[Halld-physics] Random subtraction and uniqueness tracking

Tue Mar 20 18:43:18 EDT 2018

Justin,

Sure, I will do the first one, on photon tagging. I will be prepared to
give a 10 minute overview at the next physics mtg.

-Richard J.

On Tue, Mar 20, 2018 at 6:40 PM, Justin Stevens <jrsteven at jlab.org> wrote:

> Hi Richard,
>
> Thanks for the suggestion, I agree this would be quite useful.  We are
> aiming for an abbreviated analysis tutorial at the June Collaboration
> Meeting, but these writeups discussed briefly during the Physics WG
> meetings would certainly be useful to define “best practices”.  Would you
> like to volunteer for the first topic you suggested?
>
> -Justin
>
>
> On Mar 20, 2018, at 8:41 PM, Stuart Fegan <sfegan at jlab.org> wrote:
>
> 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. Meyer MCS Associate Dean for Research
> Phone:    (412) 268-2745 Professor of Physics
> Cell:        (412) 260-6290 Carnegie Mellon University
> Fax:         (412) 681-0648 Pittsburgh, PA 15213
> cmeyer at cmu.edu https://urldefense.proofpoint.com/v2/url?u=http-3A__www.curtismeyer.com_&d=DwIFaQ&c=lz9TcOasaINaaC3U7FbMev2lsutwpI4--09aP8Lu18s&r=tkzhhpt64rRw6UYYOiZUvX2EnoOb8Z04QVfRqLSRE8Q&m=ORm4JuZ385Upi7bQr89ZnZBIXZUPCDL03QGFvsOlUKY&s=0BKi4gCvJ7DqL4QDY04V7cmINYEs5dYEUcWwPv_wAHk&e= 
>
> On Mar 20, 2018, at 2:15 PM, Richard Jones <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> 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
>> ================================
>>
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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 <(757)%20269-7473>
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