×¥ + n ïƒ K 0 + › With decays: K 0 ...
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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)
+ n K0 +With decays: K0 0 + 0 0 + n 0 + Net reaction: + n 6 + n
The elementary strangeness photoproduction reactions
+ pK+ + + pK+ + 0 + pK0 + + + nK0 + + nK0 + 0 + nK+ + -
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 -pK0 as a function of c.m. energy WPrior PWAs and quark-model predictions suggest appreciable K 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 pK+ and nK0 using two different parameter sets(a) and (c): predicted angular distributions at E = 1.05 GeV
(b) and (d): predicted total cross sections
These calculations show the urgent need for nK0 data to constrain the models.
Theoretical considerationsThe nK0 reaction is expected to help clarify the strangeness production mechanism because of the following features:
In contrast to pK+, the Born term in the t channel does not contribute to nK0 because no charge is involved.
The strong coupling constants in the u channel for 0 and other isovector exchanges have the same value but are of opposite sign to those in pK+ because of isospin symmetry.
The electromagnetic coupling constants of resonances in the s channel (e.g., gN*n) and in the t channel are different from those in pK+.
The nK0 reaction excites only I= N* resonances in the s channel. At MAMI-C, we expect good statistics up to E = 1400 MeV, corresponding to a c.m. energy W = 1.85 GeV. Thus, we have full coverage of the second resonance region.
Prior measurementsUntil very recently, there were NO experimental investigations of nK0:
2006 Data were measured in Fall 2006 as part of the g13 experiment at JLab for E = 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-Turoski (CLAS Collaboration), AIP Conf. Proc. 947, 146 (2007).]
2007 Quasifree production of neutral kaons on 12C was measured for E = 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 d/d 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 E = 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 nK0 calculated from MC simulation
Detector efficiency for background reaction pK0+
December 2007 Test Run at MAMI-CDuring 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 GeVTagged photon energy range : 0.4 1.4 GeVBeam current: 10-20 nARadiator: 10 m CuDiameter of collimator: 4 mmTarget: Liquid deuteriumTarget cell length: 4.76 0.03 cmCB multiplicity: 2+
Some results of our analysis of these data will now be presented using kinematic fitting for event selection.
Invariant mass of 2 from all 6-cluster events (no kinematic fitting)(Possible Combination of 6 to yield a 0 )+ = 0
Kinematic fit and confidence level
Z-vertex of primary interaction from kinematic fit
Distance travelled by K0 and
Invariant mass of 2 photons from pions produced in K0 decays in nK0 with kinematic fittingInvariant mass of 2 photons from decay KS 204 in events identified as from nK0.
Invariant mass of 4 photons in nK0Invariant mass of 4 photons fromdecay of KS in events identified as from nK0.
Missing mass of 4 photons in nK0Missing mass of 4 photons fromdecay of KS in events identified as from nK0.
Missing mass of 4 photons in pK0+Missing mass of 4 photons fromdecay of KS in events identified as from pK0+.
Summary and beam-time requestOur main objective is to measure d/d for nK0 with a precision of about 11%. We will also measure the 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 d/d for pK0+, 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.