First Gamma-Ray Spectroscopy of sd -shell Hypernucleus, 𝚳 𝟐𝟘 𝐆 21 st , November, 2016 -Neutron Star Matter 2016- YANG Seongbae Department of Physics and Astronomy Seoul National University 1
1. Introduction 2
1. Introdu oduction tion Previous Gamm-ray Spectroscopies ■ Previous γ -ray spectroscopies for s- shell hypernuclei *NaI detector 4 H *Ge detector Λ 4 He 4 He Λ Λ @PRL, 115, 222501 (2015) @PLB, 83, 252 (1979) 3
1. Introdu oduction tion ■ Previous γ -ray spectroscopies for p- shell hypernuclei (Hyperball project) @NPA, 835, 3 (2010) The next step is awaited for heavier hypernuclei. 4
1. Introdu oduction tion Gamma-ray Spectroscopy of 𝚳 𝟐𝟘 𝐆 ■ It is the first γ -ray spectroscopy for sd -shell hypernuclei. ■ Energy spacing of ground state doublet (1/2 + , 3/2 + ) Radial dependency of the Λ N spin-spin interaction? Λ N spin-dependent interaction with different wave-function? Λ p + 16 O Spin-spin interaction n Λ low-lying energy levels of Λ 19 F *A. Umeya and T. Motoba NPA 116, 122501 (2016). 5
1. Introdu oduction tion 4 H 7 Li 19 F Λ Λ Λ Four-body p p p + Λ + Λ n + Λ 4 He 16 O Cluster n n n model Wave- 𝒕 𝑶 𝒕 𝜧 𝒒 𝑶 𝒕 𝜧 (𝒕𝒆) 𝑶 𝒕 𝜧 function 3.4 ( 1𝑡 1/2 ) 3.0 ( 0𝑞 1/2 ) N, RMS 3.5 ( 0𝑞 1/2 ) 2.5 ( 0𝑡 ) 2.9 ( 0𝑞 3/2 ) radius [fm] 3.3 ( 0𝑒 5/2 ) @by Millener, private communication Λ , RMS 3.5 ( 0𝑡 ) 2.6 ( 0𝑡 ) 2.3 ( 0𝑡 ) radius [fm] @by Millener, private communication ? ∆𝐹 𝑦 0.695 MeV (ground 1.1 MeV ( Δ 𝑞 𝑂 𝑇 Λ =0.43 MeV) state doublet) 6
2. Experimental Setup 7
2. Experi rime mental tal Setup Experimental Setup of J-PARC E13 ■ Reaction: 19 F(𝐿 − , 𝜌 − ) Λ 19 F ■ K1.8 Beamline : High intensity and high purity 𝐿 − beam Intensity of 𝐿 − beam: ~350 k/spill 𝐿 − / 𝜌 − = ~2.5 1.8 GeV/c beam momentum ■ SKS & K1.8 Beamline Spectrometers High resolution of missing mass Large acceptance for (𝐿 − , 𝜌 − ) good beam decay suppressor (SP0, SMF) Target: Liquid. H 2 Liquid. CF 4 8
2. Experi rime mental tal Setup ■ Hyperball-J 19 F ∗ → 𝛿 + 19 F ∗ , Λ 19 F(𝐿 − , 𝜌 − ) Λ 19 F Λ ~25 HPGe detectors - ∆E ~4.5 keV @ 1MeV PWO counters - Fast background suppression Mechanical cooling system Crystal temp. ~70 K *a view of K1.8 experimental hall @NPA, 835, 3 (2012) 9
2. Experi rime mental tal Setup Data Sample for 𝚳 𝟐𝟘 𝐆 ■ 05.2015~06.2015 at the J-PARC K1.8 Beamline Target Momentum Data Number of K (Thickness [g/cm 2 ]) [GeV/c] Beam 1.37, 1.5, . . through and 1.8 Σ + and Λ CH 2 (6.6) 1.8 0.6 G 12 C CF 2 (6.6) 1.8 2.3 G 19 F Λ Physics Run Liquid. CF 4 (20) 1.8 63 G 10
3. Analysis 11
3. Analysi ysis (K, pi) Vertex Point (z-direction) and Reaction Angle ■ CF 4 target during physics run vertex (z) cut Reaction angle: 2~12 deg. *CF 4 target real length: 125 mm 12
3. Analysi ysis (K, pi) Particle Identification for 𝑳 − and 𝝆 − ■ At trigger line, K − and π − are identified by using AC counters. In addition, M 2 is used for identification of π − . M 2 distribution of scattered particle 13
3. Analysi ysis (K, pi) Calibration run with CH 2 target (6.6 g/cm 2 ) 1 H(𝐿 − , 𝜌 − )Σ + 12 C(𝐿 − , 𝜌 − ) Λ 12 C *2< θ <12 *2< θ <12 Σ + g.s. of Λ 12 C MPV: 1.1901 ± 0.0004 ± 0.0001 GeV/𝑑 2 MPV: -11.06 ± 0.18 ± 0.21 MeV FWHM: 0.0060 ± 0.0001 ± 0.0002 GeV/𝑑 2 FWHM: 6.04 ± 0.47 ± 0.40 MeV +0.7 MeV level. Absolute scale of missing mass: −0.7 Expected missing mass resolution (FWHM) with CF 4 target: 8.7 ± 0.4 MeV 14
3. Analysi sis ( γ ray ) Analysis for γ rays ■ By using γ rays from normal nuclei, energy resolution (FWHM) and accuracy of absolute energy level are estimated. Energy Resolution Energy Calibration Energy Resolution: ~4.5 keV @1.0 MeV (the sum of all germaniums) γ rays were measured under ~0.5 keV accuracy level at E < 3 MeV. 15
4. Results 16
4. Results lts - B 𝚳 Distribution of 𝚳 𝟐𝟘 𝐆 with CF 4 target (20 g/cm 2 ) ■ -21 MeV<- B Λ <-8 MeV is selected to observe the γ rays from low lying energy states. Threshold of Λ 15 N + α g.s. of Λ 12 C For γ rays from 𝚳 𝟐𝟘 𝐆 17
4. Results lts γ -ray spectra ■ γ -ray spectra: energy range: 0~1800 keV and without Doppler shift correction. There are two more peaks. 18
4. Results lts γ (315) and γ (895) γ (315) γ (895) +0.6 keV +0.6 keV Energy: 315.5 ±0.4 −0.5 Energy: 895.2 ±0.3 −0.5 19
4. Results lts ■ At the forward reaction angle, we found two more gamma-ray peaks at 953 keV and 1267 keV. γ (953) +0.5 keV E: 952.8 ±1.2 −0.6 ~313 keV γ (1267) E: 1265.9 ± 1.2 ± 0.7 keV The energy difference is consistent with the γ (315) energy. 20
5. Discussion 21
5. Discus ussion sion Transition Assignments ■ Based on theoretical calculations, the gamma rays are assigned to their gamma transitions. γ (952) γ (1267) γ (895) γ (315) 22
5. Discus ussion sion Spin-Spin Interaction in sd -shell Hypernuclei Shell-model Shell-model with Λ N spin- Theoretical with NSC97f model dependent Experiment Calculation by Umeya and interaction at p - Motoba shell hypernuclei by Millener Δ𝐹 ( 3/2 + , 1/2 + ) 419 305 +0.3 315.5 ±0.4 −0.2 [keV] The measured energy spacing is well represented by the spin-dependent interaction in p -shell hypernuclei. It also indicates the ΛΣ coupling effect is negligible for the energy spacing. The results will be soon published in a major physics journal. 23
6. Summary 24
6. Summar ary Summary ■ A new 𝛿 -ray spectroscopy of sd-shell hypernucleus ( Λ 19 F ) via the (𝛬 − , 𝜌 − ) reaction with 1.8 GeV/𝑑 beam was performed at the J-PARC K1.8 beamline. ■ Several 𝛿 rays from 19 F are observed. The 19 F (315), 19 F (895), 19 F Λ Λ Λ Λ 19 F (1267) are assigned to the M1(3/2 + → 1/2 + ) , E2(5/2 + → (953), and Λ 1/2 + ) , E1(1/2 − → 3/2 + ) , and E1(1/2 − → 1/2 + ) transitions, respectively. ■ The measured energy spacing (315 keV) between the ground state doublet is well represented by the spin-dependent interaction at p- shell hypernuclei. ■ It is meaningful to extend the 𝛿 -ray spectroscopy to medium hypernuclei, and it will be a guide for future experiments. 25
*Back Up 26
*Back Up Up K1.8 Beamline ■ K1.8 Beamline : High intensity and high purity 𝐿 − beam Intensity of 𝐿 − beam: ~350 k/spill 𝐿 − / 𝜌 − = ~2.5 *J-PARC Hadron facility Secondary Beam Proton Beam 27 @PTEP , 2012, 02B009
* Back up up Energy calibration Energy of γ ray is calibrated through two steps. 1. Off-beam calibration: spill-off condition for each runs 2. In-beam calibration: spill-on condition Off-beam calibration: Three γ ray from 238 Th source Fit by 1 st polynomial 28
* Back up up In-beam calibration: 10 γ rays from normal nuclei Fit by 1 st polynomial Fit by 1 st polynomial +Exponential functions 29
*Back up up - B 𝚳 Distribution of 𝚳 𝟐𝟘 𝐆 with CF 2 Target (6.6 g/cm 2 ) *Reaction angle, 2< θ <12 Structure of 19 F Λ *Background from Λ 12 C is estimated using calibration data with CH 2 target. 30
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