[Clascomment] OPT-IN: Measurement of the Sigma Pi Photoproduction Line Shapes Near the Lambda(1405)

[Keith Griffioen]

This is a very nice analysis and a well-constructed paper. Congratulations on your fine work!   However, the paper has not yet been properly edited.  There are many little things that should be corrected before it goes to a journal.  I've made some suggestions below.

Thanks,
Keith


50: use parallel construction: Although there has been continual theoretical interest in the Lambda(1405), there have been
remarkably few measurements of this state with a 4-star rating by the PDG [25] that has been known for more than half a century.

53:  the line shape, and that with barely adequate statistics.  The mass and width...
55: development of experiments with higher statistics, there has
56:  "a measurement" three times in this sentence.
59: "this" has an ambiguous antecedent.  Do you mean "used in our measurement"?
59: use parallel construction:  "their results depended on broad averaging over kinematics and line-shape comparisons with existing theoretical curves,
rather than on new and decisive fits to the data.
64: "GeV"?  Please check the document for consistency.  I would be happy with GeV for all masses, but the beginning of the article uses GeV/c2.  Here
it's just GeV.  also "up to 2.85 GeV, which allowed us to measure"
65: "for each energy;"
66: another paper that is in preparation will show the differential cross sections for each energy [32].
67: Use parallel construction: "The line shapes are differential in the Sigma pi invariant mass, m, and the initial-state gamma p invariant energy W."
73: Sections II-IV present
74: Use parallel construction:  "...various final states, the acceptance corrections and the data normalization."
75:  use "presents" or "describes" rather than "shows"  (multiple times)
77: Section VIII explains the method.  Again, use parallel structure with the previous sentences.
81: "were obtained during May and June of 2004 using the CLAS detector..."
83: real-photon beam
84: Bremsstrahlung photons with an endpoint energy of 4.019 GeV were created using the CEBAF....
85: ...were identified with...
89: The field was chosen such that positive particles were bent away from the beam line.
89: ...provided charge polarity and momentum...
91: ...used in the trigger to select charged particles leaving the target...
92: ...which determined the time of flight of each charged particle.  
94:  A sector trigger required hits in a Start Counter paddle and a TOF paddle within 150 ns of each other.
95: ...20 billion events, including...
101: The main final states of interest...
105: The ground-state hyperon decays, ..., are detected in our analysis.
FIG2: Representation of the reaction... The particles X were reconstructed via kinematic fitting or missing mass determination (parallel constructions!)
The right-most column lists the figures related to the given channel.
110: final-state particles but one were detected.  Otherwise, the missing...for the case of the...
111: From this, the ground state hyperons Lambda or Sigma...
113: final-state
128: The incident photon energy was corrected for the known mechanical sagging of the tagger hodoscope.
129: events for which a pi+ was misidentified...
130: A primary vertex cut along...
132+: with the particle's momentum p.  From this information, the measured time of flight was calculated as... Alternatively, we assumed a mass hypothesis...
and used the measured momentum to calculate the particle's velocity...Combining this with the flight distance $\ell$, we obtained the calculated time of flight... Momentum-dependent cuts were applied to the difference \Delta TOF =...
FIG3:  \Delta TOF versus momentum for pi+... and 2.35<W<2.45$ GeV.  Good events were selected between the magenta lines.
The other horizontal bands correspond to accidental coincidences arising from the 2ns accelerator beam pulse structure.
144:  ...in a previous study [34].  The confidence-level...
FIG4: \Delta TOF versus momentum...for 2.35<W<2.45 GeV...  after in-time pi- selection as shown...; and after selection of both...
150: example of the fits to the Lambda...
153: because the Lambda peak is very narrow (about 1.3 MeV for all bins, compared to about 6.3 MeV for the Sigma+ peak)
157: projections...which comes from...
158: Lambda(1405),
159: but removed it later by background subtraction.
FIG5: use "versus" rather than "against"
FIG6: The data are shown as histograms....The outer...range of the fits;  the inner lines show +-3\sigma, which is used to define...
170: against->versus
FIG7: against->versus... contours, as well as the dashed lines, show... M_0\pm \Gamma, and M_0...  (two 'where's is confusing)
176: versus
181: and a second-order polynomial for the signal region.  We required MM2 to be more than 3 sigma ...
FIG8: versus! for four bins of increasing energy from (a) to (d)... Lambda(1405), Lambda(1520), and higher Y* resonances... M_0\pm \Gamma, and M_0... 
185: Gaussian peak and a second-order polynomial background...
186: missing mass of the...
187: there are possible hyperon as well as K*+ resonances.  In Section V...
186: this section (no capital letter)
189: Further selections to isolate the states of interest will be shown later.
193: events of interest, we passed them through the detector simulation, where momenta were smeared...
194: An earlier detailed analysis of the g11a data showed [38] that the trigger conditions...
FIG10: The data are shown as histograms... and the inner lines show \pm 2\sigma around the peaks, which was used to select events.
197: applied to the events of interest that had...
201: beyond the Start Counter...
FIG11 versus!  see comments on previous figures
204: ground-state hyperons \Sigma+...  c\tau = 2.404...
205: effect of \sigma^\pm decays beyond the Start Counter...
210: trigger, and to account for the DAQ livetime of ~85%  (parallel constructions!)
212: final-state yields ... simulate the signal and background reactions of interest in each channel.  
214: ...to match the data.  (end here; the rest of the sentence is confusing and unnecessary)
223:  was generated
224: plotted as a function of the missing mass...
227+: We noticed a peculiarity that the Sigma(1384) line shape could not be fit to a relativistic Breit-Wigner function with a mass-dependent width.  Rather...
228: ..., in which q (q_0) is the...
230: momentum in this case is L=1.
231: generated with the forms of Eqs. 5 and 6.
232: well, because the q^3 factor
FIG13: events are plotted versus the missing...
FIG14: put (a) and (b) into the caption, not in the figure itself.  Sample invariant-mass spectra for W=2.6 GeV and \cos...=0.65 
showing the Sigma_0(1385) peak from data (magenta) and from the Monte Carlo templates based on ...(a) a relativistic... and 
(b) a non-... The relativistic Breit-Wigner form clearly does not fit the data.  
235: Wigner fits the data better is not clear...
236: mass and width based on hadronic reactions [25] also had difficulties with a relativistic P-wave... line shape...
238: Because these papers measured...
241: Therefore, we conclude that this ...
footnote:  Refs. [39-41] used the reaction...  "It should be noted" is totally unnecessary.
244: cross sections were calculated using acceptances based on simulations and the photon flux normalizations.
245: differential cross sections will be discussed in a separate...along with those for the Lambda(1385)...
246: for which the yields for the ...are necessary.
248: for the Lambda...
249: scaled up using the branching ratio...  Because the \Sigma^0 yield
250: it was not allowed to vary when extracting the yields of the \Lambda(1405).
254: versus!
256:  You say here "referred to as templates" after having used this term over and again.
257: [25].  We assumed
262: result for the \Sigma...
263: function that fits the Y* resonance around 1670 MeV.
264: our goal is to extract the...shape with the least model-dependence, we start with a relativistic...mass and width for the Lambda(1405).  This is shown
266: This Breit-Wigner function does not describe the data well.
271: Because this residual distribution is the best measure of the raw...yield, we applied an acceptance correction based on...
272: was generated,
273: corrected as a function of the \Sigma+pi- invariant...
275: for each energy and angle...
FIG15: strong final state \Sigma... ...done versus the \Sigma+\pi- invariant mass.  The data are shown with black crosses for the full set (a) and after
two iterations to match data and Monte Carlo (b).  The Monte Carlo calculations for \Lambda(1520) are shown in green, for \Lambda(1405) in red, 
for K0Sigma_ in blue, for Sigma(1384) in dark green and for Y*0 in magenta.  The total simulation is shown in cyan.
276:  the Lambda(1405) was not adequately...
278: The iteration process made use of data summed over all kaon angles within each energy bin.  
279: The iteration of templates converged to stable line shapes, and the total Monte Carlo fit is now close to the data.  
281:  off components such as...
282: Remove  "As the extracted Lambda...as the final template."  You've said this already.
284: (parallelism!)  ...was acceptance-corrected and normalized to the photon flux, yielding our intermediate results for d2sigma...
286: ...exactly the same as for Sigma_p+pi-, because the physics.
28y: Line shapes were obtained for each energy and kaon angle.  By comparing the two Sigma+pi- channels, we were able to check our results, as
discussed in Section VI.
290: as above, but in this case, with the strong final state K+Sigma-pi+, the Kpi combination is exotic, and therefore...
292: phase-space distribution of K+Sigma-pi+ events was generated
293: line shapes were iterated as before and then acceptance corrected.
299: similar to the previous cases, but 
300: ,due to the vanishing isospin factor,
301: with templates for Lambda(1405)...
303: were isolated in order to extract the line shape of the Lambda(1405) based on fits to the data.
304: were generated iteratively using the data...
307: The Sigmapi mass distributions dsigma/dcosthetadm (line shapes) were obtained...statistics we have summed over... to obtain a single line
shape dsigma/dm for each bin in energy.  
309: Alternatively, we can sum over mass to obtain the differential cross section dsigma/dcostheta.
310: Here we compare the results...
312: Line Shapes for the Sigma+pi- Channels
314: Comparing these two...
315: for each Sigma+pi- channel.  The inner error bars are the combined statistical errors for data and Monte Carlo background subtraction.
321: errors above.  These are shown as the outer...
322: The outer error bars are the total point-to-point uncertainties.
326:  and added the errors in quadrature
329: The agreement...channels is generally good.  The average of these two measurements will be used...
FIG16:  shown with light magenta open circles...is shown with light...as red downward triangles...at the bottom shows...
335: Line Shapes for All SigmaPi Channels
336: Our main results [42], the line...channels, is shown in Fig. 17.  The Sigma+pi- channel is the weighted...
339: and the outer bars include point-to-point systematic and statistical errors
341: over the full range of measured kaon production angles.  The large-angle...acceptances.  Since the cross section gets...we can neglect these differences...
345: unlikely that the effects are due to...
348: is largest for W between...
350: Our own best estimates for the mass and width of the Lambda...distributions will be shown in Section IX.
354: 18 that they are indeed different... channel.  In the chiral unitary theory this was explained...
358: ...an energy and angle-independent Weinberg-Tomozawa contact interaction, allowing us to compare...
359: Our Sigma+pi- channel is shifted to a higher mass with a narrower with...wider, in comparison to the model...
363: of what we see.
FIG18: W=2.10 GeV and E_gamma=1.88 GeV.
and the vertical dashed lines at 1.405 GeV and 1.437 GeV mark the nominal...
366: However, here we subtracted off... and still we were left
369: indicating a serious quantitative discrepancy.
373: there were global contributions from the yield extraction, acceptance corrections, flux normalization and line-fitting procedure.
374: Start the sentence:  The main cuts that influenced the yield extraction
376: ground-state
377: Variations in the DeltaTOF width by 0.2 ns changed the yield by 2-6%.  
379: Changing the confidence level of the cuts from 1% to 10% changed the acceptance-corrected yields by 3-12%.
385: omega production yields
368: The live-time correction to the photon flux introduced...
393: missing mass of the...
396: the resolution \sigma was better than 6 MeV...
399: high W and large angles (parallelism!)
405: final-state
406: seen in the various...
408: Both the Lambda(1405) line shape and the K* overlap depend strongly on W.  
409: Fig. 8 shows no K* interference at low W below the K* threshold, strong interference at intermediate W and again little effect at high W.
411: centered on the K* mass in multiples...
417: In Fig. (period, not comma) 19(b), the line shape changes significantly only for...
418: removes about 300 MeV of K+pi- invariant mass centered on the K*.  This is reflected in the Dalitz-like plot...Fig. 8, where
425: Because the photoproduction line shape of the Lambda(1405) is not precisely know, we do not...
427: this state
FIG19: Final results for the line shape... removed successively in W-intervals centered on the K* mass with widths that are integer multiples of
the K* width \Gamma as quoted in the PDG.
430: We have shown that the line shapes...
439: state in which the Sigma pi system...
443: final-state
444: the probability of populating the |pi-Sigma+> state...
445: in which the real relative...
451: Before going on, we assumed that the I=2 amplitude...and that all of the interference is between the I=0 and I=1 amplitudes only.
455+:  wrt Eq. 16, do you mean strengths rather than amplitudes, since the amplitudes are squared.
458+: in which C_I(W) is a real number...
459: in which
Eq.20  reverse m_R and m, so you don't have mm_R
461: center-of-mass system
462: phase-space factor (no quotes, but a hyphen)
before Eq. 21:  on the mass and is written as...
466: (Later we will analytically continue q below threshold)
467: as required for the odd-parity...
469: (no comma)
470: Eq. (19).  We take these to be fixed... (It's better not to combine two unlike sentences with 'and')
474+: single channel denoted "1".
after eq. 22: described by the width
after eq. 24: Decay Mode 2, the total...
478: over the whole range of W
482: requires the use of
483: K+Y*
484: into Sigma pi
485: final state is q
486: The invariant production amplitude TpiSigma is defined by... (no variables starting sentences)
486+: we measure the decay distribution of Y*->Sigmapi over the full solid angle Omega_Sigma so the data are automatically integrated over angles.
488: the larger pk+ becomes, the smaller m and therefore q must be.
491: represent the less-than-perfect subtraction...
500: This is crucial for understanding the contribution from the true Lambda...and anything else that is happening in the reaction.
505: was added to include the Sigma+pi- and...
506: However, a much better fit...
517: is controlled by the opening...
519: high-mass
522: as W exceeds this threshold.
523: data with the corresponding fit...
524: line shape, which is the same for all W bins.
525: due to the Flatte effect.526: in the Sigma pi distributions.
526: problems for W=...
529: a narrow I=1 contribution (dotted lines) plus a wide contribution (dashed lines).
530: Only the narrow line was allowed to have...
533: Fig. 21 shows only...data and the corresponding fits, ("Similar to Fig. 20" is confusing, since Fig 20 is not Sigma0pi0 only).
535: amplitudes could be considered...
537: alone, and is no better when using two...  (fix: "one one")
539: help us determine which amplitude...
540: data with the corresponding fits, including the underlying separate isospin contributions.
542: magnitudes, which are the same in Figs. 20, 21 and 22 at each W.
543: The fit comfortably...  (get rid of "What is notable is that", which says nothing.)
546: model [18].  (You don't need to mention that you mentioned this earlier.  An astute reader would know this from the reference number.)
548: is hard to interpret because it is so wide.  It could result from a non-resonant coherent 3-body amplitude.  The fit...
550: it is crucial for providing different threshold behaviors for the three charge states.
552: The fits to dsigma/dm using one I=0 and two I=1 states are the same shape but different magnitudes on all plots.
553: Clearly, the I=0 strength is the largest contribution to the reaction, but the I=1 contributions are not insignificant.
555: magnitude).  Above 2.2 GeV, the I+1 ...
557: broad I=1 amplitude
558: phase-dependence
559: as given in Table III.  For this we have...
560: Our analysis suggests that the Lambda(1405), as seen...
562: distribution, which differs...
565: In this case, we arrived at a satisfactory...  Even our best fits do not reproduce the data fully, and we cannot tell whether...unresolved systematic
effects or additional physics required in the model.  ("Elucidated" isn't quite the right word, in any case).  
FIG23 "amplitudes" does not need italics.
571: This I=1 strength has nothing to do with the standard...
572: and by demonstration that it cannot... (parallelism!)
573: Although our angular coverage is not complete, a majority of the range has been measured.
575: We can now discuss the quantum numbers of our BW amplitudes in the light of recent theoretical models.  First,...
577: for which the lower...
581: whereas the I=1 pole...
582: closer to our results.
584: We find the lower of these at the Sigma pi threshold.
586: positions in the various models...
587: comparisons are only qualitative.
588: Our work can shed light on previous efforts to identify....
591: models, the dominant configuration of some excited baryons consists of two diquarks...
592: low-mass, negative-parity, isovector
593: We observe that the line shape of the Sigma(1385) does not conform to its expected P-wave character...
596: No need to repeat oneself: Remove "We emphasize once again that a P-wave...interference."
599: The CLAS results for the...
602: not a player in this reaction, and we...
603: also does not play a role.
604: given in Table III
606: line shapes (no quotes)  mass distributions have been in the region (no plural) of the
608: none is well-represented
609: well-controlled
610: by scaling using the dominant...
610: interference with K*Sigma final states has no effect on the line shape.
612: ...channels appears to lie at the root of the differing line shapes for the three Sigma pi final states.
615: From the same analysis, even the Sigma0pi0...
619: find some evidence for a two-pole
621: The choice of one I=0...  (get rid of "We note that")
627: Clearly, more theoretical modeling and additional experimental data are needed.  In this context, the present work has provided a set
of Breit-Wigner amplitudes that show the importance...