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Open Access item On the background in the gamma p -> omega(pi(0)gamma)p reaction and mixed event simulation

Authors:Kaskulov, Murat
Hernández, Eliecer
Oset, Eulogi
Issue Date:Nov-2010
Publisher:Springer
Citation:European Physical Journal A - Hadrons and Nuclei 46 (2): 223-230 (2010)
Abstract:In this paper we evaluate sources of background of the gamma p -> omega p reaction, with the omega detected through its pi(0)gamma decay channel, to compare with the experiment carried out at ELSA. We find background from gamma p -> pi(0)pi(0)p followed by decay of a pi(0) into two gamma, recombining one pi(0) and one gamma, and from the gamma p -> pi(0)eta p reaction with subsequent decay of the eta into two photons. This background accounts for the data at pi(0)gamma invariant masses beyond 700 MeV, but strength is missing at lower invariant masses which was attributed to photon misidentification events, which we simulate to get a good reproduction of the experimental background. Once this is done, we perform an event mixing simulation to reproduce the calculated background and we find that the method provides a good description of the background. A closer look reveals this is accidental. We show that the mixed event generated background in the region of the omega mass and beyond is completely tied to the events at low pi(0)gamma invariant masses where the d sigma/dM(pi 0 gamma) distribution is much larger. This has as a consequence that the mixed event method produces the same background at high invariant masses independently of the actual background in that region, as a consequence of which, the method is unsuited to give the background at energies around the peak of the omega and beyond.
Publisher version (URL):http://dx.doi.org/10.1140/epja/i2010-11033-x
URI:http://hdl.handle.net/10261/32089
ISSN:1434-6001
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