Rivet
1.8.0
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Get the e+ e- thrust basis and the thrust, thrust major and thrust minor scalars. More...
#include <Thrust.hh>
Public Member Functions | |
Thrust () | |
Constructor. | |
Thrust (const FinalState &fsp) | |
virtual const Projection * | clone () const |
Clone on the heap. | |
double | thrust () const |
double | thrustMajor () const |
The thrust major scalar, ![]() | |
double | thrustMinor () const |
The thrust minor scalar, ![]() | |
double | oblateness () const |
The oblateness, ![]() | |
const Vector3 & | thrustAxis () const |
const Vector3 & | thrustMajorAxis () const |
The thrust major axis (axis of max thrust perpendicular to thrust axis). | |
const Vector3 & | thrustMinorAxis () const |
The thrust minor axis (axis perpendicular to thrust and thrust major). | |
const Vector3 & | axis1 () const |
AxesDefinition axis accessors. | |
const Vector3 & | axis2 () const |
The 2nd most significant ("major") axis. | |
const Vector3 & | axis3 () 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. | |
Protected Member Functions | |
void | project (const Event &e) |
Perform the projection on the Event. | |
int | compare (const Projection &p) const |
Compare projections. |
Get the e+ e- thrust basis and the thrust, thrust major and thrust minor scalars.
The scalar (maximum) thrust is defined as
, with the direction of the unit vector which maximises
being identified as the thrust axis. The unit vector which maximises the thrust scalar in the plane perpendicular to
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 . 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.
double Rivet::Thrust::thrust | ( | ) | const [inline] |
Thrust scalar accessors The thrust scalar, , (maximum thrust).
const Vector3& Rivet::Thrust::thrustAxis | ( | ) | const [inline] |