MadGraph5_aMC@NLO

qurak and anti-quark treatment at LHE level

Asked by Lata Panwar

Dear experts,

I have a query regarding the quark and anti-quark treatment in process I generate for ee collision. I generate events using:
define q = u d u~ d~
generate e+ e- > Z > q q [QCD]

For these events, when I see pz/p distribution, I find it is asymmetric when I treat quark (q) and antiquark (qbar) separately from LHE file. Under the assumption that I can't distinguish q and qbar, I get symmetric distribution of pz/p (black line in plot given below) which I expected for q and qbar separately as well (red and blue line in the plot).
Plot is given here https://drive.google.com/file/d/1h94ptlWgaihzc3nOssMwZAyt7MB5jVHn/view?usp=sharing

Is my understanding is right if it is a limitation how particle information is written at LHE level and one should not treat q and qqbar as distinguishable particle at LHE level?

Or there is problem with way I generate the process given above.

Best,

Lata

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

lhef file are recording information at parton level which the goal to be used for parton-shower study.
Not all information can be translated to observable within the detector.

In itself all your plot are fine/physical at parton level. But those plots are not what you will observe in your detector (at least not always) this is in particular true for quark that will radiates and then hadronize.

However I will not call that a limitation of the lhef format. (But this depends of the point of view)

Cheers,

Olivier

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Lata Panwar (lpanwar6) said : 		#2

Thanks for your prompt response.

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Lata Panwar (lpanwar6) said : 		#3

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