GE

n at High momentum transfer

Hall A experiment - E02-013

Bogdan Wojtsekhowski,also for G.Cates and N.Liyanage

Hall A collaboration meeting, June 22rd, 2006

Students, experts, run coordinators and shift takers (>3 shifts)

S. Abramyan, B. Craver, A. Kellerher, A. Kolarkar, J. Miller, S. Riordan; J.P. Chen, R. Michaels , E. Chudakov, A. Shahinyan , D. W. Higinbotham, J. Singh,

Al Tobias, S. Wood, V. Nelyubin, S. Tajima, A. Camsonne, N. Gevorgyan;

B. Sawatzky, M. Jones, R. Feuerbach, N. Liyanage, D. Day, T. Holstrom, Ole Hansen, T. Averett, R. Holmes;

V. Punjabi, O. Rondon, G. Urciuoli, K. Allada, B. Anderson, A. Beck, S. Beck, B. Crowe, F. Cusanno, C. Dutta, S. Fuchs, K. Grimm, D. Howell, Joe Katich, B. Moffit, C. Perdrisat, D. Protopopescu, A. Puckett, Xin Qian, Yi Qiang, P. Reimer, D. Rohe, A. Saha, J. Wright, X. Zhu, J. Arrington, S. Frullani, L. Kaufman, J. Lopez, D. Margaziotis, F. Wesselmann, H. Yao, C.Fernandez, R. Lindgren, M. Khandaker, W. Korsch, W. Boeglin, L. Coman, O. Glamazdin, J. Kelly, P. Markowitz, L. Pentchev, S. Stepanyan, V. Sulkosky, A. Acha, K. Aniol, J. Annand, C. Ferdi, L. Fraile, F. Garibaldi, X. Jiang, J. LeRose, B. Quinn, S. Sirca, Tim Ngo, Eli Piasetzky, G. Rosner, J. Udias, R. Ransome, Ron Gilman.

+ an important list of experts, who design and built GEN systems (UVA, YerPhI, BINP, ITEP, ... )

Outline

Motivation of the experiment or Why high momentum transfer measurement of GE

n is so much needed?

The results of 75 days of running 2/25-5/10:

comissioning; development; statistics collection

Milestones of data analysis

Perspectives for even higher momentum transfer with the same detector package

30 s

Motivation - Form factors

Form factors (FFs) are functions in a hadron current operator

In one photon approximation scattering cross section is factorisable and FFs could be calculated (first Born approximation) At low momentum transfer in first BA FFs are related to the classical charge and magnetic distributions of the nucleonAt intermediate momentum transfer the FFs deal with a convolution of the hadronic structure of the photon (Vector Mesons) and the nucleon structure (including the pion cloud)

At large momentum transfer the valence quark components of the nucleon are providing a dominant contribution into FFs Asymptotic properties of the FFs are predicted in the pQCD limit Connections to Deep Inelastic electron Scattering, VDCS, and RCS were discovered recently in the GPD formalism 30 sec

Expectation for accuracy of the result

30 sec

One photon approximation

Nucleon vertex:

Sachs form factors:

Cross Section:

Motivation - GPDs

Motivation - Neutron Electric Form Factor

Motivation - Neutron Electric Form Factor and its importance for GPDs

Experimental approach: Beam / Target Asymmetry

Asymmetry:

Experiments either:

measure both components (by rotating target spin)

orrely on polarimetry

Main difficulties and our solutions

Number of events ~ L /(Q

2)4, so we need 100+ times higher L than it was obtained in best prev. experiment Q2 ~ 1 GeV2

Quasi elastic scattering vs inelastic channels (pion,two pions, delta..) for 2.5 GeV/c neutron 1- = 0.07. Achievable resolution is of 0.008.

3He target allows for of 10 times higher luminosity than polarized ND3 target

Nuclear effects in 3He target unfavor at Q2 < 1 GeV2, at the Q2 value of our interest 3He target is a way to go!

Need also 10 times larger acceptance of the electron detector --> BigBite! Is 1% resolution enough? Is it possible to run at 105 higher luminosity than it used at NIKHEF ?

Cut on Ptransv,recoil

selects QES, it is possible because of quite good angular resolution of the neutron detector!

Cut on Plong,recoil

is modest: just +/-250 MeV/c

Asymmetry vs P_miss - FSI effectsas from 2002 proposal

This type plot we need to get ASAP from GEN data

JLab Hall A During E02-013

BigHand

BigBite

Hall A E02-013: 3D View

Hall A Neutron Detector (BigHAND)

Hall A with BigBite

New technology approach and results

Target:

Hybrid pumping approach K-> Rb-> He

Fiber optics lines for laser light with optimized optics for multi-fiber source

High temperature ceramic oven

8 hours spinup time, 55% polarization with 8 mkA beam

NMR in both pumping/target chambers

Holding field with skinny dipole magnet “iron box”

Precision field direction - air supported compass

Beam line elements: air cooling jets, non-conductive W collimators, He bags, Be/Al windows

Beam line/cell alignment

Beam line local shielding

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New technology approach and results

Electron Arm

Wire chamber type, constr. quality

Front end electronics

Shielding, W blocks, wood, ..

Shower trigger

Shower PID

Timing plane

HV system

Gas system

TDC (VME)

TDC (FastBus)

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New technology approach and results

Neutron arm

Detector reliability - 99%-99.9%

Front end electronics

Trigger

HV system

Mechanical system/shielding (1-3 hours)

TDC F1

TDC FastBus

ADC FastBues

Cabling system

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Analysis team and time line (goal)

Six PhD students and one MD student with thesis projects, more plan join for learning opportunity Robert is leading GEN analyzer and analysis with help from Ole Spokespeople and students advisers (Averett, Egiyan,Franklin, Kelly, Korsch, Liyanage)

Preliminary results for 1.8 GeV2 kinematics by October 2006 Final analysis of all four kinematics is a requirement for every PhD from this experiment, expected before end of 2007

Summary

Ideas in GEN proposal about operation of the open detectors at luminosity of the polarized target are working. Hall A GEN has Figure-of-Merit by a factor of 100 higher than best of previous experiments with any polarized targets.

The novel target concept and both arms detector equipment had operate with very good up time.

Collaboration had succeed to be ready for experiment in time and collected very good data at four kinematics.

We are sure that all effort (hope you agree) directed to GEN preparation pay back very efficiently for physics of the form factor and for at least of 100 PAC days already approved “A” rated experiments based on the BigBite spectrometer.

Thanks collaborators and contributors for support of E02-013 and continuing efforts in analysis.

Stay tune to learn about neutron “shape” during next year.

Measurement at Q2=4.5 GeV2 could be done today with present setup.