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D(e,epRTPC)X D(e,epRTPCpCLAS)X

N(e,e)X D(e,epCLAS)X

E = 5.3GeV

Simulation ProcedureEvent Generator Geant4 RTPC

gsim (CLAS) RECSIS (reconstruct)

LOGO

Exclusive - Electro-production from the Neutron in the Resonance Region

Jixie Zhang for the BoNuS CollaborationOld Dominion University

LOGO

Radial Time Projection Chamber

D(e,e’p)p StudyNeutron Resonances

Kinematic

Acknowledgements

The study of baryon resonances is crucial to our understanding of nuclear structure and dynamics. The excited states of the proton have been studied in great detail. One would like to characterize the neutron in the same fashion.

The ratio of spectral functions with and without FSI corrections is shown as a function of spectator momenta ps and θpq (the angle between spectator proton and virtual photon).

Simulation is one of my major contribution in BoNuS experiment. I developed the Geant4 simulation for RTPC, then modified the exist gsim code and RECSIS to fit our purpose.

We checked the reconstruction software base on the fake tracks from the simulation. I have also developed the energy loss correction for CLAS and RTPC particles. Currently I am running to simulation to finish the acceptance correction.

•A long and thin target of deuterium gas at 7 atm with a diameter of 6 mm and a length of 20 cm.

•Drift region locates at 3 to 6 cm from the target and is filled with a drift gas (helium-DME).

•The ionized electrons are avalanched by the 3 layer of Gaseous Electron Multipliers (GEMs) and finally collected by the readout pad array on the surface of the detector cylinder.

MAGBOLTZ simulation

I would like to express my sincere gratitude to the DOE, the entire CLAS and BoNuS collaborations. Many, many thanks go to my advisors G. Dodge and S. Kuhn for all of their encouragement, suggestion, guidance and patience. Also I’d like to acknowledge the significant contributions of my fellow graduate students N. Baillie, N. Kalantarians and S. Tkachenko.

However, a free neutron target is impossible due to its instability.

Most of the neutron data were taken with deuteron targets, so we do not know the initial state of the neutron (binding, Fermi motion effects, and nucleon off-shellness …).

“spectator tagging” technique may help

•5 tesla magnetic filed point to the opposite direction to the beam line.

• Placed inside the center of Hall-B to work conjugate with CLAS.

BoNuS ExperimentW = (mn

2 + 2mn - Q2)1/2

q2 = -Q2 = 4′sin2(e/2) * = angle between the emitted - and the virtual

photon in the CM frame* = angle between the leptonic and hadronic

scattering planes

q

*

*

n

p

Hadronic plane

’,k’

,k

Leptonic plane

3200 channels

Sensitive to protons with momenta of 67-

250 Mev/c

Particle ID by dE/dx

(charge/track_length)

Helium/DME at 80/20 ratio

140 µm

3-D tracking:time of drift -> rpad position -> ,

z

dE/dX

FSI in Spectator Tagging

Ciofi degli Atti and Kopeliovich, Eur. Phys. J. A17(2003)133

For low spectator momenta, ps<100 MeV/c, the effects at backward angles (θpq >120o) are quite small, ≤ 5%, for both models.

Require the low Ps and large θpq allow us to ignore the FSI.

The red lines in the left figure show the drift path of each ionization electron that would appear on a given channel. In green is the spatial reconstruction of where the ionization took place.

The figures on the right show various views of an event reconstructed in three dimensions. Hits which are close to each other in space are linked together and fit to a helical trajectory. This resulting helix tells us the vertex position and the initial three momentum of the particle. The blue curve is fit to the simulated hits; the red curve is fit to the reconstructed hits.

Simulation

Jefferson Lab Experiment E03-012

Barely off-shell Nucleon Structure • Electron beam energies: 2.1, 4.2, 5.3 GeV• Spectator protons were detected by the newly

built Radial Time Projection Chamber (RTPC), other particles were detected by CEBAF Large Acceptance Spectrometer (CLAS)

• Target: 7 atm deuterium gas• Data were taken from Sep. to Dec. in 2005

• Both CLAS and RTPC calibration completed ①

• Quality checks completed ②

• CLAS Fiducial region for electrons defined• Electron and identification defined ②

• Target contaminations studied • Beam line (position) and correction is ready ②

• Energy loss corrections for CLAS particles and RTPC proton base on simulation are ready ②

• Momentum correction is ready• Acceptance correction is ongoing …… ②

• More simulation is running…… ② ① Only the EC time calibration is my contribution ② My major contribution

Current Status

A MAGBOLTZ simulation of the crossed E and B fields, together with the drift gas mixture, determines the drift path and the drift velocity of the electrons.

Electrons measured by CLAS and in RTPCPublic in NIM-A. doi:10.1016/j.nima.208.04.047

W (

GeV

)

Q2 (GeV2)

cos(θpq)

Ps

(MeV

)

Kinematic Coverage

•RTPC effectively reconstructed and identified slow protons

•Spectator tagging technique works

•RTPC can save 20% more date for exclusive - channel

D(e, e p)p

D(e, e pCLAS)ps

D(e, e pRTPC)pCLAS

N(1520)D13, N(1535)S11

(1620)S31, N(1650)S11, N(1675)D15, N(1680)D15, (1700)D33, N(1720)P13

(1232)P33

Baryonic

Resonances

D(e,e-p)p

E = 5.262 GeV

preliminary

2/

ˆ

,

D

SSS

SSS

M

qpE

pEp

Sn

SSDn pEMp

2

,

W 2 M 2 2M Q2

22

222

)2(2*

)(2*

QMM

QqpEMppqpW

S

nsDnnn

preliminary

FC