1. NN2012 Slide 1 Exploring the neutron dripline two neutrons at a time: Observations of 26 O and 16 Be ground state resonances Zach Kohley for the MoNA Collaboration National Superconducting Cyclotron Laboratory Michigan State University, E. Lansing, MI International Conference on Nucleus-Nucleus Collisions May 31, 2012 26 O 16 Be

2. NN2012 Slide 2 Outline Motivation Experiments / Analysis 26 O Results 16 Be Results Summary Acknowledgements 26 O 16 Be

3. NN2012 Slide 3 Motivation Explore nuclear structure at extreme neutron-to-proton ratios. (Evolution of Shell Model) Otsuka et al. PRL. 87, 082502 (2001). N=16 24 O 30 Si Decay mechanisms and 3-body correlations http://www.cenbg.in2p3.fr/desir/Beta-delayed-charged-particle Sequential 3-body dineutron(proton)

4. NN2012 Slide 4 Experiment 82 MeV/u 27 F Be production target Producing 26 O and 16 Be from 1-proton knockout rxns: 140 MeV/u 48 Ca 120 MeV/u 22 Ne 82 MeV/u 27 F 53 MeV/u 17 B A1900 fragment separator Coupled Cyclotrons

5. NN2012 Slide 5 Experiment RIBs from A1900 27 F(-p)  26 O  24 O + n + n 17 B(-p)  16 Be  14 Be + n + n 4 Tm Sweeper Modular Neutron Array (MoNA)

6. NN2012 Slide 6 Experiment Invariant mass spectroscopy: 3-body: 1 st and 2 nd hit in MoNA E decay = M 24O+n+n – M 24O – M 2n

7. NN2012 Slide 7 Experiment n1,hit1 n1,hit2 2n-condition R 1,2 > 50 cm v 1,2 > v beam 2n-condition R 1,2 > 50 cm v 1,2 > v beam 100 cm 80 cm Need to remove false 2n hits from true 2n hits n2,hit1 v 1,2 = R 1,2 / (t 2 – t 1 ) Effic. with cuts: 10-20%  90-95% true 2n

8. NN2012 Slide 8 26 O

9. NN2012 Slide 9 Motivation Baumann et al. Rep. Prog. Phys. 75, 036301 (2012). Understanding drastic change in neutron dripline between Z=8 and Z=9 Z=8 dripline: 24 O 16 neutrons bound Z=9 dripline > 31 F > 22 neutrons bound 26 O

10. NN2012 Slide 10 Motivation Experiments show 26 O to be unbound: Tarasov et al. PLB. 409, 64 (1997).  limit = 0.7 pb Schiller et al. PRC. 72, 037601 (2005).  limit = 3.0 mb D. Guillemaud-Mueller et al. PRC. 41, 937 (1990).  limit = 7 pb

11. NN2012 Slide 11 Motivation Predictions for 26 O: Bound or Unbound? S 2n = M 26O – M 24O – 2M n S 2n > 0 unbound S 2n < 0 bound

12. NN2012 Slide 12 Motivation Otsuka et al. PRL. 105, 032501 (2010). Predictions for 26 O: Bound or Unbound?

13. NN2012 Slide 13 Experiment Previous MoNA Experiment: Hoffman et al. PRL 2008 Measured g.s. of 25 O @ 770 keV Current work: Presence of low-energy neutrons Dashed-lines CSM predictions Volya & Zelevinsky PRL 2005

14. NN2012 Slide 14 Simulation Decay Mechanisms: Direct population of 26 O(g.s.)  24 O + n + n BW + 3-body phase-space decay[2] Indirect population of 25 O g.s. through 1 st excited state of 26 O. Sequential Decay: 26 O(2 MeV)  25 O(770 keV) + n  24 O + n + n Direct population of 25 O(g.s.)  24 O + n BW: E r = 770 keV [1] B. Roeder EURISOL Design Study, Report: [10-25-2008-006-In-beamvalidations.pdf, pp 31-44] (2008). [2] F. James, CERN Yellow Report 68-15 (1968); ROOT - TGenPhaseSpace class Monte Carlo Simulation includes: Reaction and decay mechanisms Geometrical acceptances Energy/positions/timing resolutions Transport of charged particles through magnet Geant4 + MENATE_R[1] simulation for neutron interactions in MoNA

15. NN2012 Slide 15 Results and Discussion   minimization 26 O(g.s.) resonance E decay = 150 +50 -150 keV  = insensitive (5 keV shown) 2-body 3-body Fit experiment with 3 decay channels, using Monte Carlo simulation (with Geant4). Lunderberg, DeYoung, Kohley, et al, PRL.108(2012)102501

16. NN2012 Slide 16 Results and Discussion - Cross Talk: 1 neutron can interact twice within MoNA producing a false 2n signal. - Multiple neutron interactions included in simulation.

17. NN2012 Slide 17 Results and Discussion Confirm 3-body signal through removal of false 2n events. Lunderberg, DeYoung, Kohley, et al, PRL.108(2012)102501 26 O unbound by < 200 keV

18. NN2012 Slide 18 Results and Discussion Confirm 3-body signal through removal of false 2n events. Causality cut: D 12 > 25 cm & V 12 > 7 cm/ns Applied to both exp. and sim. Efficiency decreases by ~50% Cross-talk reduced by factor of 3. 26 O unbound by < 200 keV Lunderberg, DeYoung, Kohley, et al, PRL.108(2012)102501

19. NN2012 Slide 19 Outlook Grigorenko et al. PRC 84, 021303(R) (2011)

20. NN2012 Slide 20 16 Be

21. NN2012 Slide 21 Motivation A. Spyrou, J.K. Smith et al, Phys Rev C84(2011)044309 NuShell, WBP interaction 16 Be predicted to be: - unbound with respect to 2n decay - bound with respect to 1n decay Scenario for “true” 2n emission

22. NN2012 Slide 22 Motivation n1n1 n2n2 16 Be 15 Be+n 14 Be+2n n1n1 n2n2 16 Be 14 Be+2n

23. NN2012 Slide 23 Motivation - Dineutron Ieki et al., PRC54(1996)1589 Zinser et al., NPA619(1997)151 Halo neutrons on the same side of 6 He P. Mueller, PRL 99, 252501 (2007) Nakamura, PRL 96, 252502 (2006) Strong low-lying dipole strength 11 Li indicating strong nn correlation. n-n correlations from 11 Li decay are reproduced by 3-body phase space decay Ieki et al., PRC54(1996)1589 Zinser et al., NPA619(1997)151 Theory Hagino et al., PRL 99(2007)022506 Strong dineutron component in 11 Li wavefunction

24. NN2012 Slide 24 Results: Decay Energy Sequential 14 Be+n 1 +n 2 14 Be+n 1 14 Be+n 2 A. Spyrou, Z. Kohley et al, Phys Rev Lett. 108(2012)102501

25. NN2012 Slide 25 Results: Decay Energy Sequential 14 Be+n 1 +n 2 14 Be+n 1 14 Be+n 2 A. Spyrou, Z. Kohley et al, Phys Rev Lett. 108(2012)102501

26. NN2012 Slide 26 Results: Correlations E(n 1 +n 2 ) θ(n 1 +n 2 )θ( 14 Be+n 1 ) Sequential A. Spyrou, Z. Kohley et al, Phys Rev Lett. 108(2012)102501

27. NN2012 Slide 27 Summary Observation of 26 O ground state, which is unbound by < 200 keV. S 2n = M 26O – M 24O – 2M n S 2n > 0 unbound S 2n < 0 bound 16 Be ground state at 1.35 MeV, showed strong dineutron signatures

28. NN2012 Slide 28 MoNA-LISA LISA detectors were built and tested at 10 undergraduate institutions LISA installed successfully at NSCL in Spring 2011 Commissioning experiment in June 2011 was successful. New experiment coming up summer 2012 LISA detectors were built and tested at 10 undergraduate institutions LISA installed successfully at NSCL in Spring 2011 Commissioning experiment in June 2011 was successful. New experiment coming up summer 2012 Augustana College, IL Central Michigan University, MI Concordia College, MN Florida State University, FL Gettysburg College, PA Hope College, MI Indiana University at South Bend, IN Marquette University, WI Michigan State University, MI Ohio Wesleyan University, OH Rhodes College, TN Wabash College, IN Western Michigan University, MI Westmont College, CA Augustana College, IL Central Michigan University, MI Concordia College, MN Florida State University, FL Gettysburg College, PA Hope College, MI Indiana University at South Bend, IN Marquette University, WI Michigan State University, MI Ohio Wesleyan University, OH Rhodes College, TN Wabash College, IN Western Michigan University, MI Westmont College, CA MRI-Consortium: Development of a Neutron Detector Array by Undergraduate Research Students for Studies of Exotic Nuclei.

29. NN2012 Slide 29 Acknowledgments Thomas Baumann Daniel Bazin Greg Christian Shea Mosby Michelle Mosby Jenna Smith Jesse Snyder Artemis Spyrou Michael Strongman Michael Thoennessen Theory Alex Brown Jeff Tostevin Alexander Volya Hope College: E. Lunderberg P. A. DeYoung

30. NN2012 Slide 30 Side Note: Validation of Simulation Used a “clean” 1 neutron reaction to compare simulation: Compared “standard” G4 physics classes to custom MENATE_R neutron interaction code Reproduce causality cut observables Manuscript submitted to NIMA, Z. Kohley et al. (2012).

31. NN2012 Slide 31 Acknowledgments

32. NN2012 Slide 32 Backup

33. NN2012 Slide 33 Hagen et al. arXiv:1202.2839v1 [nucl-th] (2012) Accepted to PRL.

34. NN2012 Slide 34

35. NN2012 Slide 35 27 F and 26 O  27 F  26 O -p

36. NN2012 Slide 36 Backup