LW7445
Evidence for quark effects in polarization measurements of high-energy deutero
Wijesooriya,K./Afanasev,A./Amarian,M./Aniol,K./Becher,S./Benslama,K./Bim

        Dear Dr. Gilman:

              The above manuscript has been reviewed by our
        referee(s). A critique drawn from the report(s) is
        enclosed. On this basis, we judge that while the work
        probably warrants publication in some form, it does not
        meet the special criteria of importance and broad
        interest required for Physical Review Letters.

              The paper, with revision as appropriate, might be
        suitable for publication in Physical Review C. If you
        submit the paper to Physical Review, the editors of that
        journal will make the decision on publication of the
        paper, and may seek further review; however, our complete
        file will be available.

              If you submit this manuscript or a revision of it to
        Physical Review C, be sure to respond to all referee
        comments and cite the code number assigned to the paper to
        facilitate transfer of the records.

                                   Sincerely,

                                   Christopher Wesselborg
                                   Assistant Editor
                                   Physical Review Letters

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                               Referee A


              This paper reports interesting experimental results
        from measurements of polarization observables in high
        energy deuteron photodisintegration. These results are of
        substantial scientific importance in the field of
        high-energy nuclear physics. However, the manuscript is of
        such poor quality that I can not recommend publication in
        Physical Review Letters.

              This paper claims that the observed effects are
        "Evidence for Quark Effects..." right in the title. The
        absurdity of this claim can be seen in the fact that the
        observed polarization transfers are inconsistent with
        perturbative QCD (pQCD). Since quarks (at least the
        current quarks of pQCD) are not consistent with the data,
        the title is at least confusing, probably misleading, and
        almost certainly incorrect. The fact that the title of the
        manuscript is inconsistent with the reported data
        immediately implies that the "scientific validity" and
        "suitability for a broad audience" criteria are not (even
        nearly) satisfied. The text of the paper does not improve
        the situation; the authors repeatedly confuse QCD with
        perturbative QCD and use loose language regarding quarks
        and meson-baryon models.

              I am also quite concerned about a technical issue:
        the possibility of systematic error in the measured proton
        polarizations. The previous measurement of the elastic
        form factors of the proton used only the ratio of C_x to
        C_z (PRL 84, 1398 (2000)). That measurement could have
        nicely tested the absolute polarization capability of this
        apparatus, but no such report is available. Thus there is
        no calibration of the absolute analyzing efficiency
        presented for the spectrometer/polarimeter combination,
        and the reader has no way of judging the accuracy of the
        method.

              In my view, the submitted manuscript is unsuitable
        for publication in Physical Review Letters. While it is
        possible that a total rewrite could eventually meet the
        criteria for PRL, I do not believe that any conceivable
        revision of the present manuscript would be acceptable.
        Therefore, I recommend rejection of this paper.

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                               Referee B


              This paper reports on the first measurement of the
        spin transfer between the incoming photon and the outgoing
        proton, in the two body photodisintegration of the
        deuteron, in the GeV range.

              In addition the induced polarization of the emitted
        proton has been determined with a far better accuracy than
        in previous measurement.

              Together with the differential cross section,
        already reported by the sam group, these new data provides
        us with a benchmark in the field against which any
        theoretical analysis will be confronted.

              Although these data point toward an interpretation
        in term of quark degrees of freedom, it is too early to
        draw definite conclusion. However these data are important
        enough to justify a rapid publication as a letter.

              I do not see any reason to delay the publication of
        this important letter.


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                               Referee C


              This paper reports on new measurements of the proton
        polarization p_y and the polarization transfers C_x and
        C_y for circularly polarized photons to the proton in
        deuteron photodisintegration between .5 to 2.4 GeV
        (although 2.5 GeV is mentioned as highest energy, the data
        show the highest point at 2.4 GeV). The polarization p_y
        is found to be strongly negative and somewhat larger than
        previous measurements at the lowest energy, while it tends
        rapidly to zero at higher energies remaining close to zero
        above 1 GeV. Above .8 GeV the data are at variance with
        previous data from Kharkov. The polarization transfers C_x
        and C_y are found to possess a sizeable negative minimum
        around 1 GeV tending to zero at higher energies. These
        results are very interesting and deserve publication.

              Comparison with theoretical predictions shows that
        these results are at variance on the one hand with
        predictions from hadron helicity conservation giving zero
        for these observables, on the other hand with predictions
        obtained in the framework of a conventional meson-baryon
        picture resulting in a quite strongly varying p_y between
        .5 and 1.6 GeV. The results on C_x and C_y are also
        compared to "predictions" using perturbative QCD-arguments
        from which the t-dependence is invoked with arbitrary
        normalization. Thus the seeming agreement above 1 GeV is
        not very convincing, moreover one might doubt the
        applicability of perturbative QCD-arguments in this energy
        regime.

              The failure of conventional meson-baryon theory to
        describe p_y is then interpreted as evidence for quark
        effects. Although we all are interested to find genuine
        quark effects, I do not see strigent evidence in this
        case. Because first of all, it is not clear whether the
        predictions of Kang et al. using several approximations
        can be considered as typical for any conventional
        meson-baryon theory, and secondly, it is also not clear
        whether a quark gluon approach will be able to describe
        the data. Possible theoretical approaches are mentioned in
        refs. 30 - 35. But none of them has produced any
        predictions of these polarization observables. Then I
        wonder why they are mentioned here. In view of the very
        indirect "evidence", at least there should be a question
        mark at the end of the title.

              In view of the inconclusive result, namely what
        these data tell us about the appropriate theoretical
        framework, I cannot recommend this paper for publication
        in Phys. Rev. Letters, rather it might be reconsidered as
        a Rapid Communication in Phys. Rev. C.