Dipole resonances in 4 He

Transcription

1 Dipole resonances in He σ( 7 Li, 7 Be), σ(ν,ν ), and σ γ S. Nakayama (Univ of Tokushima) Neutrino-induced reactions (neutral current) He(ν,ν ) in SN ν-heating He( 7 Li, 7 Be) Application of the He( 7 Li, 7 Be) reaction to σ γ Astrophysical phenomena Deduction of σ γ as a function of E x via ( 7 Li, 7 Be) spectra 2007/3/2 1

2 Motivation Response of CE reaction are similar to weak and EM responses. Neutrino-induced reaction (neutral current) GT/M1 and E1-transitions in (ν,ν ) GDR/SDR in He (SN ν-heating of He) Application to deduce σ γ Astrophysical phenomena Low-multipole transitions in CE reaction GDR strength distribution in He E γ -Excitation function CEX Spectrum σ M1 (γd) deduced from D( 7 Li, 7 Be) S. Nakayama et al., Phys. Rev. C72, 01001(R) (2005) 2007/3/2 2

3 Charge Exchange Reactions Analogous states ΔT=1, ΔT z = -1 (p,n) ( 3 He,t) ( 6 Li, 6 He) etc ΔT=1, ΔT z = +1 (n,p) (d, 2 He) (t, 3 He) ( 7 Li, 7 Be) etc 2007/3/2 3

4 ( 7 ( Li, 7 Li, 7 Be) 7 Be) 反応 7Li 7Be transition and spin-selectivities 1/2-3/2-7 Li Be γ 1/2 - (Be1) : 3/2 - (Be0) : Ejectile excitation ΔS= 1 ΔS= 0,1 7 Be-γ coincidence Separation between Be0 and Be1 Be0 : Without 7 Be-γ coincidence Be1 : With 7 Be-γ coincidence Electric-type Excitation (ΔS=0) Magnetic-type Excitation (ΔS=1) σ ( ΔS σ ( ΔS = 0) = σ (Be = 1) = σ (Be ) / B 1 0 ) σ (Be ) R GT 1 (Be Charge exchange Spin-flip & Spin-nonflip Reaction 1 ) COUNTS Nakayama, S. et al. Nucl. Instrum Methods A0 (1998) 3. Phys. Rev. Lett. 83 (1999) 690. Phys. Rev. Lett. 85 (2000) 262. Phys. Rev. Lett. 87 (2001) Li + A 7 Be + B T z = +1/2 T z = -1/2 J π = 3/2-7Be (J π = 3/2-) ΔT z = +1 ΔS=0 / ΔS=1 7 Be* (J π =1/2-) ΔT z = +1 ΔS=1 7 Be + γ R = BGT ( Be0) / BGT (Be1) 0 = 1.25/1.11 = /3/2 EXCITATION ENERGY (MeV) C ( 7 Li, 7 Be) 12 B, E L = 55 MeV, θ L <1.5 GT, 1 + τσ 2 -, - τσry 1 SDR (0 -, 1 -, 2 - ) τr Y 1 GDR, 1 - ΔS=1 ΔS=0

5 Nucleon-nucleon Interactions of Charge Exchange Reactions Central part: T T S 10LJ S 11LJ = g = g S 10LJ S 11LJ τ τ L L [ i r YL ] ; Electric type excitation ( ΔS = 0) L L L [ i r Y σ ] ; Magnetic type excitation ( ΔS = 1) L J L = 0 ( g / g ( E s s L ) / 55) 2 / 3 from (p,n) Non-central part: Tensor force ; V S T = V T ( r) τ S 12 ; S 12 ( σ1 r)( σ 2 r) = 3 σ 2 1 σ 2 r Tensor force has a sizable contribution for unnatural-parity transitions. 2007/3/2 5

6 Probe for Nuclear Weak and EM Responses Weak operators (neutral current); T T W 10LJ W 11LJ = g = g W 10LJ W 11LJ τ τ L L [ i r YL ] L L L [ i r Y σ ] L L = 0 J ( g W 1101 / g W 1000 ) from β - decay EM operators ; ~10-3 T T E 10 LJ M 11 LJ = = g g E 10 LJ M 11 LJ τ τ L L [ i r Y L ] [1 + f ( μ )] L L L L L {[ i r Y σ ] + [ i r Y l ] } 2007/3/2 6 L J Spin part Orbital part Their contributions are strongly dependent on the relevant states. L J

7 Scenario of Super Nova Explosion Core collapse ρ c ~ g/cc T c ~ 1 MeV e-capture Core bounce ρ c ~ 10 1 g/cc T c ~ 5 MeV ν ν ν ν 1000 km 2007/3/2 7 ν ν Neutron star 10 km ν ν ν ν-trapping ρ c ~ g/cc T c ~ 2 MeV 1 A massive star becomes gravitationally unstable, and outgoing shock wave is driven Shock wave ν-heating E ν ~10 53 erg E matter ~10 51 erg Explosion R-process 2 Outgoing shock wave loses due to iron-dissociation, ν-radiation, etc. 3 The shock wave is then revived due to ν-heating of collapsing layers. (protons, neutrons, electrons, and He nuclei) R-process nucleosynthesis proceeds via ν-spallations in He-layer. But this scenario can not be proven via thermo-dynamical simulation!!

8 Trajectories of Mass Elements Delayed explosion bounce Bethe-Wilson ApJ 295 (1985) /3/2 8

9 He-Abundance in SN Composition at t =150 ms from bounce Mass fractions n He C,O,... p Sumiyoshi et al., ApJ 629 (2005) /3/2 9

10 Neutrino-energy distribution in SN Neutrino temperature ν e anti-ν e ν τ ν μ T=8 T=6.26 T=5 T=3.5 in MeV MeV f ( E) = ν ν e ν e 2 3 E / T N 1+ exp[ E / T α], : < E > = μ ν τ : < E > = ( T, α) = (8 MeV, 0) MeV MeV = (6.25 MeV, 3) ( T, α) = (3.5 MeV, 0) : < E > = 16 MeV ( T, α) = (5 MeV, 0) Nuclear excitations up to E x ~50MeV are useful to study nuclear responses to weak neutral current. 2007/3/2 10

11 Neutrino-neutral reaction on He Vector operators ~6% Axial vector operators ~9% He(ν,ν T = 10 MeV D. Gazit and N. Barnea, Phys. Rev. C70, (200) 2007/3/2 11

12 Experimental procedure - Beam: 55 MeV, 7 Li 3+ at RCNP, Osaka Univ. - Targets: He (7mg/cm 2 ), Aramid (12μm x) (C 1 O 2 N 2 H 10 ) n - 7 Be:Grand RAIDEN θ L = 0 and 3 deg. ΔE ~ 500 kev - γ-rays: NYMPHS ε =12.5% for 0.3-MeV γ 2007/3/2 12

13 Singles and coincidence spectra (a) Singles spectrum, θ L < 1 deg. He+Aramid Aramid He for He( 7 Li, 7 Be) H 10 E x =25 MeV x1.0 E x =30 MeV x1. E x =35 MeV x (b) Coincidence spectrum, θ L < 1 deg. He+Aramid Aramid He ΔL= (deg.) θ cm 2007/3/ EXCITATION ENERGY in He

14 Comparison with He(p,p ) spectrum He(p,p ) at E L =300 MeV and θ L =8 deg. (ΔL=1 dominance) 1500 He (singles) 1000 He (coin) EXCITATION ENERGY in He Yamagata et al., Phys. Rev. C7, (2006) 2007/3/2 1

15 Derivation of ΔS=0 and ΔS=1 spectra (a) Singles spectrum, θ L < 1 deg. He+Aramid Aramid He for He( 7 Li, 7 Be) H σ(singles) = σ(δs=0)+1.25 x σ(δs=1) σ(coin) = 1.11 x σ(δs=1) (b) Coincidence spectrum, θ L < 1 deg. σ(δs=0) = σ(singles) x σ(coin)/ε σ(δs=1) = 0.9 x σ(coin)/ε He+Aramid Aramid He In-beam calibration Aramid-target ( 12 C) 12 C B 1 + (g.s), 2 - (E x =. MeV) = Spin-flip (ΔS=1) transitions Derivation of He spectra γ-detection efficiency ε for NYMPHS 2007/3/ EXCITATION ENERGY in He

16 Efficiency ε for NYMPHS Dependence of γ-detection efficiency ε 150 ΔS=0 spectrum for Aramid ε=11.2% x1.0 ε=11.8% x0.9 ε=12.5% x0.8 N=13.3% x EXCITATION ENERGY in He (MeV) 2007/3/2 16

17 GDR (ΔS=0) and SDR (ΔS=1) for 12 C ε=12.5% for 0.3-MeV 7Be γ-ray 5 Aramid ( 7 Li, 7 Be) E L =55 MeV, θ L <1 deg. 3 2 ΔS=0 ΔS= EXCITATION ENERGY in 12 C (MeV) 2007/3/2 17

18 ΔS=0 spectrum for He ε=11.2% x1.0 ε=11.8% x0.9 ε=12.5% x0.8 ε=13.3% x0.7 ΔS=0 spectrum for He EXCITATION ENERGY in He (MeV) 2007/3/2 18

19 GDR (ΔS=0) and SDR (ΔS=1) for He ε=12.5% for 0.3-MeV 7 Be γ-ray He( 7 Li, 7 Be) E L =55 MeV, θ L <1 deg. ΔS=0 ΔS= EXCITATION ENERGY in He (MeV) 2007/3/2 19

20 ΔS=0 and ΔS=1 strength distributions , GT SDR 12 C( 7 Li, 7 Be) E L =55 MeV, θ L < 1 deg. GDR singles ΔS=0 ΔS=1 in 12 C 0 e. g., EXCITATION ENERGY in 12 B (MeV) ΔL = 0 ( g / g ) 0.5 A s s /3/2 20 W W 2 ( g1101 / g1000) 1.25 from β - decay H( Li, Be)

21 ΔS=0 and ΔS=1 strength distributions in He 1500 He( 7 Li, 7 Be) E L =55 MeV, θ L < 1 deg SDR singles ΔS=0 ΔS=1 GDR EXCITATION ENERGY in He (MeV) 2007/3/2 21

22 Giant Dipole Resonance in He (γ,p) - There is no excited state upto E x =20 MeV in He. - Strongly suppressed GT - Dominant dipole excitation (γ,n) - But, GDR shape is not still settled. -The ( 7 Li, 7 Be) may provide relative distribution of GDR. J.R. Calarco, B.L. Berman, T.W. Donnelly Phys. Rev. C27, 1866 (1983) - Huge abundance of He He, 12 C(γ,γ α), 16 O(γ,γ α), - He may play an important role In ν-heating during SN explosion. - How does the GDR of He distribute? 2007/3/2 22

23 Interaction of GDR/SDR excitation 1.GDR E1γ-excitation: V = 3 [ 1 ] 1 g E 1011 τ iry CEX E1 -excitation: V [ ] 1 s = g 1011 τ + iry 1 1- / 0-,1-,2-1- H ΔL=1 V τ,v στ ( 7 Li, 7 Be) 2.SDR s CEX M2 -excitation: V = g101 Jτ + [ iry1 σ ] J = 0,1, 2 SDR strength distribution ν heating in SN? V τ He γ /3/2 23 C.Gaarde, et al., Nucl. Phys. A22, 189 (198)

24 σ γ (GDR) from E1γ strength E1 γ width [=Γ γ (E1)] is described in terms of B(E1) For a discrete transition: 16π 3 Γγ (E1) = D B(E1) 9 where D = hc/ Eγ, E Application to a continuum transition: One replaces B(E1) into db(e1)/de γ + 16π 3 Γγ ( Eγ, 0 1 ) = D 9 Here the cross section σ is defined with Γ γ as follows 1- H ΔL=1 V τ ( 7 Li, 7 Be) 1- V τ He 0+ γ σ( E Finally one gets = hω K τ is determined by normalizing σ(δs=0) to the σ γ data around E x =0 MeV. 2007/3/2 2 γ, ) = π D 2 γ =.0 E γ γ Γ ( E db(e1) de γ, 0 γ db(e1) de γ + 1 )

25 σ E ΔS=0 spectrum and σ γ in He 2 d σ 1 ( E, γ ) =.0Kτ Eγ ( ΔS = 0, ΔL = 1), K = dedω τ Gazit et al., PRL96, (2006) FSI via LIT method with AV18(NN) FSI via LIT method with AV18(NN)+UIX(3NF) Present work Shima et al., PRC72,000 (2005) EXCITATION ENERGY in He (MeV) Nilsson et al., PLB626,65(2005) σ(γ,n) x2 Wells et al., PRC6, 9 (1992) Calarco et al., PRC27,1866 (1983) σ(γ,p)+σ(γ,n) 2007/3/2 25

26 Summary Neutrino-heating for He during SN explosion SDR in He has a shape peak around at Ex=2 MeV. For ν-heating in SN, is the SDR more important than GDR? CE reaction for self-conjugate nuclei is feasible to deduce the σ γ as a function of excitation energy. σ ( 7 Li, 7 Be) σ γ CE spectrum Excitation function of γ-energy Application to deduce σ γ to E1 excitations Resonance shape for the GDR in He has a pronounced peak around Ex=27 MeV 2007/3/2 26

27 Collaboration for E263 University of Tokushima S. Nakayama, E. Matsumoto, R. Hayami, K. Fushimi, H. Kawasuso, K. Yasuda Konan University T. Yamagata, H. Akimune, H. Ikemizu RCNP, Osaka University M. Fujiwara, M. Yosoi, K. Kawase, K. Nakanishi, H. Hashimoto, T Oota Kyushu University K. Sagara, T. Kudou, S. Asaji, T. Ishida Kobe Tokiwa Jr. College M. Tanaka ICU M.B. Greenfield 2007/3/2 27

28 Calculations for σ γ (γ,n) (γ,p) (γ,total) Quaglioni et al., PRC69, 0002 (200) LIT method with MTI-III including full FSI Gazit et al., PRL96, (2006) LIT method with MTI-III including full FSI 2007/3/2 28