a -cluster states in electron scattering *
DESCRIPTION
Darmstadt 2008. TU DARMSTADT. S-DALINAC. a -Cluster States in Electron Scattering *. Maksym Chernykh Institut für Kernphysik, TU Darmstadt. M. Chernykh 1 , H. Feldmeier 2 , T. Neff 2 , P. von Neumann-Cosel 1 , and A. Richter 1 1 Institut für Kernphysik , TU Darmstadt - PowerPoint PPT PresentationTRANSCRIPT
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-Cluster States in Electron Scattering *
S-DALINAC
TU DARMSTADT
Darmstadt 2008
Maksym Chernykh Institut für Kernphysik, TU Darmstadt
M. Chernykh1, H. Feldmeier 2, T. Neff 2, P. von Neumann-Cosel1, and A. Richter1
1 Institut für Kernphysik, TU Darmstadt2 Gesellschaft für Schwerionenforschung (GSI), Darmstadt
* Supported by DFG under contract SFB 634
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Motivation: structure of the Hoyle state
Hoyle state is a prototype of -cluster states in light nuclei
Cannot be described by shell-model approaches
Comparison of high-precision electron scattering data with predictions of FMD and -cluster models
-cluster models predict Hoyle state as a dilute gas of weakly interacting particles resembling the properties of a Bose-Einstein Condensate (BEC)
M. Chernykh, H. Feldmeier, T. Neff, P. von Neumann-Cosel, and A. Richter, Phys. Rev. Lett. 98 (2007) 032501
Hoyle state cannot be understood as a true Bose-Einstein Condensate !
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Triple alpha reaction rate
Motivation: astrophysical importance
http://outreach.atnf.csiro.au
Reaction rate with accuracy ~ 6% needed
(,’) (p,p’) (e,e’)(p,p’)
S.M. Austin, Nucl. Phys A758 (2005) 375c
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Motivation: astrophysical importance
Total uncertainty r3/r3 = 11.6% only
Crannell et al. (2005)
Crannell et al. (1967)
Strehl (1970)
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Transition form factor to the Hoyle state
Extrapolation to zero momentum transfer: Crannell (1967), Strehl (1970)
Fourier-Bessel analysis: Crannell (2005)
H. Crannell, data compilation
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Model-independent PWBA analysis
Model-independent extraction of the partial pair width
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ME = 5.37(22) fm2, Rtr = 4.24(30) fm
P. Strehl, Z. Phys. 234 (1970) 416
Monopole matrix element
Large uncertainty because of narrow momentum transfer region
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Lintott spectrometer
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Detector system
Si microstrip detector system: 4 modules, each 96 strips with pitch of 650 m
Count rate up to 100 kHz
Energy resolution 1.5x10-4
10 cm
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Measured spectra
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Monopole matrix element
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Triple alpha reaction rate
Total uncertainty r3/r3 = 10%
Only need to be improved
Crannell et al. (2005)
Strehl (1970)
Crannell et al. (1967)
Present work
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Summary and outlook
– Hoyle state is important for stellar nucleosynthesis
– Monopole matrix element can be extracted by extrapolation of cross section to zero momentum transfer
– for decay of the Hoyle state with uncertainty 2.5% extracted
Thank you!
Outlook
– 16O: broad 0+ state at 15 MeV
– Hoyle state: independent Fourier-Bessel analysis
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–
Astrophysical importance
Motivation:
Model-independent PWBA analysis
High-resolution electron scattering measurements
Summary and outlook
Results
Outline
–
Extraction of monopole matrix element ME
–
Comparison with FMD and -cluster model predictions
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Model-independent PWBA analysis
Model-independent extraction of monopole matrix element ME
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12C densities
Ground state density can be tested via elastic form factor
Transition density can be tested via transition form factor
↔
↔
“BEC”: Y. Funaki et al., Phys. Rev. C 67 (2003) 051306(R)
FMD : R. Roth, T. Neff, H. Hergert, and H. Feldmeier, Nucl. Phys. A745 (2004) 3
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Elastic form factor
Described well by FMD
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Described better by -cluster models
Transition form factor to the Hoyle state
H. Crannell, data compilation
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What is actual structure of the Hoyle state ?
But in the FMD and -cluster model the leading components of the Hoyle state are cluster-like and resemble 8Be + 4He configurations
In the “BEC” model the relative positions of clusters should be uncorrelated
Overlap with FMD basis states
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Summary and outlook
Outlook
Summary
– 16O: broad 0+ state at 15 MeV
– for decay of the Hoyle state with uncertainty 2.5% extracted
– 12C: 03 and 22 states+ +
– Hoyle state is not a true Bose-Einstein condensate
– 8Be + structure
– Hoyle state: Fourier-Bessel analysis of all available data