[Halld-offline] selection of p pi+ pi-, p pi+ pi- pi0 events

Richard Jones richard.t.jones at uconn.edu
Fri Mar 14 13:38:51 EDT 2014


Kei,

You wrote,
|  If we are not losing any particles, I don't understand
|  how this can happen.

If you look back again at my earlier message, I explain how it can go
either up or down.  There is another more obvious explanation than extra
hadrons from interactions of extra beam photons, and that is that the
random numbers that seed all events (except the first one in the file) are
completely different if you change anything about how the simulation
proceeds.  Thus, you can gain or lose tracks because of interactions,
decays, etc. which happen (or don't happen) differently when the random
number changes.

-Richard Jones


On Fri, Mar 14, 2014 at 12:49 PM, Kei Moriya <kmoriya at indiana.edu> wrote:

>
> Hi Richard,
>
> Within the program I check that the momentum difference between
> all particles I select and the original photon and proton
> is less than 1 MeV, and the difference in energy is less than
> 0.1 MeV. I would assume, since as you say EM background
> does not produce many hadrons, that we wouldn't get any pions
> that satisfy these tight conditions. The other thing is that
> if you look at the numbers I got, the no EM setting
> has *more* events than with the background turned on.
> If we are not losing any particles, I don't understand
> how this can happen.
>
>         Kei
>
>
> On 3/14/14 12:38 PM, Richard Jones wrote:
>
>> Kei,
>>
>> You wrote,
>> |  If people could give me comments on why I don't get
>> |  exactly the same number of events when running with
>> |  different EM backgrounds, I would be grateful.
>>
>> The short answer is that hdgeant appends new particles to the end of the
>> event Monte Carlo record (Reaction tag) depending on the secondaries that
>> are produced during tracking.  You cannot lose particles from the Monte
>> Carlo record, but you can gain more.  This can either increase or decrease
>> your event count in a given channel, either by moving events into the
>> channel by adding particles that it was missing, allowing it to satisfy
>> the
>> particle counts for the channel, or by moving events out the channel by
>> pushing the particle counts outside the ranges required for the channel.
>>   EM background is very poor in hadrons, so this explains why your
>> different
>> channel counts differ by only a couple dozen when you change the bg
>> conditions.
>>
>> -Richard Jones
>>
>>
>> On Fri, Mar 14, 2014 at 12:24 PM, Kei Moriya <kmoriya at indiana.edu> wrote:
>>
>>
>>> I've updated the code to select specific reactions.
>>> The files are in
>>> trunk/sim-recon/src/programs/Utilities/hddm_select_events
>>>
>>> You can run on non-REST files with
>>> hddm_select_events -s 5 -i [input hddm] -o [output hddm]
>>> To run over REST files use the -r option.
>>> The option -s [selectType] specifies which events you
>>> want to select. 5 is for p pi+ pi-, 6 is for p pi+ pi- pi0.
>>>
>>> If people could give me comments on why I don't get
>>> exactly the same number of events when running with
>>> different EM backgrounds, I would be grateful.
>>>
>>>          Kei
>>> _______________________________________________
>>> Halld-offline mailing list
>>> Halld-offline at jlab.org
>>> https://mailman.jlab.org/mailman/listinfo/halld-offline
>>>
>>>
>>
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