hep.lcd.contrib.physics
Class TransMassReco

java.lang.Object
  |
  +--hep.lcd.contrib.physics.TransMassReco

public class TransMassReco

extends Object

TransMassReco implements the two body mass reconstruction of J. Feng and D. Finell. (This is what Uriel calls "transverse mass".) See their paper on reconstructing squark masses in:

   @article{feng:squarks,
     author="Jonathan L. Feng and Donald E. Finnell",
     title="Squark mass determination at the next generation of linear
            $e^+e^-$ colliders",
     journal="Phys. Rev. D",
     volume="49",
     year="1994",
     pages="2369",
     note="hep-ph/9310211"
   }
 

We assume symmetric production of e+e- -> A + A followed by decays of A -> B + C. We assume that B is invisible (e.g. a neutralino) but that its mass has been measured by previous experiments. The particles C are observed, and their momenta and angles should be correlated. We can determine the minimum and maximum kinematically allowed mass of particle A for a given pair of particles C. The maximum of the minimum mass (and the minimum of the maximum mass) should approach the mass of A.

We conventionally label particles A as 1 and 2, particles B as 3 and 5, and particles C as 4 and 6.

To use this class, create a new TransMassReco object, passing the beam energy and the mass of the invisible particle (B) to the constructor. Then pass the 4-momenta of the two visible particles (for example, electrons in selectron events) or combined jets (for squarks) to the getMinMass or getMaxMass methods.

Version:

1.00

Author:

David Wagner

Source Code:

TransMassReco.java

Constructor Summary

TransMassReco(double ebeam, double massB)
Constructor; store the known quantities

Method Summary

double	getMaxMass(HepLorentzVector fmom4, HepLorentzVector fmom6) GetMaxMass performs the actual mass calculation.
double	getMinMass(HepLorentzVector fmom4, HepLorentzVector fmom6) GetMinMass performs the actual mass calculation.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TransMassReco

public TransMassReco(double ebeam,
                     double massB)

Constructor; store the known quantities

Parameters:

ebeam - The energy of each beam

massB - The energy of particle B (i.e. the invisible particle, presumably the neutralino or other LSP)

Method Detail

getMinMass

public double getMinMass(HepLorentzVector fmom4,
                         HepLorentzVector fmom6)

GetMinMass performs the actual mass calculation.

It calculates the mass of the particle A in the process e+e- -> A + A followed by A -> B + e, given that the mass of B is known. It looks at the correlation between the angles of the two electrons.

Parameters:

fmom4 - Four-momentum of one particle (or the sum of the four-momenta of all the particles assumed to come from one particle)

fmom6 - Four-momentum of another particle

Returns:

mimimum kinematically allowed mass

getMaxMass

public double getMaxMass(HepLorentzVector fmom4,
                         HepLorentzVector fmom6)

GetMaxMass performs the actual mass calculation.

It calculates the mass of the particle A in the process e+e- -> A + A followed by A -> B + e, given that the mass of B is known. It looks at the correlation between the angles of the two electrons.

Parameters:

fmom4 - Four-momentum of one particle (or the sum of the four-momenta of all the particles assumed to come from one particle)

fmom6 - Four-momentum of another particle

Returns:

maximum kinematically allowed mass