Publications (52)133.24 Total impact
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Article: Observation of the _{Λ}^{7}He Hypernucleus by the (e, e^{'}K^{+}) Reaction.
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ABSTRACT: 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 resolution is the best reported to date for hypernuclear reaction spectroscopy. The _{Λ}^{7}He binding energy supplies the last missing information of the A=7, T=1 hypernuclear isotriplet, providing a new input for the charge symmetry breaking effect of the ΛN potential.Physical Review Letters 01/2013; 110(1):012502. · 7.37 Impact Factor -
Article: Direct Measurements of the Lifetime of Heavy Hypernuclei
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ABSTRACT: The lifetime of a Lambda particle embedded in a nucleus (hypernucleus) decreases from that of free Lambda decay due to the opening of the Lambda N to NN weak decay channel. However, it is generally believed that the lifetime of a hypernucleus attains a constant value (saturation) for medium to heavy hypernuclear masses, yet this hypothesis has been difficult to verify. The present paper reports a direct measurement of the lifetime of medium-heavy hypernuclei produced with a photon-beam from Fe, Cu, Ag, and Bi targets. The recoiling hypernuclei were detected by a fission fragment detector using low-pressure multi-wire proportional chambers. The experiment agrees remarkably well with the only previously-measured single-species heavy-hypernucleus lifetime, that of Fe56_Lambda at KEK, and has significantly higher precision. The experiment disagrees with the measured lifetime of an unknown combination of heavy hypernuclei with 180<A<225 and, with a small statistical and systematic uncertainty, strongly favors the expected saturation of the lifetime decrease.12/2012; -
Article: Observation of the Helium 7 Lambda hypernucleus by the (e,e'K+) reaction
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ABSTRACT: 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. This resolution is the best reported to date for hypernuclear reaction spectroscopy. The he 7 Lambda binding energy supplies the last missing information of the A=7, T=1 hypernuclear iso-triplet, providing a new input for the charge symmetry breaking (CSB) effect of \Lambda N potential.07/2012; -
Article: Kaon, pion, and proton associated photofission of Bi nuclei
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ABSTRACT: 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 which is ∼3 times larger than the proton and pion associated fission probabilities and ∼2 times larger than inclusive ones. The kaon associated excess fission events are explained in terms of bound Λ residual states and their weak nonmesonic decays.Physics of Atomic Nuclei 04/2012; 73(10):1707-1712. · 0.57 Impact Factor -
Article: New measurements of high-momentum nucleons and short-range structures in nuclei.
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ABSTRACT: We present new measurements of electron scattering from high-momentum nucleons in nuclei. These data allow an improved determination of the strength of two-nucleon correlations for several nuclei, including light nuclei where clustering effects can, for the first time, be examined. The data also include the kinematic region where three-nucleon correlations are expected to dominate.Physical Review Letters 03/2012; 108(9):092502. · 7.37 Impact Factor -
Article: Binding Energy of 7ΛHe and Test of Charge Symmetry Breaking in the ΛN Interaction Potential
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ABSTRACT: 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 7ΛBe, the shifts in binding energies are opposite to those predicted by a recent cluster model calculation, which assumes that the unexplained part of the binding energy difference between 4ΛH and 4ΛHe, is due to the CSB of the ΛN potential. Further examination of CSB in light hypernuclear systems is required both experimentally and theoretically.Journal of Physics Conference Series 09/2011; 312(2):022015. -
Article: Nuclear transparency and effective kaon-nucleon cross section from the A(e, e'K+) reaction
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ABSTRACT: We have determined the transparency of the nuclear medium to kaons from $A(e,e^{'} K^{+})$ measurements on $^{12}$C, $^{63}$Cu, and $^{197}$Au targets. The measurements were performed at the Jefferson Laboratory and span a range in four-momentum-transfer squared Q$^2$=1.1 -- 3.0 GeV$^2$. The nuclear transparency was defined as the ratio of measured kaon electroproduction cross sections with respect to deuterium, ($\sigma^{A}/\sigma^{D}$). We further extracted the atomic number ($A$) dependence of the transparency as parametrized by $T= (A/2)^{\alpha-1}$ and, within a simple model assumption, the in-medium effective kaon-nucleon cross sections. The effective cross sections extracted from the electroproduction data are found to be smaller than the free cross sections determined from kaon-nucleon scattering experiments, and the parameter $\alpha$ was found to be significantly larger than those obtained from kaon-nucleus scattering. We have included similar comparisons between pion- and proton-nucleon effective cross sections as determined from electron scattering experiments, and pion-nucleus and proton-nucleus scattering data.03/2011; -
Article: Semi-inclusive charged-pion electroproduction off protons and deuterons: Cross sections, ratios, and access to the quark-parton model at low energies
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ABSTRACT: A large set of cross sections for semi-inclusive electroproduction of charged pions (π±) from both proton and deuteron targets was measured. The data are in the deep-inelastic scattering region with invariant mass squared W2>4 GeV2 (up to ≈7 GeV2) and range in four-momentum transfer squared 2<Q2<4 (GeV/c)2, and cover a range in the Bjorken scaling variable 0.2<x<0.6. The fractional energy of the pions spans a range 0.3<z<1, with small transverse momenta with respect to the virtual-photon direction, Pt2<0.2 (GeV/c)2. The invariant mass that goes undetected, Mx or W′, is in the nucleon resonance region, W′<2 GeV. The new data conclusively show the onset of quark-hadron duality in this process, and the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark→pion production mechanisms. The x, z, and Pt2 dependences of several ratios (the ratios of favored-unfavored fragmentation functions, charged pion ratios, deuteron-hydrogen and aluminum-deuteron ratios for π+ and π−) have been studied. The ratios are found to be in good agreement with expectations based upon a high-energy quark-parton model description. We find the azimuthal dependences to be small, as compared to exclusive pion electroproduction, and consistent with theoretical expectations based on tree-level factorization in terms of transverse-momentum-dependent parton distribution and fragmentation functions. In the context of a simple model, the initial transverse momenta of d quarks are found to be slightly smaller than for u quarks, while the transverse momentum width of the favored fragmentation function is about the same as for the unfavored one, and both fragmentation widths are larger than the quark widths.Phys. Rev. C. 03/2011; 85(1). -
Article: The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles
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ABSTRACT: 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 dedicated apparatus. It consists of specialized beam-monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cerenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed.03/2011; -
Article: Scaling of the F2 structure function in nuclei and quark distributions at x>1.
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ABSTRACT: We present new data on electron scattering from a range of nuclei taken in Hall C at Jefferson Lab. For heavy nuclei, we observe a rapid falloff in the cross section for x>1, which is sensitive to short-range contributions to the nuclear wave function, and in deep inelastic scattering corresponds to probing extremely high momentum quarks. This result agrees with higher energy muon scattering measurements, but is in sharp contrast to neutrino scattering measurements which suggested a dramatic enhancement in the distribution of the "superfast" quarks probed at x>1. The falloff at x>1 is noticeably stronger in 2H and 3He, but nearly identical for all heavier nuclei.Physical Review Letters 11/2010; 105(21):212502. · 7.37 Impact Factor -
Article: Probing quark-gluon interactions with transverse polarized scattering.
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ABSTRACT: 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˜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 Burkhardt-Cottingham sum rule is valid. The fundamental Bjorken sum rule obtained from the a0 matrix element is satisfied at our low momentum transfer.Physical Review Letters 09/2010; 105(10):101601. · 7.37 Impact Factor -
Article: Proton and deuteron F2 structure function at low Q2
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ABSTRACT: Measurements of the proton and deuteron F2 structure functions are presented. The data, taken at Jefferson Lab Hall C, span the four-momentum transfer range 0.06<Q2<2.8 GeV2 and Bjorken x values from 0.009 to 0.45, thus extending the knowledge of F2 to low values of Q2 at low x. Next-to-next-to-leading-order calculations using recent parton distribution functions start to deviate from the data for Q2<2 GeV2 at the low and high x values. Down to the lowest value of Q2, the structure function is in good agreement with a parametrization of F2 based on data that have been taken at much higher values of Q2 or much lower values of x, and which are constrained by data at the photon point. The ratio of the deuteron and proton structure functions at low x remains well described by a logarithmic dependence on Q2 at low Q2.Phys. Rev. C. 05/2010; 81(5). -
Article: Experimental study of the A(e,e′π+) reaction on 1H, 2H, 12C, 27Al, 63Cu, and 197Au
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ABSTRACT: Cross sections for the 1H(e,e′π+)n process on 1H, 2H, 12C, 27Al, 63Cu, and 197Au targets were measured at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) to extract nuclear transparencies. Data were taken from Q2=1.1–4.7 GeV2 for a fixed center-of-mass energy of W=2.14 GeV. The ratio of σL and σT was extracted from the measured cross sections for 1H, 2H, 12C, and 63Cu targets at Q2=2.15 and 4.0 GeV2, allowing for additional studies of the reaction mechanism. In this article, we present the experimental setup and the analysis of the data in detail, including systematic uncertainty studies. Differential cross sections and nuclear transparencies as a function of the pion momentum at different values of Q2 are presented. Our results are consistent with the predicted early onset of color transparency in mesons. Global features of the data are discussed and the data are compared with model calculations for the 1H(e,e′π+)n reaction from nuclear targets.Phys. Rev. C. 05/2010; 81(5). -
Article: The proton and deuteron F_2 structure function at low Q^2
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ABSTRACT: Measurements of the proton and deuteron $F_2$ structure functions are presented. The data, taken at Jefferson Lab Hall C, span the four-momentum transfer range $0.06 < Q^2 < 2.8$ GeV$^2$, and Bjorken $x$ values from 0.009 to 0.45, thus extending the knowledge of $F_2$ to low values of $Q^2$ at low $x$. Next-to-next-to-leading order calculations using recent parton distribution functions start to deviate from the data for $Q^2<2$ GeV$^2$ at the low and high $x$-values. Down to the lowest value of $Q^2$, the structure function is in good agreement with a parameterization of $F_2$ based on data that have been taken at much higher values of $Q^2$ or much lower values of $x$, and which is constrained by data at the photon point. The ratio of the deuteron and proton structure functions at low $x$ remains well described by a logarithmic dependence on $Q^2$ at low $Q^2$. Comment: 3 figures, submitted paper02/2010; -
Article: Kaon, pion, and proton associated photofission of Bi nuclei
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ABSTRACT: 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 which is ∼3 times larger than the proton and pion associated fission probabilities and ∼2 times larger than inclusive ones. The kaon associated excess fission events are explained in terms of bound Λ residual states and their weak nonmesonic decays.Physics of Atomic Nuclei 01/2010; 73(10):1707-1712. · 0.57 Impact Factor -
Article: New measurements of the European Muon Collaboration effect in very light nuclei.
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ABSTRACT: New Jefferson Lab data are presented on the nuclear dependence of the inclusive cross section from (2)H, (3)He, (4)He, (9)Be and (12)C for 0.3 < x < 0.9, Q(2) approximately 3-6 GeV(2). These data represent the first measurement of the EMC effect for (3)He at large x and a significant improvement for (4)He. The data do not support previous A-dependent or density-dependent fits to the EMC effect and suggest that the nuclear dependence of the quark distributions may depend on the local nuclear environment.Physical Review Letters 11/2009; 103(20):202301. · 7.37 Impact Factor -
Article: Applications of quark-hadron duality in the F2 structure function
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ABSTRACT: Inclusive electron-proton and electron-deuteron inelastic cross sections have been measured at Jefferson Lab (JLab) in the resonance region, at large Bjorken x, up to 0.92, and four-momentum transfer squared Q2 up to 7.5 GeV2 in the experiment E00-116. These measurements are used to extend to larger x and Q2 precision, quantitative, studies of the phenomenon of quark-hadron duality. Our analysis confirms, both globally and locally, the apparent “violation” of quark-hadron duality previously observed at a Q2 of 3.5 GeV2 when resonance data are compared to structure function data created from CTEQ6M and MRST2004 parton distribution functions (PDFs). More importantly, our new data show that this discrepancy saturates by Q2~4 GeV2, becoming Q2 independent. This suggests only small violations of Q2 evolution by contributions from the higher-twist terms in the resonance region that is confirmed by our comparisons to ALEKHIN and ALLM97. We conclude that the unconstrained strength of the CTEQ6M and MRST2004 PDFs at large x is the major source of the disagreement between data and these parametrizations in the kinematic regime we study and that, in view of quark-hadron duality, properly averaged resonance region data could be used in global quantum chromodynamics fits to reduce PDF uncertainties at large x.Phys. Rev. C. 09/2009; 80(3). -
Article: Neutral Pion Electroproduction in the Resonance Region at High $Q^2$
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ABSTRACT: The process $ep \to e^{\prime}p^{\prime}\pi^0$ has been measured at $Q^2$ = 6.4 and 7.7 GeV/c$^2$)$^2$ in Jefferson Lab's Hall C. Unpolarized differential cross sections are reported in the virtual photon-proton center of mass frame considering the process $\gamma^{\ast}p \to p^{\prime}\pi^0$. Various details relating to the background subtractions, radiative corrections and systematic errors are discussed. The usefulness of the data with regard to the measurement of the electromagnetic properties of the well known $\Delta(1232)$ resonance is covered in detail. Specifically considered are the electromagnetic and scalar-magnetic ratios $R_{EM}$ and $R_{SM}$ along with the magnetic transition form factor $G_M^{\ast}$. It is found that the rapid fall off of the $\Delta(1232)$ contribution continues into this region of momentum transfer and that other resonances Comment: 41 pages including numerical cross section tables, updates include new phenomenological fit for multipole extraction in addition to simplified previous method, These fits are seen in figures 24,26 and 27 and the values are reported in Table VIII06/2009; -
Article: New measurements of the EMC effect in very light nuclei
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ABSTRACT: New Jefferson Lab data are presented on the nuclear dependence of the inclusive cross section from 2H, 3He, 4He, 9Be and 12C for 0.3<x<0.9, Q^2 approximately 3-6 GeV^2. These data represent the first measurement of the EMC effect for 3He at large x and a significant improvement for 4He. The data do not support previous A-dependent or density-dependent fits to the EMC effect and suggest that the nuclear dependence of the quark distributions may depend on the local nuclear environment. Comment: 5 pages, 4 figures, submitted to PRL. fixed error in author list, minor text revision04/2009; -
Article: Search for Sub-threshold Photoproduction of J/Psi Mesons
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ABSTRACT: A search was made for sub-threshold $J/\psi$ production from a carbon target using a mixed real and quasi-real Bremsstrahlung photon beam with an endpoint energy of 5.76 GeV. No events were observed, which is consistent with predictions assuming quasi-free production. The results place limits on exotic mechanisms that strongly enhance quasi-free production.10/2008;
Top co-authors
Top Journals
Institutions
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2012
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Los Alamos National Laboratory
Los Alamos, CA, USA
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2001–2012
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Yerevan Physics Institute
Yerevan, K'aghak' Yerevan, Armenia -
University of Illinois, Urbana-Champaign
- Department of Physics
Urbana, IL, USA
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2011
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California Institute of Technology
Pasadena, CA, USA
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2007–2010
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University of Virginia
- Department of Physics
Charlottesville, VA, USA -
VU University Amsterdam
Amsterdam, North Holland, Netherlands
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2008–2009
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Massachusetts Institute of Technology
- Laboratory for Nuclear Science
Cambridge, MA, USA
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2005–2007
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College of William and Mary
- Department of Physics
Williamsburg, VA, USA -
Argonne National Laboratory
Downers Grove, IL, USA
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2004
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Houston Baptist University
Houston, TX, USA -
Universität Basel
Basel, BS, Switzerland
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2003
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Tohoku University
- Department of Physics
Sendai-shi, Miyagi-ken, Japan -
Kent State University
Kent, OH, USA
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