Direct Reactions with Exotic Nuclei Recent results and developments. Alexandre Obertelli. CEA Saclay, IRFU/SPhN

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1 Direct Reactions with Exotic Nuclei Recent results and developments Alexandre Obertelli CEA Saclay, IRFU/SPhN

2 Outline 1) Current treatment of direct reactions and associated limits 2) One nucleon transfer and one nucleon knockout Are structure information extracted from knockout and transfer consistent? 3) Future studies 4) The MINOS project

3 stability Neutron dripline Why are direct reactions of importance? [From T. Otsuka] Bridging cross sections and nuclear structure Spectroscopic Factors SF + μ = φ A+1 μ a + A 2 p φ 0 SF n = φ A 1 A n a p φ 2 0 p H 1 p H 1 Effective Single Particle Energies can be obtained via SFs and final-state energies e cent p = SF μ + E μ A+1 μ H A+1 + SF n n H A 1 [M. Baranger, Nucl. Phys. A149, 225 (1970)] A 1 E n [Courtesy V. Soma (2012)]

4 Structure and reactions: a delicate topic SFs are not observable modified through Unitary Transforms [R.J. Furnstal and H.W. Hammer, Phys. Lett. B 531, 203 (2002)] [T. Duguet and G. Hagen, Phys. Rev. C 85, (2012)] What should be done: Consistent approach of reaction and structure (same Hamiltonian) Clearly assess which theoretical framework is used (which Hamiltonian) [P. Navratil and S. Quaglioni, Phys. Rev. Lett. 108, (2012)] [Th. Neff, Phys. Rev. Lett. 106, (2011)] What is done (i.e. what can be done today): Most often highly-truncated model space (shell model) Inconsistent treatment of structure and reaction mechanism Theoretical cross section to populate a final state m σ μ theo = φ μ A 1 a p φ 0 A 2 σ p p H<H 1 structure theory reaction theory

5 Knockout and transfer: dedicated to shell structure studies 700 MeV/u [C. Rodriguez-Tajes et al., Phys.Rev. C 82, (2010)] [A. Navin et al., Phys. Rev. Lett. 85, 266 (2000)] [L. Gaudefroy et al., Phys.Rev. Lett. 97, (2006)]

6 Nucleon removal from exotic nuclei ΔS = S n S p (MeV) Intermediate-energy knockout Disagreement between theory and experiment ΔS = S n S p (MeV) Low-energy (p,d) transfer Constant reduction ~30% Data for DS up to 12 MeV

7 Nucleon removal from exotic nuclei Reanalysis of 34,36,46 Ar at 33 MeV/nucleon F.M Nunes et al., Phys. Rev. C 83, (2011). 46 Ar(p,d)

8 One nucleon transfer from 14 O at 18 MeV/nucleon 14 O pure beam, 18 MeV/nucleon, pps, SPIRAL (GANIL) Beam Tracking Detectors F. Flavigny Target: CD 2 Reactions: (d,d), (d, 3 H) and (d, 3 He) MUST2 array MUST2 10x10 cm μm DSSSD + SiLi or CsI VAMOS spectrometer in dispersive mode Fully exclusive measurements

9 Elastic scattering 14 O + 2 H and transfer 14 O(d, 3 H) 13 O 13 O + 3 H λ V = 1.1, λ W = O + 2 H 13 N + 3 He 6020 =1.2MeV /2-1/ Sp = 1516 kev Δl = 1 Expt. (3/2-) 13 O SP-SM 3/2-

10 14 O(d, 3 He) 13 N

11 Prescription for overlap functions Woods-Saxon single-particle wave function V 0, r 0 : parameters fixed to reproduce RMS of a given Skyrme prediction and Sep. Energy a = 0.65 fm DS/S= 6 Drms/rms

12 Results δ (RMS) δ r o box Error bars due to exp. uncertainties 48 analysis: 2 sets of SF th: - WBT Interaction 0p shell + 2ħΩ - Utsuno int. 0p1s0d space 3 HF calculations for radii 8 combinations of optical potentials for entrance and exit channels R s = a DS + b c 2 a = (24)(12) MeV -1 [F. Flavigny et al., submitted for publication (2012)]

13 Ab initio form factors FF from C. Barbieri, A. Cippolone R s = a DS + b a = (28)(36) MeV -1 b = 0.636(34)(42) [F. Flavigny et al., submitted for publication (2012)]

14 Spec. Factor Ab initio calculations [O. Jensen et al., Phys. Rev. Lett (2011)] ΔS = S n S p (MeV) [C. Barbieri, W.H. Dickhoff, Int. Jour. Mod. Phys. A 24, 2060 (2009)] a MeV -1 a MeV -1

15 Other type of calculation from Surrey [N.K. Timofeyuk, Phys. Rev. Lett. 103, (2009)] Oxygen isotopes a MeV -1

16 Stripping cross sections at intermediate energies Projectile energy large enough to consider that the intrinsic degrees of freedom are frozen Probability to leave the core intact Probability to remove the nucleon A A-1 NN cross section Core density No explicit treatment of core excitations

17 Questioning the «inert core» approximation Intranuclear Cascade Model (INC) (with nuclear-structure input) evaporation excited core A A-1 A-2,A-3 Reduction of the -1 nucleon removal cross section Importance of core excitations for loosely-bound cores and deeply-bound nucleons? [C. Louchart et al., Phys. Rev. C 83, (R) (2011)]

18 More transfer data: accepted experiments at GANIL 18 Ne(d,t) & (d, 3 He) at 20 MeV/nucleon 24 Si(p,d) 23 Si & (p,t) 22 Si at 35 MeV/nucleon Foreseen in Ne(d, 3 He) 17 F 18 Ne(d,t) 17 Ne 24 Si(p,d) 23 Si

19 Relativistic energies R3B campaign at GSI in 2010: neutron AND proton knockout from oxygen O isotopes at 700 MeV/nucleon Hydrogen and carbon targets Polarized target knockout at RIBF/RIKEN in 2012: 14,22,24 O(p,2p) at about 200 MeV/nucleon Foreseen proposal at GSI with AGATA (2013): neutron AND proton knockout from nickel Ni isotopes at 200 MeV/nucleon Ni isotopes Simulation

20 Towards the most exotic nuclei New picture of Shell Closures away from stability Some nuclei of interest produced at less than 1 pps 110 Zr 78 Ni 54,60 Ca 28 O 40 Mg

21 In-beam gamma spectroscopy coupled to knockout reactions Velocity spread b magic b target In flight: velocity b needed for Doppler correction b not measured today not magic 28 [B. Bastin et al., Phys. Rev. Lett. 99, (2007)] Target thickness: balance between statistics and resolution limiting factor

22 In-flight g spectroscopy with MINOS Specificities: thick target higher luminosity TPC reconstruction of q and b dx<3 mm FWHM e>85%

23 In-flight g spectroscopy with MINOS and DALI2 GAIN IN LUMINOSITY: factor 5 wrt Be target Eg=1 MeV, 53 K (220 MeV/u) + X 52 Ar + p + X s=2 mb 1 week of BT and 0.5 pps -- 1 cm Be cm LH cm LH2+ aatracking thickness (at/cm²) LH 2 (150 mm) 6.41*10 23 Be (10 mm) 1.23*10 23 GAIN IN RESOLUTION: from 250 kev to 100 kev (FWHM) with a 20-cm LH 2 target angle q total intrinsic velocity b

24 Long term: MINOS + AGATA Example: MINOS+AGATA 1/3: gain >20 1 pps, 300 MeV/u, 1 week beam time total velocity b intrinsic angle q

25 MINOS status and Agenda Simulations R&D, conception In-beam validation Experiments RIKEN

26 Summary One-nucleon stripping and pickup necessary to address ESPEs Today, inconsistent treatment of structure and reactions theoretical uncertainties Discrepancy between knockout (<100 MeV/u) and transfer for exotic nuclei Indirect processes may impact significantly the nucleon removal cross section Several new experiments to be performed or proposed New developments dedicated to the spectroscopy of very exotic nuclei: DALI2+SAMURAI+MINOS at RIKEN

27 Thank you! N. Alamanos, L. Audirac, A. Corsi, F. Flavigny, S. Boissinot, C. Louchart, A. Gillibert, V. Lapoux, L. Nalpas, E.C. Pollacco, A. Signoracci, CEA SPhN D. Beaumel, S. Giron, J. Guillot, F. Hammache, A. Matta, N. de Séreville, IPN Orsay G. Burgunder, G. Grinyer, R. Raabe, M. Rejmund, A. Shrivastava, GANIL Caen J. Gibelin, LPC Caen N. Keeley, NCNR Warsaw C. Barbieri, A. Cippolone, N. Timofeyuk, Surrey