WHIZARD

An error in doing Z-lineshape

Asked by Dayun Qiu

Hi,
When I make a Z-linshape with reference to the example, I add the integral method statement “ $integration_method = "midpoint" ”. Then running, whizard reports an error:
              *** FATAL ERROR: Attempt to initialize single-channel integrator for multiple channels

But if I don't add the above statement, there will be no error. So what's going on?

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WHIZARD Edit question
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Juergen Reuter Edit question
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Juergen Reuter
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Dayun Qiu (dayun-sysu) said : 		#1

When I use the Z-lineshape example, I only set a structure “isr“ for the beam，just like "beams = e1, E1 => isr". Then the calculated cross section is all zero.

=============================================================================|
| It Calls Integral[fb] Error[fb] Err[%] Acc Eff[%] Chi2 N[It] |
|=============================================================================|
    1 0 0.0000000E+00 0.00E+00 0.00 0.00* 0.00
Warning: MC sampler initialization: sum of channel weights is zero
   2 0 0.0000000E+00 0.00E+00 0.00 0.00 0.00
|-----------------------------------------------------------------------------|
    2 0 0.0000000E+00 0.00E+00 0.00 0.00 0.00 0.00 2
|-----------------------------------------------------------------------------|
    3 0 0.0000000E+00 0.00E+00 0.00 0.00 0.00
|-----------------------------------------------------------------------------|
    3 0 0.0000000E+00 0.00E+00 0.00 0.00 0.00

The file I use is Z-linshape.sin, which can be found in the share/examples folder of the WHIZARD installation.
So how should I solve this problem?

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Best Juergen Reuter (j.r.reuter) said : 		#2

Hi Dayun,
He midpoint Integration cannot be used for phasespaces with more than one Integration channel. Please use the default, i.e. VAMP.
For the Z-lineshape, I assume it is the radiative process with an additional photon that vanishes. The reason is that when switching ISR on Whizard applies the photon cut also to the ISR photon. There you would have to use a selection of the photon.
Cheers,
     JRR

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Dayun Qiu (dayun-sysu) said : 		#3

Thanks Juergen Reuter, that solved my question.