Parity-transfer reaction for study of spin-dipole 0- mode

Masanori Dozono Center for Nuclear Study, the University of Tokyo

The 5th International Conference on “Collective Motion in Nuclei under Extreme Conditions” (COMEX5) 14-18 September 2015, Krakow

Scientific motivation

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Spin-Dipole (SD) mode • (Isovector) SD operator !!• ΔL=1, ΔS=1, ΔT=1 • ΔJπ=0-, 1-, 2-

SD 0- mode (particular interest) • Carries quantum numbers of pion (Jπ=0-, T=1) • Reflects pion-like (tensor) correlations in nuclei

Protons Neutrons

・Anti-phase vibration between 　protons and neutrons 　(ΔL=1, ΔT=1) ・Spin-flip mode (ΔS=1)

Spin-isospin modes (ΔS=1,ΔT=1) in nuclei play an essential role in understanding of nuclear structure

M. N. Harakeh et al., “Giant Resonances”, Oxford, 2001 M. Ichimura et al., PPNP 56, 446 (2006).

Tensor effects on 0- strengths

Results of HF+RPA calc. • Tensor effects • 0- peak shifts by several MeV • Skyrme-type tensor int.

• Triplet-Even : Constrained by GT data • Triplet-Odd : NOT well constrained

C. L. Bai, H. Sagawa et al., PRC 83, 054316 (2011); Private communication

Triplet-Even (T)

Triplet-Odd (U)

0 10 20 30 40Excitation energy of 12B (MeV)

SD stren

gth (fm

2 /MeV

) (T,U) : (500,-350) : (600,0) : (650,200)

12C → 12B

SD 0-

SD 1-

SD 2-

0- distribution is sensitive to tensor ⇒ Exp. data of 0- are important to pin down tensor force effects

Experimental studies of 0- states

Exp. data of 0- are highly desired ⇒ Selective tool for 0- !

Red points are the nuclei in which some 0- states are identified.

Exp. information on 0- states is very limited

Figure by H. Okamura

Parity-transfer (16O,16F(0-)) reaction

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Parity-trans. (16O,16F(0-)) • 16O (g.s., 0+) → 16F (g.s.,0‒)

Advantages • Selectively excite unnatural-parity states • No 1- contribution • Single Jπ for each ΔLR • Jπ (0-, 1+, 2-,...) can be assigned

only by the angular distribution (⇔ ΔLR)

Clean probe for SD 0- search

Parity-transfer reaction is selective tool for 0- !

16O, 0+ 16F, 0̶

0+ 0̶

(ΔLR=0)

Projectile

ΔJ = 0 Δπ = ̶ ΔLR

Target

Parity-trans. reaction

Parity-transfer (16O,16F(0-)) reaction

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Parity-trans. (16O,16F(0-)) • 16O (g.s., 0+) → 16F (g.s.,0‒)

Advantages • Selectively excite unnatural-parity states • No 1- contribution • Single Jπ for each ΔLR • Jπ (0-, 1+, 2-,...) can be assigned

only by the angular distribution (⇔ ΔLR)

Clean probe for SD 0- search

Parity-transfer reaction is selective tool for 0- !

DWBA calculations with FOLD/DWHI

12B(0-), ΔLR=0 12B(1+), ΔLR=1 12B(2-), ΔLR=2

First parity-transfer measurement : 12C(16O,16F(0-))12B at 250 MeV/u

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Why 12C ? • Known 0- at Ex=9.3 MeV in 12B⇒ Confirm effectiveness of parity-trans. reaction

• Experimentally more feasible • High luminosity, • Low B.G. compared with heavier nuclei

We apply parity-trans. reaction to 12C target

GOAL Establish parity-trans. reaction as a new tool for the 0- study

H. Okamura et al. PRC 66 (2002) 054602

12C(16O,16F(0-)) experiment @ RIBF & SHARAQ

Beam : Primary 16O • 250MeV/u, 107 pps (radiation limit) • Dispersive matched beam • (ΔP/P)beam ~ 0.1% • (x|δ)beamline = -10 m

Target : 12C • Segmented plastic scinti.

(active C target, 103.2 mg/cm2) • Determine beam x-position @ S0

(NOT used in present analysis)

Coincidence measurement of 16F -> 15O + p • 15O : 2 LP-MWDCs @ S2 • p : 2 MWDCs @ S1

80 mm

30 m

m

5 mm

Thickness 1mm (12C=103.2 mg/cm2)

SDQ D1

Q3

GEM D2

CRDC

S0S1

S2

12C

15O

p

SHARAQSpectrometer

16O

SHARAQ spectrometer

Segment scinti.

・Invariant-mass of 15O+p ⇒ Identify 16F(0-) ・Missing-mass ⇒ Deduce Ex in 12B and θ

16F -> 15O+p decay

16F

p

15OP16F

P15O

Ppθopen

0

10

20

30

40

50

60

660 680 700 720 740 760 780 800

10740

10760

10780

10800

10820

10840

10860

660 680 700 720 740 760 780 800 0

10

20

30

40

50

60

10740 10760 10780 10800 10820 10840 10860

15O momentum P15O (MeV/c)

15O momentum P

15O (MeV/c)

p momentum Pp (MeV/c)

p momentum Pp (MeV/c)

opening angle θopen (mrad)

opening angle θopen (mrad)

0-

p(16O,16F) at θreac < 6 mrad

Decay kinematics curves are clearly observed

proton angular acceptance

1-2-

Relative energy Erel vs Excitation energy Ex

• δErel = 80 keV (FWHM)⇒ Successfully identify 16F(0-) ! !

• δEx @ p(16O,16F) = 3 MeV (FWHM)(Include effect of kinematics curve)⇒ δEx ~ 2 MeV (FWHM)

15O+p

16F0-,g.s.

1-, 0.19 MeV

2-, 0.42 MeV

3-, 0.72 MeV

Excitation energy of 12B (MeV)-20 0 20 40

Relative energy (MeV)

0.0

0.4

0.8

1.2

Yield (a.u.)

Yield (a.u.)

θreac < 0.25o

p(16O,16F)

80 keV

3 MeV

Different structurecompared with (d,2He) • GT(1+) at 0 MeV

• Hindered

12C(16O,16F(0-))12B spectrum

Counts/1 MeV

dσ/dΩdE (mb/sr MeV)

0.0

1.0

2.0

3.0

0 5 10 15 20 25Excitation energy of 12B (MeV)

02.557.51012.51517.52022.5

0 5 10 15 20 25

02.557.51012.51517.520

0 5 10 15 20 250

10

20

0 5 10 15 20 25

12C(16O,16F(0-)) θreac=0ο - 0.25o

GT, 1+

SDR(2-)

SDR(2-)SDR (2-&1-)

12C(d,2He) 270 MeV

θcm = 0ο - 1o

Preliminary

GT, 1+

H. Okamura et al. PLB 345 (1995) 1.

Different structurecompared with (d,2He) • GT(1+) at 0 MeV

• Hindered

• SDR(2-) at 4.5 MeV

• SDR(2- & 1-) at 7.5 MeV

• SD 0- at 9.3 MeV ?

• Enhancement

12C(16O,16F(0-))12B spectrum

Counts/1 MeV

dσ/dΩdE (mb/sr MeV)

0.0

1.0

0 5 10 15 20 25Excitation energy of 12B (MeV)

02.557.51012.51517.52022.5

0 5 10 15 20 25

02.557.51012.51517.520

0 5 10 15 20 250

10

20

0 5 10 15 20 25

12C(16O,16F(0-)) θreac=0ο - 0.25o

12C(d,2He) 270 MeV

θcm = 0ο - 1o

GT, 1+

SDR(2-)

SD, 0- ?Preliminary

SDR(2-)SDR (2-&1-)

GT, 1+

H. Okamura et al. PLB 345 (1995) 1.

More analysis (ang. dist. etc.) required, but (16O,16F(0-)) seems promising for 0- study

Summary

We propose parity-transfer reaction (16O,16F(0-)) for 0- study To confirm its effectiveness, we applied this reaction to 12C. ⇒ 12C(16O,16F(0-)) at 250A MeV @ RIBF & SHARAQ Preliminary results

• Successful identification of 16F(0-)

• Enhancement at ~9 MeV in 12B ⇒ Known 0- at 9.3 MeV ?⇒ (16O,16F(0-)) seems promising for 0- study

This is FIRST-STEP study to apply parity-trans. reaction to Collective 0- strengths in heavier nuclei (40Ca, 90Zr,…)

⇒　Systematic 0- study

Collaborators

RIKEN Nishina Center • T. Uesaka, M. Sasano, J. Zenihiro, H. Sakai, T. Kubo, K. Yoshida, Y. Yanagisawa, N. Fukuda, H. Takeda, D. Kameda, N. Inabe

CNS, University of Tokyo • S. Shimoura, K. Yako, S. Michimasa, S. Ota, M. Matsushida, H. Tokieda, H. Miya, S. Kawase, K. Kisamori, M. Takaki, Y. Kubota, C. S. Lee, R. Yokoyama, M. Kobayashi, K. Kobayashi

Kyushu University • T. Wakasa, K. Fujita, S. Sakaguchi, A. Okura, S. Shindo, K. Tabata

Aizu University • H. Sagawa, M. Yamagami

Backup

0- Search via Polarization Measurements

Azz in 12C(d,2He)H. Okamura et al., PRC 66, 054602 (2002).

Dij in 12C(p,n)

Clear observation of 0- at Ex~9MeV in A=12 system

M. Dozono et al., JPSJ 77, 014201 (2008).

SDR D

0 ∞1 0

2 ～1

SDR A

0 -2

1 +1

2 ～0

Need to separate SD 0-,1-,2- ⇒ Polarization observables

Azz measurement for (d,2He) at KVI

SDR at 7.5 MeV • Low-energy part : 2- • High-energy part : 1-

2- 1-

M.A. de Huu et al., PLB 649, 35 (2007).

Coincidence measurement of p + HI @ SHARAQ

Use SHARAQ as TWO spectrometers • Proton : Q-Q-D (S0→S1) • HI (A/Z~2) : Q-Q-D-Q-D (S0→S2)

Proton (S0→S1) Momentum resolution : dp/p = 1/4330 Angular resolution　　 : ~ 2 mrad Momentum acceptance　: ±12% Angular acceptance　　 : ~2.2 msr !HI (S0→S2) Momentum resolution : dp/p = 1/15300 Angular resolution　　 : ~ 1 mrad Momentum acceptance　: ±1% Angular acceptance　　 : ~3 msr

Invariant mass resolution : ~100 keV Missing mass resolution : ~1 MeV

Ion-optics study of S0 → S1

Trajectories measured with secondary proton beam

Measured matrix elements (units: m,rad)

Angle at S0 aS0 [mrad]

Ang

le a

t S1 a S

1 [m

rad]

Angle at S0 aS0 (mrad)

Angle at S1 a S1 (mrad)

magnet field settings

S0

S1

LP-MWDCsMWDCs

SDQ D1

Proton beam

Comparison with (d,2He) • GT(1+) at 0 MeV

• Hindered

• SDR(2-) at 4.5 MeV

• SDR(2-&1-) at 7.5 MeV

• SD 0- at 9.3 MeV

• Enhancement ?

12C(16O,16F(0-))12B Spectrum

Counts/1 MeV

dσ/dΩdE (mb/sr MeV)

0.00 5 10 15 20 25Excitation energy of 12B (MeV)

02.557.51012.51517.52022.5

0 5 10 15 20 25

02.557.51012.51517.520

0 5 10 15 20 250

10

20

0 5 10 15 20 25

12C(16O,16F(0-)) θreac=0ο - 0.25o

GT, 1+

SDR(2-)

SD, 0- ?Preliminary

More analysis (ang. dist. etc.) required, but (16O,16F(0-)) seems promising for 0- study

0-遷移とパイ中間子(テンソル)相関• なぜ0-はパイ中間子(テンソル)相関に敏感か？ • 純粋なπ交換(σ・q)による遷移⇔ 他のスピン•アイソスピン遷移　(1+,2-,…)にはρ交換(σxq)も混じる

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• 高運動量(q~2 fm-1)で大きな遷移密度⇒ π交換力に敏感　(π交換力は高運動量領域で大)⇔ 例えば、　 GT 1+はq~0 fm-1で大きな密度

有効(残留)相互作用

運動量

運動量

π交換力

π交換力＋短距離斥力(g’)