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Before it was realized that major background in the
sample
comes from neutral
decay, we tried to use the CPV as a handle
to suppress the background. In Fig. 3 is shown the
energy loss distribution in the CPV without any cuts (left) and
with standard cuts:
,
,
GeV
(right) for all 79 reactions.
The minimum-ionization peak (MIP) is very pronounced in both cases.
The second peak that comes from multiple tracks is more visible for the high
energy threshold. The MIP, calculated from the Bethe-Bloch
formula for the energy loss of charged
in a 0.4 cm scintillator
[4],
MeV is very close to the one observed.
Thus, requiring no hits in the CPV with energy above the MIP threshold,
say 0.5 MeV, can veto charged particle reconstruction in the LGD.
Fig. 4 shows the effects of this requirement on mass distributions
in the case of the 4.0 GeV energy threshold. It should be noted that with the
CP veto turned on, increasing the energy threshold does not play as significant
a role as before. Although it is clear that the CPV cannot be used to
distinguish the
from the
in
, it might be used to
enrich the
in
or the
in
events.
Figure 3:
The energy loss distribution in the CPV from all 79 reactions
with no cuts (left) and with standard cuts:
,
,
GeV (right).
![\begin{figure}
\begin{center}
\mbox{\epsfxsize =6.0cm\epsffile{ecpv_0.eps}}
\...
...cm}
\mbox{\epsfxsize =6.0cm\epsffile{ecpv_4.eps}}
\end{center}
\end{figure}](img47.png) |
Figure 4:
The invariant mass distributions after CP veto has been applied.
![\begin{figure}
\begin{center}
\mbox{\epsfxsize =6.0cm\epsffile{pi0gammaE40Cpv0...
...epsfxsize =6.0cm\epsffile{pi0pi0gammaE40Cpv0.eps}}
\end{center}
\end{figure}](img48.png) |
Next: BGV handle
Up: mc
Previous: Invariant mass spectra from
Mihajlo Kornicer
2001-11-30