[Gdh_lowq2] Your_manuscript CU10463 Zheng

Tue Aug 16 20:47:09 EDT 2016

Hi Xiaochao,

I want to comment on your second question.

a) The photoproduction data do not select D13(1520), but the cross 
section consists of 3 resonance (S11(1535), P11(1440), and D13(1520)). 
The two states S11 and P11 hav eonly sigma_1/2 contribution and 
compensate for some of the D13 sigma_3/2 contributions. Moreover, there 
is also quite a bit of background that can contribute, and we don't know 
what the helicity structure of the background is.  So, it is not clear 
what the sign of the integrated cross section should look like.

b) In electroproduction, the D13 is changing its spin structure rapidly, 
from sigma_3/2 to sigma_1/2 dominance, while the other two resonance 
remain fully sigma_1/2. Therefore with increasing Q^2 we expect 
sigma_1/2 - sigma_3/2 > 0 with sigma_1/2 becoming increasingly dominant.

c) In the F15 region the situation is even more complicated because we 
have even more resonances contributing (S11(1650), S31(1620), F15(1680), 
P13(1720), D33(1700), D13(1700). While F15 is dominant in photoproduction
it is not clear how all the other states mix it up. One really has to 
isolate individual partial waves and isolate the resonance contributions.

d) You try to compare pi0 and pi+ production. Pi0 production is less 
sensitive to isopin-1/2 resonances than pi+ production is. Since all 3 
resonances in the 2nd resonance region are I=1/2, your pi+ data are more 
affected by the 3 resonances than the CBELSA pi0 data are.

So, I conclude your data are perfectly consistent with what one might 
expect from the pi0 photoproduction data if one considers the complexity 
of the amplitude structure underlying the pi0 and the pi+ data.

For you info I attached graphs showing what we know about the helicity 
amplitudes of resonances that have
been isolated in partial wave analysis procedures  as discussed in these 
paper:

I.G. Aznauryan et al (CLAS Collaboration), Phys.Rev. C80 (2009) 055203
I.G. Aznauryan and V. D. Burkert, Prog.Part.Nucl.Phys. 67 (2012) 1-54

Best regards,
Volker

On 8/16/16 3:58 PM, Xiaochao Zheng wrote:
> Dear All:
>
> I have started looking into these comments and I can use some help, as follows:
>
> 1) (Fig.6) Does anyone recall what happened to the beam polarization during the 1.3 GeV NH3 run period? The Moller polarization jumps up and down quite a bit and they were definitely not statistical fluctuations.  Did the beam change a lot (that is, at least 4 times) during that period because other halls requested different beam energy, pass number, or polarization?
>
> 2) THe reference mentioned by the referee on the pion photoproduction data, PRL112(2014)012003 seems to show that A_LL (our definition, as 1/2-3/2) should be >0 for D13(1520) and <0 for F15(1680), while I think our data indicate that both are <0 in the lowest Q2 bin. Should I say something about the inconsistency with the photon data for the D13(1520)?   (Or, should I not comment on it because the observables in photo- and electro-production may not be a one-one mapping?)  I am also puzzled why the D13 has >0 sign (1/2-dominance) from the photoprod data, opposite to PDG(2000)?
>
> For your convenience, the submitted version (or nearly) can be downloaded from http://arxiv.org/pdf/1607.03924.pdf (it is nearly identical to the version read by the referee. Differences did exist due to the PDF rendering processer on different websites, which explains the missing labels...)
>
> More questions to come.  Thanks in advance!
>
> Xiaochao
>
> ----- Original Message -----
> From: "Xiaochao Zheng" <xiaochao at jlab.org>
> To: "gdh lowq2" <gdh_lowq2 at jlab.org>
> Sent: Thursday, August 4, 2016 3:29:23 PM
> Subject: Fwd: Your_manuscript CU10463 Zheng
>
> Hello all:
>
> Below please find comments on the EG4 exclusive paper.
>
> I will work with Marco on details of the cherenkov and then will work on all other comments as well.  Help will be appreciated in dealing with these comments, so please feel free to comment.
>
> Thanks,
>
> Xiaochao
>
> ----- Forwarded Message -----
> From: prc at aps.org
> To: "Xiaochao Zheng" <xiaochao at jlab.org>
> Sent: Thursday, August 4, 2016 3:02:18 PM
> Subject: Your_manuscript CU10463 Zheng
>
> Re: CU10463
>      Measurement of target and double-spin asymmetries for the  vec e vec p
>      rightarrow e pi  +(n) reaction in the nucleon resonance region at low
>      Q 2
>      by X. Zheng, K. P. Adhikari, P. Bosted, et al.
>
> Dear Dr. Zheng,
>
> The above manuscript has been reviewed by one of our referees. Comments
> from the report appear below.
>
> These comments suggest that specific revisions of your manuscript are
> in order. When you resubmit your manuscript, please include a summary
> of the changes made and a succinct response to all recommendations or
> criticisms contained in the report.
>
> Yours sincerely,
>
> Bradley Rubin
> Senior Assistant Editor
> Physical Review C
> Email: prc at aps.org
> http://journals.aps.org/prc/
>
>
> COLOR REMINDER:
>    You have requested to have some color figures in the print
>    journal (5,9,10).  If your paper is accepted you will
>    be invoiced for the cost before your paper is sent to our
>    production vendor for the amount of US$2010.
>    (See: http://journals.aps.org/authors/color-figures-print)
>
> ----------------------------------------------------------------------
> Report of the Referee -- CU10463/Zheng
> ----------------------------------------------------------------------
>
> The authors report about new measurements of pi+ electroproduction
> with the CLAS spectrometer at JLab using a polarized beam and a
> polarized target. The data cover the center-of-mass energy range of
> the full nucleon resonance region in particular at very low values of
> 4-momentum transfer. This is valuable new information about the
> transition of transverse amplitudes from photoproduction to finite
> virtualities as well as about longitudinal amplitudes which cannot be
> accessed with real photons.
>
> In the paper no LT-separation is performed but the data are presented
> in terms of target and beam-target asymmetries and are compared to
> model calculations. The paper is well written and covers the relevant
> experimental issues. I have no reservations on the main content, the
> analysis procedures, the discussion of systematics and the
> presentation of the results. A publication in PRC is fully
> appropriate.
>
> I suggest the following checks and modifications which would improve
> to quality of the paper:
>
> (1.) I propose to use the nomenclature for baryon resonances suggested
> by PDG:
>
> e.g. P33(1232) -> Delta(1232)3/2+ (similar for all states).
>
> (2.) Page 3, line 159- 163:
>
> The authors mention pion photoproduction data but refer only to
> upcoming CLAS data. Here the published work of other labs should be
> mentioned as well (e.g PRL 112 (2014) 012003, ...).
>
> (3.) page 5
>
> In Fig.2 the labeling inside the picture is missing. I see only the
> arrows.
>
> (4.) page 5, line 313-324.
>
> The new Cerenkov counter is introduced but no details are given. I
> assume that its structure and performance (gas, efficiency,..) are
> similar to the existing Cerenkov detectors and Ref.35 is also relevant
> for the new device. If this is correct one could make such a statement
> or give some numbers and further reference should be given.
>
> (5.) page 7, line 482
>
> "Beam charge asymmetry ...." replace by: "A helicity dependence of the
> integrated beam charge...."
>
> (6.) page 8, Fig.6
>
> I do not understand the interpretation of the data points and
> extrapolation bands. What happened e.g. before run number 51500 (1.3
> GeV data)? Two Moller measurements are significantly lower compared to
> other. It should be explained why the inter-(extra-)polation was done
> as indicated by the gray bands. I assume, that its due to changes in
> the configuration or breaks during data taking. Same question comes up
> when looking at the extrapolation of the last 2 data points.
>
> (7.) page 8, Fig.7
>
> axis labels missing
>
> (8.) page 8, line 549
>
> "ep -> e'pi+(n)" replace by "ep -> e'pi+(X)" as correctly done in the
> caption of Fig.8
>
> (9.) page 9, caption of Fig 8.
>
> .... (the proton mass) replace by .... (the neutron mass).
>
> (10.) page 9, eq.(26) and eq.(27)
>
> There are more recent form-factor data at low Q2 which where not
> available in 1995 when the fit of Ref.(45) was performed. I assume
> that details in the form-factor parametrization at low Q2 are not very
> important for the method and additional errors from uncertainties in
> our knowledge on proton form factors are small. Probably even a simple
> dipole parametrization would work. If my assumptions are correct, a
> short statement about the sensitivity of the method to the form factor
> parametrization should be added.
>
> (11.) page 10, Fig.9
>
> The variable "dil" is not defined. I would use the name "f_el^incl" as
> in the text.
>
> (12.) page 9, line 578-580
>
> A reference for the formula A^el_th = ... should be given. I think
> that in the second term of the denominator G_M^p should be replaced by
> (G_M^p)^2.
>
> (13.) page 8/9
>
> In the description of the reconstruction of elastic events the authors
> refer to an invariant mass (e.g. page 9 line 584). To be consistent
> with the other chapters, this quantity should be called "missing
> mass".
>
> (14.) page 10, line 675
>
> The authors claim that their run-by-run values of Pb*Pt determined via
> elastic scattering are consistent with all configuration changes. I
> propose to include a figure similar to Fig.6 where Pb*Pt is shown as
> function of the run number (or blocks of runs). Such a figure would be
> helpful for the reader to get an impression about the data taking and
> the consistency.
>
> (15.) page 11, section E.
>
> It should be made clear that the discussion about the asymmetry
> extraction is only valid in each single kinematic bin
> (Q^2,W,theta,Phi). Only later in the text it becomes clear that this
> was correctly done. I propose to introduce the 4-dimensional grid of
> the kinematic variables used to extract the asymmetries already at
> this point.
>
> (16.) page 13, Fig. 10
>
> I assume that the missing mass distributions are integrated over all
> other kinematic variables. I suggest to show also the missing mass
> spectra for e.g. 2 typical kinematic bins, which have been used in the
> real analysis.
>
> Replace the label "dil" in the figure by "f_dil^pi" as given in the
> text.
>
> (17.) Presentation of results
>
> The way the results are presented and compared to model calculations
> is reasonable for this experimental paper. I have two suggestions:
>
> a) The authors stress several times that the new data are consistent
> with previous data at higher Q2. But no comparison is shown. I propose
> to include a plot which shows the consistency to previous data or to
> add previous data in existing plots.
>
> b) Results for the beam asymmetry A_LU were obtained but are not
> discussed in the paper.
>
> The authors say that A_LU was just used as a cross-check and that the
> results are available for download. This is reasonable as this
> observable can be better obtained with a hydrogen target. Nevertheless
> a short comments about these data should be made (E.g. are the data
> consistent with existing data? What is the contribution of quasi-free
> events?). Maybe a reference (thesis?) could be added.
> _______________________________________________
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> Gdh_lowq2 at jlab.org
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