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Standard Model goes pear-shaped in CERN experiment The Register

Standard Model goes pear-shaped in CERN experiment The Register Physicists get a good look at pear-shaped atomic nuclei The Los Angeles Times Exotic atoms could explain why Big Bang created more matter Newstrack India.

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Standard Model goes pear-shaped in CERN experiment The Register

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  1. Standard Model goes pear-shaped in CERN experiment • The Register • Physicists get a good look at pear-shaped atomic nuclei • The Los Angeles Times • Exotic atoms could explain why Big Bang created more matter • Newstrack India The lopsided nuclei, described today (May 8) in the journal Nature, could be good candidates for researchers looking for new types of physics beyond the reigning explanation for the bits of matter that make up the universe (called the Standard Model), said study author Peter Butler, a physicist at the University of Liverpool in the United Kingdom. The findings could help scientists search for physics beyond the Standard model, said Witold Nazarewicz. An electric dipole moment would provide a way to test extension theories to the Standard Model, such as supersymmetry, which could help explain why there is more matter than antimatter in the universe. Until now, only one pear-shaped nucleus had been found experimentally: radium 226, whose shape was sketched out back in 1993. H.J. Wollersheim, H. Emling, H. Grein, R. Kulessa, R.S. Simon, C. Fleischmann, J. de Boer, E. Hauber, C. Lauterbach, C. Schandera, P.A. Butler, T. Czosnyka; Nucl. Phys. A 556, 261 (1993).

  2. The Standard Model describes four fundamental forces or interactions „If equal amounts of matter and antimatter were created at the Big Bang, everything would have been annihilated, and there would be no galaxies, stars, planets or people“ (Tim Chupp Univ. Michigan)

  3. Elementary Particles Quarks Force Carriers Leptons Gauge bosons I II III Three Generations of Matter

  4. Shape parameterization axially symmetric quadrupole axially symmetric octupole l=2 a20≠0, a2±1= a2±2= 0 l=3 a30≠0, a3±1,2,3 = 0 a20≠0, a2±1,2 = 0

  5. Y30 coupling Δℓ=3 Δj=3 Octupole collectivity (W.u.) some subshells interact via the r3Y30 operator e.g. in light actinide nuclei one has an interaction between j15/2 and g9/2neutron orbitals i13/2and f7/2proton orbitals R.H. Spear At. Data and Nucl. Data Tables 42 (1989), 55

  6. Octupole collectivity Octupole correlations enhanced at the magic numbers: 34, 56, 88, 134 Microscopically … Intruder orbitals of opposite parity and ΔJ, ΔL = 3 close to Fermi level 226Ra close to Z=88 N=134

  7. - + - + - + + - + - 226Ra 226Ra Octupole collectivity In an octupole deformed nucleus the center of mass and center of charge tend to separate, creating a non-zero electric dipole moment.

  8. β3 β3 octupole vibrational The double oscillator V V0 -a a octupole deformed Merzbacher ‘Quantum Mechanics’

  9. Coulomb excitation impact parameter scattering angle

  10. 0+ 2+ 3- counts 4+ channel number Scattered α-spectrum of 226Ra (t1/2= 1600 yr) 4He → 226Ra Eα = 16 MeV θlab = 1450 226Ra-target beam direction Si-detector q 226Ra: t1/2= 1600 yr

  11. 0+ 2+ 3- counts 4+ 4+ If channel number E2 In 2+ E2 E4 Ii 0+ Scattered α-spectrum of 226Ra 4He → 226Ra Eα = 16 MeV θlab = 1450 226Ra-target beam direction Si-detector q

  12. Ge 5 Ge8 Ge 6 Ge 7 Ge 1 PPAC ring counter 150≤ΘL≤450, 00≤φL≤3600 Ge 4 Ge 2 4 PPAC counter 530≤ΘL≤900, 00≤φL≤840 208Pb beam Ge 3 226Ra Experimental set-up 226RaBr2 (400 μg/cm2) on C-backing (50 μg/cm2) and covered by Be (40 μg/cm2)

  13. Coulomb excitation of 226Ra

  14. γ-ray spectrum of 226Ra 208Pb → 226Ra Elab = 4.7 AMeV 150 ≤ θlab ≤ 450 00 ≤ φlab ≤ 3600 counts energy [keV]

  15. γ-ray spectrum of 224Ra 224Ra → 60Ni / 120Sn Elab = 2.83 AMeV

  16. β2= 0.16 β3=-0.11 β4= 0.10 Signature of an octupole deformed nucleus π: + π: - E2 E1 Single rotational band with spin sequence: I = 0+, 1-, 2+, 3-, … excitation energy E ~ I·(I+1) competition between intraband E2 and interband E1 transitions E1 transition strength 10-2 W.u.

  17. Signature of an octupole deformed nucleus π: + π: - E2 E1 224Ra Observation of unexpectedly small E1 moments in 224Ra, R.J. Poynter, P.A. Butler et al., Phys. Lett. B232 (1989), 447

  18. Signature of an octupole deformed nucleus Energy displacement δE between the positive- and negative-parity states if they form a single rotational band W. Nazarewicz et al.; Nucl. Phys. A441 (1985) 420

  19. negative parity states positive parity states Electric transition quadrupole moments in 226Ra rigid rotor model: liquid drop: β2= 0.21 Q2(exp) = 750 fm2 Q2(theo) = 680 fm2 H.J. Wollersheim et al.; Nucl. Phys. A556 (1993) 261 W. Nazarewicz et al.; Nucl. Phys. A467 (1987) 437

  20. negative parity states positive parity states Static quadrupole moments in 226Ra rigid rotor model: rigid triaxial rotor model: H.J. Wollersheim et al.; Nucl. Phys. A556 (1993) 261 Davydov and Filippov, Nucl. Phys. 8, 237 (1958)

  21. 0.1 β3 0 - 0.1 0.1 β3 0 - 0.1 0.16 β2 Electric transition octupole moments in 226Ra liquid drop: β3 0.18 0.12 0.06 H.J. Wollersheim et al.; Nucl. Phys. A556 (1993) 261 W. Nazarewicz et al.; Nucl. Phys. A467 (1987) 437

  22. Electric transition octupole moments in 224Ra

  23. Intrinsic electric dipole moments in 226Ra liquid-drop contribution: rigid rotor model: H.J. Wollersheim et al.; Nucl. Phys. A556 (1993) 261 G. Leander et al.; Nucl. Phys. A453 (1986) 58

  24. Intrinsic electric dipole moments in 226Ra liquid-drop contribution: G. Leander et al.; Nucl. Phys. A453 (1986) 58

  25. forbidden – density change! forbidden – CM moves! time Collective parameters In general, λ=0 λ=1 OK... λ=2 λ=3

  26. Center of mass conservation The coordinates (x, y, z) can be expressed by The dipole coordinate is not an independent quantity. It is non-zero for nuclear shapes with both quadrupole and octupole degrees of freedom.

  27. Intrinsic electric dipole moment The local volume polarization of electric charge can be derived from the requirement of a minimum in the energy functional. (Myers Ann. of Phys. (1971)) where ρp and ρn are the proton and neutron densities, CLD is the volume symmetry energy coefficient of the liquid drop model and VC is the Coulomb potential generated by ρp inside the nucleus (r < R0) Keeping the center of gravity fixed, the integral

  28. Intrinsic electric dipole moment

  29. Intrinsic electric dipole moment CLD≈ 20 MeV

  30. Summary • single rotational band for • no backbending observed • β2, β3, β4 deformation parameters are in excellent agreement with calculated values • octupole deformation is three times larger than in octupole- vibrational nuclei • equal transition quadrupole moments for positive- and negative- parity states • static quadrupole moments are in excellent agreement with an axially symmetric shape • electric dipole moments are close to liquid-drop value ( ) • octupole deformation seems to be stabilized with increasing rotational frequency

  31. Coulomb excitation of 226Ra 226Ra target broken after 8 hours Christoph Fleischmann

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