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Invariant mass distributions are formed for the events where 3 and 5 clusters
have been reconstructed in the LGD, and passed through a mass filter to identify
,
, and
events.
Current sample sizes are too small to allow the study of
in the case of
events. The requirements for
selecting events of interest are as follows.
- 1
- -
- 2
- -
The following additional cuts define the
selection.
- 3
- - exactly 3 clusters reconstructed in the LGD
- 4
- - the lightest pair has to have invariant
mass within the
window (0.1-0.18 GeV).
For
the additional cuts were as follows.
- 3
- - exactly 3 clusters reconstructed in the LGD
- 4
- - the lightest pair has to have invariant mass
greater than 0.18 GeV.
- 5
- - at least one pair has to have a mass within
the
window (0.45-0.65 GeV).
For
the additional cuts were as follows.
- 3
- - exactly 5 clusters reconstructed in the LGD
- 4
- - the lightest pair has to have invariant mass
within the
window (0.1-0.18 GeV)
- 5
- - the lightest pair from the remaining three
clusters must also fall within the
window (0.1-0.18 GeV).
In Fig. 1 are shown invariant mass distributions for two
values of the energy threshold:
GeV (first row)
and
GeV (second row).
The black curves in Fig. 1 represent sum from all reactions
from the list [1], while the colored curves show contributions
from the most prominent meson channels for the given selection criteria.
For example, one can see two peaks from reactions when
is reconstructed in the
sample with
GeV.
One of them represents the fully reconstructed
from
decays, while the one near 0.3 GeV
is an artifact of false reconstruction. It is possible to have
where
one charged
converts to
in the LGD, which is then
reconstructed as a single photon. The same feature is visible
in the case of
events where we see two peaks in
reactions,
one when the
decays to
and one when
goes to
.
This kind of background is suppressed when the energy threshold in the LGD
is increased. Thus increasing the value of
makes the
and
peaks more prominent in the case of
decays. This same effect was observed in the analysis of
experimental data [3].
In the case of
events, requiring more energy in the LGD
produces a similar reduction in the charged particle background,
although in this case a single prominent peak does not emerge in
the one-dimensional mass plot after charged reactions are suppressed.
In Fig. 2 are shown particular contributions
from neutral and charged
and
channels
to the total invariant mass in the
event sample
for a 4.0 GeV energy threshold. It can be seen that
our "
peak" contains a real
contribution
as well as a contribution from false reconstructions of the
.
It is clear that missed reconstructions of the
decay is going to
enhance the apparent
signal in
. Note that
the
background in
comes primarily from the
decay of the
even though
its rate is an order of magnitude smaller than
channel.
The ratio of
/(
) under the peak is
.
This can explain why we see
times more
relative to
in our experimental data [3]
than we expected based upon the known
and
cross sections.
Figure:
Invariant mass distributions for two energy cuts in the LGD,
GeV (the first row) and
GeV
(the second row) and three classes of events:
,
,
(the first, second and third column respectively).
![\begin{figure}
\begin{center}
\mbox{\epsfxsize =6.0cm\epsffile{pi0gamma30.eps}...
...box{\epsfxsize =6.0cm\epsffile{pi0pi0gamma40.eps}}
\end{center}
\end{figure}](img43.png) |
Figure:
Contribution of particular reactions to invariant mass for
GeV.
![\begin{figure}
\begin{center}
\mbox{\epsfxsize =6.0cm\epsffile{phipeak.eps}}
\mbox{\epsfxsize =6.0cm\epsffile{b1peak.eps}}
\end{center}
\end{figure}](img44.png) |
Next: CPV handle
Up: mc
Previous: Introduction
Mihajlo Kornicer
2001-11-30