arXiv subjects

C. Shen

Publications and source records attributed to C. Shen.

53 records · Page 3Linked to original sources

arXiv2020

Multi-stage evolution of heavy quarks in the quark-gluon plasma

The interaction of heavy flavor with the quark-gluon plasma (QGP) in relativistic heavy-ion collisions is studied using JETSCAPE, a publicly available software package containing a framework for Monte Carlo event generators. Multi-stage (and multi-model) evolution of heavy quarks within JETSCAPE provides a cohesive description of heavy flavor quenching inside the QGP. As the parton shower develops, a model becomes active as soon as its kinematic region of validity is reached. Two combinations of heavy-flavor energy-loss models are explored within a realistic QGP medium, using parameters which were tuned to describe {\it light-flavor} partonic energy-loss.

nucl-th↗

arXiv2020

Revisiting Bayesian constraints on the transport coefficients of QCD

Multistage models based on relativistic viscous hydrodynamics have proven successful in describing hadron measurements from relativistic nuclear collisions. These measurements are sensitive to the shear and the bulk viscosities of QCD and provide a unique opportunity to constrain these transport coefficients. Bayesian analyses can be used to obtain systematic constraints on the viscosities of QCD, through methodical model-to-data comparisons. In this manuscript, we discuss recent developments in Bayesian analyses of heavy ion collision data. We highlight the essential role of closure tests in validating a Bayesian analysis before comparison with measurements. We discuss the role of the emulator that is used as proxy for the multistage theoretical model. We use an ongoing Bayesian analysis of soft hadron measurements by the JETSCAPE Collaboration as context for the discussion.

nucl-th↗

arXiv2019

The JETSCAPE framework: p+p results

The JETSCAPE framework is a modular and versatile Monte Carlo software package for the simulation of high energy nuclear collisions. In this work we present a new tune of JETSCAPE, called PP19, and validate it by comparison to jet-based measurements in $p+p$ collisions, including inclusive single jet cross sections, jet shape observables, fragmentation functions, charged hadron cross sections, and dijet mass cross sections. These observables in $p+p$ collisions provide the baseline for their counterparts in nuclear collisions. Quantifying the level of agreement of JETSCAPE results with $p+p$ data is thus necessary for meaningful applications of JETSCAPE to A+A collisions. The calculations use the JETSCAPE PP19 tune, defined in this paper, based on version 1.0 of the JETSCAPE framework. For the observables discussed in this work calculations using JETSCAPE PP19 agree with data over a wide range of collision energies at a level comparable to standard Monte Carlo codes. These results demonstrate the physics capabilities of the JETSCAPE framework and provide benchmarks for JETSCAPE users.

nucl-th↗

arXiv2019

The JETSCAPE framework

The JETSCAPE simulation framework is an overarching computational envelope for developing complete event generators for heavy-ion collisions. It allows for modular incorporation of a wide variety of existing and future software that simulates different aspects of a heavy-ion collision. The default JETSCAPE package contains both the framework, and an entire set of indigenous and third party routines that can be used to directly compare with experimental data. In this article, we outline the algorithmic design of the JETSCAPE framework, define the interfaces and describe the default modules required to carry out full simulations of heavy-ion collisions within this package. We begin with a description of the various physics elements required to simulate an entire event in a heavy-ion collision, and distribute these within a flowchart representing the event generator and statistical routines for comparison with data. This is followed by a description of the abstract class structure, with associated members and functions required for this flowchart to work. We then define the interface that will be required for external users of JETSCAPE to incorporate their code within this framework and to modify existing elements within the default distribution. We conclude with a discussion of some of the physics output for both $p$-$p$ and $A$-$A$ collisions from the default distribution, and an outlook towards future releases. In the appendix, we discuss various architectures on which this code can be run and outline our benchmarks on similar hardware.

nucl-th↗

arXiv2019

Jet substructure modification in a QGP from a multi-scale description of jet evolution with JETSCAPE

The modification of jet substructure in relativistic heavy-ion collisions is studied using JETSCAPE, a publicly available software package containing a framework for Monte Carlo event generators. Multi-stage jet evolution in JETSCAPE provides an integrated description of jet quenching by combining multiple models, with each becoming active at a different stage of the parton shower evolution. Jet substructure modification due to different aspects of jet quenching is studied using jet shape and jet fragmentation observables. Various combinations of jet energy loss models are exploed, with medium background provided by (2 + 1)-D VISHNU with TRENTo+freestreaming initial conditions. Results reported here are from simulations performed within JETSCAPE framework.

nucl-th↗

arXiv2019

Multi-stage jet evolution through QGP using the JETSCAPE framework: inclusive jets, correlations and leading hadrons

The JETSCAPE Collaboration has recently announced the first release of the JETSCAPE package that provides a modular, flexible, and extensible Monte Carlo event generator. This innovative framework makes it possible to perform a comprehensive study of multi-stage high-energy jet evolution in the Quark-Gluon Plasma. In this work, we illustrate the performance of the event generator for different algorithmic approaches to jet energy loss, and reproduce the measurements of several jet and hadron observables as well as correlations between the hard and soft sector. We also carry out direct comparisons between different approaches to energy loss to study their sensitivity to those observables.

nucl-th↗

arXiv2018

Towards QCD-assisted hydrodynamics for heavy-ion collision phenomenology

Heavy-ion collisions are well described by a dynamical evolution with a long hydrodynamical phase. In this phase the properties of the strongly coupled quark-gluon plasma are reflected in the equation of state (EoS) and the transport coefficients, most prominently by the shear and bulk viscosity over entropy density ratios $η$/s(T) and $ζ$/s(T), respectively. While the EoS is by now known to a high accuracy, the transport coefficients and in particular their temperature and density dependence are not well known from first-principle computations yet, as well as the possible influence they can have once used in hydrodynamical simulations. In this work, the most recent QCD-based parameters are provided as input to the MUSIC framework. A ratio $η$/s(T) computed with a QCD based approach is used for the first time \cite{Haas:2013hpa,Christiansen:2014ypa}. The IP-Glasma model is used to describe the initial energy density distribution, and UrQMD for the dilute hadronic phase. Simulations are performed for Pb--Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV, for different centrality intervals. The resulting kinematic distributions of the particles produced in the collisions are compared to data from the LHC, for several experimental observables. The high precision of the experimental results and the broad variety of observables considered allow to critically verify the quality of the description based on first-principle input to the hydrodynamic evolution.

nucl-th↗

arXiv2016

Implementing and characterizing precise multi-qubit measurements

There are two general requirements to harness the computational power of quantum mechanics: the ability to manipulate the evolution of an isolated system and the ability to faithfully extract information from it. Quantum error correction and simulation often make a more exacting demand: the ability to perform non-destructive measurements of specific correlations within that system. We realize such measurements by employing a protocol adapted from [S. Nigg and S. M. Girvin, Phys. Rev. Lett. 110, 243604 (2013)], enabling real-time selection of arbitrary register-wide Pauli operators. Our implementation consists of a simple circuit quantum electrodynamics (cQED) module of four highly-coherent 3D transmon qubits, collectively coupled to a high-Q superconducting microwave cavity. As a demonstration, we enact all seven nontrivial subset-parity measurements on our three-qubit register. For each we fully characterize the realized measurement by analyzing the detector (observable operators) via quantum detector tomography and by analyzing the quantum back-action via conditioned process tomography. No single quantity completely encapsulates the performance of a measurement, and standard figures of merit have not yet emerged. Accordingly, we consider several new fidelity measures for both the detector and the complete measurement process. We measure all of these quantities and report high fidelities, indicating that we are measuring the desired quantities precisely and that the measurements are highly non-demolition. We further show that both results are improved significantly by an additional error-heralding measurement. The analyses presented here form a useful basis for the future characterization and validation of quantum measurements, anticipating the demands of emerging quantum technologies.

quant-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↗

arXiv2015

Thermal photon radiation in high multiplicity p+Pb collisions at the Large Hadron Collider

The collective behaviour of hadronic particles has been observed in high multiplicity proton-lead collisions at the Large Hadron Collider (LHC), as well as in deuteron-gold collisions at the Relativistic Heavy-Ion Collider (RHIC). In this work we present the first calculation, in the hydrodynamic framework, of thermal photon radiation from such small collision systems. Owing to their compact size, these systems can reach temperatures comparable to those in central nucleus-nucleus collisions. The thermal photons can thus shine over the prompt background, and increase the low $p_T$ direct photon spectrum by a factor of 2-3 in 0-1% p+Pb collisions at 5.02 TeV. This thermal photon enhancement can therefore serve as a clean signature of the existence of a hot quark-gluon plasma during the evolution of these small collision systems, as well as validate hydrodynamic behavior in small systems.

nucl-th↗

arXiv2013

Strong thermalization of the two-component Bose-Hubbard model at finite temperatures

We study thermalization of a two-component Bose-Hubbard model by exact diagonalization. Initially the two components do not interact and are each at equilibrium but with different temperatures. As the on-site inter-component interaction is turned on, perfect thermalization occurs. Remarkably, not merely those simple "realistic" physical observables thermalize but even the density matrix of the \textit{whole} system---the time-averaged density matrix of the system can be well approximated by that of a canonical ensemble. A conjecture about this fact is put forward.

cond-mat.stat-mech↗

arXiv2012

Suppression of the high $p_T$ charged hadron $R_{AA}$ at the LHC

We present a parameter free postdiction of the high-$p_T$ charged-hadron nuclear modification factor ($R_{AA}$) in two centralities, measured by the CMS collaboration in $Pb$-$Pb$ collisions at the Large Hadron Collider (LHC). The evolution of the bulk medium is modeled using viscous fluid dynamics, with parameters adjusted to describe the soft hadron yields and elliptic flow. Assuming the dominance of radiative energy loss, we compute the medium modification of the $R_{AA}$ using a perturbative QCD based formalism, the higher twist scheme. The transverse momentum diffusion coefficient $\hat{q}$ is assumed to scale with the entropy density and normalized by fitting the $R_{AA}$ in the most central $Au$-$Au$ collisions at the Relativistic Heavy-Ion Collider (RHIC). This set up is validated in non-central $Au$-$Au$ collisions at RHIC and then extrapolated to $Pb$-$Pb$ collisions at the LHC, keeping the relation between $\hat{q}$ and entropy density unchanged. We obtain a satisfactory description of the CMS $R_{AA}$ over the $p_{T}$ range from 10-100 GeV.

hep-ph↗

arXiv2012

Correcting detection error in quantum computation and state engineering through data processing

Quantum error correction in general is experimentally challenging as it requires significant expansion of the size of quantum circuits and accurate performance of quantum gates to fulfill the error threshold requirement. Here we propose a method much simpler for experimental implementation to correct arbitrary detection errors. The method is based on processing of data from repetitive experiments and can correct detection error of any magnitude, as long as the error magnitude is calibrated. The method is illustrated with its application to detection of multipartite entanglement from quantum state engineering.

quant-ph↗

arXiv2011

Quantum quench dynamics of the Bose-Hubbard model at finite temperatures

We study quench dynamics of the Bose-Hubbard model by exact diagonalization. Initially the system is at thermal equilibrium and of a finite temperature. The system is then quenched by changing the on-site interaction strength $U$ suddenly. Both the single-quench and double-quench scenarios are considered. In the former case, the time-averaged density matrix and the real-time evolution are investigated. It is found that though the system thermalizes only in a very narrow range of the quenched value of $U$, it does equilibrate or relax well in a much larger range. Most importantly, it is proven that this is guaranteed for some typical observables in the thermodynamic limit. In order to test whether it is possible to distinguish the unitarily evolving density matrix from the time-averaged (thus time-independent), fully decoherenced density matrix, a second quench is considered. It turns out that the answer is affirmative or negative according to the intermediate value of $U$ is zero or not.

cond-mat.stat-mech↗

arXiv2009

From Di-Nucleus to Mono-Nucleus - Neck Evolution in Fusion of Massive Systems -

Dynamics of the neck degree of freedom during fusioning process between heavy ions is studied. Time scales of the three degrees of freedom (the relative distance, the neck and the mass-asymmetry) are studied, showing an early equilibration of the neck. This means that a di-nucleus formed by the incident combination of ions quickly forms a mono-nucleus with a superdeformation during the fusion process and that the other two degrees of freedom have to be solved in a coupled way. A brief introduction of Langevin approach and dissipation-fluctuation dynamics is also given and of the application to the synthesis of the superheavy elements.

nucl-th↗

arXiv2005

EMMA - A New Underground Cosmic-Ray Experiment

A new type of cosmic-ray experiment is under construction in the Pyhäsalmi mine in the underground laboratory of the University of Oulu, Finland. It aims to study the composition of cosmic rays at and above the knee region. The experiment, called EMMA, will cover approximately 150 square-metres of detector area. The array is capable of measuring the multiplicity and the lateral distribution of underground muons, and the arrival direction of the air shower. The full-size detector is expected to run by the end of 2007.

astro-ph↗

arXiv2005

Measurements of muon flux in the Pyhäsalmi underground laboratory

The cosmic-ray induced muon flux was measured at several depths in the Pyhäsalmi mine (Finland) using a plastic scintillator telescope mounted on a trailer. The flux was determined at four different depths underground at 400 m (980 m.w.e), at 660 m (1900 m.w.e), at 990 m (2810 m.w.e) and at 1390 m (3960 m.w.e) with the trailer, and also at the ground surface. In addition, previously measured fluxes from depths of 90 m (210 m.w.e) and 210 m (420 m.w.e) are shown. A relation was obtained for the underground muon flux as a function of the depth. The measured flux follows well the general behaviour and is consistent with results determined in other underground laboratories.

hep-ex↗