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HPS-SOFTWARE  May 2014

HPS-SOFTWARE May 2014

Subject:

Re: Repeating Events in Slic

From:

Sho Uemura <[log in to unmask]>

Reply-To:

Software for the Heavy Photon Search Experiment <[log in to unmask]>

Date:

Sat, 31 May 2014 11:34:22 -0700

Content-Type:

TEXT/PLAIN

Parts/Attachments:

Parts/Attachments

TEXT/PLAIN (118 lines)

The pattern in the plots you attached in your first e-mail looks like 
binning - you have 4 bins per 5 crystals on your X-axis, so if you 
histogram ix (always an integer) or the hit position (always the crystal 
center) you are always going to get this checkerboard pattern because 
every 4th bin gets filled with double the number of hits.

This doesn't explain what you say about positions - unless you're using 
the position of the ECal hit. That is always the crystal center, so two 
hits in the same crystal will always have exactly the same position.

I don't know if /random/seed does the same thing as the "-d" option to 
SLIC. The latter has always worked for me.

On Sat, 31 May 2014, Holly Vance wrote:

> Hi Maurik,
>
> For the cosmics I used a plane above the ECal, and for the electrons firing
> into the ECal, I used a point source located at the origin. This gives good
> results for tracking (cosmics) but not such good results for rates. I also
> used a cosine angular distribution for the cosmics.
>
> When I look at the actual positions of the MC Particle in the ECal for both
> of these hits, I observe similar patterns in positions-repeats of using the
> same numbers (out to several decimal places) which I find unusual. I don't
> believe there to be a roundoff error, but I certainly won't rule it out.
>
>
>
> On Sat, May 31, 2014 at 9:59 AM, Maurik Holtrop <[log in to unmask]>
> wrote:
>
>> Hello Holly,
>>
>> Perhaps Jeremy can comment on the random engine being used.
>>
>> I only know of a flaw in the CLHEP::RanecuEngine, which is used by GEANT4.
>> The flaw is that for very different seeds the engine will give the exact
>> same sequence. The periodicity of the engine (i.e. starting with one seed,
>> how long before the sequence repeats) is huge, as it is for all the CLHEP
>> random engines. So on a single run, with a single seed, you should NOT see
>> any repeat or pattern in this engine. I alerted Lynn Garren of this flaw
>> back in 2010 and they were going to look into it, but never heard anything
>> since. Best to avoid that particular engine.
>>
>> There are many other things that can cause a pattern like the one you are
>> seeing. One possibility is that there is some subtle effect in roundoff.
>> Are the cosmics coming from a single point good distance from the ECAL, and
>> could it thus be numerical limits on the accuracy of the angles? Something
>> like that?
>>
>> Best,
>> Maurik
>>
>>
>> On May 31, 2014, at 9:45 AM, Holly Vance <[log in to unmask]> wrote:
>>
>> Hi,
>>
>> When I am running my own events in SLIC from a macro, for small numbers of
>> events (3k) the distribution looks ok. However, when I run something a bit
>> larger like 100k events, I keep getting strange checkered patterns. I've
>> been setting a /random/seed number for different runs, but this seems to
>> have no effect (using this vs not using this and setting it at different
>> values).
>>
>> I am attaching a photo of what the cosmic run looks like.  While the
>> underlying events look good, there is a very distinct pattern that I need
>> to get rid of. I also see this same pattern if I shoot electrons at the
>> ECal. Any suggestions would be very useful.
>>
>> I am wondering if GEANT4 is using the TRandom random number generator? I
>> know there are errors with this. I am not sure what is being used with the
>> SLIC interface.
>>
>> --
>> Respectfully,
>> Holly
>>
>>
>> ------------------------------
>>
>> Use REPLY-ALL to reply to list
>>
>> To unsubscribe from the HPS-SOFTWARE list, click the following link:
>> https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=HPS-SOFTWARE&A=1
>> <cosmics.png><electrons.png>
>>
>>
>>  ------------------------------
>>
>> Spam
>> <https://www.spamtrap.odu.edu/canit/b.php?i=01M8BXL9f&m=e42a440e8e1d&t=20140531&c=s>
>> Not spam
>> <https://www.spamtrap.odu.edu/canit/b.php?i=01M8BXL9f&m=e42a440e8e1d&t=20140531&c=n>
>> Forget previous vote
>> <https://www.spamtrap.odu.edu/canit/b.php?i=01M8BXL9f&m=e42a440e8e1d&t=20140531&c=f>
>>
>
>
>
> -- 
> Respectfully,
> Holly
>
> ########################################################################
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>
> To unsubscribe from the HPS-SOFTWARE list, click the following link:
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>

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