E852 experiment

Analysis of Eta Pi0 system with the decay Eta -> Pi+ Pi- Pi0

 

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Draft 4

Date: 29 Mar 2006 From: John Dowd

Some comments on draft 4 of the eta-pizero paper.

In general this paper shows the result of a careful analysis by two different methods that yield substantially the same result. It looks fine, but the analysis technique needs to be presented more clearly, and the English needs to be polished.

Page 2 description of ratio background to data events. The ratio is said to be between 15% and 25% between 0.78 and 1.74. But the next sentence says the "ratio is more in the region below 1.10". More than 25%? Or is it that the 25% ratio is in the lower mass region?

Response

Corrected

Page 3 Fig. 2 The discussion of the fits refers to the NPE and the UNPE events as (1) and (2) respectively, as in n2/n1=0.71. However in the figure they are labeled as (2) and (3). Probably clearer if the figure is relabeled to match the formulae.

Response

Doen

Page 4 "The spreads of ambiguous solutions are very large for UNPW but it is not the same for D+ wave and relative phase between D+ and P+ waves." This is unclear. Perhaps reword as "The spreads of the ambiguous solutions are very large for UNPW waves, but are relatively small for the D+ wave and the relative phase between D+ and P+ waves."

Response

Corrected

Pages 4 and 5 The discussion of the MDF results in table 1 is concise and clear.

Page 5 The MDPWA is described as free from ambiguous solutions. I realized that I had understood this incorrectly when I looked at the fits in figure 4 which seem to show the 8 ambiguous solutions. Are the 8 solutions shown for each bin the same solutions obtained by the MDF (method 1)? And the point of the MDPWA is that instead of averaging the solutions (yellow dots in figure 3) and fitting to the averages (red line in figure 3), that the MDPWA forms its own best fit (black line in figure 4) without the need for averaging the 8 ambiguous solutions?

Response

We have to say "free from a problem of the ambiguous solution". In fig.3 and fig.4 the experemental points are the same. In fig.4 the lines are not fitted to the points. The points of PWA in each mass bin are shown only for visual comparison with the lines of MDPWA.The lines are calculated with parameters of MDPWA from the fitting of likelihood function (2).

That seems to be what is being said in the last paragraph before the conclusions but it is not clear to us non-experts. At any rate the statement about "free from ambiguous solutions" should be reconciled in a clearer way with the presentation of 8 ambiguous solutions in figure 4.

Response

Corrected

Page 6. I am confused by the description of the mass dependent part of the MDPWA fit. Some of the confusion is probably just in the English. At any rate it appears that the functions W1, W2, W3 were all tried at some time or the other as mass descriptions for P0, P- and D- waves. (The sentence introducing these three functions begins "Two shapes ." It's correct but confusing.) The D0 was parameterized as a BW and as a smooth shape --- both at the same time? Or in different fits? The final choice seems use the form W1 and D0 as a resonant shape. How was this choice made? Are there Xsq criteria?

Response

Corrected

Figures 3c and 4c. Both of these are labeled as the phase (P+ - D+) but they seem to be the "flip" of each other.

Response

Corrected

Finally the committee needs to tighten up the English, particularly in the MDPWA section and in the Conclusions.