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TOF (and Global) PID. F. Pierella for the TOF-Offline Group INFN & Bologna University PPR Meeting, January 2003. Summary and Highlights. TOF-PID Probability approach has been implemented (on time-of-flight basis), so TOF is ready to provide its own probability;

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Tof and global pid

TOF (and Global) PID

F. Pierella

for the TOF-Offline Group

INFN & Bologna University

PPR Meeting, January 2003


Summary and highlights
Summary and Highlights

  • TOF-PID Probability approach has been implemented (on time-of-flight basis), so TOF is ready to provide its own probability;

  • A more general approach to TOF PID (based on various particle bands) has been considered;

  • Global (TOF+TPC+ITS) PID is “in fieri” and results are on the way;


Definition of probability for from tof
Definition of Probability for (from) TOF

  • From track length and momentum (given by reconstruction), and after a mass hypothesis for the current track, it is possible to derive the corresponding (“a priori”) time-of-flight;

  • A gaussian is generated

    • around the measured time-of-flight,

    • with a (fixed for each track) sigma equal to to the current measurement of the (mean) double-stack MRPC resolution;

  • Probabilities (after normalization) are derived from the gaussian in the previously calculated “a priori” times-of-flight



General constraint on probability space from previous definition
General Constraint on Probability Space from previous definition

  • Positivness and unitarity






Tof pid
TOF PID B=0.4T)

  • TOF PID “stand alone” is based (at least for kaons and protons) on particle bands in a given scatter plot (usually m vs p);

  • Contour cuts are introduced to define regions where a particle is said to be of a certain type (or not to be of a certain other type);

  • The contour cuts themselves are arbitrary (in the sense that they depend on the physical problem);


Tof pid1
TOF PID B=0.4T)

  • Moreover, PID based on contour cuts (2D, for the time being) is not the unique way to do PID (see e.g. the probability approach with which a “combination” of different detectors is possible, no cuts at all needed)

  • In any case, it is worth to introduce some generalization on particle bands (and not limit ourselves exclusively on reconstructed mass vs momentum scatter plot)


E g time of flight spectra 250 hijing ev b 0 4t
(e.g.) Time of Flight Spectra (250 HIJING ev., B=0.4T) B=0.4T)

  • Momentum vs Time-of-Flight: separation of the “bands” at high momentum (low particle statistics)

  • 1/Momentum vs Time-of-Flight: separation of the “bands” at low momentum (large particle statistics)


More on bands for tof pid as in phenix
More on Bands for TOF PID (as in PHENIX) B=0.4T)

  • Momentum vs Mass

  • Momentum vs Square Mass

  • Momentum vs Time-of-Flight difference from electron

  • 1/Momentum vs Time-of-Flight difference from electron

  • 1/() vs Momentum


Mass hypothesis and time of flight
Mass Hypothesis and time of flight B=0.4T)

  • Back step to probability approach based on times of flight;

  • Measured time-of-flight and à priori time-of-flight difference (mass hypothesis: pion, kaon, proton);

  • Bands for different particle types appear also there.


Example of global pid
Example of Global PID B=0.4T)

  • dE/dX from ITS-TPC

  • Reconstructed Momentum

  • Mass from Time-of-Flight

  • Notice that different combinations are possible (see the section on ‘bands’)

  • Moreover, if dE/dX is profitable for TOF (it provides a separation at low momentum –large statistics-, where TOF PID contamination is “high” for protons and kaons), the reverse is also true (TOF provides a separation in another “direction”, “mass direction” in this case).


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