1 X. Zheng, University of Virginia, Talk at OCPA7, August 1-5, Kaotsiung, Taiwan Recent Results from Parity Violation Electron Scattering Experiments at

1X. Zheng, University of Virginia, Talk at OCPA7, August 1-5, Kaotsiung, Taiwan

Recent Results from Parity Violation Electron Scattering Experiments at JLab

(and elsewhere)

Xiaochao Zheng 郑晓超 (Univ. of Virginia)

August 2, 2011The Physics of PVES on nucleon/nuclear targets

Nucleon strangeness structure study: results from MAINZ A4, G0 and HAPPEX-III

Nuclear Physics study: results from PREX

Standard Model study: Qweak and PVDIS

Plan for PVDIS (and Moller) at the upgraded JLab


Parity ViolationThe parityparity symmetry: the physical laws behind all phenomena is the same as those behind their mirror images (The Lagrangian is invariant under transformation ) ;

This symmetry is broken in weak interactions;

Weak interaction is carried by charged or neutral weak currents, described under the framework SU(2)LxU(1)Y

Chen-Ning Yang Tsung-Dao LeeChien-Shiung Wu

"for their penetrating investigation of the so-called parity laws which has led to important discoveries regarding the elementary particles"

1957 Nobel Prize in Physics:1957 Nobel Prize in Physics:

r −r

with W.

experimental proof using beta decay of 60Co.


Parity Violating Electron Scattering

Weak Neutral Current (WNC) Interactions at Q2 << MZ2

Longitudinally Polarized Electron Scattering off Unpolarized Fixed Targets ∝∣AAweak∣

2

Asym≡ L− R

L R

≈100 ppm Q 2

GeV 2

longitudinallypolarized e

The Physics accessible by PVES:

elastic scattering

from the proton: strange form factors or nucleon weak charge

from (heavy) nuclei: nuclear physics

deep inelastic scattering: weak structure of the nucleon, quark neutral weak couplings

A4, HAPPEX, G0

PREX

Qweak

PVDIS


Nucleon Strange Form Factors


Nucleon in QCDNucleon Form Factors

Electromagnetic probe hadronic flavor structure:

(these encode information on spatial distributions of charge & magnetization, but not enough for flavor separation)

s and s have different spatial distributions

What would non-zero strange form factors imply?

GsE≠ 0

GsM≠ 0 s and s have different magnetization

distributions, may contribute to magnetic moment, etc.

s.

s.

Neutral weak probe the same hadronic flavor structure, with different couplings:

GE /M =

23

GE /Mu −

13

GE /Md −

13

GE /Ms

GE /MZ =1−

83

sin2W GE /M

u −1−43

sin2W GE /M

d −1−43

sin2W GE /M

s

cVu cV

d cVs


G E , Ms =1− sin 2W G E , M

p , −G E , Mn , −G E , M

p , Z

Isolating individual form factors: vary kinematics or target

Forward angle Backward angle

A p ,elPV =[ −G F Q 2

4 2 ] G Ep G E

ZG Mp G M

Z −1−4 sin 2W ' G Mp G A

e

p

“anapole” radiative corrections are

problematicproton

GE /Mp , =

23

GE /Mu −

13

GE /Md −

13

GE /Ms

G E /Mp , Z =2 cV

u G E / Mu

2 cVd G E /M

d 2 cVs G E /M

s

+

isospin rotation, and assuming Gs,p = Gs, n

+

linear combinations of GEZ and GM

Z

linear combinations of GES and GM

S


Experimental Overview

SAMPLE

HAPPEXPrecision spectrometer, integratingForward angles

A4

open geometry, integrating, back-angle only

Open geometryFast counting calorimeter for background rejectionForward and Backward angles

G0

Open geometryFast counting w/ magnetic spectrometer + TOFForward and Backward angles over a range of Q2


Nucleon Strange Form Factor Program

Expt/Lab Target/ Angle

Q2

(GeV2)Apv

(ppm)

Sensitivity Complete

SAMPLE/BatesSAMPLE I LH2/145 0.1 -6 GM + 0.4GA 2000SAMPLE II LD2/145 0.1 -8 GM + 2GA 2004SAMPLE III LD2/145 0.04 -4 GM + 3GA 2004

HAPPEx/JLabHAPPEx LH2/12.5 0.47 -15 GE + 0.39GM 1999HAPPEx II LH2/6 0.11 -1.6 GE + 0.1GM 2006, 2007HAPPEx He 4He/6 0.11 +6 GE 2006, 2007HAPPEx III LH2/14 0.63 -24 GE + 0.5GM 2011

PV-A4/MainzLH2/35 0.23 -5 GE + 0.2GM 2004LH2/35 0.11 -1.4 GE + 0.1GM 2005LH2/145 0.23 -17 GE + ηGM +

η’GA2009

LH2/35 0.63 -28 GE + 0.64GM (2009)

G0/JLabForward LH2/35 0.1 to 1 -1 to -40 GE + ηGM 2005Backward LH2/LD2/110 0.23, 0.63 -12 to -45 GE + ηGM +

η’GA2009


World Data on Gs

all forward-angle proton data

“Form Factor” error: precision of EMFF (including 2γ) and Anapole correction


World Data on Gs


At Q2 ~ 0.1 GeV2, Gs < few percent of Gp



World Data on Gs




Q2 ~ 0.22G

0-b

ackw

ard

A4-b

ack

ward

A4-forward


World Data on Gs




Q2 ~ 0.22 Q2 ~ 0.62G

0-b

ackw

ard

A4-b

ack

ward

A4-forward


World Data on Gs




Q2 ~ 0.22 Q2 ~ 0.62G

0-b

ackw

ard

A4-b

ack

ward

A4-forward

Strange form factors contribute at most a few % to overall vector form factors… except maybe near Q2 =

0.6…


HAPPEX-III Results (“Close-book” measurement)

APV = -23.80 0.78 (stat) 0.36 (syst) ppm at Q2 = 0.6241 ± 0.0028 GeV2

GsE + 0.52 Gs

M = 0.003 ± 0.010(stat) ± 0.004(syst) ± 0.009(FF)

Ahmed et al. (HAPPEX Collaboration) arXiv:1107.0913 [nucl-ex]

HAPPEX-III: Ran in Aug-Oct 2009


HAPPEX-III Results (“Close-book” measurement)

APV = -23.80 0.78 (stat) 0.36 (syst) ppm at Q2 = 0.6241 ± 0.0028 GeV2

GsE + 0.52 Gs

M = 0.003 ± 0.010(stat) ± 0.004(syst) ± 0.009(FF)

Ahmed et al. (HAPPEX Collaboration) arXiv:1107.0913 [nucl-ex]

HAPPEX-III: Ran in Aug-Oct 2009Strange form factors contribute at most a few % to overall vector form factors at all Q2 measured s and sbar have

similar spatial distribution and their spin/magnetic moments largely cancel, when viewed via electron elastic

scattering.


Weak Charge Distribution of Heavy Nuclei – Testing Nuclear Physics and Beyond


Weak Charge Distribution of Heavy Nuclei

Nuclear theory predicts a neutron “skin” on heavy nuclei

208Pb

Neutron distribution is challenging to interpret from strongly interacting probes (protons, pions, etc.), and is not accessible to the charge-sensitive photon.

proton neutron

Electric charge 1 0

Weak charge ~0.08 1

But the weak interaction sees the neutrons clearly:

M EM=4

Q2 F p Q2

M NC=GF

2[1−4 sin2W F pQ

2−F nQ2 ]

A PV=G F Q 2

4 2 [ 1−4 sin 2W −F n Q

2

F pQ2 ]


A crucial calibration point for nuclear theory

( R.J. Furnstahl )

The single measurement of Fn translates to a measurement of Rn via mean-field nuclear models

Rn calibrates the equation of state of neutron rich matter

neutron stars

208Pb


PREX (Pb Radius EXperiment) Results and Interpretation

A PV=0.6571±0.0604 stat ±0.0130 syst ppm

at Q2 = 0.00906 GeV2, 5o angle,

Statistics limited (9%)Systematic error goal achieved ! (2%)

9.2 % 2.0 %

APV ~ 0.6 ppm, original goal: 3%

errorRan in April-June 2010:

R N− R P=0.34−0.170.15 fm

Preliminary estimate from C.J. Horowitz,

confirming the confirming the “neutron skin” ! “neutron skin” !

RN−RP=0


PREX-II (25 PAC days, submitted to PAC38)

PREX-II projectedPREX-II projected


Testing the EW Standard Model – SU(2)LxU(1)Y


Select Results on the Weak Mixing Angle

(expected)

figure from K. Kumar, Seattle 2009 EIC Workshop EW talks

SLAC E158: Moller scattering, ran in 2002-2003


Weak Neutral Couplings

C 1q≡2 g Ae g V

q

A

V

V

A

C 2q≡ 2 g Ve g A

q

gA,V follow PDG

convention

C 1u=2 g Ae

gVu=−

12

43

sin2W C 1u≈ 0.19

C 1d=2 g Ae g V

d= 12− 2

3sin 2W C 1d≈ 0.35

C 2u=2 gVe g A

u=− 122 sin 2W C 2u≈−0.030

C 2d=2 gVe g A

d=12−2 sin 2W C 2d≈ 0.025

Different conventions exist, here:


SAMPLE

C2

u+C

2d

1.25

1.5

1.75

1.0

0.75

0.5

0.25

0

0.25

-0.5

-0.75

C2u-C2d

- 0.25 0.50.250- 0.5

PVES provides a factor of 5 increase in precision of Standard Model testPRL99,122003(2007)

Quark Weak Neutral Couplings C1,2q

with recent PVES data without JLab data

all are 1 limit

PDG best fit

SLAC/ Prescott


SAMPLE

C2

u+C

2d

1.25

1.5

1.75

1.0

0.75

0.5

0.25

0

0.25

-0.5

-0.75

C2u-C2d

- 0.25 0.50.250- 0.5

Quark Weak Neutral Couplings C1,2q

with recent PVES data and Qweak (projected)

without JLab data

all are 1 limit

PDG best fit

SLAC/ Prescott

Qweak in Hall C (2010-): another factor of 5 improvement in knowledge of C1q, New Physics scale from 0.9 to 2

TeV

1H + e e’ + p


Parity Violation in Deep Inelastic Scattering

For an isoscalar target (2H), structure

functions largely simplifies:

0 1

at high x

PVDIS: Only way to measure C2q

A PV=G F Q 2

2 [a x Y y b x ]

x≡x Bjorken y≡ 1− E ' / E

q i− . x = q i

V x ≡q i x − q i. x

a x =12

g Ae F1

Z

F1 =

12

∑iC1iQ i f i

.x

∑iQi

2 f i. x

b x =gVe F 3

Z

F 1 =

12

∑iC2i Qi f i

−. x

∑iQi

2 f i. x

a x = 310

2 C 1u−C 1d 1 0.6 s.

u.d. b x = 310

2 C 2u−C 2d uVd V

u.d.

q i . x ≡ q i x q i

. x


PVDIS at 6 GeV (JLab E08-011)

100uA, 90% polarized beam, 20-cm LD2 targetScaler-based fast counting DAQ specifically built to accommodate the 500kHz DIS rate with 104 pion rejection


PVDIS at 6 GeV (JLab E08-011)

Q2=1.1 Q2=1.9

Ran in Oct-Dec 2009, measured Ad at Q2=1.1 and 1.9 GeV2 to 3%

and 4% (stat.), resp. Systematics dominated by beam polarization (2%).Data being analyzed, may finish by late 2011.

spokespeople: R. Michaels, P.E. Reimer ，郑晓超Grad students: 邓晓燕 (UVa M.A.), 王殿成(UVa), 潘凯 (MIT)Postdoc: Ramesh Subedi

Statistical quality of data:


E08-011 Projected Results on C2q

with recent PVES data and Qweak with JLab 6 GeV

all are 1 limit

SAMPLE

SLAC/ Prescott

C2

u+C

2d

1.25

1.5

1.75

1.0

0.75

0.5

0.25

0

0.25

-0.5

-0.75

C2u-C2d

- 0.2 0.40.20- 0.4

PVDIS @6GeV: potential to improve C2 q by factor of six if hadronic

effects are small.


PVDIS at Higher Precision – Hadronic Physics Study

Sensitivity will be further enhanced if u+d falls off more rapidly than u-d as

x 1

u-d mass differenceEM effects

• Direct observation of parton-level CSV would be very exciting!

• Important implications for high energy collider pdfs

• Could explain significant portion of the NuTeV anomaly

For APV in electron-2H DIS:

u x ≡u p x −d nx d x≡d px −u p x

CSV

Higher Twist (non-perturbative nature of strong interactions)

APV

APV

=0.28 u− d

ud

u p x =d nx ?d p x=u p x ?


Strategy: requires precise kinematics and broad range

x y Q2

New Physics no yes no

CSV yes no no

Higher Twist yes no yes

A=A [1 β HT1

1− x 3 Q 2 β CSV x2 ]Fit data to:

Coherent PVDIS Program with SoLID @ 11 GeV

““SoLID” SoLID” spectrometerspectrometer


Coherent PVDIS Program with SoLID @ 11 GeV


Error bar σA/A (%)shown at center of binsin Q2, x

4 months at 11 GeV

2 months at 6.6 GeV


SAMPLE

R. Young (combined)

all are 1 limit

PVDIS@11 GeV with SoLID: potential to improve C2q knowledge by

another order of magnitude and better separation from hadronic effects.

Knowledge on C1,2q with Projected JLab 12 GeV Results

C2u-C2d

C2

u+C

2d


Nee ~ 25 TeV

JLab MøllerLHC

New Contact Interactions

Møller Parity-Violating Experiment: New Physics Reach

(a large installation experiment with 11 GeV beam energy)

Czarnecki and Marciano (2000)Erler and Ramsey-Musolf (2004)

Expected precision comparable to the two most precise measurements from colliders, but at lower energy.

No other experiment with comparable precision in the forseeable future!

12 GeV

12 GeV

6 GeV


Summary and Perspectives

Recent Results:Program on nucleon strange form factors now concluded: GS

E,M < a few percents of GPE,M at all Q2 studied;

PREX provided the first results on the neutron skin of heavy nuclei, follow-up measurement proposed

Future:PVDIS @ 6 GeV completed, results on C2q coming soon

Qweak ongoing, best results on C1q expected

New “construction” experiments at JLab 12 GeV:PVDIS @ 11 GeV will provide sensitivity to Standard Model test, observation of CSV, and the higher twist effectsMoller @ 11 GeV

Many thanks to K. Paschke, D. Armstrong, R. Michaels, P. Souder for helping me to put these slides together.


Backup Slides


SoLID Spectrometer

Baffles

GEM’s

Gas Cerenkov ShashlykCalorimeter

ANL design

JLab/UVA prototype

Babar Solenoid

International Collaborators:China (Gem’s)Italy (Gem’s)Germany (Moller pol.)


PVDIS on the Proton: d/u at High x

Deuteron analysis has largenuclear corrections (Yellow)

APV for the proton has no such corrections

(complementary to BONUS)

The challenge is to get statistical and systematic errors ~ 2%

)(25.0)(

)(91.0)()(

xdxu

xdxuxaP

3-month run


Beyond Strangeness:Parity-Violating Electron Scattering as a Standard Model Test


PV-A4: Forward angle (MAMI) Q2

(GeV2)APV ± stat ± syst

(ppm)GE

s + ηGMs

0.230 -5.44 ± 0.54 ± 0.26 GEs + 0.225 GM

s = 0.039 ±

0.034

0.110 -1.36 ± 0.29 ± 0.13 GEs + 0.106 GM

s = 0.071 ±

0.036

Counting – fast energy

histograms

At Q2=~0.1 GeV2, Gs < few percent of Gp

all low Q2 data


“Parity Quality” of JLab polarized beam

Beam Parameter HAPPEx-I HAPPEx-II PREX

Charge asymmetry < 0.1 ppm 0.41 ppm 200 ppb

Position difference

-11±2.3 nm,-10±1.0 nm

0.56±0.53 nm, 1.69±0.83 nm

2 nm

angle difference 0.2±0.6 nrad, 3±0.2 nrad

-0.26±0.24 nrad, 0.21±0.25 nrad

1 nrad

Energy difference -4±1 ppb 0.2ppb (0.6 eV) 1 eV

Total correction -0.02 ± 0.02 ppm

0.08 ± 0.03 ppm

HAPPEx-II (2005): • superlattice

(PB>85%)

• 35 A

e ePREX (2010): • superlattice

(PB>85%)

• 50-100 A

HAPPEx-I (1999): • strained GaAs

(PB~69%)

• 40 A beam current

High “parity-quality”, negligible uncertainties due to beam; Most of 6 GeV experiments measured strange quark

contribution to proton form factors: less than 5% to GEp and

less than 20% to GMp


JLab 6 GeV Experiment 08-011

100-105 A, 6 GeV, 87% polarized beam on a 20-cm LD2 target;

Two Hall A High Resolution Spectrometers detect scattered electrons;

Measured PV asymmetry Ad at Q2=1.10 and 1.90 GeV2 to 3 and 4%

(stat.), respectively.

Ad at Q2=1.10 will set a limit on the higher twist effects;

If HT is small, can extract 2C2u-C2d from Ad at Q2=1.90 to ±0.05-

0.06 (or with reduced precision if higher twists are unexpectedly large)

Co-spokesperson & contact: X. ZhengCo-spokesperson: P.E. Reimer, R. Michaels

(Hall-A Collaboration Experiment, approved by PAC27; Re-approved by PAC33 for 32 days, rated A-; Ran Nov-Dec 2009)


PV DIS and Other SM Test ExperimentsE158/Moller (SLAC)

NuTeV (FNAL)Atomic PV

PVDIS (JLab)Qweak (JLab)

2 (2C1u+C1d)

Coherent quarks in the proton

Purely leptonicWeak CC and NC differenceNuclear structure?Other hadronic effects?

Coherent Quarks in the Nucleus- 376C1u - 422C1d

Nuclear structure?

(2C1u-C1d)+Y(2C2u-C2d)

Isoscalar quark scattering

Cartoons borrowed from R. Arnold (UMass)

Different ExperimentsProbe Different

Parts of Lagrangian,

PVDIS is the only one accessing C2q


Hall A large acceptance “solenoid” device: PR09-012

Measure Ad to 1% for a wide range of (x,Q2,y), clean separation of

New Physics (via C2q and sin2W), HT and CSV possible;

Extract d/u at large x from PVDIS on a proton target, free of nuclear effects;

Other hadronic physics study possible: A1n at large x, Semi-inclusive

DIS.

Higher precision, possibly sensitive to 1) New Physics beyond the SM; 2) Charge Symmetry Violation (CSV)

Two approaches:

Hall C “baseline” SHMS+HMS: PR12-07-102 (P.E. Reimer, X-C. Z, K. Paschke,

1% on Ad, extraction of C2q, sin2W (if higher-twists and CSV are

negligible);

PVDIS Program at JLab 12 GeV

(conditionally approved)


N

ee ~ 25 TeV

JLab MøllerLHC

New Contact Interactions

Møller Parity-Violating Experiment: New Physics Reach

(example of large installation experiment with 11 GeV beam energy)

AFB(b) measures product of e- and b-Z couplingsALR(had) measures purely the e-Z couplings

Proposed APV(b) measures purely thee-Z couplings at a different energy scale

Not “just another measurement” of sin2(w)


Projected PVDIS Measurement with SOLID@11 GeV



ONGOING CONSTRUCTION EFFORTS

Hall D - Central Drift Chamber Endplates @ CMU

Hall C – Drift Chambers @ HU & Scintillators @ JMU

Hall B - Drift Chambers @ JLab,

ODU and ISU

12 GeV Groundbreaking

(Apr2010

)

Hall D Concrete Wall Erection

(Apr 2009)


Backup Slides


Staff: ~650

User community: ~1300

A CB


Beam was first delivered in 10/95

In full operation for ~13 years (since 11/97);

283 PRL and PL to date: ½ expt, ½ theory)

334 PhDs to date and 249 in progress (~1/3 of US PhDs in Nuclear Physics)


Three Experimental Halls (Present)Hall A:pair of high resolution spectrometers (HRS), E' up to 4 GeV/c, = 7 msrluminosity up to 1039 cm-2 s-1

Hall C:High Momentum (HMS and Short-Orbit Spectrometers (SOS)luminosity up to 1039 cm-2 s-1

Hall B:CEBAF Large Acceptance Spectrometer (CLAS) luminosity up to 1034 cm-2 s-1


Measurement of P-V Asymmetries

610

LR

LRLRA

e.g. 5% Statistical Precision on 1 ppm

-> requires 4x1014 counts

Rapid Helicity Flip: Measure the asymmetry at 10-4 level, 10 million times

High luminosity: thick targets, high beam currentControl noise (target, electronics) High beam polarization and rapid flip

LR

LRLR NN

NNA


Facilities Accelerator Beam Time

low 1995 - ... ...

SLAC Stanford Linear Accelerator 1962 - ... ... 0.03%

“CW”

CERN low 1989-2000

DESY low

MAINZ 1979 - ... ... “CW”

MIT Bates MIT Bates Linear Accelerator 1975-2005

Energy, polarization

Luminosity (cm-2 s-1)

duty factor

FermiLab Tevatron 1.96 TeV

50 GeV, 80% 1036

J LabContinuous Electron Beam Accelerator Facility (CEBAF)

6 GeV, 85% 12 GeV, 85%

1038-39 1985 - ... ... 2015 - ... ...

Large e-/e+ Collider (LEP) 90-209 GeV

Deutsches Elektronen Synchrotron 27.5 GeV 1987 - ... ... (DESY-II)

Mainz Microtron MAMI 0.8/1.6 GeV 1038

0.8 GeV 1037

Medium & High Energy Physics Facilities for Lepton Scattering

e−.

e−.

e−. ,e.

,

e−. ,e.

,

e−. ,e.

High luminosity, yet “continuous” polarized beam makes JLab an unique facility.

~ns: “continuous”>>ns: “pulsed”


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 ?

Strange star ? Quark Star ?

Cooling by neutrino emission (URCA)

0.2 fm URCA probable, else not

Phase Transition to “Exotic” Core ?


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


Deuterium:

PVDIS Asymmetries

APV

= +

Ad= 540 ppmQ2

2 C1u[1R

C x ]−C

1d[1R

S x ]Y 2 C

2u−C

2dR

V x

5RS x 4 R

C x

+

L=LSM

PVLNEW

PV

LSM

PV=−G

F

2e e∑q

C2qq

5 q LNEW

PV =g2

4 2e e∑ f

hA

q q 5q

g: coupling constant, : mass limit, hAq: effective coefficient

New physics sensitivity:

g≈ [8G

F∣ 2 C2u−C 2d∣]

−1/2

Sensitive to: Z' searches, compositeness, leptoquarks

Mass limit:


Plan View of the Spectrometer

BaBarSolenoid?

Documents

1 X. Zheng, University of Virginia, Talk at OCPA7, August 1-5, Kaotsiung, Taiwan Recent Results from Parity Violation Electron Scattering Experiments at