arXiv subjects

D. Zhang

Publications and source records attributed to D. Zhang.

72 records · Page 4Linked to original sources

arXiv2013

Magnetoelectric coupling in the paramagnetic state of a metal-organic framework

Although the magnetoelectric effects - the mutual control of electric polarization by magnetic fields and magnetism by electric fields, have been intensively studied in a large number of inorganic compounds and heterostructures, they have been rarely observed in organic materials. Here we demonstrate magnetoelectric coupling in a metal-organic framework [(CH3)2NH2]Mn(HCOO)3 which exhibits an order-disorder type of ferroelectricity below 185 K. The magnetic susceptibility starts to deviate from the Curie-Weiss law at the paraelectric-ferroelectric transition temperature, suggesting an enhancement of short-range magnetic correlation in the ferroelectric state. Electron spin resonance study further confirms that the magnetic state indeed changes following the ferroelectric phase transition. Inversely, the ferroelectric polarization can be improved by applying high magnetic fields. We interpret the magnetoelectric coupling in the paramagnetic state in the metal-organic framework as a consequence of the magnetoelastic effect that modifies both the superexchange interaction and the hydrogen bonding.

cond-mat.mtrl-sci↗

arXiv2013

Emerging understanding of the ΔI = 1/2 Rule from Lattice QCD

There has been much speculation as to the origin of the ΔI = 1/2 rule (Re A_0/Re A_2 \simeq 22.5). We find that the two dominant contributions to the ΔI=3/2, K \to ππ correlation functions have opposite signs leading to a significant cancellation. This partial cancellation occurs in our computation of Re A_2 with physical quark masses and kinematics (where we reproduce the experimental value of A_2) and also for heavier pions at threshold. For Re A_0, although we do not have results at physical kinematics, we do have results for pions at zero-momentum with m_π \simeq 420 MeV (Re A_0/Re A_2=9.1(2.1)) and m_π \simeq 330 MeV (Re A_0/Re A_2=12.0(1.7)). The contributions which partially cancel in Re A_2 are also the largest ones in Re A_0, but now they have the same sign and so enhance this amplitude. The emerging explanation of the ΔI=1/2 rule is a combination of the perturbative running to scales of O(2 GeV), a relative suppression of Re A_2 through the cancellation of the two dominant contributions and the corresponding enhancement of Re A_0. QCD and EWP penguin operators make only very small contributions at such scales.

hep-lat↗

arXiv2012

Magnetically induced spin reorientation on the surface of a topological insulator (a surface magnetic topological insulator MBE film)

The surface of topological insulators is proposed as a promising platform for spintronics and quantum information applications. In particular, when time- reversal symmetry is broken, topological surface states are expected to exhibit a wide range of exotic spin phenomena for potential implementation in electronics. Such devices need to be fabricated using nanoscale artificial thin films. It is of critical importance to study the spin behavior of artificial topological MBE thin films associated with magnetic dopants, and with regards to quantum size effects related to surface-to-surface tunneling as well as experimentally isolate time-reversal breaking from non-intrinsic surface electronic gaps. Here we present observation of the first (and thorough) study of magnetically induced spin reorientation phenomena on the surface of a topological insulator. Our results reveal dramatic rearrangements of the spin configuration upon magnetic doping contrasted with chemically similar nonmagnetic doping as well as with quantum tunneling phenomena in ultra-thin high quality MBE films. While we observe that the spin rearrangement induced by quantum tunneling occurs in a time-reversal invariant fashion, we present critical and systematic observation of an out-of-plane spin texture evolution correlated with magnetic interactions, which breaks time-reversal symmetry, demonstrating microscopic TRB at a Kramers' point on the surface.

cond-mat.mes-hall↗

arXiv2012

Tevatron Beam Position Monitor Upgrade

This paper describes the development of a digital-based Beam Position System which was designed, developed, and adapted for the Tevatron during Collider Run II.

physics.acc-ph↗

arXiv2012

High Resolution BPM Upgrade for the ATF Damping Ring at KEK

A beam position monitor (BPM) upgrade at the KEK Accelerator Test Facility (ATF) damping ring has been accomplished, carried out by a KEK/FNAL/SLAC collaboration under the umbrella of the global ILC R&D effort. The upgrade consists of a high resolution, high reproducibility read-out system, based on analog and processing, and also implements a new automatic gain error correction schema. The technical concept and realization as well as results of beam studies are presented.

physics.acc-ph↗

arXiv2012

The MINER$ν$A Data Acquisition System and Infrastructure

MINER$ν$A (Main INjector ExpeRiment $ν$-A) is a new few-GeV neutrino cross section experiment that began taking data in the FNAL NuMI (Fermi National Accelerator Laboratory Neutrinos at the Main Injector) beam-line in March of 2010. MINER$ν$A employs a fine-grained scintillator detector capable of complete kinematic characterization of neutrino interactions. This paper describes the MINER$ν$A data acquisition system (DAQ) including the read-out electronics, software, and computing architecture.

physics.ins-det↗

arXiv2012

Arachne - A web-based event viewer for MINERvA

Neutrino interaction events in the MINERvA detector are visually represented with a web-based tool called Arachne. Data are retrieved from a central server via AJAX, and client-side JavaScript draws images into the user's browser window using the draft HTML 5 standard. These technologies allow neutrino interactions to be viewed by anyone with a web browser, allowing for easy hand-scanning of particle interactions. Arachne has been used in MINERvA to evaluate neutrino data in a prototype detector, to tune reconstruction algorithms, and for public outreach and education.

hep-ex↗

arXiv2011

Black Hole Mass Estimates Based on CIV are Consistent with Those Based on the Balmer Lines

Using a sample of high-redshift lensed quasars from the CASTLES project with observed-frame ultraviolet or optical and near-infrared spectra, we have searched for possible biases between supermassive black hole (BH) mass estimates based on the CIV, Halpha and Hbeta broad emission lines. Our sample is based upon that of Greene, Peng & Ludwig, expanded with new near-IR spectroscopic observations, consistently analyzed high S/N optical spectra, and consistent continuum luminosity estimates at 5100A. We find that BH mass estimates based on the FWHM of CIV show a systematic offset with respect to those obtained from the line dispersion, sigma_l, of the same emission line, but not with those obtained from the FWHM of Halpha and Hbeta. The magnitude of the offset depends on the treatment of the HeII and FeII emission blended with CIV, but there is little scatter for any fixed measurement prescription. While we otherwise find no systematic offsets between CIV and Balmer line mass estimates, we do find that the residuals between them are strongly correlated with the ratio of the UV and optical continuum luminosities. Removing this dependency reduces the scatter between the UV- and optical-based BH mass estimates by a factor of approximately 2, from roughly 0.35 to 0.18 dex. The dispersion is smallest when comparing the CIV sigma_l mass estimate, after removing the offset from the FWHM estimates, and either Balmer line mass estimate. The correlation with the continuum slope is likely due to a combination of reddening, host contamination and object-dependent SED shapes. When we add additional heterogeneous measurements from the literature, the results are unchanged.

astro-ph.CO↗

arXiv2011

Harry Potter's Cloak

The magic "Harry Potter's cloak" has been the dream of human beings for really long time. Recently, transformation optics inspired from the advent of metamaterials offers great versatility for manipulating wave propagation at will to create amazing illusion effects. In the present work, we proposed a novel transformation recipe, in which the cloaking shell somehow behaves like a "cloaking lens", to provide almost all desired features one can expect for a real magic cloak. The most exciting feature of the current recipe is that an object with arbitrary characteristics (e.g., size, shape or material properties) can be invisibilized perfectly with positive-index materials, which significantly benefits the practical realization of a broad-band cloaking device fabricated with existing materials. Moreover, the one concealed in the hidden region is able to undistortedly communicate with the surrounding world, while the lens-like cloaking shell will protect the cloaked source/sensor from being traced back by outside detectors by creating a virtual image.

physics.class-ph↗

arXiv2010

Review of Experimental Studies of $ψ(3770)$ non-$D\bar D$ Decays

We review the progress on experimental studies of the non-$D\bar D$ decays of the $ψ(3770)$ resonance. With the world average of the observed cross sections for $D\bar D$ production measured at 3.773 GeV by the MARK-I, MARK-II, BES and CLEO Collaborations, combined together with the cross section for $ψ(3770)$ production at its peak as well as initial state radiative correction factor, we find that the non-$D\bar D$ branching fraction of $ψ(3770)$ decays is $B[ψ(3770)\to {\rm non}-D\bar D]=(19.8\pm 1.8 \pm 5.6)%$, which is consistent within error with $B[ψ(3770)\to {\rm non}-D\bar D]=(14.7\pm 3.2)%$ measured previously by the BES Collaboration. In addition, a global amplitude analysis of the cross sections for $e^+e^- \to {\rm LH}$ (LH= light hadron) measured by the CLEO Collaboration shows that the light hadron branching fraction of $ψ(3770)$ decays can be as large as about 11%. Combing the totally measured hadronic and electromegnatic transition rate together with the light hadron branching fraction in the decays of $ψ(3770)$ yields the total non-$D\bar D$ branching fraction in the decays of $ψ(3770)$ to be about 13%.

hep-ex↗

arXiv2010

Are there the VP couplings in the psi(3770) non-charmed decays hidden behind the current experiment measurements?

A global analysis of the full amplitudes for $e^+e^- \to$ VP (Vector and Pseudoscalar) channels at $\sqrt{s}$ =3.773 GeV and 3.670 GeV, which were measured by the CLEO-c Collaboration, shows that those measurements are essentially nontrivial for searching for the $ψ(3770)$ non-$D\bar D$ decays. Unlike the nearly negative verdict on the $ψ(3770)$ strong decays to the VP channels in the original analysis of the CLEO-c data, there exist some unusual solutions that predict the remarkable strength of SU(3) symmetry VP decay of $ψ(3770)$ resonance, which give some clue to understand the mechanism of $ψ(3770)$ non-$D\bar D$ decays and to reexplain the well-known $ρ-π$ puzzle in the J/$ψ$ and $ψ(3686)$ decays.

hep-ex↗

arXiv2006

Study on N Omega-bar systems in a chiral quark model

The N Omega-bar systems with spin S=1 and S=2 are dynamically investigated within the framework of the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving the resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a good description of the energies of the baryon ground states, the binding energy of deuteron, and the experimental data of the nucleon-nucleon (NN) and nucleon-hyperon (NY) scattering processes. The results show that N Omega-bar states with spin S=1 and S=2 can be bound both in the chiral SU(3) and extended chiral SU(3) quark models, and the binding energies are about 28-59 MeV. When the annihilation effect is considered, the binding energies increase to about 37-130 MeV, which indicates the annihilation effect plays a relatively important role in forming an N Omega-bar bound state. At the same time, the N Omega-bar elastic scattering processes are also studied. The S, P, D partial wave phase shifts and the total cross sections of S=1 and S=2 channels have been calculated by solving the RGM equation for scattering problems.

nucl-th↗

arXiv2006

A Monte Carlo Generator for Full Simulation of e+e- to hadrons Cross section Scan Experiment

A generator with $α^2$ order radiative correction effects, including both the initial state radiative corrections and the photon vacuum polarization corrections, is built for the full simulation of $e^+e^- \to hadrons $ in cross section scan experiment in the quarkonium energy region. The contributions from the hadron production structures including the resonances of $1^{--}$ quarkonium families and the light hadrons spectrum below 2 GeV as well as the QED continuum hadron spectrum are all taken into account in the event generation. It was employed successfully to determine the detection efficiency for selection of the events of $e^+e^-\to hadrons$ from the data taken in the energy region from 3.650 GeV to 3.872 GeV covering both the $ψ(3686)$ and $ψ(3770)$ resonances in BES experiment. The generator reproduces the properties of hadronic event production and inclusive decays well.

hep-ph↗

arXiv2005

Coupled-channels study of Lambda K and Sigma K states in the chiral SU(3) quark model

The $S$-wave $ΛK$ and $ΣK$ states with isospin $I=1/2$ are dynamically investigated within the framework of the chiral SU(3) quark model by solving a resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a good description of the energies of the baryon ground states, the binding energy of the deuteron, and the experimental data of the nucleon-nucleon ($NN$) and nucleon-hyperon ($NY$) scattering. Assumed not to give important contributions in the scattering processes, the s-channel quark-antiquark ($q\bar q$) annihilation interactions are not included as a first step. The results show a strong attraction between $Σ$ and $K$, which consequently results in a $ΣK$ quasi-bound state with about 17 MeV binding energy, unlike the case of $ΛK$ which is unbound. When the channel coupling of $ΛK$ and $ΣK$ is considered, a sharp resonance state near 1670 MeV with spin-parity $J^P=1/2^-$ is found. The narrow gap of the $ΛK$ and $ΣK$ thresholds, the strong attraction between $Σ$ and $K$, and the sizeable off-diagonal matrix elements of $ΛK$ and $ΣK$ are responsible for the appearance of this resonance.

hep-ph↗

arXiv2005

Further study on 5q configuration states in the chiral SU(3) quark model

The structure of the $5q$ configuration states with strangeness ${\cal{S}}=+1$ is further studied in the chiral SU(3) quark model based on our previous work. We calculate the energies of fifteen low configurations of the $5q$ system, four lowest configurations of $J^π={1/2}^-$ with $4q$ partition $[4]_{orb}(0s^4)[31]^{σf}$, four of $J^π={1/2}^+$ with $4q$ partition $[31]_{orb}(0s^30p)[4]^{σf}$ and seven of $J^π={1/2}^+$ with $4q$ partition $[4]_{orb}(0s^30p)[31]^{σf}$. Some modifications are made in this further study, i.e., the orbital wave function is extended as an expansion of 4 different size harmonic oscillator forms; three various forms (quadratic, linear and error function form) of the color confinement potential are considered; the states with $4q$ partition $[4]_{orb}(0s^30p)[31]^{σf}$ are added, which are unnegligible in the $J^π={1/2}^+$ case and were not considered in our previous paper, further the mixing between configurations $[31]_{orb}(0s^30p)[4]^{σf}$ and $[4]_{orb}(0s^30p)[31]^{σf}$ is also investigated. The results show that the T=0 state is still always the lowest one for both $J^π={1/2}^-$ and $J^π={1/2}^+$ states, and $J^π={1/2}^-, T=0$ state is always lower than that of $J^π={1/2}^+$. All of these modifications can only offer several tens to hundred MeV effect, and the theoretical value of the lowest state is still about 245 MeV higher than the experimental mass of $Θ^+$. It seems to be difficult to get the calculated mass close to the observed one with the reasonable parameters in the framework of the chiral SU(3) quark model when the model space is chosen as a $5q$ cluster.

nucl-th↗

arXiv2003

The DZERO Level 3 Data Acquistion System

The DZERO experiment located at Fermilab has recently started RunII with an upgraded detector. The RunII physics program requires the Data Acquisition to readout the detector at a rate of 1 KHz. Events fragments, totaling 250 KB, are readout from approximately 60 front end crates and sent to a particular farm node for Level 3 Trigger processing. A scalable system, capable of complex event routing, has been designed and implemented based on commodity components: VMIC 7750 Single Board Computers for readout, a Cisco 6509 switch for data flow, and close to 100 Linux-based PCs for high-level event filtering.

physics.ins-det↗

arXiv2003

The DZERO DAQ/Online Monitoring System and Applications, Including an Active Auto-recovery Tool

The DZERO experiment, located at the Fermi National Accelerator Laboratory, has recently started the Run 2 physics program. The detector upgrade included a new Data Acquisition/Level 3 Trigger system. Part of the design for the DAQ/Trigger system was a new monitoring infrastructure. The monitoring was designed to satisfy real-time requirements with 1-second resolution as well as non-real-time data. It was also designed to handle a large number of displays without putting undue load on the sources of monitoring information. The resulting protocol is based on XML, is easily extensible, and has spawned a large number of displays, clients, and other applications. It is also one of the few sources of detector performance available outside the Online System's security wall. A tool, based on this system, which provides for auto-recovery of DAQ errors, has been designed. This talk will include a description of the DZERO DAQ/Online monitor server, based on the ACE framework, the protocol, the auto-recovery tool, and several of the unique displays which include an ORACLE-based archiver and numerous GUIs.

physics.ins-det↗

arXiv1998

Quasielastic 12C(e,e'p) Reaction at High Momentum Transfer

We measured the 12C(e,e'p) cross section as a function of missing energy in parallel kinematics for (q,w) = (970 MeV/c, 330 MeV) and (990 MeV/c, 475 MeV). At w=475 MeV, at the maximum of the quasielastic peak, there is a large continuum (E_m > 50 MeV) cross section extending out to the deepest missing energy measured, amounting to almost 50% of the measured cross section. The ratio of data to DWIA calculation is 0.4 for both the p- and s-shells. At w=330 MeV, well below the maximum of the quasielastic peak, the continuum cross section is much smaller and the ratio of data to DWIA calculation is 0.85 for the p-shell and 1.0 for the s-shell. We infer that one or more mechanisms that increase with $ω$ transform some of the single-nucleon-knockout into multinucleon knockout, decreasing the valence knockout cross section and increasing the continuum cross section.

nucl-ex↗