[b1_ana] b1 phone meeting April 29 (note time)
J. P. Chen
jpchen at jlab.org
Wed May 1 10:52:48 EDT 2013
2pm is fine for me.
On 5/1/2013 10:51 AM, Karl Slifer wrote:
>
> OK,
>
> I think 1/2 hour is not sufficient, so how about 2:00pm. (I'll skip my
> student office hours.)
>
> JP?
> Dustin?
> Oscar?
>
> Ellie and Patricia have already said they are free this time, and
> anytime today is unfortunately difficult for Narbe.
>
> thanks
>
> -Karl
>
>
>
> On Wed, May 1, 2013 at 10:40 AM, Oscar Rondon-Aramayo
> <or at cms.mail.virginia.edu <mailto:or at cms.mail.virginia.edu>> wrote:
>
> Hi Karl,
>
> We met with Dustin last evening and after going in detail over
> the formulas
> for the ratio Npol/Nun, we found that the unpolarized sigma_N,
> sigma_D and
> sigma_He (see my last email) can be collected in one group, which
> cancels
> with the denominator (all unpolarized), leaving a term
> sigma_D*Azz*Pzz/denominator, which I realized can be written as
> f*Azz*Pzz, f
> = dilution factor.
>
> With the dilution factor, the formulas in Dustin's third row of
> equalities
> in his Observables2 report, which are valid only for pure D (the
> HERMES
> case), can also be used for ND3 targets.
>
> In summary, we can take the ratio of the pol to unpol counts,
> which takes us
> to Azz, at the price of the dilution factor and its error, plus
> the need to
> use some form of F1 to get b1 from Azz, or the difference, which
> takes us
> directly to b1.
>
> In both cases the systematic errors, other than the charge and
> detector
> efficiency are normalizations, and since the error on Pzz is
> expected to
> dominate, it really is a matter of taste, once we have the numbers
> on hand.
> We'll surely try both.
>
> For the statistical errors, f enters in the Azz time estimate, but
> Q*A*l*pf
> enter in the difference (Pzz is in both). I need to do some
> numbers yet
> (everyone should try) to compare the two approaches.
>
> Finally, today we have the SANE meeting at 3:30, so I can join b1
> from 1:00
> to 3:30.
>
> Cheers,
>
> Oscar
>
> On Wed, 1 May 2013 09:18:48 -0400
> Karl Slifer <karl.slifer at unh.edu <mailto:karl.slifer at unh.edu>>
> wrote:
> > Hi all,
> >
> > The methodology is the central question and I think we have to
> resolve any
> > lingering doubts today. I highly encourage that everyone really
> read
> > Oscar's note (Eq 19 and 20) and his last email before we discuss
> today.
> >
> > I would really not like to delay till tomorrow if possible since
> time is
> >so
> > tight. I hope we can get a majority to participate at 3pm.
> Please let me
> > know if you can't.
> >
> > -Karl
> >
> >
> >
> > ---
> > Karl J. Slifer
> > Assistant Professor
> > University of New Hampshire
> > Telephone : 603-722-0695 <tel:603-722-0695>
> >
> >
> > On Tue, Apr 30, 2013 at 5:59 PM, O. A. Rondon <or at virginia.edu
> <mailto:or at virginia.edu>> wrote:
> >
> >> Hi Dustin,
> >>
> >> Dustin Keller wrote:
> >> > You can only benefit from the systematic reduction if you us
> Azz as
> >> > discussed yesterday. But at this point I am not partial.
> >> >
> >> > dustin
> >> >
> >>
> >> In the experiment, we only have counts. What we need to show to
> the PAC
> >> is how we go from the counts Npol and Nu, to Azz or b1. A measured
> >> quantity needs to be on one side and physics on the other. Lets
> say we
> >> start with your ratio Npol/Nu - 1 = Pzz*Azz, which only
> requires Pzz >0.
> >>
> >> We need to prove that the lhs reproduces the rhs. We have, in
> general,
> >> N = Q*e*A*l*sigma. But since N are counts from everything in
> the target,
> >> it is not a simple matter of canceling quantities that stay the
> same
> >> when the polarization changes:
> >>
> >> Npol = Qpol*epol*Apol*lpol*sigma_pol
> >> = Qpol*epol*Apol*lpol*[(sigma_N+3*sigma_Dpol)*pf +
> sigma_He*(1-pf)]
> >>
> >> Nu = Qu*eu*Au*lu*[(sigma_N+3*sigma_D)*pf + sigma_He*(1-pf)]
> >>
> >> sigma_N and sigma_He are the same, always unpol. And
> >> sigma_Dpol = sigma_D(1+Pzz*Azz).
> >>
> >> Then, since Apol = Au = A, and lpol = lu = l,
> >>
> >> Npol/Nu =
> >> (Qpol/Qu)*(epol/eu)*[(sigma_N+3sigma_D(1+
> Azz*Pzz))*pf+..)]/[(sigma_N+..
> >>
> >> where I just put ..., because I don't see how it can be
> simplified to
> >> just leave Azz*Pzz + 1, to equal the rhs.
> >>
> >> On the other hand, if instead of taking the ratio Npol/Nu
> first, we take
> >> the difference first, it's indeed possible to isolate the required
> >> Pzz*b1 on on side, like I do in my draft, eq. (19) or (20). And in
> >> fact, we don't even need to bother with Azz, because we get b1
> without
> >> having to multiply Azz by F1, introducing one more systematic
> error.
> >>
> >> So, in summary, once one substitutes all the ingredients for
> your sigmas
> >> we get, or ought to get, eq.(19) or (20) back.
> >>
> >> In both of those equations, the systematics for Pzz, A, and
> l(pf) are
> >> normalization factors, just like we want them to be, for control of
> >> systematics, but the charge and the detector efficiency are not
> common
> >> factors, they depend on the period when the data are taken,
> either pol.
> >> or unpol.
> >>
> >> My point is that for the proposal, we must spell this all out,
> to give
> >> explicit sources of errors, and to calculate times or
> statistical errors
> >> correctly. For example, the statistical error must be sqrt(Npol
> + N_U) ~
> >> sqrt(2N), because it is just the error of a difference, etc.
> >>
> >> We need to have a consensus on how the method is going to be
> described
> >> in the proposal, which needs to be done in the most precise way
> to avoid
> >> any confusion due to ambiguities.
> >>
> >> Cheers,
> >>
> >> Oscar
> >>
> >>
> >> > On Tue, 30 Apr 2013, O. A. Rondon wrote:
> >> >
> >> >> Hi,
> >> >>
> >> >> Since I couldn't stay until the end of the meeting, and I
> don't think
> >> >> there will be minutes of it, I would like to share some
> ideas for the
> >> >> proposal draft.
> >> >>
> >> >> Basically, what we need is an equation with the measured
> quantity on
> >>one
> >> >> side and b1 or Azz on the other. Based on what I think the
> consensus
> >> >> was, to measure polarized minus unpolarized counts on a
> single cup with
> >> >> the target field aligned along the beam, I've updated the
> draft of my
> >> >> method, see subsection 0.2, which discusses this. Eq. (19)
> or eq. (20)
> >> >> meet the conditions stated above. This is the approach I would
> >>subscribe
> >> >> to, unless there is another version that is shown to also
> represent the
> >> >> procedure, which should be circulated as soon as possible.
> The draft
> >> >> is here
> >> >> http://twist.phys.virginia.edu/~or/b1/b1_method-v2.pdf
> <http://twist.phys.virginia.edu/%7Eor/b1/b1_method-v2.pdf>
> >> >>
> >> >> Cheers,
> >> >>
> >> >> Oscar
> >> >>
> >> >> _______________________________________________
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> >> >>
> >> >
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
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