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Units and constants in the HEP system of units

Project description

Scikit-HEP project package PyPI Build Status Coverage

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

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