R. Michaels, Jlab Seminar, Apr 27, 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) First Results from
76
Embed
R. Michaels, Jlab Seminar, Apr 27, 2011 Lead ( Pb) Radius Experiment : PREX 208 208 Pb E = 1 GeV, electrons on lead Elastic Scattering Parity Violating.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
R. Michaels, Jlab Seminar, Apr 27, 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)
First Results from
R. Michaels, Jlab Seminar, Apr 27, 2011
Standard Electroweak Model
Gauge bosons
Left –handed fermion fields (quarks and leptons) = doublets under SU(2)
Right-handed fields = singlets under SU(2)
Also
3 fermion families + single complex Higgs doublet
Spontaneous symmetry breaking of the Lagrangian.
Symmetries Lagrangian
iW Bi = 1,2,3 and
Parity Violation
R. Michaels, Jlab Seminar, Apr 27, 2011
A piece of the weak interaction violates parity (mirror symmetry)
which allows to isolate it.
Negative longitudinal spin
Positive longitudinal spin
Pb208
P
S (spin)
(momentum)
Incident electron
Target
R. Michaels, Jlab Seminar, Apr 27, 2011
Parity Violating Asymmetry 624 10~10~
QALR
LRPV
0Z
e e
+
2
Applications of PV at Jefferson Lab
• Nucleon Structure (strangeness) -- HAPPEX / G0
• Standard Model Tests -- Qweak, Moller
• Nuclear Structure (neutron density) : PREX
W2sin
Applications of PV at Jefferson Lab
R. Michaels, Jlab Seminar, Apr 27, 2011
)(sin41
22 22
2
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
5
R. Michaels, Jlab Seminar, Apr 27, 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 Seminar, Apr 27, 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 Seminar, Apr 27, 2011
str
mb
d
d
1fmq
Reminder: Electromagnetic Scattering determines
r
r
Pb208
(charge distribution)
1 2 3
R. Michaels, Jlab Seminar, Apr 27, 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
10
R. Michaels, Jlab Seminar, Apr 27, 2011
How to Measure
Neutron Distributions, Symmetry Energy • Proton-Nucleus Elastic• Pion, alpha, d Scattering• Pion Photoproduction• Heavy ion collisions• Rare Isotopes (dripline)
• Magnetic scattering
• PREX (weak interaction)
• Theory MFT fit mostly by data other than neutron densities
Involve strong probes
Most spins couple to zero.
R. Michaels, Jlab Seminar, Apr 27, 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 Seminar, Apr 27, 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 Seminar, Apr 27, 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 Seminar, Apr 27, 2011
Skx-s15Thanks, Alex Brown
PREX Workshop 2008
E/N
N
R. Michaels, Jlab Seminar, Apr 27, 2011
Skx-s20Thanks, Alex Brown
PREX Workshop 2008
R. Michaels, Jlab Seminar, Apr 27, 2011
Skx-s25Thanks, Alex Brown
PREX Workshop 2008
R. Michaels, Jlab Seminar, Apr 27, 2011
rdrZrNG
H eePWNF
PNC35/2 )()sin41()(
22
Application: Atomic Parity Violation• Low Q test of Standard Model
• Needs RN (or APV measures RN )
2
0
APV
Isotope Chain Experiments e.g. Berkeley Yb
17
R. Michaels, Jlab Seminar, Apr 27, 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 Seminar, Apr 27, 2011
)(P
Fig from: Dany Page.
J.M. Lattimer & M. Prakash, Science 304 (2004) 536.
Inputs:
Eq. of state (EOS)
Hydrostatics (Gen. Rel.)
Astrophysics Observations
Luminosity LTemp. TMass M from pulsar timing
PREX helps here
424 TRL B(with corrections … )
Mass - Radius relationship
pres
sure
dens
ity
19
R. Michaels, Jlab Seminar, Apr 27, 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 ?
Intensity FeedbackAdjustmentsfor small phase shiftsto make close tocircular polarization
Low jitter and high accuracy allows sub-ppmcumulative charge asymmetry in ~ 1 hour
~ 2 hours
27
R. Michaels, Jlab Seminar, Apr 27, 2011
Methods to Reduce Systematics
Voltage change of 58 Volts, added to both the + and - voltages, would zero the asymmetry.
A rotatable /2 waveplate downstream of the P.C. allows arbitrary orientation of DoLP
A simplified picture: asymmetry=0 corresponds
to minimized DoLP at analyzer
Perfect DoCP
Scanning the Pockels Cell Scanning the Pockels Cell voltage = scanning the voltage = scanning the retardation phase = retardation phase = scanning residual DoLPscanning residual DoLP
Inte
nsit
y A
sym
metr
y
(pp
m)
Pockels cell voltage offset (V)
R. Michaels, Jlab Seminar, Apr 27, 2011
• Two Wien Spin Manipulators in series• Solenoid rotates spin +/-90 degrees (spin rotation as B but focus as B2).
Flips spin without moving the beam !
Double Wien FilterCrossed E & B fields to rotate the spin
Want small time constants, and same for detectors and bcm
time time
Response to pulsed beam
R. Michaels, Jlab Seminar, Apr 27, 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