PaPid Class Reference

functions for RICH particle identification. More...

#include <PaPid.h>

Public Member Functions
bool	CheckRichInfo (PaTrack track)
	Check the RICH buffer in mDST; false if no RICH information is found.
float	GetLike (int tag, PaTrack track)
	Gives Likelihood values.
float	GetLikeToBackground (int tag, PaTrack track)
	Gives Likelihood values divided to the background likelihood value:.
bool	IsKaon (PaTrack track, float qmom, float polar_rich)
	True if particle is identified as K, otherwise false.
int	LikePid (PaTrack track)
	Function to identify the particles with Likelihood; suggested as a starting point for identification.
float	SecondLike (PaTrack track)
	Gives the ratio of the likelihood of the identified particle (from function LikePid) to the second maximum likelihood.
double	Mass (PaTrack track, double n, double mom)
	Compute hadron mass starting from n (refractive index value) and momentum values.
double	Theta_Ch (PaTrack track)
	Gives Cherenkov angle (in rad) from ring fit.

Detailed Description

functions for RICH particle identification.

This class can be used to identify particles using the RICH informations (likelihoods - LH).

A starting point for the identification is provided in the function "LikePid" in which the hadrons are identified choosing the mass hypothesis giving the maximum likelihood.

To have a cleaner identification, afterwards cuts on the ratios LH/LH_{background} and LH/LH_{2nd max} are usually done: the two ratios are provided from the class members "GetLikeToBackground" and "SecondLike"; the cuts have to be tuned on data from the user.

The function IsKaon is given just as an example of cuts tuned as a function of the phase space of the particle.

NB: In the function explanation, the sentence "old versions of RICH code" indicates the RICH code used before 2004, in which the muon and electron LH were not computed.

Author:: Federica Sozzi <fsozzi@mail.cern.ch>

Member Function Documentation

float PaPid::GetLike	(	int	tag,
		PaTrack	track
	)

Gives Likelihood values.

Parameters:

	tag	0 - pion 1 - kaon 2 - proton 3 - electron (not available in old versions of RICH code) 4 - muon (not available in old versions of RICH code) 5 - background (equal to 1 in old versions of RICH code)
	track	PaTrack object

Returns:: Likelihood value (-1 if no RICH info available)

Warning:: in the old versions of RICH code, the likelihood values are divided for likelihood background.

References CheckRichInfo(), PaTrack::NRichInf(), and PaTrack::RichInf().

Referenced by LikePid(), and SecondLike().

float PaPid::GetLikeToBackground	(	int	tag,
		PaTrack	track
	)

Gives Likelihood values divided to the background likelihood value:.

Parameters:

	tag	0 - pion 1 - kaon 2 - proton 3 - electron (not available in old versions of RICH code) 4 - muon (not available in old versions of RICH code) 5 - background
	track	PaTrack object

Returns:: Likelihood value divided to the background likelihood value (-1 if no RICH info available)

Warning:: in the old code of the RICH, this function is equivalent to the GetLike, since likelihood values are already divided for likelihood background in the buffer.

References CheckRichInfo(), PaTrack::NRichInf(), and PaTrack::RichInf().

Referenced by IsKaon().

bool PaPid::IsKaon	(	PaTrack	track,
		float	qmom,
		float	polar_rich
	)

True if particle is identified as K, otherwise false.

The identification is made asking the kaon to have the maximum LH value (function LikePid) and then performing a cut on the 2 variables: LH/LH_{background} and LH/LH_{2nd max}

The cuts depend on the particle charge, on the momentum and on the polar angle (in rad) at the RICH entrance. The parameters have been tuned on phi samples in data.

Warning:: This function is given only as a possible example of identification procedure; it should be better to tune the cuts of identification independently in every analysis.

References CheckRichInfo(), GetLikeToBackground(), LikePid(), PaTrack::NRichInf(), and SecondLike().

int PaPid::LikePid ( PaTrack track )

Function to identify the particles with Likelihood; suggested as a starting point for identification.

Select the mass hypothesis corresponding to the max likelihood value

Returns:: 0 pion hypothesis; 1 kaon; 2 proton; 3 electron (not available in old versions of RICH code - in this function excluded from identification if p > 8 GeV/c); 4 muon (not available in old versions of RICH code - in this function excluded from identification); 5 background (not available in old versions of RICH code); -1 if no RICH info available or no maximum found or momentum > 50 GeV/c.

Warning:: RICH is not expected to distinguish between pions and muons, and between pions and electron above ~ 8 GeV/c

References CheckRichInfo(), GetLike(), PaTPar::Mom(), PaTrack::NRichInf(), and PaTrack::vTPar().

Referenced by IsKaon(), and SecondLike().

double PaPid::Mass	(	PaTrack	track,
		double	n,
		double	mom
	)

Compute hadron mass starting from n (refractive index value) and momentum values.

Returns:: -1 if no RICH info available or cherenkov angle from the ring fit is zero.

References CheckRichInfo(), and Theta_Ch().

float PaPid::SecondLike ( PaTrack track )

Gives the ratio of the likelihood of the identified particle (from function LikePid) to the second maximum likelihood.

Returns:: -1 if no RICH info available or no max LH found

References GetLike(), LikePid(), PaTPar::Mom(), PaTrack::NRichInf(), and PaTrack::vTPar().

Referenced by IsKaon().

double PaPid::Theta_Ch ( PaTrack track )

Gives Cherenkov angle (in rad) from ring fit.

Returns:: -1 if no RICH info available

References CheckRichInfo(), and PaTrack::RichInf().

Referenced by Mass().

The documentation for this class was generated from the following files:

lib/PaPid.h
lib/PaPid.cc

PaPid Class Reference

Public Member Functions

Detailed Description

Member Function Documentation