Search for the with PHENIX

Abstract

Abstract. The PHENIX experiment at RHIC should be sensitive to decays of the the anti-pentaquark Θ − via the K − n channel. Charged kaons can be identified using the standard tracking and time of flight up to a momentum of 1.5 GeV/c. Antineutron candidates are detected via their annihilation signal in the highly segmented electromagnetic calorimeter (EMCal). In order to assess the quality of the anti-neutron identification we reconstruct the Σ → nπ. As an additional crosscheck the invariant mass of K + n is reconstructed where no resonance in the pentaquark mass range is expected. At the present time no enhancement at the expected pentaquark mass is observed in dAu collisions at √ s N N = 200 GeV.The possibility of five quark systems (pentaquarks) has been discussed for more than two decades (see, e.g. Ref The reconstruction of the Θ + pentaquark is technically difficult in PHENIX [12], due to the relatively small acceptance for 3-body final states and the difficulty of detecting neutrons. However, due to the unique signature of anti-neutrons in the highly segmented PHENIX electromagnetic calorimeter, a search for decays of the antipentaquark Θ − → K − n is technically feasible.Charged particles are tracked using the central arm spectrometers [13]. The kaon identification is accomplished by combining their momentum obtained from the tracking detectors with their time-of-flight as measured by the EMCal, shown in fig. 1. The upper limit of the momenta for separating kaons is 1.5 GeV/c, beyond which the contamination by pions becomes too large.The anti-neutron candidates are selected via their annihilation signal in the EMCal. Since there is no independent measurement of anti-neutrons to calibrate the EMCal response, guidance for identifying the anti-neutron signal is provided § For the full PHENIX Collaboration author list and acknowledgments , see Appendix "Collaborations" of this volume.

Hadron production in central nucleus–nucleus collisions at chemical freeze-out

“…For the beam energies of 2, 4, 6, and 8 AGeV, the yields of protons [45,46], pions [47,48] and kaons [48] are available (there are no K − data at 2 AGeV). The Λ yields are only available integrated over 4π [49] and for the energy of 6 AGeV the integrated Ξ − yield was also measured [50]. In these cases we have derived the mid-rapidity values assuming the same ratio between 4π and dN/dy as for protons [45].…”

Ultrarelativistic Nucleus–Nucleus Collisions and the Quark–Gluon Plasma

“…11 we present excitation functions for a selection of strange particle yields over the whole energy range from lowest AGS to LHC energy. The experimental ratios K ± /π ± , Λ/π + and Ξ − /Λ are calculated from measurements of absolute yields of π ± [29,48,31,32,49,50], K ± [51,31,32,49,50], Λ [52] and Ξ − [53]. The errors reflect the systematic uncertainties.…”

Strangeness observables and pentaquarks

“…It can certainly happen that a systematic error can lead to a peak coinciding with the real one or the expected one, in which case it may be missinterpreted. Another example is PHENIX which presented a peak at 1.540 GeV in the nK − invariant mass, candidate for the θ − → nK − which has been later understood to be due to a calibration error [109].…”