# How to find a new particle

1. ### HAMJOOP

32
To find a new particle, the energy and momentum of the (decayed) particles are measured
Evaluate the expression m^2 = E^2 - p^2 and plot a histogram.

I just don't understand why there is a resonance particle if there is a peak in the histogram.
Is it because the probability is very high and we regard it as a particle ??

2. ### Simon Bridge

15,279
Where else would the peak come from?

3. ### Bill_K

4,157
A threshold cusp, for one thing. http://arxiv.org/abs/hep-ph/0406293

Indication of a resonance comes not just from a peak in the partial-wave scattering amplitude, but also a rapid increase in its phase. This recently played a role in the identification of Z(4430) as a candidate for a four-quark state. http://arxiv.org/abs/1404.1903

Last edited: Jun 26, 2014
4. ### Simon Bridge

15,279
... OK, but I wanted HAMJOOP to think about it first.
(In the context in which the question was asked...)

5. ### Bill_K

4,157
Sorry, I just thought it was an interesting question. Did I get it right?

6. ### Simon Bridge

15,279
Well it is the interesting form of the original question yes.
A narrow resonance in a spectra could be a wigner cusp - usually a scattering experiment... occurs near the threshold where one channel comes to dominate another one.

Particle detection experiments try to avoid these thresholds.
It's the other half fo the answer OP is looking for. The graph, by itself, is not the whole story.