Workshop Summary: Experiment

Abstract

A summary of experimental results from the Pentaquark 2004 Workshop held at the SPring-8 facility in Japan is given. New results from the LEPS collaboration are highlighted, and older results are reviewed. Non-observations are also discussed in light of theoretical estimates of possible Θ + production mechanisms. The problem of the narrow width and the parity of the Θ + are explored and point to future experimental work that is needed.

Pentaquarks in chiral soliton models

“…A natural thing is that the masses of exotic states within soft rotator model are greater than in the rigid rotor approximation: the strange, or kaonic inertia Θ K becomes smaller for slow rotator, as explained above, (17). However, it looks somewhat unexpected that increase of masses is so great, up to ∼ 200 MeV .…”

“…The following problems and questions can be pointed out, many of them have been, of course, noted in previous discussions [19,18]: * High statistics confirmation of existence of narrow pentaquarks seems to be necessary, especially for the resonances Φ/Ξ 3/2 and Θ c , see [29]. Some information about experiments performed or to be performed is contained in [29,17,19,30].…”

“…There are different possibilities to have exotic baryon states: a) positive strangeness S > 0 (or negative charm C < 0, or positive beauty), since s-quark has S = −1 and c-quark C = +1, b) large (in modulus) negative strangeness S < −3B, B -baryon number; similar for charm or beauty, c) large enough isospin I > (3B + S)/2 , if −3B ≤ S ≤ 0, or charge Q > 2B + S or Q < −B in view of Gell-Mann -Nishijima relation Q = I 3 + Y /2. 1 Based partly on the talks presented at the International Seminar on High Energy Physics Quarks-2004, Pushkinogorie, Russia, May [24][25][26][27][28][29][30]2004; International Workshop on Quantum Field Theory and High Energy Physics QFTHEP-04, Saint-Petersburg, Russia, June [17][18][19][20][21][22][23]2004, and Symposium of London Mathematical Society "Topological Solitons and their Applications", Durham, UK, August 2- 12,2004. Slightly reduced version of this paper is available as E-print hep-ph/0507028.…”

“…Several experiments, mostly at higher energies, did not confirm existence of Θ, pessimistic point of view was formulated, e.g., in [16]. More complete list of references to negative results, many of them being not published yet, and their critical discussion can be found in [17,18,19]. Most serious seems to be recent negative result on Θ + photoproduction on protons, obtained at spectrometer CLAS (JLAB) with high statistics, where no resonance has been observed in K + n final state in the mass interval 1520 − 1600 MeV scanned with 5 MeV steps [20].…”

QCD Sum Rules of Pentaquarks

“…The newly discovered pentaquark Θ + [1,2] and its siblings are quite mysterious from the QCD viewpoint. Many questions are raised including • Why are they so narrow?…”