use particle package to get PDG data

[peterstangl]

This PR replaces the functions for reading PDG data files by an interface to the python package particle as suggested and discussed in isse #112.

The main changes are:

• Particles are now identified by their flavio_name, which is the name used e.g. in the mass parameters, and by their PDG IDs. Translating the former into the latter is done using the pdg_particles dictionary, replacing the old lists pdg_include and pdg_translate.
• Masses and widths are now obtained from particle. PDG data files and the old function _read_pdg_masswidth are removed.
• The latex names are now obtained from particle, but simplified using the new _pdg_tex_simplify function. The result is equivalent to the one of the old _pdg_particle_string_to_tex function, which is removed.
• New tests are added that check the masses and latex names of all particles currently contained in pdg_particles.

[coveralls]

Coverage increased (+0.002%) to 93.876% when pulling 2b8e496 on peterstangl:particles into b91383c on flav-io:master.

[DavidMStraub]

Shouldn't this be name in ["W", "Z", ...]? I think "\\mu" in "\\mu" is False since it iterates character by characters.

[peterstangl]

"\\mu" in "\\mu" is True since in tests for substring containment (cf. https://docs.python.org/3/reference/expressions.html#membership-test-details).
But I agree that it's maybe not a good idea to just test for substring containment since e.g. also names a, u, and au would be in '\\tau'.

[DavidMStraub]

Oh, you're right, sorry! But yeah, list might still be better.

[DavidMStraub]

not in "1S" matches everything except 1 and S

[peterstangl]

Good point, I think this should maybe better be ... and name != 'J/\\psi'.
The idea was to add a subscript with what is inside the parentheses of the latex name in case this is more than just a number (usually corresponding to the mass) and if there is no other subscript. So e.g. 'D^{*}(2007)^{0}' becomes'D^{*0}' since the parentheses contain only a number, but '\\psi(2S)' becomes '\\psi_{2S}' since the parentheses do not contain only a number. (Checking the content of the parentheses is currently done using par.upper().isupper() but should probably better be done by not par.isdigit())
The only exception from this rule is 'J/\\psi(1S)', which should become 'J/\\psi'. So I guess it's clearer to apply this exception only to 'J/\\psi' and not to anything contained 1S.

[DavidMStraub]

Great! Possibly all the particle-specific stuff could be collected in a class (e.g. class FlavioParticle(Particle)), which would allow to make the read_pdg much more concise. Just a thought.

[peterstangl]

Great! Possibly all the particle-specific stuff could be collected in a class (e.g. class FlavioParticle(Particle)), which would allow to make the read_pdg much more concise. Just a thought.

This is a very good idea and I have now moved everything to the new FlavioParticle class in commit da46a40.
Since it is a class, should it be moved to flavio.classes?
I'm also not sure what to do with the pdg_particles dictionary. In principle this is more like a config setting that one could move to a yaml file. Do you have a good idea in which file this could fit?

[DavidMStraub]

Nice!

Since it is a class, should it be moved to flavio.classes?

I think it's fine... classes is anyway a bit of a silly name for a module. There are also classes in other modules like probability.

I'm also not sure what to do with the pdg_particles dictionary. In principle this is more like a config setting that one could move to a yaml file. Do you have a good idea in which file this could fit?

It's a constant and it's only needed by the class, so I think it naturally fits as a class attribute:

class FlavioParticle(Particle):
    """..."""

    PDG_PARTICLES = {...}

which can be accessed as cls.PDG_PARTICLES in the class methods and self.PDG_PARTICLES in the instance methods.

[peterstangl]

It's a constant and it's only needed by the class, so I think it naturally fits as a class attribute:

Yes, I agree and have implemented this in 0582522.
In 2b8e496, I now also added the class method flavio_all, which returns a set of all instances used in flavio. This simplifies looping over the particles, as e.g. done in the read_pdg function.

This now looks quite complete and I would merge this PR soon.