Re: [BLAST_ANAWARE] latest results and projection

From: William Bertozzi (bertozzi@lns.mit.edu)
Date: Sun Jul 25 2004 - 16:22:01 EDT


Chi:

Thanks for the results. I want a longer discussion on Monday about noon,
as we discussed with Tancredi on Saturday, on these data and the +pion
results from hydrogen.

Here are some questions:
1: Using world data imposes some errors in T21 and T22. Are these properly
estimated in the results? In particular how do you fold the disagreements
in these numbers within the world data sets? It is not sufficient to only
use Abott's fits as the guide here. I want to understand just how you fold
these results into our data and how the experimental disagreements are
included. Notable also is the fact that some data points "normalize" to
low q-data to determine their polarizations of the targets. Have you
factored this type of 1=1 situation in the analysis?

I assume that you have derived two values for Pzz using the perp and parr
situations and then used the average for deriving T20. Is this
correct? If so how big are the differences in Pzz and how do these
differences enter the error bars?

What data point are you using for Pzz, the next to lowest q value as we
discussed earlier?

See you Monday about noon.

Bill

At 02:36 PM 7/25/2004 -0400, Chi Zhang wrote:

>Hi all,
>
>attatched is my latest results in terms of T20 projection. I hope it is
>not too late yet. The change is more bins in projection.
>
>in the last couple days, there have been scores of email exchanges
>discussing the error propagation, luminosity estimation and T20 projection.
>
>I would like to list my understanding of the current situation:
>
>1. We narrow down the issue to the estimation on luminosity and believe
>apart from this issue, Genya, Zilu(proposal) and me are in agreement. It
>is my impression that if we adopt a common ground in luminosity, we would
>give same results.
>
>2. I realized that my original method to extract T20 is not the most
>efficient in terms of using the statistics we gather. By using world data
>to fix T21, we reduce the "statistical error" in T21 by a huge amount by
>using all world data. Thus we are able to reduce statistical error in
>Blast measurement of T20 by almost a factor of 2. The systematic error
>introduced in this method is well worth it. I believe it is only
>fair to compare results form this new developement to world data.
>
>I implemented both old and new method into my analysis. The old method
>seems to provide a very good consistancy check by measuring T20 and T21 at
>the same time.
>
>3. I realized that I should be able to adapt binning almost as fine as the
>proposal in the projection. It is in fact important to have multiple bins
>at the maximum region of T20.
>
>The error bar in each projection point is about three and a half times as
>big as the proposal. This is a result of a few factors.
> * A factor of 7.5 difficiency in luminosity in data than
> proposal(estimated from ed elastic rate)
> * a 10% lower tensor polarization,
> * a misterously limitted azimuthal acceptance to within +-10 degree
> as oppose to +-15 shown in MC. (believe to be bugs in
> software, confirmed with Chris, same is seen in ep
> elastic)
>The minor difference in beam energy used than in proposal, the
>disadvantage in running with current spin states probably is made up by
>the longer running projected.
>
>I hope the dust is settling down a bit now and I made one new plot. It is
>Blast data up to July(180kC running), with projection binned into 11
>points. At low Q2 side of the maximum, we are hopeful of making the most
>statistically significant measurement so far. At the neighborhood of the
>maximum, our statistical errors will compete with the lastest VEPP-3
>results in 2003. To the high Q2 end, we are at about same level as Bates
>1994 data.
>
>The plot is provided in eps and gif format.
>
>Thanks to every body who provided insights and suggestions which helped me
>a lot to gain deepened understanding on my thesis analysis.
>
>I deeply apologize for such a big confusion for such a long period at such
>a critical time.
>
>Chi
>

William Bertozzi
Professor of Physics
Room 26-437
Massachusetts Institute of Technology
77 Massachusetts Avenue
Cambridge, MA 02139
Tel: 617-253-5167



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