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Page 1: ץ  + n   K 0  + Λ With decays:                        K 0     π 0   +  π 0 Λ   π 0   + n

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 +Λ + ץ With decays: K0 π0 + π0

Λ π0 + n π0 ץ + ץ Net reaction:n + ץn 6 + ץ

Page 2: ץ  + n   K 0  + Λ With decays:                        K 0     π 0   +  π 0 Λ   π 0   + n

The elementary strangeness photoproduction reactions

1. γ + p→K+ + Λ2. γ + p→K+ + Σ0

3. γ + p→K0 + Σ+

4. γ + n→K0 + Λ5. γ + n→K0 + Σ0

6. 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.

Page 3: ץ  + n   K 0  + Λ With decays:                        K 0     π 0   +  π 0 Λ   π 0   + n

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.

Page 4: ץ  + n   K 0  + Λ With decays:                        K 0     π 0   +  π 0 Λ   π 0   + n

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.

Page 5: ץ  + n   K 0  + Λ With decays:                        K 0     π 0   +  π 0 Λ   π 0   + n

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”.

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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).]

Page 7: ץ  + n   K 0  + Λ With decays:                        K 0     π 0   +  π 0 Λ   π 0   + n

Detector efficiency for γn→K0Λ calculated from MC simulation

Page 8: ץ  + n   K 0  + Λ With decays:                        K 0     π 0   +  π 0 Λ   π 0   + n

Detector efficiency for background reaction γp→K0Σ+

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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.

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Invariant mass of 2ץ from all 6-cluster events (no kinematic fitting)

(Possible Combination of 6ץ to yield a π0 )

ץ+ ץ = π0

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Kinematic fit and confidence level

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Z-vertex of primary interaction from kinematic fit

Page 13: ץ  + n   K 0  + Λ With decays:                        K 0     π 0   +  π 0 Λ   π 0   + n

Distance travelled by K0 and Λ

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Invariant mass of 2 photons from pions produced in K0 decays in γn→K0Λ with kinematic fitting

Invariant mass of

2 photons from decay

KS →2π0→4γ in events

identified as from γn→K0Λ.

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Invariant mass of 4 photons in γn→K0Λ

Invariant mass of

4 photons from

decay of KS in events identified as from γn→K0Λ.

Page 16: ץ  + n   K 0  + Λ With decays:                        K 0     π 0   +  π 0 Λ   π 0   + n

Missing mass of 4 photons in γn→K0Λ

Missing mass of

4 photons from

decay of KS in events identified as from γn→K0Λ.

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Missing mass of 4 photons in γp→K0Σ+

Missing mass of

4 photons from

decay of KS in events identified as from γp→K0Σ+.

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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.