arXiv subjects

Min He

Publications and source records attributed to Min He.

At least 91 records · Page 5Linked to original sources

arXiv2017

The LAMOST Complete Spectroscopic Survey of Pointing Area (LaCoSSPAr) in the Southern Galactic Cap I. The Spectroscopic Redshift Catalog

We present a spectroscopic redshift catalog from the LAMOST Complete Spectroscopic Survey of Pointing Area (LaCoSSPAr) in the Southern Galactic Cap (SGC), which is designed to observe all sources (Galactic and extra-galactic) by using repeating observations with a limiting magnitude of $r=18.1~mag$ in two $20~deg^2$ fields. The project is mainly focusing on the completeness of LAMOST ExtraGAlactic Surveys (LEGAS) in the SGC, the deficiencies of source selection methods and the basic performance parameters of LAMOST telescope. In both fields, more than 95% of galaxies have been observed. A post-processing has been applied to LAMOST 1D spectrum to remove the majority of remaining sky background residuals. More than 10,000 spectra have been visually inspected to measure the redshift by using combinations of different emission/absorption features with uncertainty of $σ_{z}/(1+z)<0.001$. In total, there are 1528 redshifts (623 absorption and 905 emission line galaxies) in Field A and 1570 redshifts (569 absorption and 1001 emission line galaxies) in Field B have been measured. The results show that it is possible to derive redshift from low SNR galaxies with our post-processing and visual inspection. Our analysis also indicates that up to 1/4 of the input targets for a typical extra-galactic spectroscopic survey might be unreliable. The multi-wavelength data analysis shows that the majority of mid-infrared-detected absorption (91.3%) and emission line galaxies (93.3%) can be well separated by an empirical criterion of $W2-W3=2.4$. Meanwhile, a fainter sequence paralleled to the main population of galaxies has been witnessed both in $M_r$/$W2-W3$ and $M_*$/$W2-W3$ diagrams, which could be the population of luminous dwarf galaxies but contaminated by the edge-on/highly inclined galaxies ($\sim30\%$).

astro-ph.GA↗

arXiv2017

Molecular Gas and Star-Formation In Low Surface Brightness Galaxies

We have obtained CO(J=2-1) spectra of nine face-on low surface brightness galaxies(LSBGs) using the JCMT 15-meter telescope and observed Ha images using the 2.16-meter telescope of NAOC. As no CO has been detected, only upper limits on the H2 masses are given. The upper limits of total molecular hydrogen masses are about (1.2-82.4) x 10^7 Msun. Their star formation rates are mainly lower than 0.4 Msun/yr and star formation efficiencies are lower than 1.364 x 10^10 /yr. Our results show that the absence of molecular gas content is the direct reason for the low star formation rate. The low star formation efficiency probably resulted from the low efficiency of HI gas transforming to H2 gas.

astro-ph.GA↗

arXiv2017

Gluo-dissociation of Heavy Quarkonium in the Quark-Gluon Plasma Revisited

Using an effective Hamiltonian derived from the QCD multipole expansion, we calculate the cross sections of gluo-dissociation of heavy quarkonia in the quark-gluon plasma, by including both the chromo-electric dipole ($E_1$) as well as the chromo-magnetic dipole ($M_1$) transition mechanisms. While the former allows to reproduce the results from operator-product-expansion calculations in the Coulomb approximation, the latter as a novel contribution is shown to be significant at low energies close to the threshold. Using thus obtained cross sections, we further carry out a full calculation of the gluo-dissociation rates for various charmonia and bottomonia within a non-relativitic in-medium potential model. The $M_1$ contribution turns out to be most prominent for the $J/ψ$ and accounts for $\sim 10\%-25\%$ of the total ($E1+M1$) dissociation rate at temperatures close to the transition temperature.

nucl-th↗

arXiv2017

In-Medium Bottomonium Production in Heavy-Ion Collisions

We study bottomonium production in heavy-ion collisions using a transport model which utilizes kinetic-rate and Boltzmann equations to calculate the energy, centrality and transverse-momentum ($p_T$) dependence of the yields. Both gluo-dissociation and inelastic parton-induced break-up including interference effects are improved over previous work by using in-medium binding energies from a thermodynamic $T$-matrix approach. A coalescence model with bottom-quark spectra from Langevin simulations is implemented to account for thermal off-equilibrium effects in the $p_T$-spectra of the regeneration contribution. We also update the equation of state for the bulk medium by extracting it from lattice-QCD results. A systematic analysis of bottomonium observables is conducted in comparison to RHIC and LHC data. In particular, the off-equilibrium bottom-quark spectra are found to play an important role in the bottomonium $p_T$ spectra.

hep-ph↗

arXiv2017

Dark Photon Search at A Circular $e^+e^-$ Collider

One of the interesting portals linking a dark sector and the standard model (SM) is the kinetic mixing between the SM $U(1)_Y$ field with a new dark photon $A'$ from a $U(1)_{A'}$ gauge interaction. Stringent limits have been obtained for the kinetic mixing parameter $ε$ through various processes. In this work, we study the possibility of searching for a dark photon interaction at a circular $e^+e^-$ collider through the process $e^+ e^-\to γA^{\prime *} \to γμ^+μ^-$. We find that the constraint on $ε^2$ for dark photon mass in the few tens of GeV range, assuming that the $μ^+μ^-$ invariant mass can be measured to an accuracy of $0.5\%m_{A'}$, can be better than $3\times 10^{-6}$ for the proposed CEPC with a ten-year running at 3$σ$ (statistic) level, and better than $2\times 10^{-6}$ for FCC-ee with even just one-year running at $\sqrt{s} = 240$ GeV, better than the LHC and other facilities can do in a similar dark photon mass range. For FCC-ee, running at $\sqrt{s}=160$ GeV, the constraint can be even better.

hep-ph↗

arXiv2017

Deterministic Role of Concentration Surplus of Cation Vacancy over Anion Vacancy in Bipolar Memristive NiO

Migration of oxygen vacancies has been proposed to play an important role in the bipolar memristive behaviors since oxygen vacancies can directly determine the local conductivity in many systems. However, a recent theoretical work demonstrated that both migration of oxygen vacancies and coexistence of cation and anion vacancies are crucial to the occurrence of bipolar memristive switching, normally observed in the small-sized NiO. So far, experimental work addressing this issue is still lacking. In this work, with conductive atomic force microscope and combined scanning transmission electron microscopy & electron energy loss spectroscopy, we reveal that concentration surplus of Ni vacancy over O vacancy determines the bipolar memristive switching of NiO films. Our work supports the dual-defects-based model, which is of fundamental importance for understanding the memristor mechanisms beyond the well-established oxygen-vacancy-based model. Moreover, this work provides a methodology to investigate the effect of dual defects on memristive behaviors.

cond-mat.mtrl-sci↗

arXiv2016

Insulating phase at low temperature in ultrathin La0.8Sr0.2MnO3 films

Metal-insulator transition is observed in the La0.8Sr0.2MnO3 thin films with thickness larger than 5 unit cells. Insulating phase at lower temperature appeared in the ultrathin films with thickness ranging from 6 unit cells to 10 unit cells and it is found that the Mott variable range hopping conduction dominates in this insulating phase at low temperature with a decrease of localization length in thinner films. A deficiency of oxygen content and a resulted decrease of the Mn valence have been observed in the ultrathin films with thickness smaller than or equal to 10 unit cells by studying the aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy of the films. These results suggest that the existence of the oxygen vacancies in thinner films suppresses the double-exchange mechanism and contributes to the enhancement of disorder, leading to a decrease of the Curie temperature and the low temperature insulating phase in the ultrathin films. In addition, the suppression of the magnetic properties in thinner films indicates stronger disorder of magnetic moments, which is considered to be the reason for this decrease of the localization length.

cond-mat.mtrl-sci↗

arXiv2016

A $γγ$ Collider for the 750 GeV Resonant State

Recent data collected by ATLAS and CMS at 13 TeV collision energy of the LHC indicate the existence of a new resonant state $ϕ$ with a mass of 750 GeV decaying into two photons $γγ$. The properties of $ϕ$ should be studied further at the LHC and also future colliders. Since only $ϕ\to γγ$ decay channel has been measured, one of the best ways to extract more information about $ϕ$ is to use a $γγ$ collider to produce $ϕ$ at the resonant energy. In this work we show how a $γγ$ collider helps to verify the existence of $ϕ$ and to provide some of the most important information about the properties of $ϕ$, such as branching fractions of $ϕ\to V_1V_2$. Here $V_i$ can be $γ$, $Z$, or $W^\pm$. We also show that by studying angular distributions of the final $γ$'s in $γγ\to ϕ\to γγ$, one can obtain crucial information about whether this state is a spin-0 or a spin-2 state.

hep-ph↗

arXiv2015

Physics perspectives of heavy-ion collisions at very high energy

Heavy-ion collisions at very high colliding energies are expected to produce a quark-gluon plasma (QGP) at the highest temperature obtainable in a laboratory setting. Experimental studies of these reactions can provide an unprecedented range of information on properties of the QGP at high temperatures. We report theoretical investigations of the physics perspectives of heavy-ion collisions at a future high-energy collider. These include initial parton production, collective expansion of the dense medium, jet quenching, heavy-quark transport, dissociation and regeneration of quarkonia, photon and dilepton production. We illustrate the potential of future experimental studies of the initial particle production and formation of QGP at the highest temperature to provide constraints on properties of strongly interaction matter.

nucl-th↗

arXiv2015

Some Predictions of Diquark Model for Hidden Charm Pentaquark Discovered at the LHCb

The LHCb has discovered two new states with preferred $J^P$ quantum numbers $3/2^-$ and $5/2^+$ from $Λ_b$ decays. These new states can be interpreted as hidden charm pentaquarks. It has been argued that the main features of these pentaquarks can be described by diquark model. The diquark model predicts that the $3/2^-$ and $5/2^+$ are in two separate octet multiplets of flavor $SU(3)$ and there is also an additional decuplet pentaquark multiplet. Finding the states in these multiplets can provide crucial evidence for this model. The weak decays of b-baryon to a light meson and a pentaquark can have Cabibbo allowed and suppressed decay channels. We find that in the $SU(3)$ limit, for $U$-spin related decay modes the ratio of the decay rates of Cabibbo suppressed to Cabibbo allowed decay channels is given by $|V_{cd}|^2/|V_{cs}|^2$. There are also other testable relations for b-baryon weak decays into a pentaquark and a light pseudoscalar. These relations can be used as tests for the diquark model for pentaquark.

hep-ph↗

arXiv2015

CP Violating Polarization Asymmetry in Charmless Two-Body Decays of Beauty Baryons

Several baryons containing a heavy b-quark, the b-baryons, have been discovered. The charmless two-body decays of b-baryons can provide a new platform for CP violating studies in a similar way as charmless two-body decays of B-meson. In b-baryon decays there are new CP violating observable related to baryon polarization. We show that in the flavor $SU(3)$ limit there exist relations involve different combinations of the decay amplitudes compared with those in CP violating rate asymmetry. These new relations therefore provide interesting tests for the mechanism of CP in the standard model (SM) and flavor $SU(3)$ symmetry. Future data from LHCb can test these relations.

hep-ph↗

arXiv2015

Longitudinal wave function control in single quantum dots with an applied magnetic field

Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots.

cond-mat.mes-hall↗

arXiv2014

Modifications of Heavy-Flavor Spectra in $\sqrt{s_{\rm NN}}=62.4~{\rm GeV}$ Au-Au Collisions

We calculate open heavy-flavor (HF) production in Au+Au collisions at $\sqrt{s_{\rm NN}}$=62.4 GeV utilizing a nonperturbative transport approach as previously applied in nuclear collisions at top RHIC and LHC energies. The effects of hot QCD matter are treated in a strong-coupling framework, by implementing heavy-quark diffusion, hadronization and heavy-flavor meson diffusion within a hydrodynamic background evolution. Since in our approach the heavy-flavor coupling to the medium is strongest in the pseudo-critical region, it is of interest to test its consequences at lower collision energies where the sensitivity to this region should be enhanced relative to the hotter (early) fireball temperatures reached at top RHIC and LHC energies. We find that the suppression and flow pattern of the non-photonic electrons from heavy-flavor decays at 62.4 GeV emerges from an intricate interplay of thermalization and initial-state effects, in particular a Cronin enhancement which is known to become more pronounced toward lower collision energies.

nucl-th↗

arXiv2014

Pseudo-Critical Enhancement of Thermal Photons in Relativistic Heavy-Ion Collisions

We compute the spectra and elliptic flow of thermal photons emitted in ultrarelativistic heavy-ion collisions (URHICs) at RHIC and LHC. The thermal emission rates are taken from complete leading-order rates for the QGP and hadronic many-body calculations including baryons and antibaryons, as well as meson-exchange reactions (including Bremsstrahlung). We first update previous thermal fireball calculations by implementing a lattice-QCD based equation of state and extend them to compare to recent LHC data. We then scrutinize the space-time evolution of Au-Au collisions at RHIC by employing an ideal hydrodynamic model constrained by bulk- and multistrange-hadron spectra and elliptic flow, including a non-vanishing initial flow. We systematically compare the evolutions of temperature, radial flow, azimuthal anisotropy and four-volume, and exhibit the temperature profile of thermal photon radiation. Based on these insights, we put forward a scenario with a "pseudo-critical enhancement" of thermal emission rates, and investigate its impact on RHIC and LHC direct photon data.

nucl-th↗

arXiv2014

Heavy Flavor at the Large Hadron Collider in a Strong Coupling Approach

Employing nonperturbative transport coefficients for heavy-flavor (HF) diffusion through quark-gluon plasma (QGP), hadronization and hadronic matter, we compute $D$- and $B$-meson observables in Pb+Pb ($\sqrt{s}$=2.76\,TeV) collisions at the LHC. Elastic heavy-quark scattering in the QGP is evaluated within a thermodynamic $T$-matrix approach, generating resonances close to the critical temperature which are utilized for recombination into $D$ and $B$ mesons, followed by hadronic diffusion using effective hadronic scattering amplitudes. The transport coefficients are implemented via Fokker-Planck Langevin dynamics within hydrodynamic simulations of the bulk medium in nuclear collisions. The hydro expansion is quantitatively constrained by transverse-momentum spectra and elliptic flow of light hadrons. Our approach thus incorporates the paradigm of a strongly coupled medium in both bulk and HF dynamics throughout the thermal evolution of the system.

nucl-th↗

arXiv2013

Relativistic Langevin Dynamics in Expanding Media

We study the consequences of different realizations of diffusion processes in relativistic Langevin simulations. We elaborate on the Ito-Stratonovich dilemma by showing how microscopically calculated transport coefficients as obtained from a Boltzmann/Fokker-Planck equation can be implemented to lead to an unambiguous realization of the Langevin process. Pertinent examples within the pre-point (Ito) and post-point (Hänggi-Klimontovich) Langevin prescriptions are worked out explicitly. Deviations from this implementation are shown to generate variants of the Boltzmann distribution as the stationary (equilibrium) solutions. Finally, we explicitly verify how the Lorentz invariance of the Langevin process is maintained in the presence of an expanding medium, including the case of an "elliptic flow" transmitted to a Brownian test particle. This is particularly relevant for using heavy-flavor diffusion as a quantitative tool to diagnose transport properties of QCD matter as created in ultrarelativistic heavy-ion collisions.

nucl-th↗

arXiv2012

Non-perturbative Heavy-Flavor Transport at RHIC and LHC

We calculate open heavy-flavor (HF) transport in relativistic heavy-ion collisions by applying a strong-coupling treatment in both macro- and microscopic dynamics (hydrodynamics and non-perturbative diffusion interactions). The hydrodynamic medium evolution is quantitatively constrained by bulk and multi-strange hadron spectra and elliptic flow. The heavy quark (HQ) transport coefficient is evaluated from a non-perturbative $T$-matrix approach in the Quark-Gluon Plasma (QGP) which, close to the critical temperature, leads to resonance formation and feeds into the recombination of heavy quarks on a hydrodynamic hypersurface. In the hadronic phase, the diffusion of HF mesons is obtained from effective hadronic theory. We compute observables at RHIC and LHC for non-photonic electrons and HF mesons, respectively.

nucl-th↗

arXiv2012

$\mathbf{D_s}$-Meson as Quantitative Probe of Diffusion and Hadronization in Nuclear Collisions

The modifications of $D_s$-meson spectra in ultrarelativistic heavy-ion collisions are identified as a quantitative probe of key properties of the hot nuclear medium. This is enabled by the unique valence-quark content of the $D_s$=$c\bar{s}$ which couples the well-known strangeness enhancement with the collective-flow pattern of primordially produced charm quarks. We employ a consistent strong-coupling treatment with hydrodynamic bulk evolution and nonperturbative $T$-matrix interactions for both heavy-quark diffusion and hadronization in the Quark-Gluon Plasma (QGP). A large enhancement of the $D_s$ nuclear modification factor ($R_{AA}$) at RHIC is predicted, with a remarkable maximum of $\sim$1.5-1.8 at transverse momenta around 2 GeV/$c$. We show this to be a direct consequence of the strong coupling of the heavy quarks to the QGP and their hadronization via coalescence with strange quarks. We furthermore introduce the effects of diffusion in the hadronic phase and suggest that an increase of the $D$-meson elliptic flow compared to the $D_s$ can disentangle the transport properties of hadronic and QGP liquids.

nucl-th↗