NN2012 Slide 1 Exploring the neutron dripline two neutrons at a time: Observations of 26 O and 16 Be...
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Transcript of NN2012 Slide 1 Exploring the neutron dripline two neutrons at a time: Observations of 26 O and 16 Be...
NN2012 Slide 1
Exploring the neutron dripline two neutrons at a time:Observations of 26O and 16Be ground state resonances
Zach Kohley for the MoNA Collaboration
National Superconducting Cyclotron LaboratoryMichigan State University, E. Lansing, MI
International Conference on Nucleus-Nucleus CollisionsMay 31, 2012
26O
16Be
NN2012 Slide 2
Outline
• Motivation
• Experiments / Analysis
• 26O Results
• 16Be Results
• Summary
• Acknowledgements
26O
16Be
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=1624O
30Si
Decay mechanismsand
3-body correlations
http://www.cenbg.in2p3.fr/desir/Beta-delayed-charged-particle
Sequential
3-body
dineutron(proton)
NN2012 Slide 4
Experiment
82 MeV/u 27F
Be production target
Producing 26O and 16Befrom 1-proton knockout rxns:
140 MeV/u 48Ca120 MeV/u 22Ne
82 MeV/u 27F53 MeV/u 17B
A1900 fragmentseparator
Coupled Cyclotrons
NN2012 Slide 5
Experiment
RIBs from A1900
27F(-p) 26O 24O + n + n17B(-p) 16Be 14Be + n + n
4 Tm Sweeper
Modular Neutron Array(MoNA)
NN2012 Slide 6
Experiment
Invariant mass spectroscopy:
3-body: 1st and 2nd hit in MoNA
Edecay = M24O+n+n – M24O – M2n
Neutron 4-vectors
Fragment 4-vector
NN2012 Slide 7
Experiment
n1,hit1
n1,hit2
2n-condition
• R1,2 > 50 cm
• v1,2 > vbeam
100 cm 100 cm 80 cm
Need to remove false 2n hits from true 2n hits
n2,hit1
v1,2 = R1,2 / (t2 – t1)
Effic. with cuts: 10-20% 90-95% true 2n
NN2012 Slide 8
26O
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: 24O16 neutrons bound
Z=9 dripline > 31F> 22 neutrons bound
26O
NN2012 Slide 10
Motivation
Experiments show 26O to be unbound:
Tarasov et al. PLB. 409, 64 (1997).
slimit = 0.7 pb
Schiller et al. PRC. 72, 037601 (2005).
slimit = 3.0 mb
D. Guillemaud-Mueller et al. PRC. 41, 937 (1990).
slimit = 7 pb
NN2012 Slide 11
Motivation
Predictions for 26O: Bound or Unbound?
S2n = M26O – M24O – 2Mn
S2n > 0 unbound
S2n < 0 bound
NN2012 Slide 12
Motivation
Otsuka et al. PRL. 105, 032501 (2010).
Predictions for 26O: Bound or Unbound?
NN2012 Slide 13
Experiment
Previous MoNA Experiment:Hoffman et al. PRL 2008Measured g.s. of 25O @ 770 keV
Current work:Presence of low-energy neutrons
Dashed-lines CSM predictionsVolya & Zelevinsky PRL 2005
NN2012 Slide 15
Results and Discussion
c2 minimization 26O(g.s.) resonance
Edecay = 150+50-150 keV
G = 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
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
26O unbound by < 200 keV
NN2012 Slide 19
Outlook
Grigorenko et al. PRC 84, 021303(R) (2011)
NN2012 Slide 20
16Be
NN2012 Slide 21
Motivation
A. Spyrou, J.K. Smith et al, Phys Rev C84(2011)044309
NuShell, WBP interaction
16Be predicted to be: - unbound with respect to 2n decay - bound with respect to 1n decay
Scenario for “true” 2n emission
NN2012 Slide 22
Motivation
n1
n2
16Be
15Be+n
14Be+2n
n1n2
16Be14Be+2n
NN2012 Slide 23
Motivation - Dineutron
Halo neutrons on the same side of 6He
P. Mueller, PRL 99, 252501 (2007)
Nakamura, PRL 96, 252502 (2006)
Strong low-lying dipole strength 11Li indicating strong nn correlation.
n-n correlations from 11Li 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 in11Li wavefunction
NN2012 Slide 24
Results: Decay Energy
Sequential
14Be+n1+n214Be+n1
14Be+n2
A. Spyrou, Z. Kohley et al, Phys Rev Lett. 108(2012)102501
NN2012 Slide 25
Results: Decay Energy
Sequential
14Be+n1+n214Be+n1
14Be+n2
A. Spyrou, Z. Kohley et al, Phys Rev Lett. 108(2012)102501
NN2012 Slide 26
Results: Correlations
E(n1+n2) θ(n1+n2) θ(14Be+n1)
Sequential
A. Spyrou, Z. Kohley et al, Phys Rev Lett. 108(2012)102501
NN2012 Slide 27
Summary
Observation of 26O ground state, which is unbound by < 200 keV.
S2n = M26O – M24O – 2Mn
S2n > 0 unbound
S2n < 0 bound
16Be ground state at 1.35 MeV,showed strong dineutron signatures
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
Augustana College, ILCentral Michigan University, MIConcordia College, MNFlorida State University, FLGettysburg College, PAHope College, MIIndiana University at South Bend, INMarquette University, WIMichigan State University, MIOhio Wesleyan University, OHRhodes College, TNWabash College, INWestern Michigan University, MIWestmont College, CA
MRI-Consortium: Development of a Neutron Detector Array by Undergraduate Research Students for Studies of Exotic Nuclei.
NN2012 Slide 29
Acknowledgments
Thomas BaumannDaniel BazinGreg ChristianShea MosbyMichelle MosbyJenna SmithJesse SnyderArtemis SpyrouMichael StrongmanMichael Thoennessen
TheoryAlex BrownJeff TostevinAlexander Volya
Hope College: E. Lunderberg P. A. DeYoung
NN2012 Slide 31
Acknowledgments
NN2012 Slide 32
Backup
NN2012 Slide 33
Hagen et al. arXiv:1202.2839v1 [nucl-th] (2012)Accepted to PRL.
NN2012 Slide 34
NN2012 Slide 35
27F and 26O
p n
27F
p n
26O
-p
NN2012 Slide 36
Backup