Some Mysteries in Nuclear Physics Roy J. Holt Nuclear Physics: Exploring the Heart of Matter Chicago 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 2

What’s the matter? Argonne National Laboratory 3 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 Argonne National Laboratory 4 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) ; 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 Argonne National Laboratory 5 A’ target shield pair spectrometer High energy Proton beam    A’ l+l+ 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 beam SeaQuest Experiment at FNAL

Worldwide search for dark photons (exclusion plot) Argonne National Laboratory 6 JLab Projections FNAL E906 SeaQuest preliminary projections Plot credit: Arun Tadepalli

Dark photons at “SeaQuest-Light” (e + e - detection?) Argonne National Laboratory 7 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, 1,2,3 H, 3,4 He – our simplest systems Argonne National Laboratory 8

Elastic electron scattering from a nucleon Argonne National Laboratory 9 Cross section for scattering from a point-like object Form factors describing nucleon shape/structure j  = J  = Nucleon vertex: 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 Q 2 range Thanks to Craig Roberts, R. Gilman, J. Arrington, R. McKeown, D. Beck 10 Cates, de Jager, Riordan, Wojtsekhowski, PRL 106 (2011) Q 4 F 1 q NSAC milestone HP4 (2010) completed Q4F2q/Q4F2q/ HAPPEx, G0, A4, SAMPLE  G E s = G M s = 0

Argonne National Laboratory 11 Parton model Quark charge Prob. of q in proton Structure function leptonic hadronic Partonic structure of the nucleon EIC whitepaper

Example: longitudinal structure functions Argonne National Laboratory 12 Parton model -> Upgraded JLab has unique capability to define the valence region All three measurements – F 2 n /F 2 p, A 1 p, A 1 n - are required to sort out the models! C. D. Roberts, RJH, S. Schmidt, PLB 727 (2013) 249 Six JLab 12 GeV experiments Thanks to R. Milner, H. Jackson, Z.-E. Meziani, X. Zheng, J. Arrington, C. Keppel

Physics of Nuclei Argonne National Laboratory 13

Motivation Test calculations of light nuclei. Study properties of all bound helium nuclei from 3 He to 8 He. 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 Argonne National Laboratory 15 J. Seeley et al, PRL 103 (2009) EMC effect is correlated with short range N-N interaction – L. Weinstein et al, PRL 106, (2011), J. Arrington et al, PRC 86 (2012) , N. Fomin et al, PRL 108, (2012) Plot credit: JLab whitepaper Flavor, isospin and spin dependence of EMC effect? Drell-Yan, MINERvA NSAC milestone HP5 (2010) Thanks to J. Arrington, B. Filippone, P. Solvignon

Nuclei as laboratories Argonne National Laboratory 16 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: (2010); B. Clasie et al, PRL99: (2007) ; L. El Fassi et al, PLB (2012) Thanks to R. Ent, D. Dutta, K. Hafidi, H. Gao, L. El Fassi

Parity Violation Argonne National Laboratory 17

Results and projections – electroweak mixing angle Argonne National Laboratory 18 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 21 st century tools have positioned us well for the next decade: –JLab 12 GeV, RHIC - Major U.S. facilities lead the world –FNAL, CERN, HI  S, 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 Argonne National Laboratory 19

My heartfelt thanks to the organizers 20 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