def mtrack(V, jet): #Inv. mass using all tracks in iso and core region, assuming each with pi0 mass
mpi0=0.139
jetsum = LParticle()
for i in range(len(V)):
if (track_check(V[i])):
r = delR(V[i], jet)
if (r < 0.4):
E = sqrt(mpi0**2 + V[i].x()**2 + V[i].y()**2 + V[i].z()**2)
W = LParticle(V[i].x(), V[i].y(), V[i].z(), E)
jetsum.add(W)
### print jetsum.calcMass()
return jetsum.calcMass()
