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

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