Nuclear Physics at Jefferson LabPart II

R. D. McKeownJefferson LabCollege of William and Mary

Taiwan Summer SchoolJune 29, 2011

2

• Strange Quarks

• Standard Model Tests

• Dark Matter?

Outline

3

Strange Quarks in the Nucleon

3

• Strange quarks-antiquarks virtual pairs produced by gluons

• Contribution to proton’s magnetism - (Stern’s discovery)?- QCD analog of Lamb shift in atoms

• Study using small (few parts per million) left-right difference in electron-proton force

challenging experiments!

4

Strange Quarks in the Nucleon

Mass:

u u

dp

uud

u

su

s

valence

sea

proton

4.0)(ˆ

2

NdduumN

NssmN sp-N scattering

Spin:

1.01.0

10.020.0

s

sdu

gq JLsdu 2

1

2

1Polarized deep-inelastic scattering

HERMES semi-inclusive

n-p elastic scattering

09.015.0 s

5

Electroweak charged fermion couplings

6

Weak Charges

• QWp = 1 – 4 sin2 qW ~ 0.071

• QWn = -1

7

Neutral weak form factors

•Electromagnetic interaction

•Neutral weak interaction

g

p

Z0

p

GEg,p, GM

g,p GEZ,p, GM

Z,p

GAZ,p

8

Use Isospin Symmetry

pZM

nM

pMW

sM

pZM

nM

pMW

dM

pZM

pMW

uM

GGGG

GGGG

GGG

,,,2

,,,2

,,2

)sin41(

)sin42(

)sin43(

(p n) = (u d)

For vector form factors theoretical CSB estimates indicate < 1% violations (unobservable with currently anticipated uncertainties)

(Miller PRC 57, 1492 (1998) Lewis and Mobed, PRD 59, 073002(1999)

9

Parity-violating electron scatteringPolarized electrons on unpolarized target

For a proton: (Cahn & Gilman 1978)

LR

LRA

g Z0

g 2

Forward angles Backward angles

10

(VMD)

l Soliton, NJL, …l Dispersion Integralsl Lattice QCD

Theoretical Approaches

11

Theoretical predictions for ms

12

SAMPLE ExperimentPolarizedInjector

WienFilter

AcceleratorE = 125 MeV600 pulses/sIpk = 3 mAIave = 44 APB = 36%

Energy

BeamCurrent

Fast phase shift(energy) feedback

K11

Beam currentfeedback

SAMPLEDetector

Lumi

Position,Angle,Charge

Halo

MollerPolarimeter

Beam positionfeedback

13

Experimental procedure

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Positive Helicity Negative Helicity 60 Hz

Random (New)Sequence

ComplementSequence

Pulse Pair

AY Y

Y YMeasured

Positive Negative

Positive Negative

• Asymmetry between pulses separated by 1/60 sremove effects due to 60 Hz

• Rapid helicity reversal reduce effects of long-term drifts

• Slow helicity reversal remove helicity-correlated electronics effects

14

15

GMs(Q2=0.1) =

0.37 +- 0.20 +- 0.26 +- 0.07

SAMPLE result

16

s Theory and Experiment

17

Other Experiments

HAPPEX @ JLAB

A4 @ Mainz

G0 @ JLAB

18

Global Analysis

19

• Nucleon models continue to struggle, with some indication that higher mass poles are important

• Precise lattice QCD - motivated prediction:

(Leinweber, et al., PRL 97, 022001 (2006)

• New unquenched lattice QCD result:

Doi, et al., arXiv:0903.3232

Theory Update

20

HAPPEX-III Results

A(Gs=0) = -24.158 ppm ± 0.663 ppm Gs

E + 0.52 GsM = 0.005 ± 0.010(stat) ± 0.004(syst) ± 0.008(FF)

APV = -23.742 ± 0.776 (stat) ± 0.353 (syst) ppm

preliminary

preliminary

21

Measuring the Neutron “Skin” in the Pb Nucleus

21

crust

Neutron Star Lead Nucleus

skin

10 km

10 fm

• Parity violating electron scattering• Sensitive to neutron distribution• First clean measurement• Relevant to neutron star physics• Currently running in Hall A

22Page 22

Lead (208Pb) Radius Experiment : PREXElastic Scattering Parity-Violating Asymmetry

Z0 : Clean Probe Couples Mainly to Neutrons

Applications : Nuclear Physics, Neutron Stars, Atomic Parity, Heavy Ion Collisions

• The Lead (208Pb) Radius Experiment (PREX) determines the neutron radius to be larger than the proton radius by +0.35 fm (+0.15, -0.17).

• This result represents model-independent confirmation of the existence of a neutron skin, with relevance for neutron star calculations.

• Plans for follow-up experiment to reduce uncertainties by factor of 3. This can quantitatively pin down the symmetry energy, an important contribution to the nuclear equation of state.

A neutron skin of 0.2 fm or more has implications for our understanding of neutron stars and their ultimate fate

Rel. mean field

Nonrel. skyrme

PREXPREX data

23

Running of the Weak Coupling

24

Global Fits

25

PV electron-quark couplings

General Form:

Standard model:

26

Qweak

Luminosity monitors

Luminosity monitors

scanner

Precise determination of the weak charge of the proton

Qw= -2(2C1u+C1d) =(1 – 4 sin2 qW)

27

Qweak Overview

28

Target cell

• 35 cm target cell, designed with CFD • Target tested and stable up to 160 A. Sufficient reserve cooling power to easily reach 180 A. Highest power LH2 target.

• When using 960Hz spin flip rate, the target density fluctuations (an unknown before commissioning) appear to be small compared to expected counting statistical uncertainty (per quartet) of ~220 ppm.

Qweak LH2 Cryotarget

29

Accelerator Performance for Qweak

30

Qweak Projection

31

Radiative Correction Uncertainty

(Ramsey-Musolf)

32

Constraints on Couplings

HAPPEx: H, HeG0 (forward): H,PVA4: HSAMPLE: H, Dprojection

33

New combination of: Vector quark couplings C1q Also axial quark couplings C2q

PV Deep Inelastic Scattering

iii fff

For an isoscalar target like 2H, structure functions largely cancel in the ratio at high x

b(x)

3

10(2C2u C2d )

uv dv

u d

a(x) =C1i Qi fi

+(x)i

Qi

2 fi+(x)

i

e-

N X

e-

Z* *

y 1 E / E b(x) C2i Qi fi

(x)i

Qi

2 fi(x)

i

x xBjorken

At high x, APV becomes independent of x, W, with well-defined SM prediction for Q2 and y

Sensitive to new physics at the TeV scale

a(x) 3

10(2C1u C1d ) 1

2s

u d

6.0

APV GFQ2

2a(x) Y (y) b(x)

0

1

at high x

a(x) and b(x) contain quark distribution

functions fi(x)

PVDIS: Only way to measure C2q

34

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.)

35

Statistical Errors (%)

4 months at 11 GeV

2 months at 6.6 GeV

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

Strategy: sub-1% precision over broad kinematic range for sensitive Standard Model test and detailed study of hadronic structure contributions

3636

Sensitivity: C1 and C2 Plots

Cs

PVDIS

Qweak PVDIS

World’s data

Precision Data

6 GeV

37

SoLID: Comprehensive PVDIS Study

• Measure AD in NARROW bins of x, Q2 with 0.5% precision• Cover broad Q2 range for x in [0.3,0.6] to constrain HT• Search for CSV with x dependence of AD at high x• Use x>0.4, high Q2, and to measure a combination of the Ciq’s

Strategy: requires precise kinematics and broad range

x y Q2

New Physics no yes no

CSV yes no no

Higher Twist yes no yes

2

23)1(

11 x

QxAA CSVHT Fit data to:

C(x)=βHT/(1-x)3

38

PV Møller Scattering

SLAC E158 result: APV = (-131 ± 14 ± 10) x 10-9

39

E158 Result

40

New JLab Experiment

Polarized Beam• Unprecedented polarized luminosity

• unprecedented beam stability

Liquid Hydrogen Target• 5 kW dissipated power (2 X Qweak)

• computational fluid dynamics

Toroidal Spectrometer• Novel 7 “hybrid coil” design

• warm magnets, aggressive cooling

Integrating Detectors• build on Qweak and PREX

• intricate support & shielding

• radiation hardness and low noise

41

Toroidal Spectrometer

Mollerse-p elastic

Separate Moller events from background

42

Projected MOLLER Results

Projected systematic error: dA/A = 1%

43

Systematic Error Estimate

44

Future PV Program at Jlab

PV Moller Scattering:

• Custom Toroidal Spectrometer• 5kw LH Target

SOLID (PVDIS):• High Luminosity on LD2 and LH2 • Better than 1% errors for small bins• Large Q2 coverage• x-range 0.25-0.75• W2> 4 GeV2

44INT EIC Workshop, Nov. 2010

45

Weak Mixing in the Standard Model

JLab Future

45INT EIC Workshop, Nov. 2010

46

Beyond the Standard Model

INT EIC Workshop, Nov. 2010

46

Kurylov, et al.

47

Muon g-2

Momentum

Spin

e

SUSY?47INT EIC Workshop, Nov.

2010

48

On the horizon: A New Muon g-2 Experiment at Fermilab  

Update: Oct 2010: Dam(Expt – Thy) = 297 ± 81 x 10-11

3.6 s

BNL E821

2010 e+e- Thy

3.6 s

x10-11

Future Goals

Goal: 0.14 ppm

Expected Improvement

D. Hertzog

48INT EIC Workshop, Nov. 2010

49

Cosmology and Dark Matter

R. D. McKeown June 15, 2010

49

• Dark sector is new physics, beyond the standard model• Many direct searches for dark matter interacting with

sensitive detectors (hints, no established signal yet…)• Controversial evidence for

excess astrophysical positrons…

→ many predictions for new physics

50

PAMELA Data on Cosmic Radiation

Va. Tech. Physics Colloquium, Dec. 3, 2010

50

Surprising rise in e+ fraction

But not p

• Could indicate low mass A’ (MA’ < 1 GeV )

• Or local astrophysical origin??

51

NEW! Confirmation from Fermi

52

AMS-02 Launched May 16, 2011slide from Andrei Kounine

TeVPA 2010

53

New Opportunity: Search for A’ at JLab

Search for new forces mediated by ~100 MeV vector boson A’

with weak coupling to electrons:

Irrespective of astrophysical anomalies: • New ~GeV–scale force carriers are important category of physics beyond the SM• Fixed-target experiments @JLab (FEL + CEBAF) have unique capability to explore this!

53Va. Tech. Physics Colloquium, Dec. 3, 2010

g – 2 preferred!

54

APEX in Hall A

• Uses existing equipment• Successful 2010 test run

(results soon!)

55

HPS in Hall B• Forward, compact spectrometer/vertex detector identifies heavy photon candidates with invariant mass and decay length.

• EM Calorimeter provides fast trigger and electron ID.

• Small cross sections and high backgrounds demand large luminosities. HPS survives beam backgrounds by spreading them out maximally in time, capitalizing on 100% CEBAF duty cycle and employing high rate DAQ.

• All detectors are split above and below the beam to avoid the “wall of flame” from multiple Coulomb scattered primaries, bremsstrahlung, & degraded electrons.

56

DarkLight at JLab FEL

100 MeV10 mA

Reconstruct all final stateparticles and achieve aninvariant mass resolutionof 1 MeV/c2 or betterover the range 10 to 100MeV/c2.

Toroidal magneticspectrometer with abending power of 0.05 to 0.16 T-m with a wirechamber tracker for theleptons, a radial TPC for proton detection and a scintillator for triggering.

57

Jlab Future

• Clearly we have a exciting and growing program to search for new physicsbeyond the standard model.

• But we have a substantial program ofimportant experiments exploring QCD

- confinement mechanism- nucleon tomography

• And there are prospects for a future newfacility: Electron Ion Collider (EIC)

One more lecture…