Nuclear Physics at Jefferson LabPart II

R. D. McKeownJefferson LabCollege of William and Mary

Taiwan Summer SchoolJune 29, 2011

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• Strange Quarks

• Standard Model Tests

• Dark Matter?

Outline

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Strange Quarks in the Nucleon

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• 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!

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Strange Quarks in the Nucleon

Mass:

u u

dp

uudu

su

s

valence

sea

proton

4.0)(ˆ

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NdduumNNssmN sp-N scattering

Spin:

1.01.010.020.0

ssdu

gq JLsdu 21

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Polarized deep-inelastic scattering

HERMES semi-inclusive

n-p elastic scattering

09.015.0 s

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Electroweak charged fermion couplings

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Weak Charges

• QWp = 1 – 4 sin2 qW ~ 0.071

• QWn = -1

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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

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Use Isospin Symmetry

pZM

nM

pMW

sM

pZM

nM

pMW

dM

pZM

pMW

uM

GGGG

GGGG

GGG

,,,2

,,,2

,,2

)sin41(

)sin42(

)sin43(

gg

gg

g

q

q

q

(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)

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Parity-violating electron scatteringPolarized electrons on unpolarized target

For a proton: (Cahn & Gilman 1978)

LR

LRA

g Z0

g 2

Forward angles Backward angles

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(VMD)

l Soliton, NJL, …l Dispersion Integralsl Lattice QCD

Theoretical Approaches

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Theoretical predictions for ms

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SAMPLE ExperimentPolarizedInjector

WienFilter

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

Energy

BeamCurrent

Fast phase shift(energy) feedback

K11

Beam currentfeedback

SAMPLEDetector

Lumi

Position,Angle,Charge

Halo

MollerPolarimeter

Beam positionfeedback

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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

A Y YY Y

MeasuredPositive 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

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15

GMs(Q2=0.1) =

0.37 +- 0.20 +- 0.26 +- 0.07

SAMPLE result

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ms Theory and Experiment

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Other Experiments

HAPPEX @ JLAB

A4 @ Mainz

G0 @ JLAB

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Global Analysis

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• 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

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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

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Measuring the Neutron “Skin” in the Pb Nucleus

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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

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Running of the Weak Coupling

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Global Fits

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PV electron-quark couplingsGeneral Form:

Standard model:

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Qweak

Luminosity monitors

Luminosity monitors

scanner

Precise determination of the weak charge of the proton

Qw= -2(2C1u+C1d) =(1 – 4 sin2 qW)

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Qweak Overview

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Target cell

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

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Accelerator Performance for Qweak

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Qweak Projection

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Radiative Correction Uncertainty

(Ramsey-Musolf)

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Constraints on Couplings

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

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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)

310

(2C2u C2d )uv dv

u d

a(x) =C1i Qi fi

+(x)i

Qi

2 fi+(x)

i

e-

N X

e-

Z* g*

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

2pa(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

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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.)

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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

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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 noCSV yes no no

Higher Twist yes no yes

2

23)1(11 x

QxAA CSVHT Fit data to:

C(x)=βHT/(1-x)3

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PV Møller Scattering

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

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E158 Result

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New JLab Experiment

Polarized Beam• Unprecedented polarized luminosity• unprecedented beam stabilityLiquid Hydrogen Target• 5 kW dissipated power (2 X Qweak)• computational fluid dynamicsToroidal Spectrometer• Novel 7 “hybrid coil” design• warm magnets, aggressive coolingIntegrating Detectors• build on Qweak and PREX• intricate support & shielding• radiation hardness and low noise

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Toroidal Spectrometer

Mollerse-p elastic

Separate Moller events from background

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Projected MOLLER Results

Projected systematic error: dA/A = 1%

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Systematic Error Estimate

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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

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Weak Mixing in the Standard Model

JLab Future

45INT EIC Workshop, Nov. 2010

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Beyond the Standard Model

INT EIC Workshop, Nov. 2010

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Kurylov, et al.

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Muon g-2

Momentum

Spin

e

SUSY?47INT EIC Workshop, Nov.

2010

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

Update: Oct 2010: am(Expt – Thy) = 297 ± 81 x 10-11 3.6

BNL E821

2010 e+e- Thy

3.6

x10-11

Future Goals

Goal: 0.14 ppm

Expected Improvement

D. Hertzog

48INT EIC Workshop, Nov. 2010

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Cosmology and Dark Matter

R. D. McKeown June 15, 2010

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• 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

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PAMELA Data on Cosmic Radiation

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

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Surprising rise in e+ fraction

But not p

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

• Or local astrophysical origin??

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NEW! Confirmation from Fermi

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

TeVPA 2010

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New Opportunity: Search for A’ at JLabSearch 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!

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APEX in Hall A

• Uses existing equipment• Successful 2010 test run

(results soon!)

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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.

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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.

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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…