hepunits 1.1.1

Units and constants in the HEP system of units

hepunits collects the most commonly used units and constants in the HEP System of Units, as derived from the basic units originally defined by the CLHEP project, which are not the same as the SI system of units:

Quantity	Name	Unit
Length	millimeter	mm
Time	nanosecond	ns
Energy	Mega electron Volt	MeV
Positron charge	eplus
Temperature	kelvin	K
Amount of substance	mole	mol
Luminous intensity	candela	cd
Plane angle	radian	rad
Solid angle	steradian	sr

It is largely based on the international system of units (SI)

Quantity	Name	Unit
Length	meter	m
Time	second	s
Mass	kilogram	kg
Electric current	ampere	A
Temperature	kelvin	K
Amount of substance	mole	mol
Luminous intensity	candela	cd

but augments it with handy definitions, changing the basic length and time units.

Installation

Install hepunits like any other Python package:

pip install hepunits

or similar (use e.g. virtualenv if you wish).

Getting started

The package contains 2 modules - constants and units, whose names are self-explanatory. It may be more readable to import quantities explicitly from each of the modules though everything is available from the top-level as from hepunits import ....

The module hepunits.constants contains 2 sorts of constants: physical constants and commonly used constants.

The typical usage is the following:

>>> from hepunits.constants import c_light
>>> from hepunits.units     import picosecond, micrometer
>>> tau_Bs = 1.5 * picosecond    # a particle lifetime, say the Bs meson's
>>> ctau_Bs = c_light * tau_Bs   # ctau of the particle, ~450 microns
>>> print ctau_Bs                # result in HEP units, so mm
0.449688687
>>> print ctau_Bs / micrometer   # result in micrometers
449.688687

Typical usage of the hepunits.units module:

>>> # add two quantities with length units and get the result in meters
>>> from hepunits import units as u
>>> (1 * u.meter + 5 * u.cm) / u.meter
1.05
>>> # the default result is, of course, in HEP units, so mm
>>> 1 * u.meter + 5 * u.cm
1050.0

>>> from hepunits.units import MeV, GeV
>>> massWindow = 100 * MeV    # define a 100 MeV mass window
>>> def energy_resolution():
...    # returns the energy resolution of 100 MeV
...    return 100 * MeV
...
>>> energy_resolution() / GeV # get the energy resolution in GeV
0.1