- #1
Philip Land
- 56
- 3
Hey!
Let's say we have an electron and proton colliding head-on.
We will have ##|p| \sim E##
Where ##p_1=(E_1, \vec{p_1})## &##p_2=(E_2, \vec{p_2})##
If we want the available energy. We can calculate ##\sqrt{s} = \sqrt{(p_1 + p_2)^2}##
We get $$s= p_1^2 + p_2^2 + 2p_1p_2 = m_e^2 + m_p^2 + 2E_1E_2(1-cos(\theta)).$$
My question is why we get ##1-cos(\theta)## and not just ##cos(\theta)## which is one since the angle is zero?
Let's say we have an electron and proton colliding head-on.
We will have ##|p| \sim E##
Where ##p_1=(E_1, \vec{p_1})## &##p_2=(E_2, \vec{p_2})##
If we want the available energy. We can calculate ##\sqrt{s} = \sqrt{(p_1 + p_2)^2}##
We get $$s= p_1^2 + p_2^2 + 2p_1p_2 = m_e^2 + m_p^2 + 2E_1E_2(1-cos(\theta)).$$
My question is why we get ##1-cos(\theta)## and not just ##cos(\theta)## which is one since the angle is zero?