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

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…

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

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

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

Jefferson Lab

Hall B

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

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

CLAS Detection

Allows simultaneous detection of multiple particles in the final state.

EG3 Run Conditions

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

Particle Identification

∆++ Identification

∆++ = 1232 MeV

p + π+

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

Acceptance = Reconstructed / Generated Events

Reconstructed Generated Events

Acceptance

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

Corrections

Acceptance (simulation)

Timing cuts

Eloss Correction

Proton Momentum Cut

GFlux Correction

Prescale

Luminosity

Fiducial Cuts

Energy Bin Correction

Data Fits with Corrections

Cross Section Extraction

After LuminosityAfter Acceptance

Luminosity = target density * target length * Avogadro’s Number /Mole mass

Comparison of Preliminary Results

Next Steps in Analysis!

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.

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.

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

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