Study of Excited States of 12 C in Full Kinematics

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1 Study of Excited States of 12 C in Full Kinematics Martin Alcorta MAGISOL Collaboration Meeting CSIC Madrid January 18 th, 2007

2 OUTLINE Introduction Motivation Experiment How to populate excited states in 12 C Reaction at the CMAM Analysis How to reconstruct the energy in 12 C Identification of particles Results Decay mechanism of the resonances in 12 C Sequential/Direct Conclusions/Outlook

3 MOTIVATION Nuclear Astrophysics The triple-α process is crucial to overcome the mass gaps at A=5 and A=8. Above T 9 > 2 K, other excited states in 12C influence the reaction rate. Nuclear Structure Three body break-up Sequential Direct Cluster Model Exact calculations for A 12

4 The 3α process α+α 8 Be 8 Be+α 12 C+γ A+a Lbl.gov

5 Sequential vs. Direct Decay α α α 12 C* 8 Be + α α α α 12 C* 3α α α

6 Introduction Experiment How to populate excited states in 12 C Reaction at the CMAM Analysis Results Conclusions

7 How to populate excited states in 12 C Through β-decay 12 N or 12 B Through a reaction A+a C* B*+b MeV + 10 B 13 N * 17 μg/cm 2 (+3 μg/cm 2 ) 12 C * p 9 B * α

8 CMAM Universidad Autónoma de Madrid 3 He + 10 B p + 12 C* 3α Experimental Setup 2 telescopes DSSSD(60 μm)+1500 μm DSSSD(69 μm)+1500 μm+1000 μm Ω=1/9 th 4π ε 1p =11% ε 3p =0.1% April 2005

9 Introduction Experiment Analysis How to reconstruct the 12 C energy Particle Identification Results Conclusions

10 Identification of protons and alphas Plot of ΔE-E α p ΔE E Detector Thickness Max E p Max E α DSSSD ~60 μm ~2.4 MeV ~9.5 MeV Si-PAD ~1500 μm ~15 MeV ~50 MeV

11 Particle Identification ΔE-E plot α + 9 B*(g.s.) d + 11 C p + 12 C* Available energy p+ 12 C = 21.6 MeV Protons up to 19.9 MeV

12 Identification of excited states in 12 C We select the protons and calculate the excitation energy of 12 C Excitation Energy of 12 C (MeV) 3 He + 12 C p + 14 N * *

13 Detecting alpha particles in coincidence - multiplicity 1 1p - multiplicity 2 1p & 1α - multiplicity 3 1p & 2α - multiplicity 4 1p & 3α 12 C Excitation Energy (MeV)

14 Introduction Experiment Analysis Results Sequential/Direct 8 Be Energy Decay mechanism of the resonances in 12 C Conclusions

12 C * α 1 + 8 Be(2 + ) 8 Be(0 + ) E sum

15 How do we differentiate between break-up through the 8 Be (0 + ) and 8 Be (2 + )? 12 C * α Be(2 + ) 8 Be(0 + ) E sum =3/2*E MeV E 12C (MeV) E sum (α) (MeV) E i (α) (MeV)

16 Selection rules prohibit some decays through the 8 Be (0 + ) J 12C J 8Be < l < J 12C + J 8Be π( 12 C)=π 1 ( 8 Be)*π 2 (α)*(-1) l

17 Calculate the 8 Be energy using alpha pairs MeV 8 Be(g.s.) (0.09 MeV) 8 Be(2 + ) ( MeV) 8 Be Energy (MeV)

18 Separating events which decay via the 0 + state in 8 Be and the 2 + state in 8 Be

Separate the events which go through the 8 Be(2 + ) and 8 Be(0 + ) to obtain branching ratios 12 C * α 1 + 8 Be(2 + ) 8

19 Separate the events which go through the 8 Be(2 + ) and 8 Be(0 + ) to obtain branching ratios 12 C * α Be(2 + ) 8 Be(0 + ) -States which decay through the 2 + state - State which decay through the 0 + state Excitation Energy in 12 C (MeV)

20 Excitation Energy of 12 C (MeV) Determine the decay mechanism: Compare the energy distribution of the alphas with simulations based on the R-matrix formalism Some 12 C states of interest: MeV Sequential with interference MeV J π (2 - or 4 - )?

21 The 12.71(1 + ) MeV state in 12 C Candidate for direct decay (Korsheninnikov): Narrow width (Γ=18.1 ev) Forbidden 8 Be (0 + ) decay Q α =2.2 MeV and Γ=1.37 MeV for 8 Be (2+) decay Sequential decay with interference effects included (Balamuth): E α1 =1.52 MeV E α2 = E α3 = 1.58 MeV Balamuth PRC Korsheninnikov SJNP

22 Comparison of the MeV resonance to previous experimental results green: sequential red: seq. with interferences blue: direct Fynbo et al. PRL E i (α) MeV black: data (this work) red: seq. with interf.

23 13.35 MeV What is the J π Literature as 2 - New models 4 - Cluster Model (11.8 MeV) Data simulation with 2 - simulation with 4 - E R (MeV) E i (α) MeV MeV + E R =E 12C* Alvarez-Rodriguez in preparation

24 Conclusions We concentrated on the study of the excited states in 12 C*. We selected events of three alphas to study the decay mechanism through the 8 Be(gs) and the 8 Be(2 + ). The J π of several states have been confirmed and we tentatively determined the J π of the MeV state. The study of the 12.7 MeV state in 12 C gives us confidence to further study the decay mechanism of the 16.1 MeV state in 12 C Decay via 8 Be(4 + )? Direct/Sequential We determined branching ratios of decay through the 8 Be(gs) and 8 Be(2 + ).

25 April telescopes ISOLDE Si-ball Outlook MeV y 4.5 MeV ε 1p =18% ε 3p =0.5% ~30 hours 10 B ~40 min. 7 Li ε 1p =14% ε 3p =0.3% 10 B( 3 He,pααα) ~21 hours 10 B ~1.5 hours 7 Li 7 Li( 3 He,p) 9 Be* ~4 hours MeV ~2 hours MeV

26 Future Analysis Ab Initio calculations from Argonne is ongoing Dalitz plots to determine decay mechanism (direct/sequential) Astrophysical relevance: search to see if decay of e.g MeV state is through narrow 8 Be(0 + ) or its tail Take a more detailed look at 9 B* + α channel Get definitive results for branching ratios

27 Collaborators M. Alcorta 1, H.B. Jeppesen 1,2, M.J.G. Borge 1, H.O.U. Fynbo 3, G. Garcia 4, O. Kirsebom 3, M. Madurga 1, G. Nyman 5, D. Obradors 1,4, O. Tengblad 1 1 Inst. Estructura de la Materia, CSIC, Serrano 113bis, E28006 Madrid, Spain. 2 CERN, ISOLDE, PH Department, CH1211 Geneve 23, Switzerland. 3 Inst. for fysik og astronomi, Aarhus Universitet, DK8000 Aarhus C, Denmark. 4 CMAM, Universidad Autónoma de Madrid, Cantoblanco, Madrid, Spain. 5 Fundamental Fysik, Chalmers Tekniska Högskola, S41296 Göteborg, Sweden.

28 Hoyle state a linear chain of alphas? Determine mass of 8Be from 2 alphas? To study states around MeV (although only 600 kev, so maybe can try to study anyway regardless of higher E since wont help much) Giant resonance? Would have to increase energy in order to go higher up in the spectrum

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