Hi everyone,
I'm writing regarding some troubling observations I've made about
gismo-simulated events -- specifically, regarding monte carlo
information in an event.
There are several sources of monte carlo information in a given event.
To be specific, let me talk about ttbar events in the lepton + jets
decay channel, so t1 -> lep + nu + b1 and t2 -> u + d + b2. I'll call
these 6 decay products "primary decay products".
(1) LCDEvent has a list of monte carlo particles.
(2) Each of the primary decay products has a list of daughters.
(3) Each calorimeter cluster has a list of associated monte carlo
particle.
Using (2), I made a list of FINALSTATE particles with no daughters. I
found that the b-quark has many such particles. However, bbar almost
always has zero such particles. The up-type and down-type particles
from hadronic W decay comes somewhere in between -- often they would
have zero such particles, but not as often as bbar. The leptons looked
normal -- i.e. neutrinos had only one such particle, electrons had quite
a few (electron + brem. photons), muons usually had one or several (muon
+ brem. photons), and taus ranged from few to dozens.
The above observation leads me to think that monte carlo information is
being truncated somehow. In a separate study, I examined the
association between lists (2) and (3). I found that there is a 1-to-1
correspondence between particles in lists (2) and (3). This suggests
that, not only is the list of monte carlo particles being truncated, but
the missing monte carlo particles aren't contributing to cluster
energy. In other words, it seems as if the truncation is happening
before detector simulation.
Let me give some other indication of problems:
* In a list of particles from (2), I found a charmed meson that was
INTERMEDIATE, but it had no daughters.
* The number of particles in (1) and (2) are often similar (within a
couple). But not infrequently, (2) has many more particles than (1).
Has anybody noticed such a problem? Can anybody shed some light to this
problem?
Gene
