Isovector channel (T=1)

Study of precursor phenomena of pionic condensation
via parity conversion nuclear reaction on 40Ca
Masaki Sasano

Pion condensation


Physics of nuclear matter



Equation of state
Exotic structure (ex. Alternating layer spin, T. Takatsuka et al., Prog.
Theo. Phys. 59 (1978) 1933.
Astrophysics


Phase transition above n~2n0
A. B. Migdal, Zh. Eksp. Teor. Fiz. 61 (1971) 2210
Pion condensation in neutron star
⇒ stronger neutrion emission
⇒ resolve the probem of
surface temprature of neutron star
At n~n0,
Precursor phenomena : pionic enhancement
⇒ Jπ=0－, T=1 (same as π)
Measurements of 0- in 40Ca by
Parity conversion nuclear reaction

Parity conversion nuclear reaction
0+; g.s.→0－; 6.9 MeV
 16O; 0+; g.s.→0－; 11.0 MeV
 18O;

Experimental method
 16,18O
@ 300MeV/n
(primary beam, 100 pnA)
DALI2
 SHARAQ, DALI2
target
γ
NaI
SHARAQ
パリティ反転核反応プローブ
パリティ反転プローブ
従来の核反応プローブ: (p,p’)反応
Jt ＝ΔL±1, ΔL
Parity: (－)ΔL
Lt＝ΔL
0+, 1+
(ΔL=0）
Jt ＝ΔL
Parity: (－)ΔL+1
Lt＝ΔL+1
ΔL
ΔL
0+
Jp=1/2
プローブ粒子
0－
(ΔL=0）
0－
0+
0+
プローブ粒子
標的粒子
• プローブ粒子の内部構造を無視
• プローブ側が励起しない
標的粒子
• プローブ粒子が複合核
• プローブ側が励起：パリティのみ変化
16,18O核によるパリティ反転核反応
Isoscalar channel (T=0)
Isovector channel (T=1)
18O
16O
(T=1)
6.9 MeV；0－
(T=0)
11.0 MeV；0－
ガンマ線脱励起
2.4 MeV⇒検出
4.5 MeV；1－
一段階非弾性散乱
0+; g.s.
→0-; 6.9 MeV
g.s. 0+
ガンマ線脱励起
3.8 MeV⇒検出
7.2 MeV；1－
一段階非弾性散乱
0+; g.s.
→0-; 11.0 MeV
g.s. 0+
Isovector channel は実際には純粋なT=1ではなく、isoscalar 成分（T=0)も
少量ながら混ざっている。両チャンネルを測定することで純粋なisovector成分を導出。
パリティ反転核反応のスペクトル
散乱角度分布
従来のプローブ
(p,p’) : 0－, 1－, 2－状態が混じる
⇒ 角度による分離が不可能
パリティ反転核反応： 0－のみ0度ピーク
⇒ 分離が容易
⇒ 標的：2重閉殻核(16O, 40Ca)
1+状態の0度への染み出し
を完全に除去可能。
パリティ反転核反応
16O標的
0度
最適入射エネルギーの選択
1. 多段階過程の効果を最小化
2. Isovector /Isoscalar (spin flip) を最大化
核子当たりの入射エネルギー300MeV
実験手法
1. ビーム(16O,18O)
•
入射エネルギー: 300A MeV
•
カレント: 10 pnA
•
分散整合
2. 標的: 40Ca: 10mg/cm2
3. 磁気分析器:
Spectroscopy with High-resolution
Analyzer and RadioActive Quantum
beams (SHARAQ)
標的
4. ガンマ線検出器系:
NaI検出器アレイ DALI2
検出効率1%、エネルギー分解能400 keV
γ
NaI
SHARAQ
統計量100events/day 16O(0－,T=1, 12.8MeV)、分解能 ~0.6MeV
パリティ反転核反応のスペクトル
散乱角度分布
従来のプローブ
(p,p’) : 0－, 1－, 2－状態が混じる
⇒ 角度による分離が不可能
パリティ反転核反応： 0－のみ0度ピーク
⇒ 分離が容易
パリティ反転核反応
Parity-conversion reaction
Existing nuclear probe: ex. (p,p’)
Parity-conversion reaction
Jt ＝ΔL±1, ΔL
Parity: (－)ΔL
Lt＝ΔL
0+, 1+
(ΔL=0）
Jt ＝ΔL
Parity: (－)ΔL+1
Lt＝ΔL+1
ΔL
ΔL
0+
Jp=1/2
probe
0－
(ΔL=0）
0－
0+
0+
probe
target
• no (negligible) internal structure
of probe particle
• Probe particle is not excited
target
• Probe has internal structures
• Probe can be excited
(parity conversion)
Precursor phenomena of pion
condensation
Pionic enhancement
Jπ=0－, T=1 (isovector) state, which has the same J, T, parity as pion,
is enhanced
Existing study：
16O(p,p’)16O(0-,T=1,12.8 MeV)
⇒ support precursor phenomena
• Limited to known low-lying discrete
states
• How about continuum?
T. Wakasa et al.,
PLB 632, 485 (2006).
18O
parity conversion reaction
Isovector channel (T=1)
18O
(T=1)
6.9 MeV；0－
Gamma ray
2.4 MeV⇒NaI
4.5 MeV；1－
One-step process
0+; g.s.
→0-; 6.9 MeV
g.s. 0+
Expected spectra for
parity-conversion reaction
Angular distribution
(p,p’) : 0－, 1－, 2－ are mixed
Parity-conversion：
only 0- has peak at 0 degrees
⇒ can be easily separated
⇒ target：double closed nuclei
(16O, 40Ca)
1+ states are
strongly suppressed.
16O標的
0度
Plan
of
Exp.
1. Beam ( O)
18
•
energy: 300A MeV
•
current: 10 pnA
•
Dispersion matching
2. Target : 16O, 40Ca: 10mg/cm2
3. Spectrometer:
Spectroscopy with High-resolution
Analyzer and RadioActive Quantum
beams (SHARAQ)
標的
4. Gamma-ray dector:
NaI detection array DALI2
eff. 1%、 resolution ~400 keV
γ
NaI
SHARAQ
statistics100events/day 16O(0－,T=1, 12.8MeV)、res. ~0.6MeV
Summary





Charge exchange reactions at intermediate energies are
a useful probe of spin-isospin responses.
The (p,n) reaction at 300 MeV is simplest probe for the
GT transition.
The GT unit cross sections has been successfully
determined at 200 & 300 MeV.
It is shown by using SM calc. & DWIA calc. that the GT
unit cross section works well.
B(GT) distrib. Have been deduced for double beta decay
nuclei using the above obtained GT unit cross sections.
Parity-conversion reaction
Parity-conversion reaction
Jt ＝ΔL
Parity: (－)ΔL+1
Lt＝ΔL+1
0－
(ΔL=0）
0－
ΔL
0+
0+
probe
target
• Probe has internal structures
• Probe can be excited
(parity conversion)
Precursor phenomena of pion
condensation
Pionic enhancement
Jπ=0－, T=1 (isovector) state, which has the same J, T, parity as pion,
is enhanced
Existing study：
16O(p,p’)16O(0-,T=1,12.8 MeV)
⇒ support precursor phenomena
• Limited to known low-lying discrete
states
• How about continuum?
T. Wakasa et al.,
PLB 632, 485 (2006).
18O
parity conversion reaction
Isovector channel (T=1)
18O
(T=1)
6.9 MeV；0－
Gamma ray
2.4 MeV⇒NaI
4.5 MeV；1－
One-step process
0+; g.s.
→0-; 6.9 MeV
g.s. 0+
Expected spectra for
parity-conversion reaction
Angular distribution
(p,p’) : 0－, 1－, 2－ are mixed
Parity-conversion：
only 0- has peak at 0 degrees
⇒ can be easily separated
⇒ target：double closed nuclei
(16O, 40Ca)
1+ states are
strongly suppressed.
16O標的
0度
Plan
of
Exp.
1. Beam ( O)
18
•
energy: 300A MeV
•
current: 10 pnA
•
Dispersion matching
2. Target : 16O, 40Ca: 10mg/cm2
3. Spectrometer:
Spectroscopy with High-resolution
Analyzer and RadioActive Quantum
beams (SHARAQ)
標的
4. Gamma-ray dector:
NaI detection array DALI2
eff. 1%、 resolution ~400 keV
γ
NaI
SHARAQ
statistics100events/day 16O(0－,T=1, 12.8MeV)、res. ~0.6MeV
Summary





Charge exchange reactions at intermediate energies are
a useful probe of spin-isospin responses.
The (p,n) reaction at 300 MeV is simplest probe for the
GT transition.
The GT unit cross sections has been successfully
determined at 200 & 300 MeV.
It is shown by using SM calc. & DWIA calc. that the GT
unit cross section works well.
B(GT) distrib. Have been deduced for double beta decay
nuclei using the above obtained GT unit cross sections.

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