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some options for eta_c analysis [message #12709]

Tue, 11 October 2011 14:55

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

first-grade participant

From: *fuw.edu.pl

Hi,

I have tried several options in eta_c reconstruction as its was suggested by Stefano and here are the results.

I used for analysis data on grid run 925oldnocu (release july11).

1. Instead of selecting best eta_c candidate after vertex fit (using its chi2) I tried a preselection of best candidate using chi2 defined as (totalreco_mass-etac_mass)^2/sigma(eta_c)^2+(phi1reco_mass-phimass)^2/si gma(phi)+(phi2reco_mass-phimass)^2/sigma(phi).

And here there is a small improvement in efficiency and eta_c resolution and no improvement in phi mass resolution (efficiency 24.0%, sigma(eta_c)=32.8 MeV, sigma(phi)= 3.92 MeV).
index.php?t=getfile&id=6667&private=0

For comparison with selection of best candidate after vertex fit (efficiency 22.8%, sigma(eta_c)=33.2 MeV, sigma(phi)= 3.92 MeV)

index.php?t=getfile&id=6668&private=0

.

2. I also tried to perform a mass fitter for phi mass and here is the eta_c mass resolution after combining 2 phi after this fitter (PndKinFitter).

index.php?t=getfile&id=6669&private=0

Here the best candidate is selected by difference between reconstructed and nominal eta_c mass and resolution is 34.7 MeV, i.e worse than with vertex fit. So I would exclude this option in eta_c analysis.

Dima

Attachment: m_vertex_fit_preselection.png
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Attachment: m_vertex_fit.png
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Attachment: m_mass_fit.png
(Size: 12.11KB, Downloaded 664 times)

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Re: some options for eta_c analysis [message #12710 is a reply to message #12709]

Tue, 11 October 2011 15:28

StefanoSpataro
Messages: 2736
Registered: June 2005
Location: Torino

first-grade participant

From: 193.205.228*

Hi Dima,
thanks for the checks.
If I compare the maximum of etac peaks with the last plot, it seems to me that with the mass fitter you have higher statistics (or maybe higher bg). Quite strange...

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