Study of two pion channel from photoproduction on the deuteron Lewis Graham Proposal Phys 745 Class May 6, 2009
Overview • Physics Motivation • EG3 Data Set • Analysis • Outlook
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
The main motivations are to provide… • 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!
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
Missing States 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 Spectroscopy information was obtained from N N(X) reactions Therefore, missing states may be observed in the channels of multihadron production by photons for instance in two pion channel. From S. Capstick and W. Roberts, Phys. Rev. D49, (1994) 4570 (Relativized 3P0 model)
Jefferson Lab Hall B
CEBAFLarge Acceptance Spectrometer Torus magnet 6 superconducting coils Large angle calorimeters Lead/scintillator, 512 PMTs Liquid D2 (H2)target, NH3, ND3 g start counter; e minitorus Gas Cherenkov counters e/p separation, 216 PMTs Drift chambers argon/CO2 gas, 35,000 cells Electromagnetic calorimeters Lead/scintillator, 1296 PMTs Time-of-flight counters plastic scintillators, 684 PMTs
Particle production in CLAS CLAS 4pdetector • 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
CLAS Detection Allows simultaneous detection of multiple particles in the final state.
p- ∆++ g p d π+ (n) on a deuteron target Analysis of γd →∆++(pπ+)π- • Particle Identification Cuts Timing • Extracting Yield Fitting Procedure Detector Simulation • GSIM Parameters (MC Events) • Normalization GFlux Method • Systematic Errors
∆++ Identification p + π+ ∆++ = 1232 MeV
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.
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.
Acceptance Calculation Reconstructed Generated Events Acceptance Acceptance = Reconstructed / Generated Events
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
Cross Section Extraction After Luminosity After Acceptance Luminosity = target density * target length * Avogadro’s Number /Mole mass
Fit of p+p-p single differential cross-sections and the contributions from particular mechanisms with the JLAB-MSU (JM) model. Full calculations gpp-D++ gpp+D0 gpp+D13(1520) gprp gpp-P++33(1600) gpp+F015(1685) direct2p production Combined fit of various 1-diff. cross-sections allowed to establish all significant mechanisms.
Complete set of unpolarized 1-differential cross-sections in gr,v→p-p+p reactions. For unpolarized beam/target, the final state, gr,v→p-p+preaction offers 9 independent single-differential cross-sections in each (W&Q2) bin. All these cross-sections are available from CLAS for the first time.
Resonant and non-resonant contributions fit within the framework of JM model 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.
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