The PREX and CREX Experiments Measurements of Parity-Violating Electron Scattering
Asymmetries off 208Pb and 48Ca:The first PREX Result at Jefferson Laboratory and Future Plans
Krishna S. KumarUniversity of Massachusetts, Amherst
Acknowledgements: C. Horowitz
The PREX, CREX and Hall A Collaboration and the Accelerator Division at Jefferson Laboratory
3rd International Symposium on Nuclear Symmetry Energy, NSCL/FRIB, East Lansing, MI
July 25, 2013
Krishna S. Kumar The PREX and CREX Experiments at JLab
Outline
Introduction to Parity-Violating Electron ScatteringRelativistic electron scattering and substructureParity Violation (PV) in weak interactionsNeutral weak interactionsOverview of an electron beam parity violation experiment
PREX at Jefferson LaboratoryExperimental technique
Unique features of Jefferson Lab Hall APhysics Run (March-June 2010)
PREX first resultFuture Plans
Improvements for Approved PREX-II ApparatusRecent PAC Approval of the CREX ExperimentNew idea for an improved Pb measurement at Mainz
Conclusion and Outlook
2
PRL 108 (2012) 112502PRC 85 (2012) 032501
Krishna S. Kumar The PREX and CREX Experiments at JLab
Outline
Introduction to Parity-Violating Electron ScatteringRelativistic electron scattering and substructureParity Violation (PV) in weak interactionsNeutral weak interactionsOverview of an electron beam parity violation experiment
PREX at Jefferson LaboratoryExperimental technique
Unique features of Jefferson Lab Hall APhysics Run (March-June 2010)
PREX first resultFuture Plans
Improvements for Approved PREX-II ApparatusRecent PAC Approval of the CREX ExperimentNew idea for an improved Pb measurement at Mainz
Conclusion and Outlook
2
Challenging experimental technique has been
successfully demonstrated
PRL 108 (2012) 112502PRC 85 (2012) 032501
Krishna S. Kumar The PREX and CREX Experiments at JLab
Outline
Introduction to Parity-Violating Electron ScatteringRelativistic electron scattering and substructureParity Violation (PV) in weak interactionsNeutral weak interactionsOverview of an electron beam parity violation experiment
PREX at Jefferson LaboratoryExperimental technique
Unique features of Jefferson Lab Hall APhysics Run (March-June 2010)
PREX first resultFuture Plans
Improvements for Approved PREX-II ApparatusRecent PAC Approval of the CREX ExperimentNew idea for an improved Pb measurement at Mainz
Conclusion and Outlook
2
Challenging experimental technique has been
successfully demonstrated
Definite plans to obtain higher statistics
PRL 108 (2012) 112502PRC 85 (2012) 032501
Krishna S. Kumar Parity-Violating Electron Scattering: MeV to TeV Physics
Introduction to Parity-Violating
Electron Scattering
3
Krishna S. Kumar The PREX and CREX Experiments at JLab
Relativistic Electron Scattering
4
e
e
γ
Differential Cross Section
Heavy, spinlessnucleus
� d⇥
d�
⇥
Mott=
4Z2�2E2
q4
and nuclear size
Q2: -(4-momentum)2 of the virtual photon
€
q2 = −4E ʹ′ E sin2 θ2
4-momentum transfer
Krishna S. Kumar The PREX and CREX Experiments at JLab
Relativistic Electron Scattering
4
e
e
γ
Differential Cross Section
Heavy, spinlessnucleus
� d⇥
d�
⇥
Mott=
4Z2�2E2
q4
d�
d�=
⇥d�
d�
⇤
Mott
�� F (q)��2
Neglec&ng recoil, form factor F(q) is the Fourier transform of charge distribu&on
As Q increases, nuclear size modifies formula
and nuclear size
Q2: -(4-momentum)2 of the virtual photon
€
q2 = −4E ʹ′ E sin2 θ2
4-momentum transfer
Krishna S. Kumar The PREX and CREX Experiments at JLab
Relativistic Electron Scattering
4
e
e
γ
Differential Cross Section
Heavy, spinlessnucleus
� d⇥
d�
⇥
Mott=
4Z2�2E2
q4
d�
d�=
⇥d�
d�
⇤
Mott
�� F (q)��2
Neglec&ng recoil, form factor F(q) is the Fourier transform of charge distribu&on
As Q increases, nuclear size modifies formula
and nuclear size
Q2: -(4-momentum)2 of the virtual photon
€
q2 = −4E ʹ′ E sin2 θ2
4-momentum transfer
Krishna S. Kumar The PREX and CREX Experiments at JLab
Measurement Approach
5
€
APV ≈GFQ
2
4πα 2Fn Q
2( )Fp Q
2( )
An Electroweak Observable Sensitive to the Neutron RMS Radius
v090M
Sk7HFB-8
SkP
HFB-17SkM
*
Ska
Sk-RsSk-T4
DD-ME2
DD-ME1
FSUGold
DD-PC1PK1.s24
NL3.s25
G2
NL-SV2PK1NL3
NL3*
NL2NL1
0 50 100 150 L (MeV)
0.1
0.15
0.2
0.25
0.3
!rnp
(fm
)
Linear Fit, r = 0.979Nonrelativistic modelsRelativistic models
D1S
D1NSG
II
Sk-T6SkX SLy5
SLy4
MSkA
MSL0
SIVSkSM
*SkM
P
SkI2SV
G1
TM1
NL-SHNL-RA1
PC-F1
BCP
RHF-PKO3
Sk-Gs
RHF-PKA1PC-PK1
SkI5
Roca-Maza et al
Mean Field Theory fit mostly by data other than neutron densities
electroweak probe
R. Furnstahl
Krishna S. Kumar The PREX and CREX Experiments at JLab
Measurement Approach
5
€
APV ≈GFQ
2
4πα 2Fn Q
2( )Fp Q
2( )
An Electroweak Observable Sensitive to the Neutron RMS Radius
v090M
Sk7HFB-8
SkP
HFB-17SkM
*
Ska
Sk-RsSk-T4
DD-ME2
DD-ME1
FSUGold
DD-PC1PK1.s24
NL3.s25
G2
NL-SV2PK1NL3
NL3*
NL2NL1
0 50 100 150 L (MeV)
0.1
0.15
0.2
0.25
0.3
!rnp
(fm
)
Linear Fit, r = 0.979Nonrelativistic modelsRelativistic models
D1S
D1NSG
II
Sk-T6SkX SLy5
SLy4
MSkA
MSL0
SIVSkSM
*SkM
P
SkI2SV
G1
TM1
NL-SHNL-RA1
PC-F1
BCP
RHF-PKO3
Sk-Gs
RHF-PKA1PC-PK1
SkI5
Roca-Maza et al
Mean Field Theory fit mostly by data other than neutron densities
electroweak probe
R. Furnstahl
In the following, I focus on the measurements; other talks, including the
one following mine, address interpretation and potential implications
Note: R. Michaels (JLab) here during the last week
Krishna S. Kumar The PREX and CREX Experiments at JLab
Weak Interactions
6
Fermi Theory for weak interactionsNeutron & nuclear β Decay
“Effective” low energy theory that explains many observed properties of radioactive nuclear decays
Universal strength: coupling constant GF
charge and flavor-changing
Krishna S. Kumar The PREX and CREX Experiments at JLab
Weak Interactions
6
Fermi Theory for weak interactionsNeutron & nuclear β Decay
“Effective” low energy theory that explains many observed properties of radioactive nuclear decays
Universal strength: coupling constant GF
€
x,y,z→−x,−y,−zparity transformation (reflection)
�p = ��p�L = �L
�s = �s
Observed NOT to be invariant under parity transformations
charge and flavor-changing
Krishna S. Kumar The PREX and CREX Experiments at JLab
Weak Interactions
6
Fermi Theory for weak interactionsNeutron & nuclear β Decay
“Effective” low energy theory that explains many observed properties of radioactive nuclear decays
Universal strength: coupling constant GF
Weak decay of60Co Nucleus
60Co
60Ni
€
x,y,z→−x,−y,−zparity transformation (reflection)
�p = ��p�L = �L
�s = �s
Observed NOT to be invariant under parity transformations
observed anisotropy in beta-emission when nuclei aligned to a magnetic field
signature of parity violation1957
charge and flavor-changing
Krishna S. Kumar The PREX and CREX Experiments at JLab
Weak Interactions
6
Fermi Theory for weak interactions
“Effective” low energy theory that explains many observed properties of radioactive nuclear decays
Universal strength: coupling constant GF
Weak decay of60Co Nucleus
60Co
60Ni
€
x,y,z→−x,−y,−zparity transformation (reflection)
�p = ��p�L = �L
�s = �s
Observed NOT to be invariant under parity transformations
observed anisotropy in beta-emission when nuclei aligned to a magnetic field
signature of parity violation1957
B
observed not observed
ν-
e -
e-
ν-reflection
Krishna S. Kumar The PREX and CREX Experiments at JLab
Charge/Flavor Conserving Analog?
7
Zel’dovich speculation: Is Electron Scattering Parity-Violating?
1958
Krishna S. Kumar The PREX and CREX Experiments at JLab
Charge/Flavor Conserving Analog?
7
Neutron β Decay Electron-protonWeak Scattering
Zel’dovich speculation: Is Electron Scattering Parity-Violating?
1958
Krishna S. Kumar The PREX and CREX Experiments at JLab
Charge/Flavor Conserving Analog?
7
Neutron β Decay Electron-protonWeak Scattering
Zel’dovich speculation: Is Electron Scattering Parity-Violating?
1958
Krishna S. Kumar The PREX and CREX Experiments at JLab
Charge/Flavor Conserving Analog?
7
Neutron β Decay Electron-protonWeak Scattering
Parity-violating
Zel’dovich speculation: Is Electron Scattering Parity-Violating?
1958
Krishna S. Kumar The PREX and CREX Experiments at JLab
Charge/Flavor Conserving Analog?
7
Neutron β Decay Electron-protonWeak Scattering
Parity-violating
Zel’dovich speculation: Is Electron Scattering Parity-Violating?
1958
Krishna S. Kumar The PREX and CREX Experiments at JLab
Charge/Flavor Conserving Analog?
7
Neutron β Decay Electron-protonWeak Scattering
Parity-violating
θE
E’
€
Q2 = 4E ʹ′ E sin2 θ2
4-momentum transfer
Zel’dovich speculation: Is Electron Scattering Parity-Violating?
1958
Krishna S. Kumar The PREX and CREX Experiments at JLab
Parity Violation Signature
8
How to observe parity violation in electron scattering
p pp
p
pe-
p
e-
e-
e-longitudinallypolarized
e-e-reflection
rotation
Krishna S. Kumar The PREX and CREX Experiments at JLab
Parity Violation Signature
8
•One of the incident beams longitudinally polarized•Change sign of longitudinal polarization•Measure fractional rate difference
How to observe parity violation in electron scattering
p pp
p
pe-
p
e-
e-
e-longitudinallypolarized
e-e-reflection
rotation
Krishna S. Kumar The PREX and CREX Experiments at JLab
Parity Violation Signature
8
•One of the incident beams longitudinally polarized•Change sign of longitudinal polarization•Measure fractional rate difference
How to observe parity violation in electron scattering
p pp
p
pe-
p
e-
e-
e-longitudinallypolarized
e-e-reflection
rotation
Krishna S. Kumar The PREX and CREX Experiments at JLab
Parity Violation Signature
8
•One of the incident beams longitudinally polarized•Change sign of longitudinal polarization•Measure fractional rate difference
€
10−4 ⋅Q2APV ~ (GeV2)
How to observe parity violation in electron scattering
p pp
p
pe-
p
e-
e-
e-longitudinallypolarized
e-e-reflection
rotation
Krishna S. Kumar The PREX and CREX Experiments at JLab
Neutral Weak Interaction Theory
9
Glashow, Weinberg and Salam: SU(2)L X U(1)Y
W Charge
Left- Right-
zero
€
T = ±12€
0,±1,± 13,± 23
€
0,±1,± 13,± 23γ Charge
One free parameter: weak mixing angle θW
Z Charge
€
T − qsin2θW
€
−qsin2θW
The Z boson incorporated
Krishna S. Kumar The PREX and CREX Experiments at JLab
Neutral Weak Interaction Theory
9
Glashow, Weinberg and Salam: SU(2)L X U(1)Y
W Charge
Left- Right-
zero
€
T = ±12€
0,±1,± 13,± 23
€
0,±1,± 13,± 23γ Charge
One free parameter: weak mixing angle θW
Z Charge
€
T − qsin2θW
€
−qsin2θW
μ
νμ W+
-
Charged Current
The Z boson incorporated
Krishna S. Kumar The PREX and CREX Experiments at JLab
Neutral Weak Interaction Theory
9
Glashow, Weinberg and Salam: SU(2)L X U(1)Y
W Charge
Left- Right-
zero
€
T = ±12€
0,±1,± 13,± 23
€
0,±1,± 13,± 23γ Charge
One free parameter: weak mixing angle θW
Z Charge
€
T − qsin2θW
€
−qsin2θW
νμ
νμ Z0
Neutral Current
μ
νμ W+
-
Charged Current
The Z boson incorporated
Krishna S. Kumar The PREX and CREX Experiments at JLab
Neutral Weak Interaction Theory
9
Glashow, Weinberg and Salam: SU(2)L X U(1)Y
W Charge
Left- Right-
zero
€
T = ±12€
0,±1,± 13,± 23
€
0,±1,± 13,± 23γ Charge
One free parameter: weak mixing angle θW
Z Charge
€
T − qsin2θW
€
−qsin2θW
νμ
νμ Z0
Neutral Current
μ
νμ W+
-
Charged Current
The Z boson incorporated
g
cos ✓WZµ
¯f�µ(T3f � 2Qf sin
2 ✓W � T3f�5)f, T3f = ±1/2f fZ0
Krishna S. Kumar The PREX and CREX Experiments at JLab
Neutral Weak Interaction Theory
9
Glashow, Weinberg and Salam: SU(2)L X U(1)Y
W Charge
Left- Right-
zero
€
T = ±12€
0,±1,± 13,± 23
€
0,±1,± 13,± 23γ Charge
One free parameter: weak mixing angle θW
Z Charge
€
T − qsin2θW
€
−qsin2θW
νμ
νμ Z0
Neutral Current
μ
νμ W+
-
Charged Current
The Z boson incorporated
Do lepton-nucleon neutral current interactions exhibit parity violation?
g
cos ✓WZµ
¯f�µ(T3f � 2Qf sin
2 ✓W � T3f�5)f, T3f = ±1/2f fZ0
Parity is violated
Parity is conserved
APV ⇠ 10�4
Weinberg model
Krishna S. Kumar The PREX and CREX Experiments at JLab
Neutral Weak Interaction Theory
9
Glashow, Weinberg and Salam: SU(2)L X U(1)Y
W Charge
Left- Right-
zero
€
T = ±12€
0,±1,± 13,± 23
€
0,±1,± 13,± 23γ Charge
One free parameter: weak mixing angle θW
Z Charge
€
T − qsin2θW
€
−qsin2θW
νμ
νμ Z0
Neutral Current
μ
νμ W+
-
Charged Current
The Z boson incorporated
Do lepton-nucleon neutral current interactions exhibit parity violation?
g
cos ✓WZµ
¯f�µ(T3f � 2Qf sin
2 ✓W � T3f�5)f, T3f = ±1/2f fZ0
First table-top atomic parity violation searches: negative!
Parity is violated
Parity is conserved
APV ⇠ 10�4
Weinberg model
Krishna S. Kumar The PREX and CREX Experiments at JLab
Neutral Weak Interaction Theory
9
Glashow, Weinberg and Salam: SU(2)L X U(1)Y
W Charge
Left- Right-
zero
€
T = ±12€
0,±1,± 13,± 23
€
0,±1,± 13,± 23γ Charge
One free parameter: weak mixing angle θW
Z Charge
€
T − qsin2θW
€
−qsin2θW
νμ
νμ Z0
Neutral Current
μ
νμ W+
-
Charged Current
The Z boson incorporated
Do lepton-nucleon neutral current interactions exhibit parity violation?
g
cos ✓WZµ
¯f�µ(T3f � 2Qf sin
2 ✓W � T3f�5)f, T3f = ±1/2f fZ0
First table-top atomic parity violation searches: negative!
Parity is violated
Parity is conserved
APV ⇠ 10�4
Weinberg model
large rate at large Q2
electron-nucleon deep inelastic
scatteringdiscovery of scaling
M. Breidenbach et al.
Krishna S. Kumar The PREX and CREX Experiments at JLab
Neutral Weak Interaction Theory
9
Glashow, Weinberg and Salam: SU(2)L X U(1)Y
W Charge
Left- Right-
zero
€
T = ±12€
0,±1,± 13,± 23
€
0,±1,± 13,± 23γ Charge
One free parameter: weak mixing angle θW
Z Charge
€
T − qsin2θW
€
−qsin2θW
νμ
νμ Z0
Neutral Current
μ
νμ W+
-
Charged Current
The Z boson incorporated
Do lepton-nucleon neutral current interactions exhibit parity violation?
g
cos ✓WZµ
¯f�µ(T3f � 2Qf sin
2 ✓W � T3f�5)f, T3f = ±1/2f fZ0
First table-top atomic parity violation searches: negative!
Parity is violated
Parity is conserved
APV ⇠ 10�4
Weinberg model
large rate at large Q2
electron-nucleon deep inelastic
scatteringdiscovery of scaling
M. Breidenbach et al.
pressing problem in mid-70’s
Z*?
e- e-
N X
Krishna S. Kumar The PREX and CREX Experiments at JLab
Anatomy of a Parity Experiment
10
C.Y. Prescott, et al.
Krishna S. Kumar The PREX and CREX Experiments at JLab
Anatomy of a Parity Experiment
10
C.Y. Prescott, et al.
² Beam helicity sequence is chosen pseudo-randomly• Helicity state, followed by its complement• Data analyzed as “pulse-pairs”
Krishna S. Kumar The PREX and CREX Experiments at JLab
Anatomy of a Parity Experiment
10
C.Y. Prescott, et al.
• Beam Monitors to measure helicity-correlated changes in beam parameters
• High-power cryotarget 30 cm long for high luminosity
Krishna S. Kumar The PREX and CREX Experiments at JLab
Anatomy of a Parity Experiment
10
C.Y. Prescott, et al.
• Polarimetry
Krishna S. Kumar The PREX and CREX Experiments at JLab
Anatomy of a Parity Experiment
10
C.Y. Prescott, et al.
• Magnetic spectrometer directs flux to background-free region
• Flux Integration measures high rate without deadtime
Krishna S. Kumar The PREX and CREX Experiments at JLab
-810 -710 -610 -510 -410 -310-1010
-910
-810
-710
-610
-510
-410
PVeS Experiment Summary
100%
10%
1%
0.1%
G0
G0
E122
Mainz-Be
MIT-12C
SAMPLE H-I
A4A4
A4
H-IIH-He
E158
H-III
PVDIS-6
PREX-IPREX-II
CREX
Qweak
SOLID
MollerMESA-P2
MESA-12CILC-MOLLER
PioneeringNuclear Studies (1998-2010)S.M. Study (2003-2012)Future
PVA
)PV
(Aδ
3 Decades of Technical Progress
11
photocathodes, polarimetry, high power cryotargets, nanometer beam stability, precision beam diagnostics, low noise electronics, radiation hard detectors
•Beyond Standard Model Searches•Strange quark form factors•Neutron skin of a heavy nucleus•QCD structure of the nucleon
SLACMIT-Bates
MainzJefferson Lab
• sub-part per billion statistical reach and systematic control• sub-1% normalization control
Parity-violating electron scattering has become a precision tool
Mainz & MIT-Bates in the mid-80sJLab program launched in the mid-90s
Continuous interplay between probing hadron structure and electroweak physics
E158 at SLAC measured PV Møller scattering
State-of-the-art:
Krishna S. Kumar Parity-Violating Electron Scattering: MeV to TeV Physics
PREX at Jefferson Lab
12
22
208Pb208Pb208Pb208Pb
Krishna S. Kumar The PREX and CREX Experiments at JLab
PREX Concept
13
γ
€
MEM =4παQ2
Fp Q2( )
€
MPVNC =
GF21− 4sin2θW( )Fp Q2( ) − Fn Q2( )[ ]
€
APV ≈GFQ
2
4πα 2Fn Q
2( )Fp Q
2( )proton neutron
Electric charge 1 0
Weak charge ~0.08 -‐1
Q2 ~ 0.01 GeV2
APV ~ 0.6 ppmRate ~ 1 GHz
5o scattering angle
Pb-Radius EXperiment
QpEM ~ 1 Qn
EM ~ 0
QpW ~ 1 - 4sin2θWQn
W ~ -1
δ(APV) ~ 20 ppb!
Krishna S. Kumar The PREX and CREX Experiments at JLab
PREX Concept
13
γ
€
MEM =4παQ2
Fp Q2( )
€
MPVNC =
GF21− 4sin2θW( )Fp Q2( ) − Fn Q2( )[ ]
€
APV ≈GFQ
2
4πα 2Fn Q
2( )Fp Q
2( )proton neutron
Electric charge 1 0
Weak charge ~0.08 -‐1
Q2 ~ 0.01 GeV2
APV ~ 0.6 ppmRate ~ 1 GHz
5o scattering angle
Pb-Radius EXperiment
QpEM ~ 1 Qn
EM ~ 0
QpW ~ 1 - 4sin2θWQn
W ~ -1
0 0.4 0.8 1.2 1.6q(fm-1)
0
0.2
0.4
0.6
0.8
1
F wk(
q)
48Ca [0.207(6)]208Pb[0.223(6)]PREX [0.204(28)]
FSUGoldqC
REX
J. Piekarewicz
v090M
Sk7HFB-8
SkP
HFB-17SkM
*
Ska
Sk-RsSk-T4
DD-ME2
DD-ME1
FSUGold
DD-PC1PK1.s24
NL3.s25
G2
NL-SV2PK1NL3
NL3*
NL2NL1
0 50 100 150 L (MeV)
0.1
0.15
0.2
0.25
0.3
!rnp
(fm
)
Linear Fit, r = 0.979Nonrelativistic modelsRelativistic models
D1S
D1NSG
II
Sk-T6SkX SLy5
SLy4
MSkA
MSL0
SIVSkSM
*SkM
P
SkI2SV
G1
TM1
NL-SHNL-RA1
PC-F1
BCP
RHF-PKO3
Sk-Gs
RHF-PKA1PC-PK1
SkI5Roca-Maza et al
Mean Field Theory fit mostly by data other than neutron densities
electroweak probe
R. Furnstahl
δ(APV) ~ 20 ppb!
Krishna S. Kumar The PREX and CREX Experiments at JLab
PREX Concept
13
γ
€
MEM =4παQ2
Fp Q2( )
€
MPVNC =
GF21− 4sin2θW( )Fp Q2( ) − Fn Q2( )[ ]
€
APV ≈GFQ
2
4πα 2Fn Q
2( )Fp Q
2( )proton neutron
Electric charge 1 0
Weak charge ~0.08 -‐1
Q2 ~ 0.01 GeV2
APV ~ 0.6 ppmRate ~ 1 GHz
5o scattering angle
Pb-Radius EXperiment
QpEM ~ 1 Qn
EM ~ 0
QpW ~ 1 - 4sin2θWQn
W ~ -1
0 0.4 0.8 1.2 1.6q(fm-1)
0
0.2
0.4
0.6
0.8
1
F wk(
q)
48Ca [0.207(6)]208Pb[0.223(6)]PREX [0.204(28)]
FSUGoldqC
REX
J. Piekarewicz
v090M
Sk7HFB-8
SkP
HFB-17SkM
*
Ska
Sk-RsSk-T4
DD-ME2
DD-ME1
FSUGold
DD-PC1PK1.s24
NL3.s25
G2
NL-SV2PK1NL3
NL3*
NL2NL1
0 50 100 150 L (MeV)
0.1
0.15
0.2
0.25
0.3
!rnp
(fm
)
Linear Fit, r = 0.979Nonrelativistic modelsRelativistic models
D1S
D1NSG
II
Sk-T6SkX SLy5
SLy4
MSkA
MSL0
SIVSkSM
*SkM
P
SkI2SV
G1
TM1
NL-SHNL-RA1
PC-F1
BCP
RHF-PKO3
Sk-Gs
RHF-PKA1PC-PK1
SkI5Roca-Maza et al
Mean Field Theory fit mostly by data other than neutron densities
electroweak probe
R. Furnstahl
δ(APV) ~ 20 ppb!
as direct as it gets!
Krishna S. Kumar The PREX and CREX Experiments at JLab
PREX Overview
14
A B C
D1 GeV electron beam, 50-70 µAhigh polarization, ~89%helicity reversal at 120 Hz
0.5 mm isotopically pure 208Pb target5° scattered electrons Q2 =0.0088 GeV2/c2
new thin quartz detectors
Krishna S. Kumar The PREX and CREX Experiments at JLab
PREX Overview
14
A B C
D1 GeV electron beam, 50-70 µAhigh polarization, ~89%helicity reversal at 120 Hz
0.5 mm isotopically pure 208Pb target5° scattered electrons Q2 =0.0088 GeV2/c2
new thin quartz detectors
Krishna S. Kumar The PREX and CREX Experiments at JLab
HRS at JLab
15
Flux Integration TechniqueHAPPEX: 2 MHz
HAPPEXII: 100 MHz PREX: 1 GHz
ElasticInelastic detector
Q Q
Dipole
Quad
target
Hall A High Resolution Spectrometers
Krishna S. Kumar The PREX and CREX Experiments at JLab
HRS at JLab
15
Flux Integration TechniqueHAPPEX: 2 MHz
HAPPEXII: 100 MHz PREX: 1 GHz
ElasticInelastic detector
Q Q
Dipole
Quad
target pure, thin 208Pb target
~10 cm
hardware resolution: ∆p/p ~ 10-3
Hall A High Resolution Spectrometers
Krishna S. Kumar The PREX and CREX Experiments at JLab
“Parity Quality” Beam
16
•Active feedback of charge asymmetry•Careful laser alignment•Precision beam position monitoring•Active calibration of detector slopes
Aphys ~ 500 ppb Acorr = Adet - AQ + α ΔE+ Σβi Δxi
Krishna S. Kumar The PREX and CREX Experiments at JLab
“Parity Quality” Beam
16
•Active feedback of charge asymmetry•Careful laser alignment•Precision beam position monitoring•Active calibration of detector slopes
Aphys ~ 500 ppb Acorr = Adet - AQ + α ΔE+ Σβi Δxi
Krishna S. Kumar The PREX and CREX Experiments at JLab
raw average: ~ 20 nm
“Parity Quality” Beam
16
•Active feedback of charge asymmetry•Careful laser alignment•Precision beam position monitoring•Active calibration of detector slopes
Aphys ~ 500 ppb Acorr = Adet - AQ + α ΔE+ Σβi Δxi
mic
rons
Krishna S. Kumar The PREX and CREX Experiments at JLab
raw average: ~ 20 nm
“Parity Quality” Beam
16
•Active feedback of charge asymmetry•Careful laser alignment•Precision beam position monitoring•Active calibration of detector slopes
Aphys ~ 500 ppb Acorr = Adet - AQ + α ΔE+ Σβi Δxi
mic
rons
Krishna S. Kumar The PREX and CREX Experiments at JLab
raw average: ~ 20 nm
“Parity Quality” Beam
16
•Active feedback of charge asymmetry•Careful laser alignment•Precision beam position monitoring•Active calibration of detector slopes
2 methods of “slow” reversal
Aphys ~ 500 ppb Acorr = Adet - AQ + α ΔE+ Σβi Δxi
mic
rons
Krishna S. Kumar The PREX and CREX Experiments at JLab
raw average: ~ 20 nm
“Parity Quality” Beam
16
Electron Beam
•Active feedback of charge asymmetry•Careful laser alignment•Precision beam position monitoring•Active calibration of detector slopes
2 methods of “slow” reversal
Sign flips using ½ wave plate & Wien filter ++ -+ +- --
corrections:< 5 nm or 100 ppb
Aphys ~ 500 ppb Acorr = Adet - AQ + α ΔE+ Σβi Δxi
mic
rons
Krishna S. Kumar The PREX and CREX Experiments at JLab
Aspects of the Apparatus
17
Krishna S. Kumar The PREX and CREX Experiments at JLab
Raw Asymmetry Data
18
171 ppm width@ 30 Hz
integrated rate ~ 1 GHz
120 Hz flipping
Statistical behavior of data consistent with detector noise being
dominated by electron counting statistics
Grand averages of all 4
combinations of slow reversal
flips are statistically consistent
606 ± 113496 ± 107566 ± 095685 ± 092
594 ± 50parts per billion (ppb)
systematic error due to beam
fluctuations: 7 ppb
Physics Data: April/May 2010
parts per million # std. deviations
Krishna S. Kumar The PREX and CREX Experiments at JLab
Normalization Errors
19
Systematic Error Absolute (ppm)
Relative ( %)
Polarization 0.0083 1.3
Detector Linearity 0.0076 1.2Beam current normalization
0.0015 0.2
Rescattering 0.0001 0
Transverse Polarization
0.0012 0.2
Q2 0.0028 0.4
Target Backing 0.0026 0.4
Inelastic States 0 0
TOTAL 0.0140 2.1
Goal for total systematic error ~ 2% achieved!
Krishna S. Kumar The PREX and CREX Experiments at JLab
Normalization Errors
19
Systematic Error Absolute (ppm)
Relative ( %)
Polarization 0.0083 1.3
Detector Linearity 0.0076 1.2Beam current normalization
0.0015 0.2
Rescattering 0.0001 0
Transverse Polarization
0.0012 0.2
Q2 0.0028 0.4
Target Backing 0.0026 0.4
Inelastic States 0 0
TOTAL 0.0140 2.1
Goal for total systematic error ~ 2% achieved!
€
Q2 = 4E ʹ′ E sin2 θ2
4-momentum transfer
E: spin precession in machineE’: NMR in HRS B fieldscattering angle: survey ~ 1 mr
Q2 distribution obtained by low rate runs; trigger on quartz pulse-height
calibration
Krishna S. Kumar The PREX and CREX Experiments at JLab
Normalization Errors
19
Systematic Error Absolute (ppm)
Relative ( %)
Polarization 0.0083 1.3
Detector Linearity 0.0076 1.2Beam current normalization
0.0015 0.2
Rescattering 0.0001 0
Transverse Polarization
0.0012 0.2
Q2 0.0028 0.4
Target Backing 0.0026 0.4
Inelastic States 0 0
TOTAL 0.0140 2.1
Goal for total systematic error ~ 2% achieved!
€
Q2 = 4E ʹ′ E sin2 θ2
4-momentum transfer
E: spin precession in machineE’: NMR in HRS B fieldscattering angle: survey ~ 1 mr
Q2 distribution obtained by low rate runs; trigger on quartz pulse-height
calibration
Sca<ered Electron Energy
Absolute angle calibration via nuclear recoil
variation
Water cell target
Recoil is large for H, small for nuclei
0.2% absolute calibration achieved:0.4% on Q2
Krishna S. Kumar The PREX and CREX Experiments at JLab
Final Result
20
Rn
Mean Field and Other ModelsAtomic Parity
ViolaDon
Assume surface thickness good to 25% (MFT)
Neutron density at one Q2
Small correcDons for MEC
Neutron Stars
Weak density at one Q2
Correct for Coulomb DistorDons
Measured APV
FW (q̄) = 0.204± 0.028(exp)
±0.001(model) fm
Rn = 5.751± 0.175(exp)
±0.026(model)
±0.005(strange) fm
q̄ = 0.475 fm�1
PRL 108 (2012) 112502 PRC 85 (2012) 032501
Krishna S. Kumar The PREX and CREX Experiments at JLab
The Neutron Skin
21First electroweak indication of a neutron skin of a heavy nucleus (CL ~ 90-95%)
Rn �Rp = 0.302± 0.175(exp)± 0.026(model)± 0.005(strange) fm
Krishna S. Kumar Parity-Violating Electron Scattering: MeV to TeV Physics
PREX-II Proposal
22
Achieve original proposal goal for accumulated statistics
Krishna S. Kumar The PREX and CREX Experiments at JLab
New Beamline Design
23
•Redesign beamline seals to eliminate o-ring•Neck down tungsten collimator to confine neutrons to one location and add water cooling•Neutrons moderated by new shielding•Small adjustment to septum current will realize an additional ~25% gain in statistical reach
Krishna S. Kumar The PREX and CREX Experiments at JLab
PREXII Proposal
24
PREx II improvements• Metal o-‐rings• RadiaAon hard electronics• Reduce neutron backgrounds
Recent Rn predicDons:
Hebeler et al. Chiral EFT calcula2on of neutron ma7er. Correla2on of pressure with neutron skin by Brown. Three-‐neutron forces!
Steiner et al. X-‐Ray n-‐star mass and radii observa2on + Brown correla2on. (Ozel et al finds soJer EOS, would suggest smaller Rn).
Tamii et al. Measurement of electric dipole polarizability of 208Pb + model correla2on with neutron skin.
Tsang et al. Isospin diffusion in heavy ion collisions, with Brown correla2on and quantum molecular dynamics transport model.
δ(APV)/APV ~ 3%δ(Rn)/Rn ~ 1%
PREX-‐II
(Summ
er 2015)
Full precision in 25 additional PAC daysPresented to JLab PAC in June 2011: Approved with strong endorsement
HebelerSteinerTamiiTsang
δ(Rn) ~ ± 0.06 fm
Krishna S. Kumar The PREX and CREX Experiments at JLab
PREXII Proposal
24
PREx II improvements• Metal o-‐rings• RadiaAon hard electronics• Reduce neutron backgrounds
Recent Rn predicDons:
Hebeler et al. Chiral EFT calcula2on of neutron ma7er. Correla2on of pressure with neutron skin by Brown. Three-‐neutron forces!
Steiner et al. X-‐Ray n-‐star mass and radii observa2on + Brown correla2on. (Ozel et al finds soJer EOS, would suggest smaller Rn).
Tamii et al. Measurement of electric dipole polarizability of 208Pb + model correla2on with neutron skin.
Tsang et al. Isospin diffusion in heavy ion collisions, with Brown correla2on and quantum molecular dynamics transport model.
δ(APV)/APV ~ 3%δ(Rn)/Rn ~ 1%
PREX-‐II
(Summ
er 2015)
Full precision in 25 additional PAC daysPresented to JLab PAC in June 2011: Approved with strong endorsement
HebelerSteinerTamiiTsang
How badly does the community want this?
δ(Rn) ~ ± 0.06 fm
Krishna S. Kumar Parity-Violating Electron Scattering: MeV to TeV Physics
CREX Proposal
25
Measurement of APV in elastic scattering off 48Ca
Approved by PAC last month!
Important Workshop in March 2013 at JLab
Krishna S. Kumar The PREX and CREX Experiments at JLab
CREX at JLab
26
δ(Rn) ~ ± 0.02 fm
G. Hagen et al
PRL 109 (2012) 032502test coupled
cluster models
Approved by JLab PAC in Summer 2013
Krishna S. Kumar The PREX and CREX Experiments at JLab
CREX at JLab
26
δ(Rn) ~ ± 0.02 fm
G. Hagen et al
PRL 109 (2012) 032502test coupled
cluster models
Approved by JLab PAC in Summer 2013
Krishna S. Kumar The PREX and CREX Experiments at JLab
CREX at JLab
26
δ(Rn) ~ ± 0.02 fm
G. Hagen et al
PRL 109 (2012) 032502test coupled
cluster models
Approved by JLab PAC in Summer 2013
separate elastic events cleanly
Krishna S. Kumar The PREX and CREX Experiments at JLab
CREX at JLab
26
δ(Rn) ~ ± 0.02 fm
G. Hagen et al
PRL 109 (2012) 032502test coupled
cluster models
Approved by JLab PAC in Summer 2013
Could run in 2016 depending
on schedule and funding
separate elastic events cleanly
Krishna S. Kumar The PREX and CREX Experiments at JLab
FRIB and PVES
27
• Less precise measurements of thicker neutron skins with radioactive beams complimentary to precise parity violating measurements on stable nuclei.
Neutron skins predicted by average of 4 Skyrme energy functionals smoothly increase with neutron #. 48Ca skin slightly larger than 208Pb.
Skin of Ca isotopes increases with N. Example measure (nearly twice as large vs 48Ca?) skin in 54Ca with hadronic probe using radioactive beam. Calibrate hadronic reaction mechanism by comparing with CREX for 48Ca.
48Ca54Ca
Kortelain et al. ArXiv:1307.4223
C. Horowitz
Krishna S. Kumar The PREX and CREX Experiments at JLab
Improved 208Pb Rn?
28
200 MeV FOM peaks around 25 degrees
S. Ban and C. Horowitz
C. SfientiM. Thiel
K.K.
Explore a PREX-style
measurement usingsame
solenoidal magnet to be used for P2
Krishna S. Kumar The PREX and CREX Experiments at JLab
solenoidal spectrometer will separate inelastics over the full range of the azimuth
Improved 208Pb Rn?
28
200 MeV FOM peaks around 25 degrees
S. Ban and C. Horowitz
C. SfientiM. Thiel
K.K.
Explore a PREX-style
measurement usingsame
solenoidal magnet to be used for P2
Krishna S. Kumar The PREX and CREX Experiments at JLab
solenoidal spectrometer will separate inelastics over the full range of the azimuth
Improved 208Pb Rn?
28
200 MeV FOM peaks around 25 degrees
S. Ban and C. Horowitz
C. SfientiM. Thiel
K.K.
Explore a PREX-style
measurement usingsame
solenoidal magnet to be used for P2
Krishna S. Kumar The PREX and CREX Experiments at JLab
solenoidal spectrometer will separate inelastics over the full range of the azimuth
Improved 208Pb Rn?
28
200 MeV FOM peaks around 25 degrees
S. Ban and C. Horowitz
C. SfientiM. Thiel
K.K.
Explore a PREX-style
measurement usingsame
solenoidal magnet to be used for P2
δ(Rn) ~ ± 0.03 fm
Krishna S. Kumar The PREX and CREX Experiments at JLab
Conclusions
29
PREX produced the first electroweak measurement of the neutron RMS radius in a heavy nucleusMany new technical challenges overcome
High luminosity Pb targetPrecision 1 GeV polarimetrySpectrometer optics optimization to produce compact elastic footprint“Parity quality” beamPb transverse asymmetry measured and introduces negligible uncertaintyNovel integrating detectors can count at GHz rates
Followup run approved by JLab PAC in Summer 2011Likely to be scheduled to run in mid-2015 (after first commissioning of beams after JLab upgrade shutdown)
Potential for precise Rn measurements demonstratedPREX-II: allocated the beam time and demonstrated ability to achieve ±0.06 fmCREX approved: 48Ca Rn goal: ±0.02 fmPotential to measure 208Pb to ±0.03 fm at Mainz
Krishna S. Kumar The PREX and CREX Experiments at JLab
Personal Remarks
We are in an era of constrained budgetsPREX and CREX running time must compete with a diverse programHow important are these measurements to the community?
I believe these measurements form critical anchors for Symmetry Energy constraintsBut if the community is lukewarm about these measurements, they wont happen!So, if you are enthusiastic about these measurements, keep making it known!For example, a Mainz experiment will not materialize unless there is sustained interest
Shameless plugI am about to advertise for a postdoc position to work on JLab PV program
Please direct your best graduating students to look for my ad in the next few weeks!
30
Thank you for your support:critical for obtaining beamtime allocation for PREX-I