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Vertex fitter for eta_c analysis [message #12251]

Wed, 13 July 2011 16:31

Dima Melnychuk
Messages: 213
Registered: April 2004
Location: National Centre for Nucle...

first-grade participant

From: *fuw.edu.pl

Dear colleagues,

I would like to inform you that Elisa has found a bug in my eta_c analysis macro related to usage of vertex fitter and after correction it gives reasonable results in the sense of mass distribution.

Using PndKinVtxFitter eta_c and phi mass looks like
index.php?t=getfile&id=6499&private=0

And for comparison using 4C kinematics fit

index.php?t=getfile&id=6500&private=0

So in both cases mass resolution loos almost identical.

In case of 4C-fit daughter particles are not updated after the fit, i.e. it shouldn't modify the shape of mass distribution, but for vertex fit daughter particles are updated and I would expect bigger improvement/difference of at least eta_c mass, but it's not the case.

And I didn't look yet how position of the vertex is reconstructed, i.e. (reconstructed - MonteCarlo).

But in principle now both fitters could be used in analysis.

Dima

Attachment: m_etac_stt_vtx.png
(Size: 12.53KB, Downloaded 985 times)
Attachment: m_etac_stt_4c.png
(Size: 12.48KB, Downloaded 1000 times)

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Re: Vertex fitter for eta_c analysis [message #12252 is a reply to message #12251]

Wed, 13 July 2011 17:07

Klaus Götzen
Messages: 293
Registered: June 2006
Location: GSI

first-grade participant

From: *gsi.de

Hi Dima,

that's good news! Concerning the vertex fit I wouldn't expect too much improvement in mass resolution. In my Babar analysis I never observed significant mass resolution improvements from vertex fits, in particular for short living resonances.

Concerning updating of daughters I thought it's the other way around: I observed that the 4C fitter updates the daughters, but the vertex fitter doesn't...

However I'm taking a closer look at it anyways...

Cheers,
Klaus

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Re: Vertex fitter for eta_c analysis [message #12254 is a reply to message #12251]

Wed, 13 July 2011 19:20

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: *11-79-r.retail.telecomitalia.it

Do you see any differences with tpc?

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