An experiment measuring electroproduction of hypernuclei has been performed in Hall A at Jefferson Lab on a \(^{12}\)C target. In order to increase counting rates and provide unambiguous kaon ...identification two superconducting septum magnets and a Ring Imaging CHerenkov detector (RICH) were added to the Hall A standard equipment. An unprecedented energy resolution of less than 700 keV FWHM has been achieved. Thus, the observed \lam{12}{B} spectrum shows for the first time identifiable strength in the core-excited region between the ground-state {\it s}-wave \(\Lambda\) peak and the 11 MeV {\it p}-wave \(\Lambda\) peak.
The Spin Asymmetries of the Nucleon Experiment (SANE) measured two double spin asymmetries using a polarized proton target and polarized electron beam at two beam energies, 4.7 GeV and 5.9 GeV. A ...large-acceptance open-configuration detector package identified scattered electrons at 40\(^{\circ}\) and covered a wide range in Bjorken \(x\) (\(0.3 < x < 0.8\)). Proportional to an average color Lorentz force, the twist-3 matrix element, \(\tilde{d}_2^p\), was extracted from the measured asymmetries at \(Q^2\) values ranging from 2.0 to 6.0 GeV\(^2\). The data display the opposite sign compared to most quark models, including the lattice QCD result, and an apparently unexpected scale dependence. Furthermore when combined with the neutron data in the same \(Q^2\) range the results suggest a flavor independent average color Lorentz force.
Phys. Rev. C 101, 035206 (2020) The ratio of the electric and magnetic form factor of the proton, $\mu_p
G_E^p/G_M^p$, has been measured for elastic electron-proton scattering with
polarized beam and ...target up to four-momentum transfer squared, $Q^2=5.66$
(GeV/c)$^2$ using the double spin asymmetry for target spin orientation aligned
nearly perpendicular to the beam momentum direction.
This measurement of $\mu_p G_E^p/G_M^p$ agrees with the $Q^2$ dependence of
previous recoil polarization data and reconfirms the discrepancy at high $Q^2$
between the Rosenbluth and the polarization-transfer method with a different
measurement technique and systematic uncertainties uncorrelated to those of the
recoil-polarization measurements. The form factor ratio at $Q^2$=2.06
(GeV/c)$^2$ has been measured as $\mu_p G_E^p/G_M^p = 0.720 \pm 0.176_{stat}
\pm 0.039_{sys}$, which is in agreement with an earlier measurement with the
polarized target technique at similar kinematics. The form factor ratio at
$Q^2$=5.66 (GeV/c)$^2$ has been determined as $\mu_p
G_E^p/G_M^p=0.244\pm0.353_{stat}\pm0.013_{sys}$, which represents the highest
$Q^2$ reach with the double spin asymmetry with polarized target to date.
Phys.Rev.C75:055208,2007 A high-resolution (sigma_instr. = 1.5 MeV) search for narrow states (Gamma <
10 MeV) with masses of M_x approx 1500-1850 MeV in ep -> e'K^+ X, e'K^- X and
e' pi^+ X ...electroproduction at small angles and low Q^2 was performed. These
states would be candidate partner states of the reported Theta^+(1540)
pentaquark. No statistically significant signal was observed in any of the
channels at 90% C.L. Upper limits on forward production were determined to be
between 0.7% and 4.2% of the Lambda(1520) production cross section, depending
on the channel and the assumed mass and width of the state.
We present an updated extraction of the proton electromagnetic form factor ratio, mu_p G_E/G_M, at low Q^2. The form factors are sensitive to the spatial distribution of the proton, and precise ...measurements can be used to constrain models of the proton. An improved selection of the elastic events and reduced background contributions yielded a small systematic reduction in the ratio mu_p G_E/G_M compared to the original analysis.
This paper described a digital data handler for storing information in a magnetic core memory during the pulse of a synchrotron and transferring it to a slow memory during the dead time. Digital ...measurements of trajectory, pulse height, time of flight, run number, etc., are typical data. The magnetic core memory provides capacity for storing 32 words (events) of 96 bits during a burst. The information contained in the core memory is then transferred to one inch magnetic tape during the dead time of the accelerator. Thence the information may be fed to a computer for future study. For economy, the data handler has one buffer which serves as the input, output and shift register.
The difference in proton radii measured with \(\mu p\) atoms and with \(ep\) atoms and scattering remains an unexplained puzzle. The PSI MUSE proposal is to measure \(\mu p\) and \(e p\) scattering ...in the same experiment at the same time. The experiment will determine cross sections, two-photon effects, form factors, and radii independently for the two reactions, and will allow \(\mu p\) and \(ep\) results to be compared with reduced systematic uncertainties. These data should provide the best test of lepton universality in a scattering experiment to date, about an order of magnitude improvement over previous tests. Measuring scattering with both particle polarities will allow a test of two-photon exchange at the sub-percent level, about a factor of four improvement on uncertainties and over an order of magnitude more data points than previous low momentum transfer determinations, and similar to the current generation of higher momentum transfer electron experiments. The experiment has the potential to demonstrate whether the \(\mu p\) and \(ep\) interactions are consistent or different, and whether any difference results from novel physics or two-photon exchange. The uncertainties are such that if the discrepancy is real it should be confirmed with \(\approx\)5\(\sigma\) significance, similar to that already established between the regular and muonic hydrogen Lamb shift.
The strong interaction is not well understood at low energy, or for interactions with low momentum transfer \(Q^2\), but one of the clearest insights we have comes from Chiral Perturbation Theory ...(\(\chi\)PT). This effective treatment gives testable predictions for the nucleonic generalized polarizabilities -- fundamental quantities describing the nucleon's response to an external field. We have measured the proton's generalized spin polarizabilities in the region where \(\chi\)PT is expected to be valid. Our results include the first ever data for the transverse-longitudinal spin polarizability \(\delta_{LT}\), and also extend the coverage of the polarizability \(\bar{d_2}\) to very low \(Q^2\) for the first time. These results were extracted from moments of the structure function \(g_2\), a quantity which characterizes the internal spin structure of the proton. Our experiment ran at Jefferson Lab using a polarized electron beam and a polarized solid ammonia (NH\(_3\)) target. The \(\delta_{LT}\) polarizability has remained a challenging quantity for \(\chi\)PT to reproduce, despite its reduced sensitivity to higher resonance contributions; recent competing calculations still disagree with each other and also diverge from the measured neutron data at very low \(Q^2\). Our proton results provide discriminating power between existing calculations, and will help provide a better understanding of this strong QCD regime.
Nucl.Instrum.Meth. A414 (1998) 446-458 Compton backscattering polarimetry provides a fast and accurate method to
measure the polarization of an electron beam in a storage ring. Since the
method is ...non-destructive, the polarization of the electron beam can be
monitored during internal target experiments. For this reason, a Compton
polarimeter has been constructed at NIKHEF to measure the polarization of the
longitudinally polarized electrons which can be stored in the AmPS ring. The
design and results of the polarimeter, the first Compton polarimeter to measure
the polarization of a stored longitudinally polarized electron beam directly,
are presented in this paper.
