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 ・Anti-phase vibration between Spin-Dipole (SD) mode an essential role in understanding of nuclear structure Spin-isospin modes (ΔS=1,ΔT=1) in nuclei play 
 ・Spin-flip mode (ΔS=1) (ΔL=1, ΔT=1) SD 0 - mode (particular interest) protons and neutrons Protons Neutrons � � M. N. Harakeh et al., “Giant Resonances”, Oxford, 2001 � M. Ichimura et al., PPNP 56, 446 (2006). • (Isovector) SD operator � � • ΔL=1, ΔS=1, ΔT=1 • ΔJ π =0 - , 1 - , 2 - • Carries quantum numbers of pion (J π =0 - , T=1) • Reflects pion-like (tensor) correlations in nuclei

Tensor effects on 0 - strengths 20 ⇒ Exp. data of 0 - are important 0 - distribution is sensitive to tensor SD 2 - SD 1 - SD 0 - 12 C → 12 B Excitation energy of 12 B (MeV) Results of HF+RPA calc. 30 40 10 0 to pin down tensor force effects C. L. Bai, H. Sagawa et al., PRC 83, 054316 (2011); Private communication • Tensor effects • 0 - peak shifts by several MeV • Skyrme-type tensor int. SD strength (fm 2 /MeV) • Triplet-Even : Constrained by GT data • Triplet-Odd : NOT well constrained Triplet-Even (T) Triplet-Odd (U) ( T , U ) : (500,-350) : (600,0) : (650,200)

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 ( 16 O, 16 F(0 - )) reaction 16 O, 0 + Target ΔL R Δπ = ̶ ΔJ = 0 Projectile (ΔL R =0) 0 ̶ 0 + 16 F, 0 ̶ Parity-transfer reaction is selective tool for 0 - ! Clean probe for SD 0 - search only by the angular distribution (⇔ ΔL R ) Advantages Parity-trans. ( 16 O, 16 F(0 - )) Parity-trans. reaction � • 16 O (g.s., 0 + ) → 16 F (g.s.,0 ‒ ) • Selectively excite unnatural-parity states • No 1 - contribution • Single J π for each ΔL R • J π (0 - , 1 + , 2 - ,...) can be assigned 


Parity-transfer ( 16 O, 16 F(0 - )) reaction Parity-trans. ( 16 O, 16 F(0 - )) Advantages only by the angular distribution (⇔ ΔL R ) Clean probe for SD 0 - search Parity-transfer reaction is selective tool for 0 - ! DWBA calculations with FOLD/DWHI 12 B(0 - ), ΔL R =0 12 B(1 + ), ΔL R =1 12 B(2 - ), ΔL R =2 � • 16 O (g.s., 0 + ) → 16 F (g.s.,0 ‒ ) • Selectively excite unnatural-parity states • No 1 - contribution • Single J π for each ΔL R • J π (0 - , 1 + , 2 - ,...) can be assigned 


First parity-transfer measurement : 
 12 C( 16 O, 16 F(0 - )) 12 B at 250 MeV/u Why 12 C ? ⇒ Confirm effectiveness 
 of parity-trans. reaction We apply parity-trans. reaction to 12 C target GOAL Establish parity-trans. reaction as a new tool for the 0 - study � � H. Okamura et al . PRC 66 (2002) 054602 • Known 0 - at E x =9.3 MeV in 12 B 
 • Experimentally more feasible • High luminosity, • Low B.G. compared with heavier nuclei

12 C( 16 O, 16 F(0 - )) experiment @ RIBF & SHARAQ • ・Invariant-mass of 15 O+p ⇒ Identify 16 F(0 - ) Segment scinti. spectrometer SHARAQ 16 O Beam : Primary 16 O Thickness 1mm 5 mm 80 mm 15 O : 2 LP-MWDCs @ S2 ( 12 C=103.2 mg/cm 2 ) 16 F -> 15 O + p (active C target, 103.2 mg/cm 2 ) Target : 12 C Coincidence measurement of 
 ・Missing-mass ⇒ Deduce E x in 12 B and θ (NOT used in present analysis) • 250MeV/u, 10 7 pps (radiation limit) • Dispersive matched beam 30 mm • (ΔP/P) beam ~ 0.1% CRDC • (x|δ) beamline = -10 m S2 15 O • Segmented plastic scinti. 
 • Determine beam x-position @ S0 
 GEM D2 p S0 Q3 S1 SHARAQ SDQ D1 • p : 2 MWDCs @ S1 Spectrometer 12 C

16 F -> 15 O+p decay 16 F 1 - acceptance proton angular are clearly observed Decay kinematics curves p( 16 O, 16 F) at θ reac < 6 mrad 0 - opening angle θ open (mrad) opening angle θ open (mrad) p momentum P p (MeV/c) p momentum P p (MeV/c) 15 O momentum P 15O (MeV/c) 15 O momentum P 15O (MeV/c) 2 - P 15O P p 15 O P 16F θ open 60 50 40 30 p 20 10 0 660 680 700 720 740 760 780 800 60 10860 50 10840 40 10820 10800 30 10780 20 10760 10 10740 0 660 680 700 720 740 760 780 800 10740 10760 10780 10800 10820 10840 10860

Relative energy E rel vs Excitation energy E x -20 0 20 40 80 keV p( 16 O, 16 F) θ reac < 0.25 o Yield (a.u.) Yield (a.u.) 1.2 0.8 0.4 0.0 Relative energy (MeV) Excitation energy of 12 B (MeV) 3 - , 0.72 MeV 2 - , 0.42 MeV 1 - , 0.19 MeV 0 - ,g.s. 16 F 15 O+p ⇒ δE x ~ 2 MeV (FWHM) (Include effect of kinematics curve) 
 ⇒ Successfully identify 16 F(0 - ) ! 3 MeV • δE rel = 80 keV (FWHM) 
 � • δE x @ p( 16 O, 16 F) = 3 MeV (FWHM) 


Different structure 
 3.0 10 0 compared with (d, 2 He) 0 5 10 15 20 25 Excitation energy of 12 B (MeV) 0 5 10 15 20 25 20 2.0 1.0 0.0 dσ/dΩdE (mb/sr MeV) Counts/1 MeV 12 C( 16 O, 16 F(0 - )) 12 B spectrum 20 SDR(2 - ) 12 C( 16 O, 16 F(0 - )) 17.5 θ reac =0 ο - 0.25 o GT, 1 + 15 Preliminary 12.5 • GT(1 + ) at 0 MeV 10 7.5 • Hindered 5 2.5 0 0 5 10 15 20 25 12 C( d , 2 He) GT, 1 + 270 MeV θ cm = 0 ο - 1 o H. Okamura et al . SDR(2 - ) PLB 345 (1995) 1. SDR (2 - &1 - )

Different structure 
 0 5 10 15 20 25 ( 16 O, 16 F(0 - )) seems but More analysis (ang. dist. etc.) required, 0 5 10 15 20 25 20 10 0 compared with (d, 2 He) Excitation energy of 12 B (MeV) promising for 0 - study 1.0 dσ/dΩdE (mb/sr MeV) 0.0 12 C( 16 O, 16 F(0 - )) 12 B spectrum Counts/1 MeV 20 SDR(2 - ) 12 C( 16 O, 16 F(0 - )) 17.5 θ reac =0 ο - 0.25 o GT, 1 + 15 SD, 0 - ? Preliminary 12.5 • GT(1 + ) at 0 MeV 10 7.5 • Hindered 5 • SDR(2 - ) at 4.5 MeV 2.5 0 • SDR(2 - & 1 - ) at 7.5 MeV 0 5 10 15 20 25 GT, 1 + 12 C( d , 2 He) • SD 0 - at 9.3 MeV ? 270 MeV θ cm = 0 ο - 1 o • Enhancement SDR(2 - ) SDR (2 - &1 - ) H. Okamura et al . PLB 345 (1995) 1.

Summary We propose parity-transfer reaction ( 16 O, 16 F(0 - )) for 0 - study To confirm its effectiveness, we applied this reaction to 12 C. 
 ⇒ 12 C( 16 O, 16 F(0 - )) at 250A MeV @ RIBF & SHARAQ Preliminary results ⇒ ( 16 O, 16 F(0 - )) seems promising for 0 - study This is FIRST-STEP study to apply parity-trans. reaction to Collective 0 - strengths in heavier nuclei ( 40 Ca, 90 Zr,…) ⇒ Systematic 0 - study • Successful identification of 16 F(0 - ) • Enhancement at ~9 MeV in 12 B ⇒ Known 0 - at 9.3 MeV ? 


Collaborators RIKEN Nishina Center Y. Yanagisawa, N. Fukuda, H. Takeda, D. Kameda, N. Inabe CNS, University of Tokyo H. Tokieda, H. Miya, S. Kawase, K. Kisamori, M. Takaki, Y. Kubota, 
 C. S. Lee, R. Yokoyama, M. Kobayashi, K. Kobayashi Kyushu University Aizu University • T. Uesaka, M. Sasano, J. Zenihiro, H. Sakai, T. Kubo, K. Yoshida, 
 • S. Shimoura, K. Yako, S. Michimasa, S. Ota, M. Matsushida, 
 • T. Wakasa, K. Fujita, S. Sakaguchi, A. Okura, S. Shindo, K. Tabata • H. Sagawa, M. Yamagami

Backup

0 - Search via Polarization Measurements 2 ～0 2 +1 1 -2 0 A SDR ～1 0 A zz in 12 C(d, 2 He) 1 ∞ 0 D SDR Clear observation of 0 - at E x ~9MeV in A=12 system D ij in 12 C(p,n) Need to separate SD 0 - ,1 - ,2 - ⇒ Polarization observables M. Dozono et al., JPSJ 77, 014201 (2008). H. Okamura et al., PRC 66, 054602 (2002).

A zz measurement for (d, 2 He) at KVI SDR at 7.5 MeV • Low-energy part : 2 - • High-energy part : 1 - M.A. de Huu et al., PLB 649, 35 (2007). 2 - 1 -

Coincidence measurement of p + HI @ SHARAQ HI (S0→S2) Invariant mass resolution : ~100 keV Angular acceptance : ~3 msr Momentum acceptance : ±1% Angular resolution : ~ 1 mrad Momentum resolution : dp/p = 1/15300 Missing mass resolution : ~1 MeV Use SHARAQ as TWO spectrometers Angular acceptance : ~2.2 msr Momentum acceptance : ±12% Angular resolution : ~ 2 mrad Momentum resolution : dp/p = 1/4330 Proton (S0→S1) • Proton : Q-Q-D (S0→S1) • HI (A/Z~2) : Q-Q-D-Q-D (S0→S2) �

Ion-optics study of S0 → S1 Trajectories measured 
 with secondary proton beam Measured matrix elements (units: m,rad) Angle at S0 a S0 (mrad) Angle at S1 a S1 (mrad) magnet field settings S0 S1 LP-MWDCs MWDCs SDQ D1 Proton beam

Comparison with (d, 2 He) 0 5 10 15 20 25 ( 16 O, 16 F(0 - )) seems but More analysis (ang. dist. etc.) required, 0 5 10 15 20 25 20 10 0 Excitation energy of 12 B (MeV) promising for 0 - study 0.0 12 C( 16 O, 16 F(0 - )) 12 B Spectrum Counts/1 MeV dσ/dΩdE (mb/sr MeV) 20 SDR(2 - ) 12 C( 16 O, 16 F(0 - )) 17.5 θ reac =0 ο - 0.25 o GT, 1 + • GT(1 + ) at 0 MeV 15 SD, 0 - ? Preliminary 12.5 • Hindered 10 7.5 • SDR(2 - ) at 4.5 MeV 5 • SDR(2 - &1 - ) at 7.5 MeV 2.5 0 • SD 0 - at 9.3 MeV 0 5 10 15 20 25 • Enhancement ?