[G12] Missing mass plot for pKK -- Advice needed

[Dennis Weygand]

I can make no sense of your email: you must provide more information:

Begin with the final state or topology you are investigating.
Next: what was your selection criteria and what skims did you use?
What is "E" and what is "P"?
How exactly did you calculate the mm_p variables?
How did you choose the photon? 

The obvious reason your events are not physical, i.e. the mm is imaginary, is because your K's are really pi's, or you have chosen the wrong photon.

Dennis

On Nov 12, 2009, at 5:38 PM, Mukesh Saini wrote:

> Hello all,
> 
> I am attaching a few plots and need help to understand the negative masses we get. I am using ClasEvent and bos2ntuple code to make my ntuples.
> 
> Code to make the plots:
> 
> root [30] ntp->Draw("sqrt( -mm_px**2 - mm_py**2 - mm_pz**2 + mm_t**2 ) -mm","","")
> root [31] ntp->Draw("sqrt( -mm_px**2 - mm_py**2 - mm_pz**2 + mm_t**2 ) ","","")   
> root [32] ntp->Draw("mm","","")                                                    
> 
> As you can see majority of mm is less than 0,hence I lose a lot of events when i make my cuts. The other way that I can calculate sqrt(E**2 - P**2) seems to give me the wrong answer too (All values positive even when I switch the signs on all terms inside the sqrt). I am sure this is some famous functionality that I am just unaware of. Please do let me know how to understand this and if needed fix this. 
> 
> Thanks,
> Mukesh.
> 
> Graduate Student,
> Florida State University.
> <mm.gif><mm_calc.gif><mm-mm.gif>_______________________________________________
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--
Dennis Weygand
weygand at jlab.org
(757) 269-5926