Some Mysteries in Nuclear Physics

Roy J. Holt

Nuclear Physics: Exploring the Heart of Matter Chicago

26-27 September 2014

Outline - contemporary mysteries in physics

Why is there more visible matter than anti-matter in the Universe?

– CP violation, EDM

What is the nature of neutrinos? What is the nature of dark matter? What is confinement and how is it

connected with mass generation?– Hadron structure– Transition from nonperturbative to

perturbative QCD

How do nuclei emerge from QCD?– Nuclear pions, antiquark excess– EMC effect, short-range correlations

What forces, now hidden, were present in the early Universe?

– Parity violation

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What’s the matter?

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Dark matter is:

•one of the greatest mysteries of modern physics

•a central element of cosmology and astronomy

•about 80% of the mass of the Universe

Hypothesis: The dark sector couples to the Standard Model sector

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Standard Model

Quarks, leptons

g W Z

Standard Model

Quarks, leptons

g W Z

Hidden Sector

dark matter

A’

Hidden Sector

dark matter

A’

J. D. Bjorken et al, PRD 80 (2009) 075018; B. Holdom, PLB 166 (1986) 196

~ 0.01 to 1x10-8 from loops of heavy particles

• Dark photons would provide a “portal” to the dark sector• Discovery of dark photons would be revolutionary• Dark photons could explain:

• positron excess in high energy Cosmic rays• Gamma ray excess near Galactic Center• …

Production and detection of dark photons

Proton bremsstrahlung

0, , … decay

Drell-Yan

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A’

target shield pair spectrometer

High energy Proton beam

A’

l+

l-

• Based on projections, the trigger was modified to include dark photon detection at 50% efficiency• Thanks to D. Geesaman , P. Reimer, C. Brown, E. McClellan, A.Tadepalli

Ideal beam stop experiment

Our apparatus: designed for Drell-Yan

120 GeV

proton beamSeaQuest

Experiment at FNAL

Worldwide search for dark photons (exclusion plot)

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JLab Projections

FNAL E906SeaQuestpreliminaryprojections

Plot credit: Arun Tadepalli

Dark photons at “SeaQuest-Light” (e+e- detection?)

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e+e- detection detection radiative decay

Very preliminary

Visible matter - What should we measure?

Measure everything possible about our only stable hadron, the proton

Measure everything possible about our long-lived hadrons –there aren’t that many

Measure “scattering” from , K, 1,2,3H, 3,4He – our simplest systems

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Elastic electron scattering from a nucleon

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Cross section for scattering from a point-like object

Form factors describing nucleon shape/structure

j=<e’||e>

J=<p’||p>

Nucleon vertex:

)2(22

)2(1

', QFν

M

qiQFpp

Dirac Pauli

1990 Nobel Prize

1961 Nobel Prize

Deep inelastic scattering

Example: Flavor separation of nucleon form factors

Very different behavior for u & d quarks

Evidence for diquark correlations – axial diquark -> soft f.f.

Six 12-GeV experiments to extend Q2 range

Thanks to Craig Roberts, R. Gilman, J. Arrington, R. McKeown, D. Beck

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Cates, de Jager, Riordan, Wojtsekhowski, PRL 106 (2011) 252003

Q4 F1q

NSAC milestone HP4 (2010) completed

Q4F2q/

HAPPEx, G0, A4, SAMPLE GE

s = GMs = 0

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Parton model

Quark charge

Prob. of q in proton

Structure function

leptonic hadronic

Partonic structure of the nucleon

EIC whitepaper

Example: longitudinal structure functions

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Parton model ->

Upgraded JLab hasunique capability todefine the valence region

All three measurements – F2n/F2

p, A1

p, A1n - are required to sort out

the models!

C. D. Roberts, RJH, S. Schmidt, PLB 727 (2013) 249 Six JLab 12 GeV experimentsThanks to R. Milner, H. Jackson, Z.-E. Meziani, X. Zheng, J. Arrington, C. Keppel

Physics of

Nuclei

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Motivation

• Test calculations of light nuclei.

• Study properties of all bound helium nuclei

from 3He to 8He.

From the lowest to highest N/Z on Earth.

Isospin dependence of the nuclear force

L.-B. Wang et al, PRL (2005}, P. Mueller et al, PRL (2007), Z.-T. Lu et al RMP (2013)

Thanks to V. Pandharipande, S. Pieper, R. Wiringa, Z-T. Lu, P. Mueller, L. B. Wang

Quarks in the nucleus: the EMC effect and short range N-N interactions

EMC effect depend on local nuclear density

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J. Seeley et al, PRL 103 (2009) EMC effect is correlated with short range N-N interaction – L. Weinstein et al, PRL 106, 052301 (2011) , J. Arrington et al, PRC 86 (2012) 065204, N. Fomin et al, PRL 108, 092502 (2012)

Plot credit: JLab whitepaper

Flavor, isospin and spin dependence of EMC effect? JLab@12, Drell-Yan, MINERvA

NSAC milestone HP5 (2010)Thanks to J. Arrington, B. Filippone, P. Solvignon

Nuclei as laboratories

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Prehadron: small object with a smaller cross section than that of quark-N or hadron-N interaction

Future: JLab at 12 GeV

Credit: J. Rubin

Plot credit: JLab whitepaper

X. Qian et al., PRC81:055209 (2010);B. Clasie et al, PRL99:242502 (2007) ;L. El Fassi et al, PLB (2012)

Thanks to R. Ent, D. Dutta, K. Hafidi, H. Gao, L. El Fassi

Parity Violation

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Results and projections – electroweak mixing angle

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Thanks to W. Marciano, P. Reimer, X. Zheng

Concluding statement

Even after a century of discoveries in nuclear physics, many mysteries have emerged

Understanding these mysteries will be tremendous contributions to science and lead to new applications

New 21st century tools have positioned us well for the next decade: – JLab 12 GeV, RHIC - Major U.S. facilities lead the world– FNAL, CERN, HIS, Mainz, J-PARC, FAIR provide targeted experiments

that complement the central program– Far future: EIC

We are camped on the most interesting frontier in science

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My heartfelt thanks to the organizers

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A. Bernstein (Argonne National Lab)

D. F. Geesaman (Argonne National Lab)

K. Hafidi (Argonne National Lab)

R. V. F. Janssens (Argonne National Lab)

Z.-E. Meziani (Temple University)

D. (Morrison) Beres (Argonne National Lab)

And to all the speakers and colleagues

And a special thank you to Kawtar Hafidi

And to Debbie Beres, the Symposium Secretary

And to Nancy for a life in the real world

And to Barbara Fletcher for the nostalgic video