[Halld-physics] Random subtraction and uniqueness tracking
Stuart Fegan
sfegan at jlab.org
Tue Mar 20 15:41:13 EDT 2018
Seconded. The most recent physics workshop was in 2016, before many of
us working on GlueX data started. There's been a few subtle changes in
software and procedures, and some of those who developed these tools and
processes are no longer around to explain them. It'd at least make
things easier for future newbies to get things moving...
Cheers,
Stuart
On 20/03/18 18:29, Curtis Meyer wrote:
> Hi Richard -
>
> that sounds like a good suggestion. We take a lot of things for
> granted that may not be so obvious after all. More important would be
> the worked out examples…
>
> Curtis
> ---------
> Curtis A. MeyerMCS Associate Dean for Research
> Phone: (412) 268-2745Professor of Physics
> Cell: (412) 260-6290Carnegie Mellon University
> Fax: (412) 681-0648Pittsburgh, PA 15213
> cmeyer at cmu.edu <mailto:cmeyer at cmu.edu>http://www.curtismeyer.com/
>
>> On Mar 20, 2018, at 2:15 PM, Richard Jones <richard.t.jones at uconn.edu
>> <mailto:richard.t.jones at uconn.edu>> wrote:
>>
>> Justin,
>>
>> I wonder if it might make sense to devote 10 minutes at the beginning
>> of each physics meeting to a "How-To" presentation on basics of our
>> data analysis. Accidentals subtraction is something that seems to
>> keep coming up over and over. An alternative to a "basics of physics
>> analysis" series, we could also commission a series of short Tech
>> Notes. Maybe the first one could be, "How photon tagging works", just
>> a couple of pages with a worked-out example would do.
>>
>> -Richard J.
>>
>> On Tue, Mar 20, 2018 at 1:18 PM, Peter Pauli <ppauli at jlab.org
>> <mailto:ppauli at jlab.org>> wrote:
>>
>> Hello everybody,
>>
>> I apologise in advance for this lengthy email.
>> I am trying to understand how to properly do the random
>> subtraction while avoiding double counting. After talking to a
>> couple of people at the collaboration meeting and during shifts I
>> found that this seems to be non trivial and it seemed that some
>> people where not to sure about it either.
>>
>> According to Paul's talk that he gave at the 2016 software
>> workshop the rule is to always include all the variables into
>> your uniqueness tracking that are used to calculate the
>> histogrammed quantity.
>> Let's say I look at gp->p pip pim. I want to histogram the pip
>> pim invariant mass and do the random subtraction. Although I only
>> use the pip and pim tracks to calculate the invariant mass I have
>> to include the beam photon in my uniqueness tracking because I
>> also use that quantity (timing) in the following step to get the
>> random subtracted histogram. But as far as I understand in the
>> voting on the best RF bunch each track gets a vote. So do I need
>> to include the proton in the uniqueness tracking as well?
>>
>> What happens if I use the track vectors coming out of the kin
>> fit? The standard 4-mom fit that is usually used will include
>> information from all tracks in the combo. Does that mean as soon
>> as I plot e.g. the invariant mass using kin fitted tracks I need
>> to include everything in the uniqueness tracking?
>>
>> What about binned quantities. Many results are shown in bins of
>> momentum transfer squared. In my analysis I look at gp->kp
>> Lambda(->km proton) and calculate the momentum transfer as t^2 =
>> (g_P4-kp_P4)^2. If I now want to bin the proton Kminus inv mass
>> in t-bins does that mean I need to include the beam particle and
>> Kplus in my uniqueness tracking? Aren't bins in principle like a
>> 2D plot? Binning means effectively histogramming a 2D plot I
>> would say, therefore I need to include them. But what is if now
>> make my bins really large (e.g. 0 to -inf)? This would
>> effectively be unbinned and I would just track the beam particle,
>> proton and km. Does that mean I need uniqueness tracking of beam,
>> km, proton for each of my bins individually but not include kp in
>> the tracking?
>>
>> If there is a document somewhere that clarifies those issues I
>> would be happy if you could point me to it. I didn't find
>> anything but maybe I missed it.
>>
>> These are only a couple of questions I have about this but I
>> think it is enough for one email. I thought about this stuff for
>> quite some time now and feel like I start to confuse myself about
>> some of the issues. Therefore I thought I just send it to the
>> physics mailing list. Maybe there are straight forward answers
>> and I just don't see them or maybe this is worth a discussion at
>> an analysis meeting. Either way I am sure this is interesting for
>> more people than just me.
>>
>> Cheers,
>> Peter
>>
>> --
>> ================================
>> Peter Pauli
>>
>> Dept. of Physics & Astronomy
>> University of Glasgow,
>> Glasgow G12 8QQ.
>> Scotland. UK.
>>
>> Tel: +44 (0)141 330 6398 <tel:%2B44%20%280%29141%20330%206398>
>> ================================
>>
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--
Dr Stuart Fegan
Postdoctoral Researcher
George Washington University/Hall-D
F351, CEBAF Center
E-mail: sfegan at jlab.org
Telephone: (757)-269-7473
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