C. Yan's research while affiliated with Thomas Jefferson National Accelerator Facility and other places

Publications (83)

Article
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Structure functions, as measured in lepton-nucleon scattering, have proven to be very useful in studying the quark dynamics within the nucleon. However, it is experimentally difficult to separately determine the longitudinal and transverse structure functions, and consequently there are substantially less data available for the longitudinal structu...
Article
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Background: Measurements of forward exclusive meson production at different squared four-momenta of the exchanged virtual photon, ${Q}^{2}$, and at different four-momentum transfer, $t$, can be used to probe QCD's transition from meson-nucleon degrees of freedom at long distances to quark-gluon degrees of freedom at short scales. Ratios of separate...
Article
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Since the pioneering experiment E89-009 studying hypernuclear spectroscopy using the (e,e′K+) reaction was completed, two additional experiments, E01-011 and E05-115, were performed at Jefferson Lab. These later experiments used a modified experimental design, the “tilt method,” to dramatically suppress the large electromagnetic background, and all...
Article
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Since the pioneering experiment, E89-009 studying hypernuclear spectroscopy using the $(e,e^{\prime}K^+)$ reaction was completed, two additional experiments, E01-011 and E05-115, were performed at Jefferson Lab. These later experiments used a modified experimental design, the "Tilt Method", to dramatically suppress the large electromagnetic backgro...
Article
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Background: Measurements of forward exclusive meson production at different squared four-momenta of the exchanged virtual photon, Q[superscript 2], and at different four-momentum transfer, t, can be used to probe QCD's transition from meson-nucleon degrees of freedom at long distances to quark-gluon degrees of freedom at short scales. Ratios of sep...
Article
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The study of exclusive $\pi^{\pm}$ electroproduction on the nucleon, including separation of the various structure functions, is of interest for a number of reasons. The ratio $R_L=\sigma_L^{\pi^-}/\sigma_L^{\pi^+}$ is sensitive to isoscalar contamination to the dominant isovector pion exchange amplitude, which is the basis for the determination of...
Article
Through the study of light hypernuclei, we can learn about hyperon nucleon interaction. The hypernuclear spectroscopy with electron beams is one of most powerful methods to study detailed structure of light hypernuclei thanks to its high energy resolution. With a decade of efforts at Jefferson Lab, the spectroscopy of Λ hypernuclei with an electron...
Article
An experiment with a newly developed high-resolution kaon spectrometer and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab. The ground state of a neutron-rich hypernucleus, _{Λ}^{7}He, was observed for the first time with the (e, e^{'}K^{+}) reaction with an energy resolution of ∼0.6 MeV. This r...
Article
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An experiment with a newly developed high-resolution kaon spectrometer (HKS) and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab (JLab). The ground state of a neutron-rich hypernucleus, He 7 Lambda, was observed for the first time with the (e,e'K+) reaction with an energy resolution of ~0.6 MeV....
Article
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The binding energy of 7ΛHe has been obtained for the first time with reaction spectroscopy using the (e, e'K+) reaction at Jefferson Lab's Hall C. A comparison among the binding energies of the A = 7 T = l iso-triplet hypernuclei, 7ΛHe, 7ΛLi*and 7ΛBe, is made and possible charge symmetry breaking (CSB) in the ΛN potential is discussed. For 7ΛHe and...
Article
In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part per million in the scattering of a polarized electron beam are determined using a d...
Article
The first measurement of proton, pion, and kaon associated fission of Bi nuclei has been performed in a photon energy range 1. 45 < E γ < 1. 55 GeV. The fission probabilities are compared with an inclusive fission probabilities obtained with photons, protons and pions. The fission probability of Bi nuclei in coincidence with kaons is 0. 18 ± 0. 06...
Article
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We have extracted QCD matrix elements from our data on doubly polarized inelastic scattering of electrons on nuclei. We find the higher twist matrix element (d) over tilde (2), which arises strictly from quark-gluon interactions, to be unambiguously nonzero. The data also reveal an isospin dependence of higher twist effects if we assume that the Bu...
Article
The first measurement of proton, pion, and kaon associated fission of Bi nuclei has been performed in a photon energy range 1. 45 < E γ < 1. 55 GeV. The fission probabilities are compared with an inclusive fission probabilities obtained with photons, protons and pions. The fission probability of Bi nuclei in coincidence with kaons is 0. 18 ± 0. 06...
Article
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Cross sections for the reaction 1H(e,e'π+)n were measured in Hall C at Thomas Jefferson National Accelerator Facility (JLab) using the high-intensity Continuous Electron Beam Accelerator Facility (CEBAF) to determine the charged pion form factor. Data were taken for central four-momentum transfers ranging from Q2=0.60 to 2.45 GeV2 at an invariant m...
Article
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The charged pion form factor, Fπ(Q2), is an important quantity that can be used to advance our knowledge of hadronic structure. However, the extraction of Fπ from data requires a model of the 1H(e,e'π+)n reaction and thus is inherently model dependent. Therefore, a detailed description of the extraction of the charged pion form factor from electrop...
Article
Hypernuclear production by the (e,e′K+) reaction has unique advantages in hypernuclear spectroscopy of the S=−1 regime. The second-generation spectroscopy experiment on 12C, 7Li and 28Si targets has been recently carried out at JLab Hall C with a new experimental configuration (Tilt method) and also using a new high-resolution kaon spectrometer (HK...
Article
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Kaon electroproduction from light nuclei and hydrogen, using 1 H, 2 H, 3 He, 4 He, and carbon targets has been measured at Jefferson Laboratory. The quasifree angular distributions of Λ and Σ hyperons were determined at Q 2 = 0.35 (GeV/c) 2 and W = 1.91 GeV. Electroproduction on hydrogen was measured at the same kinematics for reference.
Chapter
We propose a device measuring bunch time structure of continuous wave beams, based on radio frequency (RF) analysis of low energy secondary electrons, (SEs). By using a currently developed 500 MHz RF deflector it is possible to scan circularly and detect the SEs, amplified in multi-channel plates (MCP). It is demonstrated that the noise induced by...
Article
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We have measured the beam-normal single-spin asymmetry in elastic scattering of transversely polarized 3 GeV electrons from unpolarized protons at Q2=0.15, 0.25 (GeV/c)2. The results are inconsistent with calculations solely using the elastic nucleon intermediate state and generally agree with calculations with significant inelastic hadronic interm...
Article
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Kaon electroproduction from light nuclei and hydrogen, using 1H, 2H, 3He, 4He, and Carbon targets has been measured at Jefferson Laboratory. The quasifree angular distributions of Lambda and Sigma hyperons were determined at Q^2= 0.35(GeV/c)^2 and W= 1.91GeV. Electroproduction on hydrogen was measured at the same kinematics for reference.
Article
The HKS (Jlab E01-011) experiment on spectroscopy of Λ-hypernuclei using (e,e'K+) reaction was successfully carried out in 2005. This paper gives a brief description of the experiment and its technique and shows some of the preliminary spectra that are still under analysis.
Article
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The data analysis for the reaction {sup 1}H(e,e{sup '}{pi}{sup +})n, which was used to determine values for the charged pion form factor F{sub {pi}} for values of Q{sup 2}= 0.6-1.6 GeV{sup 2}, has been repeated with careful inspection of all steps and special attention to systematic uncertainties. Also the method used to extract F{sub {pi}} from th...
Article
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We have examined the spin structure of the proton in the region of the nucleon resonances (1.085 GeV<W<1.910 GeV) at an average four momentum transfer of Q2=1.3 GeV2. Using the Jefferson Lab polarized electron beam, a spectrometer, and a polarized solid target, we measured the asymmetries A|| and A(perpendicular) to high precision, and extracted th...
Article
We propose a photon detector for recording low-level and ultra-fast optical signals, based on radio frequency (RF) analysis of low-energy photoelectrons (PEs). By using currently developed 500 MHz RF deflector, it is possible to scan circularly and detect single PEs, amplified in multi-channel plates (MCPs). The operation of the tube is investigate...
Article
The ratio of the proton's electric to magnetic form factor, GE/GM, can be extracted in elastic electron-proton scattering by measuring cross sections, beam-target asymmetry, or recoil polarization. Separate determinations of GE/GM by cross sections and recoil polarization observables disagree for Q2>1 (GeV/c)2. Measurement by a third technique migh...
Article
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The data analysis for the reaction H(e,e' pi^+)n, which was used to determine values for the charged pion form factor Fpi for values of Q^2=0.6-1.6 GeV^2, has been repeated with careful inspection of all steps and special attention to systematic uncertainties. Also the method used to extract Fpi from the measured longitudinal cross section was crit...
Article
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Recoil polarimetry was used to extract the ratio of the proton electromagnetic form factors, mu(p)G(E)(p)/G(M)(p) = 0.878 +/- 0.064(stat) 0.012(sys), at Q(2) = 1.13 (GeV/c)(2) from the reaction H-1((e) over right arrow ,e (p) over right arrow). This was an ancillary measurement in which the proton polarization was determined as part of a larger pro...
Article
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We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12 < or =Q2 < or =1.0 GeV2. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange-quark contributions to the currents of the proton. The measurements were ma...
Article
Encouraged by the success of the first hypernuclear spectroscopy through the (e,e′K+)(e,e′K+) reaction (JLab E89-009), a new improved experiment with a newly developed High resolution Kaon Spectrometer (HKS) and a new configuration of the electron spectrometer is planned at the JLab Hall C. The introduction of the HKS will improve by a factor of tw...
Article
An experimental technique for single‐Λ spectroscopy of the light and medium‐heavy mass Λ‐hypernuclei developed at the Jlab by the E01‐011 Collaboration has been described. The technique is based on the electroproduction of Λ‐hypernuclei by the (e,e′K+) reaction and newly constructed 2nd generation high resolution large solid angle kaon spectrometer...
Article
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The A(e,e′K+)X reaction has been investigated at Jefferson Laboratory. Data were taken for Q2 ≈ 0.35 GeV2 at a beam energy of 3.245 GeV for 1H,3He and 4He targets. Evidence for Λ‐hypernuclear bound states is seen for 3,4He targets. This is the first time that the electroproduction of these hypernuclei has been observed. © 2005 American Institute of...
Article
Based on the H-bridge switch technique a linear beam raster system was developed in 2002. The system generates a rectangular raster pattern with highly uniform (∼95%) raster density distribution on cryogenic targets. The two raster frequencies are 24.96 and 25.08kHz. The turning time at the vertex is 200ns and the scan linearity is 98%. The beam-he...
Article
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The (3,4)(Lambda)H and (4)(Lambda)H hypernuclear bound states have been observed for the first time in kaon electroproduction on (3,4)He targets. The production cross sections have been determined at Q(2)=0.35 GeV2 and W=1.91 GeV. For either hypernucleus the nuclear form factor is determined by comparing the angular distribution of the (3,4)He(e,e(...
Article
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Electroproduction of the ω meson was investigated in the 1H(e,e′p)ω reaction. The measurement was performed at a four-momentum transfer Q2≈0.5 GeV2. Angular distributions of the virtual photon-proton center-of-momentum cross sections have been extracted over the full angular range. These distributions exhibit a strong enhancement over t-channel par...
Article
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A pioneering experiment in Lambda hypernuclear spectroscopy, undertaken at the Thomas Jefferson National Accelerator Facility (Jlab), was recently reported. The experiment used the high- precision, continuous electron beam at Jlab, and a special arrangement of spectrometer magnets to measure the spectrum from {nat}C and 7Li targets using the (e,e'...
Conference Paper
The A(e,e ' K+)YX reaction has been investigated in Hall C at Jefferson Laboratory for 6 different targets. Data were taken for Q(2) approximate to 0.35 and 0.5 GeV2 at a beam energy of 3.245 GeV for H-1, H-2, He-3, He-4, C and Al targets. The missing mass spectra are fitted with Monte Carlo simulations taking into account the production of A and E...
Article
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The electric form factor of the neutron was determined from measurements of the d-->(e-->,e'n)p reaction for quasielastic kinematics. Polarized electrons were scattered off a polarized deuterated ammonia (15ND3) target in which the deuteron polarization was perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic...
Article
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We report the results from a systematic study of the quasielastic (e,e′p) reaction on 12C, 56Fe, and 197Au performed at Jefferson Lab. We have measured nuclear transparency and extracted spectral functions (corrected for radiation) over a Q2 range of 0.64–3.25 (GeV∕c)2 for all three nuclei. In addition, we have extracted separated longitudinal and...
Conference Paper
The ratio G{sub c}{sup n}/G{sub m}{sup n} of the electric to the magnetic form factor of the neutron has been measured by analyzing the polarization of the recoiling neutron in quasi-elastic scattering of longitudinally polarized electrons from deuterium at the Q{sup 2} values of 0.45, 1.15, and 1.47 (GeV/c){sup 2}. The experiment has been performe...
Article
The measurements of GEn/GMn obtained via recoil polarimetry from the quasielastic 2H(e→,e′n→)1H reaction at three central Q2 values of 0.45, 1.15 and 1.47 (GeV/c)2 were reported. A beam of longitudinally polarized electrons was found to scatter quasielastically from a neutron in a 15-cm liquid deuterium target. A scattered electron was detected in...
Article
High-energy, cw electron beams at new accelerator facilities allow electromagnetic production and precision study of hypernuclear structure, and we report here on the first experiment demonstrating the potential of the (e,e'K+) reaction for hypernuclear spectroscopy. This experiment is also the first to take advantage of the enhanced virtual photon...
Article
The results of the (e, e1K+) experiment were used to confirm that a future experiment with a dedicated Kaon spectrometer will provide resolutions of a few hundred keV with rates increased by a factor of 60. It was noted that the experiment used a small quantity of target material so that almost any nuclear isotope can be investigated. Thus, the exp...
Article
We report measurements of cross sections for the reaction [Formula Presented] for both the Λ and [Formula Presented] hyperon states, at an invariant mass of [Formula Presented] and four-momentum transfers [Formula Presented] Data were taken for three values of virtual photon polarization [Formula Presented] allowing the decomposition of the cross s...
Article
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We report measurements of cross sections for the reaction p(e,e'K)Y, for both the Lambda and Sigma_0 hyperon states, at an invariant mass of W=1.84 GeV and four-momentum transfers 0.5<Q2<2 (GeV/c)2. Data were taken for three values of virtual photon polarization, allowing the decomposition of the cross sections into longitudinal and transverse comp...
Article
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The first experiment in Λ-hypernuclear spectroscopy using the high-precision electron beam at Jefferson laboratory (JLab) has been carried out. The hypernuclear spectrometer system (HNSS) was used to measure spectra from the 12C(e,e′K+)12ΛB reaction with sub-1-MeV resolution, the best energy resolution obtained thus far in hypernuclear spectroscopy...
Conference Paper
The A(e,eiK+)YX reaction on H, D, {sup 3}He, and {sup 4}He was investigated in Hall C at CEBAF. Data were obtained for Q{sup 2} {approx} 0.35 and 0.5 GeV{sup 2} at 3.245 GeV. The missing mass spectra for both H and D are fitted with Monte-Carlo simulations incorporating peaks corresponding to Lambda production on the proton and Sigma production on...
Article
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We report the first measurement using a solid polarized target of the neutron electric form factor G(n)(E) via d-->(e-->,e(')n)p. G(n)(E) was determined from the beam-target asymmetry in the scattering of longitudinally polarized electrons from polarized deuterated ammonia ( 15ND3). The measurement was performed in Hall C at Thomas Jefferson Nation...
Article
The A(e,e'Κ+)YX reaction on H, D, 3He, and 4He was investigated in Hall C at CE-BAF. Data were obtained for Q2 ≈ 0.35 and 0.5 GeV2 at 3.245 GeV. The missing mass spectra for both H and D are fitted with Monte-Carlo simulations incorporating peaks corresponding to Λ production on the proton and Σ production on both the proton and neutron. For D, the...
Article
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Separated longitudinal and transverse structure functions for the reaction 1H(e,e(')pi(+))n were measured in the momentum transfer region Q2 = 0.6--1.6 (GeV/c)(2) at a value of the invariant mass W = 1.95 GeV. New values for the pion charge form factor were extracted from the longitudinal cross section by using a recently developed Regge model. The...
Article
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Inclusive electron scattering data are presented for ^2H and Fe targets at an incident electron energy of 4.045 GeV for a range of momentum transfers from Q^2 = 1 to 7 (GeV/c)^2. Data were taken at Jefferson Laboratory for low values of energy loss, corresponding to values of Bjorken x greater than or near 1. The structure functions do not show sca...
Article
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A newly obtained sample of inclusive electron-nucleon scattering data has been analyzed for precision tests of quark-hadron duality. The data are in the nucleon resonance region, and span the range 0.3<Q^2<5.0 (GeV/c)^2. Duality is observed both in limited and extended regions around the prominent resonance enhancements. Higher twist contributions...
Article
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A separation of the longitudinal and transverse C-12(e,e'p) cross sections in the quasifree region has been performed in parallel kinematics at Q(2) of 0.64 and 1.8 GeV2 for initial proton momentum <80 MeV. The separated transverse and longitudinal spectral functions at Q(2) = 0.64 GeV2 show significant differences for missing energy between 25 and...
Article
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Tensor polarization observables (t20, t21 and t22) have been measured in elastic electron-deuteron scattering for six values of momentum transfer between 0.66 and 1.7 (GeV/c) 2. The experiment was performed at the Jefferson Laboratory in Hall C using the electron HMS Spectrometer, a specially designed deuteron magnetic channel and the recoil deuter...
Article
A rigorous extraction of the deuteron charge form factors from tensor polarization data in elastic electron-deuteron scattering, at given values of the 4-momentum transfer, is presented. Then the world data for elastic electron-deuteron scattering is used to parameterize, in three different ways, the three electromagnetic form factors of the deuter...
Article
The differential cross section for 2H(γ,d)π0 has been measured at deuteron center-of-mass angles of 90° and 136°. This work reports the first data for this reaction above a photon energy of 1 GeV, and permits a test of the apparent constituent counting rule and reduced nuclear amplitude behavior as observed in elastic ed scattering. Measurements we...
Article
In elastic electron-deuteron scattering, the tensor polarization moments t20, t21 and t22, together with the unpolarized cross-sections, have been measured up to a momentum transfer of 1.8 (GeV/c)2, or 6.8 fm−1. The experiment was performed at Jefferson Laboratory using the recoil deuteron polarimeter POLDER. Preliminary results are presented and d...
Article
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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 scalin...
Article
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The A͑Q 2 ͒ structure function in elastic electron-deuteron scattering was measured at six momentum transfers Q 2 between 0.66 and 1.80 ͑GeV͞c͒ 2 in Hall C at Jefferson Laboratory. The scattered electrons and recoil deuterons were detected in coincidence, at a fixed deuteron angle of 60.5 ± . These new precise measurements resolve discrepancies bet...
Article
Kaon electroproduction on deuterium and hydrogen targets has been measured at beam energies of 3.245 and 2.445 GeV and momentum transfer Q2 = 0.38 and 0.5 (GeV/c)2. Associated Λ production off a proton in the deuteron exhibits a quasifree production mechanism. The electroproduction of a Σ− off the neutron could be extracted for the first time with...
Article
The 1H(e,e'K+)Λ and 1H(e,e'K+)Σ0 reactions were studied as a function of the squared four-momentum-transfer, Q2, and the virtual photon polarization, ɛ, thus enabling the separation of the longitudinal and transverse parts of the cross section. The existence of a sizable longitudinal component for the 1H(e,e'K+)Λ reaction seems to be indicated by t...
Article
The first measurements of the differential cross section for the d(gamma,p)n reaction up to 4.0 GeV were performed at the Continuous Electron Beam Accelerator Facility (CEBAF) at Thomas Jefferson Laboratory. We report the cross sections at the proton center-of-mass angles of 36{sup o}, 52{sup o}, 69{sup o}, and 89{sup o}. These results are in reaso...