# ISR effects vary with particle mass

dear expert

I tried to use Madgraph version 3.2.0 to test the effect of ISR on the e+e->Twb process.

where T is the new physical particle, which means its mass can be arbitrary, and wb is the particle in SM.

In this process, the energy of the center of mass I set is 3TeV, and the range of T mass is 400-3000GeV. I found that when the mass of T particles is below 1400GeV, the ISR will raise the scattering cross section of this process, and when the mass of T particles is above 1400GeV , the ISR will depress the scattering cross section of this process.

Raising the scattering cross section I can understand: the Breit-wigner shape of the Z which boost the contribution. But as the quality changes first up and then down it confuses me.

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