η and η’ scattering: A probe of the strange-quark (ss¯) content of the nucleon?

Abstract

We propose that the relative cross sections for the reaction processes r\p,r\ 'p^^ rip,ri'p,K^h and K~p-^ r\n,r]n, induced by pseudoscalar mesons on a proton target, provide a sensitive test for the presence of a strange-antistrange (55) quark component in the nucleon's wave function.PACS numbers: l2.40.Aa, 14.2aDh In the naive quark model, the structure of the proton is |p)= \uud). The question of the quark content has been raised again by recent analyses of measurements' of the polarized structure function of the proton. Some authors^ argue that these data imply a significant admixture of strange-antistrange iss) pairs in the nucleon, even for small momentum transfers (large distances), while others^ dispute this interpretation. The 55 content in the nucleon can also be probed in low-energy pionnucleon scattering"* (via the so-called "cr term") or in nucleon-antinucleon (A^A^) annihilation processes. In the latter case, it has been suggested^ that the 55"component is revealed in terms of a breakdown of the OkuboZweig-Iizuka (OZI) rule at some level. This interpretation has been questioned.^ According to the OZI rule,^ for example, the ratio of cross sections G(A-^B-* (p +X)/G{A +5-(o-^-X), where A, B, and X do not contain strange quarks, is of order 1%. The dynamical origin of the OZI rule has been recently discussed by Lipkin.^ Tests of the type mentioned above involve an amplitude proportional to the square of the ss component of the nucleon wave function.In this Letter, we propose a first-order test of the strange-quark content of the nucleon. Specifically, we consider the pseudoscalar meson-baryon reactions K~p-^ rin.rj'n and r\p,ri'p-* rjp.rj'p.K'^A. We focus on the T] and 77' , since these mesons contain significant components of both strange (rjs =ss/^) and nonstrange lriud^(tiu-dd)/2] quark-antiquark (QQ) configurations. Because of this fortunate circumstance, interference effects between the 77^ and rfud components could be substantial in the reaction amplitudes. These amplitudes contain a term linear in the strength C^^ of the ss component of the proton, written schematically as I /?) == CI uud) + Css I uudss) -f(1)In contrast, the amplitude for Kp-^ np is quadratically dependent on Q^, since the pion has no ss component.An interference effect in r\,r] reactions arises because the relative phase of the r]ud and r\s components is opposite in the 77 and r\. Explicitly, we have the flavor wave functions ri=a7]ud-pr]s , ri'=Pr]ud-^ar]s , where we have ignored a possible gluonic component of the 77' . Our normalization is thus a^H-j3^=2. In terms of the conventional mixing angle 0, defined by (2) 9-11 77=cos^|8)-sin0| 1), (3) 77'=sin0|8) + cos^| l>, where \S}^(uu-\-dd-2ss)/^ and |l)==(ww+rfj -\-ss)/y/3 are SU(3) octet and singlet combinations, respectively, we have a = P = 1/2 COS0 -2sin6> V3 1/2 sin^-f 2cos^ V3Most recent decay analyses'^ suggest 0^ -20° which a^ 1.162,^=^^0.806. We now define the following amplitudes: A^<'r]udp\T\T]udP>. B=-{T],P\ T\T]SP} , C=^{r]udp\ T\T]SP) .(4)for (5) Some quark ...

Hadronic probes of the polarized intrinsic strangeness of the nucleon

“…Similar arguments were used in [26], where it was demonstrated that the experimental data on the production of η and η ′ mesons exclude 0 −+ quantum numbers for thess admixture in the nucleon wave function.…”

Effective Lagrangian approach to the theory of η photoproduction in theN*(1535) region

“…The choice is Z = 1 2 , Y = 0, k (2) R = 0. One curious consequence of this, arising from the absence of the gauge coupling k (2) R , is that the dynamical freedom of two independent electromagnetic multipoles at the γN N * vertex is lost. Thus, the magnetic quadrupole (M 2) to the electric dipole (E1) amplitude ratio for the N * (1520) radiative decay is fixed kinematically, rather than dynamically, yielding the ratio [79] give 31% ≤ M 2/E1 ≤ 56%, inconsistent with k (2) R = 0 for the transition.…”

“…In the present analysis, α will be varied from −1 to 3 and the other two parameters (β, δ) will be determined from the fit to the data. Also, varying the g (2) p electromagnetic coupling of the D 13 has not improved the fit considerably and therefore the ratio g (2) p /g (1) p is fixed to the P DG value of 0.69. An improved version of the CERN fitter routine, M IN U IT is used to minimize the weighted least-squares function χ 2…”

ϕmeson production inpp¯annihilation at rest

“…where A and B are the amplitudes for the 3-and 5-quark components in the proton, respectively [18]. The possible spin-flavor structures of the 5-quark components discussed in the NN annihilation process are considered in the next three subsections.…”

“…The strangeness magnetic moment µ s depends explicitly on α 0,1 , which is related to the amplitude for the ss quark cluster with spin 0. Setting α 0,1 = 0 is equivalent to excluding the quantum number J P C = 0 −+ for the ss admixture in the nucleon wave function connected to the the production of η and η ′ in NN annihilation as discussed in [18,25]. The chiral quark model always gives results for µ s and σ s which are negative, the size of the strangeness contribution depends on the coupling g All the three models yield negative values for the strangeness contribution to the proton spin, which is consistent with present experimental results [7,8].…”