Hoi,
the comments are in. Unless I missed a really relevant point in my
first quick reading, there is not much. The first referee's main point
is the absence of a comparison to excl b->ulnu decays and two minor
points about eff(mX) and the statistical significance of the different
mX results (1.55, 1.40, 1.70). The second referee's main point is
that he wants a PRD. Apart from that it's mostly a description of the
difficulties reading a compressed PRL.
No mention whatsoever of shape functions, Parameters, values, errors,
b->s gamma, ...
Cheers,
--U.
PS: Thorndike, that is, no Hill ...
------- start of forwarded message -------
From: Physical Review Letters <[log in to unmask]>
To: [log in to unmask]
Subject: Your_manuscript LG9660 Aubert
Date: Thu, 11 Sep 2003 19:10:30 +0000 (UT)
Re: LG9660
Measurement of the inclusive charmless semileptonic branching
ratio of B mesons and determination of $|V sub {ub}|$
by B. Aubert, R. Barate, D. Boutigny, J.-M. Gaillard, et al.
Dr. U. Langenegger
SLAC, M/S 95
P.O. Box 20450
Stanford, CA 94309
Dear Dr. Langenegger,
The above manuscript has been reviewed by our referees. We ask you
to consider the enclosed comments from the reports.
While we cannot make a definite commitment, the probable course of
action if you choose to resubmit is indicated below.
( ) Acceptance, if the editors can judge that all or most of the
criticism has been met.
(X) Return to the previous referee(s) for review if available.
( ) Submittal to new referee(s) for review.
Please accompany any resubmittal by a summary of the changes made, and
a brief response to all recommendations and criticisms.
Yours sincerely,
Robert Garisto
Senior Assistant Editor
Physical Review Letters
Email: [log in to unmask]
Fax: 631-591-4141
http
://prl.aps.org/
----------------------------------------------------------------------------
Report of Referee A -- LG9660/Aubert
----------------------------------------------------------------------------
This paper reports an interesting measurement of V_ub using inclusive
charmless B decays. The very high statistics data sample collected by
BaBar allows a much higher purity sample to be obtained, limiting the
systematic errors from background that plague the earlier
measurements. It is therefore very welcome, and deserves publication
in PRL. The paper is generally well written, but some parts are very
dense and hence unclear, lacking in necessary detail. I have a number
of questions and comments, together with some suggestions for minor
improvements in the text. If these can be addressed satisfactorily, I
will be happy to recommend the paper for publication as soon as
possible.
1) Neither the introduction or conclusion makes any reference to the
other main method of measuring
V_ub, namely the measurement of
exclusive branching ratios B->pi l nu, B->rho l nu etc. Since the
two methods are complementary and the systematics rather different,
I think at least some mention of this should be made in the
introduction, and the e.g. the precision achieved (including both
experimental and theoretical uncertainties) compared with that from
exclusive techniques in the conclusion. A reference to the most
recent publications on exclusive branching ratios (e.g. the Babar
paper PLB 90, 181801 (2003) and others) would be useful.
2) The inclusive method used here requires the assumption of
parton-hadron duality, which is not universally accepted in this
context. This is alluded to by the mechanism of reference [5] cited
in the introduction, but I think this should be stated in the main
text - it is an important assumption.
3) Introduction line 11: `..and by measuring the fraction of charmless
semileptonic decays...' This phrase in context
sounds like this
technique is new, whereas it is the same as used by previous
experiments. The sample purity has been improved, but the basic
technique is the same, so this should be rephrased.
4) Figure 1(b): There seems to be a big dip in efficiency for m_X
values just above 1 GeV - the dip in the spectrum is much more
pronounced for the `all requirements' histogram than the `p*>1 GeV'
histogram. What is the cause of this ? More generally, there is no
comment on how the efficiency varies as a function of m_X.
5) Table 1: The first three variations (changing the m_X cut) have
highly correlated data samples. Are the statistical errors on the
R_u values calculated from all the data, or only the part which is
independent in the two samples ? If it is all the data, the
variations look a bit large to be coming from pure statistical
fluctuations as is suggested in the text. E.g. for m_X<1.55 GeV the
result is 2.06+-0.25, then for m_X<1.70 it is 2.35+-0.28.
Taking
the quadrature difference of the statistical errors as an
(admittedly crude) estimate of the uncorrelated part, the
difference is 0.29+-0.13.
6) Page 13 2 lines after the R_u result, the double ratio between R_u
for B+ and B0 is quoted, but no discussion is given of what this
result means, or why it is interesting. Is it expected to be unity
? Some interpretation would be helpful, if the result is
interesting enough to derive and quote.
Minor points
------------
a) Abstract line 5:
'hadronic mass distribution' is ambiguous in this context. I
suggest something like 'mass of the hadronic system accompanying
the lepton'.
b) Page 9 line 3:
'estimated as the fraction of signal events with m_ES>5.27 GeV'.
This is difficult to understand without the context of the fit
shown in Figure 2 - moving the figure reference and mention of the
fit earlier would help.
c) Page 9, last paragraph line 3:
Presumably the m^2_miss<0.5 GeV^2 requirem
ent is applied before the
kinematic fit setting it to zero - it would be clearer to mention
that this value is calculated before the fit.
d) Page 9, last two lines:
The pi_s rejection is a little obscure. Is this test applied to all
pions (which are then used to calculate the neutrino mass), or only
those accompanied by an exclusive D0 ? The text could be clearer on
the procedure which is actually followed.
e) Page 10, after the equation:
Several numbers are quoted with errors. What are the errors - do
they include both statistical and systematic effects, or only a
subset? This should be stated.
f) Page 11, line 3:
What is the error on the 6.8% lepton background?
g) Page 11, paragraph 2 line 6:
'the first bin is extended to m_X < 1.55 GeV' This is hard to
understand - extended from where ? Presumably you want to say that
it covers the whole region from 0-1.55 GeV ?
h) Page 12 line 3/4:
plurals: '... and kaons *are* estimated...
by var
ying *efficiencies* by...'.
----------------------------------------------------------------------------
Report of Referee B -- LG9660/Aubert
----------------------------------------------------------------------------
This is certainly an important result pioneering a new method of
measuring a crucial parameter in the Standard Model of particle
interactions. All that is said in the first paragraph is correct. It
deserves prompt publication.
On the other hand this letter is very difficult to read leading to a
great deal of confusion about what is actually done. Perhaps this
results from presenting a very condensed version of a result that
should be described in a longer format. This letter would be much more
clear if it could reference a longer, more complete description of the
analysis. Failing that the authors need to address the specific points
I make below to clarify and improve the reader's ability to understand
the analysis.
Footnote 5) is overstated. The extraction of the c
harmless
semileptonic branching fraction has little to do with quark-parton
duality. On the other hand the extraction of Vub depends on duality.
Not enough information is given about DeltaE used in the selection of
B_reco. A plot of some sort would be most useful, presumably DeltaE
after a selection on m_ES comparing data and simulation, but failing
that some words on the average resolution on DeltaE and the quality of
the agreement between the simulation and data.
It would be valuable to know what fraction of the 1097 B decay modes
are actually used after the requirement on purity.
I find "The purity of events with a high momentum lepton..." to be
imprecise and confusing. I suggest "For B's decaying semileptonically
to a high momentum electron or muon recoiling against B_reco the
purity of the B_reco selection is 67% (see Figure 2a)."
"Prompt" is jargon well known to those interested in semileptonic
meson decays, but is otherwise confusing. It is not defined in the
letter. The senten
ce, "For charged..." should be rewritten to
eliminate "prompt" or "prompt" should be defined on its first usage. I
suggest, "For charged B_reco candidates, we require the charge of the
selected lepton to be that expected from the decay of a b-quark with
the proper flavor for a B meson recoiling against the candidate."
The sentence, "For neutral..." has me completely confused. I think the
authors are trying to say that when signal fraction and backgrounds
are used later in the analysis they take into account the known rate
of mixing of neutral B mesons which can result in either charge of
lepton appearing in B's recoiling against B_reco. If this is what they
mean then they should say it later since it is of no consequence at
this point. If they mean something else then they must rewrite this
sentence to make it clear.
I am confused on the selection sequence for B->X_u l nu candidates.
Prior to the paragraph beginning "To select..." the neutrino mass
equivalent to the missing mass is fixed t
o zero by the kinematic fit
for m_X. Then the missing mass is required to be consistent with zero.
I think the authors are trying to draw a distinction between the
neutrino four vector which they require to have zero mass in the
kinematic fit and thus no longer is equal to the missing mass four
vector which for B->X_u l nu candidates is selected to have mass
consistent with zero. They do this with the subscript nu and miss. If
this is what they mean then this distinction needs to be made more
clear. Perhaps the order of these should should inverted to make it
clearer.
Is the reported resolution on m_x for candidates that also pass the
B->X_u l nu selection criteria? As written it appears to not be so in
which case what is point of giving this number? The fit to the m_X
distribution is done on those events passing the B->X_u l nu
selection.
The language describing the D*lnu partial reconstruction is unclear.
Instead of "...and require for the neutrino...", it would more clear
to say "...a
nd eliminate if the neutrino..." At least I think that is
what is done. If not then the authors need to tell us what they do
with the recovered D*lnu events.
Figure 1 is confusing. Is it before or after a detector simulation? It
is hard to tell if any resolution in the figure agrees with what is in
the text as the text gives the average resolution on m_x which is
clearly much larger than what is apparent in the figure for low values
of m_x. Also "Signal MC" in the caption is jargon. Better is "MC
Simulation of the B->X_u l nu signal".
It would be good to report the effect of the selections made going
from the initial sample of B->X_u l nu candidates. Do the fractions
cut away by the various selections (1 lepton, charge, D*lnu partial
reconstruction, kaon veto) agree with the predictions of the
simulation? If so this would strengthen the belief that the background
is well modeled.
Does the shape of m_ES distribution for the B_reco signal agree with
the prediction of the simulation? Again
if so it would strengthen
belief that simulation is a good model of the data.
Table I and the description of the fit to Figure 3a is very confusing.
First when N_sl is first mentioned in the text, Table I is not
referenced. Thus I was left trying to figure out if the N_sl in the
table was the same as the one in the text. I think it is, but
reference to the table in the text when the fit to m_ES to extract
N_sl is explained is necessary to clarify. Second the first three rows
of the table leads one to believe that the fit is only performed on
the subsample that passes the indicated m_X cut. Careful reading of
the text indicates that this is not the case, but rather the cut only
defines, I think, the size of the first bin in which N_u and N_c are
reported. This is confusing as the table leads one to believe that the
first three fits are performed on different subsamples and even after
reading the text many times I am not sure that m_X < y means what I
think it does. The meaning of m_X in the
table needs to be made clear.
The entire description of the fit could be made more clear by adding
some guidance as to how the fit to the m_X distribution works. N_c is
essentially determined by the data in the m_X bins above 2.0, and is
extrapolated into the low region by the shape of the m_X for this
background as predicted by the simulation. Saying this explicitly
would aid understanding the discussion of the systematics.
It would very much aid understanding if the m_X distribution for the
control sample is shown comparing data and simulation. At least
characterize in words the agreement between data and simulation for
high values of m_X. At the moment the authors are asking to accept on
faith that they have a good understanding of the m_X distribution of
the B->clnu background.
How is the 1% error for track finding efficiency applied? Is it 1% per
track or is 1% the overall effect of the uncertainty? It is not clear
that the identification efficiency errors are reasonable. The author
s
need to give some evidence that the variations is ID efficiencies and
mis-ID rates given in the paper are reasonable.
No error seems to appear for the choice of m_X. Why not? While the
variation in R_u shown for the choice of m_X in Table I is probably an
over estimate of the error, the Table shows a trend, the highest R_u
for the lowest m_X and the lowest for the highest, that seems to
indicate that the choice of m_X and the fit value of R_u are
correlated. At least the authors should comment on the trend and
explain why the choice of m_X does not contribute to the systematic
uncertainty.
There is no comparison with other, exclusive measurements of V_ub. One
PRL 90, 181801 (2003) is even by the authors collaboration. Besides
comparisons with other inclusive measurements something should be said
about the exclusive measurements.
------- end of forwarded message -------
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