Hoi,
today we got the following. Keep reading, especially to the last
paragraph.
We should discuss this next week. For various reasons, it looks
difficult before Thursday. Thursday 8:30 am PDT?
Cheers,
--U.
> From: Ed Thorndike <[log in to unmask]>
> To: [log in to unmask], [log in to unmask]
> Subject: Concerns with Vub PRL
> Date: Fri, 19 Sep 2003 18:02:54 -0400 (EDT)
>
> Hi Vera, Hi Urs,
> As Dave Cassel conveyed to Vera by phone in late July, I was in shock that
> you continued to use HQET OPE values of /\bar, lambda_1 in the shape function.
> I apologize for being so slow in getting my concerns to you. My lateness in
> writing in no way is due to a lack of concern. Let me try to be very explicit
> about my concerns.
>
> You do explicitly say what you do, which is good. However, you bury it in a
> Reference, Ref. 18, which is not so good. In Ref. 18 you say: "We assume
> that the shape function parameters in Ref. [9] can be related to the HQET
> parameters /\bar and lambda_1." We can all agree that this is true, but the
> essential point is that nobody knows exactly what this relationship is!
> Hence, the statement is misleading to the casual reader who is not aware that
> the relationship between the two sets of parameters is not known. Also,
> you do not include an estimate of error for the assumption that the
> two sets of parameters are IDENTICAL, rather than related somehow in
> a way that is not understood. I understand that not all theorists
> feel as strongly as Neubert that your assumption that they are
> identical is unreasonable, but don't they all feel that SOME error
> must be assigned to this assumption?
>
> In our phone meeting of 3 July, the question was raised as to whether the
> range of exponential shape function parameters (/\bar, lambda_1) gave
> <E_gamma> values and errors consistent with CLEO's published values. In Email
> on July 4 I gave you the numbers showing that it did. A correlary of this is
> that if one calculates <E_gamma> using the values of (/\bar, lambda_1) that YOU
> have been using, one will get an <E_gamma> value, with error, not in good
> agreement with CLEO's measurement and error. We have carried out this
> exercise, and find:
>
> Measured 2.346 +/- 0.032 GeV
> calculated, using correct /\bar, lambda_1 2.353 +/- 0.031 GeV
> calculated, using your /\bar, lambda_1 2.377 +/- 0.043 GeV
>
> Note the differnce in the central value, 31 MeV. Your values of /\bar and
> lambda_1 come from our <E_gamma>, with its error, 2.346 +/- 0.032. Your
> procedure should, MUST get that back, to an accuracy small compared to the
> statistical error on the measurement (32 MeV), if using the HQET /\bar and
> lambda_1 in the shape function is reasonable. You don't, and the only possible
> interpretation is that HQET /\bar, lambda_1 don't mean the same thing as
> Light Cone /\bar, lambda_1. This conclusion is TOTALLY INDEPENDENT of what any
> theorist tells you, or us. It's an empirical fact, the output must match the
> input, if what you're doing is right, and it doesn't.
> (As an aside, our /\bar, lambda_1 Shape Function are obtained from a fit to the
> spectrum down to 1.5 GeV, and so what we obtain (line 2) needn't perfectly match
> line 1, as line 3 should. Nonetheless, it differs by only 7 Mev, and matches
> the error perfectly. The latter is probably fortuitous.)
>
> If you choose not to use CLEO's determination of the shape function, but
> instead use CLEO's determination of HQET parameters /\bar and lambda_1, as you
> have done, then shouldn't you include SOME error for this approximation? I
> think the answer is a clear "Yes". How big? Hard to say. Would it matter?
> YES! This is your dominant error. You're clearly better off having it
> determined by an objective procedure than by a guess. And you're clearly
> better off having it determined by a guess than by setting it equal to zero!
>
> I recall, and Dave Cassel recalls, that you mentioned that the range of
> uncertainty in /\bar, lambda_1 that we obtain from our b -> s gamma measurement
> gives a varaiation in M_X distribution that you find in poor agreement with your
> measured M_X distribution. If this is true, if you indeed can reduce the errors
> on the shape function parameters, that is great! It certainly deserves mention
> in your paper, since we're talking about the dominant error.
>
>
> On a somewhat separate matter, I disagree with the first sentence in your
> conclusions paragraph "This result is consistent with previous measurements [4],
> but has a smaller systematic error, ..." Ref. [4] is to the four LEP
> experiments, and to CLEO's endpoint result. Far be it for me to defend the LEP
> experiments. However, let's compare your result with CLEO's endpoint result.
> For statistical plus experimental systematic errors, you quote +/-0.28,
> +/-0.27 => +/-0.39, 8.4%. We quote +/-0.34, 8.3%. Pretty comparable. Your
> fourth error, +/-0.26, corresponds to our third, for which we quote +/-0.16, but
> would quote +/-0.23 for a treatment consistent with yours. Those errors, going
> from branching fraction to |Vub|, are 100% correlated. Finally there is your
> third error, for which you quote +/-0.40, but I say you should quote +/-0.60,
> 13.0%. ("I say you should" means that's what you would get if you used the
> light cone /\bar, lambda_1 from our b -> s gamma determination.)
> That is to be compared with our second (+/-0.44) and fourth (+/-0.24)
> error, => +/-0.50, 12.3%. These errors, yours and ours, in addition to being
> comparable (13% vs. 12.3%), are HIGHLY CORRELATED. So, collecting errors,
> 8.4% vs. 8.3% (uncorrelated), 5.6% (completely correlated), 13.0% vs. 12.3%
> (highly correlated). The correlated errors dominate.
> Conclusions from this part.
> 1. Your statement of smaller systematic errors is incorrect,if you
> include theory errors in the systematic errors.
> 2. Putting all the errors together, your analysis and our analysis have
> very nearly equal errors, if theory errors are treated in a
> consistent way.
> 3. There is very substantial correlation between your errors and ours.
> I think Point (3.) is worth your mentioning.
>
>
>
> If you are not able to show that the issues that I raise here are incorrect,
> I very much hope that you will revise your paper before it appears in
> PRL. If it is too late for that, then I think that you should submit an
> Erratum. Failing that, we would feel forced to submit a Comment, calling
> attention to the unresolved scientific contraversy concerning the key
> theoretical assumption in your paper. Clearly this would be good for
> none of us.
>
> Regards,
> Ed
