1. Properties of the Initial Participant Interaction Zone in Near Fermi-Energy HI Collision
Jiansong Wang for NIMROD Collaboration
Institute of Modern Physics, Lanzhou China
Texas A&M University, TX, USA
Title
2018/9/20
6th China-Japan Joint Nuclear Physics Shanghai

2. 6th China-Japan Joint Nuclear Physics Symposium @ Shanghai
Outline
Motivation
Experimental set up
Coalescence model analysis
Properties of the participant zone
Summary
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6th China-Japan Joint Nuclear Physics Shanghai

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Motivation
Hot topics of HI collisions at intermediate energy: Isospin Physics and Liquid-Gas Phase Transition
Does the equilibrium reach during the dynamic evolution? If yes, when? ( J. Wang et al., Phys. Rev. C 72(2005)024603)
Entry channel independence in HI collision at near Fermi energies?(J. Wang et al., Phys. Rev. C71(2005)054606)
Studying the impact parameter dependence of the interaction zones is of interest too. (J. Wang et al., nucl-ex/ )
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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6th China-Japan Joint Nuclear Physics Shanghai

4. NIMROD (Neutron Ion Multidetector for Reaction Oriented Dynamics)
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6th China-Japan Joint Nuclear Physics Shanghai

5. The NIMROD Collaboration
E. Bell1, M. Cinausero2, Y. El Masri 6,D. Fabris3, K. Hagel1, J. Iglio1, A. Keksis1, T. Keutgen6, M. Lunardon3, Y.G. Ma1, Z. Majka4, A. Martinez-Davalos,5 A. Menchaca-Rocha5, S. Kowalski1,T. Materna1, J. B. Natowitz1, G. Nebbia3, L. Qin1, G. Prete,2 R. Murthy1, V. Rizzi,3 D. V. Shetty1, S. Soisson1, B. Stein1, G. Souliotis1, P. M. Veselsky1, A. Wieloch1, G. Viesti,3 R. Wada1, J. Wang1, S. Wuenshel1, and S. J. Yennello Texas A&M University, College Station, Texas 2INFN Laboratori Nazionali di Legnaro, Legnaro, Italy 3INFN Dipartimento di Fisica, Padova, Italy 4Jagellonian University, Krakow, Poland 5UNAM, Mexico City, Mexico 6UCL, Louvain-la-Neuve, Belgium
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6. 6th China-Japan Joint Nuclear Physics Symposium @ Shanghai
Reaction Systems
47MeV/u 65Zn+92Mo
40MeV/u 40Ar+112Sn
55MeV/u 27Al + 124Sn
Dividing the events into four
bins with total multiplicity
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6th China-Japan Joint Nuclear Physics Shanghai

7. Selection of time clock
the surface velocity of the emitted particle is used as a clock based on the dynamic model calculations
J. Wang et al., Phys. Rev. C， 72(2005)
v// (cm/ns) vl -
K. Hagel et al., Phys. Rev. C62(2000)034607
R. Wada et al. Phys. Rev. C, 69 (2004)
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8. Energy spectra of particle emitted from spherical thermal source
Surface emission
Volume emission
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9. 6th China-Japan Joint Nuclear Physics Symposium @ Shanghai
Moving Source Fits
Target-like Source (surface emission)
Mid-Rapidity Source (volume emission)
Projectile-like Source (surface emission)
R. Wada et al. PRC39(1989)p497, D. Prindle et al PRC57(1998)p1305,
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10. An example of moving fit
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11. 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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6th China-Japan Joint Nuclear Physics Shanghai

12. 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)836, A Mekjian PRL38(1977)640 )
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.
2018/9/20
6th China-Japan Joint Nuclear Physics Shanghai

13. 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 is the binding energy and ‘s’ is spin of the composite particle and T is the temperature of the source
A. Mekjian et al. PRL38(1977)640, PRC17(1978)1051
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14. Evolution of the t/3He Ratios
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15. 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
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16. Evolution of HHe Isotope Ratio Temperature
ZnMo47
ArSn40
AlSn55
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17. 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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18. Evolution of the Coalescence Radii
Coalscence Radii of different particle for reaction ZnMo47
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6th China-Japan Joint Nuclear Physics Shanghai

19. 6th China-Japan Joint Nuclear Physics Symposium @ Shanghai
Glauber Model
Nucleon density a RA
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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20. Results of Glauber model simulation
Impact Parameter (fm)
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6th China-Japan Joint Nuclear Physics Shanghai

21. The Coalescence radii at different surface velocities
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6th China-Japan Joint Nuclear Physics Shanghai

22. Relationship Between Coalescence Radii and the Participant number
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23. 6th China-Japan Joint Nuclear Physics Symposium @ Shanghai
Summary
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. The total multiplicity is sensitive to the impact parameter
The coalescence analysis is a good technique for experimentally understanding the process of dynamic evolution in HI collisions
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6th China-Japan Joint Nuclear Physics Shanghai

24. 6th China-Japan Joint Nuclear Physics Symposium @ Shanghai
The End
Thank you !
2018/9/20
6th China-Japan Joint Nuclear Physics Shanghai