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PipiJpsiAlg.md
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PipiJpsiAlg.md
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# PipiJpsiAlg
See full Doxygen documentation for the `PipiJpsiAlg` on GitPages.
## What does this example package teach?
This example package analyzes $\psi' \rightarrow \pi\pi J/\psi \rightarrow \pi\pi l l$
(di-lepton) events. In particular, it will teach you:
- How to access Monte Carlo truth from a DST file using
[Event::McParticle](http://bes3.to.infn.it/Boss/7.0.2/html/classEvent_1_1McParticle.html).
- How to store arrays to a `TTree` using
[NTuple::Array](https://dayabay.bnl.gov/dox/GaudiKernel/html/classNTuple_1_1Array.html)
and
[NTuple::addIndexedItem](https://dayabay.bnl.gov/dox/GaudiKernel/html/classNTuple_1_1Tuple.html#a663c6d9a0d9ed46303d836994d3876e8).
This is useful for storing e.g. an $n$-array of information for $n$ tracks in an
event. Here, the array is used to store Monte Carlo truth.
- Identifying muons versus electrons using energy of the EMC shower: electrons deposit
more energy in the EMC.
```{todo}
Still has to be written.
This package introduces several concepts additional to `RhopiAlg`.
```