J/Ψ event selection algorithm - status

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11.10.2005, 3rd Futur eDAQ M.Krauze, J/Ψ event selection algorit hm - status 1 J/Ψ event selection algorithm - status Maciej Krauze Institute of Physics University of Silesia, Katowice

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J/Ψ event selection algorithm - status. Maciej Krauze Institute of Physics University of Silesia, Katowice. Motivations. there are many background events due to very low J/ Ψ multiplicity reduction of the number of events in order to make it possible to store the data - PowerPoint PPT Presentation

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  • J/ event selection algorithm - statusMaciej Krauze Institute of PhysicsUniversity of Silesia, Katowice

    M.Krauze, J/ event selection algorithm - status

  • MotivationsRequirements of the methodfast because we measure at the full beam luminosityusing as less detector information as possible (currently: 3 stations of the Transition Radiation Detector)efficient to reduce the bulk of data passed to the next level analysis system

    there are many background events due to very low J/ multiplicityreduction of the number of eventsin order to make it possible to store the datato make the online analysis feasible

    M.Krauze, J/ event selection algorithm - status

  • Software toolsThe detector layout used in our studies

    UrQMD, Pluto, Geant & ROOTas a software base, CBM framework package was used; this package incorporates TRD detectors layout

    M.Krauze, J/ event selection algorithm - status

  • it can provide information about the particles trajectory and momentum (estimation!)it can distinguish between e+e- and hadrons (, p)95-99% of hadron rejection (depends on the particles momentum)

    the detector has large material budget so the the multiple scattering process has an influence on obtained resultsnot very high resolutionWhy TRD can be usefull for background event reduction

    M.Krauze, J/ event selection algorithm - status

  • Event selection methods & ideasHow?the main selection critterion is the invariant mass valuewe take every 2 particles of unlike charge within the same event and calculate the invariant mass of the pairfor the J/ particles, the invariant mass of the decay pair is 3.1 GeV/c2if the event does not contain any pairs of invariant mass greater than 2 GeV/c2, it is REJECTED

    to supress as many background events as possibleto preserve the signal

    M.Krauze, J/ event selection algorithm - status

  • Transversal momentum cutFurther reduction of the number of particles taken to the combinatorics (speed!)non-bending plane cut (Y):removes low-energy particles from backgroundremoves some fraction of signal (depends on the threshold value)to perform it we need a magnetic field and a method of momentum reconstruction

    M.Krauze, J/ event selection algorithm - status

  • Further reduction of the number of particles taken to the combinatorics (continued)bending plane cut (X):XZ1 mTRD1 TRD2Targetthese two geometric cuts combined reject 75% of secondaries while only 3% of signal is lost

    M.Krauze, J/ event selection algorithm - status

  • Requirements of the methodSummary and next stepsthe algorithm has roughly 90% efficiency or more (depends on the parameters used)we have to consider realistic track finderone can use some additional cuts (Pt angle, opening angle, momentum value etc.)to achieve greater efficiency, it may be necessary to use information from additional detector(s)

    fast track finder (at present we consider ideal tracks)precise track fitter (Kalman Filter)momentum determination method (fast and precise)

    M.Krauze, J/ event selection algorithm - status