1. Reaction Dynamics in Near-Fermi-Energy Heavy Ion Collisions
Jiansong Wang and NIMROD Collaboration
Texas A&M University, TX, USA
Institute of Modern Physics, Lanzhou China
Title
2018/11/24

2. Outline Motivation Experimental set up Goshal-like test
The impact parameter dependence of Coalescence radii
Summary
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2018/11/24

3. Motivation
Hot topics of HI collisions at intermediate energy: Isospin Physics and Liquid-Gas Phase Transition
Goshal like tests in these Fermi energy collisions are of interest.
Ghoshal et al. find the independence of entrance channel on compound nuclei at low energy collisions
Is it still true in these collisions at near fermi energy?
Studying the impact parameter dependence of the interaction zones is of interest too
What is the properties of the nuclear matter in the interaction zone?
What is the relationship between the Coalescence radius and the interaction zone
Nucl-ex/ P. Chomaz
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4. NIMROD (Neutron Ion Multidetector for Reaction Oriented Dynamics)
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5. Selecting the Violent Collisions
There are many variables to select the centrality, Such as Transverse Energy of LCP, Multiplicity, Flow Angle etc.
In our case, total multiplicity of neutron and charged particle is used to select the most violent collisions
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6. Reaction systems 35MeV/u 64Zn+92Mo 40MeV/u 40Ar+112Sn
55MeV/u 27Al+124Sn
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7. Energy spectra of particle emitted from spherical thermal source
Surface emission
Volume emission
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8. Moving Source Fits Target-like Source (surface emission)
Mid-Rapidity Source (volume emission)
Projectile-like Source (surface emission)
PRC39(1989)p497, R. Wada et al. PRC57(1998)p1305, D. Prindle et al
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9. An example of moving fit
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10. Temperature Determination
Double Ratio Isotope Temperature (S. Albergo et al., Nuovo Cimento A 89(1985)p1)
Assumptions in the model:
Free nucleons and composite fragments are contained within a certain volume
The thermal and chemical equilibrium are reached
The yield follows the Maxwell distribution
The experimental yield of a fragment is proportional to the density inside the volume
All detected fragment originate from a single source
For the isotopes of d,t,he3,he4, The formula of temperature for a certain velocity zone is as the following,
CASST Workshop
2018/11/24

11. Time Evolution of Temeprature
the temperature evolution curves rises to a maximum and then decreases.
Maximum temperatures of MeV are observed at times in the range of 95 to 110 fm/c.
Freezing out at the time corresponding Vsurf=3.5 cm/ns, temperatures at these time are very similar to the limiting temperatures.
Time (fm/c)
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12. Excitation Energy
The excitation energy remaining in the TLF source was determined using calorimetric technique
Reaction
Acomp Ex
MeV/u
THHe
Tslope
Aevap
Ex/A
35 AMeV 64Zn+92Mo
96.4±8.7
4.88±0.49
5.93±0.59
5.10±0.50
38.7±3.5
12.1±1.7
40 AMeV
40Ar +112Sn
107±9.6
4.98±0.50
5.98±0.60
5.80±0.30
41.0±3.7
13.0±1.8
47 AMeV
64Zn+92Mo
85.4±7.8
5.14±0.51
5.60±0.56
5.50±0.03
35.5±3.3
12.4±1.8
55 AMeV
27Al+124Sn
114±10
5.31±0.53
6.00±0.60
5.60±0.10
44.5±4.1
13.6±1.9
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13. Comparison of initial properties of the hot nuclei
For each individual system, deviations from those averages are seen to be relatively small
The neutron multiplicity for the 55 MeV/u 27Al + 124Sn reaction is an exception
The calculated values (SMM-- Δ, GEMINI--□) of the multiplicities and average energies show quite similar trends in comparison with those of the experiments,
suggesting that the statistical picture has some validity
CASST Workshop
2018/11/24

14. Cut events into 4 bins
The total multiplicity of charged particles and neutron particles is used to select the collision as an impact parameter sensitive paramter
We divide the total HM events into 4 parts corresponding the small impact parameter (central collisions) to the larger ones (peripheral collisions) respectively
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15. Results of three source fits
Multiplicity decrease from central bin to peripheral bin.
Temperatures and velocities of NN source keep similar for different bins while they are reasonably changing from central events to peripheral events
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16. How to study the dynamic in the early stage of nuclear reaction
the kinetic energy of the emitted particle is used as a clock with a dynamic model calculation
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17. Coalescence Model I : determining P0
In Coalescence Model, the density of composite particle momentum space with Z protons and N neutrons is directly related to the density of free neutrons and protons momentum space as the following formula, (T. Butler and C.A.Pearson, PRL7(1961)69, PhysRev129(1963)p836, A Mekjian PRL38(1977)p640
Because of the difficulty to measure the neutron spectra, we assume the neutron has the same shape of momentum distribution and the yield is related to the isospin of the system, then the equation become as the following,
CASST Workshop
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18. Coalescence Model II: determining size of the system
In Mekjian thermal Coalescence model, assuming the chemical equilibrium is reached and the particle are emitted at the freeze-out density. The relationship of coordinate volume and momentum volume is as the following,
EB and s is the binding energy and spin of the composite particle and T is the temperature of the source
A. Mekjian et al. PRL77(1977)p640, PRC17(1978)p1051
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19. Evolution of the t/3He Ratios
Vsurf
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20. Evolution of HHe Isotope Ratio Temperature
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21. Evolution of coalescence Parameter P0
Coalescence Parameter P0 changes with surface velocity for different particle and different bins
Peaks at Vsurf about 5 cm/ns
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22. Evolution of the Coalescence Radii
Coalscence Radii of different particle for reaction ZnMo47
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23. Glauber Model l b impact Nucleon density RA a
r(fm)
(r)
“Spectators”
“Participants”
b impact l
Sampling the positions of the nucleons according to Woods-Saxon density
Sampling an impact parameter
Calculate the distance d between the nucleon in projectile and that in target
If d < R_interaction, these two nucleons are counted as participant nucleons
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24. Results of Glauber model simulation
Impact Parameter (fm)
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25. Relationship Between Coalescence Radii and the Participant number
Total multiplicity of LCP and neutron is sensitive to the impact parameter
Coalescence analysis can give the reasonable size of the overlapped zone in heavy ion reaction
CASST Workshop
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26. Summary
The very similar hot nuclei are indeed produced for the central HI collisions at near fermi energy.
The dynamic evolution of the interaction zone from the central to the peripheral collisions are very similar.
The Radius from the coalescence analysis is well correlated with the impact parameter.
CASST Workshop
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27. The End
Thank you !
CASST Workshop
2018/11/24