J/Ψ event selection algorithm - status

8
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

description

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

Transcript of J/Ψ event selection algorithm - status

Page 1: J/Ψ event selection algorithm - status

11.10.2005, 3rd FutureDAQ

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

1

J/Ψ event selection algorithm - status

Maciej KrauzeInstitute of PhysicsUniversity of Silesia, Katowice

Page 2: J/Ψ event selection algorithm - status

11.10.2005, 3rd FutureDAQ

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

2

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

Page 3: J/Ψ event selection algorithm - status

11.10.2005, 3rd FutureDAQ

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

3

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

Page 4: J/Ψ event selection algorithm - status

11.10.2005, 3rd FutureDAQ

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

4

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

Page 5: J/Ψ event selection algorithm - status

11.10.2005, 3rd FutureDAQ

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

5

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

Page 6: J/Ψ event selection algorithm - status

11.10.2005, 3rd FutureDAQ

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

6

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

Page 7: J/Ψ event selection algorithm - status

11.10.2005, 3rd FutureDAQ

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

7

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

Page 8: J/Ψ event selection algorithm - status

11.10.2005, 3rd FutureDAQ

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

8

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)