Parity-Violating Electron Scattering & Charge Symmetry Breaking

18 June 2005 PVES & CSB

Parity-Violating Electron Scattering & Charge Symmetry Breaking

Krishna KumarUniversity of Massachusetts

thanks to:C. Horowitz, T. Londergan, W. Marciano, G. Miller, M.J. Ramsey-Musolf,

A. Thomas, B. van Kolck

Workshop on Charge Symmetry BreakingTrento, June18, 2005

In collaboration with: Kent Paschke (UMass)Paul Souder (Syracuse)Robert Michaels (Jlab)


Outline

• Parity-Violating Electron Scattering• Deep Inelastic Scattering• Physics with 11 GeV Electrons

– Beyond the Standard Model– Search for Charge Symmetry Violation– d/u

• Towards a 11 GeV Program• Elastic Electron-Nucleon Scattering

– Strangeness in Nucleons– Recent Results– Charge Symmetry Assumption

• Outlook


PV Asymmetries

€

10−4 ⋅Q2

€

10−5 ⋅Q2

to

For electrons scattering off nuclei or nucleons:

Z couplings provide access to different linear combination of underlying quark substructure

(gegT)


2005: MeV to TeV Physics1970s

1980s

1990s

Recent Results

FutureResult Today!

• Steady progress in technology• part per billion systematic control• 1% normalization control

Three different avenues of investigation:

•Are there new interactions at very high energy?•Do strange quarks in the nucleon affect its charge and magnetization distributions?•How thick is the neutron skin in a heavy nucleus?

GeV Physics

TeV Physics

MeV Physics•Valence quark structure of the nucleon: Jlab at 12 GeV


Electroweak Physics at Low Q2

LEPII, Tevatron, LHC access scales greater than ~ 10 TeV

Logical to push to higher energies, away from the Z resonance

Parity Conserving Contact Interactions

Parity Violating Contact Interactions

Q2 << scale of EW symmetry breaking


Weak Neutral Current at low Q2

Purely leptonic reaction Qe

W ~ 1 - 4sin2WZ0

Fixed Target Møller Scattering

E158 at Stanford Linear Accelerator Center

InstitutionsCaltech SyracusePrinceton Jefferson LabSLAC UC BerkeleyCEA Saclay UMass AmherstSmith College U. of Virginia

60 physicists, 7 Ph.D. students


3%

sin2eff = 0.2397 ± 0.0010 ± 0.0008

Czarnecki and MarcianoErler and Ramsey-MusolfSirlin et. al.Zykonov

SLAC E158 Final Result

6

sin2WMS(MZ)

hep-ex/0504049, To be published in PRL

* Limit on LL ~ 7 or 16 TeV

* Limit on SO(10) Z’ ~ 1.0 TeV* Limit on lepton flavor violating coupling ~ 0.01GF

(95% confidence level)


Future Possibilities (Leptonic)-e in reactorSLAC E158

Kurylov, Ramsey-Musolf, Su

95% C.L.JLab 12 GeVMøller

Does Supersymmetry (SUSY) provide a candidate for dark matter?•Neutralino is stable if baryon (B) and lepton (L) numbers are conserved•B and L need not be conserved (RPV): neutralino decay

can test neutrino coupling: sin2W to ± 0.002

Møller at 11 GeV at Jlab sin2W to ± 0.00025!ee ~ 25 TeV reach!Higher luminosity and acceptance

Longstanding discrepancy between hadronic and leptonic Z asymmetries:Z pole asymmetries


Future Possiblities (Semileptonic)Qweak at Jlab

• measure sin2W to ± 0.0007• nail down fundamental low energy lepton-quark WNC couplings

NuTeV

€

C1i ≡ 2gAe gV

i

€

C2i ≡ 2gVe gA

i

A

V

V

A

• C2i’s small & poorly known: difficult to measure in elastic scattering• PV Deep inelastic scattering experiment with high luminosity 11 GeV beam

APV in elastic e-p scattering

(2008)


Lepton Deep Inelastic Scattering

b ~ 0.2 fm/sqrt(t) t=(p-p‘)2

r ~ 0.2 fm/Q (0.02 – 0.2 fm for 100>Q2>1 GeV2) transverse size of probe*

ct

b

ct ~ 0.2 fm (1/2x) (<1 fm to 1000‘s fm) – scale over which photon fluctuations survive. For x~1: valence quark structure

€

x ≡ xBjorken =Q2

2M(E − ′ E )

Fraction of proton momentum carried by struck quark

r

Cross-sections fall steeply with (1-x)nNeed high luminosity at high energy

Jefferson Lab upgraded to 11 GeV, 90 µA CW beam

Courtesey A. Caldwell

Parton distribution functions fi(x) poorly measured at high x

Lacking some fundamental knowledge of proton structure


Parity Violating Electron DIS

€

APV =GFQ2

2παa(x) + f (y)b(x)[ ]

€

a(x) =

C1iQi f i(x)i

∑

Qi2 f i(x)

i

∑

€

fi(x) are quark distribution functions

e-

N X

e-

Z* *

For an isoscalar target like 2H, structure functions largely cancel in the ratio:

€

a(x) =3

10(2C1u − C1d )[ ] +L

€

b(x) =3

10(2C2u − C2d )

uv (x) + dv (x)

u(x) + d(x)

⎡

⎣ ⎢ ⎤

⎦ ⎥+L

Provided Q2 >> 1 GeV2 and W2 >> 4 GeV2 and x ~ 0.2 - 0.4

Must measure APV to fractional accuracy better than 1%

• 11 GeV at high luminosity makes very high precision feasible• JLab is uniquely capable of providing beam of extraordinary stability• Systematic control of normalization errors being developed at 6 GeV

€

y ≡1− ′ E / E

€

b(x) =

C2iQi f i(x)i

∑

Qi2 f i(x)

i

∑

€

x ≡ xBjorken


2H Experiment at 11 GeV

E’: 5.0 GeV ± 10% lab = 12.5o

APV = 217 ppm

Ibeam = 90 µA 60 cm LD2 target

• Use both HMS and SHMS to increase solid angle• ~2 MHz DIS rate, π/e ~ 2-3

xBj ~ 0.235, Q2 ~ 2.6 GeV2, W2 ~ 9.5 GeV2

1000 hours

(APV)=0.65 ppm

(2C2u-C2d)=±0.0086±0.0080

PDG (2004): -0.08 ± 0.24 Theory: +0.0986

Advantages over 6 GeV:•Higher Q2, W2, f(y)•Lower rate, better π/e•Better systematics: 0.7%


Physics Implications

Examples:•1 TeV extra gauge bosons (model dependent)•TeV scale leptoquarks with specific chiral couplings

Unique, unmatched constraints on axial-vector quark couplings:Complementary to LHC direct searches

(2C2u-C2d)=0.012

(sin2W)=0.0009


PV DIS and Nucleon Structure• Analysis assumed control of QCD uncertainties

– Higher twist effects– Charge Symmetry Violation (CSV)– d/u at high x

• NuTeV provides perspective– Result is 3 from theory prediction– Generated a lively theoretical debate– Raised very interesting nucleon structure issues:

cannot be addressed by NuTeV• JLab at 11 GeV offers new opportunities

– PV DIS can address issues directly• Luminosity and kinematic coverage• Outstanding opportunities for new discoveries• Provide confidence in electroweak measurement


Search for CSV in PV DIS

Sensitivity will be further enhanced if u+d falls off more rapidly than u-d as x 1

•measure or constrain higher twist effects at x ~ 0.5-0.6•precision measurement of APV at x ~ 0.7 to search for CSV

Strategy:

•u-d mass difference•electromagnetic effects

•Direct observation of parton-level CSV would be very interesting•Important implications for high energy collider pdfs•Could explain significant portion of the NuTeV anomaly€

up (x) = dn (x)?

d p (x) = un (x)?

For APV in electron-2H DIS:

€

APV

APV

= 0.28δu −δd

u + d

€

u(x) = up (x) − dn (x)

δd(x) = d p (x) − un (x)


Potential Sensitivity


11

110

)(32)(

31

)(31)(

181)(

21

SS

SSS

uuduud

uduuduudup

d(x)/u(x) as x1

Proton Wavefunction (Spin and Flavor Symmetric)

SU(6):d/u~1/2

Valence Quark: d/u~0

Perturbative QCD: d/u~1/5

€

APV =GFQ2

2παa(x) + f (y)b(x)[ ]

€

a(x) =u(x) + 0.91d(x)

u(x) + 0.25d(x)

•Allows d/u measurement on a single proton!•Vector quark current! (electron is axial-vector)

PV-DIS offhydrogen

Longstanding issue in proton structure


A New APV DIS Program

•2 to 3.5 GeV scattered electrons•20 to 40 degrees•Factor of 2 in Q2 range•High statistics at x=0.7, with W>2


A PV DIS Program with upgraded JLab• Hydrogen and Deuterium targets• Better than 2% errors

– It is unlikely that any effects are larger than 10%

• x-range 0.25-0.75• W2 well over 4 GeV2

• Q2 range a factor of 2 for each x point– (Except x~0.7)

• Moderate running times

•CW 90 µA at 11 GeV•40 cm liquid H2 and D2 targets•Luminosity > 1038/cm2/s

•solid angle > 200 msr•Count at 100 kHz• online pion rejection of 102 to 103


Dynamics of Low Energy QCD( 0.2 fm)

Profound qualitative and quantitative implications!


Strangeness in Nucleons

?

Breaking of SU(3) flavor symmetry introduces uncertainties

€

Δs ~ N s γ μγ 5s N

€

N s γ μ s N ≠ 0?

Kaplan & Manohar (1988)McKeown (1990)

GEs(Q2), GM

s(Q2)


NuuNJ qqq

qEM

μμ ∑= Q

€

M EM =4πα

Q2QEM l μ Jμ

EM [ ][ ]NCNCAV

FNC JJggG

M 55

22μμ

μμ ++= ll

[ ]NCV

NCA

FNCPV JgJg

GM 5

5

22μ

μμ

μ ll +=

NuuNJ qqq

NCμμ ∑= q

Vg

Parity Violating Amplitude dominated by NC terms:

NC vector current probes same hadronic flavor structure, with different couplings:

Electron Elastic Electroweak Scattering


Q gV gA

e −1 −1 + 4 sin2W +1

u +2/3 1 − 8/3 sin2W −1

d,s −1/3 −1 + 4/3 sin2W −1

NFM

qiFNNuuNJ

Nqq

qq

EM

⎥⎥⎦

⎤

⎢⎢⎣

⎡+==∑

μ

μμμ

21 2

Q

τ 2121 FFGFFG ME +=+=commonly used Sachs FF:

sME

dME

uMEME GGGG //// 3

1

3

1

3

2−−=

Decompose by Quark Flavor:

sMEW

dMEW

uMEW

ZME GGGG /

2/

2/

2/ sin

3

41sin

3

41sin

3

81 ⎟

⎠

⎞⎜⎝

⎛ −−⎟⎠

⎞⎜⎝

⎛ −−⎟⎠

⎞⎜⎝

⎛ −=

Flavor Decomposed Form Factors


Charge symmetry: u-quark distribution in the proton is the same as the d-quark distribution in the neutron

snME

spME

unME

dpME

dnME

upME GGGGGG ,

/,/

,/

,/

,/

,/ ,, ===

GpE,M

GsE,M

GuE,M

GdE,MGn

E,MIsospin

symmetry

GpE,M

<N| sμ s |N>

GnE,M

GpE,M

GsE,M

Pick ‘n Choose

Well Measured

sME

dME

uME

pME GGGG ///

,/ 3

1

3

1

3

2−−=

sME

uME

dME

nME GGGG ///

,/ 3

1

3

1

3

2−−=

Charge Symmetry


How Big?

Various theoretical approaches:

•Quark models•Dispersion Relations•Lattice Gauge theory•Skyrme models

)0( 2 =≡μ QGsMs

rs,M2 =

6π

dtImGM

s (t)t2

4mK2

∞

∫

?

€

€

K +

s s

HammerRamsey-Musolf

Dispersion Theory


Elastic Electroweak Measurements•APV measurements ranging 0.1 < Q2 < 1•forward and backward angles•Hydrogen, Deuterium and Helium targets•Statistical and systematic errors < 10%Rough guide: GE

n(Q2=0.2) ~ 0.05, μ ~ -0.6SAMPLE

GM

s

GA(T=1)

GEs + (Q2) GM

s

Q2 (GeV/c)2

•Cancellations? •Q2 dependence? •Accuracy?

HAPPEX: Second Generation E=3 GeV, =6 deg, Q2=0.1 (GeV/c)2

1H: APV=-1.4 ppm, goal ± 0.08 (stat.)

(GsE+0.08Gs

M ) = 0.010 (GsE ) = 0.014

4He: APV=+7.6 ppm, goal ± 0.18 (stat.)


HAPPEX at JLab

The HAPPEX CollaborationCalifornia State University, Los Angeles -

Syracuse University -DSM/DAPNIA/SPhN CEA Saclay -

Thomas Jefferson National Accelerator Facility- INFN, Rome - INFN, Bari -

Massachusetts Institute of Technology - Harvard University – Temple University –

Smith College - University of Virginia - University of Massachusetts – College of William and Mary

Hall A Proton Parity EXperiment

1998-99: Q2=0.5 GeV2, 1H2004-05: Q2=0.1 GeV2, 1H, 4He


Spectrometers & Detectors

Beam diagnostics

Quadrupole magnets

Bending magnet

Target

Septum magnets

Comptonpolarimeter

Cherenkovcones

PMT

12 m dispersion sweeps away

inelastic events


4He Asymmetry Result

Q2 = 0.091 (GeV/c)2

Araw = 5.63 ppm 0.71 ppm (stat)

Araw correction < 0.2 ppm

Helicity Window Pair Asymmetry

3.3 M pairs, total width ~1300 ppm

June 8-22, 2004

APV = 6.720.84(stat)0.21(syst) ppm

Submitted to PRL: nucl/ex-0506010

Data: (after all corrections)

A(Gs=0) = +7.51 0.08 ppmTheory


1H Asymmetry Result

Q2 = 0.099 (GeV/c)2

Araw = -0.95 ppm 0.20 ppm (stat)

Helicity Window Pair Asymmetry

9.5 M pairs, total width ~620 ppm

Araw correction ~ 0.06 ppm

June 24-July 25, 2004

APV = -1.140.24(stat)0.06(stat)ppmSubmitted to PRL: nucl/ex-0506011

Data: (after all corrections)

A(Gs=0) = -1.44 ppm 0.11 ppm

Theory


(S.L.Zhu et. al.)

Summary of 1H and 4He Results Gs

E = -0.039 0.041(stat) 0.010(syst) 0.004(FF)

GsE + 0.08 Gs

M = 0.032 0.026(stat) 0.007(syst) 0.011(FF)


GEs + (Q2) GM

s

Q2 [GeV2]

Current Status and Prospects

•Each experiment consistent with Gs=0•Some indication of positive GM

s

•G0 data consistent and provocative!•Cancellations might play a role

Let us revisit the charge symmetry assumption


Charge Symmetry Violation EstimatesSimple estimate on GM

s C. Horowitz

leads to different magnetic moments

Assume mu different from md is only source

Propagates to 0.007 n.m.

Non-relativistic constituent quark models G. Miller

Account for mass difference, Coulomb and hyperfine interaction

GMs effects less than 1% over relevant range of Q2

GEs effects between 1 and 2% at Q2 ~ 0.1 GeV2

Are relativistic effects important?

Pion cloud effects small and calculable

Chiral Perturbation Theory Lewis and Mobed GMs effects similar

Unknown normalization at Q2=0?

GEs estimated at LO: NLO not parameter-free

Can one carry isospin violation effects in GE to NLO?


Strange Quarks or CSV?

Need consensus on effects of CSV on GEs:

•Better quark models?•Additional work on chiral perturbation theory?•Handles from observed CSB effects in nucleon systems?

We would like to be able to claim non-trivial dynamics of the sea in the static properties of the nucleon: is that viable?

Any other experimental CSV handles?

95% C.L.


Summary• CSV in parton distributions at high x

– Parity violating DIS quite sensitive– Could be part rich 11 GeV program

• CSV in nucleon form factors– Parity violating elastic scattering increasingly

sensitive: strange quarks or CSV?– Can theory help constrain effects in GE?– Can existing data on CSV help?– Are there new experimental handles on CSV in

the context of nucleon form factors?– Critical to resolve the issue if strange quark

interpretation is to be clean

Documents

Parity-Violating Electron Scattering & Charge Symmetry Breaking