Isoscalar Spin Response in the Continuum Studied via the 12 C(d,d ) - PowerPoint PPT Presentation

SQS04 symposium, Tokyo Tech., February 19-21 (2004) Isoscalar Spin Response in the Continuum Studied via the 12 C(d,d ’ ) Reaction at 270 MeV Y.Satou Tokyo Institute of Technology S.Ishida, H.Kato, H.Sakai, A.Tamii, K.Yako, M.Hatano, Y.Maeda University of Tokyo H.Okamura, T.Uesaka, K.Suda Saitama University N.Sakamoto, T.Ohnishi, K.Sekiguchi, T.Ichihara Institute of Physical and Chemical Research (RIKEN) T.Wakasa Research Center for Nuclear Physics

Introduction • Polarization studies in the (p,p ’ ) and (p,n) reactions at intermediate energies (100 ～ 1000 MeV) – Reaction mechanisms – Spin dependent modes of nuclear excitation via S nn (spin-flip probability) Gamow-Teller (GT) resonance, spin-flip dipole resonance • Spin-flip study in the (d,d ’ ) reaction – Selective excitation of isoscalar ΔT=0 transitions – Possible probe of double spin-flip ΔS=2 state

Isoscalar Spin-flip Transitions ・ Much less is known about this mode due to - the lack of efficient probes - the weakness of the effective interaction V σ ・ Information on the isoscalar spin response is useful in elucidating - the quenching mechanism of spin transitions - the residual interaction in the isoscalar ΔT=0, spin ΔS=0 channel Interaction V0 Vτ Vσ Vσ・τ Spin transfer ΔS=0 ΔS=1 Isospin transfer ΔT=0 ΔT=1 ΔT=0 ΔT=1 Resonance GMR(E0) GDR(E1) GTR, M1 ? GQR(E2) IAS SDR (p,p ’ ),( α , α ’ (p,p ’ ),(p,n (d,d ’ ) (p,p ’ ),(p,n) Reaction ) )

Double Spin-flip Transitions Proposed double Gamow-Teller (DGT) ΔS=2 state • P.Vogel et al., PLB212(88)259 – N.Auerbach et al., Ann. Phys. 192(89) 77 – Experimental information on the DGT strength distribution • – A better understanding of spin-isospin properties of nuclei – An excellent way to calibrate double beta decay matrix elements Necessary ingredients in extracting the neutrino mass from the double beta decay life time measurements

Observable Spin-flip probability: fractions of deuterons undergoing spin-flip by 1 and 2 units along an axis normal to the reaction plane (y-axis) • Single spin-flip probability ΔＳｙ=1 y-axis 1 Δs y =0 = − − − y ' y ' y ' y ' S ( 4 P A 2 K ) 1 yy yy 9 Δs y =1 • Double spin-flip probability ΔＳｙ＝２ 1 = + + − + Δs y =2 y ' y ' y ' y ' y ' S ( 4 2 P 2 A 9 K K ) 2 yy y yy 18 A: Analyzing power, P: Polarizing power, K: Polarization transfer coefficient To measure S1 and S2, vector and tensor polarized beams and a vector and tensor polarimeter are needed.

Objective • To investigate isoscalar spin-flip transitions using the deuteron spin-flip measurement as a probe – focal plane deuteron polarimeter Principle of the present scheme tested with the first polarization transfer measurement on 12 C. New measurement performed up to around 40 MeV, in search for isoscalar single and double spin-flip strengths in highly excited continuum region Spin structure in 12 C above 20 MeV in excitation energy Y.Satou et al., PLB521(01)153

Experimental Condition Facility RIKEN Accelerator Research Facility Beam Polarized deuteron, 270 MeV, 10 nA Target 12 C, 87.2 mg/cm 2 Observable dσ/dΩ, A y , A yy ,P y ’ ,P y ’ y ’ ,K y y ’ ,K y y ’ y ’ ,K yy y ’ ,K yy y ’ y ’ ・Ring Cyclotron (K=540) ・AVF Cyclotron (K=70) ・Beam line polarimeter ・Spectrometer SMART ・Polarization: (p y ,p yy )=(0,0), ・Θ Range: (0,2),(2/3,0), 2.5°～ (-1/3,1) 7.5 ° ・Magnitude ・E x range: ～ 60 – 70% 7～38 MeV

Spectrometer SMART

Deuteron POLarimeter DPOL Vector ・Vector & tensor components CM 12 C(d,d 0 ) iT 11 , T 20 , T 21 , T 22 Tensor ・Enhanced double scattering HOD 1 H(d,2p) efficiencies 12 C(d,d 0 )～ 1.7 % Scatterer 1 H(d,2p) ～ 0.09 % (plastic + CH 2 ) ・Encompass the whole focal plane d H : 0.538 g/cm 2 80 cm × 16 cm C : 4.314 g/cm 2 p ・Calibrated at E d =210 ～ 270 MeV MWDC p Hodoscope Scatterer d d MWDC 1 m φ θ p d p σ=σ 0 (1+2iT 11 ・it 11 cosφ+T 20 ・t 20 + 2T 21 ・t 21 cosφ+2T 22 ・t 22 cos2φ) MWDC2

Calibration Results 12 C(d,d 0 ) 270 MeV ・Large vector analyzing power 250 MeV iT 11 230 MeV ・Double scattering efficiency 210 MeV ～ 1.7 % ・Optical model works σ iT11 T20 T21 T22

Calibration Results 1 H(d,2p) ・Large tensor 270 MeV analyzing powers T 20 , T 22 , T 21 250 MeV ・Double scattering 230 MeV efficiency ～ 0.09 % 210 MeV ・Impulse approximation model works σ iT11 T20 T21 T22

Excitation Energy Spectrum 0 + 2 - 3 - 2 - , 18.3 MeV 1 + 1 + ,12.71 MeV 3 - , 9.64 MeV 0 + , 7.65 MeV 2 + , 4.44 MeV 12 C

Single Spin-Flip Spectrum ・In the spin-flip spectrum, the non-spin-flip 0 + , 3 - 2 - states vanish, while the ｓpin- 0 + 3 - σ flip 1 + , 2 - states remain. 1 + Usefulness of S 1 in ? 1 + 2 - identifying spin transitions. S 1 ・A peak structure at 20.5 MeV （Γ～ 1 MeV）. 2 - ? 1 + σ×S 1 An isoscalar spin-flip transition

Spectra with a smaller angular bin size ・We observe the 20.5 MeV peak in each of the spectra. We can be confident on the presence of this peak. ・Previously reported only in one experiment. B.N.Johnson et al, PLC51(1995)1726 What is the spin-parity for the peak at 20.5 MeV ?

Comparison with Shell Model ・ Assumptions 2 - - Cohen-Kurath w.f. for 1 + 1 + states S.Cohen and D.Kurath, NP73(1965)1 - Millener-Kurath w.f. for 2 - , 1 - , 0 - (L=1) states D.J.Millener and D.Kurath, NPA255(1975)315 σ×S 1 - Distorted wave impulse approximation (DWIA) for reaction model ・For known 1 + and 2 - states, agreement is good. ・Shell model predicts 2 - (4th), 2 - (5th), 1 - (2nd), 0 - (2nd) states at around 20 MeV.

Double Spin-Flip Spectrum ・Natural and unnatural parity transitions vanish 2 - 0 + 3 - σ in the double-spin-flip 1 + spectra. ・S 2 values are close to zero over the measured excitation energy range up to 40 MeV. S ２ ・No indication of double spin -flip states could be obtained. σ×S ２

Summary We measured single and double spin-flip probabilities, S 1 and S 2 , • in inelastic deuteron scattering on 12 C at 270 MeV up to 40 MeV in excitation energy. – a focal plane deuteron polarimeter, DPOL. In the spin-flip spectrum, an isoscalar spin-flip transition is • identified at 20.5 MeV (Γ～ 1 MeV）. Comparison with shell model suggests a possibility that this peak • consists of several transitions with different J π values, most likely 2 - , 1 - and 0 - . Double spin-flip S 2 values are close to zero; no indication of • double spin-flip states could be obtained up to 40 MeV.