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

[Kei Moriya]

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
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>