g rays from giant resonances of 12 C and 16 O Makoto Sakuda for C01 - PowerPoint PPT Presentation

Study of Gd(n, g ) reaction and g rays from giant resonances of 12 C and 16 O Makoto Sakuda for C01 Efforts (Okayama) @ “Revealing the History of the Universe with Underground Particle and Nuclear Research 2019”, Tohoku, 2019.03.09 Outline: 1. g -ray spectrum of Gd(n, g ) and ANNRI-Gd model for SK-Gd project 2. g rays from giant resonances of 12 C and 16 O 3. Evaluation of O,C( n , n ’ g ) events for SN neutrinos (10kpc) 4. Summary

Giant Resonances (GR) and g rays from resonances 158,156 Gd, 12 C and 16 O. 160 Gd 160 Gd resonance seen  (~ 158 Gd) in photo-absorption=Photon Strength Function f(E g ) (PSF). - We study 157 Gd(n, g ) 158 Gd and g rays from 158 Gd. 12 C and 16 O GR  in (p,p ’) reaction

1. Study of g rays from 157,155,nat Gd(n, g ) reaction and MC (ANNRI-Gd) Model for SK-Gd project  We performed a series of measurements of Gd(n, g ) reactions using high intensity pulsed neutron beam and ANNRI Germanium spectrometer. 1. g -ray spectrum from thermal neutron capture on 157 Gd, K. Hagiwara, T. Yano, T. Tanaka, M.S. Reen, P.K. Das, S. Lorenz, I. Ou, T. Sudo, Y. Yamada, T. Mori, T. Kayano, R. Dhir, Y. Koshio, M. Sakuda, A. Kimura, S. Nakamura, N. Iwamoto, H. Harada, M. Wurm, W. Focillon, M. Gonin, A. Ali and G. Collazuol (ANNRI-Gd), PTEP 2019, 023D01 (29pages). 2. g -ray spectrum from 155, nat Gd(n, g ), A.Ali et al. (ANNRI-Gd), PoS (ICHEP2018) 120 (4 pages), in preparation for PTEP. 3. 2 g angular correlations in 155, 157 Gd(n, g ) reaction b -version of MC (ANNRI-Gd) model is already being used in SK-Gd,  XENONnT and NEOS (IBS, Korea).

1. Feature of g -ray spectrum from 157,155 Gd(n, g ) - ~4 g rays/event (E tot =8MeV)-  Probability Distribution from E x  E a = E x – E g  Fermi Golden Rule: Probability=|Amptilude| 2 *(Number of States) 3 favors Large E g , f(E g ) favors Large E g , But r (E a ) favors Very Small E g .  E g 2 - E x x r (E a ) E a 0 +

1-1) 157,155 Gd(n, g ) E g spectrum (Data) and MC(ANNRI-Gd model), Tested for multiplicity=1,2,3,4. 157 Gd(n, g ) E g (single) spectrum 155 Gd(n, g ) E g spectrum  157 Gd(n, g ) Multiplicity=2,3,4 E g spectrum   Data and MC in reasonable agreement.

1-2) g-g angular correlation W(z) in 157,155 Gd(n, g ) (p6  The definition of angular correlation W(z) for z=cos q =[-1,1].  Select 2 g- ray dataset (E 1 and E 2 ) and make z distribution.

1-2) Angular correlation W(z) of 2 g rays in cascade (J A  J B  J C ), z=cos q (skip-7)  For the angular momentum (j,m) of g 1 in z-direction, only L=0 and m=+1 and -1 are allowed. Thus, the weight p(M) on M of (J,M) for g 2 is restricted. Then, W(z) is not uniform.  BUT, If p(M)=1 for all M, W(z)=uniform, because

Angular correlation of 2 g rays for 157 Gd(n, g ) (specially chosen) cascades  We observe the expected angular correlations for 2 -  2 +  0 + and 2 -  2 +  2 + cascade transitions.

No angular correlations of 2 g rays from continuum (bulk) of 157,155 Gd(n, g )  We observe no correlations for bulk of 2 g rays from continuum.

2. RCNP E398 12 C, 16 O( p,p’ g ) -Study of g emission rate R g (E x ) from Giant Resonance- (10) 12 C and 16 O are being used as a target material in large scale  neutrino experiments, since they are abundant (cheap). [Nulcear Physics] No systematic measurements of g rays from giant  resonance region (E x =16-35MeV). (1) Hadronic decay (2) Electromagnetic decay [Supernova Detection] Neutral-Current g production cross sections n - 12 C/ 16 O  may be significant, next to dominant inverse b -decay cross section. + + → p p ’ C C* E x 11 B* (1) p (2) 𝛿 0 𝛿 S p 11 B 12 C

2-1) E398 Experiment at RCNP(Osaka) - Magnetic Spectrometer (E x ) and NaI array (E) – Target Focal plane • Excitation energy E x =E p -E p’ detectors NaI Array • ∆ E x = 100-200 keV • 𝜄 scat = 0 o (covers 0 o ~ 3 o ) 392 MeV 25cm 25cm

RCNP Magnetic Spectrometer “Grand Raiden” - E x = 392MeV - E p’ , D E x =100keV - Grand Raiden Spectrometer (E p’ ) Target Focal Plane (E p =392MeV) 12

g ray detector(NaI) →γ 線が検出器内でのエネルギー損失を最終的に電気信号に変え測定 13

Analysis Method: E x and E (NaI) For each event, we measure: (1) E x (Excitation energy) (2) E ( g -ray energy deposited in NaI detectors) E =11 MeV 40. • E x > 16 MeV:Giant resonance Region 1 Region 2 30. • Region 1 : Hadronic Decays E x = E E x (MeV) • Region 2 : Electromagnetic 20. Decays E x =16 MeV B.G. S p 10. . 0 0 10.0 20.0 30.0 40.0 1 E (MeV) 1

[Region 1] g rays from hadronic decays (16)  g -rays are emitted from the excited states of 11 B and 11 C after hadronic decay. As E x increases, R g increases. For E x >27MeV, GR cross section becomes small and R g decreases. S p ~11MeV=max E g p n 2.0 4.0 6.0 8.0 10.0 2.0 4.0 6.0 8.0 10.0 E (MeV) 1

g -ray emission rate R γ (E x ) from hadronic decay - R g ~45% ( 12 C) and 60% ( 16 O) at max. - Data （ ---) are lower by 20-30% than the simple transmission  calculations using optical potential （ --- ） . 12 C 16 O 0.8 𝛿 -ray emission probability ( R 𝛿 ) 0.6 0.4 0.2 QE Contribution 0 16 18 20 22 24 26 28 30 32 E x (MeV)

(Region 2): Search for Electromagnetic decays -Make E x -E plot - E =11 MeV 40. • E x > 16 MeV:Giant resonance Region 1 Region 2 30. • Region 1 : Hadronic Decays E x = E E x (MeV) • Region 2 : Electromagnetic 20. Decays E x =16 MeV B.G. S p 10. . 0 0 10.0 20.0 30.0 40.0 1 E (MeV) 1

[Region 2] g rays from Direct Electromagnetic Decay (p19 We are beginning to observe the high energy g rays (E=11-33MeV) from  direct electromagnetic decay at R γ0 =(0.37 ± 0.04 ± 0.04)%. To establish the result, we must work on the systematic errors. R 𝜹𝒑 (E x ) x 10 -2 True Events 0.6 MC prediction(Scaled) 0.5 400 16< E x <33 MeV 350 Signal E 𝜹 >11 MeV 0.4 Events/2 MeV 300 250 0.3 200 Background 0.2 150 100 0.1 50 0 0.0 0. - - - - 40000 30000 20000 10000 0 10000 20000 16 18 20 22 24 26 28 30 32 E x -E 𝛿 (keV) 18 E x (MeV)

Interpretation of Direct EM decay ( 12 C and 208 Pb) in terms of E1 transition Calculation using ( g ,total) 𝛿 -ray emission probability ( R 𝛿0 ) 0.6 (Shape only) J 𝜌 = 1 - 12 C* 0.5 x 10 -2 E γ 0.4 E1 0.3 J 𝜌 = 0 + 12 C (g.s.) 0.2 0.1 3 𝐶 𝐹1 𝑆 𝛿0 ∝ Γ 𝛿0 ∝ 𝐹 𝛿0 0.0 16 18 20 22 24 26 28 30 32 𝐹 𝛿0 = Energy of emitted γ -ray E x (MeV) Comparison with 208 Pb x 10 -2 𝛿 -ray emission probability ( R 𝛿0 ) 2  Only one result on direct EM decay of 1.6 Data(Averaged) a heavy nucleus 208 Pb is reported. Calculations 1.2 Beene et al., Phys.Rev C 41, 920(1990). (normalized with carbon) 12 C rate is 5 times smaller, due to the  0.8 small B(E1) = coupling of the photon 0.4 to the giant resonance for 12 C w.r.t. 208 Pb. 0 12 C 208 Pb 1 2 19

3. Estimation of O,C( n , n ’ g ) events for SN (10kpc) (20)  SN n flux d F /dE n : we use MB/FD or Nakazato Flux  MB/FD T=3MeV ( n e ), 5 MeV ( n e ) and T=8MeV ( n m ,n t ).  Nakazato flux (Nakazato,Suzuki et al., ApJS.205,2(2013)).  Cross sections d s (E n )/dE x : we use 12 C [T.Yoshida et al., ApJ686,448(2008)] and 16 O[T.Suzuki et al. PRC98,034613(2018)]. Shell Model calculation.  The g -ray emission rate R g (E x ) : we use our own data.

SN rate evaluation: 12 C and 16 O targets Expected number of neutrino events from a core-collapse supernova at 10 kpc  to be detected at JUNO (20 kton). [Very preliminary] For NC events For CC events MB and FD, MB and FD, T = 8 MeV T = 5 MeV Expected number of neutrino events from a core-collapse supernova at 10 kpc  to be detected at Super-K (32.8kton). [Very preliminary] Charged-current scattering off 16 O nucleus as a detection channel for supernova  neutrinos, K.Nakazato, T.Suzuki, MS, PTEP 2018,123E02.

Summary (23) Measurement of g -ray spectrum from 157, 155, nat Gd(n, g ) and ANNRI-Gd Model  157 Gd(n, g ) data and model: PTEP2019,023D01.  155,nat Gd(n, g ) and 2 g correlation, papers in preparation.   Download Web Page in preparation. Measurement of g emission probabability R g (E x )= σ p,p′γ / σ p,p ′ from Giant  Resonance in 12 C, 16 O( p,p’ g ) reaction We measure R γ (E x ) = σ p,p′γ / σ p,p ′ for the first time for 12 C for E x = 16-32 MeV for the  hadronic decay mode. R γ (E x ) starts from zero at E x = 16 MeV and increases to R γ (E x )= 47.9 ± 0.5 ± 3.5% at E x =27 MeV and then decreases. The paper for 12 C( p,p’ g ) was submitted for publication. We are beginning to observe the high energy g rays (E=16-33MeV) from electromagnetic  decay with R γ (E x )=(0.37 ± 0.04 ± 0.04)%. To establish the result, we must work on the systematic errors. We have similar result on 16 O.  We use d F /dE n (Nakazato et al.)+d s /dE(T.Suzuki) ＋ R g (E x ) (our hadronic  decay rate) to evaluate NC g production rate from SN neutrinos. (Ongoing)

Future We hope to extend E398 experiment by replacing a NaI array by  Clover (Ge) Array (on-going at RCNP), and obtain a comprehensive understanding of both the hadronic and electromagnetic decay of 12 C and 16 O giant resonances. We can evaluate the NC g production rate for SN neutrinos very  precisely.