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LIVING WITH TRANSFER AS AN EXPERIMENTAL SPECTROSCOPIST

LIVING WITH TRANSFER AS AN EXPERIMENTAL SPECTROSCOPIST. WILTON CATFORD. TRENTO WORKSHOP 4-8 Nov 13 FROM NUCLEAR STRUCTURE TO PARTICLE-TRANSFER REACTIONS AND BACK. NIGEL WILTON. FRIENDS, …. LET’S TALK FRANKLY

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LIVING WITH TRANSFER AS AN EXPERIMENTAL SPECTROSCOPIST

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  1. LIVING WITH TRANSFERAS AN EXPERIMENTAL SPECTROSCOPIST WILTON CATFORD TRENTO WORKSHOP 4-8 Nov 13 FROM NUCLEAR STRUCTURE TO PARTICLE-TRANSFER REACTIONS AND BACK

  2. NIGEL WILTON FRIENDS, …. LET’S TALK FRANKLY …. here is (almost) everything that confuses me and which I think is challenging in the interpretation of transfer reaction data

  3. 1p3/2 1p3/2 1p3/2 1p3/2 Exotic Exotic Stable Stable Utsuno et al., PRC,60,054315(1999) Monte-Carlo Shell Model (SDPF-M) Exotic Stable N=20 N=20 Note: This changes collectivity, also… Removing d5/2 protons (Si O) gives relative rise in n(d3/2)

  4. 1s 1/2 0d 5/2 A. SINGLE PARTICLE STATES – EXAMPLE Example of population of single particle state: 21O 0d 3/2 energy of level measures this gap 1s 1/2 Jp = 3/2+ 0d 5/2 The mean field has orbitals, many of which are filled. We probe the energies of the orbitals by transferring a nucleon This nucleon enters a vacant orbital In principle, we know the orbital wavefunction and the reaction theory But not all nuclear excited states are single particle states… x 1/2+ Jp = 3/2+ 2+ We measure how the two 3/2+ states share the SP strength when they mix

  5. SINGLE PARTICLE STATES – SPLITTING If we want to measure the SPE, splitting due to level mixing means that all components must be found, to measure the true single particle energy Plot: John Schiffer

  6. Things to consider in measurements of the single-particle strength for a state • can use single-nucleon transfer and “standard” spectroscopic factor method • can use alternative ANC method that avoids some ambiguities in parameters • can combine the two, to avoid model dependence (TexasA&M, MSU, Surrey) • use high energy removal reactions (e.g. J.A. Tostevin approach) for hole states • Also need to consider • quenching of pure shell model spectroscopic factors for strongly bound nucleons • effect of using realistic wavefunctions for transferred nucleon, or “standard well” • breakup of deuteron (treat with R.C. Johnson approach, “Johnson-Soper” ADWA) • And what do we really compare with? • Clearly, the Large Basis Shell Model, but how exactly? • Using a standard parameter set and ADWA, compare (unquenched) SM values • Using realistic wavefunctions and ADWA, compare quenched values (cf knockout) But, in the presence of all these interesting issues, remember…

  7. Ultimately, with single particle transfer reactions, we can certainly: • make the measurements to highlight strong SP states • measure the spin/parity for strong states • associate experimental and Shell Model states and see • when the shell model works (energies and spectroscopic factors) • when the shell model breaks down • whether we can adjust the interaction and fix the calculation • how any such modifications can be interpreted in terms of NN interaction • And clearly: • monopole shifts need to be measured and understood because the changes • In energy gaps fundamentally affect nuclear structure (collectivity, etc.)

  8. A PLAN for how to STUDY STRUCTURE • Use transfer reactions to identify strong single-particle states, • measuring their spins and strengths • Use the energies of these states to compare with theory • Refine the theory • Improve the extrapolation to very exotic nuclei • Hence learn the structure of very exotic nuclei • N.B. The shell model is arguably the best theoretical approach • for us to confront with our results, but it’s not the only one. • The experiments are needed, no matter which theory we use. • N.B. Transfer (as opposed to knockout) allows us to study orbitals • that are empty, so we don’t need quite such exotic beams.

  9. USING RADIOACTIVE BEAMS in INVERSE KINEMATICS Single nucleon transfer will preferentially populate the states in the real exotic nucleus that have a dominant single particle character. Angular distributions allow angular momenta and (with gammas) spins to be measured. Also, spectroscopic factors to compare with theory. Around 10A MeV/A is a useful energy as the shapes are very distinctive for angular momentum and the theory is tractable. Calculated differential cross sections show that 10 MeV/A is good (best?)

  10. W.N. Catford et al., PRL 104, 192501 (2010) Negative parity states (cross shell) also identified ( = 3) 4030 0.73 7/2 – p = – 3330 0.75 3/2 –  = 1 In 25Ne we used gamma-gamma coincidences to distinguish spins and go beyond orbital AM FIRST QUADRUPLE COINCIDENCE (p-HI-g-g ) RIB TRANSFER DATA Inversion of 3/2+ and 5/2+ due to monopole migration Summary of 25Ne Measurements 5/2+ 7/2+ 9/2+ 0.004 5/2+ 0.11 3/2+  = 2 0.44 2030 3/2+ 5/2+ 0.10 1680 0.15 5/2+  = 2 3/2+ 0.49  = 0 1/2+ 0.80 1/2+ 0.63 n+24Negs USD

  11. N=17 ISOTONES 1.80 7/2 0.76 3/2 27Ne17 4.03 ISOTOPE CHAINS 3.33 1.80 0.76 27Ne 25Ne Mg Ne d3/2 level is 2.030 25Ne

  12. 27Ne results • we have been able to • reproduce the observed • energies with a modified • WBP interaction, full 1hw • SM calculation • the SFs agree well also • most importantly, the new • interaction works well • for 29Mg, 25Ne also • so we need to understand • why an ad hoc lowering • of the fp-shell by 0.7 MeV • is required by the data!

  13. More on N=15 Odd d5/2 proton 25Ne states Probe p-n interaction across N=20 25Na (d,p) 26Na

  14. 26Na had been studied a little, beforehand (N=15, quite neutron rich) negative parity ALL of the states seen in (d,p) are NEW (except the lowest quadruplet) We can FIND the states with simple structure, Measure their excitation energies, and feed this back into the shell model CX FUSION-EVAP positive parity

  15. Spectroscopic Factor Shell Model: overlap of  (N+1)  with  (N) core  n ( j) Reaction: the observed yield is not just proportional to this, because the overlap integral has a radial-dependent weighting or sampling REACTION MODEL FOR (d,p) TRANSFER – the ADWA • Johnson-Soper Model: an alternative to DWBA that gives a simple prescription for taking into account coherent entangledeffects of deuteron break-up on (d,p) reactions [1,2] • does not use deuteron optical potential – uses nucleon-nucleus optical potentials only • formulated in terms of adiabatic approximation, which is sufficient but not necessary [3] • uses parameters (overlap functions, spectroscopic factors, ANC’s) just as in DWBA • [1] Johnson and Soper, PRC 1 (1970) 976 • [2] Harvey and Johnson, PRC 3 (1971) 636; Wales and Johnson, NPA 274 (1976) 168 • [3] Johnson and Tandy NPA 235 (1974) 56; Laid, Tostevin and Johnson, PRC 48 (1993) 1307 WILTON CATFORD JUNE 2008

  16. Spectroscopic Factor Shell Model: overlap of  (N+1)  with  (N) core  n ( j) Reaction: the observed yield is not just proportional to this, because the overlap integral has a radial-dependent weighting or sampling overlap integral Hence the observed yield depends on the radial wave function and thus it depends on the geometry of the assumed potential well or other structure model spectroscopic factor REACTION MODEL FOR (d,p) TRANSFER – the ADWA WILTON CATFORD JUNE 2008 Actual wave function: orbital n ( j) in (N+1)  may not be the same as the shell model n ( j) as implicitly assumed in SM spectroscopic factor

  17. Peripheral: forward angles, lower energies Eb defines the wavefunction asymptotics Independence of the ANC on geometry Geometry REMARKS ABOUT INTERPRETING (d,p) TRANSFER Geometry Correlations Desire Relatives Dependence of high energy (d,p) on geometry surface region V(r) u(r) Is the effective well geometry even the same for all orbitals? (coupled channels treatments address this)

  18. Must use SM SF’s (not quenched) WEIGHTED ExS.P. energies WEIGHTED ExS.P. energies (traditional approach) If the quenched SF’s are used REMARKS ABOUT INTERPRETING (d,p) TRANSFER Geometry Correlations Desire Relatives States built in SM space J states are mixed by residual interactions … and are not pure SP states J mixing via SHORT RANGE correlations J MY ANSWER: • Don’t use “traditional” method of calculating weighted SPE • Do use the “traditional” SF that can be compared to SM • Use SM SF to associate experimental and SM states • Use this to refine SM residual interaction • Gain improved understanding of important structural effects

  19. WHAT DO WE WANT TO MEASURE? Occupancy of SM geometry orbital (cf e.g. Oxbash output) Occupancy of actual nuclear orbital Is it the occupancy of some defined orbital that may not equal the actual orbital in the real nucleus? Do we want to measure the “quenched” (= “real”) or the “shell model” (= “comparable”) SF ? REMARKS ABOUT INTERPRETING (d,p) TRANSFER Geometry Correlations Desire Relatives THE SPECTROSCOPIC FACTOR HAS TWO (at least!) PROBLEMS: MY ANSWER: • Both “quenched” and “SM comparable” are interesting • They tell us about different things • We need to be clear, always, which we think we are discussing • There is still this problem that (SM orbital)  (actual orbital) • e.g. halo state

  20. If so, is this good enough? Possible to live with? If not, um… really? Can we really believe the quenching measured with transfer SF’s ? As much as for knockout? If not, what about astrophysics ? REMARKS ABOUT INTERPRETING (d,p) TRANSFER Geometry Correlations Desire Relatives ARE RELATIVE SF’s MORE ACCURATE THAN ABSOLUTE? … ALWAYS?

  21. Formalism used in present work

  22. M.B. Tsang and J. Lee et al., PRL 95, 222501 (2005) SFEXP=SFSM No short term NN correlations and other correlations included in SM. Why the agreement? Predictions of cross-sections Test of SM interactions Extraction of structure information Ground state USDA/USDB Excited states GXPF1A Excited states

  23. BOUND STATES:d(20O,t)19O (pick-up)‏ Full strengthfor0d5/2and1s1/2measured ! Jπ= 5/2+ C2S=4.76(94) 1s1/2 =2.04(39) 0d5/2 =6.80(100) A. Ramus PhD. Thesis Universite Paris XI Sum Rules: M. Baranger et al., NPA 149, 225 (1970) Jπ= 1/2+ C2S=0.50(11) v1s1/2 partially occupied in 20O : correlations

  24. Updates on the different trends from transfer and knockout Slide credit: Jenny Lee

  25. Preliminary results for 26Ne(d,t)25Ne and also (p,d) JEFFRY THOMAS, SURREY 26Ne(d,t)25Ne 26Ne(p,d)25Ne g.s. 1/2+ g.s. 1/2+ 26Ne(d,t)25Ne GAMMA ENERGY PRELIMINARY Second excited 5/2+ 1600 keV 1.703 5/2+ 1.703 5/2+ First 5/2+ 1701 keV 3.300 5/2+ INDIVIDUAL DECAY SPECTRA OF EXCITED 5/2+ STATES

  26. A PLAN for how to STUDY STRUCTURE • Use transfer reactions to identify strong single-particle states, • measuring their spins and strengths • Use the energies of these states to compare with theory • Refine the theory • Improve the extrapolation to very exotic nuclei • Hence learn the structure of very exotic nuclei • N.B. The shell model is arguably the best theoretical approach • for us to confront with our results, but it’s not the only one. • The experiments are needed, no matter which theory we use. • N.B. Transfer (as opposed to knockout) allows us to study orbitals • that are empty, so we don’t need quite such exotic beams.

  27. LIVING WITH TRANSFERAS AN EXPERIMENTAL SPECTROSCOPIST WILTON CATFORD TRENTO WORKSHOP 4-8 Nov 13 FROM NUCLEAR STRUCTURE TO PARTICLE-TRANSFER REACTIONS AND BACK

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