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Z. Ye

Publications and source records attributed to Z. Ye.

69 records · Page 4Linked to original sources
arXiv2014

A Precision Measurement of the Neutron Twist-3 Matrix Element $d_2^n$: Probing Color Forces

Double-spin asymmetries and absolute cross sections were measured at large Bjorken $x$ (0.25 $ \le x \le $ 0.90), in both the deep-inelastic and resonance regions, by scattering longitudinally polarized electrons at beam energies of 4.7 and 5.9 GeV from a transversely and longitudinally polarized $^3$He target. In this dedicated experiment, the spin structure function $g_2$ on $^3$He was determined with precision at large $x$, and the neutron twist-three matrix element $d_2^n$ was measured at $\left< Q^2\right>$ of 3.21 and 4.32 GeV$^2$/$c^2$, with an absolute precision of about $10^{-5}$. Our results are found to be in agreement with lattice QCD calculations and resolve the disagreement found with previous data at $\left< Q^2\right> =$ 5 GeV$^2$/$c^2$. Combining $d_2^n$ and a newly extracted twist-four matrix element, $f_2^n$, the average neutron color electric and magnetic forces were extracted and found to be of opposite sign and about 30 MeV/fm in magnitude.

nucl-ex↗
arXiv2014

Hall A Annual Report 2013

Report over the experimental activities in Hall A at Thomas Jefferson National Accelerator Facility during 2013.

nucl-ex↗
arXiv2013

3D Technologies for Large Area Trackers

We describe technologies which can be developed to produce large area, low cost pixelated tracking detec- tors. These utilize wafer-scale 3D electronics and sensor technologies currently being developed in industry. This can result in fully active sensor/readout chip tiles which can be assembled into large area arrays with good yield and minimal dead area. The ability to connect though the bulk of the device can also provide better electrical performance and lower mass.

physics.ins-det↗
arXiv2013

Bucking Coil Implementation on PMT for Active Cancelling of Magnetic Field

Aerogel and water Cerenkov detectors were employed to tag kaons for a lambda hypernuclear spectroscopic experiment which used the (e,e'K+) reaction in experimental Hall C at Jefferson Lab (JLab E05-115). Fringe fields from the kaon spectrometer magnet yielded ~5 Gauss at the photomultiplier tubes (PMT) for these detectors which could not be easily shielded. As this field results in a lowered kaon detection efficiency, we implemented a bucking coil on each photomultiplier tubes to actively cancel this magnetic field, thus maximizing kaon detection efficiency.

physics.ins-det↗
arXiv2013

The HERMES Recoil Detector

For the final running period of HERA, a recoil detector was installed at the HERMES experiment to improve measurements of hard exclusive processes in charged-lepton nucleon scattering. Here, deeply virtual Compton scattering is of particular interest as this process provides constraints on generalised parton distributions that give access to the total angular momenta of quarks within the nucleon. The HERMES recoil detector was designed to improve the selection of exclusive events by a direct measurement of the four-momentum of the recoiling particle. It consisted of three components: two layers of double-sided silicon strip sensors inside the HERA beam vacuum, a two-barrel scintillating fibre tracker, and a photon detector. All sub-detectors were located inside a solenoidal magnetic field with an integrated field strength of 1 T. The recoil detector was installed in late 2005. After the commissioning of all components was finished in September 2006, it operated stably until the end of data taking at HERA end of June 2007. The present paper gives a brief overview of the physics processes of interest and the general detector design. The recoil detector components, their calibration, the momentum reconstruction of charged particles, and the event selection are described in detail. The paper closes with a summary of the performance of the detection system.

physics.ins-det↗
arXiv2013

Hall A Annual Report 2012

Report over the experimental activities in Hall A at Thomas Jefferson National Accelerator Facility.

physics.ins-det↗
arXiv2013

Direct Measurements of the Lifetime of Heavy Hypernuclei

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.

nucl-ex↗
arXiv2011

High Precision Measurement of the Proton Elastic Form Factor Ratio $μ_pG_E/G_M$ at low $Q^2$

We report a new, high-precision measurement of the proton elastic form factor ratio μ_p G_E/G_M for the four-momentum transfer squared Q^2 = 0.3-0.7 (GeV/c)^2. The measurement was performed at Jefferson Lab (JLab) in Hall A using recoil polarimetry. With a total uncertainty of approximately 1%, the new data clearly show that the deviation of the ratio μ_p G_E/G_M from unity observed in previous polarization measurements at high Q^2 continues down to the lowest Q^2 value of this measurement. The updated global fit that includes the new results yields an electric (magnetic) form factor roughly 2% smaller (1% larger) than the previous global fit in this Q^2 range. We obtain new extractions of the proton electric and magnetic radii, which are ^(1/2)=0.875+/-0.010 fm and ^(1/2)=0.867+/-0.020 fm. The charge radius is consistent with other recent extractions based on the electron-proton interaction, including the atomic hydrogen Lamb shift measurements, which suggests a missing correction in the comparison of measurements of the proton charge radius using electron probes and the recent extraction from the muonic hydrogen Lamb shift.

nucl-ex↗
arXiv2005

Can the total angular momentum of u-quarks in the nucleon be accessed at HERMES?

We investigate the possibility to acquire information on the generalized parton distribution E and, through a model for E, also on the u-quark total angular momentum J_u by studying deeply virtual Compton scattering and hard exclusive rho0 electroproduction on a transversely polarized hydrogen target at HERMES. It is found that a change in J_u from zero to 0.4 corresponds to a 4σ(2σ) difference in the calculated transverse target-spin asymmetry in deeply virtual Compton scattering (rho0 electroproduction), where σis the total experimental uncertainty.

hep-ph↗
arXiv2003

Comment on "Total Negative Refraction in Real Crystals for Ballistic Electrons and Light" (Phys. Rev. Lett. 91, 157404 (2003))

Recently, Zhang et al. (Phys. Rev. Lett. 91, 157404 (2003)) have demonstrated that an amphoteric refraction, i. e. both positive and negative refraction, may prevail at the interface of two uniaxial anisotropic crystals when their optical axes are in different directions. The authors subsequently made a correspondence between such a refraction with the negative refraction expected for Left Handed Materials (LHMs). Here we comment that the amphoteric refraction can be observed even with one uniaxial crystal, and the refraction is not related to the negative refraction expected for the much debated LHM. Rather, the phenomenon is a natural result of anisotropic media.

cond-mat↗
arXiv2003

Band gap or negative refraction effects?

By a rigorous numerical simulation based on the standard multiple scattering theory, we investigate the optical transmission in photonic crystal structures, formed by dielectric cylinders embedded in parallel in a uniform medium. In contrast to previous conjectures, the results indicate that the imaging effect which has been interpreted as a signature of the negative refractive effects is caused by a tunnelling effect in the presence of partial band gaps. There is no need for an all-angle negative refraction effect to understand some peculiar phenomena of photonic crystals.

cond-mat↗
arXiv2003

Electronic localization in two dimensions

By an improved scaling analysis, we suggest that there may appear two possibilities concerning the electronic localization in two dimensional random media. The first is that all electronic states are localized in two dimensions, as already conjectured previously. The second possibility is that the electronic behaviors in two and three dimensional random systems are similar, in agreement with a recent calculation based on a direct calculation of the conductance with the use of the Kubo formula. In this case, non-localized states is possible in two dimensions, and possess some peculiar properties. A few predictions are proposed. Moreover, the present analysis seems accommodating results from previous scaling analysis.

cond-mat.dis-nn↗
arXiv2002

Water wave propagation and scattering over topographical bottoms

Here I present a general formulation of water wave propagation and scattering over topographical bottoms. A simple equation is found and is compared with existing theories. As an application, the theory is extended to the case of water waves in a column with many cylindrical steps.

physics.flu-dyn↗