M1 Excitations in (p,p ) Reactions

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1 M1 Excitations in (p,p ) Reactions A. Tamii Research Center for Nuclear Physics, Osaka University Strong, Weak and Electromagnetic Interactions to Probe Spin-Isospin Excitations, September 28th October 2nd, 2009, at Trento 1

2 Contents M1 strength in 208 Pb Isoscalar and Isovector M1 Excitations in N=Z Nuclei Summary

3 M1 strength in 208 Pb September 29th, 2009, at Trento

4 Collaborators Ε282 RCNP, Osaka University A. Tamii, H. Matsubara, T. Adachi, K. Fujita, H. Hashimoto, K. Hatanaka, Y. Tameshige and M. Yosoi September 29th, 2009, at Trento Dep. of Phys., Osaka University Y. Fujita Dep. of Phys., Kyoto University H. Sakaguchi and J. Zenihiro CNS, Univ. of Tokyo T. Kawabata, K. Nakanishi, Y. Shimizu and Y. Sasamoto CYRIC, Tohoku University M. Itoh and Y. Sakemi Dep. of Phys., Kyushu University M. Dozono Dep. of Phys., Niigata University Y. Shimbara KVI, Univ. of Groningen L.A. Popescu IFIC-CSIC, Univ. of Valencia B. Rubio and A.B. Perez-Cerdan Sch. of Science Univ. of Witwatersrand J. Carter and H. Fujita ithemba LABS F.D. Smit IKP, TU-Darmstadt P. von Neumann-Cosel, A-M. Heilmann, A. Richter, I. Poltoratska, V. Ponomarev and K. Zimmer 4

5 Prediction of the M1 strengths in 208 Pb with 1p-1h basis 1p-1h excited states of protons π{h 9/2 -h 11/2-1 }> and neutrons ν{i 11/2 -i 13/2-1 }> strongly couples to each other due to spin-orbit splittings of p and n orbits are similar orbital angular momentum l s are similar i 11/2 and yield a lower-lying state at ~ 5.4 MeV with B(M1) ~ 1 μ N 2 a higher-lying state at ~ 7.5 MeV with B(M1) ~ 50 μ N 2 h 9/2 h 11/2 i 13/2 in Tamm-Dancoff approximation. see e.g. J.D. Vergados, Phys. Lett. 36B (1971) 12. Bohr and Mottelson, Nuclear Structure vol II (1975)636. p 208Pb n

6 Fragmentation of the M1 strengths in 208 Pb The low-lying strength is considered to be exhausted by a state located at MeV. observed by (p,p ) S.I. Hayakawa et al., PRL49(1982)1624, (e,e ), and (d,d ). 1p-1h The higher-lying strength is fragmented into many tiny states by mechanisms: core-polarization or g.s. correlation coupling to 2p-2h states coupling to Δ-h states meson exchange current 1p-1h and 2p-2h Experimentally, only a strength of ~10 μ N 2 has been observed (until 1988) comparing with theoretical calc. by Lee and Pittel PRC11(1975)607. predictions of ~10 μ N 2. Missing M1 strength in 208 Pb

7 Prediction of the M1 strengths in 208 Pb Many theoretical works have been done for reproducing the observed M1 strengths spreading by the coupling to 2p-2h states: 20% of reduction ground state correlation: 20% of reduction coupling to Δ-h states and MEC: 20% of reduction If all these mechanisms additively contribute, the best that be expected from theoretical predictions is 20 μ N2 I.S. Towner, Phys. Rep 155 (1987) 263.

8 Search for M1 strengths by experiments Experimentally many reactions have been used to observe the M1 strengths: 208 Pb(γ,γ), 208 Pb(γ,n), 207 Pb(n,n), 207 Pb(n,γ), 208 Pb(e,e ), and 208 Pb(p,p ) September 29th, 2009, at Trento In 1988, R.M. Laszewsky et al. have identified 8.8μ N2 below Sn by a 208 Pb(γ,γ) measurement. In total the higher-lying strength became 15.6μ N 2 which came closer to the best (smallest) theoretical prediction of 20μ N2. Determination of the M1 strength distribution in 208 Pb over a large Ex range is important to know the M1 quenching mechanism. R.M. Laszewski et al, PRL61(1988)1710

9 High-Resolution (p,p ) measurement at and close to zero degrees September 29th, 2009, at Trento

10 Merit of (p,p ) scattering measurement at 0 deg. (1/2) ΔL=0 excitations are favored at 0 (and Coulomb excitation of E1) ΔL information can be obtained from angular distribution of dσ/dω at forward angles. dσ/dω at 0 is approximately proportional to the relevant reduced matrix elements. dσ ST 2 ST = K N J ( q) B ( q, ω) dω ΔS is model-independently identified by measuring polarization transfer coefficients at 0 (ΔS decomposition of the strengths) D SS + D NN + D LL 1 for ΔS = 1 = 3 for ΔS = 0 e.g. M1 e.g. E1 T.Suzuki, PTP103(2000)859 D SS =D NN at 0deg High-resolution measurement (20 kev) is feasible. Other reaction data, e.g. (d,d ), (α,α ), ( 3 He, t), (γ,γ ) and (e,e ), provide complementary information

11 Merit of (p,p ) scattering measurement at 0 deg. (2/2) Excitation strengths can be measured in a wide E x range (5<E x <25 MeV) by a single-shot measurement (missing-mass spectroscopy) independent of the decay channel flat and high detection efficiency total width (or total excitation strength) Sensitivity to B(M1) of various probes Comparison with (e,e ) complimentary: B(σ) by (p,p ) B(M1) by (e,e ) no radiative tail large cross-section reaction mechanism is not very well-known R.M. Laszewski and J. Wambach, Comments Nucl. Part. Phys. 14 (1985) 321. Demerits Reduction of instrumental B.G. is essential... requires a high-quality halo-free beam and beam stability Absolute normalization of the strength is not straightforward

12 Experimental Method High-Resolution (p,p ) measurement at close to zero degrees A. Tamii et al., ΝΙΜ Α605, 326 (2009)

13 High-resolution Spectrometer Grand Raiden High-resolution WS beam-line (dispersion matching)

14 Spectrometers in the 0-deg. experiment setup As a beam spot monitor in the vertical direction Proton Beam at 295 MeV Transport : Dispersive mode Intensity : 3 ~ 8 na Feb defense

15 Grand Raiden in the 0deg Measurement Setup September 29th, 2009, at Trento

16 Grand Raiden in the 0deg Measurement Setup September 29th, 2009, at Trento Target foil: ~2 mg/cm 2

17 Grand Raiden in the 0deg Measurement Setup September 29th, 2009, at Trento primary beam

18 Grand Raiden in the 0deg Measurement Setup September 29th, 2009, at Trento primary beam

19 Grand Raiden in the 0deg Measurement Setup September 29th, 2009, at Trento primary beam scattered proton

20 Grand Raiden in the 0deg Measurement Setup September 29th, 2009, at Trento primary beam scattered proton θ double scattering polarized

21 Grand Raiden in the 0deg Measurement Setup September 29th, 2009, at Trento p y' = 1 A y L L + R R in spin-transfer measurements R L double scattering polarized

22 Spectrometers in the 0-deg. experiment setup As a beam spot monitor in the vertical direction Scattering Chamber FC (>6deg) Apply dispersion matching Intensity : 3 ~ 8 na Feb defense

23 Grand Raiden in the setup of E282 September 29th, 2009, at Trento D SS measurement in Nov D LL measurement in Dec Pb 5.4 mb/cm 2 polarized ~1-2nA D SS (=D NN ) Measurement 23

28 Comparison of B(E1) September 29th, 2009, at Trento Analysis by I. Poltratska

31 ΔS can be model-independently extracted by measuring polarization transfer coefficients at 0 (ΔS decomposition of the strengths) 2D NN + D LL 1 for ΔS = 3 for ΔS = 1 = 0 e.g. M1 e.g. E1 (Coulomb-Excitation) T.Suzuki, PTP103(2000)859 E1(Coulomb-Ex.) and M1 strengths can be decomposed. Total SpinTransfer 3 (2DSS + D = 4 1 for ΔS = 1 = 0 for ΔS = 0 LL ) 3 ( D at 0deg NN + D 4 SS + D LL )

34 J. Enders et al., NPA724(2003)243 N. Ryezayeva et al., PRL27(2002) A. Veyssiere et al., NPA159(1970)561 Z.W.Bell et al., PRC25(1982)791 September 29th, 2009, at Trento

35 R.M.Laszewski et al, PRL59(1987)431. R. Kohler et al., PRC35(1987)1646.

36 Isoscalar and Isovector M1 Excitations in N=Z nuclei H. Matsubara et al.

37 E299 Collaborators September 29th, 2009, at Trento RCNP, Osaka U. H. Matsubara, A. Tamii, T. Adachi, K. Fujita, K. Hatanaka, D. Ishikawa, M. Kato, H. Okamura, Y. Tameshige, K. Suda, M. Yosoi Univ. of Witwatersrand J. Carter, H. Fujita IKP, Tech. U. of Darmstadt P. Von Neumann-Cosel, B. Ozel, I. Poltoratska, A. Richter, A. Shevchenko Kyusyu U. Dept. of Phys. M. Dozono, S. Kuroita, Y. Yamada Osaka U. Dept. of Phys. Y. Fujita CNS, Univ. of Tokyo Chiba U. Dept. of Phys. T. Kawabata, K. Nakanishi, S. Sakaguchi, H. Nakada Y. Sasamoto, Y. Shimizu Miyazaki U. Dept. of App. Phys. IFIC-CSIC, Valencia CYRIC, Tohoku U. N. Fujita, A. Nonaka, B. Rubio M. Itoh, Y. Sakemi H. Sakaguchi ithemba LABs Niigata U. Kyoto U. Dept. of Phys. F.D. Smit, R. Neveling Y. Shimbara, J. Zenihiro R. Yamada

Gaarde, NP A396, 127c(1983) Quenching ~ 50% By sophisticated measurements and analysis of (p,n) and (n,p) reactions 50 88% of the strength was

38 Quenching of the GT strengths Gamow-Teller (GT) quenching problem: The observed GT strengths are systematically smaller the sum-rule value. GT sum rule : S S = 3( N Z) Quenching Factor β + Strength(exp.) Q Strength( theory) β C. Gaarde, NP A396, 127c(1983) Quenching ~ 50% By sophisticated measurements and analysis of (p,n) and (n,p) reactions 50 88% of the strength was observed in 90 Zr upto E x =50 MeV T. Wakasa et al., PRC55(1997)2909 K. Yako et al., PLB615(2005)193 2 quenching schemes: - Mixing of multi-particle multi-hole states - Mixing of Δ-hole states dominant contribution

39 M1 excitations and analogous excitations September 29th, 2009, at Trento Isovector (ΔT=1) M1 excitation is analogous to GT. Similar quenching is expected Isoscalar (ΔΤ=0) M1 excitation: Δ-h mixing does not take place N=Z+2 =even N=Z-2 Different quenching between isoscalar and isovector excitations?

40 M1 quenching problem 32 S 28 Si T=0 (IS) T=1 (IV) np-nh Δ-h possible impossible possible possible 18 O 20 Ne 22 Ne 24 Mg 26 Mg Quenching factor : exp. sum / theory sum. Why is IS smaller than IV? How about in other nuclei? High res. at RCNP would find IS in other nuclei July LNL

41 Study of isoscalar/isovector M1 excitations over the sd-shell region For all the N=Z even-even stable nuclei over the sd-shell (isoscalar/isovector excitations do not mix to each other) 16 O, 20 Ne, 24 Mg, 28 Si, 32 S, 36 Ar, 40 Ca 16 O: Ice target (H 2 O) 32 S: Cooled target (for preventing sublimation) 36 Ar: Gas target 20 Ne: Cooled gas target

Matsubara et al, NIM B accepted. Ice sheet ~10 mg/cm^2 Sulfur target 5.9 ±0.

42 Cooled solid target system Self-supporting target H 2 O (ice sheet), 32 S with cooling system (liquid N 2 ) T. Kawabata et al., NIMA 459 (2001) 171. H. Matsubara et al, NIM B accepted. Ice sheet ~10 mg/cm^2 Sulfur target 5.9 ±0.2 mg/cm^2 Preparation for NIM, H. Matsubara Required a large sheet to pass a dispersed beam.

43 Cooled gas target system September 29th, 2009, at Trento Applicable for high-res. exp.(<30kev at < 6 deg) Cooled by liq. N 2 Gas recycling system H. Matsubara H. Matsubara et al, in preparation for NIMA. Aramide window foils 6μm

44 1 + ; MeV September 29th, 2009, at Trento

46 1 + ; MeV 17 kev

48 The shape and height of the instrumental b.g. can be experimentally determined and be subtracted. B.G. level

50 16 O(p,p ) at E p =300MeV no IS and 3 IVs (preliminary) After b.g. subtraction Excitation energy [MeV] IV IS

51 no IS and 1 IV (preliminary) 20 Ne(p,p ) at E p =300MeV After b.g. subtraction Contaminated with Aramid windows (C,O,N,Cl,H) Excitation energy [MeV] IV IS

52 24 Mg(p,p ) at E p =300MeV 1 IS and 6 IVs (preliminary) After b.g. subtraction Excitation energy [MeV] IV IS

53 28 Si(p,p ) at E p =300MeV 4 ISs and 12 IVs After b.g. subtraction FWHM ΔE~20keV Excitation energy [MeV] IV IS

54 32 S(p,p ) at E p =300MeV 2 ISs and 6 IVs (preliminary) After b.g. subtraction Excitation energy [MeV] IV IS

55 36 Ar(p,p ) at E p =300MeV no IS and 6 IVs (preliminary) After b.g. subtraction Contaminated with Aramid windows (C,O,N,Cl,H) Excitation energy [MeV] IV IS

56 40 Ca(p,p ) at 0- no IS and 1 IV (preliminary) 0.5 E p =300MeV After b.g. subtraction Excitation energy [MeV] IV IS

57 L and T assignments Distorted wave Born approximation (DWBA) by DW91 Trans. density : USD (from shell model calculation) NN interaction. : Franey and Love, PRC31(1985)488. (325 MeV data) Optical potential : K. Lin, M.Sc. thesis., Simon Fraser U T=0 ; IS T=1 ; IV 28 Si at Ex = 9.50 MeV ; T=0 28 Si Ex = MeV ; T=1 dσ/dω [mb/sr] 0.35, T=0 dσ/dω [mb/sr] 2.50, T=0 0.11,T=1 0.77, T=1 Θ cm [deg] Θ cm [deg] Isospin can be assigned from an angular distribution. July LNL

58 Other states identified as 1 September + in 29th, , Si at Trento 1 +, T=0 states 1 +, T=1 states MeV MeV MeV MeV dσ/dω [mb/sr] MeV MeV dσ/dω [mb/sr] MeV MeV MeV MeV MeV MeV MeV MeV Θ CM [deg] T=0 : IS T=1 : IV Θ CM [deg]

59 Strength distribution 28 Si shell model calculation: OXBASH + USD interaction September 29th, 2009, at Trento preliminary

60 M1 strength in 28 Si Cumulative Sum T=0 ; 1+ T=1 ; I+ September 29th, 2009, at Trento preliminary Quenching factor B(σ) [μ n 2 ] B(σ) [μ n 2 ] Crawley et al, (preliminary) Followings should be checked more carefully. B(σ) is determined from dσ/dω(q=0) relying on the eff. interaction and DWIA calculation. Bare g-factor is used in the S.M. calculation. Quenching Factor = ΣB( σ ) ΣB( σ ) exp shell model

61 Total B(σ) strengths September 29th, 2009, at Trento very preliminary IS IV preliminary preliminary Total B(σ) [μ n 2 ] Total B(σ) [μ n 2 ] C O 20 Ne 2 4 Mg 28 Si S 36 Ar 40 Ca C 16 O 20 Ne 2 4 Mg 28 Si S 36 Ar 40 Ca Calc. = OXBASH shell model calculation (0 hw) with USD or CK int. and the free-g factors. (~10% ambiguities)

62 Comparison of Q-factors IS and IV Q-factor very preliminary preliminary Exp. / Calc (bare-g) IS IV C 16 O 20 Ne 2 4 Mg 28 Si S 36 Ar 40 Ca IS seems generally to be less than IV in the sd-shell.

63 Summary September 29th, 2009, at Trento High-resolution (p,p ) measurements at forward angles including zero degrees are established and are extensively performed. Polarization transfer coefficients of the 208 Pb(p,p ) reaction were partly taken. Spin flip strength (supposed M1) is clearly seen at 7 ~8 MeV.. Isoscalar and Isovector M1 excitation strengths and distributions are measured for N=Z even-even nuclei over the sd-shell region.

np Spin-Correlation in the Ground State Studied by Spin-M1 Transitions

np Spin-Correlation in the Ground State Studied by Spin-M1 Transitions Atsushi Tamii Research Center for Nuclear Physics (RCNP) Osaka University, Japan for RCNP-E299 Collaborations 2nd International Workshop