Group eventdata-charge¶

group eventdata-charge

Track parameters store a single coefficient that describes charge and momentum.

This is either charge/momentum or 1/momentum, but the interpretation depends on what type of particle is described. In this code base this coefficient is always referred to as qOverP (or charge-over-momentum) even for uncharged particles. The following types are used to restrict the particle charge magnitude (at compile time) and support the umambigous extraction of charge and absolute momentum from said track parameter coefficient.

All types are designed to be interchangeable. Each one can be constructed with the input charge magnitude

Charge c(1_e);

and can then be used to extract the charge value

auto q = c.extractCharge(qOverP);

or the absolute momentum

auto p = c.extractMomentum(qOverP);

from the charge-over-momentum track parameter.

Functions

ACTS_STATIC_CHECK_CONCEPT(ChargeConcept, Neutral)¶

ACTS_STATIC_CHECK_CONCEPT(ChargeConcept, SinglyCharged)¶

ACTS_STATIC_CHECK_CONCEPT(ChargeConcept, NonNeutralCharge)¶

ACTS_STATIC_CHECK_CONCEPT(ChargeConcept, AnyCharge)¶

class AnyCharge

#include <Acts/EventData/Charge.hpp>

Charge and momentum interpretation for arbitrarily charged particles.

Only a charge magnitude identical to zero is interpreted as representing a neutral particle. This avoids ambiguities that might arise from using an approximate comparison with an arbitrary epsilon.

Public Functions

inline constexpr AnyCharge(float absQ) noexcept: Construct with the magnitude of the input charge.

inline constexpr AnyCharge(SinglyCharged) noexcept

inline constexpr AnyCharge(Neutral) noexcept

inline constexpr float absQ() const noexcept

template<typename T> inline constexpr auto extractCharge(T qOverP) const noexcept

template<typename T> inline constexpr auto extractMomentum(T qOverP) const noexcept

template<typename P, typename Q> inline constexpr auto qOverP(P momentum, Q signedQ) const noexcept

Friends

inline friend constexpr bool operator==(AnyCharge lhs, AnyCharge rhs) noexcept: Compare for equality.

struct Neutral

#include <Acts/EventData/Charge.hpp>

Charge and momentum interpretation for neutral particles.

Public Functions

constexpr Neutral() = default

inline constexpr Neutral(float absQ) noexcept

Construct and verify the input charge magnitude (in debug builds).

This constructor is only provided to allow consistent construction.

inline constexpr float absQ() const noexcept

template<typename T> inline constexpr auto extractCharge(T) const noexcept

template<typename T> inline constexpr auto extractMomentum(T qOverP) const noexcept

template<typename P, typename Q> inline constexpr auto qOverP(P momentum, Q signedQ) const noexcept

Friends

inline friend constexpr bool operator==(Neutral, Neutral) noexcept

Compare for equality.

This is always true as Neutral has no internal state. Must be available to provide a consistent interface.

class NonNeutralCharge

#include <Acts/EventData/Charge.hpp>

Charge and momentum interpretation for arbitrarily charged but not neutral particles.

Public Functions

inline constexpr NonNeutralCharge(float absQ) noexcept: Construct with the magnitude of the input charge.

inline constexpr NonNeutralCharge(SinglyCharged) noexcept

inline constexpr float absQ() const noexcept

template<typename T> inline constexpr auto extractCharge(T qOverP) const noexcept

template<typename T> inline constexpr auto extractMomentum(T qOverP) const noexcept

template<typename P, typename Q> inline constexpr auto qOverP(P momentum, Q signedQ) const noexcept

Friends

inline friend constexpr bool operator==(NonNeutralCharge lhs, NonNeutralCharge rhs) noexcept: Compare for equality.

struct SinglyCharged

#include <Acts/EventData/Charge.hpp>

Charge and momentum interpretation for particles with +-e charge.

Public Functions

constexpr SinglyCharged() = default

inline constexpr SinglyCharged(float absQ) noexcept

Construct and verify the input charge magnitude (in debug builds).

This constructor is only provided to allow consistent construction.

inline constexpr float absQ() const noexcept

template<typename T> inline constexpr auto extractCharge(T qOverP) const noexcept

template<typename T> inline constexpr auto extractMomentum(T qOverP) const noexcept

template<typename P, typename Q> inline constexpr auto qOverP(P momentum, Q signedQ) const noexcept

Friends

inline friend constexpr bool operator==(SinglyCharged, SinglyCharged) noexcept

Compare for equality.

This is always true as SinglyCharged has no internal state. Must be available to provide a consistent interface.