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Markowitz, P.

Publications and source records attributed to Markowitz, P..

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Spectroscopy of Li Λ 9 by electroproduction

Background: In the absence of accurate data on the free two-body hyperon-nucleon interaction, the spectra of hypernuclei can provide information on the details of the effective hyperon-nucleon interaction. Purpose: To obtain a high-resolution spectrum for the 9 Be(e,e'K + ) 9 Λ Li reaction. Method: Electroproduction of the hypernucleus 9 Λ Li has been studied for the first time with sub-MeV energy resolution in Hall A at Jefferson Lab on a 9 Be target. In order to increase the counting rate and to provide unambiguous kaon identification, two superconducting septum magnets and a Ring Imaging CHerenkov detector (RICH) were added to the Hall A standard equipment. Results: The cross section to low-lying states of 9 Λ Li is concentrated within 3 MeV of the ground state and can be fitted with four peaks. The positions of the doublets agree with theory while a disagreement could exist with respect to the relative strengths of the peaks in the doublets. A Λ separation energy, B Λ , of 8.36±0.08 (stat.) ±0.08 (syst.) MeV was measured, in agreement with an earlier experiment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Separated response functions in exclusive, forward π ± electroproduction on deuterium

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 separated response functions in π⁻ and π⁺ electroproduction are particularly informative. Ratio for transverse photons may allow this transition to be more easily observed, while the ratio for longitudinal photons provides a crucial verification of the assumed pole dominance, needed for reliable extraction of the pion form factor from electroproduction data. Method: Data were acquired with 2.6-5.2 GeV electron beams and the HMS+SOS spectrometers in Jefferson Lab Hall C, at central Q 2 values of 0.6, 1.0, 1.6 GeV 2 at W=1.95 GeV, and Q 2 =2.45 GeV 2 at W=2.22 GeV. There was significant coverage in Φ And ϵ, which allowed separation of σ L,T,LT,TT . Results: σL shows a clear signature of the pion pole, with a sharp rise at small -t. In contrast, σ T is much flatter versus t. The longitudinal/transverse ratios evolve with Q 2 and t, and at the highest Q 2 =2.45 GeV 2 show a slight enhancement for π⁻ Production compared to π⁺. The π⁻/π⁺+ ratio for transverse photons exhibits only a small Q 2 -dependence, following a nearly universal curve with t, with a steep transition to a value of about 0.25, consistent with s-channel quark knockout. The σ TT /σ T ratio also drops rapidly with Q 2 , qualitatively consistent with s-channel helicity conservation. The π⁻/π⁺ ratio for longitudinal photons indicates a small isoscalar contamination at W=1.95 GeV, consistent with what was observed in our earlier determination of the pion form factor at these kinematics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Measurement of Double-Polarization Asymmetries in the Quasielastic He → 3 ( e → , e ' d ) Process

We present a precise measurement of double-polarization asymmetries in the 3 He(e,e'd) reaction. This particular process is a uniquely sensitive probe of hadron dynamics in 3He and the structure of the underlying electromagnetic currents. The measurements have been performed in and around quasi-elastic kinematics at Q 2 =0.25(GeV/c) 2 for missing momenta up to 270MeV/c. The asymmetries are in fair agreement with the state-of-the-art calculations in terms of their functional dependencies on pm and omega, but are systematically offset. Beyond the region of the quasi-elastic peak, the discrepancies become even more pronounced. Thus, our measurements have been able to reveal deficiencies in the most sophisticated calculations of the three-body nuclear system, and indicate that further refinement in the treatment of their two- and/or three-body dynamics is required.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Measurement of “pretzelosity” asymmetry of charged pion production in semi-inclusive deep inelastic scattering on a polarized He 3 target

An experiment to measure single-spin asymmetries in semi-inclusive production of charged pions in deep-inelastic scattering on a transversely polarized ³He target was performed at Jefferson Lab in the kinematic region of 0.16 < x < 0.35 and 1.4 < Q² < 2.7 GeV². Our results show that both π ± on 3 He and on neutron pretzelosity asymmetries are consistent with zero within experimental uncertainties.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Single spin asymmetries in charged kaon production from semi-inclusive deep inelastic scattering on a transversely polarized He 3 target

We report the first measurement of target single spin asymmetries of charged kaons produced in semi-inclusive deep inelastic scattering of electrons off a transversely polarized 3He target. Both the Collins and Sivers moments, which are related to the nucleon transversity and Sivers distributions, respectively, are extracted over the kinematic range of 0.1 < x bj <0.4 for K + and K – production. While the Collins and Sivers moments for K + are consistent with zero within the experimental uncertainties, both moments for K – favor negative values. The Sivers moments are compared to the theoretical prediction from a phenomenological fit to the world data. While the K + Sivers moments are consistent with the prediction, the K – results differ from the prediction at the 2-sigma level.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Measurement of the Target-Normal Single-Spin Asymmetry in Deep-Inelastic Scattering from the Reaction He 3 ↑ ( e , e ' ) X

We report here the first measurement of the target-normal single-spin asymmetry in deep-inelastic scattering from the inclusive reaction He 3 ↑ ( e , e ' ) X on a polarized He 3 gas target. Assuming time-reversal invariance, this asymmetry is strictly zero in the Born approximation but can be nonzero if two-photon-exchange contributions are included. The experiment, conducted at Jefferson Lab using a 5.89 GeV electron beam, covers a range of 1.7 < W < 2.9 GeV , 1.0 < Q 2 < 4.0 GeV 2 and 0.16 < x < 0.65 . Neutron asymmetries were extracted using the effective nucleon polarization and measured proton-to- He 3 cross-section ratios. The measured neutron asymmetries shown are negative with an average value of ( - 1.09 ± 0.38 ) × 1 0 - 2 for invariant mass W > 2 GeV , which is nonzero at the 2.89 σ level. Our measured asymmetry agrees both in sign and magnitude with a two-photon-exchange model prediction that uses input from the Sivers transverse momentum distribution obtained from semi-inclusive deep-inelastic scattering.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Separated Response Function Ratios in Exclusive, Forward π ± Electroproduction

The study of exclusive π{sup ±} electroproduction on the nucleon, including separation of the various structure functions, is of interest for a number of reasons. The ratio R{sub L}=σ{sup π{sup -}}{sub L}/σ{sup π{sup +}}{sub L} is sensitive to isoscalar contamination to the dominant isovector pion exchange amplitude, which is the basis for the determination of the charged pion form factor from electroproduction data. A change in the value of R{sub T}=σ{sup π{sup -}}{sub T}/σ{sup π{sup +}}{sub T} from unity at small -t, to 1/4 at large -t, would suggest a transition from coupling to a (virtual) pion to coupling to individual quarks. Furthermore, the mentioned ratios may show an earlier approach to pQCD than the individual cross sections. We have performed the first complete separation of the four unpolarized electromagnetic structure functions above the dominant resonances in forward, exclusive π± electroproduction on the deuteron at central Q{sup 2} values of 0.6, 1.0, 1.6 GeV{sup 2} at W=1.95 GeV, and Q{sup 2}=2.45 GeV{sup 2} at W=2.22 GeV. Here, we present the L and T cross sections, with emphasis on R{sub L} and R{sub T}, and compare them with theoretical calculations. Results for the separated ratio RL indicate dominance of the pion-pole diagram at low -t, while results for R{sub T} are consistent with a transition between pion knockout and quark knockout mechanisms.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Single spin asymmetries of inclusive hadrons produced in electron scattering from a transversely polarized 3 He target

We report the first measurement of target single-spin asymmetries (A N ) in the inclusive hadron production reaction, e + 3 He↑→h+X, using a transversely polarized 3 He target. This experiment was conducted at Jefferson Lab in Hall A using a 5.9-GeV electron beam. Three types of hadrons (π ± , K ± and proton) were detected in the transverse hadron momentum range 0.54 < p T < 0.74 GeV/c. The range of x F for pions was -0.29 < x F < -0.23 and for kaons -0.25 < x F <-0.18. The observed asymmetry strongly depends on the type of hadron. A positive asymmetry is observed for π + and K + . A negative asymmetry is observed for π–. The magnitudes of the asymmetries follow |A π – |<|A π + |<|A K + |. The K – and proton asymmetries are consistent with zero within the experimental uncertainties. The π + and π – asymmetries measured for the 3 He target and extracted for neutrons are opposite in sign with a small increase observed as a function of p T .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Electroproduction of K+ Λ at JLab Hall-C

A Λ hypernuclear spectroscopic experiment, JLab E05-115 was performed at JLab Hall-C in 2009 by the (e, e' K + ) reaction. Data of Λ hypernuclei with mass numbers from A = 7 to A = 52 were successfully taken, and the analyses are in progress. A polyethylene (CH 2 ) target was used as a proton target to calibrate energy scales, and to study elementary process of the p(e, e' K + )Λ, Σ 0 reaction. We report a preliminary differential cross section of K + Λ electro-production at low Q 2 [~0.01 (GeV/c) 2 ] and at small kaon angles (cosΘ$CM\atop{K}$ ~0.97) in the present article.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Observation of the Λ ⁷He Hypernucleus by the (e, e'K⁺) Reaction

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, He Λ ⁷, 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 Λ ⁷ 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.

Nakamura, S. N.↗
DOE OSTI2012

Final analysis of proton form factor ratio data at Q 2 = 4.0, 4.8, and 5.6 GeV 2

Recently published measurements of the proton electromagnetic form factor ratio R = μ p G E p /G M p at momentum transfers Q 2 up to 8.5 GeV 2 in Jefferson Lab Hall C deviate from the linear trend of previous measurements in Jefferson Lab Hall A, favoring a slower rate of decrease of R with Q 2 . While statistically compatible in the region of overlap with Hall A, the Hall C data hint at a systematic difference between the two experiments. This possibility was investigated in a reanalysis of the Hall A data. We find that the original analysis underestimated the background in the selection of elastic events. The application of an additional cut to further suppress the background increases the results for R, improving the consistency between Halls A and C.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

New Measurements of High-Momentum Nucleons and Short-Range Structures in Nuclei

We present new, high-Q 2 measurements of inclusive electron scattering from high-momentum nucleons in nuclei. This yields an improved extraction 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 extend to the kinematic regime where three-nucleon correlations are expected to dominate and we observe significantly greater strength in this region than previous measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Beam-Target Double-Spin Asymmetry A LT in Charged Pion Production from Deep Inelastic Scattering on a Transversely Polarized He 3 Target at 1.4 < Q 2 < 2.7 GeV 2

We report the first measurement of the double-spin asymmetry A LT for charged pion electroproduction in semi-inclusive deep inelastic electron scattering on a transversely polarized 3 He target. The kinematics focused on the valence quark region, 0.16 < x < 0.35 with 1.4 < Q 2 < 2.7 GeV 2 . The corresponding neutron A LT asymmetries were extracted from the measured 3 He asymmetries and proton/ 3 He cross section ratios using the effective polarization approximation. These new data probe the transverse momentum dependent parton distribution function g 1T q and therefore provide access to quark spin-orbit correlations. Our results indicate a positive azimuthal asymmetry for π - production on 3 He and the neutron, while our π + asymmetries are consistent with zero.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Probing the High Momentum Component of the Deuteron at High Q{sup 2}

The {sup 2}H(e,e{sup '}p)n cross section at a momentum transfer of 3.5 (GeV/c){sup 2} was measured over a kinematical range that made it possible to study this reaction for a set of fixed missing momenta as a function of the neutron recoil angle {theta}{sub nq} and to extract missing momentum distributions for fixed values of {theta}{sub nq} up to 0.55 GeV/c. In the region of 35 deg. {<=}{theta}{sub nq}{<=}45 deg. recent calculations, which predict that final-state interactions are small, agree reasonably well with the experimental data. Therefore, these experimental reduced cross sections provide direct access to the high momentum component of the deuteron momentum distribution in exclusive deuteron electrodisintegration.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗