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## Reconstructing Momenta from a Decay

Forum: Event and Track Management
Date: 27 Apr, 2015
From: Chelsea Bartram <Chelsea Bartram>

 Hi all, I am currently trying to reconstruct the angle between two outgoing particles from a decay. The decay physics comes from a generator which I wrote myself. In my code, the angle between these two vectors is pulled from a specific angular distribution. The momenta is then set using G4DynamicParticle. I then retrieve the two outgoing particles in my SteppingAction code and pass them to a function in my EventAction class which reconstructs the angle between the two. Unfortunately, the angular distribution has a tail. It seems that frequently, the angle between the two particles is reconstructed to be smaller than it actually is. I can think of 3 possible solutions to this problem. 1) I am not accurately identifying the events which I need 2) I am not obtaining the momentum at the vertex of the decay and therefore some scattering is occurring 3) the momentum direction is not defined how I think it is. I am using the GetVertexMomentum() function in the stepping action to retrieve the momenta at the vertex. My question is, is this momentum defined such that the origin is the world reference frame, or is the origin the decay vertex? What is the proper way to do this? I have included some histograms for reference. Any help would be much appreciated! Thank you, Chelsea ``` Attachment: http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2015/04/27/14.37-6072-Psi_Input.png http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2015/04/27/14.37-52540-Psi_Recon.png http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2015/04/27/14.37-62932-Possible_Psi_Problem.pdf ```

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1 Re: Reconstructing Momenta from a Decay   (Gumplinger Peter - 30 Apr, 2015)
 to: "Reconstructing Momenta from a Decay"
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