systematic studies of neutron-proton pairing in sd-shell...
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Jenny Lee
The University of Hong Kong / RIKEN
Systematic studies of neutron-proton pairing
in sd-shell nuclei using (p,3He) and (3He,p)
transfer reactions
The University of Hong Kong
July 6-9, 2015
n p
n p
T=1
T=0
In nuclei: 4 types of Pairs
Neutron-Proton Pair Correlations
Isovector (T=1) np-pairing
Well defined from the
Isospin Symmetry
Isoscalar (T=0) np-pairing
A lot of uncertainties !!
Isoscalar (T=0, S=1) np pair (deuteron-like)
new phase of nuclear matter
Isovector (T=1, S=0) nn, pp, np pair
np should be similar to nn & pp
○ Nature of T=0 pair in nuclear medium ?
○ Mutual Strength & Interplay of T=0 and T=1 np, nn, pp pairs ?
○ Does T=0 pairing give rise to collective modes ?
Long-standing open fundamental questions:
Theoretical & experimental efforts since
60’s Contradicting opinions & results !
N=Z unique system !
Previous Observables for np-pairingExtra Binding Energy of N=Z nuclei
“Wigner Energy”
Proof of existence of T=0 pairing collectivity
using B.E. depends on interpretations
J. Dobaczewski, arXiv:nucl-th/0203063v1
T(T+1) – simple
symmetry energy
Mean-field term T2 as symmetry
energy, T as np pairing
Rotational properties (high-spin aspect):
moments of inertia, alignments
Coriolis effect T=0
T=1
Two-nucleon Transfer Reactions
Two-nucleon transfer reactions like (t,p) or (p,t)
specific tool to probe T=1 pair correlations
Similarity between pairing field and 2-body transfer operator
R.A. Broglia et al., Adv. Nucl. Phys. 6, 287 (1973)
Ground-state composed of BCS pairs, two-
nucleon transfer cross sections enhanced
S.J. Freeman et al. PRC 75 051301(R) (2007)
Spectra from (p,t) reactions
76Ge & 76,78Se(p,t) strength: predominately to
the ground states simple BCS paired states
Neutron-Proton pairing using np transfer ?
Two-nucleon Transfer Reactions
Interacting Boson Model (IBM-4)
Reactions
(p, 3He), (3He,p) DT=0,1
(d,a), (a,d) DT=0
(a, 6Li), (6Li,a) DT=0
T=0 (T=1) pairing:
enhanced transfer probabilities
0+ → 1+ (0+ → 0+) levels
Measure the np transfer cross section to T=1 and T=0 states
Absolute σ(T=1) and σ(T=0) – character and strength of the correlations
σ(T=1) /σ(T=0) – interplay of T=1 and T=0 pairing modes
T=0 stronger
T=1 stronger
np-Transfer Reactions using Radioactive Beams
3He(44Ti,p) @ 4.5 AMeV at ATLAS
48Cr, 72Kr – (3He,p)
•Approved experiments at ISAC2
• Plan: ReA3/NSCL using AT-TPC (LBNL)
LBNL, ANL, TRIUMF
• Proof of Principle (LBNL) – successfully completed
• Experiments at GANIL
54Fe, 56Ni -- (p,3He), (d, α) @ ~30 AMeV
Insight / physics of np-pairing ?
Methodology / framework established ?
Physics from light N=Z stable nuclei ?
• RIKEN with Degraded Beams !
D. Beaumel et al.,
A. Macchiavelli et al.,
Ratio of cross section (T=1/ T=0)
- reducing systematic effects of
absolute normalization
Shiro Yoshida, NP 33, 685 (1962)
Systematics of T=0 & T=1 np-pairing in sd-shell
Closed-shell nuclei 16O, 40Ca NOT follow single-particle estimate ?
Doubtful increase of > a factor of 10 from 24Mg to 28Si ?
No intuitive understanding – 20Ne, 24Mg follow single-particle prediction ?
Inconsistencies in the trends (sd-shell):
N=Z nuclei in sd-shell
(3He,p)
from A. Macchiavelli (LBNL)
Previous Measurements
J=0+ J=1+
No FA, arbitrary unit
PRC23, 1305 (1981)
NPA407, 45(1983)
No FA, not consistent with
another measurement No FA
NPA265, 220 (1976)
NPA198, 11 (1972)
No FA, insufficient
data quality
• Measurements in different
experimental conditions, different
groups, over 15 years !
○ Consistency Systematics
• One measurement for each
reaction No consistency check
Need measurements dedicated to np-pairing studies !
○ Absolute & good quality (dσ/dΩ)
Microscopic studies
• L=0 transfer dominant at forward
angles (FA)
○ FA Meaningful & Clear
Qualitative Comparisons
np-transfer:
0+ 0+ (S=0, T=1): L=0
0+ 1+ (S=1, T=0): L=0, 2
Goals: Insight & quantitative knowledge of T=0 and T=1 np-pairing mechanism
Systematic measurements spanning sd-shell
nuclei under SAME condition
Consistent absolute (dσ/dΩ) + forward
angle data Reliable systematics
– Interplay of T=0 and T=1 np pairing
– Individual T=0 & T=1 collectivity
Joint analysis (3He,p) & (p,3He)
complete understanding – addition &
removal transfer reactions for np-pairing
Systematic framework -- studies of np pairing in heavier N=Z nuclei (RI Beams)
24Mg(3He,p), 32S(3He,p) @ 25 MeV
24Mg(p,3He), 28Si(p,3He) & 40Ca(p,3He) @ 65 MeV
Five reactions performed:
Angular distribution with 2nd peak
– quantitative understanding compared to
calculations
RCNPRCNP Cyclotron Facility
大阪大学・核物理研究中心
Osaka UniversityResearch Center
for Nuclear Physics
Grand Raiden
Spectrometer
RCNPRCNP Cyclotron Facility
大阪大学・核物理研究中心
Osaka UniversityResearch Center
for Nuclear Physics
WS course for
beam analysis
Grand Raiden
Spectrometer
RCNPRCNP Cyclotron Facility
大阪大学・核物理研究中心
Osaka UniversityResearch Center
for Nuclear Physics
WS course for
beam analysisLarge Acceptance
Spectrometer
Grand Raiden
Spectrometer
RCNP Cyclotron Facility
大阪大学・核物理研究中心
Osaka UniversityResearch Center
for Nuclear Physics
WS course for
beam analysis
WS course for
beam analysis
Large Acceptance
Spectrometer
Grand Raiden Spectrometer Large Acceptance
Spectrometer
Two MWDCs -- position
One plastic scintillator
-- E, TOF for PID
65 MeV proton / 25 MeV 3He beams from
injector AVF cyclotron (bypass Ring-Cyclotron)
Plastic
scintillators(front of FP)
Grand Raiden
3He beam at 25 MeV
24Mg(3He,p), 32S(3He,p)
Proton beam at 65 MeV
24Mg(p,3He),28Si(p,3He),40Ca(p,3He)
RCNP E365 (Completed in 2012):
Systematic studies of neutron-proton pairing in sd-shell
nuclei using (p,3He) and (3He,p) transfer reactions
Grand Raiden recoil particles
LAS elastic scattering reaction
at 60° (Compared to calculations
check beam normalization & target
thickness measurement)
LAS
RCNP E365 (Completed in 2012):
Systematic studies of neutron-proton pairing in sd-shell
nuclei using (p,3He) and (3He,p) transfer reactions
Target Thickness of 300 μg/cm2 Good resolution
24Mg, 28Si, 40Ca -- Isao Sugai (KEK)
32S (AgS) -- Véronique Petitbon-Thevenet (IPN)
2n-transfer reactions
Compare to np-transfer24Mg(p,t),28Si(p,t),
1N-transfer reactions
Experimental spectroscopic factor
for 2N-transfer calculations24Mg(p,d), 32S(p,d), 40Ca(p,d),24Mg(3He,d)
np-transfer reactions24Mg(3He,p), 32S(3He,p) 24Mg(p,3He),28Si(p,3He),40Ca(p,3He)
Measurements:
Elastic scattering
check beam normalization & target
thickness measurement
24Mg(3He, 3He), 32S(3He, 3He), 28Si(p, p),40Ca(p, p)
PID and Excitation Spectrum
• p and 3He identified by time of flight
& energy in focal plane
• Excitation energy spectra kinematically
corrected (no position dependence)
• Measurements at very forward angles
• Measurements at every 2º interval
to angular distributions with 2 peaks
Data Analysis by Yassid Ayyad (RCNP)
Excitation energy spectrum
Energy (MeV)
24Mg(p,3He)22Na at θlab= 8º
• 0+ and 1+ states unambiguously
identified for each reaction
• Absolute cross sections (Faraday Cup)
• Resolution: 40 keV (target: 300μg/cm2)
g.s.
0.58 (1+) 0.66 (0+)
• Background subtracted
• Correction of target thickness
Excitation Energy (MeV)
Po
siti
on X
(m
m)
Differential Cross Sections for the lowest J=0+ & J=1+
3He beam at 25 MeV24Mg(3He,p), 32S(3He,p)
Proton beam at 65 MeV24Mg(p,3He),28Si(p,3He), 40Ca(p,3He)
Ratio of σ(J=0+) to σ(J=1+)
1-step DWBA Calc. (TWOFNR)
• L=0 transfer dominant at
forward angles (FA)
np-transfer:
0+ 0+ (S=0, T=1): L=0
0+ 1+ (S=1, T=0): L=0, 2
This work: Ratios are taken
at ≤ 5º (some at 0º)
Shiro Yoshida, NP 33, 685 (1962)
Plot from Augusto Macchiavelli
A+2(p, 3He)A
Previous work
A(3He,p)A+2
This work
For this case, proton and neutron are
in the last accessible single particle level d3/2
See next talk by J.A. Lay: np-transfer in 2nd order DWBA and other
applications of two-nucleon transfer
Reaction Model:• Second order DWBA calculations
with FRESCO
• Simultaneous and sequential transfer
G. Potel et al., Phys. Rev. Lett 107, 092501
Extend to np-transfer with T=0 pairing included
Calculations of np-transfer reactionsJ.A. Lay, G. Potel
Calculations reproduce Sn(p,t) cross sections
data w/o normalization
Summary
(I) Systematic studies of neutron-proton pairing in sd-shell nuclei
Five Reactions: 24Mg(3He,p), 32S(3He,p), 24Mg(p,3He), 28Si(p,3He) & 40Ca(p,3He)
Tool : np-Transfer Reactions -- Cross section measurements
Establishing systematic framework & methodology
(II) Comparison to the np-transfer Calculations
Quantitative understanding
Fundamental Nature & Interplay between T=0 & T=1 neutron-proton pairing
Baseline for systematic studies of np-pairing in heavier nuclei
RIKEN
J. Lee, Z, Li, H. Liu, J. Zenihiro,
Y. Aoki
LBNL
A.O. Macchiavelli
IPN Orsay
D. Beaumel, V. Petitbon-Thevenet
RCNP, Osaka U.
N. Aoi Y. Ayyad
Y. Fujita, K. Hatanaka,
K. Miki H. J. Ong,
T. Suzuki, A. Tamii,
Y. Yasuda
Dep. Phys., Osaka Univ.
H. Fujita
CNS, Univ. of Tokyo
H. Matsubara
Dep. Of Physics, Kyoto Univ.
T. Kawabata, N. Yokota
Science Faculty, Istanbul Univ.
E. Ganioglu, G. Susoy
RCNP E365 Collaborators:
Systematic studies of neutron-proton pairing in sd-shell
nuclei using (p,3He) and (3He,p) transfer reactions
KEK
I. Sugai
MSU/LLNL
G. Potel
University of Padova - INFN
J.A. Lay
Acknowledgement:
G. Bertsch (WU)
support letter to PAC
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