invariant mass mass





P

μ


=
m

U

μ


=
m
γ
(
v
)
(
c
,

v

x


,

v

y


,

v

z


)
=

(



E
c


,

p

x


,

p

y


,

p

z



)

=

(



E
c


,

p


)

.


{\displaystyle P^{\mu }=mU^{\mu }=m\gamma (v)(c,v_{x},v_{y},v_{z})=\left({\frac {E}{c}},p_{x},p_{y},p_{z}\right)=\left({\frac {E}{c}},\mathbf {p} \right).}


where m is the invariant mass.
