Proposal for an Experiment: Photoproduction of Neutral Kaons on Deuterium Spokespersons: D. M. Manley (Kent State University) W. J. Briscoe (The George Washington University) A. Starostin (UCLA) ץ + n  K0 +Λ With decays: K0  π0 + π0 Λ  π0 + n π0  ץ + ץ Net reaction: ץ + n  6ץ + n

The elementary strangeness photoproduction reactions γ + p→K+ + Λ γ + p→K+ + Σ0 γ + p→K0 + Σ+ γ + n→K0 + Λ γ + n→K0 + Σ0 γ + n→K+ + Σ- Kaon photoproduction is a fundamental process and an important tool for gaining new insights into nucleon resonances. Focus of this proposal is reaction (4), which serves as an isospin filter for N* resonances. Until very recently, there have been no experimental studies of this reaction.

Integrated cross section for π-p→K0Λ as a function of c.m. energy W Prior PWAs and quark-model predictions suggest appreciable KΛ couplings for S11(1650) and P11(1710). There is a possible hint of a narrow structure in the cross section near 1.7 GeV that merits investigation.

Isobar-model predictions for γp→K+Λ and γn→K0Λ using two different parameter sets (a) and (c): predicted angular distributions at Eγ = 1.05 GeV (b) and (d): predicted total cross sections These calculations show the urgent need for γn→K0Λ data to constrain the models.

Theoretical considerations The γn→K0Λ reaction is expected to help clarify the strangeness production mechanism because of the following features: In contrast to γp→K+Λ, the Born term in the t channel does not contribute to γn→K0Λ because no charge is involved. The strong coupling constants in the u channel for Σ0 and other isovector exchanges have the same value but are of opposite sign to those in γp→K+Λ because of isospin symmetry. The electromagnetic coupling constants of resonances in the s channel (e.g., gN*nγ) and in the t channel are different from those in γp→K+Λ. The γn→K0Λ reaction excites only I=½ N* resonances in the s channel. At MAMI-C, we expect good statistics up to Eγ = 1400 MeV, corresponding to a c.m. energy W = 1.85 GeV. Thus, we have full coverage of the “second resonance region”.

Prior measurements Until very recently, there were NO experimental investigations of γn→K0Λ: 2006 – Data were measured in Fall 2006 as part of the g13 experiment at JLab for Eγ = 0.4-1.9 GeV and 0.5-2.5 GeV using tagged photons with circular polarization; no results of analysis have yet been published. [E. Munevar, B.L. Berman, and P. Nadel-Turoński (CLAS Collaboration), AIP Conf. Proc. 947, 146 (2007).] 2007 – Quasifree production of neutral kaons on 12C was measured for Eγ = 0.8-1.1 GeV using tagged photons at LNS of Tohoku University in Sendai, Japan. Momentum spectra and integrated cross sections were obtained, but dσ/dΩ could not be obtained due to limited kinematical acceptance. [T. Watanabe et al., Phys. Lett. B 651, 269 (2007).] 2008 – First measurement of K0 photoproduction on deuterium was reported. Data were measured for Eγ = 0.8-1.1 GeV using tagged photons at LNS of Tohoku University in Sendai, Japan. Extracted momentum spectra differed considerably in shape and magnitude from those predicted with Kaon-MAID. [K. Tsukada et al., Phys. Rev. C 78, 014001 (2008).]

Detector efficiency for γn→K0Λ calculated from MC simulation

Detector efficiency for background reaction γp→K0Σ+

December 2007 Test Run at MAMI-C During 5-21 December 2007, 277 hours of beam time using unpolarized tagged photons incident on a LD2 target were obtained. Experimental parameters are listed below: Electron maximum beam energy: 1.508 GeV Tagged photon energy range : 0.4 – 1.4 GeV Beam current: 10-20 nA Radiator: 10 μm Cu Diameter of collimator: 4 mm Target: Liquid deuterium Target cell length: 4.76 ± 0.03 cm CB multiplicity: 2+ Some results of our analysis of these data will now be presented using kinematic fitting for event selection.

Invariant mass of 2ץ from all 6-cluster events (no kinematic fitting) (Possible Combination of 6ץ to yield a π0 ) ץ+ ץ = π0

Kinematic fit and confidence level

Z-vertex of primary interaction from kinematic fit

Distance travelled by K0 and Λ

Invariant mass of 2 photons from pions produced in K0 decays in γn→K0Λ with kinematic fitting 2 photons from decay KS →2π0→4γ in events identified as from γn→K0Λ.

Invariant mass of 4 photons in γn→K0Λ 4 photons from decay of KS in events identified as from γn→K0Λ.

Missing mass of 4 photons in γn→K0Λ 4 photons from decay of KS in events identified as from γn→K0Λ.

Missing mass of 4 photons in γp→K0Σ+ 4 photons from decay of KS in events identified as from γp→K0Σ+.

Summary and beam-time request Our main objective is to measure dσ/dΩ for γn→K0Λ with a precision of about 11%. We will also measure the Λ recoil polarization. We need the maximum beam energy for MAMI-C, a 5-cm liquid deuterium target, and unpolarized (or circularly polarized) photons. We require a high multiplicity trigger. We will simultaneously measure dσ/dΩ for γp→K0Σ+, which will provide a check of systematics since there are published cross sections for this reaction with which to compare our results. Our requested beam time for data taking is 400 hours.