The main kinematical quantities for the particles and their combinations are:
Px Py Pz E Mass Theta Phi
mu+ 5.130 -1.150 10.137 11.420 0.106 27.4 347.4
mu- -6.707 13.987 -10.862 18.937 0.106 125.0 115.6
gamma1 -23.109 1.231 -13.218 26.651 0.000 119.7 177.0
gamma2 26.474 -15.376 14.961 34.075 0.000 64.0 329.9
mu+mu- -1.576 12.837 -0.726 30.357 27.455 93.2 97.0
gamma1gamma2 3.364 -14.145 1.743 60.727 58.935 83.2 283.4
mu-gamma1 -29.816 15.218 -24.081 45.589 19.439 125.7 153.0
mu+gamma2 31.604 -16.527 25.098 45.496 12.962 54.9 332.4
mu+gamma1gamma2 8.495 -15.295 11.880 72.147 68.978 55.8 299.0
mu-gamma1gamma2 -3.343 -0.158 -9.119 79.664 79.070 159.9 182.7
mu+mu-gamma1gamma2 1.788 -1.309 1.017 91.084 91.052 65.3 323.8
The energy missing in the event is negligibly small and it can thus be
assumed that all particles are observed. The effective masses of the
(Mu,gamma) pairs exclude that Tau's are at their origin.
After fitting the momenta from the angles, assuming E-p conservation, the
mass of the two gammas is 59.25 +- 0.25 GeV and of the Mu+Mu- is
26.8 +- 0.3 GeV.
The event could be interpreted as a Mu+ Mu- with two photons radiated
in the initial or final state, but the large mass (about 60 GeV) of the
2-gamma system and the large angles between the muons and photons (the
smallest is 38 degree) is very unlikely for this explanation.
This event shows the same characteristics as the L3 events with two hard
gammas and the same mass of the 2-gamma system.Ref : Presented by U.Amaldi after the seminar of S.C.C.Ting (CERN, 26 Nov 1992) on high mass photon pairs.