thin 208 Pb Target
Momentum (GeV/c)
Lead 5- State
2.6 MeV
High Resolution Spectrometers
DETECTOR footprint
25
R. Michaels, Jlab UGM, June, 2011
Diamond LEAD
• Three bays
• Lead (0.5 mm) sandwiched by diamond (0.15 mm)
• Liquid He cooling (30 Watts)
Lead / Diamond Target
R. Michaels, Jlab UGM, June, 2011
Performance of Lead / Diamond Targets
Last 4 days at 70 uA
Targets with thin diamond backing (4.5 % background) degraded fastest.
Thick diamond (8%) ran well and did not melt at 70 uA.
meltedmelted
NOT melted
Solution: Run with 10 targets.
R. Michaels, Jlab UGM, June, 2011
y
z
xS
k
+ -
AT > 0 means
)'( eeeT kkSA
Beam-Normal Asymmetry in elastic electron scatteringi.e. spin transverse to scattering plane
Possible systematic if small transverse spin component
New results PREX
ppmAC T 35.036.052.6:12
ppmAPb T 36.019.013.0:208
• Small AT for 208Pb is a big (but pleasant) surprise. • AT for 12C qualitatively consistent with 4He and available calculations (1) Afanasev ; (2) Gorchtein & Horowitz