Phase Space Example

This page is basically to demonstrate, how the PhaseSpace class with N particles can be used to generate the Events.

import HydraPython as hp

Above line will bring the classes in HydraPython in the scope of interpreter with the alias hp.

I will be using the Generate method of PhaseSpace here.

ps = hp.PhaseSpace4([3.096916, 0.493677, 0.13957018, 0.0195018])

Above will create a PhaseSpace class object with N=4 number of particles in the final state. Since the number HydraPython currently supports particles up-to N=10 in the final state each PhaseSpace class have a suffix number from 1 to 10 is associated with it. The argument to the PhaseSpace class constructor is the list of daughter masses. The size of this list should be equal to the number of particles in the final state.

Now that we have defined a PhaseSpace object, let’s create an Event container to contain or save the states of the particle generated by the Generate method.

e_host = hp.host_events_4(3)

Above I have defined a host Event container with N=4 particle and number of states as 3. So this container will contain the 3 states of 4 particles each generated by the PhaseSpace.

Above will generate the events or states of N particles using host and save the result in the passed e_host container.

Iterating over e_host will produce the output like this.

iterator = e_host.Events()
for state in iterator:
    print(state)

The output is similar to this.

(0.0005371556105645586, (3.26523953659142, 0.8636638960657156, 0.0039751958746361005, -0.5700608675519644), (0.5205929150762441, 0.1361899815237809, 0.005650876525868165, -0.09338286473236444), (0.20194244730558714, -0.1422365383415909, 0.02243309740186762, 0.023800003783548303), (1.0705417836594209, -0.8576173392479055, -0.03205916980237188, 0.6396437285007806))

(0.05958088064572496, (3.165087693874953, -0.03009443713313225, 0.6184073639056892, 0.2087056683071267), (0.5809611490129989, -0.016410682480807473, -0.054177669092790454, -0.30098894665035486), (0.7999891064682725, 0.08709929588193556, -0.6686502155923885, -0.40721411710277927), (0.5122787332764478, -0.04059417626799582, 0.10442052077948974, 0.4994973954460073))

(0.03738710351970522, (3.376147992537914, -0.4901521345374072, 1.085407051180553, 0.6238020316717038), (1.0297008095722722, 0.22021896692371404, -0.8251558826920553, -0.29527640063259364), (0.49365860519565796, 0.27558785182792184, -0.33498661390711465, -0.18987966654280578), (0.15880927532682793, -0.005654684214228855, 0.07473544541861718, -0.13864596449630434))

So what is this? It is the tuple of output in which the first element of tuple represent the weight and the remaining number of elements are the Vector4R of each particle for N particle. (In this case 4)

If you will closely follow the result, you will see that the each particle in every event has the mass specified by the list of daughter masses at the time of the creation of PhaseSpace.

state1 = e_host[0]  # first state particle
d_particle0, d_particle1, d_particle2, d_particle3 = state1[1], state1[2], state1[3], state1[4]

d_particle0 = hp.Vector4R(d_particle0)
d_particle1 = hp.Vector4R(d_particle1)
d_particle2 = hp.Vector4R(d_particle2)
d_particle3 = hp.Vector4R(d_particle3)

print(d_particle0.mass(), d_particle1.mass(), d_particle2.mass(), d_particle3.mass(), sep=', ')

# Output is
# 3.096916, 0.493677, 0.13957017999999996, 0.01950179999999231
# This is exactly the weight given for each daughter while creation of PhaseSpace
# Same thing is true for rest of the states.

So this is a simple PhaseSpace example of 4 particles in the final state. For the sake of completeness, all the code showed in the doc is below.

import HydraPython as hp

mother_particle = hp.Vector4R(5.2795, 0.83859, 0.77825, 0.98876)
daughter_masses = [3.096916, 0.493677, 0.13957018, 0.0195018]
print("Daughter masses at the time of creation of PhaseSpace:", daughter_masses)
print()

ps = hp.PhaseSpace4(daughter_masses)
e_host = hp.host_events_4(3)
ps.Generatehost(mother_particle, e_host)

iterator = e_host.Events()
for idx, state in enumerate(iterator):
    print("State", idx, ": ", state)

state1 = e_host[0]  # first state particle
d_particle0, d_particle1, d_particle2, d_particle3 = state1[1], state1[2], state1[3], state1[4]

d_particle0 = hp.Vector4R(d_particle0)
d_particle1 = hp.Vector4R(d_particle1)
d_particle2 = hp.Vector4R(d_particle2)
d_particle3 = hp.Vector4R(d_particle3)

print('\nDaughter masses:', d_particle0.mass(), d_particle1.mass(), d_particle2.mass(), d_particle3.mass(), sep=', ')