34
S. Mallik et al.
distributions. With changing the projectile beam energy, the freeze-out time will also
change, for example, by doing similar analysis for 40 MeV per nucleon reaction
freeze-out time is determined as approximately t = 400 fm/c.
3.4 Dynamical Bimodality
In this section, we will concentrate on the behavior of probability distribution of
largest cluster ( A max ) and asymmetry of largest and second largest clusters (a 2 =
(A max − A 2 )/(A max + A 2 )) calculated at the end of transport simulation at freezeout condition. P(A max ) and P(a 2 ) distribution at constant projectile beam energy 100
MeV/nucleon but four different impact parameters ranging from central to peripheral
collisions are shown in Figs. 3.4 and 3.5, respectively.
For central collision (b = 0 fm), two peaks of P(A max ) as well as P(a 2 ) distributions are seen which can be interpreted as dynamical bimodality very similar to
the phenomenon described in [15]. Fluctuations in the collision rates lead to fluctuations in the momentum distribution, that is, in the degree of stopping of the reaction.
We have fixed a mass cut of A cut = 37 (corresponds to the minimum between the
two peaks at b = 0 fm to distinguish the two event classes as it corresponds to the
minimum between the two peaks. Fragments with A max ≥ A cut represent stopped
events having nearly zero z-component (beam direction) of momentum and scattered
isotropically in the center of mass frame, whereas fragments with A max < A cut represent crossed events having high z-component of momentum and scattered either
in the forward direction (projectile-like fragments) or backward direction (targetlike fragments). This is shown in Fig. 3.6. For non-central collisions, due to lesser
Fig. 3.4 Largest cluster
probability distribution
P(A max ) at freeze-out stage
(t = 175 fm/c) for constant
projectile beam energy 100
MeV/nucleon but for four
different impact parameters
a b = 0 fm, b b = 3 fm, c
b = 6 fm, d b = 9 fm
calculated from BUU model
S. Mallik et al.
distributions. With changing the projectile beam energy, the freeze-out time will also
change, for example, by doing similar analysis for 40 MeV per nucleon reaction
freeze-out time is determined as approximately t = 400 fm/c.
3.4 Dynamical Bimodality
In this section, we will concentrate on the behavior of probability distribution of
largest cluster ( A max ) and asymmetry of largest and second largest clusters (a 2 =
(A max − A 2 )/(A max + A 2 )) calculated at the end of transport simulation at freezeout condition. P(A max ) and P(a 2 ) distribution at constant projectile beam energy 100
MeV/nucleon but four different impact parameters ranging from central to peripheral
collisions are shown in Figs. 3.4 and 3.5, respectively.
For central collision (b = 0 fm), two peaks of P(A max ) as well as P(a 2 ) distributions are seen which can be interpreted as dynamical bimodality very similar to
the phenomenon described in [15]. Fluctuations in the collision rates lead to fluctuations in the momentum distribution, that is, in the degree of stopping of the reaction.
We have fixed a mass cut of A cut = 37 (corresponds to the minimum between the
two peaks at b = 0 fm to distinguish the two event classes as it corresponds to the
minimum between the two peaks. Fragments with A max ≥ A cut represent stopped
events having nearly zero z-component (beam direction) of momentum and scattered
isotropically in the center of mass frame, whereas fragments with A max < A cut represent crossed events having high z-component of momentum and scattered either
in the forward direction (projectile-like fragments) or backward direction (targetlike fragments). This is shown in Fig. 3.6. For non-central collisions, due to lesser
Fig. 3.4 Largest cluster
probability distribution
P(A max ) at freeze-out stage
(t = 175 fm/c) for constant
projectile beam energy 100
MeV/nucleon but for four
different impact parameters
a b = 0 fm, b b = 3 fm, c
b = 6 fm, d b = 9 fm
calculated from BUU model