Parity-transfer reaction for study of spin-dipole 0 - mode Masanori - - PowerPoint PPT Presentation

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

• 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)

10 20 30 40

Excitation energy of 12B (MeV) SD strength (fm2/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

• 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 

• nly 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

• 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 

• nly 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

• Why 12C ?
• Known 0- at Ex=9.3 MeV in 12B


⇒ Confirm effectiveness 


• f 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 mm

5 mm

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

SDQ D1 Q3 GEM D2 CRDC

S0 S1 S2

12 C 15 O

p SHARAQ Spectrometer

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

15O

P16F P15O

Pp

θopen

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 10 20 30 40 50 60 10740 10760 10780 10800 10820 10840 10860

15O momentum P15O (MeV/c) 15O momentum P15O (MeV/c)

p momentum Pp (MeV/c) p momentum Pp (MeV/c)

• pening angle θopen (mrad)
• pening 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 16F

0-,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 structure
 compared 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 25

Excitation energy of 12B (MeV) 2.5 5 7.5 10 12.5 15 17.5 20 5 10 15 20 25

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 structure
 compared 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 25

Excitation energy of 12B (MeV)

2.5 5 7.5 10 12.5 15 17.5 20 5 10 15 20 25

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

∞

1 2 ～1 SDR A

• 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) Angle at S1 aS1 (mrad)

magnet field settings

S0 S1

LP-MWDCs MWDCs

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)

0.0 0 5 10 15 20 25

Excitation energy of 12B (MeV)

2.5 5 7.5 10 12.5 15 17.5 20 5 10 15 20 25

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

• 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’)