A New Instrument for Jefferson Lab Hall A Multi Purpose Spectrometer

Transcription

1 A New Instrument for Jefferson Lab Hall A Multi Purpose Spectrometer B. Wojtsekhowski TJNAF, Newport News, VA A. Glamazdin Kharkov Physics Institute, Ukraine E. Cisbani INFN, Rome, Italy L.P. Pentchev College of William and Mary C.F. Perdrisat College of William and Mary V. Punjabi Norfolk State University May 6, 2008 Abstract The principle considerations and parameters of the Multi Purpose Spectrometer are reported. Momentum resolution of 0.8% at 8 GeV/c and solid angle up to 70 msr of this device should find wide range of applications in 12 GeV physics program of Hall A TJNAF. 1

2 1 Introduction A rigorous new physics program is expected with the 12 GeV cw electron beam at TJNAF [1]. Doubling of CEBAF energy allows to increase achievable momentum transfer in elastic electron-nucleon scattering to 18 GeV 2. Separated form factors of proton will be measured to 15 GeV 2, almost twice larger than achievable with present CEBAF machine. Even more dramatic advances will be in the studies of deep-inelastic scattering and semi inclusive deep-inelastic scattering, where the kinematics will be well in the scaling regime. Small cross section for the most interesting channels put severe constrain on the maximum momentum transfer in actual experiment and requires optimization of the experimental apparatus. Use of large solid angle detectors is the approach chosen in the two 12 GeV projects of CLAS++ and GlueX. It is important to do optimization between the cost of running, which is defined mainly by a duration of the experiment, and the cost of construction of the specialized setup. When the beam-on-target time for an experiment approaches several months, the specialized setup could be cost effective approach if it allows several times faster collection of the data. The Figure-of-Merit (FOM) of experiment is the product of the usable luminosity, L, and the solid angle, Ω. In an experiment with the polarization observables there are additional components of FOM, such as the target polarization and/or the polarimeter efficiency and analyzing power. An experiment with unpolarized target and 11 GeV beam could run with electron-nucleon luminosity up to L max cm 2 /s. However such huge luminosity is difficult to use with the detector of solid angle larger than few msr, unless the reaction of interest has unique kinematical correlations, as for example in the case of elastic ep scattering [2]. A large portion of the CDR program [1] deals with experiments from polarized targets, which can accommodate only much lower luminosity than L max. Presently solid polarized targets, like NH 3 and ND 3, have maximum total electron-polarized nucleon luminosity on the level of cm 2 /s. A luminosity larger by a factor 4-5 is expected with a specialized magnet for providing a transverse (vertical) magnetic field [3]. Today a gas polar- 2

3 ized target of 3 He can operate at a polarized electron-nucleon luminosity of cm 2 /s, and has potential to reach several times larger luminosity in a couple of years [4]. The discovery of the difference in Q 2 dependences for G Ep and G Mp [7, 8] and the almost linear falloff G Ep /G Mp up to Q 2 = 5.6 GeV 2 [9, 10] is an important experimental result of JLab. Presently a third round of G Ep measurements is in progress in Hall C [11]. A new experiment [2], approved by PAC32, will measure G Ep /G Mp at 13 and 15 GeV 2, for which the new Multi Purpose Spectrometer, MPS discussed here, will be constructed. Study of the Transversity Distributions is an important component of the 12 GeV physics program. It involves measurements of Semi-Inclusive Deep-Inelastic Scattering with an electron and a meson in the final state, e, e M, where M is most often a pion or a kaon with a large momenta P directed along the momentum of a virtual photon. For kinematic of interest a perpendicular component of meson momenta, P is limited by GeV/c. Such process has geometry similar to the quasi-elastic scattering. As a result FOM depends linearly on the electron arm acceptance. The solid angle for the meson arm does not need to be much larger than π (P /P ) 2 plus that of the electron arm. It should match the electron arm solid angle and allow for the required range of meson P. In high-x DIS experiments a momentum resolution for the electron of 1% is sufficient. A large solid angle spectrometer, based on a dipole, capable of operating at a luminosity of cm 2 /s, was recently considered for high Q 2 G En experiment [5]. In the 2006 report to the Hall A collaboration meeting, the advantages of a dipole spectrometer for a number of important experiments using polarized targets were outlined [6]. In this report we present the parameters of this spectrometer, and show that the MPS could be applied to a wide range of studies from Exclusive scattering, to DIS and to SIDIS. 3

4 2 Concept of the spectrometer The key considerations for this spectrometer are: Dipole magnet; Vertical bend; High resolution tracker; Beam path through the opening in the magnet return yoke. There are a number of large acceptance spectrometers constructed with a big magnet and high resolution tracking device, for example HERMES spectrometer [12]; this spectrometer is suitable for low luminosity experiment which allows installation of a tracking detector in front of the magnet, and has almost full azimuthal coverage in the range of the polar angles from 2.3 to 8.0 with good momentum resolution of 0.8% for 10 GeV particle. For high momentum transfer experiments with 11 GeV electron beam, detector should cover polar angles up to In high luminosity experiment with electron beam the exit beam line after the target is required to provide about ±25 mr opening to the beam dump, because of large probability of electron elastic scattering to small angle. Magnetic field on the beam line should be as low as possible to avoid deflection of the background particles out of the exit beam line. The configuration chosen in the GEP5 experiment [2] has two separate arms: one for a scattered electron with the central angle of 37 and another for a recoiled proton with the central angle of 14. Here we present a concept of the hadron arm, for which we have selected a dipole magnet with vertical bend configuration. A magnetic field vector is oriented parallel to the plane of electron scattering, so one can use the electron beam position in the reconstruction of the particle trajectory. It is a critically important for obtaining a good momentum resolution at high luminosity because it allows to put the whole detector package behind the strong magnetic field at a distance of several meters from the target, and avoids tracking detectors in-front of the magnet, where counting rate is very large. 4

5 Acceptance of the proposed spectrometer covers 1-2 radian in the azimuthal angle and 5-10 in the polar angle, pending of a central scattering angle (see Tab. 1). A successful example of similar device is BigBite built at NIKHEF [13]. It was a spectrometer with medium momentum resolution for very low luminosity experiments with an internal target at the AmPS ring. For E experiment we replaced its integrated readout wire chambers and two-paddle scintillator trigger by a highly segmented multi-plane drift chamber system with a well segmented two-layer shower calorimeter for the trigger. It was successfully operated at luminosities million times larger than used at NIKHEF, up to [16], for the scattering angle of and the solid angle of 76 msr. A major conceptual advance was proposed in the GEP5 [2], where a solution for a large solid angle device at small scattering angle was found by using a cut in the magnet yoke and the wire chamber tracker will be replaced by a GEM tracker. In addition to the GEP5 experiment, which will measure G Ep /G Mp at 13 and 15 GeV 2, the large acceptance simple dipole spectrometer will allow several other high impact experiments in SIDIS, from polarized and unpolarized targets [15]. Figure 1 shows a top view of the spectrometer planned for the GEP5 experiment. 2.1 Dipole magnet The dipole labeled 48D48 is a warm coil magnet, with a 3 Tesla-meter field integral at excitation current of 4 ka. It was used at BNL for the fixed target program. This dipole will be used in the MPS spectrometer. Figure 2 shows a drawing of the magnet as it was used at BNL. The vertical bend will be achieved by rotation of the magnet by 90, so the magnetic field direction will be in the horizontal plane. Installation of the magnet at small angle is possible by means of a deep cut in the iron yoke (see Fig. 3). Because orientation of the cut is parallel to the field lines in the iron and the cut starts about 2.5 inches from the surface of the pole the cut leads to a minimum distortion of the magnetic flux flow in the yoke and field 5

6 GEM 228 inch 128 inch GEM Hadron Calorimeter Target 63 inch CC1 48D48 CH2 CC Gauss +/ 25 mr Figure 1: The layout of the new spectrometer to be built for the GEP5 experiment: 48D48 magnet, front GEM tracker, double polarimeter with two GEM trackers, and a hadron calorimeter. Figure 2: The assembly drawing of the 48D48 magnet for vertical field orientation as it was used at BNL. 6

7 distribution in the gap. Total weight of the magnet is 100 tons. It consists of five iron slabs of 20 tons each, so it can be assembled inside the Hall A by means of the existing overhead crane. Figure 4 shows a design model of the MPS magnet in Hall A. TOSCA calculations of the 48D48 magnet field were performed. The iron Beam Left coil Right coil Beam line opening Right yoke A A 173" 92" Target Figure 3: The concept of the beam path through the dipole. magnetization is shown in Fig. 5. In the Fig. 5 beam is going from left to right through the conical hole which is close to the pole surface specially on the left side. As it is shown by colors (see color scales in the insert) the field is lower in the area of the left corner of upper pole. The reduction is seen also in Fig. 6 which shows the field along particle trajectories. Overall reduction of the field leads for just 1% loss of the field integral along trajectory which is close to the beam line. The field along the central ray and left/right rays are shown in Fig. 6 with the cylindrical cut for the beam path in the yoke. The field with modified coils (needed for the beam path) presented in Fig. 7 for 2 ka level of magnet excitation. Results for the magnetic field on beam line are shown in Fig. 7. Remaining field on the beam line inside 48D48 will be cancelled by a combination of a µ-metal tube and low current compensation 7

8 Figure 4: The view of the magnet in Hall A. Figure 5: The magnetization of the iron for 2 ka current of the coils shown in the horizontal plane on the level of the beam line. The insert on left side shows the color scale for the field. 8

9 Figure 6: The field along three trajectories at 2 ka current of the coils. magnets. The section of beam line outside 48D48 require additional small appeture magnets. Nominal field integral of the 48D48 magnet could be up to 3 Tesla-meter for 4 ka excitation current, however at such excitation the iron in the pole has very low µ and the field in the cut because of 4 kg, which is difficult to compensate or shield. For this reason we are planning to use 2 ka excitation current and resulting 2 Tesla-meter field integral. 2.2 GEM tracker A recent invention of Gas Electron Amplifier (GEM) detector by F. Sauli [14], made the new spectrometer concept possible. The GEM detector consists of a gas volume with a set of GEM foils and low noise readout from strips or pads as illustrated in Fig. 8. A single detector allows determination of both coordinates of the track at the detector location with a typical accuracy of 70 µm. An assembly of several detectors will be used in the tracker for measurement of coordinates and direction of the particle trajectory. 9

10 Figure 7: The field along the beam path at 2 ka current in the coils. 2.3 Acceptance Figure 8: The concept of the Gas Electron Amplifier. The solid angle at different central angles of the spectrometer is shown in Table 1. Other parameters in the table are: D, the distance from a target 10

11 center to the iron of 48D48, the range of horizontal, and the range of vertical angles. Out-of-plane angle coverage is about at scattering angle below 15 and drops to 45 for θ central equals to 30 when the distance D become limited by the size of the target vacuum chamber and by the HRS bearing diameter. θ central, Ω, D, Hor. range, Vert. range, degree msr meter degree degree ± 1.3 ± ± 1.9 ± ± 3 ± ± 4.8 ± ± 4.9 ±12.5 Table 1: The solid angle of MPS vs. central scattering angle. 3 Particle Identification and Trigger The precise organization of the trigger and particle identification will be specific for each experiment and required luminosity. In GEP5 the trigger will be a coincidence between the electron arm calorimeter and a hadron arm calorimeter, each of which will be segmented. A correlation between elements of electron and hadron modules will be used for trigger optimization (see Fig. 9). In lower luminosity experiments with polarized targets the total sum from the whole calorimeter can be used for trigger. In J/Ψ photoproduction experiment, trigger and PID can use combine energy deposited in the calorimeters of two arms. The particle ID in all experiments will probably be done off-line. 3.1 Particle Identification Several detectors could be used for particle identification in the MPS: Ring Image Cherenkov Counter. Threshold Cherenkov Counter. 11

12 Lead-glass two-layer calorimeter. In Hall A there are several sets of lead-glass calorimeters from which one can assemble of 4 m 2 frontal area two-layer calorimeter. The RICH detector from HERMES could be used for preparation of similar detector for the MPS Luminosity and PID The maximum beam current at 11 GeV energy will be 75 µa [1], so with 40 cm long liquid hydrogen target the luminosity is L max = cm 2 /s. For photo-production experiments with a radiator of 10% radiation length the background corresponds to a four times larger luminosity of cm 2 /s. The usable luminosities will be defined by the type of experiment, PID required for event selection, and trigger options. For example in the GEP5 experiment, the on-line use of angular correlations and high energy threshold in calorimeters of both arms will allow to use full L max. For SIDIS experiments with π ± and K ± in final state the particle ID and acceptance will require to limit a total luminosity below cm 2 /s. An example for Transversity experiment will be discussed in the next chapter. 3.2 Trigger In GEP5 there are two key considerations of the trigger. They are: the calorimetry of the particle energies and online use of the particle angular correlations. Good energy resolution of the electromagnetic calorimeter will allow for electron arm trigger rate of 60 khz at the maximum luminosity. Large energy of a recoiled proton (of 8 GeV) will allow relatively high threshold in the proton arm calorimeter of 4.5 GeV. High segmentation of the calorimeters will allow to use online angular correlation between electron and proton for reduction of accidental rate. Recent GEN experiment [16] also used the lead-glass calorimeter with high threshold trigger in the large acceptance spectrometer. Second level trigger could use coincidence with another arm and/or with Threshold Cherenkov counter. 12

13 Figure 9: The trigger organization in GEP5 experiment. 4 Optics calibration The relatively small field integral of the magnet, 2 Tesla-meter, and the dipole configuration of the field simplify the spectrometer optics; however a calibration is needed because of large fringe field for the large ratio of the aperture to the magnet length. Calibration will be done by using an additional small GEM tracker, installed for the period of calibration, between the target and the magnet. 5 Magnet configuration for GEP-5 In GEP-5 experiment, where only 30 msr solid angle is required, we are going to make two iron inserts in the magnet. The inserts will collimate acceptance to required value, reduce vertical size of the pole, and reduce gap between poles. Such adjustment will make no difference (or just reduce variation) for the field on the beam line, however it will allow to increase the field integral to desirable 3 Tesla-meter and spin rotation angle to the optimum value of

14 6 Experiments with new spectrometer Many experiments can be done using the proposed multi purpose spectrometer. The list includes measurements of DIS and SIDIS with polarized target(s), the elastic form factors of the proton and the neutron, photo-production of J/Ψ experiment, electro-production of φ meson and exclusive pion photo and electro-production at large momentum transfer, and some other experiments. 6.1 Exclusive processes Electron-proton elastic scattering The measurement of the form factor ratio G Ep /G Mp is the primary motivation which triggered development of the MPS spectrometer. The large acceptance of the MPS will allows measurement of the ratio G Ep /G Mp with ±0.1 accuracy in a 60-day run as shown in Fig. 10. Figure 10: The projected accuracy of GEP5 experiment. Measurement of the G Mp form factor for Q 2 up to 18 GeV 2 is approved proposal and will be done by using HRS spectrometers [23]. However, note 14

15 that with the detector setup proposed, G Mp experiment could reach the max Q 2 data points 10 times faster or with higher statistics than with standard spectrometers. Such data will be collected anyway as a calibration run before production on the deuterium target for G Mn measurement. Electron-neutron elastic scattering The measurement of G En /G Mn at a momentum transfer of 7.5 GeV 2 requires an electron spectrometer like MPS and new advance in the polarized target technology with higher polarizing power [4] and circulating He gas between the pumping and the target cells [5]. The measurement of the G Mn at the momentum transfer up to 8 GeV 2 could be done using the MPS magnet for the neutron arm with the existing BigBite spectrometer as the electron arm; see the experimental proposal [24]. The layout is shown in Fig. 11. By using the front GEM tracker of MPS behind the BigBite magnet we expect higher usable luminosity and reach Q 2 of 17 GeV 2. Additional results from this measurement could lead to a test Figure 11: Layout of the GMN experimental proposal [24]. of the A-dependence for the ratio of the proton to the neutron quasi-elastic yields at high momentum transfer in complex nuclei. 15

16 Wide Angle Compton Scattering JLab experiment on WACS find evidence for the dominant mechanism of Compton Scattering from proton in few GeV energy range [25]. That experiment did measure the polarization transfer from incident circularly polarized 3.2 GeV photon to the recoil proton. Results agree with calculation based of handbag dominance where a single quark absorbs and emits the photons. A similar experiment at higher energy will obtain a crucial information about the dominant mechanism of WACS which is one of fundamental processes with proton, just next to elastic electron scattering. Use of the polarized NH 3 target is providing the possibility of such a study (by the measurement of complimentary parameter - initial state helicity correlation effect) at moderate luminosity, which is usable with proposed MPS for WACS process in-spite of the large physics background from single π photo-production. J/Ψ photo-production from proton The cross section and mechanism of J/Ψ photo-production near energy threshold is practically unexplored. Identification of the resonance from decay e + e pairs detected in the magnetic spectrometers with % momentum resolution should be possible even at very high luminosity. Large acceptance of this two-arm experiment (see possible layout in Fig. 12) will allow also detection of the recoil proton. Single pion photo-production Hall A experiment [26] observed a large variation of the recoil proton polarization in the process of neutral pion photoproduction from the proton at a photon energy of 2.5 GeV. That result is a direct indication of a heavy mass pion-proton resonance, which was not observed before. Systematics study of this exciting new physics require a scan through a wide range of photon energy. This large project could be accomplished when the proton and the pion are detected in coincidence because it will allow to insure exclusivity of the reaction outside of the end-point of photon spectra; it avoids multiple changes of the electron beam energy. WACS experiment [25] had already collected data which will allow precise design of the pion production experiment H( γ, pπ ). 16

17 Layout for Charm photoproduction with two BNL magnets Beam degree ~14 Solid angles = 80 msr X 30 msr Momentum resolution ~ 0.5% at 5 GeV/c Figure 12: Layout of two 48D48 magnets for J/Ψ study. Color transperancy in proton quasi-elastic knockout Search for onset of color transperancy (CT) in electron-proton scattering from nuclei was done most recently in JLab experiment [27] for momentum transfer up to 8 GeV 2. With a 11 GeV beam a CT test could to be extended to GeV 2. The MPS for the proton arm and the BigBite magnet with the GEM tracker for electron arm will provide the required detector configuration for the CT experiment. 6.2 Deep-Inelastic Scattering DVCS at large Q 2 Hall A experiment [17] made a pioneering study of the Q 2 dependence for DVCS process, H( e, e γ)p, in the limited Q 2 range 1.5 and 2.3 GeV 2. Scaling property of the DVCS amplitudes is of critical importance QCD test and should be extended to 10 GeV 2. Such an experiment could be done using the large acceptance of the MPS. Parameters of the DVCS experiment (usable luminosity and required electron arm resolution) are mostly defined by operation of the photon calorimeter and are well matched to the capability of the MPS. The good energy resolution of the photon arm is very important, however it has a practical limit of 1-2% when the photon detected by a calorimeter. For example, an approved proposal [18] based on HRS requires 88 days of running which could be reduced by factor 10 or accomplished 17

18 with much lower luminosity. The lower luminosity will open perspective for recoil proton detection, which was not essential in first experiment [17], but likely will be necessary at large momentum transfer. Quark polarization at high x High x experiments are an important part of the JLab program. There are approved experiments, A1n and d2n, based on the BigBite and SHMS spectrometers [19, 20]. Both these experiments can obtain even better results with MPS because its acceptance at least 15 times larger than the acceptance of SHMS in required scattering angle of and the detector rate capability of MPS is at least 100 times higher than for the present BigBite. For these measurements, as well for the J/Ψ experiment, double layer lead-glass electromagnetic calorimeter will be installed behind the tracking devices for trigger and PID purposes. High-x u/d ratio from He/T method The large solid angle and over 50 cm long acceptance for the target makes the MPS a very attractive device for an experiment with a tritium target. For example, the well known experiment [21] proposed for measurement of u/d, requires a high luminosity tritium target. Target design and construction became expensive and handling of the large amount of radioactive material is complicated. When experiment organized with the MPS the required luminosity is lower by a factor of 10, which will allow drastic reduction of the total amount of the radioactive material required for tritium target and will help to simplify the design of the target. 6.3 Semi-Inclusive Deep-Inelastic Scattering This process provides access to the flavor-tagged quark distributions in the nucleon, measure flavor composition of the spin and quark orbital moments, and transverse momentum distributions. The important feature of this reaction is the large value of the momentum of the meson along the virtual photon direction and the relatively small value of its perpendicular momentum. In 12 GeV experiments the typical p is ten times larger than p, which typically is about 0.5 GeV/c. As a result the kinematics of the SIDIS process resembles quasi-elastic electron-nucleon scattering, which has been studied 18

19 the two spectrometer setup in Hall A with very good results Transversity Recent results from the HERMES experiment for transverse momentum distributions have demonstrated that such studies reveal new physics features of the nucleon[22]. Figure 13 shows extracted asymmetries for transversely polarized target in the reaction H( e, e π). Such results were obtained in an 2 sin(φ+φ S ) π UT π + III HERMES PRELIMINARY virtual photon asymmetry amplitudes not corrected for acceptance and smearing sin(φ+φ S ) π UT π - 6.6% scale uncertainty x z P h [GeV] Figure 13: HERMES results for transverse momentum distributions. experiment with luminosity of the order of cm 2 /s, and data taking time of the order of a year. Experiment with MPS will operate at higher luminosity (here we included only polarized 3 He in calculation of the luminosity). So, in a one month experiment, the accumulated statistics will be 30,000 times larger than obtained in the pioneering HERMES experiment. Neutron transversity There is a large difference between asymmetries for positive and negative pions in the case of the Sivers effect. An experiment with the new spectrometer will have a luminosity of the level of cm 2 /s. With the large acceptance of MPS, reactions like SIDIS have almost 19

20 full coverage in P in one setting. BigBite will be used as an electron arm with solid angle of 50 msr. Such enormous jump of the Figure-of-Merit for polarized neutron is possible because of the parameters of the 3 He target, large usable luminosity, and large acceptance of the MPS spectrometer. In addition to much more accurate determination of the Collins and Sivers functions, it will be possible to study its x, z, and Q 2 -dependences at momentum transfer up to about 10 (GeV/c) 2. Proton transversity Perspective of the experiment with proton transversely polarized to the electron scattering plan require construction of a new superconducting magnet. Such magnet will have two important advantage compare to the existing UVA polarized target magnet. First, the magnet will have a cryostat with vertical field. Second, the aperture of the magnet will allow the raster size of the beam to be increased up to 5 cm x 5 cm, and as a result a 4-fold increase of the usable beam current. New magnet will also allow a longer target, so the luminosity will be at least five times larger than that of the existing target. With an electron-nucleon luminosity of cm 2 /s a large physics program could be accomplished. 7 Conclusion The examples above present just a small part of the exiting program we envision. It includes many elements of the JLab physics CDR [28] and similar to the program which was discussed for the MAD spectrometer [29]. MAD project was rejected because of its high cost of $30M (mainly magnet related). The MPS spectrometer has parameters (solid angle/central angle, momentum range) much more attractive than were projected for the MAD, specially for the scattering angle below 20, and the projected cost is lower by a factor ten. The momentum resolution, the only parameter which is lower for the MPS, still is about 1% at 10 GeV/c particle momentum. It is sufficient for almost every experiment in the program. All presented allow to conclude that the MPS spectrometer will be a tool with large discovery potential in hadronic physics. 20

21 References [1] Conceptual Design Report (CDR) for The Science and Experimental Equipment for The 12 GeV Upgrade of CEBAF, dept/physics division/gev. [2] L. Pentchev, et al., Large Acceptance Proton Form Factor Ratio Measurements at 13 and 15 (GeV/c) 2 Using Recoil Polarization Method, JLab experiment E [3] D. Crabb and B. Wojtsekhowski, private communication, [4] G. Cates, private communication, [5] B. Wojtsekhowski, Prospect for measuring G N E at high momentum transfer, proceedings of workshop Exclusive Processes at High Momentum Transfer, eds. A.Radyushkin and P.Stoler, Jlab, 2002, p.273. [6] B. Wojtsekhowski, report on Hall A collaboration meeting, June summer/wojtsekhowski SuperBigBite.pdf [7] M. Jones, et al., Phys. Rev. Lett. 84, 1398 (2000). [8] V. Punjabi, et al., Phys. Rev. C 71, (2005), [Erratum-ibid. C 71, (2005)]. [9] O. Gayou et al., Phys. Rev. Lett. 88, (2002). [10] C.F. Perdrisat, V. Punjabi, M. Vanderhaeghen, Prog.Part.Nucl.Phys.59: ,2007. [11] C.F. Perdrisat, V. Punjabi, M.K. Jones, and E. Brash, JLab PAC20 proposal (2001); JLab PAC26 update (2006). [12] K. Ackerstaff, et al., Nucl. Instr. and Meth. A 417, 230 (1998). [13] D. J. J. de Lange, et al., Nucl. Instr. and Meth. A 406, 182 (1998). [14] F. Sauli, Nucl. Instr. Meth. A386 (1997)

22 [15] B. Wojtsekhowski, report on Hall A collaboration meeting, June [16] G. Cates, et al., [GEN collaboration], Hall A annual report 2006, p.69; [17] C. Munoz Camacho, et al., Phys. Rev. Lett. 97, (2006). [18] Ch. Hyde, et al., Measurements of the Electron-Helicity Dependent Cross Section of Deeply Virtual Compton Scattering with CEBAF at 12 GeV, JLab PAC30 Proposal. [19] B. Wojtsekhowski, et al., Measurement of neutron asymmetry A1n in the valence quark region using 8.8 GeV and 6.6 GeV beam energies and Bigbite spectrometer in Hall A. Jefferson Lab PAC30 Proposal. [20] B. Sawadzky, et al., A Path to Color Polarizabilities in the Neutron: A Precision Measurement of the Neutron g2 and d2 at High Q2 in Hall C. Jefferson Lab PAC30 Proposal. [21] M. Petratos, et al., Measurement of the F2 n /F2 p, d/u Ratios and A=3 EMC Effect in Deep Inelastic Electron Scattering off the Tritium and Helium Mirror Nuclei. Jefferson Lab PAC30 Proposal. [22] A. Airapetian, et al., Phys. Rev. Lett. 94, (2005); Phys. Rev., D71, (2005). [23] B. Moffit, et al., Prescision Measurement of the Proton Elastic Cross Section at High Q 2. Jefferson Lab PAC30 Proposal. [24] B. Quinn, et al., Precision Measurement of the Neutron Magnetic Form Factor up to Q 2 =8.0 (GeV/c) 2 by the Ratio Method. Jefferson Lab PAC33 Proposal. [25] D. Hamilton, et al., Phys. Rev. Lett. 94, (2005); A. Danagoulian, et al, Phys. Rev. Lett. 98, (2007). [26] K. Wijesooriya, et al., Phys. Rev. Lett. 86, 2975 (2001). [27] K. Garrow, et al., Phys. Rev. C66, (2002). 22

23 [28] dept/physics division/pcdr public/pcdr final/pcdr final [29] Hall A collaboration, 23