Seminar 2021
12/16/2021
Open quantum systems and quantum computing for heavy ion collisions
Xiaojun Yao, MIT
2:00 PM Thursday, online ZOOM
The purpose of relativistic heavy ion collisions is to study the properties of the quark-gluon plasma (QGP). Heavy quarks and jets have been used as important probes of the QGP. To understand their production in heavy ion collisions, it is necessary to understand their evolution inside the QGP. Many previous studies applied semiclassical transport equations, which neglected quantum effects that could be crucial. In recent years, the quantum evolution of heavy quarks and jets inside the QGP was investigated by using the open quantum system framework. In this talk, I will discuss the open quantum system framework and its application to heavy quarks and jets, with a focus on the heavy quark bound state. Then I will discuss how quantum computing can help to solve these evolution equations. I will give two explicit simple examples of using quantum computers to solve the open quantum system time evolution: one is a simple two-level system and the other is the Schwinger model, both coupled with a thermal environment.
11/10/2021
Quantum simulations for real-time observables in nuclear physics
Yukari Yamauchi, University of Maryland
1:00 PM Wednesday, online ZOOM
The application of quantum simulations to nuclear physics has been studied intensely in recent years. Important real-time observables in QCD, such as parton distribution functions (PDFs) and transport coefficients, can be computed on a large-scale quantum computer. Quantum algorithms for computing these real-time observables naively consist of five building blocks: representation of the Hilbert space of lattice QCD on qubits, implementation of the time evolution operator via QCD Hamiltonian, preparation of a suitable initial state, measurement of the expectation value of target observables, and error corrections. In this talk, I will discuss quantum algorithms for computing PDFs and transport coefficients. I will focus on two of these building blocks: initial state preparation and measurement of observables.
08/12/2021
Rodeo Algorithm for Quantum Computation
Dean Lee, Michigan State
3:00 PM Thursday, online ZOOM
The rodeo algorithm is a new algorithm for preparing quantum eigenstates on a quantum computer. It follows a strategy that is opposite to adiabatic evolution. Instead of slowly evolving a Hamiltonian to preserve the instantaneous ground state, it violently shakes off all quantum states that are not desired. I first introduce another method that works in the same modality, called the projected cooling method. I then discuss the theory, performance, and implementation of the rodeo algorithm for arbitrary eigenstate preparation, energy spectrum determination, and calculation of transition matrix elements.
07/27/2021
Debojit Sarkar, Wayne State
10:00 AM Tuesday, online ZOOM
The system created in relativistic nucleus-nucleus collisions may possess large orbital angular momentum leading to the global polarization of particles perpendicular to the reaction plane. The local asymmetries in the velocity fields due to anisotropic flow can also generate vorticity and particle polarization along the beam direction. In parity-violating weak decays of hyperons, the momentum direction of the decay baryon is correlated with the hyperon spin. This feature makes the hyperons suitable candidates to measure the polarization and thus estimate the local and global vorticity of the system created in relativistic heavy-ion collisions. In this talk, the recent experimental measurements of the local and global polarization of the Lambda and anti-Lambda hyperons in Pb-Pb collisions in ALICE will be presented. A comparison of the ALICE results with the previous STAR measurements will be shown, and the collision energy dependence of the hyperon polarization will be discussed. Also, the comparison of the measured local polarization with the hydrodynamic model calculations involving thermal and shear-induced vorticity will be discussed.
07/22/2021
Yazhou Niu, USTC
3:00 PM Thursday, online ZOOM
Driven by the physics program at the Circular Electron Positron Collider (CEPC) for Higgs and electroweak physics, all possible final states need to be separately identified and reconstructed with high sensitivity. Properties agree with the particle flow algorithm principle, which makes use of the optimal sub-detector to determine the energy/momentum of each final particle. The electromagnetic calorimeter is required to have not only good energy resolution but an unprecedented three-dimensional spatial resolution for shower separation. An electromagnetic calorimeter, which features finely segmented and highly lateral granular, has been designed and optimized within the CALICE collaboration and CEPC calorimeter working group. Scintillator strips and silicon photomultipliers (SiPMs) are instrumented as sensitive layers and tungsten-copper alloy plates as absorber material. A complete technological prototype with 32 sampling layers with over 6700 channels in total has been constructed and commissioned in the middle of 2020. The whole prototype measures around 600*600*400 mm^3 in dimensions and roughly 250 kg in weight. A long term cosmic ray test (more than one month) has been performed for detailed studies of this prototype to quantitatively evaluate the key performance, including the position resolution and cell-to-cell response calibration, etc. This talk will cover some highlight aspects in the development process and some key performances of the ScECAL prototype.
07/16/2021
Measurements of Dielectron Production with the STAR Experiment
Zaochen Ye, Rice University
3:00 PM Friday, online ZOOM
Dielectron production is suggested as an excellent probe of the hot and dense medium created in relativistic heavy-ion collisions due to their minimal interactions with the partonic and hadronic medium. They can carry the information from the initial to the final stage of a collision. The study of the dielectron mass spectrum could help to disentangle various contributions. In the low mass region (LMR, Mee < Mphi), the mass spectra of vector mesons are modified due to their interaction with the medium which could provide an access to the chiral symmetry restoration. In the intermediate mass region (IMR, Mphi < Mee < MJ/psi), dielectrons from thermal radiation are predicted as a QGP thermometer, meanwhile the contributions from heavy quark semi-leptonic decays make the extraction of the thermal radiation contribution very challenging. In this talk, I will review the recent progress of dielectron measurements with the STAR experiment and discuss the prospects of the STAR BES-II dielectron program.
07/07/2021
Zhongling Ji, Stony Brook
10:00 AM Wednesday, online ZOOM
Understanding the gluon spin contribution to the proton spin is among the primary motivations of the spin program at the Relativistic Heavy Ion Collider (RHIC). Double helicity asymmetry A_LL of direct photon production in pp collisions at RHIC is sensitive to the gluon helicity in the polarized proton. Direct photons are dominantly produced by the quark-gluon Compton process at RHIC energies, and utilizing an isolation criteria can reduce the fragmentation contributions and photons from hadronic decays. The asymmetry measurement with isolation criteria provides clean access to the polarization of the gluon. I will present the cross section and double helicity asymmetry measurements of direct photon production in longitudinally polarized proton collisions at sqrt(s} = 510 GeV at midrapidity (|eta| < 0.25). These data are expected to provide additional constraints on the gluon helicity distribution in the gluon momentum fraction range 0.02 < x < 0.08.
06/30/2021
Disappearance of Partonic Collectivity in 3 GeV Au+Au Collisions at RHIC
Shaowei Lan, CCNU/LBNL
10:00 AM Wednesday, online ZOOM
Searching for the onset of Quark-Gluon Plasma (QGP) has been one of the most important motivations of relativistic heavy-ion physics. Collectivity measurements could be served as powerful tool, since they are sensitive to dynamics of early stage of system evolution. In the lower energy collisions, measurements of light hadron collectivity would tell about the underlying collision dynamics and help to study the properties of QCD medium. On the other hand, measurements of light nuclei collectivity provide valuable information on the nucleon coalescence sum rule and lead to better understanding of light nuclei production mechanism in such collisions. In this talk, I will present new measurements of directed flow and elliptic flow for light hadron and light nuclei in Au+Au collisions at 3 GeV by the STAR experiment at RHIC. The rapidity, transverse momentum and energy dependence of and for these particles will be discussed. These results are compared with hadronic transport model calculations, indicating that baryonic interactions dominate in 3 GeV Au+Au collisions.
05/10/2021 - 05/14/2021
online ZOOM
04/06/2021
Entanglement and Quantum tomography for collider physics
Daniel Tapia Takaki, University of Kansas
11:00 PM Tuesday, online ZOOM
Quantum mechanics is experiencing an experimental and theoretical renaissance. In this talk, we will discuss novel ways to use quantum mechanics and provide several experimental applications of quantum tomography for proton-proton and heavy-ion collision experiments at the CERN Large Hadron Collider. We will discuss application of this model-independent analysis technique for Z bosons, dijets and quarkonia. The first observation of an unexpected correlation of spin and momentum in the experimental data will also be presented.
03/24/2021
Cecilia Tosciri, University of Chicago
12:00 PM Wednesday, online ZOOM
joint with HEAP seminar
The discovery of the Higgs boson at the Large Hadron Collider (LHC) in 2012 represents an outstanding success of the Standard Model (SM) of particle physics. Since then, the properties of the Higgs boson have been measured with increased precision and found to be consistent with the SM predictions. However, despite this remarkable agreement, many physical phenomena are not explained by the SM, and several questions remain unresolved. Indeed, the SM is envisioned to be only an effective manifestation of a more fundamental description of Nature. Precision measurements of the Higgs boson production cross sections and decay rates give us a sharp tool to search for new physics. Moreover, original analysis techniques, in addition to innovative technologies and computational resources, are essential to fully exploit the LHC physics potential in the next decades. In this talk I will present the VH(H->bb) signal strength analysis performed with the ATLAS experiment, leading to the observation of Higgs boson decays into pairs of bottom quarks, which is a prime example of the success of the LHC in testing the SM. A description of the cross section measurements for the VH(H->bb) processes and their interpretation based on an effective field theory approach will be also presented. This work represents an important step towards the era of precision Higgs physics measurements at the LHC. Furthermore, I will describe a novel technique for the fast simulation of the response of the forward calorimeter in ATLAS, based on an innovative unsupervised machine learning algorithm.