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
Argonne National Laboratory
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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
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
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