parity-violating electron scattering experiments @ jlab juliette mammei
TRANSCRIPT
HUGS 2
Outline
June 1-19, 2015
I. IntroductionII. Theory
A. Standard ModelB. Madam WuC. ZโeldovichD. Emmy Noether
III. Experimental ConsiderationsA. Beam qualityB. Target stabilityC. BackgroundsD. Apparatus symmetryE. Detector linearityF. Collimator precisionG. Magnet stabilityH. Raster synchronization
IV. Past ExperimentsA. SLAC E158
B. SAMPLEC. Mainz A4D. G0E. HappEx I-IVF. QweakG. PREXH. PVDIS
V. Future ExperimentsA. PREX IIB. CREXC. MOLLERD. Qweak (Mainz)E. PVDISF. SOLID
VI. Summary
HUGS 5
Why Parity-Violating Electron Scattering(PVES)?
June 1-19, 2015
o Search for physics Beyond the Standard Model (BSM) with low energy (Q2 <<M2) precision tests complementary to high energy measurements
โข Neutrino mass and their role in the early universe 0ฮฝฮฒฮฒ decay, ฮธ13, ฮฒ decay,โฆ
โข Matter-antimatter asymmetry in the present universe EDM, DM, LFV, 0ฮฝฮฒฮฒ, ฮธ13
โข Unseen Forces of the Early Universe Weak decays, PVES, gฮผ-2,โฆ
LHC new physics signals likely will need additional indirect evidence
โข Neutrons: Lifetime, P- & T-Violating Asymmetries (LANSCE, NIST, SNS...)
โข Muons: Lifetime, Michel parameters, g-2, Mu2e (PSI, TRIUMF, FNAL, J-PARC...)
โข PVES: Low energy weak neutral current couplings, precision weak mixing angle (SLAC, Jefferson Lab, Mainz)
o Study nuclear and nucleon propertiesโข Strange quark content of nucleonโข Neutron radii of heavy nuclei
HUGS 6
Standard Modelof Particles and Interactions
June 1-19, 2015
http://www.cpepweb.org/cpep_sm_large.html
9
Symmetries
HUGS
Emmy Noether(18??-19??)
June 1-19, 2015
Conservation laws imply symmetries
Conservation of:
Linear momentum
Angular momentum
Energy
Implies:
Rotational invariance
Translational invariance
Time invariance
HUGS 10
What is unitarity and why is it required?
June 1-19, 2015
(๐โฒ
๐ โฒ
๐โฒ )=(๐ ๐ข๐ ๐ ๐ข๐ ๐ ๐ข๐
๐ ๐๐ ๐ ๐๐ ๐ ๐๐
๐ ๐ก๐ ๐ ๐ก๐ ๐ ๐ก๐)(๐๐ ๐)
CKM matrix
(๐๐๐๐
๐๐)=(๐๐1 ๐๐2 ๐๐3
๐๐1 ๐๐2 ๐๐3
๐๐ 1 ๐๐ 2 ๐๐ 3)(๐1
๐2
๐3)
The adjoint times the operator must be 1:
HUGS 11
Parity
June 1-19, 2015
quantum mechanical operator that reverses the spatial sign ( P: x -> -x )
s
p
s
p
11111Tensor
111Vector Axial
111Vector
111arPseudoscal
111Scalar
CTP
5
5
)44( form theof Terms
We describe physical processes as interacting currents by constructing the most general form which is consistent with Lorentz invariance
32105 where i
Note: P (V*V) = +1 P (A*A) = + 1 P (A*V) = -1
Parity Time ReversalCharge Conjugation
h=๏ฟฝโ๏ฟฝ โ ๏ฟฝโ๏ฟฝ|๏ฟฝโ๏ฟฝ โ ๏ฟฝโ๏ฟฝ|
HUGS 12
A brief history of parity violation
June 1-19, 2015
R
R
L
L
1930s โ weak interaction needed to explain nuclear ฮฒ decay
1950s โ parity violation in weak interaction; V-A theory to describe 60Co decay
1970s โ neutral weak current events at Gargamelle
late 1970s โ parity violation observed in electron scattering - SLAC E122
HUGS 13
Nuclear beta decay
June 1-19, 2015
"Beta spectrum of RaE" by HPaul - Own work. Licensed under CC BY-SA 4.0 via Wikimedia Commons
e- ๐๐
p n
๐บ๐น
HUGS 14
EM and Weak Interactions : Historical View
June 1-19, 2015
eeppeEMpEM
Q
eJ
Q
eJM
2
2, ,
2
2,
eeFnp
eweakF
Nweak GJGJM
, ,,
EM: e + p e + p elastic scattering
Weak: n e- + p + neutron beta decay
Fermi (1932) : contact interaction, form inspired by EM
V x V
V x V
Parity Violation (1956, Lee, Yang; 1957, Wu)required modification to form of current - need axial vector as well as vector to get a parity-violating interaction
eeFnp
eweakF
Nweak GJGJM
55, ,, 11
(V - A) x (V - A)
Note: weak interaction process here is charged current (CC)
e-
e- p
p
๐ฝ๐๐ธ๐ ,๐๐ฝ๐
๐ธ๐ ,๐
๐ฝ๐๐ค๐๐๐,๐๐ฝ๐
๐ค๐๐๐,๐
e- p
n
๐บ๐น๐๐
HUGS 15
Parity-violation in charge current maximal
June 1-19, 2015
Madam Wu
Bleckneuhaus, with English language captions by Stigmatella aurantiaca
electrons favored the direction opposite to that of the nuclear spin
HUGS 16
What about a neutral weak current?
June 1-19, 2015
e- p
n
๐บ๐น๐๐
e- p
p
๐บ๐นe-
Zelโdovich โ 1959
Is there a neutral analog to decay?
Would determine the sign of
?
HUGS 17
Neutral weak currents observed
June 1-19, 2015
The prediction of the Z0 implied the existence of previously unobserved neutral current processes like:
These processes were first discovered in 1973:
Z0
e- e-
+ e- + e-
What about parity violation?
HUGS 18
The neutral weak current, ZelโDovich
June 1-19, 2015
parity non-conservation via weak โ EM interference
parity-violating asymmetry
๐ด๐๐ โค10โ6โ10โ 4
โ๐บ๐น๐
2
4๐๐ผ๐2 0.1โ1๐บ๐๐ 2
๐ด๐๐=๐+ยฟโ๐โ
๐+ยฟ+๐โโ๐๐ค๐๐๐
๐๐พ
ยฟยฟ
e-
e-
0,Z
longitudinally polarized e-
Four drops of ink in a 55-gallon barrel of water would produce an "ink concentration" of 1 ppm!!!
HUGS 19
Magnetic spectrometer
Background and kinematic separation
SLAC Experiment E122
June 1-19, 2015
Polarimetry
Integrating detectors
โข High luminosity from photoemission from NEA GaAs cathodeโข Rapid helicity-flip (sign of e- polarization)Huge achievement!
Highest P2I ever, by far. Developed for this experiment at
SLAC and used ever since
HUGS 20
SLAC Experiment E122
June 1-19, 2015
sin2ฮธW=0.20ยฑ0.03
GWS --โ Nobel Prize 1979
Parity Non-Conservation in Inelastic Electron Scattering, C.Y. Prescott
et. al, 1978
Deep inelastic scattering:Y dependence reflects quark axial/electron vector coupling strength
YxbxaQG
A FPV
210
3 2
At high x eA
dV
eA
uV ggggxa 2
eV
dA
eV
uA ggggxb 2
Left Right
ฮณ Charge
0, ยฑ1, ยฑ1/3, ยฑ2/3 0, ยฑ1, ยฑ1/3, ยฑ2/3
W Charge
T=ยฑ1/2 0
Z Charge
T-qsin2ฮธW -qsin2ฮธW
APV ~ 100 ยฑ 10 ppm
HUGS 21
Standard Model of Electroweak Interactions
June 1-19, 2015
5
22
g
Glashow-Weinberg-Salam Model (1967): unified EM and weak forces as an electroweak force SU(2)L x U(1) gauge theory with spontaneous symmetry breaking
fermions:
...,',,
...,'
,
RRR
LL
e
due
d
u
e
Interaction of fermions with gauge bosons:
e
W+,- Z0
5
cos2
f
AfV
W
ccg
ffA
fWff
V
tc
Qtc
3
23 sin2
sin2W โ โweak mixing angleโ, parameterizes the mixing between the two neutral currents
HUGS 23
Running of sin2ฮธW
June 1-19, 2015
Present:โd-quark dominatedโ : Cesium APV (QA
W): SM running verified at ~ 4 levelโpure leptonโ: SLAC E158 (Qe
W ): SM running verified at ~ 6 levelFuture:โu-quark dominatedโ : Qweak (Q
pW): projected to test SM running at
~ 10 levelโpure leptonโ: MOLLER (Qe
W ): projected to test SM running at ~ 25 level
+ +
24
Width of the Z0
HUGSJune 1-19,
2015
โข Measure a variety of electroweak processes with couplings to all possible fermions
โข Extract values of (sin2W )eff in a consistent renormalization scheme from all processes
Production of real Z0 bosons in e+e- annihilation
25
Spontaneous symmetry breaking
HUGSJune 1-19,
2015
Why do the weak bosons have mass?
Higgs mechanism
Higgs field โ scalar (not a vector) field that permeates all of space
As universe cooled, symmetry was broken and 3 of the electroweak bosons absorbed 3 of the Higgs bosons, gaining mass
(๐ +ยฟ ยฟ๐โ
๐0 ) ,๐พ
but leaving the photon massless
and one Higgs boson to be discovered at CERN
HUGS 26
Low Energy Weak Neutral Current Standard Model Tests
These three types of experiments are a complementary set for exploring new
physics possibilities well below the Z pole
Low energy weak charge โtriadโ (M. Ramsey-Musolf) probed in weak neutral current experiments
Z
N e
NZNQ WAW )sin41( 2
parity-violating Moller
scattering e
+ e e + e
Cesium Atomic Parity Violation primarily
sensitive to neutron weak charge
JLAB Qpweak: parity-violating
e-p elastic scattering
e + p e + p
)sin41( 2W
eWQ
WpWQ 2sin41
June 1-19, 2015
28
PVES Experiments at JLAB
June 1-19, 2015
HUGS
JLAB has a rich program of PVES experiments to measure nuclear and nucleon properties and to perform precision tests of the Standard Model to search for new physics
SM TestsNuclear properties Nucleon properties
Qweak MOLLERPREXCREX
G0Happex
PVDIS
SOLID
HUGS 29
Feynman Diagrams
June 1-19, 2015
Further reading: Looking for consistency in the construction and
use of Feynman diagramsPeter Dunne , Phys. Educ. 36 No 5 (September 2001) 366-374
HUGS 30
The Dirac Equation
June 1-19, 2015
0)( mi
0
0
10
01, 00
space 3,2,1 time,0
ej
0 j
Dirac equation for free electron:
0
where:
with:
leads to electron four-vector current density:
where the adjoint is:
satisfies the continuity equation:
HUGS 31
Cross section
June 1-19, 2015
dQMFd || 2
The incident flux times the differential cross section is proportional to the product of the square of the matrix element and the Lorentz invariant phase space
|| 2M
All the physics is in the matrix element
HUGS 32
the matrix element
June 1-19, 2015
xppiepu )()( )'( puie ][2q
ig
external lines
vertex factors
propagator
)(ku xkkieku )()'(
pEMeEMEM JJ
QM ,,
2
1~
HUGS 33
external lines
the matrix element
June 1-19, 2015
xppiepu )()( )'( pu
)sin41(cos4
52
WW
gi
][22
2 )/(
ZMq
Mkkgi
vertex factors
propagator
)(ku xkkieku )()'(
pNCeNCNC JJ
GM ,,
22~
eNCeA
eNCeV
eNC AgVgJ ,,, NNCNNCNNC AVJ ,,,
HUGS 34
How do we measure ?
June 1-19, 2015
2
+
= + +
2 2
2
eh
๐ด๐๐=๐+ยฟโ๐โ
๐+ยฟ+๐โโ ยฟ
ยฟ
24
2F
4
G-QBQ
Q pW
ppm1011010 56
35
Hand-waving derivation of the parity-violating asymmetry in electron-proton scattering
June 1-19, 2015
HUGS
NEMeEMe VVQ
Q,,
2
1~
pNCeNCNC JJ
GM ,,
22~
NNCeNCeA
NNCeNCeV
NNCeNCeA
NNCeNCeV AAgAVgVAgVVg
G ,,,,,,,,
22~
eEMeeee
eEM VQQJ ,,
NEMNEM VJ ,,
NNCNNCNNC AVJ ,,,
eNCeA
eNCeVeeeeW
eNC AgVgJ ,,5
2, sin41
pEMeEMEM JJ
QM ,,
2
1~
HUGS 36
Asymmetry
June 1-19, 2015
๐ ยฑโ [๐ ๐ธ๐ยฑ๐๐๐ถ ]2ยฟ|๐๐ธ๐|2ยฑ2๐ ๐ (๐๐ธ๐
โ ๐ ๐๐ถ )+|๐ ๐๐ถ|2
๐ด๐๐=๐+ยฟโ๐โ
๐+ยฟ+๐โโ
2๐ ๐ (๐๐ธ๐โ ๐ ๐๐ถ )
|๐๐ธ๐|2+โฏ
ยฟ
ยฟ
2,,
,,,,,,,,2
24 NEMeEMe
NNCeNCeV
NEMeEMe
NNCeNCeA
NEMeEMeF
VVQ
AVgVVQVAgVVQQG