arXiv subjects

S. Ryu

Publications and source records attributed to S. Ryu.

At least 19 recordsLinked to original sources

arXiv2025

Transport-based initial conditions for heavy-ion collisions at finite densities

We employ the SMASH transport model to provide event-by-event initial conditions for the energy-momentum tensor and conserved charge currents in hydrodynamic simulations of relativistic heavy-ion collisions. We study the fluctuations and dynamical evolution of three conserved charge currents (net baryon, net electric charges, and net strangeness) with a 4D lattice-QCD-based equation of state, NEOS-4D, in the hydrodynamic phase. Out-of-equilibrium corrections at the particlization are generalized to finite densities to ensure the conservation of energy, momentum, and the three types of charges. These theoretical developments are integrated within the X-SCAPE code as a unified framework for studying the nuclear matter properties in the Beam Energy Scan program.

nucl-th↗

arXiv2022

Time-resolved Coulomb collision of single electrons

Precise control over interactions between ballistic electrons will enable us to exploit Coulomb interactions in novel ways, to develop high-speed sensing, to reach a non-linear regime in electron quantum optics and to realise schemes for fundamental two-qubit operations on flying electrons. Time-resolved collisions between electrons have been used to probe the indistinguishability, Wigner function and decoherence of single electron wavepackets. Due to the effects of screening, none of these experiments were performed in a regime where Coulomb interactions were particularly strong. Here we explore the Coulomb collision of two high energy electrons in counter-propagating ballistic edge states. We show that, in this kind of unscreened device, the partitioning probabilities at different electron arrival times and barrier height are shaped by Coulomb repulsion between the electrons. This prevents the wavepacket overlap required for the manifestation of fermionic exchange statistics but suggests a new class of devices for studying and manipulating interactions of ballistic single electrons.

cond-mat.mes-hall↗

arXiv2021

In-plane quasi-single-domain BaTiO$_3$ via interfacial symmetry engineering

The control of the in-plane domain evolution in ferroelectric thin films is not only critical to understanding ferroelectric phenomena but also to enabling functional device fabrication. However, in-plane polarized ferroelectric thin films typically exhibit complicated multi-domain states, not desirable for optoelectronic device performance. Here we report a strategy combining interfacial symmetry engineering and anisotropic strain to design single-domain, in-plane polarized ferroelectric BaTiO$_3$ thin films. Theoretical calculations predict the key role of the BaTiO$_3$ / PrScO$_3$ (110)$_O$ substrate interfacial environment, where anisotropic strain, monoclinic distortions, and interfacial electrostatic potential stabilize a single-variant spontaneous polarization. A combination of scanning transmission electron microscopy, piezoresponse force microscopy, ferroelectric hysteresis loop measurements, and second harmonic generation measurements directly reveals the stabilization of the in-plane quasi-single-domain polarization state. This work offers design principles for engineering in-plane domains of ferroelectric oxide thin films, which is a prerequisite for high performance optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2020

A Silicon Beam Tracker

When testing and calibrating particle detectors in a test beam, accurate tracking information independent of the detector being tested is extremely useful during the offline analysis of the data. A general-purpose Silicon Beam Tracker (SBT) was constructed with an active area of 32.0 x 32.0 mm2 to provide this capability for the beam calibration of the Cosmic Ray Energetics And Mass (CREAM) calorimeter. The tracker consists of two modules, each comprised of two orthogonal layers of 380 {\mu}m thick silicon strip sensors. In one module each layer is a 64-channel AC-coupled single-sided silicon strip detector (SSD) with a 0.5 mm pitch. In the other, each layer is a 32-channel DC-coupled single-sided SSD with a 1.0 mm pitch. The signals from the 4 layers are read out using modified CREAM hodoscope front-end electronics with a USB 2.0 interface board to a Linux DAQ PC. In this paper, we present the construction of the SBT, along with its performance in radioactive source tests and in a CERN beam test in October 2006.

physics.ins-det↗

arXiv2017

LO-phonon emission rate of hot electrons from an on-demand single-electron source in a GaAs/AlGaAs heterostructure

Using a recently-developed time-of-flight measurement technique with 1 ps time resolution and electron-energy spectroscopy, we developed a method to measure the longitudinal-optical-phonon emission rate of hot electrons travelling along a depleted edge of a quantum Hall bar. A comparison of the experimental results to a single-particle model implies that the main scattering mechanism involves a two-step process via intra-Landau-level transition. We show this scattering can be suppressed by controlling the edge potential profile, and a scattering length > 1 mm can be achieved, allowing the use of this system for scalable single-electron device applications.

cond-mat.mes-hall↗

arXiv2017

Different Realizations of Cooper-Frye Sampling with Conservation Laws

Approaches based on viscous hydrodynamics for the hot and dense stage and hadronic transport for the final dilute rescattering stage are successfully applied to the dynamic description of heavy ion reactions at high beam energies. One crucial step in such hybrid approaches is the so called particlization, the transition between the hydrodynamic description to microscopic degrees of freedom. For this purpose, individual particles are sampled on the Cooper-Frye hypersurface. In this work, 4 different realizations of sampling algorithms are compared, where three of them incorporate global conservation laws of quantum numbers in each event. The algorithms are compared within two types of scenarios: simple "box" hypersurface consisting of only one static cell and a typical particlization hypersurface for Au+Au collisions at $\sqrt{s_\mathrm{NN}} = 200$ GeV. For all algorithms the mean multiplicities (or particle spectra) remain unaffected by global conservation laws in the case of large volumes. In contrast, the fluctuations of the particle numbers are affected considerably. The fluctuations of the newly developed SPREW algorithm based on exponential weights and the recently suggested SER algorithm based on ensemble rejection are smaller than without conservation laws and agree with the expectation from the canonical ensemble. The previously applied mode sampling algorithm produces dramatically larger fluctuations, than it is expected in the corresponding microcanonical ensemble, and therefore should be avoided in fluctuation studies. This study might be of interest for investigations of particle fluctuations and correlations, e.g. the suggested signatures for a phase transition or a critical endpoint, in hybrid approaches that are affected by global conservation laws.

hep-ph↗

arXiv2015

The importance of the bulk viscosity of QCD in ultrarelativistic heavy-ion collisions

We investigate the consequences of a nonzero bulk viscosity coefficient on the transverse momentum spectra, azimuthal momentum anisotropy, and multiplicity of charged hadrons produced in heavy ion collisions at LHC energies. The agreement between a realistic 3D hybrid simulation and the experimentally measured data considerably improves with the addition of a bulk viscosity coefficient for strongly interacting matter. This paves the way for an eventual quantitative determination of several QCD transport coefficients from the experimental heavy ion and hadron-nucleus collision programs.

nucl-th↗

arXiv2014

Measurements of Branching Fractions of $τ$ Lepton Decays with one or more $K^{0}_{S}$

We report measurements of branching fractions of $τ$ lepton decays to final states with a $K^{0}_{S}$ meson using a 669 fb$^{-1}$ data sample accumulated with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The inclusive branching fraction is measured to be $\mathcal{B}(τ^{-} \to K^{0}_{S}\ X^{-} ν_τ)=(9.15 \pm 0.01 \pm 0.15) \times 10^{-3}$, where $X^{-}$ can be anything; the exclusive branching fractions are $\mathcal{B}(τ^{-} \to π^{-} K^{0}_{S} ν_τ) = (4.16 \pm 0.01 \pm 0.08) \times 10^{-3}$, $\mathcal{B}(τ^{-} \to K^{-} K^{0}_{S} ν_τ) = (7.40 \pm 0.07 \pm 0.27) \times 10^{-4}$, $\mathcal{B}(τ^{-} \to π^{-} K^{0}_{S} π^{0} ν_τ) = (1.93 \pm 0.02 \pm 0.07) \times 10^{-3}$, $\mathcal{B}(τ^{-} \to K^{-} K^{0}_{S} π^{0} ν_τ) = (7.48 \pm 0.10 \pm 0.37)\times 10^{-4}$, $\mathcal{B}(τ^{-} \to π^{-} K^{0}_{S} K^{0}_{S} ν_τ) = (2.33 \pm 0.03 \pm 0.09) \times 10^{-4}$, $\mathcal{B}(τ^{-} \to π^{-} K^{0}_{S} K^{0}_{S} π^{0} ν_τ) = (2.00 \pm 0.22 \pm 0.20) \times 10^{-5}$, where the first uncertainty is statistical and the second is systematic. For each mode, the accuracy is improved over that of pre-$B$-factory measurements by a factor ranging from five to ten. In $τ^{-} \to π^{-} K^0_S K^0_S π^{0} ν_τ$ decays, clear signals for the intermediate states $τ^{-} \to π^- f_{1}(1285)ν_τ$ and $τ^{-} \to K^{*-}K^{0}_{S} π^{0} ν_τ$ are observed.

hep-ex↗

arXiv2013

Search for B0 to p Lambdabar pi- gamma at Belle

We search for the charmless B^0 decay with final state particles p Lambdabar pi^- gamma using the full data sample that contains 772 * 10^6 B Bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider. This decay is predicted to proceed predominantly via the b to s gamma radiative penguin process with a high energy photon. No significant signal is found. We set an upper limit of 6.5 * 10^-7 for the branching fraction of B^0 to p Lambdabar pi^- gamma at the 90% confidence level.

hep-ex↗

arXiv2013

Magnetic field tuned superconductor-to-insulator transition at the LaAlO$_3$ /SrTiO$_3$ interface

We present a study of the magnetic field tuned superconductor-to-insulator transition (SIT) in the electron gas that forms at the LaAlO$_3$/SrTiO$_3$ interface. We find that the magnetic field induces a transition into a weakly insulating state, as is observed for the electrostatically tuned SIT at this interface. Finite size scaling of the magnetoresistance yields the critical exponent product $zν\simeq$ 7/3, indicating that the transition is governed by quantum percolation effects. While such critical exponents have been reported previously for high resistance films, they have not been reported for a low resistance system like ours, with a maximum sheet resistance of $\approx$ 1.5 k$Ω$, much less than the quantum of resistance $R_Q \equiv h/4e^2 = 6.45$ k$Ω$.

cond-mat.supr-con↗

arXiv2013

Precise measurement of the branching fractions for Bs->Ds()+ Ds()- and first measurement of the Ds+ Ds- polarization using e+e- collisions

We have made a precise measurement of the absolute branching fractions of Bs->Ds(*)+ Ds(*)- decays using 121.4 fb-1 of data recorded by the Belle experiment running on the Upsilon(5S) resonance. The results are B(Bs0->Ds+ Ds-) = (0.58 +0.11 -0.09 +-0.13)%, B(Bs0->Ds*+- Ds-+) = (1.8 +-0.2 +-0.4)%, and B(Bs0->Ds*+ Ds*-) = (2.0 +-0.3 +-0.5)%; the sum is B(Bs0->Ds(*)+ Ds(*)- = (4.3 +-0.4 +-1.0)%. Assuming Bs->Ds(*)+ Ds(*)- saturates decays to CP-even final states, the branching fraction constrains the ratio Delta(Gamma_s)/cos(phi_s), where Delta(Gamma_s) is the difference in widths between the two Bs0-Bs0bar mass eigenstates, and phi_s is the CP-violating phase in Bs0-Bs0bar mixing. For phi_s=0 we obtain Delta(Gamma_s)/Gamma_s = 0.090 +-0.009 (stat.) +-0.023 (syst.), where Gamma_s is the mean decay width. We also measure for the first time the longitudinal polarization fraction of Bs->Ds*+ Ds*-; the result is 0.12 +0.30 -0.28 +0.04 -0.05.

hep-ex↗

arXiv2013

Measurements of Branching Fractions and Direct CP Asymmetries for B -> K pi, B->pi pi and B->to KK Decays

We report measurements of the branching fractions and direct CP asymmetries (A_{CP}) for B->K pi, pi pi and KK decays (but not pi^0 pi^0) based on the final data sample of 772x10^6 B B-bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider. We set a 90% confidence-level upper limit for K^+- K^-+ at 2.0x10^{-7}; all other decays are observed with branching fractions ranging from 10^{-6} to 10^{-5}. In the $B^0/B^0-bar -> K^+-π^-+ mode, we confirm Belle's previously reported large A_{CP} with a value of -0.069 +- 0.014 +- 0.007 and a significance of 4.4 sigma. For all other flavor-specific modes, we find A_{CP} values consistent with zero, including A_{CP}(K^+- π^0) = +0.043 +- 0.024 +- 0.007 with 1.8 sigma significance. The difference of CP asymmetry between B^+- -> K^+- pi^0 and B^0/B^0-bar -> K^+-π^-+ is found to be Delta A_{K pi} equiv A_{CP} (K^+ pi^0) - A_{CP}(K^+ pi^-) = +0.112 +- 0.027 +- 0.007 with 4.0 sigma significance. We also calculate the ratios of partial widths for the B-> K pi decays. Using our results, we test the validity of the sum rule A_{CP}(K^+ pi^-) + A_{CP}(K^0π^+) x Gamma(K^0π^+)/Gamma(K^+ pi^-)} - A_{CP}(K^+ pi^0)x 2Gamma(K^+ pi^0)/Gamma(K^+ pi^-) - A_{CP}(K^0 pi^0)x 2Gamma(K^0 pi^0)/Gamma(K^+ pi^-) = 0 and obtain a sum of -0.270 +- 0.132 +- 0.060 with 1.9 sigma significance.

hep-ex↗

arXiv2013

Measurement of the branching fractions and mass spectra for $τ$ lepton decays including $K_{S}^{0}$ at Belle

We report a study of $τ$ lepton decays involving $\Ks$ with a 669 fb$^{-1}$ data sample accumulated with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The branching fractions have been measured for the $\tauTO \piKs ν_τ$, $\KKs ν_τ$, $\piKspizero ν_τ$, $\KKspizero ν_τ$, $\piKsKs ν_τ$ and $\piKsKspizero ν_τ$ decays. We also provide the unfolded mass spectra for $\tauTO \piKspizero ν_τ$ and $\tauTO \KKspizero ν_τ$.

hep-ex↗

arXiv2013

Search for Lepton-Flavor-Violating and Lepton-Number-Violating tau to lhh' Decay Modes

We search for lepton-flavor-violating and lepton-number-violating tau decays into a lepton (l = electron or muon) and two charged mesons (h, h' = pion or Kaon) using 854 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We obtain 90% confidence level upper limits on the tau to lhh' branching fractions in the range (2.0-8.4)*10^{-8}. These results improve upon our previously published upper limits by factors of about 1.8 on average.

hep-ex↗

arXiv2012

The Quantum Torus Chain

We introduce a new set of one dimensional quantum lattice models which we refer to as The quantum torus chain. These models have discrete global symmetry, and projective on-site representations. They possess an integer-valued parameter which controls the presence or absence of frustration. Depending on whether this parameter is even or odd these models either exhibit gapped symmetry breaking phases with isolated critical points, or gapped symmetry breaking phases separated by gapless phases. We discuss the property of these phases and phase transitions for two special values of the parameter and point out many open problems

cond-mat.str-el↗

arXiv2012

Low energy fast events from radon progenies at the surface of a CsI(Tl) scintillator

In searches for rare phenomena such as elastic scattering of dark matter particles or neutrinoless double beta decay, alpha decays of Rn222 progenies attached to the surfaces of the detection material have been identified as a serious source of background. In measurements with CsI(Tl) scintillator crystals, we demonstrate that alpha decays of surface contaminants produce fast signals with a characteristic mean-time distribution that is distinct from those of neutron- and gamma-induced events.

astro-ph.CO↗

arXiv2012

Evidence for charge-vortex duality at the LaAlO$_3$/SrTiO$_3$ interface

The concept of duality has proved extremely powerful in extending our understanding in many areas of physics (1, 2). Charge-vortex duality has been proposed (3, 4) as a model to understand the superconductor to insulator transition (SIT) in disordered thin films (5, 6) and Josephson junction arrays (7, 8, 9). In this model, on the superconducting side, one has delocalized Cooper pairs but localized vortices; while on the insulating side, one has localized Cooper pairs but mobile vortices. Here we show a new experimental manifestation of this duality in the electron gas that forms at the interface between LaAlO$_3$ (LAO) and SrTiO$_3$ (STO) (10, 11, 12, 13, 14). The effect is due to the motion of vortices generated by the magnetization dynamics of the ferromagnet that also forms at the same interface (14, 15, 16), which results in an increase in resistance on the superconducting side of the transition, but an increase in conductance on the insulating side.

cond-mat.supr-con↗

arXiv2012

First study of η_c, η(1760) and X(1835) production via η'π^+π^- final states in two-photon collisions

The invariant mass spectrum of the η' π^+ π^- final state produced in two-photon collisions is obtained using a 673 fb^{-1} data sample collected in the vicinity of the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We observe a clear signal of the η_c and measure its mass and width to be M(η_c)=(2982.7 +- 1.8(stat) +- 2.2(syst) +- 0.3(model)) MeV/c^2 and Γ(η_c) = (37.8^{+5.8}_{-5.3}(stat) +- 2.8(syst) +- 1.4(model)) MeV/c^2. The third error is an uncertainty due to possible interference between the η_c and a non-resonant component. We also report the first evidence for η(1760) decay to η' π^+ π^-; we find two solutions for its parameters, depending on the inclusion or not of the X(1835), whose existence is of marginal significance in our data. From a fit to the mass spectrum using coherent X(1835) and η(1760) resonant amplitudes, we set a 90% confidence level upper limit on the product Γ_{γγ} \BR (η' π^+ π^-) for the X(1835).

hep-ex↗