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
Jan 19, 2016
11.10.2005, 3rd FutureDAQ
M.Krauze, J/Ψ event selection algorithm - status
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J/Ψ event selection algorithm - status
Maciej KrauzeInstitute of PhysicsUniversity of Silesia, Katowice
11.10.2005, 3rd FutureDAQ
M.Krauze, J/Ψ event selection algorithm - status
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Motivations
Requirements of the method
o fast because we measure at the full beam luminosityo using as less detector information as possible (currently: 3
stations of the Transition Radiation Detector)o efficient to reduce the bulk of data passed to the next level
analysis system
o there are many background events due to very low J/Ψ multiplicity
o reduction of the number of eventso in order to make it possible to store the datao to make the online analysis feasible
11.10.2005, 3rd FutureDAQ
M.Krauze, J/Ψ event selection algorithm - status
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Software tools
The detector layout used in our studies
o UrQMD, Pluto, Geant & ROOTo as a software base, CBM framework package was used; this
package incorporates TRD detectors layout
11.10.2005, 3rd FutureDAQ
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o it can provide information about the particle’s trajectory and momentum (estimation!)
o it can distinguish between e+e- and hadrons (Π, p)o 95-99% of hadron rejection (depends on the particle’s
momentum)
o the detector has large material budget so the the multiple scattering process has an influence on obtained results
o not very high resolution
Why TRD can be usefull for background event reduction
11.10.2005, 3rd FutureDAQ
M.Krauze, J/Ψ event selection algorithm - status
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Event selection – methods & ideas
How?
o the main selection critterion is the invariant mass valueo we take every 2 particles of unlike charge within the same
event and calculate the invariant mass of the pairo for the J/Ψ particles, the invariant mass of the decay pair is
3.1 GeV/c2
o if the event does not contain any pairs of invariant mass greater than 2 GeV/c2, it is REJECTED
o to supress as many background events as possibleo to preserve the signal
11.10.2005, 3rd FutureDAQ
M.Krauze, J/Ψ event selection algorithm - status
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Transversal momentum cut
Further reduction of the number of particles taken to the combinatorics (speed!)
o non-bending plane cut (Y):
o removes low-energy particles from backgroundo removes some fraction of signal (depends on the threshold
value)o to perform it we need a magnetic field and a method of
momentum reconstruction
Y
Z
TRD1 TRD2
Target
11.10.2005, 3rd FutureDAQ
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Further reduction of the number of particles taken to the combinatorics (continued)
o bending plane cut (X):
X
Z
1 mTRD1 TRD2
Target
these two geometric cuts combined reject 75% of secondaries while only 3% of signal is lost
11.10.2005, 3rd FutureDAQ
M.Krauze, J/Ψ event selection algorithm - status
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Requirements of the method
Summary and next steps
o the algorithm has roughly 90% efficiency or more (depends on the parameters used)
o we have to consider realistic track findero one can use some additional cuts (Pt angle, opening angle,
momentum value etc.)o to achieve greater efficiency, it may be necessary to use
information from additional detector(s)
o fast track finder (at present we consider ideal tracks)o precise track fitter (Kalman Filter)o momentum determination method (fast and precise)