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J/Ψ event selection algorithm - status PowerPoint PPT Presentation


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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

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J/Ψ event selection algorithm - status

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J event selection algorithm status

J/Ψevent selection algorithm - status

Maciej KrauzeInstitute of Physics

University of Silesia, Katowice

M.Krauze, J/Ψ event selection algorithm - status


Motivations

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

    • to make the online analysis feasible

Requirements of the method

  • fast  because we measure at the full beam luminosity

    • using 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

M.Krauze, J/Ψ event selection algorithm - status


J event selection algorithm status

Software tools

  • UrQMD, Pluto, Geant & ROOT

  • as a software base, CBM framework package was used; this package incorporates TRD detectors layout

The detector layout used in our studies

M.Krauze, J/Ψ event selection algorithm - status


J event selection algorithm status

Why TRD can be usefull for background event reduction

  • it can provide information about the particle’s trajectory and momentum (estimation!)

  • it can distinguish between e+e- and hadrons (Π, p)

    • 95-99% of hadron rejection (depends on the particle’s momentum)

  • the detector has large material budget so the the multiple scattering process has an influence on obtained results

  • not very high resolution

M.Krauze, J/Ψ event selection algorithm - status


J event selection algorithm status

Event selection – methods & ideas

  • to supress as many background events as possible

  • to preserve the signal

How?

  • the main selection critterion is the invariant mass value

    • we take every 2 particles of unlike charge within the same event and calculate the invariant mass of the pair

    • for the J/Ψ particles, the invariant mass of the decay pair is 3.1 GeV/c2

    • if the event does not contain any pairs of invariant mass greater than 2 GeV/c2, it is REJECTED

M.Krauze, J/Ψ event selection algorithm - status


J event selection algorithm status

TRD1 TRD2

Y

Target

Z

Transversal momentum cut

  • removes low-energy particles from background

  • removes some fraction of signal (depends on the threshold value)

  • to perform it we need a magnetic field and a method of momentum reconstruction

Further reduction of the number of particles taken to the combinatorics (speed!)

  • non-bending plane cut (Y):

M.Krauze, J/Ψ event selection algorithm - status


J event selection algorithm status

Further reduction of the number of particles taken to the combinatorics (continued)

  • bending plane cut (X):

X

Target

Z

these two geometric cuts combined reject 75% of secondaries while only 3% of signal is lost

TRD1 TRD2

1 m

M.Krauze, J/Ψ event selection algorithm - status


J event selection algorithm status

Requirements of the method

  • fast track finder (at present we consider ideal tracks)

  • precise track fitter (Kalman Filter)

  • momentum determination method (fast and precise)

Summary and next steps

  • the algorithm has roughly 90% efficiency or more (depends on the parameters used)

  • we have to consider realistic track finder

  • one 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)

M.Krauze, J/Ψ event selection algorithm - status


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