What does W cut mean in regards to particle physics?

[buffordboy23]

What does "W cut" mean in regards to particle physics?

I am helping a professor put together some graphs with data from particle physics experiments. I saw something called "W cut" in the data files and was wondering what exactly this means. For example, I came across the three values for W cut: 0 (none), 1.4, 2. His explanation was not very helpful, so hopefully I can find a satisfactory explanation here. Thanks.

 

[bomanfishwow]

A cut is a selection applied to data, usually to remove background events, improve the purity of the sample of interest. In this case, there will be some discriminating variable (called "W"), for which removing (or accepting, depending if you accept events above or below the cut value) events in the range 0-2 for which this variable gets rid of unwanted events (background) or accepts wanted events (signal).

What is actually being cut on depends on what "W" is, for us here it might as well be called Andy without any further information!

 

[Meir Achuz]

The W is probably the cm energy of the particles involved in GeV.

 

[humanino]

Clem is right. The name W is usual in deep inelastic experiments for the invariant mass of the system [virtual photon/target]. The W cuts above (I believe) will select [all range], [above the delta] and [deep inelastic region above resonances].

Check 16. Structure functions

edit
A paper I found very useful when I wanted an introduction :
An Introduction to Spin Dependent Deep Inelastic Scattering

 

[buffordboy23]

Thanks for the replies.

Clem and humanino are right. Humanino, thanks for the awesome resources.

 

[Sideways]

To be more specific, W is the mass of the 'final product' of the scattering process.

For example, in elastic electron-proton scattering, W = 0.938 GeV/c^2, the mass of the proton, since the 'final product' of the scattering is just a proton.

If a 'deeper' impact produces, say, a Δ baryon state (which then decays very quickly), you'll have W ≈ 1.2 GeV/c^2 (The Δ mass). W > 2.0 GeV/c^2 is generally considered the threshold for Deep Inelastic Scattering, where the proton behaves more like an assembly of three free quarks than a single particle.

A "W-cut" will often be enforced on data because only a specific resonance or set of resonances is of interest to the experimenter; or because the efficiency of a detector may not be good enough to get meaningful results in a certain W-range (especially at high W, where the scattered particle momentum is low).

Hope this helps!