[Clas_lmd] Review of analysis procedure

[Cathrina Sowa]

Dear colleagues,

I would like to present preliminary results of the analysis (gamma p -> 
p pi+ pi- (eta))
I am working on at a parallel session at the upcoming EUNPC 2015 
conference in Groningen.

The analysis was presented at the CLAS collaboration meeting in June at the
the Hadron Spectroscopy session [1]. All concerns and comments raised 
during the
discussion after the talk have been considered. The energy dependent 
scaling factor for
the differential cross section for example is now no longer needed.

In order to follow the required procedure, Johann and Mario advised me to
discuss the updated analysis with the g12 run group. Below I prepared a 
summary of the
data selection and preliminary results I would like to include in my 
presentation.

I would be happy about any comments and suggestions from your side.

Best regards,
Cathrina

[1]: https://www.jlab.org/Hall-B/secure/hadron/meetings/18jun15/sowa.pdf


MOTIVATION
Study of excited eta states in photo production, with
emphasis on the production of the glueball candidate eta(1405). The 
eta(1405)
production in photo-production can be compared to its production in
gluon-rich processes to shed further light on its nature.

As a reference and validation for the upper limit of the eta(1405) cross 
section, the
eta' differential cross section will be determined and compared to the 
published g11
results.


DATA
- run numbers: 56520-56572, 56573-56594, 56608-56646 which were 
event-sorted
according to 2-2pos1neg_not_1ckaon1ctrk

- fulfilling the same trigger conditions: 3 charged tracks in 3 
different sectors or
2 charged track in 2 different sectors with a beam energy above 3.6 GeV

EVENT SELECTION
- two positively-charged tracks for the proton and the pi+ as well as 
one negatively-charged track for the pi−.

- g12_ecor.hpp package is used for the beam energy corrections

- g12_pcor.hpp package is used for momentum correction

- Energyloss was accounted with the the standard eloss corrections

- All three particles correspond to the same beam photon

- Standard cuts on vertices (Fig1, Fig2), minimum momenta(Fig3), beta Vs 
momentum(Fig4), fiducial volume (Fig5) and timing (Fig6) are included

- Q-value method applied on the missing eta to achieve a better 
background suppression (Fig7) (Black: Before, Blue: 1-Q weighted, Red: Q 
weighted)


PRELIMINARY RESULTS

Fig8: inv. eta pi+ pi- mass spectrum

red w/ error bars: w/o Q-weight; blue: Q-weighted

Fig9: differential eta' cross section
- GEANT based Monte Carlo events are used for efficiency correction
following the procedure documented in the g12 wiki

- The photon flux is obtained as described in the g12 wiki

- To compare to the published g11 results, the same W binning is used

Fig8: Comparison of the diff. eta' cross section for g11 (pink) and g12 
(black) data
The distributions are in good agreement now.

-- 
M.Sc. Cathrina Sowa
Ph. D. student
Institut für Experimentalphysik I
Ruhr-Universität Bochum
Universitätsstr. 150
44801 Bochum

Office: NB 2/74
Tel.: 0234-32-23564
Web: www.ep1.rub.de

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