Parity-violating electron scattering

experiments @ JLAB

Juliette Mammei

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Outline

June 1-19, 2015

I. IntroductionII. Theory

A. Standard ModelB. Madam WuC. Z’eldovichD. 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

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Introduction

June 1-19, 2015

PVESHistorical view

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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

• Neutrino mass and their role in the early universe 0νββ decay, θ13, β decay,…

• Matter-antimatter asymmetry in the present universe EDM, DM, LFV, 0νββ, θ13

• Unseen Forces of the Early Universe Weak decays, PVES, gμ-2,…

LHC new physics signals likely will need additional indirect evidence

• Neutrons: Lifetime, P- & T-Violating Asymmetries (LANSCE, NIST, SNS...)

• Muons: Lifetime, Michel parameters, g-2, Mu2e (PSI, TRIUMF, FNAL, J-PARC...)

• PVES: Low energy weak neutral current couplings, precision weak mixing angle (SLAC, Jefferson Lab, Mainz)

o Study nuclear and nucleon properties• Strange quark content of nucleon• Neutron radii of heavy nuclei

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Standard Modelof Particles and Interactions

June 1-19, 2015

http://www.cpepweb.org/cpep_sm_large.html

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Interactions Particles

June 1-19, 2015

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2015

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Symmetries

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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

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What is unitarity and why is it required?

June 1-19, 2015

(𝑑′

𝑠′

𝑏′ )=(𝑉 𝑢𝑑 𝑉 𝑢𝑠 𝑉 𝑢𝑏

𝑉 𝑐𝑑 𝑉 𝑐𝑠 𝑉 𝑐𝑏

𝑉 𝑡𝑑 𝑉 𝑡𝑠 𝑉 𝑡𝑏)(𝑑𝑠𝑏)

CKM matrix

(𝜈𝑒𝜈𝜇

𝜈𝜏)=(𝑈𝑒1 𝑈𝑒2 𝑈𝑒3

𝑈𝜇1 𝑈𝜇2 𝑈𝜇3

𝑈𝜏 1 𝑈𝜏 2 𝑈𝜏 3)(𝜈1

𝜈2

𝜈3)

The adjoint times the operator must be 1:

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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=�⃑� ∙ �⃑�|�⃑� ∙ �⃑�|

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A brief history of parity violation

June 1-19, 2015

R

R

L

L

1930s – weak interaction needed to explain nuclear β decay

1950s – parity violation in weak interaction; V-A theory to describe 60Co decay

1970s – neutral weak current events at Gargamelle

late 1970s – parity violation observed in electron scattering - SLAC E122

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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- 𝜈𝑒

p n

𝐺𝐹

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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

𝐽𝜇𝐸𝑀 ,𝑝𝐽𝜇

𝐸𝑀 ,𝑒

𝐽𝜇𝑤𝑒𝑎𝑘,𝑁𝐽𝜇

𝑤𝑒𝑎𝑘,𝑒

e- p

n

𝐺𝐹𝜈𝑒

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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

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What about a neutral weak current?

June 1-19, 2015

e- p

n

𝐺𝐹𝜈𝑒

e- p

p

𝐺𝐹e-

Zel’dovich – 1959

Is there a neutral analog to decay?

Would determine the sign of

?

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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?

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The neutral weak current, Zel’Dovich

June 1-19, 2015

parity non-conservation via weak – EM interference

parity-violating asymmetry

𝐴𝑃𝑉 ≤10−6−10− 4

≈𝐺𝐹𝑄

2

4𝜋𝛼𝑄2 0.1−1𝐺𝑒𝑉 2

𝐴𝑃𝑉=𝜎+¿−𝜎−

𝜎+¿+𝜎−≈𝑀𝑤𝑒𝑎𝑘

𝑀𝛾

¿¿

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!!!

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Magnetic spectrometer

Background and kinematic separation

SLAC Experiment E122

June 1-19, 2015

Polarimetry

Integrating detectors

• High luminosity from photoemission from NEA GaAs cathode• Rapid helicity-flip (sign of e- polarization)Huge achievement!

Highest P2I ever, by far. Developed for this experiment at

SLAC and used ever since

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SLAC Experiment E122

June 1-19, 2015

sin2θW=0.20±0.03

GWS --‐ 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

γ Charge

0, ±1, ±1/3, ±2/3 0, ±1, ±1/3, ±2/3

W Charge

T=±1/2 0

Z Charge

T-qsin2θW -qsin2θW

APV ~ 100 ± 10 ppm

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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 – “weak mixing angle”, parameterizes the mixing between the two neutral currents

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Running of coupling constants

June 1-19, 2015 What about sin2θW?

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Running of sin2θW

June 1-19, 2015

Present:“d-quark dominated” : Cesium APV (QA

W): SM running verified at ~ 4 level“pure lepton”: SLAC E158 (Qe

W ): SM running verified at ~ 6 levelFuture:“u-quark dominated” : Qweak (Q

pW): projected to test SM running at

~ 10 level“pure lepton”: MOLLER (Qe

W ): projected to test SM running at ~ 25 level

+ +

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Width of the Z0

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2015

• Measure a variety of electroweak processes with couplings to all possible fermions

• Extract values of (sin2W )eff in a consistent renormalization scheme from all processes

Production of real Z0 bosons in e+e- annihilation

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Spontaneous symmetry breaking

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2015

Why do the weak bosons have mass?

Higgs mechanism

Higgs field – 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

(𝑊 +¿ ¿𝑊−

𝑍0 ) ,𝛾

but leaving the photon massless

and one Higgs boson to be discovered at CERN

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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 “triad” (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

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Some PVES Experiments

June 1-19, 2015

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PVES Experiments at JLAB

June 1-19, 2015

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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

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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

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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:

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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

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the matrix element

June 1-19, 2015

xppiepu )()( )'( puie ][2q

ig

external lines

vertex factors

propagator

)(ku xkkieku )()'(

pEMeEMEM JJ

QM ,,

2

1~

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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 ,,,

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How do we measure ?

June 1-19, 2015

2

+

= + +

2 2

2

eh

𝐴𝑃𝑉=𝜎+¿−𝜎−

𝜎+¿+𝜎−≈ ¿

¿

24

2F

4

G-QBQ

Q pW

ppm1011010 56

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Hand-waving derivation of the parity-violating asymmetry in electron-proton scattering

June 1-19, 2015

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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~

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Asymmetry

June 1-19, 2015

𝜎 ±∝ [𝑀 𝐸𝑀±𝑀𝑁𝐶 ]2¿|𝑀𝐸𝑀|2±2𝑅𝑒 (𝑀𝐸𝑀

∗ 𝑀 𝑁𝐶 )+|𝑀 𝑁𝐶|2

𝐴𝑃𝑉=𝜎+¿−𝜎−

𝜎+¿+𝜎−≈

2𝑅𝑒 (𝑀𝐸𝑀∗ 𝑀 𝑁𝐶 )

|𝑀𝐸𝑀|2+⋯

¿

¿

2,,

,,,,,,,,2

24 NEMeEMe

NNCeNCeV

NEMeEMe

NNCeNCeA

NEMeEMeF

VVQ

AVgVVQVAgVVQQG