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The European Physical Journal A

, Volume 46, Issue 2, pp 223–230 | Cite as

On the background in the \( \gamma\)p \( \rightarrow\) \( \omega\)(\( \pi^{0}_{}\) \( \gamma\))p reaction and mixed event simulation

  • M. KaskulovEmail author
  • E. Hernández
  • E. Oset
Regular Article - Theoretical Physics

Abstract.

In this paper we evaluate sources of background of the \(\ensuremath\gamma p \rightarrow \omega p\) reaction, with the \( \omega\) detected through its \(\ensuremath \pi^0 \gamma\) decay channel, to compare with the experiment carried out at ELSA. We find background from \(\ensuremath\gamma p \rightarrow \pi^0 \pi^0 p\) followed by decay of a \(\ensuremath\pi^0\) into two \( \gamma\) , recombining one \(\ensuremath\pi^0\) and one \( \gamma\) , and from the \(\ensuremath\gamma p \rightarrow \pi^0 \eta p\) reaction with subsequent decay of the \( \eta\) into two photons. This background accounts for the data at \(\ensuremath \pi^0 \gamma\) invariant masses beyond 700MeV, 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 \(\ensuremath \pi^0 \gamma\) invariant masses where the \( {{d\sigma } \mathord{\left/ {\vphantom {{d\sigma } {dM_{\pi ^0 \gamma } }}} \right. \kern-\nulldelimiterspace} {dM_{\pi ^0 \gamma } }} \) 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.

Keywords

Invariant Mass Mixed Event Rest Frame Actual Background NA60 Collaboration 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© SIF, Springer-Verlag Berlin Heidelberg 2010

Authors and Affiliations

  1. 1.Institut für Theoretische PhysikUniversität GiessenGiessenGermany
  2. 2.Departamento de Fısica Fundamental e IUFFyMUniversidad de SalamancaSalamancaSpain
  3. 3.Departamento de Fısica Teórica e IFICCentro Mixto Universidad de Valencia-CSIC, Institutos de Investigación de PaternaValenciaSpain

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