First Gamma-Ray Spectroscopy of sd -shell Hypernucleus, 21 st , - - PowerPoint PPT Presentation

First Gamma-Ray Spectroscopy of sd-shell Hypernucleus, 𝚳

𝟐𝟘𝐆

YANG Seongbae

Department of Physics and Astronomy Seoul National University

21st, November, 2016

• Neutron Star Matter 2016-

1

• 1. Introduction

2

Previous Gamm-ray Spectroscopies

■ Previous γ-ray spectroscopies for s-shell hypernuclei

• 1. Introdu
• duction

tion

3

Λ 4H

@PLB, 83, 252 (1979)

Λ 4He Λ 4He

@PRL, 115, 222501 (2015)

*NaI detector *Ge detector

4

@NPA, 835, 3 (2010)

 The next step is awaited for heavier hypernuclei.

• 1. Introdu
• duction

tion

■ Previous γ-ray spectroscopies for p-shell hypernuclei (Hyperball project)

Gamma-ray Spectroscopy of 𝚳

𝟐𝟘𝐆

■ 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 ΛN spin-spin interaction?  ΛN spin-dependent interaction with different wave-function? low-lying energy levels of Λ

19F

*A. Umeya and T. Motoba NPA 116, 122501 (2016). 5

Spin-spin interaction

16O

n p Λ + Λ

• 1. Introdu
• duction

tion

Λ 4H Λ 7Li Λ 19F

Four-body Cluster model Wave- function

𝒕𝑶𝒕𝜧 𝒒𝑶𝒕𝜧 (𝒕𝒆)𝑶𝒕𝜧

N, RMS

radius [fm]

2.5 (0𝑡) 3.0 (0𝑞1/2) 2.9 (0𝑞3/2) 3.4 (1𝑡1/2) 3.5 (0𝑞1/2) 3.3 (0𝑒5/2)

Λ, RMS radius [fm]

3.5 (0𝑡) 2.6 (0𝑡) 2.3 (0𝑡) ∆𝐹𝑦 (ground state doublet) 1.1 MeV 0.695 MeV (Δ𝑞𝑂𝑇Λ=0.43 MeV)

?

6

n n p Λ +

4He

n p Λ +

16O

n p Λ +

@by Millener, private communication @by Millener, private communication

• 1. Introdu
• duction

tion

• 2. Experimental Setup

7

Experimental Setup of J-PARC E13

■ Reaction: 19F(𝐿−, 𝜌−) Λ

19F

■ 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)

8

Target:

• Liquid. H2
• Liquid. CF4
• 2. Experi

rime mental tal Setup

■ Hyperball-J

 19F(𝐿−, 𝜌−) Λ

19F ∗, Λ 19F ∗ → 𝛿 + Λ 19F

 ~25 HPGe detectors - ∆E ~4.5 keV @ 1MeV  PWO counters - Fast background suppression

9

@NPA, 835, 3 (2012) *a view of K1.8 experimental hall

Mechanical cooling system Crystal temp. ~70 K

• 2. Experi

rime mental tal Setup

Data Sample for 𝚳

𝟐𝟘𝐆

■ 05.2015~06.2015 at the J-PARC K1.8 Beamline Data Target (Thickness [g/cm2]) Momentum [GeV/c] Number of K Beam through . 1.37, 1.5, and 1.8 . Σ+ and Λ

12C

CH2 (6.6) 1.8 0.6 G

Λ 19F

CF2 (6.6) 1.8 2.3 G Physics Run

• Liquid. CF4 (20)

1.8 63 G

10

• 2. Experi

rime mental tal Setup

• 3. Analysis

11

Vertex Point (z-direction) and Reaction Angle

■ CF4 target during physics run

• 3. Analysi

ysis (K, pi)

*CF4 target real length: 125 mm Reaction angle: 2~12 deg. vertex (z) cut

12

Particle Identification for 𝑳− and 𝝆−

M2 distribution of scattered particle ■ At trigger line, K− and π− are identified by using AC counters. In addition, M2 is used for identification of π−.

• 3. Analysi

ysis (K, pi)

13

Calibration run with CH2 target (6.6 g/cm2)

 Absolute scale of missing mass: −0.7

+0.7 MeV level.

 Expected missing mass resolution (FWHM) with CF4 target: 8.7±0.4 MeV

• 3. Analysi

ysis (K, pi)

MPV: 1.1901±0.0004±0.0001 GeV/𝑑2 FWHM: 0.0060±0.0001±0.0002 GeV/𝑑2

Σ+ g.s. of Λ

12C

MPV: -11.06±0.18±0.21 MeV FWHM: 6.04±0.47±0.40 MeV

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*2<θ<12 *2<θ<12

1H(𝐿−, 𝜌−)Σ+ 12C(𝐿−, 𝜌−) Λ 12C

■ By using γ rays from normal nuclei, energy resolution (FWHM) and accuracy

• f absolute energy level are estimated.
• 3. Analysi

sis (γ ray)

Analysis for γ rays

 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

Energy Calibration Energy Resolution

• 4. Results

16

• B𝚳 Distribution of 𝚳

𝟐𝟘𝐆 with CF4 target (20 g/cm2)

■ -21 MeV<-BΛ<-8 MeV is selected to observe the γ rays from low lying energy states.

17

Threshold of Λ

15N + α

g.s. of Λ

12C

For γ rays from 𝚳

𝟐𝟘𝐆

• 4. Results

lts

γ-ray spectra

■ γ-ray spectra: energy range: 0~1800 keV and without Doppler shift correction.

18

There are two more peaks.

• 4. Results

lts

γ(315) and γ(895)

Energy: 315.5 ±0.4−0.5

+0.6 keV

19

Energy: 895.2 ±0.3−0.5

+0.6 keV

γ(315) γ(895)

• 4. Results

lts

20

■ At the forward reaction angle, we found two more gamma-ray peaks at 953 keV and 1267 keV.  The energy difference is consistent with the γ(315) energy. ~313 keV

γ(953)  E: 952.8 ±1.2−0.6

+0.5 keV

γ(1267)  E: 1265.9 ± 1.2 ± 0.7 keV

• 4. Results

lts

• 5. Discussion

21

Transition Assignments

22

γ(895) γ(1267) γ(952) γ(315) ■ Based on theoretical calculations, the gamma rays are assigned to their gamma transitions.

• 5. Discus

ussion sion

Spin-Spin Interaction in sd-shell Hypernuclei

 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

Theoretical Calculation Experiment Shell-model with NSC97f model by Umeya and Motoba Shell-model with ΛN spin- dependent interaction at p- shell hypernuclei by Millener Δ𝐹(3/2+, 1/2+) [keV] 315.5 ±0.4−0.2

+0.3

419 305

• 5. Discus

ussion sion

• 6. Summary

24

• 6. Summar

ary

Summary

■ A new 𝛿-ray spectroscopy of sd-shell hypernucleus ( Λ

19F) via the

(𝛬−, 𝜌−) reaction with 1.8 GeV/𝑑 beam was performed at the J-PARC K1.8 beamline. ■ Several 𝛿 rays from

Λ 19F are observed. The Λ 19F(315), Λ 19F(895), Λ 19F

(953), and

Λ 19F(1267) are assigned to the M1(3/2+ → 1/2+), E2(5/2+ →

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

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 *Back Up Up

27

@PTEP , 2012, 02B009

Proton Beam Secondary Beam

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

Energy calibration

Fit by 1st polynomial Off-beam calibration: Three γ ray from 238Th source

* Back up up

28

Fit by 1st polynomial In-beam calibration: 10 γ rays from normal nuclei Fit by 1st polynomial +Exponential functions

* Back up up

29

*Back up up *Background from Λ

12C is estimated using calibration data with CH2 target.

• B𝚳 Distribution of 𝚳

𝟐𝟘𝐆 with CF2 Target (6.6 g/cm2)

Structure of

Λ 19F

30

*Reaction angle, 2<θ<12