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Fitters and hyperons [message #20502] Fri, 10 March 2017 13:36 Go to next message
Karin Schönning
Messages: 65
Registered: August 2012
Location: Uppsala University
continuous participant
From: 140.181.9*
Dear Ralph et al.,

regarding vertex fitters, tree fitters and 4C fitters: which fitters assume outgoing tracks being helices? If I understood correctly:

1) The vertex fit assumes two outgoing helix trajectories
2) The tree fitter should treat both neutral and charged tracks but one needs to fix the masses of the intermediate states
3) The 4C fit assumes helices coming from the interaction point and should therefore not be used in any hyperon channel

Is this correct?

Kindest regards,
/Karin
Re: Fitters and hyperons [message #20506 is a reply to message #20502] Mon, 13 March 2017 10:02 Go to previous message
Ralf Kliemt is currently offline  Ralf Kliemt
Messages: 507
Registered: May 2007
Location: GSI, Darmstadt
first-grade participant

From: *gsi.de
Hi Karin,

I'll go by the numbers. However, I attached an overview (from back in 2014) on the fitters which you may find interesting.

1) Our Vertex fit is properly tested with min. two helices. Neutrals were just attached to the vertex, but not included in the fit. The addition of the neutrals in the PndKinVtxFit has to be re-checked.

2) The treefitter is prepared to fit neutrals as lines and charged particles as approximated lines (to be revisited) close to a pre-calculated vertex. Setting mass constraints of narrow states is favorable.

3) The 4C fit does not care about vertices. Every particle should have been propagated on its trajectory to its creation point. The 4C fit does only use the four-momenta of the final state particles. You can make a combined particle being treated as final state particle by using Lock().

Cheers!
Ralf
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