arXiv subjects

Z. Yang

Publications and source records attributed to Z. Yang.

At least 109 records · Page 6Linked to original sources

arXiv2014

Spin physics and TMD studies at A Fixed-Target ExpeRiment at the LHC (AFTER@LHC)

We report on the opportunities for spin physics and Transverse-Momentum Dependent distribution (TMD) studies at a future multi-purpose fixed-target experiment using the proton or lead ion LHC beams extracted by a bent crystal. The LHC multi-TeV beams allow for the most energetic fixed-target experiments ever performed, opening new domains of particle and nuclear physics and complementing that of collider physics, in particular that of RHIC and the EIC projects. The luminosity achievable with AFTER@LHC using typical targets would surpass that of RHIC by more that 3 orders of magnitude in a similar energy region. In unpolarised proton-proton collisions, AFTER@LHC allows for measurements of TMDs such as the Boer-Mulders quark distributions, the distribution of unpolarised and linearly polarised gluons in unpolarised protons. Using the polarisation of hydrogen and nuclear targets, one can measure transverse single-spin asymmetries of quark and gluon sensitive probes, such as, respectively, Drell-Yan pair and quarkonium production. The fixed-target mode has the advantage to allow for measurements in the target-rapidity region, namely at large x^uparrow in the polarised nucleon. Overall, this allows for an ambitious spin program which we outline here.

hep-ex↗

arXiv2014

Microwave Nonlinearity and Photoresponse of Superconducting Resonators with Columnar Defect Micro-Channels

Micro-channels of nanosized columnar tracks were planted by heavy-ion irradiation into superconducting microwave microstrip resonators that were patterned from YBa2Cu3O7-x thin films on LaAlO3 substrates. Three different ion fluences were used, producing different column densities, with each fluence having a successively greater impact on the nonlinearity of the device, as compared to a control sample. Photoresponse images made with a 638 nm rastered laser beam revealed that the channel is a location of enhanced photoresponse and a hot spot for the generation of intermodulation distortion. The microwave photoresponse technique was also advanced in this work by investigating the role of coupling strength on the distribution of photoresponse between inductive and resistive components.

cond-mat.supr-con↗

arXiv2013

p-type doping in CVD grown MoS2 using Nb

We report on the first demonstration of p-type doping in large area few-layer films of (0001)-oriented chemical vapor deposited (CVD) MoS2. Niobium was found to act as an efficient acceptor up to relatively high density in MoS2 films. For a hole density of 4 x 1020 cm-3 Hall mobility of 8.5 cm2V-1s-1 was determined, which matches well with the theoretically expected values. XRD and Raman characterization indicate that the film had good out-of-plane crystalline quality. Absorption measurements showed that the doped sample had similar characteristics to high-quality undoped samples, with a clear absorption edge at 1.8 eV. This demonstration of p-doping in large area epitaxial MoS2 could help in realizing a wide variety of electrical and opto-electronic devices based on layered metal dichalcogenides.

cond-mat.mtrl-sci↗

arXiv2013

Probe of the Solar Magnetic Field Using the "Cosmic-Ray Shadow" of the Sun

We report on a clear solar-cycle variation of the Sun's shadow in the 10 TeV cosmic-ray flux observed by the Tibet air shower array during a full solar cycle from 1996 to 2009. In order to clarify the physical implications of the observed solar cycle variation, we develop numerical simulations of the Sun's shadow, using the Potential Field Source Surface (PFSS) model and the Current Sheet Source Surface (CSSS) model for the coronal magnetic field. We find that the intensity deficit in the simulated Sun's shadow is very sensitive to the coronal magnetic field structure, and the observed variation of the Sun's shadow is better reproduced by the CSSS model. This is the first successful attempt to evaluate the coronal magnetic field models by using the Sun's shadow observed in the TeV cosmic-ray flux.

astro-ph.SR↗

arXiv2013

Collectivity evolution in the neutron-rich Pd isotopes towards the N=82 shell closure

The neutron-rich, even-even 122,124,126Pd isotopes has been studied via in-beam gamma-ray spectroscopy at the RIKEN Radioactive Isotope Beam Factory. Excited states at 499(9), 590(11), and 686(17) keV were found in the three isotopes, which we assign to the respective 2+ -> 0+ decays. In addition, a candidate for the 4+ state at 1164(20) keV was observed in 122Pd. The resulting Ex(2+) systematics are essentially similar to those of the Xe (Z=54) isotopic chain and theoretical prediction by IBM-2, suggesting no serious shell quenching in the Pd isotopes in the vicinity of N=82.

nucl-ex↗

arXiv2013

Sparsity-Aware STAP Algorithms Using $L_1$-norm Regularization For Radar Systems

This article proposes novel sparsity-aware space-time adaptive processing (SA-STAP) algorithms with $l_1$-norm regularization for airborne phased-array radar applications. The proposed SA-STAP algorithms suppose that a number of samples of the full-rank STAP data cube are not meaningful for processing and the optimal full-rank STAP filter weight vector is sparse, or nearly sparse. The core idea of the proposed method is imposing a sparse regularization ($l_1$-norm type) to the minimum variance (MV) STAP cost function. Under some reasonable assumptions, we firstly propose a $l_1$-based sample matrix inversion (SMI) to compute the optimal filter weight vector. However, it is impractical due to its matrix inversion, which requires a high computational cost when in a large phased-array antenna. Then, we devise lower complexity algorithms based on conjugate gradient (CG) techniques. A computational complexity comparison with the existing algorithms and an analysis of the proposed algorithms are conducted. Simulation results with both simulated and the Mountain Top data demonstrate that fast signal-to-interference-plus-noise-ratio (SINR) convergence and good performance of the proposed algorithms are achieved.

cs.IT↗

arXiv2013

Constraints on the Galactic Dark Matter signal from the Fermi-LAT measurement of the diffuse gamma-ray emission

We study diffuse gamma-ray emission at intermediate Galactic latitudes measured by the Fermi Large Area Telescope with the aim of searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We set both, conservative dark matter limits requiring that the dark matter signal does not exceed the observed diffuse gamma-ray emission and limits derived based on modeling the foreground astrophysical diffuse emission. Uncertainties in several parameters which characterize conventional astrophysical emission are taken into account using a profile likelihood formalism. The resulting limits impact the range of particle masses over which dark matter thermal production in the early Universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as annihilation of dark matter.

astro-ph.HE↗

arXiv2013

Search of the Earth Limb Fermi Data and Non-Galactic Center Region Fermi Data for Signs of Narrow Lines

Since the spring of 2012 there have been many papers published using Fermi LAT public data that claim evidence for narrow spectral lines coming from the region of the Galactic center. This study uses non-Galactic center Fermi-LAT data from survey mode observations, and Earth limb Fermi data to test the dark matter interpretation of this feature and better understand its origins.

astro-ph.HE↗

arXiv2013

A Monte Carlo study to measure the energy spectra of the primary cosmic-ray components at the knee using a new Tibet AS core detector array

A new hybrid experiment has been started by ASγ experiment at Tibet, China, since August 2011, which consists of a low threshold burst-detector-grid (YAC-II, Yangbajing Air shower Core array), the Tibet air-shower array (Tibet-III) and a large underground water Cherenkov muon detector (MD). In this paper, the capability of the measurement of the chemical components (proton, helium and iron) with use of the (Tibet-III+YAC-II) is investigated by means of an extensive Monte Carlo simulation in which the secondary particles are propagated through the (Tibet-III+YAC-II) array and an artificial neural network (ANN) method is applied for the primary mass separation. Our simulation shows that the new installation is powerful to study the chemical compositions, in particular, to obtain the primary energy spectrum of the major component at the knee.

astro-ph.IM↗

arXiv2012

Full Band Gap and Defects States in Solid-in-Solid Three Dimensional Phononic Crystals

A full band gap of the longitudinal mode of elastic waves centered near 2.8 MHz with a width of ~ 1 MHz has been observed in the phononic crystals made of body centered tetragonal tungsten carbide spheres imbedded in aluminum matrix. Two defects states in the band gap due to a 7-sphere defect cluster with silicon nitride spheres have also been observed. Transmitted pressure field pattern clearly shows that at the defect state frequencies the ultrasonic waves transmitted through the doped crystal are emitted from the defect cluster.

cond-mat.mtrl-sci↗

arXiv2010

Calorimetric Evidence for Nodes in the Overdoped Ba(Fe$_{0.9}$Co$_{0.1}$)$_{2}$As$_{2}$

We present low-temperature specific heat of the electron-doped Ba(Fe$_{0.9}$Co$_{0.1}$)$_{2}$As$_{2}$, which does not show any indication of an upturn down to 400 mK, the lowest measuring temperature. The lack of a Schottky-like feature at low temperatures or in magnetic fields up to 9 Tesla enables us to identify enhanced low-temperature quasiparticle excitations and to study anisotropy in the linear term of the specific heat. Our results can not be explained by a single or multiple isotropic superconducting gap, but are consistent with multi-gap superconductivity with nodes on at least one Fermi surface sheet.

cond-mat.supr-con↗

arXiv2008

Quarkonium Production Studies in CMS

When the LHC starts its operation, CMS will have a unique opportunity to study q uarkonium production in pp collisions and later in PbPb collisions. Here we report on the methods and plans for measuring the differential pT Jpsi->mu+mu- production cross section, using data to be collected in the first LHC run by the CMS detector. Furthermore we discuss the performance of the CMS detector for quarkonium measurements in PbPb collisions.

hep-ex↗

arXiv2008

Complementarity of Gamma-ray and LHC Searches for Neutralino Dark Matter in the Focus Point Region

We study the complementarity between the indirect detection of dark matter with gamma-rays in H.E.S.S. and the supersymmetry searches with ATLAS at the Large Hadron Collider in the Focus Point region within the mSUGRA framework. The sensitivity of the central telescope of the H.E.S.S. II experiment with an energy threshold of ~ 20 GeV is investigated. We show that the detection of gamma-ray fluxes of O(10^-12) cm-2s-1 with H.E.S.S. II covers a substantial part of the Focus Point region which may be more difficult for LHC experiments. Despite the presence of multi-TeV scalars, we show that LHC will be sensitive to a complementary part of this region through three body NLSP leptonic decays. This interesting complementarity between H.E.S.S. II and LHC searches is further highlighted in terms of the gluino mass and the two lightest neutralino mass difference.

astro-ph↗

arXiv2007

A GEM TPC End-Panel Pre-Prototype

A GEM TPC end panel pre-prototype was constructed for a large LC-TPC prototype to test its basic design philosophy and some of its engineering details. Its interim test results are presented.

physics.ins-det↗

arXiv2007

Chaotic Dynamics of Spin-Valve Oscillators

Recent experimental and theoretical studies on the magnetization dynamics driven by an electric current have uncovered a number of unprecedented rich dynamic phenomena. We predict an intrinsic chaotic dynamics that has not been previously anticipated. We explicitly show that the transition to chaotic dynamics occurs through a series of period doubling bifurcations. In chaotic regime, two dramatically different power spectra, one with a well-defined peak and the other with a broadly distributed noise, are identified and explained.

cond-mat.other↗

arXiv2005

Sound Wave in Hot Dense Matter Created in Heavy Ion Collision

A model to study the sound wave in hot dense matter created in heavy ion collisions by jet is proposed.The preliminary data of jet shape analysis of PHENIX Collaboration for all centralities and two directions is well explained in this model. Then the wavelength of the sound wave, the natural frequency of the hot dense matter and the speed of sound wave are estimated from the fit.

nucl-th↗

arXiv2005

Momentum Correlations for Identical Fermions

The effects of intensity interferometry (HBT), which are mainly reflected by the measured momentum correlations, have been fully discussed since 1950's. The analogous momentum correlations between identical fermions are however less argued. Besides the fermion statistics, the momentum correlations between identical fermions are also determined by some other aspects, such as coulomb interaction, spin interactions and resonances formation. In this paper, we discussed the factors that influence the momentum correlations between $Λ$'s, especially spin interaction. It is also argued that the momentum correlations between $Λ$'s are affected significantly by the yield ratio of $Σ^0/Λ$, due to the limitation of experimental measurement. The mixture of $Σ^0$'s and $Λ$s would significantly weaken the measured two-particle momentum correlations of $Λ$'s.

nucl-th↗

arXiv2005

The Observable of Lambda Polarity Caused by Source Global Angular Momentum Localizing in Peripheral Au-Au Collision at RHIC

An observable to measure the polarity of lambda that caused by source global angular momentum in peripheral AU-AU collision at RHIC is proposed.This observable's capacity of measurement is tested by Monte Carlo method.And the main factors that influence the observable are also researched.This observable will give an effective proof of the formation of deconfined matter.

nucl-th↗