Post on 07-May-2018
Introduction Experimental Setup Analysis Results
Direct Observation of a New 2+ State in 12Cthrough the 12C + γ → 3α Reaction
William Zimmerman
Triangle Universities Nuclear Laboratory
University of Connecticut
Chiral Dynamics 2012
Introduction Experimental Setup Analysis Results
Astrophysics
Triple-α Process:
M. Hjorth-Jensen, Physics 4, 38 (2011)
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Hoyle State
12C0+
0+Hoyle State
7.65
2+4.44
8Be + α7.37
? 2+ ?
Fynbo & Freer, Physics 4, 94 (2011)
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Hoyle State
12C0+
0+Hoyle State
7.65
2+4.44
8Be + α7.37
? 2+ ?
Fynbo & Freer, Physics 4, 94 (2011)
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Hoyle State
12C0+
0+Hoyle State
7.65
2+4.44
8Be + α7.37
? 2+ ?
Fynbo & Freer, Physics 4, 94 (2011)
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Triple-α Reaction Rates
Temperature (109 K)
N2〈σ
v〉(c
m6m
ol-2s-
1)
2 4 6 810-11
10-10
10-9
NACRE
JINA
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
12C(γ,α)8Be
12C0+
3−9.64 MeV
0+10.3 MeV
2+
8Be + α
γ-ray beam will not excite0+ state and will excite 3−
state with very smallprobability.
Measuring α-particleangular distribution givesJπ of state.
Measuring cross sectionover several γ-ray beamenergies gives Γα, Γγ , andEres
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
12C(γ,α)8Be
12C0+
3−9.64 MeV
0+10.3 MeV
2+
8Be + α
γ-ray beam will not excite0+ state and will excite 3−
state with very smallprobability.
Measuring α-particleangular distribution givesJπ of state.
Measuring cross sectionover several γ-ray beamenergies gives Γα, Γγ , andEres
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
12C(γ,α)8Be
12C0+
3−9.64 MeV
0+10.3 MeV
2+
8Be + α
γ-ray beam will not excite0+ state and will excite 3−
state with very smallprobability.
Measuring α-particleangular distribution givesJπ of state.
Measuring cross sectionover several γ-ray beamenergies gives Γα, Γγ , andEres
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
12C(γ,α)8Be
12C0+
3−9.64 MeV
0+10.3 MeV
2+
8Be + α
γ-ray beam will not excite0+ state and will excite 3−
state with very smallprobability.
Measuring α-particleangular distribution givesJπ of state.
Measuring cross sectionover several γ-ray beamenergies gives Γα, Γγ , andEres
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
12C(γ,α)8Be
Measuring 12C(γ, α)8Be requires:
Intense, monoenergetic γ-ray beam
Detector capable of measuring angular distributions ofrecoiling α-particles with little or no background
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
12C(γ,α)8Be
Measuring 12C(γ, α)8Be requires:
Intense, monoenergetic γ-ray beam
Detector capable of measuring angular distributions ofrecoiling α-particles with little or no background
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
12C(γ,α)8Be
Measuring 12C(γ, α)8Be requires:
Intense, monoenergetic γ-ray beam
Detector capable of measuring angular distributions ofrecoiling α-particles with little or no background
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
HIγS Facility
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
HIγS O-TPC
drift chamber
photomultiplier tubes
mirror optics chain
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
HIγS O-TPC
Drift Chamber
cathode grid
anode grid
first avalanche grid
second avalanche grid
quartz window
γ-ray beam
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
HIγS O-TPC
Optics Chain
CCD camera
micro-channel plate
auxiliary lens assembly
electrostatic demagnifier
main lens assembly
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
HIγS O-TPC
drift chamber
photomultiplier tubes
mirror optics chain
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Background Rejection
Spark Cosmic
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Event Identification
12C(γ,α)8Be 16O(γ,α)12C
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Event Identification
12C(γ,α)8Be 16O(γ,α)12C
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Time Projection
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Time Projection
12C(γ,α)8Be
-20 -10 0 100.00
0.05
0.10
0.15
@mmD
16O(γ,α)12C
-50 -40 -30 -20 -10 0 100.00
0.02
0.04
0.06
0.08
0.10
@mmD
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Time Projection
12C(γ,α)8Be
fADC channel [10nsec/channel]900 950 1000 1050 1100 1150 1200 1250
A.U
.
0
50
100
150
200
250
300
16O(γ,α)12C
fADC channel [10nsec/channel]800 900 1000 1100 1200 1300 1400
A.U
.-20
0
20
40
60
80
100
120
140
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Time Projection
fADC channel [10nsec/channel]800 900 1000 1100 1200 1300 1400
A.U
.
-20
0
20
40
60
80
100
120
140fADC channel [10nsec/channel]
900 950 1000 1050 1100 1150 1200 1250
A.U
.
0
50
100
150
200
250
300
16O(γ,α)12C event,fit assuming 16O(γ,α)12C
12C(γ,α)8Be event,fit assuming 12C(γ,α)8Be
fADC channel [10nsec/channel]800 900 1000 1100 1200 1300 1400
A.U
.
-20
0
20
40
60
80
100
120
140fADC channel [10nsec/channel]
900 950 1000 1050 1100 1150 1200 1250
A.U
.
0
50
100
150
200
250
300
16O(γ,α)12C event,fit assuming 12C(γ,α)8Be
12C(γ,α)8Be event,fit assuming 16O(γ,α)12C
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Angular Distributions
θ was calculated for each event from the track image andfrom the time projection.
Angular distributions were fit in terms of |E1|, |E2|, φ12:
W (θ) =3
2sin2 θ
×(
3|E1|2 + 25|E2|2 cos2 θ + 10√
3|E1||E2| cosφ12 cos θ)
Since angular information is available for each event,Unbinned Maximum Likelihood fits were used.
L(|E1|, |E2|, φ12) =n∏i=1
W (θi)
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Angular Distributions
θ was calculated for each event from the track image andfrom the time projection.
Angular distributions were fit in terms of |E1|, |E2|, φ12:
W (θ) =3
2sin2 θ
×(
3|E1|2 + 25|E2|2 cos2 θ + 10√
3|E1||E2| cosφ12 cos θ)
Since angular information is available for each event,Unbinned Maximum Likelihood fits were used.
L(|E1|, |E2|, φ12) =n∏i=1
W (θi)
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Angular Distributions
θ was calculated for each event from the track image andfrom the time projection.
Angular distributions were fit in terms of |E1|, |E2|, φ12:
W (θ) =3
2sin2 θ
×(
3|E1|2 + 25|E2|2 cos2 θ + 10√
3|E1||E2| cosφ12 cos θ)
Since angular information is available for each event,Unbinned Maximum Likelihood fits were used.
L(|E1|, |E2|, φ12) =
n∏i=1
W (θi)
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Angular Distributions
θcm (deg)
Events
/(6
deg)
0 20 40 60 80 100 120 140 160 180
20
40
60
80
100 Eγ = 9.8 MeV
σE2/σ = 96.8 %
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Cross Section
Eγ (MeV)
σ(µ
b)
8 9 10 11 12 13 140
2
4
6
8
E2 cross section
E1 cross section
Fit 2+ resonance
Known 1− resonance
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Cross Section
Eγ (MeV)
σ(µ
b)
8 9 10 11 12 13 140
2
4
6
8
E2 cross section
E1 cross section
Fit 2+ resonance
Known 1− resonance
Eres Γα(res) Γγ0(res) B(E2 : 2+2 → 0+
1 )(MeV) (keV) (meV) (e2fm4)
10.03(11) 800(130) 60(10) 0.73(13)
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Phase
E1-E2 phase difference:
φ12 = δ2 − δ1 + arctan (η/2)
Nuclear phase shifts:
δ` = arctan
(Γ`
2 (Er` −∆` − Ecm)
)− φ`
Hard sphere scattering phase shift:
φ` = arctan
[F`G`
]r=a
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Phase
E1-E2 phase difference:
φ12 = δ2 − δ1 + arctan (η/2)
Nuclear phase shifts:
δ` = arctan
(Γ`
2 (Er` −∆` − Ecm)
)− φ`
Hard sphere scattering phase shift:
φ` = arctan
[F`G`
]r=a
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Phase
Eγ (MeV)
φ12(d
eg)
8 9 10 11 12 13 14
0
40
80
120
φ12 (calculated)
φ12 (measured)
δ1
δ2
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Triple-α Reaction Rates
Temperature (109 K)
N2〈σ
v〉(c
m6m
ol-2s-
1)
2 4 6 810-11
10-10
10-9
NACRE
JINA
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Triple-α Reaction Rates
Temperature (109 K)
N2〈σ
v〉(c
m6m
ol-2s-
1)
2 4 6 810-11
10-10
10-9
NACRE
HIγS
JINA
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Summary
2+2
Eres Γα(res) Γγ0(res) B(E2 : 2+2 → 0+
1 )(MeV) (keV) (meV) (e2fm4)
10.03(11) 800(130) 60(10) 0.73(13)
2+2 in 12C has been directly observed through the
12C + γ → 3α reaction.
Recent ab initio EFT lattice calculations performed byEpelbaum, Krebs, Lahde, Lee, and Meißner predict the 2+
2
2 MeV above the Hoyle State.
Revised triple-α reaction rates can affect nucleosynthesis ofheavy elements during explosive astrophysics scenarios.
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Summary
2+2
Eres Γα(res) Γγ0(res) B(E2 : 2+2 → 0+
1 )(MeV) (keV) (meV) (e2fm4)
HIγS 10.03(11) 800(130) 60(10) 0.73(13)EFT 9.65 2(1)
2+2 in 12C has been directly observed through the
12C + γ → 3α reaction.
Recent ab initio EFT lattice calculations performed byEpelbaum, Krebs, Lahde, Lee, and Meißner predict the 2+
2
2 MeV above the Hoyle State.
Revised triple-α reaction rates can affect nucleosynthesis ofheavy elements during explosive astrophysics scenarios.
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Summary
2+2
Eres Γα(res) Γγ0(res) B(E2 : 2+2 → 0+
1 )(MeV) (keV) (meV) (e2fm4)
HIγS 10.03(11) 800(130) 60(10) 0.73(13)EFT 9.65 2(1)
2+2 in 12C has been directly observed through the
12C + γ → 3α reaction.
Recent ab initio EFT lattice calculations performed byEpelbaum, Krebs, Lahde, Lee, and Meißner predict the 2+
2
2 MeV above the Hoyle State.
Revised triple-α reaction rates can affect nucleosynthesis ofheavy elements during explosive astrophysics scenarios.
William Zimmerman Direct Observation of a New 2+ State in 12C
Introduction Experimental Setup Analysis Results
Acknowledgments
Mohammad Ahmed, Seth Henshaw, Jonathan Mueller,Sean Stave, and Henry Weller
Triangle Universities Nuclear Laboratory
Moshe GaiLaboratory for Nuclear Science at Avery Point
William Zimmerman Direct Observation of a New 2+ State in 12C
Event Identification
(χ2c − χ2
o)/(χ2c + χ2
o)
Events
-1 -0.5 0 0.5 1
10
20
30
40
50
12C(γ,α)8Be 16O(γ,α)12C
William Zimmerman Direct Observation of a New 2+ State in 12C