Kruscheet al.Reply:

Abstract

does not challenge any conclusion drawn in the interpretation of our data [2] but even strengthens some of them. The Comment suggests that the effective Lagrangian analysis (ELA) [3] is better suited for a detailed interpretation of our precision data. Our analysis makes use of the fact that (1) the total cross section is dominated strongly by the excitation of the Stt(1535) resonance and (2) that its shape can be parametrized by a Breit-Wigner type resonance curve with an energy dependent width. The ELA includes nucleon Born terms and vector meson exchange in addition to the excitation of resonances. Both analyses, however, give the same results for the S&t resonance simply because (1) and (2) are valid. This statement, which in our Letter is based on the energy dependence of the total cross section and the shape of the angular distributions, is strongly supported by the results presented in the Comment. In their Table I, the authors compare the helicity amplitude At/~o btained from our data with their ELA (column 1) to those from Breit-Wigner fitting used by us (column 4). Both analyses give almost identical results; certainly there is no significant discrepancy within errors. The large differences between the rows of the table are due to the values used for the total width I R and, in particular, for the partial width I "ofthe St t resonance. As already pointed out in our Letter, these hadronic widths now dominate the uncertainty of At/2. More explicitly, our Eq. (6) [2], together with the resonance position WR = 15441 3 MeV and a corresponding cross section of tT(WR) = 16~0.8 p, b, gives the following expression for At/2. . I MVb'/ At/p[10 GeV '/ ] = (5.82~0.15) b") with b"= I "/b". All entries in Table I of the Comment can be reproduced with this expression [the authors do not quote I"~a nd b" for row (c) of their table; however, a comparison of At/2 and g yields I It/b"= 290 MeV]. The parameter $ introduced by the Comment via [2] (I + jq+ ) t/2(m /W )1/2(b /I ) t/2g 1/2 (2) obviously avoids the uncertainty in I R/b"at the expense of mixing electromagnetic and strong coupling. Assuming again the dominance of the S~~resonance, it may be calculated from our Breit-Wigner analysis via C =~2 7r l~o+(Wtt) I = I "[t7(W~)]'/' (3) 2~q*"Using the values for W~and o (Wtt) given above leads to g = (2.21~0.06) X 10 4 MeV ', which is in excellent agreement (better than 1%) with the most complete ELA fit (row c of Table I). In our Letter we had assumed a very conservative upper limit of 10% for non-5]~contributions to the total cross section, giving rise to a 5% uncertainty of~Eo+(Wlt)~. However, the agreement on the 1% level demonstrated here suggests that non-S]~contributions to this number are really negligible. We thus agree that the value of the parameter s is model independent; due to the dominance of the S&& resonance, it is entirely fixed by the measured cross section.We thank the authors of the Comment for pointing out the overall sign error of the cos(O'") term in Eq. (7) [1], which, however, has no consequence ...

Higher partial waves in pp→ppη near threshold

“…However the sign of the cos 2 θ η term is negative in the photoproduction γp → ηp a little above threshold [17] and, using vector dominance ideas, this is likely to be true for ρp → ηp as well. In a pure ρ-exchange model, the elementary distribution would contribute a ≈ −2.5 which, though too small, is of the same sign as the one apparent in our data.…”

Extraction of electrostrong parameters of from eta photoproduction

“…Our goal here is to get at the relatively small contributions from the excitation of N * (1520), 3 2 − , T = 1 2 resonance. We cannot do that from the differential cross-section data alone, even though there is a hint [1,4,12,13] of its presence from these data. It is a combination of these differential cross-section data with the recently gathered data [5,6] on polarization observables that allows us to put powerful constraints on N * (1520) amplitudes.…”

“…Though a well-established resonance from the analyses of the pion-nucleon scattering and pion photoproduction, the electromagnetic properties of N * (1520), are yet to be studied experimentally via complementary reactions such as (1) and fully understood in the framework of the QCD-inspired models. Our interest in the reaction (1) is also enhanced by the recent availability of high quality data from different photon factories: differential cross-section data from the Mainz microtron [4], the polarized target asymmetry (PTA) from the upgraded electron facility at Bonn [5] and a precise data set, just released, on the polarized photon asymmetry (PPA) from the French laser light source, GRAAL [6]. We show below that a combination of these observables provide a powerful constraint on relatively small effects from the excitation of the N * (1520) resonance and its decay, amplified by the interference with the dominant contribution of the N * (1535) resonance.…”

An isobaric model for kaon photoproduction

“…That is the reason why the PV scheme has been preferred to the PS coupling in describing the pion photoproduction near threshold. Although recent experiments [30,50] and many theoretical researches [31][32][33][34] about E 0+ show that the LET disagreed to experimental values more or less, the superior prediction of PV Born terms to that of PS Born terms remains true at the threshold. Beyond threshold two descriptions yield nearly identical predictions [35] because the contribution from ∆(1232) dominates over that of other spin 1 2 baryons.…”