(r5) 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 have 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.

---++ Modify (extend) an existing ntuple
In the previous section, we created a brand new ntuple containing our particles (a more common example is when the ntuple is generated by some fancy CMKIN routine). We can further tailor it, add or remove particles, change their properties etc. With an appropriate Fortran program (see  [[%ATTACHURL%/extendhbook.f][extendhbook.f]]) read the original ntuple, do your modifications, and write out to an other ntuple.

TODO: there _has_ to be a more elegant solution than just write out to a _second_ ntuple. Maybe =hropen(... 'U' ...)= ?

---++ 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 - 30 May 2006

Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who	Comment
f	extendhbook.f	r1	manage	3.7 K	2006-05-30 - 23:17	UnknownUser
f	writehbook.f	r1	manage	2.9 K	2006-05-25 - 09:46	UnknownUser

Topic revision: r5 - 2006-05-30 - GergelyPatay

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