# Elastic scattering of WIMPs off nuclei

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1. Mar 22, 2015

### maximus123

Hello,

My problem is as follows

I've tried differentiating to find the maximum and I've tried plotting E against $m_{\chi}$ for a range of values and this did not suggest a maximum at $m_N = m_{\chi}$. Could someone explain why it is the case that the energy transfer is maximum when these masses are equal?

Thanks a lot.

2. Mar 22, 2015

### Staff: Mentor

It is a maximum with respect to the nuclei mass (the thing we can change), not with respect to the WIMP mass (which we cannot influence).

3. Mar 23, 2015

### maximus123

Yeah I figured that out, I was being an idiot. Thanks for the help though.