(r3) EmbedParticles < CMS

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In the following we will generate manually a 'single kaon' event, which can be fed into OSCAR and ORCA.

---++ The HEPEVT ntuple structure
OSCAR expects its input in an HBOOK ntuple with the following fields:
<blockquote>
<verbatim>
Block HEPEVT:
   integer NEVHEP = event number
   integer NHEP   = number of entries (particles, partons)
   integer ISTHEP(NHEP) = status code
   integer IDHEP(NHEP)  = PDG identifier
   integer JMOHEP(2,NHEP) = position of 1st and 2nd  mother
   integer JDAHEP(2,NHEP) = position of 1st and last daughter
   real PHEP(5,NHEP)   = 4-momentum and mass            (single precision in ntuple file)
   real VHEP(4,NHEP)   = vertex xyz and production time (single precision in ntuple file), OSCAR do not care about this...

Block MC_PARAM:
   integer IRNMCP       = run number
   integer IEVMCP         = event number (must equal to NEVHEP)
   real WGTMCP         = event weight (1.0)
   real XSECN          = cross section equivalent (1.0)
   integer    IFILTER        = filter pattern (0)
   integer    NVRMCP         = number of additional variables
   real VARMCP(NMXMCP) = list of additional variables
</verbatim>
</blockquote>

---++ Writing ntuples
Writing such an ntuple is straightforward in Fortran [TODO: C/C++ interface via cfortran.h], see the attached example program [[%ATTACHURL%/writehbook.f][writehbook.f]].
   1. Define the data blocks as Fortran COMMON's.
   2. Create an ntuple with the =HROPEN= procedure (say _test.ntpl_), and define its structure with =HBNAME=. *Note:* ntuple's ID must be 100 (unpacked) or 101 (packed; a bit tricky). *Additonal note:* Ntuple variable names has to be in capital letters. Don't ask why...
   3. Do a loop over the events, generate some particles, etc; at the *end* of the loop =call hfnt(ID)=
   4. Close the ntuple.

Compile the program with =g77 -c writehbook.f= and link with =g77 -o writehbook.run writehbook.o `cernlib packlib,mathlib`=
This requires a running =g77= system with =cernlib= properly installed (on debian: =apt-get install cernlib=)

Run the executable.

Now the file _test.ntpl_ should contain the particles. You can test it by opening with PAW:
<blockquote>
<verbatim>
h/file 0 test.ntpl 4096
n/print 101
n/plot 101.idhep
</verbatim>
</blockquote>

TODO: this example program does not call Pythia to decay instable particles, but who cares anyway? We want now to control everything manually.
---++ Feed into OSCAR
This note assumes that you have a properly installed OSCAR environment.

Copy or symlink _test.ntpl_ into the OSCAR working directory (in my case, it's _OSCAR_3_9_9/src/Workspace_).

Edit _oscarrc_:
<blockquote>
<verbatim>
...
OutputDataSet = /System/sim/test
EventNtplReader:NtplFileName = test.ntpl
EventNtplReader:NtplID = 101 # or 100 if you generated unpacked ntuple
...
</verbatim>
</blockquote>

Do the ritual =eval `scram run -sh`= (or =-csh=), and run =oscar -c oscarrc=

This will produce a lot of _sim_ and _xml_ files (see [[ProduceSimulatedEvents][ProduceSimulatedEvents]])



---++ Further readings
[[http://cmsdoc.cern.ch/cmsoo/projects/CMKIN/index.html][CMKIN]]

[[http://wwwasdoc.web.cern.ch/wwwasdoc/hbook_html3/hboomain.html][HBOOK Reference]]

-- Main.GergelyPatay - 08 Mar 2006

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Topic attachments
I	Attachment	History	Action	Size	Date	Who	Comment
f	writehbook.f	r1	manage	2.9 K	2006-05-25 - 09:46	UnknownUser

Topic revision: r3 - 2006-05-25 - GergelyPatay

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