study of two pion channel from photoproduction on the deuteron lewis graham proposal phys 745 class...
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Study of two pion channel from photoproduction on the deuteron
Lewis Graham
Proposal
Phys 745 Class
May 6, 2009
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Overview
• Physics Motivation
• EG3 Data Set
• Analysis
• Outlook
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This CLAS Analysis…
will use eg3 data set
will study 2π decays measuring the cross section for γd → Δ++(pπ+)π- and the angular dependent cross sections detecting all final state particles
will study final-state interactions with the “spectator” neutron
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a first measurement of the Δ+
+π- channel covering the energies and kinematics required to investigate higher lying resonances.
a first look at cross sections for kinematic and systematic effects.
a better understanding of the eg3 systematics.
The proposal is based on results from this analysis!
The main motivations are to provide…
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N* photoproduction experiments at JLab
on the proton g1: circular beam polarization g8b: linear beam polarization FROST: polarized beam and target
Analysis of current photoproduction data on the proton finds
all PDG 2*, 3*, and 4* resonances below 2.1 GeV no 1* resonances (P31(1750), S11(2090), P11(2100), …) no ‘missing’ N* resonances
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High lying (W >1.7 GeV) nucleon resonances study. Current study of high lying (W >1.6 GeV) nucleon resonances (can compare).
Extraction of known resonances with data extending to high energy range ( ~ 5.5 GeV). Existing data is only up to 5.1 GeV.
Search for possible signals from missing baryon states.
Physics Goals
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From
S. Capstick and W. Roberts,
Phys. Rev. D49, (1994) 4570
(Relativized 3P0 model)
Predicted but not observed in the experiment states are expected to decouple from N channel
but couple to the , N, N channels. Most of the
Nucleon Spectroscopyinformation was
obtained from N N(X) reactions
Res. ()(MeV)
()(MeV)
()(MeV)
()(MeV)
N1(1880)+ 8 80 5 25
N3(1910)+ 1 300 10 70
N3(1950)+ 16 60 15 40
N1(1975)+ 4 20 6 10
N5(1980)+ 2 240 5 8
Therefore, missing states
may be observed in the channels of
multihadron production by photons for instance
in two pion channel.
Missing States
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Jefferson Lab
Hall B
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CEBAF Large Acceptance Spectrometer
Drift chambersargon/CO2 gas, 35,000 cells
Electromagnetic calorimetersLead/scintillator, 1296 PMTs
Torus magnet6 superconducting coils
Gas Cherenkov counterse/ separation, 216 PMTs
Time-of-flight countersplastic scintillators, 684 PMTs
Large angle calorimetersLead/scintillator, 512 PMTs
Liquid D2 (H2)target, NH3, ND3
start counter; e minitorus
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CLAS 4detector torodail magnetic field 3 drift chamber regions time of flight electromagnetic calorimeter Cerenkov Counter
Electron Beam Energy 5.7 GeV Luminosity 1034 cm-2 s-1
Momentum Resolution < 1% Capability of detecting multiparticle final states
Particle production in CLAS
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CLAS Detection
Allows simultaneous detection of multiple particles in the final state.
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EG3 Run Conditions
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Analysis of γd →∆++(pπ+)π-
Particle IdentificationCutsTiming
Extracting YieldFitting ProcedureDetector Simulation
GSIMParameters (MC Events)
NormalizationGFlux Method
Systematic Errors
d
∆++
p
π+
(n)
on a deuteron target
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Particle Identification
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∆++ Identification
∆++ = 1232 MeV
p + π+
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Cuts
PID:
• 3-track Requirement
• Missing Mass2 Cut (.8 GeV2< MM2 < .97 GeV2)
• Skim Cut (0.7 GeV < M < 1.2 GeV)
•Proton Momentum – 450 MeV
Timing:
• Max. Vertex time of protons and pions - 2ns
• TOF difference of photon and avg. particle – 2ns.
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Simulation
• Generated 10M Events.
• Events Generated with same parameters as Data.
• Binned in 44 Energy bins and fit with breit-wigner.
• Yield Extracted for each fit energy bin.
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Acceptance Calculation
Acceptance = Reconstructed / Generated Events
Reconstructed Generated Events
Acceptance
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Normalization
• Data was normalized by the photon flux
• Each event in the data sample is corrected by a corresponding number of photons in the flux spectrum
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Corrections
Acceptance (simulation)
Timing cuts
Eloss Correction
Proton Momentum Cut
GFlux Correction
Prescale
Luminosity
Fiducial Cuts
Energy Bin Correction
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Data Fits with Corrections
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Cross Section Extraction
After LuminosityAfter Acceptance
Luminosity = target density * target length * Avogadro’s Number /Mole mass
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Comparison of Preliminary Results
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Next Steps in Analysis!
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Fit of +-p single differential cross-sections and the contributions from particular mechanisms with the JLAB-MSU (JM) model.
Full calculationsp-++
p+0
pp
p-P++33(1600)
p+F015(1685)
direct 2production
p+D13(1520)
Combined fit of various 1-diff. cross-sections allowed to establish all significant mechanisms.
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Complete set of unpolarized 1-differential cross-sections in r,v→-+p reactions.
For unpolarized beam/target,
the final state, r,v→-+p reaction offers 9 independent single-differential cross-sections in each (W&Q2) bin. All these cross-sections are available from CLAS for the first time.
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fit within the framework of JM06 model
resonant part
non-resonant part
differences in the shapes of resonant/non-resonant cross-sections make possible to isolate N* contribution.
Resonant and non-resonant contributions fit within the framework of JM model
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What’s to Come
Angular Dependence Cross Sections
Theoretical Model Incorporation and Interpretations to Data
Comparisons to Published Data
Contribution to World Data
Possible Missing Resonances found