G E n at High momentum transfer Hall A experiment - E Bogdan Wojtsekhowski, also for G.Cates and N.Liyanage Hall A collaboration meeting, June 22 rd, 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 G E 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 nucleon At 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) or rely 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 Q 2 ~ 1 GeV 2 Quasi elastic scattering vs inelastic channels (pion,two pions, delta..) for 2.5 GeV/c neutron 1- = Achievable resolution is of He target allows for of 10 times higher luminosity than polarized ND 3 target Nuclear effects in 3 He target unfavor at Q 2 < 1 GeV 2, at the Q 2 value of our interest 3 He 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 10 5 higher luminosity than it used at NIKHEF ? Cut on P transv,recoil selects QES, it is possible because of quite good angular resolution of the neutron detector! Cut on P long,recoil is modest: just +/-250 MeV/c

Asymmetry vs P_miss - FSI effects as from 2002 proposal This type plot we need to get ASAP from GEN data

JLab Hall A During E 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 AAA+ AAA AAB AAA AAA+ AAA AAB ABC

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) AAA+ AAA AAB AAA ABC AB AAA DD AAA+

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 AAA+ AAB AAA AAB AAA+ AAB AAA AAA+

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 GeV 2 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 E and continuing efforts in analysis. Stay tune to learn about neutron shape during next year. Measurement at Q 2 =4.5 GeV 2 could be done today with present setup.