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Energy distribution of decay alpha particles

● “εi” : Highest normalized energy among three decay-α particles

M.I et al, Phys. Rev. Lett. 113, 102501 (2014)

Hoyle

8Be

α

εi ~ 0.506

Sequential Decay

SD

DDEDDΦ

Direct Decay?

Normalized energy distribution for the highest energy α particles

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12C(α,α'3α) experiment in India

● The non-zero direct components of the decay from the Hoyle state have been reported using the 12C(α,α'3α) reaction.T.K .Rana et a l,PRC88,021601(R)(2013)

0.91(14) %

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● The 10C+ C(Be) experimentThey obtained the upper limit of 3.9% for the direct 3α decay from the Hoyle state.J.Manfredi et al,PRC85,037603(2012).

● The 11B(3He,d3α) experimentThey improved the upper limit of the direct 3α decay to be 5 x10-3.O.S.Kirsebom et al,PRL108,202501(2012).

Recent experiments

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Experimental situation on the direct 3α decay

● Experiment of the 12C(12C,3α)12C reactionM.Freer et al, PRC49(1994)R1751

– Upper limits of 4% for the contribution of the direct decay process to Γα

● In 2011, the direct decay branch of 17±5% had been reported by Catania group. Among them, the direct decay with three α particles of equal energies was 7.5±4.0%.Ad.R.Raduta et al,PLB705(2011)65.

Evidence for α condensation of the Hoyle state??

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Algebraic Cluster Model in 12C

● Hoyle state: the A symmetric stretching vibration ( breathing mode) of the triangular configuration

D.J.Marín-Lámbarri et al, Phys.Rev.Lett.113, 012502 (2014)

12C(4He,α)4He experiment at Birmingham

they found 5- state at 22.4 MeV

R.Bijker and F.Iachello, PRC61(2000)067305

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Structure of the Hoyle state

● Root mean square radius

A

B

C

2.5fm

2.2fm

3.3fm

4.2fm

5.3fm

1.9fm

Rrms

~ 3.43 fm

B=C

10%

20%

10%

S.Ishikawa, Phys.Rev.C90, 061604(R)(2014)

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Misassignment of decay alpha particles

Why do the shoulders appear? … Misassignment of decay alpha particles

EX1

≈ EY1

→ α1 (X1,Y1)

Eα1

≈ Eα2

α1(X1,Y2), α2(X2,Y1)

α1(X2,Y1), α2(X1,Y2)

Misassignment

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Energy spectrum for the decay 3α particles

Einv

= Erecoil12C

+ Eα1

+ Eα2

+ Eα3

Total 3α energy spectrum in the 12C* rest frame

Invariant Mass spectrum

~103 MeV

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Accidental coincidence

● There was no accidental 3α coincidence.

Recoil 12C + 1-α Recoil 12C + 3-α

TDC TDC

accidental coincidence true coincidence

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Kinematics and Recoil 12C spectrum

● Particle Identification:TOF method

● Excitation energy is determined from the energy of the recoil 12C.

TOF spectrum of SD12C α

p

d

12C(2+)+12C(2+)12C(02+)

12C(2+)

3α coincidence

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Decay and structure of Hoyle state

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Structure of the Hoyle state 1

● Density distribution

A

B

C

2.5fm

2.2fm

3.3fm

4.2fm

5.3fm

1.9fmS.Ishikawa, Phys.Rev.C90, 061604(R)(2014)