pn12 workshop jlab, nov 2004 r. michaels jefferson lab parity violating neutron densities z of weak...
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PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
)(sin41
22 22
2
QF
QGA
PW
F
)( 2QF n
%1%3 n
n
R
dR
A
dA
Parity Violating Neutron DensitiesZ of Weak Interaction :
Clean Probe Couples Mainly to Neutrons
Low Q elastic nucleus scattering
( T.W. Donnelly, J. Dubach, I Sick )
2
0
In PWIA -- but must account for Coulomb
distortions (C. J. Horowitz)
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Parity Violating AsymmetryLR
LRPVA
0Z
e e
+
2
Applications :
• Nucleon Structure (strangeness)
• Nuclear Structure (neutron density)
• Standard Model tests ( )W2sin
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Z sees the neutrons0
proton neutron
Electric charge 1 0
Weak charge 0.08 1
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
PREX in Hall A at JLab
Hall A
Polarized e-
Source
CEBAF
Hall A
Pol. Source
Lead Foil Target
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
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
Lead Parity
Physics Impact of
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Lead Parity: pins down the symmetry energy (1 parameter)
( R.J. Furnstahl )energy cost for unequal # protons & neutrons
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Pb Parity : Neutron Stars
Crab Pulsar( from hubblesite.org )
( C.J. Horowitz, J. Piekarweicz )
R calibrates EOS of Neutron Rich Matter
Combine R with Neutron Star Radius
Some Neutron Stars too Cold
n
n
Crust ThicknessExplain Obs. Glitches in Pulsar Frequency ?
Exotic Core ? (strange matter, quark star)
Cooling by neutrino emission (URCA)
0.2 fm URCA probable, else not pn RR
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Optimum Kinematics for Lead Parity: E = 850 MeV, <A> = 0.5 ppm. Accuracy in Asy 3%
1 month run
1% in Rn
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
High Resolution Spectrometers
Elastic
Inelastic
detector
Q Q
Dipole
Quad
Spectrometer Concept:
Resolve Elastic
target
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Septum Magnets (INFN)
Electrons scatteredat 6 deg sent to theHRS at 12.5 deg.
•Superconducting magnets
•Commissioned 2003-4
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Integrating Detection
PMT
Calorimeter (for lead, fits in palm of hand)
ADC
Integrator
electrons
• Integrate in 30 msec helicity period.
• Deadtime free.
• 18 bit ADC with < 10 nonlinearity.
• But must separate backgrounds & inelastics ( HRS).
- 4
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Lead Target
Liquid Helium Coolant
Pb
C
208
12
Diamond Backing:
• High Thermal Conductivity• Negligible Systematics
Beam, rastered 4 x 4 mm
A 80at ly testedSuccessful
beam
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Halfwave plate (retractable, reverses helicity)
Laser
Pockel Cell flips helicity
Gun
GaAs Crystal
e beam-
• Rapid, random helicity reversal
• Electrical isolation from rest of lab
• Feedback on Intensity Asymmetry
Polarized Electron Source
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Beam Asymmetries
Araw
= Adet
- AQ +
E+
ix
i
•natural beam jitter (regression) •beam modulation (dithering)Slopes from
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
“Energy” BPM
BPM Y2
BPM Y1
BPM X1
BPM X2
Scale +/- 100 nm
Position Diffs avg
~ 10 nm
Negligible
Systematic Error
Helicity Correlated Differences: Position, Angle, Energy
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Polarimetry
Electron onlyPhoton only
Preliminary: 2.5% syst ( only)
Møller: Pe/Pe ~ 3 % (foil polarization)
Compton: 2% syst. At present
2 analyses based on either electron
or photon detection
Superlattice:
Pe=86% !
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Upgrade of Compton Polarimeter (Nanda, Lhuillier)
To reach 1% accuracy:
• Green Laser
• Integrating Method
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Summary -- Neutron Skin
• R is Fundamental to Nuclear Physics
• HAPPEX program to demonstrate most technical aspects
• Polarimetry Upgrade needed
• Planned 2-day test run in 2005
n
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Moller Polarimetry with Atomic Hydrogen Target
315103 cm
( E. Chudakov, V. Luppov)
H atoms
Solenoid 8T
Trapbeam
Ultra Cold Traps
• Polarization ~ 100%
• Density
• Lifetime > 10 min
Polarimetry
• 1% stat. err. in 30 min at 30 A
• Low background
• High beam currents allowed (100 A)
• Goal: ~ 0.5 % systematic error
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
controls
effective
analyzing
power
Tune residual
linear pol.
Slow helicityreversal
Intensity Attenuator
Polarized Source
High Pe
High Q.E.
Low Apower
•Optical pumping of solid-state photocathode
•High Polarization
• Pockels cell allows rapid helicity flip
•Careful configuration to reduce beam asymmetries.
•Slow helicity reversal to further cancel beam asymmetries
PN12 WorkshopJLab, Nov 2004
R. Michaels
Jefferson Lab
Beam Modulation to Calibrate Sensitivity to Beam Systematics