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Measurement of the  n(p)  K +   (p) at Jefferson Lab

Measurement of the  n(p)  K +   (p) at Jefferson Lab. Sergio Anefalos Pereira. Laboratori Nazionali di Frascati. CONTENTS. Physical Motivation CLAS/JLAB Analysis Preliminary Results Conclusion. Physics Motivation.

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Measurement of the  n(p)  K +   (p) at Jefferson Lab

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

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

  3. Physics Motivation • 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. • 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). • 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. Goals of this work: study the γn → K+Σ-channel to • study the baryon resonances not otherwise revealed, • obtain information about couplings of nucleon resonances to KY final states Few-Body Problems in Physics (FB18) August 21-26, 2006

  4. Total Cross Sections The amplitudes of the six elementary N  KY (Y  or ): γ p → K+Σ0 γ p → K+Λ γ p → K0Σ+ under CLAS analysis γp data from ABBHHM, SAPHIR and CLAS present analysis there is no Total Cross section data for γn reactions under CLAS analysis Few-Body Problems in Physics (FB18) August 21-26, 2006

  5. Differential Cross Sections γ + n → Σ- +K+ Λ data on γp (CLAS) Eγ = 1.019 – 2.949 GeV Cos ΘCM= -0.8 – 0.9 Σ0 Σ- data on γn(LEPS) Eγ = 1.5 – 2.4 GeV Cos ΘCM = 0.6 – 1.0 (blue points) Few-Body Problems in Physics (FB18) August 21-26, 2006

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

  7. Hall B: CebafLargeAcceptanceSpectrometer + Tagger Torus magnet 6 superconducting coils beam Electromagnetic calorimeters Lead/scintillator, 1296 photomultipliers Liquid D2 (H2)target +  start counter; e minitorus • Broad angularcoverage (8°  140° in LAB frame) • Charged particlemomentum resolution~0.5% forward dir Drift chambers argon/CO2 gas, 35,000 cells CLAS is designed to measure exclusive reactions with multi-particle final states Time-of-flight counters plastic scintillators, 684 photomultipliers Gas Cherenkov counters e/ separation, 256 PMTs • Tagged photon beam with energy resolutionk/k ~ 0.1% • E = (20% - 95%) Ee 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 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); γ K+ Exclusive measurement: • detection of K+ π- and n • proton as a missing particle. n Σ- n π- d p p The key points: • The correct identification of K+ • The correct identification of neutron Few-Body Problems in Physics (FB18) August 21-26, 2006

  10. K+ identification • Kaon identification cuts: • vertex time cut; • Δβ cut = βTOF – βP = ± 0.06 • Kaon momentum cut (0.4 ≤ pk ≤ 1.8 GeV) β β before cuts after cuts p (GeV/c) p (GeV/c) Few-Body Problems in Physics (FB18) August 21-26, 2006

  11. Neutron identification • 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. after corrections before corrections after corrections 0.9383 GeV 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. Few-Body Problems in Physics (FB18) August 21-26, 2006

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

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

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