SimpleParticleCollection_t

The type SimpleParticleCollection_t is a typedef described in TVar.hh. It is a vector of SimpleParticle_t objects. These correspond to the particle lists that are submitted to Mela::setInputEvent. There are a few constructors for this object, each of which depend on what suits your needs.

Constructors

There are 4 different ways to construct the SimpleParticleCollection_t object. This is due to both the aforementioned pyROOT and C++ ROOT compatibility issues alongside the usage of syntactic sugar to allow for easier columnar data entry.

collection_initializer_from_column

This initializes a SimpleParticleCollection_t from a list of PDG ids, and either a set of \(P_x\), \(P_y\), \(P_z\), \(E\) OR \(P_t\), \(\eta\), \(\phi\), mass depending on the boolean flag set (just like in particle_initializer), and is documented here.

Example:

import Mela
# Let's make a pair of opposing gluons and 4 leptons
gluon_Collection = Mela.SimpleParticleCollection_t([21, 21], [0, 0], [0, 0], [12, -12], [12, 12]) #px, py, pz, E
 
lepton_Collection = Mela.SimpleParticleCollection_t(
     [13, -13, 11, -11],
     [pt1, pt2, pt3, pt4],
     [eta1, eta2, eta3, eta4],
     [phi1, phi2, phi3, phi4],
     [mu_M, mu_M, e_M, e_M],
     ptEtaPhi=True
)

collection_initializer

This initializes a SimpleParticleCollection_t from a list of SimpleParticle_t objects, and is documented here. One benefit of operating this way is that you can mix and match particles initialized via { \(P_x\), \(P_y\), \(P_z\), \(E\)}and those via { \(P_t\), \(\eta\), \(\phi\), \(m\)}.

Example:

import Mela
# Let's make a pair of opposing gluons and 4 leptons
g1 = Mela.SimpleParticle_t(21, 0, 0, 12, 12)
g2 = Mela.SimpleParticle_t(21, 0, 0, -12, 12)
gluon_Collection = Mela.SimpleParticleCollection_t([g1, g2])
 
l1 = Mela.SimpleParticle_t(13, px1, py1, pz1, E1)
l2 = Mela.SimpleParticle_t(-13, px2, py2, pz2, E2)
l3 = Mela.SimpleParticle_t(11, pt3, eta3, phi3, e_M) #mixing bases!
l4 = Mela.SimpleParticle_t(-11, pt4, eta4, phi4, e_M)
lepton_Collection = Mela.SimpleParticleCollection_t([l1, l2, l3, l4])

Default Constructor

This is an empty initializer that simply creates a "list-like" object you can add particles to. You can use the Mela.SimpleParticleCollection_t.add_particle method to do this. Just like [collection_intializer](collection_initializer_doc), one can mix and match bases of vectors between { \(P_x\), \(P_y\), \(P_z\), \(E\)}and { \(P_t\), \(\eta\), \(\phi\), \(m\)}.

Example:

import Mela
# Let's make a pair of opposing gluons and 4 leptons
gluon_Collection = Mela.SimpleParticleCollection_t()
gluon_Collection.add_particle(Mela.SimpleParticle_t(21, 0, 0, 12, 12))
gluon_Collection.add_particle(Mela.SimpleParticle_t(21, 0, 0, -12, 12))
 
lepton_Collection = Mela.SimpleParticleCollection_t([l1, l2, l3, l4])
lepton_Collection.add_particle(Mela.SimpleParticle_t(13, px1, py1, pz1, E1))
lepton_Collection.add_particle(Mela.SimpleParticle_t(-13, px2, py2, pz2, E2))
lepton_Collection.add_particle(Mela.SimpleParticle_t(11, pt3, eta3, phi3, e_M))
lepton_Collection.add_particle(Mela.SimpleParticle_t(-11, pt4, eta4, phi4, e_M))

Methods

The SimpleParticleCollection_t object has a few methods that you can use alongside iteration capabilities.

add_particle

Simply call Mela.SimpleParticleCollection_t.add_particle(Mela.SimpleParticle_t P) to add a particle to the collection.

Example in the Default Constructor section.

toList

Simple call Mela.SimpleParticleCollection_t.toList() to return a normal Python list of SimpleParticle objects.

Example:

import Mela
# Let's make a pair of opposing gluons
gluon_Collection = Mela.SimpleParticleCollection_t()
gluon_Collection.add_particle(Mela.SimpleParticle_t(21, 0, 0, 12, 12))
gluon_Collection.add_particle(Mela.SimpleParticle_t(21, 0, 0, -12, 12))
 
print(gluon_Collection) #prints an ugly repr function
print(gluon_Collection.toList) #prints a list of SimpleParticles

Iteration

Even without converting a SimpleParticleCollection_t into a list, one can still iterate over it! Iteration over the Mela.SimpleParticle_t objects stored within can be accessed in a for loop. See the example below:

import Mela
# Let's make a pair of opposing gluons
gluon_Collection = Mela.SimpleParticleCollection_t()
gluon_Collection.add_particle(Mela.SimpleParticle_t(21, 0, 0, 12, 12))
gluon_Collection.add_particle(Mela.SimpleParticle_t(21, 0, 0, -12, 12))
 
for n, particle in enumerate(gluon_Collection):
     print(f"particle {n} has an id of {particle.id}")
     print(f"with P_x, P_y, P_z, E = {particle.vector}")

Indexing

One can also index the underlying vector for the simpleParticleCollection_t class. Indexing works as normal.

import Mela
gluon_Collection = Mela.SimpleParticleCollection_t()
gluon_Collection.add_particle(Mela.SimpleParticle_t(21, 0, 0, 12, 12))
gluon_Collection[0] = Mela.SimpleParticle_t(21, 0, 0, -12, 12)
print(gluon_Collection[0].PxPyPzE_vector)

Sum

This method returns the 4-vector that is the sum of all the 4-vectors stored inside the class. It returns them as a tuple of 4 values: \(P_x\), \(P_y\), \(P_z\), \(E\).

import Mela
gluon_Collection = Mela.SimpleParticleCollection_t()
gluon_Collection.add_particle(Mela.SimpleParticle_t(21, 0, 0, 12, 12))
gluon_Collection.add_particle(Mela.SimpleParticle_t(21, 0, 0, -12, 12))
print(gluon_Collection.Sum()) #should print (0,0,0,0)

MTotal

This function is just like SimpleParticleCollection_t.Sum, however it returns the total mass of the resultant 4-vector.

Pickling Support

Should you desire to pickle a SimpleParticleCollection_t object, this is supported through the Python MELA bindings. This support for pickling also means that SimpleParticleCollection_t supports the python multiprocessing package.