R.D. McKeown
This latest in a series of workshops on parity-violating electron scattering comes at a momentuous time in the history of this subject. The first experiments to determine strange form factors of the nucleon have produced intriguing final results, and several powerful new experiments are now producing data. In addition, the precision of the technique has been improving and new experiments testing the electroweak theory have reported remarkably precise data. There has also been a great deal of progress on both the theory of strange form factors and interpretation of electroweak symmetry tests
R.D. McKeown and P. Vogel
The recent progress in establishing the existence of finite neutrino masses and mixing between generations of neutrinos has been remarkable, if not astounding. The combined results from studies of atmospheric neutrinos, solar neutrinos, and reactor antineutrinos paint an intriguing picture for theorists and provide clear motivation for future experimental studies. In this review, we summarize the status of experimental and theoretical work in this field and explore the future opportunities that emerge in light of recent discoveries
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D.T. Spayde et al.
We report a new determination of the strange quark contribution to the proton's magentic form factor at a four-momentum transfer $Q^2=0.1$(GeV/c)$^2$ from parity-violating $e-p$ elastic scattering. The result uses a revised analysis of data from the SAMPLE experiment which was carried out at the MIT-Bates Laboratory. The data was combined with a calculation of the proton's axial form factor $G^e_A$ to determine the strange form factor $G^s_M(Q^2=0.1)=0.37\pm 0.20\pm 0.26\pm 0.07$. The extrapolation of $G^s_M$ to its $Q^2=0$ limit and comparison with calculations is also discussed
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M. Amarian et al.
We have measured the spin structure functions $g_1$ and $g_2$ of $^3$He in a double-spin experiment by inclusively scattering polarized electrons at energies ranging from 0.862 to 5.058 GeV off a polarized $^3$He target at a 15.5$^\circ$ scattering angle. Excitation energies covered the resonance and the onset of the deep inelastic regions. We have determined for the first time the $Q^2$ evolution of $\Gamma_1(Q^2)=\int^1_0 g_1(x,Q^2)dx, \Gamma_2(Q^2)=\int^1_0g_2(x,Q^2)dx$ and $d_2(Q^2)=\int^1_0x^2[2g_1(x,Q^2)+3g_2(x,Q^2)dx$ for the neutron in the range 0.1 GeV$^2\leq Q^2\leq 0.9$ GeV$^2$ with good precision. $\Gamma_1(Q^2)$ displays a smooth variation from high to low $Q^2$. The Burkhardt-Cottingham sum rule holds within uncertainities and $d_2$ is non-zero over the measured range
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T.M. Ito et al.
We report ono a new measurement of the parity-violating asymmetry in quasielastic electron scattering from the deuteron at backward angles $Q^2=0.038$ (GeV/c)$^2$. This quantity provides a determination of the neutral weak axial vector form factor of the nucleon, which can potentially receive large electroweak corrections. The measured asymmetry $A=-3.51\pm 0.57$ (stat) $\pm$0.58 (sys) ppm is consistent with theoretical predictions. We also report on updated results of the previous experiment at $Q^2=0.091$ (GeV/c)$^2$, which are also consistent with theoretical predictions
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J. Martin, J. Yuan, S.A. Hoedl, B.W. Filippone, D. Fong, T.M. Ito, E. Lin, B. Tipton and A.R. Young
We report on the first detailed measurements of electron backscattering from low $Z$ targets at energies up to 124 keV. Both energy and angular distributions of the backscattered electrons are measured and compared with electron transport simulations based on the Geant4 and Penelope Monte Carlo simulation codes. Comparisons are also made with previous, less extensive, measurements and with measurements at lower energies
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R.D. McKeown, J. Gao, M.B. Larson, A. Shoup, and G.B. Yodh
The California HIgh school Cosmic ray ObServatory (CHICOS) is a large area (presently 400 square kilometers) ground array for the study of ultra high energy cosmic rays located in the Los Angeles area. Each CHICOS station employs two 1 m$^2$ scintillation counters from the decommissioned CYGNUS array [1] instrumented with 3'' or 5'' photomuiltiplier tubes from the decommissioned Palo Verde neutrino experiment [2]. We have developed a PC-based data acquistion system for these remote stations. Data are processed and transferred automatically over the internet once per day. At present there are 43 sites operating reliably
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R.D. McKeown, J. Gao, M.B. Larson, C. Zheng, R. Seki, A. Shoup, G.B. Yodh, C. Jillings, K. Ganezer, J. Hill, W.E. Kieg, and J. Sepikas
The California HIgh school Cosmic ray ObServatory (CHICOS) is a large area ($\sim$400 km$^2$) ground array for the study of ultra-high energy cosmic rays in the Los Angeles area. The main scientific goals of CHICOS is to study the flux, energy spectrum, and angular direction of cosmic rays at energies $E>10^{19}$ eV and to demonstrate a new strategy for fielding huge future arrays using urban infrastructure. At present there are 43 CHICOS sites operating; a total of 90 sites will be deployed and operational within the next year, resulting in an aperature of about 500 km$^2$-sr at 10$^{20}$ eV
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T.M. Ito
The previous two SAMPLE experiments yielded a measurement of the axial $e-N$ form factor $G^e_A$ substantially different from the theoretical estimate. In order to confirm this obseration, a third SAMPLE experiment was carried out at a lower beam energy of 125 MeV ($Q^2=$ 0.038 (GeV/c)$^2$ on a deuterium target. The data analysis is now at the final stage and the results are consistent with the theoretical prediction of the axial form factor $G^e_A$. Also, reevaluation of the background dilution factor and the electromagnetic radiative correction for the 200 MeV deuterium data lead to updated results, which are also consistent with the theoretical prediction
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Z. Djurcic, D. Glasgow, L.-W. Hu, R.D. McKeown, A. Piepke, R. Swinney, and B. Tipton
A technique based on neutron activation has been developed for an extremely high sensitivity analysis of trace elements in organic materials. Organic materials are sealed in plastic or high purity quartz and irradiated at the HFIR and MITR. The most volatile materials such as liquid scintillator (LS) are first preconcentrated by clean vacuum evaporation. Activities of interest are separated from side activities by acid digestion and ion exchange. The technique has been applied to study the liquid scintillator used in the KamLAND neutrino experiment. Detection limits of $<2.4\times 10^{-15}$ g $^{40}$K/g LS, $<5.5\times 10^{-15}$ g Th/g LS, and $<8\times 10^{-15}$ g U/g LS have been achieved
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R.D. McKeown
An extensive program of parity-violating electron scattering experiments is providing new insight into the structure of the nucleon. Measurement of the vector form factors enables a definitive study of potential stange quark-antiquark contributions to the nucleon's electromagnetic structure, including the magnetic moment and charge distribution. Recent experimental results have already indicated that effects of strangeness are much smaller than theoretically expected. In addition, the neutral axial form factor appears to display substantial corrections as one might expect from an anapole effect
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J.W. Martin
I address the experimental feasibility of two measurements related to the photoproduction of pions, in the context of the $G^0$ experiment. The first involves an extraction of the parity-violating pion-nucleon coupling constant $h^{(1)}_{\pi NN}$ via a measurement of parity-violating threshold pion photoproduction. The second involves an extraction of $d_\Delta$, which parameterizes parity-violating photoproduction of pions on the $\Delta$-resonance. The second process might have an anomalously large symmetry, from a model based on hyperon decays
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J.W. Martin
I address the experimental feasibility of two measurements related to the photoproduction of pions, in th econtext of the $G^0$ experiment. The first involves an extraction of the parity-violating pion-nucleon coupling constant $h^{(1)}_{\pi NN}$ via a measurement of parity-violating threshold pion photoproduction. The second involves an extraction of $d_\Delta$, which parametrizes parity-violating photoproduction of pions on the $\Delta$-resonance. The second process might have an anomalously large asymmetry, from a model based on hyperon decays
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J.W. Martin
The $G^0$ experiment at Jefferson Lab will extract the strange-quark electric and magnetic form factors over a $Q^2$ range of 0.1-1.0 (GeV/c)$^2$ using the technique of parity-violating elastic scattering. To make this extraction, the experiment must measure the axial form factor of the nucleon, by performing backward-angle measurements of parity-violating quasi-elastic scattering from a deuterium target. The negative pion background experienced by the experiment for these kinematics will be large, and must be rejected in order to access the quasi-elastic signal. A Cerenkov counter will be constructed for the experiment to achieve this task. We report on progress in designing, simulating, and prototyping this detector. We also report on progress towards funding and constructing these detectors
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R.D. McKeown, J. Gao, M.B. Larson, R. Seki, A. Shoup, and G.B. Yodh
The California HIgh school Cosmic ray ObServatory (CHICOS) is a collaborative project involved Caltech, Cal State Northridge, UC Irvine, and local high schools to site a large array of particle detectors in Southern California. The detectors are located on school rooftops, and utilize the power and network infrastructure available at the schools. The main scientific goal is to study cosmic rays at ultra-high energies E>10^{19} eV. We have fielded a total of 23 sites so far, and are beginning to collect data as we continue to deploy additional sites. We have observed our first evidence of extended air showers in coincidence with a local high school. The anticipated performance of the initial array and the potential for future expansion will be discussed
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R.D. McKeown
The SAMPLE experiment at MIT-Bates provides measurements of parity-violating electron scattering at backward angles and low momentum transfer. These measurements yield unique information on the contribution of strange quarks to the magnetic moment of the proton and also electroweak corrections such as the anapole moment. Recent results, some possible interpretations, and outstanding issues for the future are discussed
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R.D. McKeown and M.J. Ramsey-Musolf
A remarkably successful program of parity-violating electron scattering experiments is providing new insight into the structure of the nucleon. Measurement of the vector form factors enables a definitive study of potential strange quark-antiquark contributions to the electromagnetic structure such as the magnetic moment and charge distribution. Recent experimental results have already indicated that effects of strangeness are much smaller than theoretically expected. In addition, the neutral axial form factor appears to display substantial corrections as one might expect from an anapole effect.
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J.G. Weisend et al.
E158 is a fixed target experiment at SLAC in which hihg energy (up to 48 GeV) polarized electrons are scattered off the unpolarized electrons in a 1.5 m long liquid hydrogen target. The total volume of liquid hydrogen in the system is 55 1. The beam can deposit as much as 700 W into the liquid hydrogen. Among the requirements for the system are: that density fluctuations in the liquid hydrogen be kept to a minimum, that the target can be oved out of the beam line while cold and replaced to within 2 mm and that the target survive lifetime radiation doses of up to $1\times 10^6$ GY. The cryogenic system for the experiment consists of the target itself, the cryostat containing the target, a refurbished CTI 4000 refrigerator providing more than 1 kW of cooling at 20 K and associated transfer lines and valve boxes. This paper discusses the requirements, design, construction, testing and operation of the cryogenic system. The unique features of the design associated with hydrogen safety and the high radiation field in which the target resides are also covered
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D.H. Beck and R.D. McKeown
The measurement of parity violation in the helicity dependence of electron-nucleon scattering provides unique information about the basic quark structure of the nucleons. In this review, the general formalism of parity-violating electron scattering is presented, with emphasis on elastic electron-nucleon scattering. The physics issues addressed by such experiments is discussed, and the major goals of the presently envisioned experimental program are identified. %General aspects of the experimental technique are reviewed and A summary of results from a recent series of experiments is presented and the future prospects of this program are also discussed
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J. Yuan, B.W. Filippone, D. Fong, T.M. Ito, J.W. Martin, J. Penoyar, and B. Tipton
An iron-free, low-energy charged-particle magnetic spectrometer is designed using a Helmholtz coil geometry. Through the fringe fields of the coils, the spectrometer provides a focusing in both the dispersive and non-dispersive planes. By choosing the optimal deflecting angle and the positions of the source and the focal distance, we expect to obtain a momentum resolution on the order of 0.3\%.
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D. T. Spayde, T. Averett, D. Barkhuff, D. H. Beck, E. J. Beise, C. Benson, H. Breuer, R. Carr, S. Covrig, J. DelCorso, G. Dodson, K. Dow, C. Eppstein, M. Farkhondeh, B. W. Filippone, P.Frazier, R. Hasty, T. M. Ito, C. E. Jones, W. Korsch, S. Kowalski, P. Lee, E. Maneva, K. McCarty, R. D. McKeown, J. Mikell, B. Mueller, P. Naik, M. Pitt, J. Ritter, V. Savu, M. Sullivan, R. Tieulent, E. Tsentalovich, S. P. Wells, B. Yang, and T. Zwart
We report a new measurement of the parity-violating asymmetry in elastic electron scattering from the proton at backward scattering angles. This asymmetry is sensitive to the strange magnetic form factor of the proton as well as electroweak axial radiative corrections. The new measurement of $A=-4.92 \pm 0.61 \pm 0.73$ ppm provides a significant constraint on these quantities. The implications for the strange magnetic form factor are discussed in the context of theoretical estimates for the axial corrections
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R.D. McKeown
The static properties of the nucleon must ultimately arise from the quark and gluon constituents and the properties of Quantum Chromodynamics. The quark spin contribution to the spin of the nucleon is experimentally rather small, and there is some evidence that strange quarks are partly responsible. In addition, new efforts to address the role of gluons are in progress. The magnetic moment of the nucleon may contain contributions from strange quark-antiquark pairs, and this aspect of nucleon structure can be studied via parity-violating electron scattering. The present status of these experimental efforts and their impact on our knowledge of nucleon structure is discussed
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T. Averett, C.E. Jones, R.D. McKeown, and M. Pitt
A piezo-electrically controlled optical correction system was successfully used to reduce the helicity-correlated pulse-to-pulse position differences of a laser spot to better than $\pm 100$ nm at a pulse rate of 600 Hz. Using a simple feedback algorithm, average position differences of $\overline{\Delta x}=-3.5 \pm 4.2$ nm and $\overline{\Delta y}=2.6\pm 6.6$ nm were obtained over a six hour period. This optical correction system was successfully used in the polarized electron source at the Bates Linear Accelerator Center to stabilize the position of the electron beam during the recent SAMPLE experiment. Because this experiment measures a parity violating signal at the $10^{-6}$ level, it is sensitive to systematic effects which are correlated with the helicity of the incident electrons. One potentially large systematic effect is the helicity-correlated motion of the incident electron beam. By using this optical correction system, electron beam position differences at the location of the experiment were routinely kept well below $\pm 100$ nm, with averages over the entire two month run of $\overline{\Delta x}=6.4 \pm 2.3$ nm and $\overline{\Delta y}=-3.5\pm 2.0$ nm.
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J. Arrington et al.
Inclusive electron scattering is measured with 4.045 GeV incident beam energy from C, Fe and Au targets. The measured energy transfers and angles correspond to a kinematic range for Bjorken $x > 1$ and momentum transfers from $Q^2 = 1 - 7$ (GeV/c)$^2$. When analyzed in terms of the $y$-scaling function the data show for the first time an approach to scaling for values of the initial nucleon momenta significantly greater than the nuclear matter Fermi-momentum (i.e. $> 0.3$ GeV/c).
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R.D. McKeown
The measurement of parity-violating observables provides unique information about the neutral weak interaction of electrons. Such experiments continue to test the limits of validity of the fundamental electroweak theory and are beginning to yield important new information about the basic quark structure of the nucleons. In this review, the general formalism of parity-violating electron scattering is presented, with emphasis on elastic electron-nucleon scattering. The physics issues addressed by such experiments is discussed, and the major goals of the presently envisioned experimental program are identified. A detailed account of recent results from the SAMPLE experiment on the neutral weak magnetic form factor of the proton is presented. Finally, the future activity in this field is briefly summarized
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R.D. McKeown
The neutral weak form factors of the nucleon provide crucial new information on the internal structure of the nucleon. In particular, experimental study of these quantities will enable a determination of the strange quark-antiquark contributions to static properties of the nucleon. The measurement of parity violation in elastic electron-nucleon scattering can be used to study these form factors. We have recently obtained the first results on the neutral weak magnetic form factor using this method in the SAMPLE experiment at the Bates Linear Accelerator Center. The status of this experiment and future experiments at other laboratories is discussed.}
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R.D. McKeown
In 1933, Frisch and Stern \cite{stern} performed the first measurement of the magnetic moment of the proton and obtained the earliest experimental evidence for the internal structure of the nucleon. At that time theorists were firmly convinced \cite{weisskopf} that the answer would be one nuclear magneton ($e \hbar / 2 M_p c$) as one would expect for a ``point'' spin 1/2 particle obeying the Dirac equation. In fact, Frisch and Stern's first experimental result was, surprisingly, ``between 2 and 3 nuclear magnetons'' \cite{stern}. This startling experimental discovery was cited when Stern was awarded the Nobel prize in physics in 1943. However, it wasn't until the early 1970's that the quark structure of the nucleon was directly observed in deep inelastic electron scattering experiments\cite{friedman}. The development of Quantum Chromodynamics (QCD) followed soon thereafter, and is now the accepted theory of the strong interactions governing the behavior of quarks and gluons associated with hadronic structure. Nevertheless, a quantitative description of nucleon stucture based on QCD remains an elusive goal. For example, a satisfactory quantitative understanding of the magnetic moment of the proton has still not been achieved, now more than 60 years after the first measurement was performed. Thus the internal structure of the nucleon is still a subject of great interest to experimentalists as well as theorists. One aspect of nucleon structure that is receiving substantial attention at present is the role of strange quark-antiquark pairs. Traditional constituent quark models treat the nucleon using only up and down quarks. But it is important to remember that, in this approximation, only the degrees of freedom associated with valence quark quantum numbers are active; the effects of sea quarks are generally considered to be ``frozen'' as inert aspects of the effective degrees of freedom. The constituent quarks actually do contain internal structure associated with gluons and sea quarks (such as $\bar s s$), so even in these simple models of the nucleon the contribution of $\bar s s$ pairs is potentially significant and therefore interesting. We will see that, just as in the case of the proton magnetic moment in 1933, the initial theoretical prejudice (that $\bar s s$ can be neglected) is not well justified and probably incorrect. The phenomenal quantitative success of the standard electroweak theory in the last decade provides a basis for the use of the weak interaction as a new precision probe of nucleon structure. For example, the neutral weak magnetism (i.e., the magnetic interaction with the $Z^0$) of the proton is a quantity that is just as important and just as fundamental as the usual magnetic moment. The value of this observable is a crucial piece of information regarding the magnetic structure of the nucleon. Indeed, the magnetic properties of the nucleon still provide important clues to the internal structure of the hadronic matter comprising our everyday world. The electroweak probes are particularly well-suited to studying the quark-antiquark structure of the nucleon. The photon and $Z^0$ do not couple to gluons, so these interactions directly probe the quark structure in a well-determined fashion. Kaplan and Manohar \cite{kaplan} have proposed that the study of neutral weak matrix elements (such as the neutral weak magnetic moment) can be used to determine the strange quark-antiquark ($\bar s s$) matrix elements. Furthermore, as discussed by Beck \cite{beck89}, one can perform a complete decomposition of these observables into contributions from the three relevant quark flavors (up, down, and strange). In this chapter we will explore the present and projected future status of investigations into strange quark-antiquark effects in nucleon structure. Particular emphasis is placed on the measurement of neutral weak matrix elements in parity-violating electron scattering \cite{bmck89,beck89} which appears especially promising for providing precise and definitive new information.
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R.D. McKeown
The neutral weak form factors of the nucleon provide crucial new information on the internal structure of the nucleon, such as a determination of the strange quark-antiquark contributions. The measurement of parity violation in elastic electron-nucleon scattering can be used to study these form factors. We have recently obtained the first results on the neutral weak magnetic form factor using this method in the SAMPLE experiment at the Bates Linear Accelerator Center. The status of this experiment and future experiments at other laboratories is discussed
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R.D. McKeown
The neutral weak magnetic form factor of the nucleon can be studied in parity-violating electron-nucleon scattering. The measurement of this form factor enables determination of the contribution of strange quark-antiquark to the proton's magnetic moment. We have recently obtained the first results on the neutral weak magnetic form factor using this method in the SAMPLE experiment at MIT/Bates.
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K. Ackerstaff et al. (The HERMES Collaboration)
Results are reported from the HERMES experiment at HERA on a
measurement of the neutron spin structure function
$g_1^n(x,Q^2)$ in deep inelastic scattering
using 27.5~GeV longitudinally polarized positrons incident on
a polarized $^3$He internal gas target. The data cover the kinematic range
$0.023
B. Mueller, D. Beck, E. Beise, E. Candell, L. Cardman, R. Carr, R. DiBari, G. Dodson, K. Dow, F. Duncan, M. Farkhondeh, B. Filippone, T. Forest, H. Gao, W. Korsch, S. Kowalski, A. Lung, R. McKeown, R. Mohring, J. Napolitano, D. Nilsson, M. Pitt, N. Simicevic, B. Terburg, and S. Wells
We report the first measurement of the parity-violating asymmetry in elastic
electron scattering from the proton. The asymmetry depends on
the neutral weak magnetic form factor of the proton which contains
new information on the contribution of strange quark-antiquark pairs
to the magnetic moment of the proton. We obtain the value
$G_M^Z= 0.34 \pm 0.09 \pm 0.04 \pm 0.05$ n.m. at $Q^2=0.1$ (GeV/c)${}^2$.
J. Arrington, D.H. Beck, E.J. Beise, E. Candell, R. Carr, G.W. Dodson, K. Dow, F. Duncan, M. Farkhondeh, B.W. Filippone, T. Forest, H. Gao, W. Korsch, S. Kowalski, A. Lung, R.D. McKeown, R. Mohring, B.A. Mueller, J. Napolitano, M.L. Pitt, N. Simicevic, B. Terburg, E. Tsentalovich, S. Wells, and M. Witkowski
The SAMPLE experiment measures the parity-violating asymmetry in the
elastic scattering of 200 MeV polarized electrons from a liquid hydrogen
target. This paper describes the SAMPLE Moller beam polarimeter, and the
spin transport methods necessary to achieve longitudinally polarized beam
at the SAMPLE target
R.D. McKeown
Measurements of the neutral weak form factors of the nucleon will allow
determination of the strange quark-antiquark contributions to these
quantities. The SAMPLE
experiment provides a measurement of the neutral weak magnetic form
factor via parity violating electron-proton scattering. This experiment
is now beginning to acquire data that will constrain the strange quark
contribution to the proton's magnetic moment.
E.J. Beise, D.H. Beck, E. Candell, R. Carr, F. Duncan, T. Forest, W. Korsch, J.W. Mark, R.D. McKeown, B.A. Mueller, M. Pitt, and S. Wells
Parity-violating electron scattering measurements on hydrogen and
deuterium, such as those underway at the Bates and CEBAF
laboratories, require luminosities exceeding $10^{38}$cm$^{-2}$s$^{-1}$,
resulting in large beam power deposition into cryogenic liquid.
Such targets must be able to absorb 500 watts or more with minimal
change in target density. A 40~cm long liquid hydrogen
target, designed to absorb 500~watts of
beam power without boiling,
has been developed for the SAMPLE experiment at Bates.
In recent tests with 40~$\mu$A
of incident beam, no evidence was seen for density fluctuations in
the target,
at a sensitivity level of better than 1\%. A summary of the
target design and operational experience will be presented.
E.J. Beise, J. Arrington, D.H. Beck, E. Candell, R. Carr, G. Dodson, K. Dow, F. Duncan, M. Farkhondeh, B.W. Filippone, T. Forest, H. Gao, W. Korsch, S. Kowalski, A. Lung, R.D. McKeown, R. Mohring, B.A. Mueller, J. Napolitano, M. Pitt, N. Simicevic, E. Tsentalovich, and S. Wells
Recently, there has been considerable theoretical interest in
determining strange quark contributions to hadronic matrix elements.
Such matrix elements can be accessed through the nucleon's neutral
weak form factors as determined in parity violating electron scattering.
The SAMPLE experiment will measure the stange magentic form factor
$G^s_M$ at low momentum transfer. By combining measurements from
hydrogen and deuterium the theoretical uncertainties in the measurement
can be greatly reduced and the result will be limited by experimental
errors only. A summary of recent progress on the SAMPLE experiment
is presented
B.W. Filippone
Color transparency is predicted to lead to the disappearance of hadronic
interactions for hadrons produced in high energy exclusive reactions.
Several experiments have searched for this phenonemon using a variety of
techniques and probes. These experiments are reviewed and on-going and
future experiments are discussed.
J. Arrington, P. Anthony, R. G. Arnold, E. J. Beise, J. E. Belz, P. E. Bosted, H.-J. Bulten, M. S. Chapman, K. P. Coulter, F. Dietrich, R. Ent, M. Epstein, B. W. Filippone, H. Gao, R. A. Gearhart, D. F. Geesaman, J.-O. Hansen, R. J. Holt, H. E. Jackson, C. E. Jones, C. E. Keppel, E. R. Kinney, S. Kuhn, K. Lee, W. Lorenzon, A. Lung, N. C. R. Makins, D. J. Margaziotis, R. D. McKeown, R. G. Milner, B. Mueller, J. Napolitano, J. Nelson, T. G. O'Neill, V. Papavassiliou, G. G. Petratos, D. H. Potterveld, S. E. Rock, M. Spengos, Z. M. Szalata, L. H. Tao, K. van Bibber, J. F. J. van den Brand, J. L. White, D. Winter, B. Zeidman
The inclusive $A(e,e')$ cross section for $x \simeq 1$ was measured on $^2$H,
C, Fe, and Au for momentum transfers $Q^2$ from 1$-$6.8 (GeV/c)$^2$. The scaling
behavior of the data was examined in the region of transition from $y$-scaling
to $x$-scaling. Throughout this transitional region, the data exhibit
$\xi$-scaling, reminiscent of the Bloom-Gilman duality seen in free nucleon
scattering.
K. I. Hahn, C. R. Brune, and R. W. Kavanagh
The absolute differential cross section for the H3
(p,\gamma) He4 reaction was measured for $0.1 <= E_p <= 6.0 MeV.
Gamma rays produced by proton bombardment of Ti--H3
targets were detected simultaneously with BGO and NaI scintillators
positioned at 90 circ with respect to the incident beam. Our
results are higher than the most recently reported (p,\gamma) data,
but in good agreement with all other previous (p,\gamma)
experiments. The present results support the He4
(\gamma,p) cross sections recommended by Calarco et. al. in
their discussions of the charge asymmetry of the nuclear force in
He4.
R. D. McKeown
Reactions involving quasielastic knockout of nucleons from nuclei at
high energies can be used to measure the transparency of the nuclear
medium and test predictions of color transparency. Experimental data
on the (p,2p) reaction exhibit an intriguing momentum-transfer dependence
that has been the subject of much speculation. The (e,e'p) reaction provides
a more direct method to study high energy nuclear transparency. We present
results from a recent SLAC experiment that provide new constraints on models
of color transparency.
T. G. O'Neill,W. Lorenzon,P. Anthony,R. G. Arnold,J. Arrington,E. J. Beise,J. E. Belz,P. E. Bosted,H.-J. Bulten,M. S. Chapman,K. P. Coulter,F. Dietrich,R. Ent,M. Epstein,B. W. Filippone,H. Gao,R. A. Gearhart,D. F. Geesaman,J.-O. Hansen,R. J. Holt,H. E. Jackson,C. E. Jones,C. E. Keppel,E. R. Kinney,S. Kuhn,K. Lee,A. Lung,N. C. R. Makins,D. J. Margaziotis,R. D. McKeown,R. G. Milner,B. Mueller,J. Napolitano,J. Nelson,V. Papavassiliou,G. G. Petratos,D. H. Potterveld,S. E. Rock,M. Spengos,Z. M. Szalata,L. H. Tao,K. van Bibber,J. F. J. van den Brand,J. L. White,B. Zeidman
The A-dependence of the quasielastic A(e,e'p) reaction has been
studied at SLAC with H2, C, Fe, and Au nuclei at momentum
transfers Q^2 = 1, 3, 5, and 6.8 (GeV/c)^2. We extract the
nuclear transparency T(A,Q^2), a measure of the average probability
that the struck proton escapes from the nucleus A without
interaction. Several calculations predict a significant increase in
T with momentum transfer, a phenomenon known as Color Transparency.
No significant rise within errors is seen for any of the nuclei
studied.
C. R. Brune, R. W. Kavanagh, and C. Rolfs
The absolute cross section of the H3 (alpha,gamma) Li7 reaction
has been measured for 50 <= E c.m. <= 1200 KeV.
Specially prepared H3 targets were
bombarded with an alpha+ beam, and gamma rays were detected
using an 85% high-purity germanium detector. Total S-factors and
the branching ratios for radiative capture to the two final bound
states are reported for the entire energy range. Angular
distributions of the capture gamma rays were measured for nine
energies in the range 115 <= E c.m. <= 1200 keV. Legendre
coefficients extracted from fits to the angular distributions are
also reported. The energy dependence of the measured S-factors is
found to be in agreement with existing theoretical calculations. The
new results are used to calculate the thermonuclear reaction rate for
temperatures below 10 GK, required for computing the Li7
abundance in primordial nucleosynthesis.
H. Gao, J. Arrington, E. J. Beise, B. Bray, R. W. Carr, B. W. Filippone, A. Lung, R. D. McKeown, B. Mueller, M. L. Pitt, C. E. Jones, D. DeSchepper, G. Dodson, K. Dow, R. Ent, M. Farkhondeh, J.-O. Hansen, W. Korsch, L. H. Kramer, K. Lee, N. Makins, R. G. Milner, D. R. Tieger, T. P. Welch, E. Candell, J. Napolitano, B. B. Wojtsekhowski, C. Tripp, W. Lorenzon
We report a measurement of the asymmetry in spin-dependent
quasielastic scattering of longitudinally polarized electrons from a
polarized He-3 target. The neutron magnetic form factor G_M^n has
been extracted from the measured asymmetry based on recent PWIA
calculations using spin-dependent spectral functions. Our
determination of G_M^n at Q^2 = 0.19 (GeV/c)^2 agrees with the dipole
parametrization, mu_n G_D, and the ratio is (G_M^n/mu_n G_D)^2 =
0.998 \pm 0.117 \pm 0.059 \pm 0.030, where the errors are
statistical, systematic, and model dependence, respectively.
This experiment represents the first measurement of the neutron
magnetic form factor using spin-dependent electron scattering.
R. D. McKeown
No abstract is available
R. D. McKeown
It has been suggested that nuclear matter would become "transparent"
to hadrons involved in exclusive reactions at high momentum transfer.
This prediction, known as "color transparency," is a consequence of
arguments based on fundamental aspects of hadronic interactions in
QCD. The quasielastic knockout of a proton in electron scattering,
(e,e'p), is a particularly clean process for the study of this
predicted effect. A recent experiment performed at SLAC and proposals
for new experiments will be discussed.
R. D. McKeown
The recent development of polarized 3-He targets for use in electron
scattering experiments has opened up a wide range of possibilities
for new experiments. A variety of fundamental issues in both nucleon
structure and the nuclear structure of 3-He will be addressed in
these experiments. Some recent preliminary measurements as well as
several new proposals will be discussed.
R. D. McKeown
The recent development of polarized 3-He targets for use in electron
scattering experiments has opened up a wide range of possibilities
for new experiments. A variety of fundamental issues in both nucleon
structure and the nuclear structure of 3-He will be addressed in
these experiments. Some recent preliminary measurements as well as
several new proposals will be discussed.
P. R. Wrean, C. R. Brune, and R. W. Kavanagh
The 9-Be(alpha,n)12-C reaction determines the rate for
neutron-catalyzed helium burning and thus plays an important role in
supernovae ejecta under alpha- and n-rich conditions which may lead
to the r-process. Cross sections for this reaction have been measured
for 0.16 leq E_{c.m.} leq 1.87 MeV using a 4 pi neutron detector, and
are used to calculate the thermonuclear reaction rates for
temperatures between 0.1 and 10 GK. During these measurements, the
thick-target yields were determined for 0.50 leq E_alpha leq 2.30
MeV, the stopping powers for alpha's in beryllium determined for 0.24
leq E_alpha leq 2.12 MeV, and the 9-Be(p,p) elastic scattering cross
sections measured at theta_{lab}=142.4 deg. for 2.34 leq E_p leq 2.66
MeV.
OAP-740 (February 1997)
Measurement of the Proton's Neutral Weak Magnetic Form Factor
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OAP-739 (February 1997)
Beam Polarimetry and Spin Transport for the SAMPLE Experiment
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OAP-738 (October 1996)
The neutral weak current of the nucleon
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OAP-737 (February 1996)
A high energy power liquid hydrogen target for parity violation experiments
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OAP-736 (February 1996)
SAMPLE: Parity violating electron scattering from hydrogen and deuterium
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OAP-735 (December 1995)
Color Transparency Experiments
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OAP-734 (March 1995)
Inclusive Electron Scattering from Nuclei at x ~= 1
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OAP-733 (August 1994)
The H-3 (p, gamma) He-4 cross section
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OAP-732 (August 1994)
Color transparency in high energy quasielastic scattering
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OAP-731 (July 1994)
A-dependence of nuclear transparency in quasielastic A(e,e'p)
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OAP-730 (June 1994)
H-3(alpha,gamma) Li-7 reaction at low energies
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OAP-729 (February 1994)
Measurement of the neutron magnetic form factor from inclusive quasielastic scattering of polarized electrons from polarized He-3
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Click here to download the associated figures (in PostScript)
OAP-728 (September 1993)
Parity violation in electron scattering
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OAP-727 (September 1993)
Color transparency and the (e,e'p) reaction
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OAP-726 (September 1993)
Electron scattering with polarized He-3 targets
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OAP-726 (September 1993)
Electron scattering with polarized He-3 targets
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OAP-725 (August 1993)
Total cross sections and thermonuclear reaction rates for Be-9(alpha,n)C-12
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