TOF (and Global) PID

F. Pierella for the TOF-Offline GroupINFN & Bologna UniversityPPR 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;

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 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

i.e.

assumption massm

momentum tedreconstruc p

length track tedreconstruc l

1pm

lt

i

ii

2

General Constraint on Probability Space from previous definition

Positivness and unitarity

Distribution of Probabilities for Pions (100 HIJING ev, B=0.4T)

Distribution of Probabilities for Kaons

Distribution of Probabilities for Protons

Expected anticorrelation on Probability space

TOF PID 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 PID 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)

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)

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 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 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).