Chapter 7
Particle Identification: Time-of-Flight,
Cherenkov and Transition Radiation
Detectors
Roger Forty and Olav Ullaland
7.1 Introduction
Particle identification, PID, is of crucial importance in most experiments. The
requirement can range from positive π/K identification in B-physics channels like
B 0
s →D ∓
s K ± against a background from B 0
s →D −
s π + which is ∼15 times more
abundant, to e/π separation at the level of ∼ 10 −2 for momenta >1 GeV/c in order
to effectively suppress a combinatorial background in channels like leptonic decays
of heavy vector resonances.
The detectors should be non-destructive and should in addition introduce as
little radiation length or interaction length as possible. We will in this chapter
examine three experimental techniques which can be deployed for charged particle
identification.
That is Time-of-Flight, Sect. 7.2, and Cherenkov detectors which measure the
particle velocity relative to the speed of light in vacuum, β = v/c, Sect. 7.4, and
transition radiation detectors which are sensitive to γ = 1/
(1 − β 2 ) of the charged
particle, Sect. 7.5. These detectors cannot be stand-alone detectors for PID purposes.
They all require that the momentum of the particle is defined by other means, see
Sect. 4.3, and then
m 2
p 2 =
1
γ 2 − 1
=
1 − β 2
β 2
(7.1)
allowing the mass m of the particle to be determined.
Only a limited amount of theory is included in this chapter as this is covered
elsewhere in this book. The main emphasis will be on the working principles of these
R. Forty () · O. Ullaland
CERN, Geneva, Switzerland
e-mail: Roger.Forty@cern.ch
© The Author(s) 2020
C. W. Fabjan, H. Schopper (eds.), Particle Physics Reference Library,
https://doi.org/10.1007/978-3-030-35318-6_7
281
Particle Identification: Time-of-Flight,
Cherenkov and Transition Radiation
Detectors
Roger Forty and Olav Ullaland
7.1 Introduction
Particle identification, PID, is of crucial importance in most experiments. The
requirement can range from positive π/K identification in B-physics channels like
B 0
s →D ∓
s K ± against a background from B 0
s →D −
s π + which is ∼15 times more
abundant, to e/π separation at the level of ∼ 10 −2 for momenta >1 GeV/c in order
to effectively suppress a combinatorial background in channels like leptonic decays
of heavy vector resonances.
The detectors should be non-destructive and should in addition introduce as
little radiation length or interaction length as possible. We will in this chapter
examine three experimental techniques which can be deployed for charged particle
identification.
That is Time-of-Flight, Sect. 7.2, and Cherenkov detectors which measure the
particle velocity relative to the speed of light in vacuum, β = v/c, Sect. 7.4, and
transition radiation detectors which are sensitive to γ = 1/
(1 − β 2 ) of the charged
particle, Sect. 7.5. These detectors cannot be stand-alone detectors for PID purposes.
They all require that the momentum of the particle is defined by other means, see
Sect. 4.3, and then
m 2
p 2 =
1
γ 2 − 1
=
1 − β 2
β 2
(7.1)
allowing the mass m of the particle to be determined.
Only a limited amount of theory is included in this chapter as this is covered
elsewhere in this book. The main emphasis will be on the working principles of these
R. Forty () · O. Ullaland
CERN, Geneva, Switzerland
e-mail: Roger.Forty@cern.ch
© The Author(s) 2020
C. W. Fabjan, H. Schopper (eds.), Particle Physics Reference Library,
https://doi.org/10.1007/978-3-030-35318-6_7
281