arXiv subjects

M. K. Jones

Publications and source records attributed to M. K. Jones.

83 records · Page 5Linked to original sources

arXiv2006

Proton G_E/G_M from beam-target asymmetry

The ratio of the proton's electric to magnetic form factor, G_E/G_M, can be extracted in elastic electron-proton scattering by measuring either cross sections, beam-target asymmetry or recoil polarization. Separate determinations of G_E/G_M by cross sections and recoil polarization observables disagree for Q^2 > 1 (GeV/c)^2. Measurement by a third technique might uncover an unknown systematic error in either of the previous measurements. The beam-target asymmetry has been measured for elastic electron-proton scattering at Q^2 = 1.51 (GeV/c)^2 for target spin orientation aligned perpendicular to the beam momentum direction. This is the largest Q^2 at which G_E/G_M has been determined by a beam-target asymmetry experiment. The result, \muG_E/G_M = 0.884 +/- 0.027 +/- 0.029, is compared to previous world data.

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arXiv2006

Determination of the Charged Pion Form Factor at Q2=1.60 and 2.45 (GeV/c)2

The H(e,e'pi+)n cross section was measured at four-momentum transfers of Q2=1.60 and 2.45 GeV2 at an invariant mass of the photon nucleon system of W=2.22 GeV. The charged pion form factor (F_pi) was extracted from the data by comparing the separated longitudinal pion electroproduction cross section to a Regge model prediction in which F_pi is a free parameter. The results indicate that the pion form factor deviates from the charge-radius constrained monopole form at these values of Q2 by one sigma, but is still far from its perturbative Quantum Chromo-Dynamics prediction.

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arXiv2006

Polarization transfer in the d(epol,e' ppol)n reaction up to Q^2=1.61 (GeV/c)^2

The recoil proton polarization was measured in the d(epol,e' ppol)n reaction in Hall A of the Thomas Jefferson National Accelerator Facility (JLab). The electron kinematics were centered on the quasielastic peak (x_{Bj}~1) and included three values of the squared four-momentum transfer, Q^2=0.43, 1.00 and 1.61 (GeV/c)^2. For Q^2=0.43 and 1.61 (GeV/c)^2, the missing momentum, p_m, was centered at zero while for Q^2=1.00 (GeV/c)^2 two values of p_m were chosen: 0 and 174 MeV/c. At low p_m, the Q^2 dependence of the longitudinal polarization, P_z', is not well described by a state-of-the-art calculation. Further, at higher p_m, a 3.5 sigma discrepancy was observed in the transverse polarization, P_x'. Understanding the origin of these discrepancies is important in order to confidently extract the neutron electric form factor from the analogous d(epol,e' npol)p experiment.

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arXiv2004

Precision Rosenbluth measurement of the proton elastic form factors

We report the results of a new Rosenbluth measurement of the proton form factors at Q^2 values of 2.64, 3.20 and 4.10 GeV^2. Cross sections were determined by detecting the recoiling proton in contrast to previous measurements in which the scattered electron was detected. At each Q^2, relative cross sections were determined to better than 1%. The measurement focussed on the extraction of G_E/G_M which was determined to 4-8% and found to approximate form factor scaling, i.e. μ_p G_E \approx G_M. These results are consistent with and much more precise than previous Rosenbluth extractions. However, they are inconsistent with recent polarization transfer measurements of comparable precision, implying a systematic difference between the two techniques.

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arXiv2002

A Search for Neutral Baryon Resonances Below Pion Threshold

The reaction p(e,e^{prime}pi^+)X^0 was studied with two high resolution magnetic spectrometers to search for narrow baryon resonances. A missing mass resolution of 2.0 MeV was achieved. A search for structures in the mass region of 0.97 < M_{X^0} < 1.06 GeV yielded no significant signal. The yield ratio of p(e,e^{prime}pi^+)X^0/p(e,e^{prime}pi^+)n was determined to be (-0.35 +/- 0.35) times 10^{-3} at 1.004 GeV and (0.34 +/- 0.42) times 10^{-3} at 1.044 GeV.

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arXiv2001

The quasielastic 2H(e,e'p)n reaction at high recoil momenta

The 2H(e,e'p)n cross section was measured in Hall A of the Thomas Jefferson National Accelerator Facility (JLab) in quasielastic kinematics (x=0.96) at a four-momentum transfer squared, Q^2=0.67 (GeV/c)^2. The experiment was performed in fixed electron kinematics for recoil momenta from zero to 550 MeV/c. Though the measured cross section deviates by 1-2 sigma from a state-of-the-art calculation at low recoil momenta, it agrees at high recoil momenta where final state interactions (FSI) are predicted to be large.

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arXiv2001

Measurement of GEp/GMp in ep -> ep to Q2 = 5.6 GeV2

The ratio of the electric and magnetic form factors of the proton, GEp/GMp, was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the recoil polarization technique. The ratio of the form factors is directly proportional to the ratio of the transverse to longitudinal components of the polarization of the recoil proton in the elastic $\vec ep \to e\vec p$ reaction. The new data presented in this article span the range 3.5 < Q2 < 5.6 GeV2 and are well described by a linear Q2 fit. Also, the ratio QF2p/F1p reaches a constant value above Q2=2 GeV2.

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arXiv1999

The ratio of proton's electric to magnetic form factors measured by polarization transfer

The ratio of the proton's elastic electromagnetic form factors was obtained by measuring the transverse and longitudinal polarizations of recoiling protons from the elastic scattering of polarized electrons with unpolarized protons. The ratio of the electric to magnetic form factor is proportional to the ratio of the transverse to longitudinal recoil polarizations. The ratio was measured over a range of four-momentum transfer squared between 0.5 and 3.5 GeV-squared. Simultaneous measurement of transverse and longitudinal polarizations in a polarimeter provides good control of the systematic uncertainty. The results for the ratio of the proton's electric to magnetic form factors show a systematic decrease with increasing four momentum squared, indicating for the first time a marked difference in the spatial distribution of charge and magnetization currents in the proton.

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arXiv1997

A Comparison of Polarization Observables in Electron Scattering from the Proton and Deuteron

Recoil proton polarization observables were measured for both the p($\vec {\rm e}$,e$^\prime\vec{\rm p}\,$) and d($\vec {\rm e}$,e$^\prime\vec{\rm p}\,)$n reactions at two values of Q$^2$ using a newly commissioned proton Focal Plane Polarimeter at the M.I.T.-Bates Linear Accelerator Center. The hydrogen and deuterium spin-dependent observables $D_{\ell\ell}$ and $D_{{\ell}t}$, the induced polarization $P_n$ and the form factor ratio $G^p_E/G^p_M$ were measured under identical kinematics. The deuterium and hydrogen results are in good agreement with each other and with the plane-wave impulse approximation (PWIA).

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arXiv1997

Measurement of the Induced Proton Polarization P_n in the 12C(e,e'\vec{p}) Reaction

The first measurements of the induced proton polarization, P_n, for the 12C (e,e'\vec{p}) reaction are reported. The experiment was performed at quasifree kinematics for energy and momentum transfer (ω,q) \approx (294 MeV, 756 MeV/c) and sampled a recoil momentum range of 0-250 MeV/c. The induced polarization arises from final-state interactions and for these kinematics is dominated by the real part of the spin-orbit optical potential. The distorted-wave impulse approximation provides good agreement with data for the 1p_{3/2} shell. The data for the continuum suggest that both the 1s_{1/2} shell and underlying l > 1 configurations contribute.

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arXiv1996

pi+ + d --> p + p reaction between 18 and 44 MeV

A study of the reaction pi+ + d --> p + p has been performed in the energy range of 18 - 44 MeV. Total cross sections and differential cross sections at six angles have been measured at 15 energies with an energy increment of 1 - 2 MeV. This is the most systematic data set in this energy range. No structure in the energy dependence of the cross section has been observed within the accuracy of this experiment.

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