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

S. Anefalos Pereira Few-Body Problems in Physics (FB18) August 21-26, 2006

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CONTENTS

Physical Motivation CLAS/JLAB Analysis Preliminary Results Conclusion


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• 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


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The amplitudes of the six elementary N KY (Y or ): γ p → K+ Σ0

γ p → K+ Λγ p → K0 Σ+

γp data from ABBHHM, SAPHIR and CLAS

Total Cross Sections

under CLAS analysis

under CLAS analysis

present analysis there is noTotal Cross section datafor γn reactions


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Differential Cross Sections

data on γp (CLAS)Eγ = 1.019 – 2.949 GeVCos ΘCM = -0.8 – 0.9

Σ0

Λ

data on γn (LEPS)Eγ = 1.5 – 2.4 GeVCos ΘCM = 0.6 – 1.0(blue points)

γ + n → Σ- + K+

Σ-


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Beam

Superconducting recirculating electron accelerator

JLab Accelerator CEBAF

Hall B

• Continuous Electron Beam

• Energy 0.8-5.7 GeV

• 200A, polarization 75%

• Simultaneous delivery to 3Halls


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Hall B: Cebaf Large Acceptance Spectrometer + Tagger

Torus magnet6 superconducting coils

Electromagnetic calorimetersLead/scintillator, 1296 photomultipliers

beam

Drift chambersargon/CO2 gas, 35,000 cells

Time-of-flight countersplastic scintillators, 684 photomultipliers

Gas Cherenkov

counterse/ separation, 256 PMTs

Liquid D2 (H2)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 designedto measure exclusive reactions with multi-particle final states

•E = (20% - 95%) Ee


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G10 ExperimentApproved 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


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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+

p

n

p

nΣ-

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-


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K+ identification

Kaon identification cuts: vertex time cut; Δβ cut = βTOF – βP = ± 0.06

Kaon momentum cut (0.4 ≤ pk ≤ 1.8 GeV)

before cuts after cuts

β β

p (GeV/c) p (GeV/c)


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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

aftercorrections0.9383 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.

beforecorrections

aftercorrections


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Σ- identification

beforecorrections

aftercorrections

the Σ- is identified in γn → K+ π - n X after Kaon selection.

3σ 3σ

M(π- n) M(π- n)

M(π- n) = 1.202 σ = 0.00798

M(π- n) = 1.198 σ = 0.00661


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Monte Carlo The CLAS package software (Genbos+Gsim+Gpp+Recsis) was

used;

K+

π -

n

p (GeV/c)

M(π- n)

1.197 GeV

simulatedExperimental data

Σ-

Θ (deg)

K+

π -

n


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ConclusionsIt 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.;

measurement of the n(p) k + (p) at jefferson lab

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