Rivet  1.8.0
Public Member Functions | Protected Member Functions | List of all members
Rivet::Thrust Class Reference

Get the e+ e- thrust basis and the thrust, thrust major and thrust minor scalars. More...

#include <Thrust.hh>

Inheritance diagram for Rivet::Thrust:
Rivet::AxesDefinition Rivet::Projection Rivet::ProjectionApplier

Public Member Functions

 Thrust ()
 Constructor.
 Thrust (const FinalState &fsp)
virtual const Projectionclone () const
 Clone on the heap.
double thrust () const
double thrustMajor () const
 The thrust major scalar, $ M $, (thrust along thrust major axis).
double thrustMinor () const
 The thrust minor scalar, $ m $, (thrust along thrust minor axis).
double oblateness () const
 The oblateness, $ O = M - m $ .
const Vector3thrustAxis () const
const Vector3thrustMajorAxis () const
 The thrust major axis (axis of max thrust perpendicular to thrust axis).
const Vector3thrustMinorAxis () const
 The thrust minor axis (axis perpendicular to thrust and thrust major).
const Vector3axis1 () const
 AxesDefinition axis accessors.
const Vector3axis2 () const
 The 2nd most significant ("major") axis.
const Vector3axis3 () const
 The least significant ("minor") axis.
Direct methods

Ways to do the calculation directly, without engaging the caching system

void calc (const FinalState &fs)
 Manually calculate the thrust, without engaging the caching system.
void calc (const vector< Particle > &fsparticles)
 Manually calculate the thrust, without engaging the caching system.
void calc (const vector< FourMomentum > &fsmomenta)
 Manually calculate the thrust, without engaging the caching system.
void calc (const vector< Vector3 > &threeMomenta)
 Manually calculate the thrust, without engaging the caching system.
- Public Member Functions inherited from Rivet::AxesDefinition
virtual ~AxesDefinition ()
 Virtual destructor.
- Public Member Functions inherited from Rivet::Projection
bool before (const Projection &p) const
virtual const std::set< PdgIdPairbeamPairs () const
virtual std::string name () const
 Get the name of the projection.
ProjectionaddPdgIdPair (PdgId beam1, PdgId beam2)
 Add a colliding beam pair.
LoggetLog () const
 Get a Log object based on the getName() property of the calling projection object.
void setName (const std::string &name)
 Used by derived classes to set their name.
 Projection ()
 The default constructor.
virtual ~Projection ()
 The destructor.
- Public Member Functions inherited from Rivet::ProjectionApplier
 ProjectionApplier ()
 Constructor.
std::set< ConstProjectionPtrgetProjections () const
 Get the contained projections, including recursion.
template<typename PROJ >
const PROJ & getProjection (const std::string &name) const
 Get the named projection, specifying return type via a template argument.
const ProjectiongetProjection (const std::string &name) const
template<typename PROJ >
const PROJ & applyProjection (const Event &evt, const PROJ &proj) const
 Apply the supplied projection on event.
template<typename PROJ >
const PROJ & applyProjection (const Event &evt, const Projection &proj) const
 Apply the supplied projection on event.
template<typename PROJ >
const PROJ & applyProjection (const Event &evt, const std::string &name) const
 Apply the named projection on event.

Protected Member Functions

void project (const Event &e)
 Perform the projection on the Event.
int compare (const Projection &p) const
 Compare projections.

Detailed Description

Get the e+ e- thrust basis and the thrust, thrust major and thrust minor scalars.

Author
Andy Buckley

The scalar (maximum) thrust is defined as

\[ T = \mathrm{max}_{\vec{n}} \frac{\sum_i \left|\vec{p}_i \cdot \vec{n} \right|}{\sum_i |\vec{p}_i|} \]

, with the direction of the unit vector $ \vec{n} $ which maximises $ T $ being identified as the thrust axis. The unit vector which maximises the thrust scalar in the plane perpendicular to $ \vec{n} $ is the "thrust major" direction, and the vector perpendicular to both the thrust and thrust major directions is the thrust minor. Both the major and minor directions have associated thrust scalars.

Thrust calculations have particularly simple forms for less than 4 particles, and in those cases this projection is computationally minimal. For 4 or more particles, a more general calculation must be carried out, based on the Brandt/Dahmen method from Z. Phys. C1 (1978). While a polynomial improvement on the exponential scaling of the naive method, this algorithm scales asymptotically as $ \mathcal{O}\left( n^3 \right) $. Be aware that the thrust may easily be the most computationally demanding projection in Rivet for large events!

The Rivet implementation of thrust is based heavily on Stefan Gieseke's Herwig++ re-coding of the 'tasso' code from HERWIG.

NB. special case with >= 4 coplanar particles will still fail. NB. Thrust assumes all momenta are in the CoM system: no explicit boost is performed. This can be dealt with by appropriate choice of the supplied FinalState.

Member Function Documentation

double Rivet::Thrust::thrust ( ) const
inline

Thrust scalar accessors The thrust scalar, $ T $, (maximum thrust).

const Vector3& Rivet::Thrust::thrustAxis ( ) const
inline

Thrust axis accessors The thrust axis.

Referenced by axis1().


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