[Nuclear] status talk for informal T2K neutrino interactions working group

[Steven L. Manly]

Hi Volker and Jerry,

GENIE is actually a fairly well evolved neutrino monte carlo.  I think it
would be unfair to say it is not ready for distribution.  It is a major
player in the neutrino experiment world.  The neutrino folks haven't the
need to worry about resonances at the level that you do in eA.  They use a
fermi gas model with nucleon-nucleon correlations and they add a nuclear
modification factor to take into account differences between the nuclear
and free nucleon structure functions.  They include intranuclear
rescattering (Intranuke).  For the hadronization model they use something
called AGKY which marries an empirical low invariant mass model with
PYTHIA/JETSET at higher energies.

The aim with the neutrino MC is to develop something that works to provide
the right distributions over the appropriate phase space on the different
target nuclei.  There is less concern over arguing over the exact
mechanisms and it is okay to average over some things.

What is new with GENIE is that they turned on the eA mode.  With this we
hope to be able to help tune the MC nuclear physics parts.

Is it useful for CLAS?  I think it is for some analyses - or parts of
analyses - where the larger phase space generator is needed and you are't
probing the guts of a particular reaction or resonance.

Check out arxiv:0905.2517  and

http://www.genie-mc.org/

for more information.

BTW Jerry, thanks for the comments.

Regards,
Steve


> Hi Volker,
>
>    Maybe yes. Steve presented results from GENIE for the first time at the
> last Nuclear Physics Working Group meeting. He showed comparisons with the
> GENEV event generator, GENIE, and the EG2 data. The GENIE results were
> clearly closer to the data. The attached plot shows one of the comparisons
> from Steve's talk of the single, charged pion production. The GENEV
> simulation (blue, dashed histogram) has too many events at low Q2 and not
> enough at higher Q2 compared to the data (solid, blue and red histograms).
> The GENIE simulation (red, dashed histogram) does much better.  Steve
> knows
> the people that have written the code and the version with the nuclear
> calculations is not quite ready for distribution (Steve will correct me if
> I'm wrong). The changes to GENIE are still in an early stage, but the
> results are encouraging. I was planning on encouraging this software
> development as it matures. Let me know what you think.
>
> Jerry
>
>
> On Mon, Jan 11, 2010 at 11:37 AM, burkert <burkert at jlab.org> wrote:
>
>> Jerry et al.,
>>  Might GENIE be also used as a suitable event generator for the CLAS
>> physics analyses?
>>
>> Volker
>>
>>
>>
>> Jerry Gilfoyle wrote: be a good evet generators for our own analyises
>> with
>> CLAS?
>>
>>> Hi Folks,
>>>
>>> Steve Manly is giving an update to one of the neutrino working groups
>>> that
>>> includes some of his recent simulation results and spectra from EG2. I
>>> have
>>> attached his talk. Please let me and him know if there are changes
>>> needed.
>>> My comments are below.
>>>
>>> Jerry
>>>
>>> ----
>>>
>>> Comments from me:
>>>
>>> The similarity of the GENIE and CLAS results is very interesting!
>>>
>>> 1. You should include a few more details on the EG2 run like the number
>>> of
>>> electron events, target configuration (thicknesses, used simultaneous
>>> multiple targets), beam energy, Q2 range (it's in the plots later on,
>>> but
>>> make it explicit).
>>>
>>> 2. For the magnetic field map on page 4, can you state the value of
>>> position along the beam line?
>>>
>>> 3. For the plots on page 6, you need some explanatory text. Should say
>>> these plots are for a proton target so they are not(?) from EG2.
>>>
>>> 4. For the plots on pages 8-10, the GENIE events were presumably run
>>> through GSIM which should be stated explicitly. It looks like the
>>> integrals
>>> of the different spectra from CLAS and GENIE are the same. How did you
>>> get
>>> this result (scale the histograms?, tune the GENIE inputs?)? This
>>> should be
>>> stated.
>>>
>>> Looks good otherwise.
>>>
>>>
>>> --
>>> Dr. Gerard P. Gilfoyle
>>> Physics Department                University of Richmond, VA 23173  USA
>>> e-mail: ggilfoyl at richmond.edu <mailto:ggilfoyl at richmond.edu>
>>>
>>> phone:  804-289-8255
>>> fax:    804-484-1542
>>> ------------------------------------------------------------------------
>>>
>>> This body part will be downloaded on demand.
>>>
>>
>>
>
>
> --
> Dr. Gerard P. Gilfoyle
> Physics Department
> University of Richmond, VA 23173  USA
> e-mail: ggilfoyl at richmond.edu
> phone:  804-289-8255
> fax:    804-484-1542
>