Photoproduction of Θ+ and other pentaquark states

Abstract

We present constraints on the relative photoproduction cross sections of positive parity pentaquark states, Σ5, Λ5, and N5, based on a minimum phenomenology gained in γN → KΘ + and their baryon-meson couplings as in the work of Close and Dudek. The possibility of anomalous signals in γp → K 0 S (Θ + ; Σ + d ) is discussed. We emphasise the importance of comparing γN → KΘ + with "conventional" states such as

K*couplings for the antidecuplet excitation

“…The dominance of the tensor coupling over the vector one in hadronic non-diagonal transitions (between different flavor multiplets) is supported by the analysis [14] of data for transitions between 10 and 8 multiplets. Regretfully, many phenomenological calculations of Θ-production (e.g., [3,4,5,6,7]) have used only the vector coupling for vector-meson exchanges, assuming non-vanishing f a 1 | q 2 →0 and neglecting f a 2 (q 2 ) . To our best knowledge, the dominance of the tensor coupling has been used only in Refs.…”

Some aspects ofΘ+parity determination in the reactionγN→Θ+<

“…The models of the Θ + photoproduction from the nucleon based on the effective Lagrangian approach have been developed in Refs. [8][9][10][11][12][13][14][15][16][17]. As has been pointed out, there are great ambiguities in calculating the (spin) unpolarized and polarized observables.…”

“…The total amplitude depends on the relative-strength parameter α which will be fixed by experimental data. The dominance of the K * exchange channel [16,17] allows us to reduce the number of relevant input parameters at a given coupling scheme to four: the sign and absolute value of α = g ΘN K * /g ΘN K and the sign and absolute value of κ * .…”

The pentaquark Θ+ in nK+ and pK0S, and its Σ+5 partner

“…Though DIANA [5] and COSY-TOF [10] determined the strangeness +1 of the narrow peak in pK 0 S , it seems they rather confirm the systematic mass shift between nK + and pK 0 S than solve the puzzle if we remember that the N K scattering analyses suggest that the width of Θ should be narrower than 1 MeV [23]. Hence, studies with increased statistics are required to confirm or place quantitative limits on the production ratio of Σ + 5 and Θ + in the pK 0 S channel [21]. (iii) In the case of (i), a clear Θ + and the absence of any other narrow structures in the region of 1.53 to 1.7 GeV could imply either Σ + 5 has a higher mass, or its signals are merged into broader octet Σ * resonances, e.g., Σ(1660).…”

“…(ii) If a stronger peak appears in the invariant mass spectrum of pK 0 S than in nK + , and at the same mass, it could be evidence not only for the Θ + , but also for the production of a degenerate Σ + 5 [19,20,21,22]. Note that the Σ + 5 in either a 10 or 8 5 is predicted to couple to pK 0 S with a strength comparable to that of the Θ + [18,22], while it will decouple from nK + .…”