1. Measurement of the  n(p)  K +   (p) at Jefferson Lab Sergio Anefalos Pereira Laboratori Nazionali di Frascati

2. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 2 CONTENTS Physical Motivation CLAS/JLAB Analysis Preliminary Results Conclusion

3. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 3 It’s important to provide data to investigate the spectrum of baryon (N* and Δ) resonances, with the decay in KY (Y ≡ Λ or Σ). Many baryon resonances are predicted studying the channels with π, but very few established. They are very broad and overlapping, making partial analysis difficult. This is the so-called “missing resonance” problem. Although the branching fractions of most resonances to KY final states are small compared to 3-body modes there are some advantages: - More often 2-body final states are easier to analyze than 3-body systems tates, - Couplings of nucleon resonances to KY final states will differ from the πN, ηN and ππN final states. Physics Motivation 1)study the baryon resonances not otherwise revealed, 2)obtain information about couplings of nucleon resonances to KY final states Goals of this work: study the γn → K + Σ - channel to

4. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 4 The amplitudes of the six elementary  N  KY (Y   or  ): γ p → K + Σ 0 γ p → K + Λ γ p → K 0 Σ + γp data from ABBHHM, SAPHIR and CLAS Total Cross Sections under CLAS analysis present analysis there is no Total Cross section data for γn reactions

5. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 5 Differential Cross Sections data on γp (CLAS) Eγ = 1.019 – 2.949 GeV Cos Θ CM = -0.8 – 0.9 Σ0Σ0 Λ data on γn (LEPS) Eγ = 1.5 – 2.4 GeV Cos Θ CM = 0.6 – 1.0 (blue points) γ + n → Σ - + K + Σ-Σ-

6. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 6 Beam Superconducting recirculating electron accelerator JLab Accelerator CEBAF Hall B Continuous Electron Beam Energy 0.8-5.7 GeV 200  A, polarization 75% Simultaneous delivery to 3Halls

7. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 7 Hall B: Cebaf Large Acceptance Spectrometer + Tagger Torus magnet 6 superconducting coils Electromagnetic calorimeters Lead/scintillator, 1296 photomultipliers beam Drift chambers argon/CO 2 gas, 35,000 cells Time-of-flight counters plastic scintillators, 684 photomultipliers Gas Cherenkov counters e/  separation, 256 PMTs Liquid D 2 (H 2 )target +  start counter; e minitorus Broad angular coverage (8°  140° in LAB frame) Charged particle momentum resolution ~0.5% forward dir Tagged photon beam with energy resolution  k/k ~ 0.1% CLAS is designed to measure exclusive reactions with multi-particle final states E  = (20% - 95%) E e

8. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 8 G10 Experiment Approved experiment for the Pentaquark research on Deuterium Data taking - March 13 – May 16, 2004; Tagged photons in the energy range from 0.8 GeV to 3.59 GeV; Target - 24 cm long liquid deuterium at Z = -25cm; Trigger - two charged particles in CLAS; Magnetic field - 2 settings of Torus magnet  I = 2250A ; Integrated luminosity ~ 25pb -1 ;  I = 3375A ; Integrated luminosity ~ 25pb -1 ; Data shown here is only for low field

9. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 9 Analysis procedure Studied channel γn → K + Σ - Energy range (W): 1.54 to 2.76 GeV; Theta range: from 10 to 120 degrees (10 degree bins); d K+K+ p n p n Σ-Σ- The key points:  The correct identification of K+  The correct identification of neutron Exclusive measurement: detection of K + π - and n proton as a missing particle. γ π-π-

10. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 10 K + identification Kaon identification cuts:  vertex time cut;  Δβ cut = β TOF – β P = ± 0.06  Kaon momentum cut (0.4 ≤ p k ≤ 1.8 GeV) before cuts after cuts β β p (GeV/c)

11. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 11 a signal in forward electromagnetic calorimeter (EC) is used, the precise interaction point inside EC can’t be determined, a correction on the neutron path length according to the interaction layer in EC (inner, outer or both) must be applied. Neutron identification after corrections 0.9383 GeV We are still working on the corrections. Next steps: 1) to correct the path length in function of neutron momentum, and 2) to take into account the Σ – decay path. before corrections after corrections

12. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 12 Σ - identification before corrections after corrections  the Σ - is identified in γn → K + π - n X  after Kaon selection. 3σ3σ 3σ3σ M(π - n) M(π - n) = 1.202 σ = 0.00798 M(π - n) = 1.198 σ = 0.00661

13. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 13 Monte Carlo The CLAS package software (Genbos+Gsim+Gpp+Recsis) was used; K+K+ π -π - n p (GeV/c) M(π - n) 1.197 GeV simulated Experimental data Σ-Σ- Θ (deg) K+K+ π -π - n

14. S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006 14 Conclusions  It is very important to provide data to investigate the baryon resonances which decay in KY in the final state in order to study the lack of the non observed predicted resonances;  The study of γn → K + Σ - reaction channel using the CLAS G10 data will give a set of results in the very poor scenario of gamma-neutron interactions.  The preliminary analysis has shown the γn → K + Σ - channel can be well identified;  The data analysis in under way, as well the Monte Carlo simulation;  This analysis will provide results in a W range of 1.54 to 2.56 GeV and angular range from 10 to 120 deg.;