Hi Roberto,
I've already talked to you in person, so ... all good for me! :-)
ciao
Vir
-----------------------------------------------------------------
.*. Two atoms bump into each other.
/V\ One says 'I think I lost an electron!'
(/ \) The other asks, 'Are you sure?',
( ) to which the first replies, 'I'm positive.'
^^-^^ -----------------------------------------------------------
On Thu, 21 Feb 2008, Roberto Sacco wrote:
> Hi All,
>
> you will find attached a first draft of our reply to the referees. Please
> have a look and let us know how they can be improved.
>
> Thanks!
>
> Concezio and Roberto
>
> ---
>
> Re: LH11701
> Measurements of partial branching fractions for $\bar{B}
> \rightarrow X_u l \bar{\nu}$ and determination of $|V_{ub}|$
> by B. Aubert, M. Bona, D. Boutigny, Y. Karyotakis, J.P. Lees, et al.
>
> Dr. R. Sacco
> Stanford Linear Accelerator Center
> Mail Stop 35
> 2575 Sand Hill Road
> Menlo Park, CA 94025
>
> Dear Dr. Sacco,
>
> 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.
>
> With any resubmittal, please include a summary of changes made
> and a brief response to all recommendations and criticisms.
>
> Yours sincerely,
>
> Robert Garisto
> Associate Editor
> Physical Review Letters
> Email: [log in to unmask]
> Fax: 631-591-4141
> http://prl.aps.org/
>
> ----------------------------------------------------------------------
> Report of Referee A -- LH11701/Aubert
> ----------------------------------------------------------------------
>
> The precise determination of |V_{ub}| is crucial to testing the CKM
> sector of the standard model. The length of the side of the unitary
> triangle opposite the angle beta is proportional to the ratio |V_ub|
> / |V_cb|, making its determination a high priority. Given the rapid
> theoretical and experimental progress in this area, it is very
> interesting to see how the determination of |V_{ub}| develops. In
> this context, the paper uses 4.3 times the data previously used by
> BaBar for the |V_{ub}| determination and significantly improves on
> the precision of the earlier measurement. For the substantial advance
> in its subfield and implications, I regard this work suitable for
> publication in PRL.
>
> The letter is well written and clear. Please consider the following,
> minor corrections:
>
> R: we have taken into account all the following remarks.
>
> Title: V_{ub} --> |V_{ub}|
>
> Abstract, L7: (and everywhere else) replace "sys" with "syst"
>
> p7, L4: "....measure branching fractions for such decays." please
> add reference 20 (PRL92_071802) at the end of this sentence, as it
> places this paper in the context of the previous measurement.
>
> p7, L9: "..we present measurements of partial branching
> fractions.." --> "..we present a measurement of partial branching
> fractions..."
>
> p7, L22: change "fb^1" into roman: {\rm fb}
>
> p8, FIG1 caption: "(points with statistical error)". One can't see
> on the PRL size whether they have a statistical error, perhaps use
> "(full circles)" to refer to them ?
>
> p8, L5: "..estimated on Monte Carlo (MC) as.." --> "..estimated
> using Monte Carlo (MC) simulation and is defined as...
>
> p8, L11: I would perhaps use a capital letter for "threshold function
> [15]" --> "Threshold function [15]"
>
> p8, L15: "p*_l >1 GeV/c" what does the * stand for? Do you label a
> particle's momentum with p* instead of simple p?
>
> p9, L2: use a long dash, with "--", between 0.473 and 0.523
>
> p10, L6: "..and $N^{out}_u$ refers.." --> "..and N^{\rm out}_u$
> refers..." that is, don't italicize "out"
>
> p10, L19: "We estimate the error due to the signal..." --> "We
> estimate the uncertainty due to the signal..."
>
> p10, L19: "The signal modeling uncertainties..." -> "The uncertainty
> on the signal modeling are due..."
>
> p10, L21: "We also calculate the errors associated with the
> uncertainties in the non-perturbative..." -> "We also calculate the
> uncertainties due to the non-perturbative..." Here and in several
> other places later on (e.g. in caption of Tab I) , you should
> change "error" with "uncertainty". By systematic "error" one
> means a constant shift to the central value of the measurement. By
> systematic "uncertainty" it is intended a distribution of the error
> with a certain width, which is the quoted number. So the +/- numbers
> in Tab I should be referred to as "uncertainties" and not "errors".
>
> p11, Tab I, caption: "Summary of the measurements of the fitted
> numbers of events..." --> "Summary of the fitted number of
> events..."
>
> p11, Tab I: Place a label for the M_X, P_+ and M_X,q^2 column. For
> example "Method", or "Cuts"
>
> p11, Tab I: Last column, add a "\times" before "10^{-3}"
>
> p11, Tab 2, caption: Add ":" after "..kinematic cuts, from" in
> order to brake the long sentence.
>
> p11, Tab2: the formatting of the first row is not easily readable.
> Remove the vertical space between "Shape" and "function" and on
> all the other two-word column headings.
>
> p11, Tab2: add "\pm" in front of numbers in the table
>
> p12, L2: "...reducing the relative error by..." --> "..reducing
> the relative uncertainty by..."
>
> p12, L3: Add "between the two measurements" after "...highly
> correlated".
>
> ----------------------------------------------------------------------
> Report of Referee B -- LH11701/Aubert
> ----------------------------------------------------------------------
>
> This Letter provides inclusive partial branching fractions for
> charmless semileptonic B meson decay in kinematic regions in which
> the dominant semileptonic decay to charm is suppressed. From these
> regions, seven different values of Vub are extracted using several
> different theoretical calculations of the corresponding partial
> widths.
>
> This paper summarizes the work for three challenging measurements.
> The measurements themselves are key to improving our knowledge
> of Vub, as they represent the kinematic regions that hold best
> theoretical promise for control of the nonperturbative effects.
> It's crucial to have a unified analysis such as this so that results
> from these different region can be compared with clear control of the
> experimental systematic uncertainties so that we can learn how well
> we can understand the theoretical uncertainties associated with Vub.
> Improved extraction of Vub is crucial to our understanding of the
> flavor sector, and particularly to CP violation within that sector.
> Therefore the paper is of interest both to the high energy physics
> community -- experimental and theoretical -- and to the broader
> physics community.
>
> I should note that the analysis itself is quite complex, and that
> much work has clearly gone into the measurements. However, with
> the terseness forced by the PRL length, it's difficult to judge the
> analysis and the completeness. The basic techniques are certainly
> sound -- but the devil for an analysis like this is in control
> of the background and exploration of how well that control is
> understood. I strongly encourage the authors to submit a companion
> PRD in which the details of the analysis are fully described.
>
> R: indeed, we plan to provide a full description of the techniques
> we employ in a PRD. The plan is to include further studies on a
> timescale of a few months.
>
> Overall the writing is clear.
>
> I recommend publication after the items below have been considered
> or addressed.
>
> 1) Since this is intended for PRL, the introduction and conclusion
> must be reworked to be more accessible to a general audience.
> For the introduction, this should be straightforward: the context
> alluded to in the first sentence could be expanded. The second
> sentence should be clarified (B->pipi is also proportional to |Vub|^2
> and doesn't have a pesky neutrino -- sharpen the argument). The
> jargon (eg, X_u, X_c) will be familiar to the specialist but are
> undefined and, in a related fashion, the basic mass difference
> explanation for why X_clnu is suppressed is not given. Etc...
>
> R: we rewrote the introduction accordingly.
>
> More serious, though, is the conclusion. Table 1 presents 7
> different values of Vub, for which the uncertainties are highly
> correlated. To me that implies that for any given comparison, the
> largest th'y error dominates the level of uncertainty. Comparing
> results for Mx vs P+ vs Mx,q2, there are differences that are over
> two "standard deviations" apart (or however one should interpret
> those theory errors). The situation is not even acknowledged
> in the paper. At the very least some statement *must* be made.
> Preferably, some more interesting questions should be addressed,
> which would truly make the analysis high quality for PRL: What
> value of Vub should the reader take away (for comparison to which
> value in the PDG, for example)? What are potential pitfalls in the
> different regions that may bias on region or another (in theory
> or exp't)? Could the pattern of differences tell us anything?
> In short, what can we learn from these 7 numbers either directly or
> relative to other measurements? If there's nothing that we can do
> immediately to learn something from these numbers, then shouldn't
> the theory errors at the very least be inflated?
>
> Also in the conclusion, but more for spirit of clarification, are
> the Vub's being compared to the inclusive/exclusive average in the
> PDG Vub+Vcb review? Are these results appreciably correlated with
> that average given the correlation with the previous Mx analysis?
> Perhaps more direct comparison with other uncorrelated experimental
> determinations with similar kinematic regions, and of "the" Vub from
> this paper with exclusive measurements, would be more beneficial
> to the general reader.
>
> The shortcomings of the conclusion for PRL are the sole reason for
> not, at this point, recommending "The paper should be published
> in PRL after minor revisions are made, without further review."
>
> R: we have reworked the conclusions in order to evaluate the
> compatibility of our different determinations of Vub. We have done
> that, in particular, in the BLNP framework after determining the
> statistical and systematic correlations between the experimental
> determination of the partial branching fractions. We see an agreement
> between the Mx and Mx-q^2 analyses, while the Pplus measurement
> differs at 2.5 sigma level (this disagreement is also seen by Belle).
> We also state that BGE and BLNP give consistent results and that the
> values we measure are in good agreement with other
> inclusive $V_{ub}$ determinations, and compatible, although
> systematically larger, with measurements from charmless
> exclusive semileptonic decays.
>
> 2) The definition of P+ refers to a jet direction -- can this
> direction be clarified? Is it the jet axis calculated from the
> hadronic X system?
>
> R: It is indeed calculated from the hadronic system, as its definition
> suggests. We decided to drop the reference to the jet direction though,
> and just give the definition of P+, along with a reference to
> theoretical papers.
>
> 3) For the Breco purity selection, does "Breco decay" simply refer
> rejection of final states with a particular particle content (ie,
> a particular decay mode) such as "5 charged pi's + 2 pi0's", or is
> it more finely structured: "5 charged pi's + 2 pi0's in particular
> kinematic regions"? As written, it sounds like the latter imposed
> on an event-by-event basis. Have I misunderstood, and it's really
> just a final state selection?
>
> R: it is not a rejection, rather a selection of decays of the other
> B in the event into a specific state. The number of final states that
> we fully reconstruct is rather large (of the order of 1000); for
> some combinations of particles we may have specific invariant mass
> requirements. However, there is not enough space inn this paper to
> embark in a detailed description of our selection; we plan to include
> a thorough description the upcoming PRD.
>
> 4) Does "photon energy loss" in the m_ES fit description refer to
> initial state radiation, final state radiation or both? The phrase
> "caused by photon energy loss" refers only to the m_ES tail,
> correct? For either ISR or FSR, does the systematic parameterization
> ansatz include uncertainty in the level of radiation (or is it not
> important on the few % scale)?
>
> R: "photon energy loss" refers to energy loss in the detector
> material.
>
> 5) The paper mentions Xclnu decays entering because of undetected
> KL's. Do D semileptonic decays also pose a problem since these
> will also give an additional undetected particle? The charged
> leptons tend to be rather soft, so depending on the lepton id
> criteria might not get vetoed... If these are important, have the
> D s.l. branching fractions and the B->D momentum spectrum been
> considered in the systematics?
>
> R: The requirements on the minimum lepton momentum (1 GeV) and
> the lepton charge reduce the background from D s.l. decays to
> a level of a few percent.
> We take into account the residual contribution by varying the D s.l.
> branching ratios in our assessment of systematic uncertainties.
>
> 6) Some idea of the effectiveness of the D*lnu veto based on
> m_nu^2 would be useful to include -- both rejection factor and
> signal efficiency. The shape in signal that one would expect is
> not so decay. For clarity in the paper, I suggest changing the
> variable name to avoid confusion with the p_nu introduced in the
> previous paragraph, whose mass this variable is not...
>
> R: the requirement m_veto<-3 reduces the
> D*lnu background by about 36% while keeping more than 90% of signal events.
>
> 7) Minor typo: In the paragraph and sentence beginning "To extract
> the distribution in the variables...", I think "subsequently
> separating" should be "subsequently separate"
>
> R: We changed the sentence.
>
> 8) Somewhat more detail on the spectral fits is warranted, since
> these are a key component of the method. For example, presumably
> N_u and N_u^out are normalizations for two different fit components
> corresponding to decays within and without the final kinematic
> region at the generator level. How are these treated in the fit?
> Are they tied together by the particular theoretical model used to
> evaluate the efficiency? Or, do the float independently? Nice to
> know, since that couples to how one needs to consider the models
> in the systematics analysis.
>
> R: N_u is, in fact, the number of data events in the signal region after
> all cuts. N_u^out is an estimate of the contribution to N_u of signal
> events reconstructed in the signal kinematic region but coming from
> outside the said region. In the fit, the MC shapes of signal and N_U^out
> components are forced to be the same, according to the theoretical model.
>
> 9) I couldn't tell how Nsl and BGsl are determined. Are these
> obtained from fits to the Breco mES distribution where an additional
> lepton has been required? If I haven't simply missed something,
> the method should be stated in the paper.
>
> R: the number of background events is determined from MC simulation.
> The corresponding systematic uncertainty due to our knowledge of
> the background composition has been taken into account.
>
> 10) Minor typo: Nsl= ... and BGsl=... are the measured *numbers of*
> semileptonic events and... "numbers of" is missing.
>
> R: We changed the sentence.
>
> 11) In systematics, at what level does modeling of hadronic showers
> (beyond KL's) in the calculation of the X system matter? Eg.,
> fluctuations or splashback could result in showers that are
> relatively isolated from tracks in the calorimeter, so will bias
> the X calculation and therefore any efficiency or spectral shape
> for Mx and P+.
>
> R: modeling of hadronic showers, including fluctuations and splashback
> is taken into account in the GEANT 4 MC simulation. The associated
> systematic uncertainties are included in what we call "detector
> systematics". The combined effect due to the reconstruction of
> neutral clusters in the calorimeter actually dominates the total
> detector systematic uncertainty, ranging from 1.4% for Mx,
> to 2.9% for Pplus, to 2.5% for Mx-q2.
>
> 12) In the systematics table, does {\cal B}(D) refer to D branching
> fractions? Can the paper clarify how these branching fractions,
> or what subset, is varied?
>
> R: we varied the branching fractions within their experimental errors
> around the central values. We have rewritten the description
> in the paper.
>
> 13) There's no mention of final state radiation, which I would assume
> to be sizable for electrons. What effect does this radiation have
> on efficiency and background smearing, and how well is it known?
> What effect does radiation have on generator level quantities
> (spectral shape biases), and at the 1-2% level of systematics
> considered in the paper, do the kinematic regions with radiation
> map well enough onto the regions the theorists have calculated
> rates for without radiation? This question can be both absolute
> in nature or refer simply to how the MC is treated -- for example,
> one could get an inappropriate generator level q2 boundary if by
> looking at the generator level (p_e + p_nu)^2 after radiation.
>
> R: in our analysis, FSR is simulated using PHOTOS.
> We checked that the effect of FSR is negligible by studying
> kinematic variables in MC samples produced with and without PHOTOS.
>
> 14) The paper notes specifically notes that the mix of charged
> and neutral B pairs is not 50-50. Is there any systematic effect
> associated with this in terms of the mass spectrum of the hadronic
> system being, in reality, somewhat different, etc., particularly
> when average B lifetimes are used in the end? From figure 2 and
> the roughly 60/40 B+B-/B0B0bar split, it looks like there should
> be enough statistics to get Vub independently from these two
> samples (and the tagging, of course, allows the separation into
> those subsamples). Are the Vub results from the two subsamples
> consistent, and do the patterns in the different kinematic regions
> manifest themselves in the same way?
>
> R: we checked that PBR obtained separating the samples by
> the charge of the reconstructed B meson are
> consistent with each other within the uncertainties and
> indeed the patterns in the different kinematic regions
> manifest themselves in the same way.
> A measurement of PBR separately for charged and neutral
> Bs is important to determine weak annihilation effects that
> are currently taken into account in the theoretical models. A more
> detailed study of experimental cross-feed between charged and neutral
> Bs is required and will be included in the upcoming PRD.
>
