Publications

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Hitting two BSM particles with one lepton-jet: search for a top partner decaying to a dark photon, resulting in a lepton-jet

K. du Plessis, M. M. Flores, D. Kar, S. Sinha, H. van der Schyf

SciPost Phys. 13, 018 (2022) · published 15 August 2022 | · pdf

A maverick top partner model, decaying to a dark photon was suggested. The dark photon decays to two overlapping electrons for dark photon masses of $\approx 100$ GeV, and results in a so-called lepton-jet. The event includes a top quark as well, which results in events with two boosted objects, one heavy and the other light. We propose a search strategy exploiting the unique signal topology. We show that for a set of kinematic selections, both in hadronic and leptonic decay channel of the SM top quark, almost all background can be eliminated, leaving enough signal events up to top partner mass of about 3 TeV for the search to be viable at the LHC.

3 citations
Phase transitions above the upper critical dimension

Bertrand Berche, Tim Ellis, Yurij Holovatch, Ralph Kenna

SciPost Phys. Lect. Notes 60 (2022) · published 12 August 2022 | · pdf

These lecture notes provide an overview of the renormalization group (RG) as a successful framework to understand critical phenomena above the upper critical dimension $d_{\rm uc}$. After an introduction to the scaling picture of continuous phase transitions, we discuss the apparent failure of the Gaussian fixed point to capture scaling for Landau mean-field theory, which should hold in the thermodynamic limit above $d_{\rm uc}$. We recount how Fisher's dangerous-irrelevant-variable formalism applied to thermodynamic functions partially repairs the situation but at the expense of hyperscaling and finite-size scaling, both of which were, until recently, believed not to apply above $d_{\rm uc}$. We recall limitations of various attempts to match the RG with analytical and numerical results for Ising systems. We explain how the extension of dangerous irrelevancy to the correlation sector is key to marrying the above concepts into a comprehensive RG scaling picture that renders hyperscaling and finite-size scaling valid in all dimensions. We collect what we believe is the current status of the theory, including some new insights and results. This paper is in grateful memory of Michael Fisher who introduced many of the concepts discussed and who, half a century later, contributed to their advancement.

7 citations
Ground-state phase diagram of quantum link electrodynamics in $(2+1)$-d

Tomohiro Hashizume, Jad C. Halimeh, Philipp Hauke, Debasish Banerjee

SciPost Phys. 13, 017 (2022) · published 12 August 2022 | · pdf

The exploration of phase diagrams of strongly interacting gauge theories coupled to matter in lower dimensions promises the identification of exotic phases and possible new universality classes, and it facilitates a better understanding of salient phenomena in Nature, such as confinement or high-temperature superconductivity. The emerging new techniques of quantum synthetic matter experiments as well as efficient classical computational methods with matrix product states have been extremely successful in one spatial dimension, and are now motivating such studies in two spatial dimensions. In this work, we consider a $\mathrm{U}(1)$ quantum link lattice gauge theory where the gauge fields, represented by spin-$\frac{1}{2}$ operators are coupled to a single flavor of staggered fermions. Using matrix product states on infinite cylinders with increasing diameter, we conjecture its phase diagram in $(2+1)$-d. This model allows us to smoothly tune between the $\mathrm{U}(1)$ quantum link and the quantum dimer models by adjusting the strength of the fermion mass term, enabling us to connect to the well-studied phases of those models. Our study reveals a rich phase diagram with exotic phases and interesting phase transitions to a potential liquid-like phase. It thus furthers the collection of gauge theory models that may guide future quantum-simulation experiments.

4 citations
Renormalization approach to the superconducting Kondo model

Steffen Sykora, Tobias Meng

SciPost Phys. 13, 016 (2022) · published 12 August 2022 | · pdf

An approach to bound states based on unitary transformations of Hamiltonians is presented. The method is applied to study the interaction between electrons in a BCS $s$-wave superconductor and a quantum spin. It is shown that known results from the t-matrix method and numerical studies are reproduced by this new method. As a main advantage, the method can straightforwardly be extended to study the topological properties of combined bound states in chains of many magnetic impurities. It also provides a uniform picture of the interplay between the Yu-Shiba-Rusinov (YSR) bound states and the Kondo singlet state.
Measurement of Intermittency for Charged Particles in Au + Au Collisions at $\sqrt{s_\mathrm{NN}}$ = 7.7-200 GeV from STAR

Jin Wu

SciPost Phys. Proc. 10, 041 (2022) · published 11 August 2022 | · pdf

Local density fluctuations near the QCD critical point can be probed by intermittency analysis of scaled factorial moments in relativistic heavy-ion collisions. We report the first measurement of intermittency for charged particles in Au + Au collisions at $\sqrt{s_\mathrm{NN}}$ = 7.7-200 GeV from the STAR experiment at RHIC. We observe scaling behaviors in central Au + Au collisions, with the extracted scaling exponent decreasing from mid-central to the most central Au + Au collisions. Furthermore, the scaling exponent exhibits a non-monotonic energy dependence with a minimum around $\sqrt{s_\mathrm{NN}}$ = 20-30 GeV in central Au + Au collisions.

2 citations
Light Nuclei Production in Au+Au Collisions at $\sqrt{s_{\mathrm{NN}}}$ = 3 GeV from the STAR experiment

Hui Liu

SciPost Phys. Proc. 10, 040 (2022) · published 11 August 2022 | · pdf

Light nuclei production is expected to be sensitive to baryon density fluctuations and can be used to probe the signatures of QCD critical point and/or a first-order phase transition in heavy-ion collisions. In this proceedings, we present the spectra and yields of protons ($p$) and light nuclei ($d$, $t$, $^{3}\mathrm{He}$, $^{4}\mathrm{He}$) in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 3 GeV by the STAR experiment. Finally, it is found that the kinetic freeze-out dynamics (temperature $T_{kin}$ $vs.$ average radial flow velocity $\langle\beta_{T}\rangle$) at 3 GeV extracted with the blast-wave model deviate from the trends at high energies ($\sqrt{s_{\mathrm{NN}}}$ = 7.7 - 200 GeV), indicating a different medium equation of state.

1 citation
The study of hadron properties and structure in high energy multi-production processes

Shi-Yuan Li

SciPost Phys. Proc. 10, 039 (2022) · published 11 August 2022 | · pdf

In high energy scattering, the multi-production process is unique in its relevance to the total cross section and in its global properties, such as rapidity and other kinematic distributions. If there is a hard interaction, the jet rate and structure is a good arena for perturbative quantum chromodynamics. However, once any hadron is specified, its properties and structure must make sense, while the global and/or perturbative chromodynamic mechanism still can put important constraints. The relation of the hadron’s properties and structure with its production cross section, distribution etc. can be much more complex than its decay width. On the one hand there are many difficulties and challenges in the calculations, while on the other hand, the production process provides a unique way to study the details of properties and structure of the hadron, which is beyond the approach of its decay process. Here I review our works on such topics in recent years, mainly on the multi-quark state production in multi-production processes and the Bethe-Salpeter wave function in exclusive processes. For the former, I emphasize the unitarity of the hadronization process and relevant models, so that almost no multi-quark state is observed in multi-production processes. I also address how to calculate hadron molecule production in multi-production processes. The most recently observed T+cc is also stated with its relevance to colour and baryon number fluctuation of the preconfinement clusters. For the latter, I emphasize the Dirac structure of the hadron-quark coupling vertex.
Measurements of $\phi$ meson and $\Xi^-$ hyperon production in Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV from STAR experiment

Yingjie Zhou

SciPost Phys. Proc. 10, 038 (2022) · published 11 August 2022 | · pdf

In this proceedings, we present our first measurements of $\phi$ meson and $\Xi^-$ hyperon production in Au+Au collisions at $\sqrt{s_{NN}}$ = 3 GeV. Various models including thermal and transport model calculations are compared to data, these results imply that the matter produced in the 3 GeV Au+Au collisions is considerably different from that at higher energies.
Hadron Production in terms of Green's Functions in Non-Equilibrium Matter

A. V. Koshelkin

SciPost Phys. Proc. 10, 037 (2022) · published 11 August 2022 | · pdf

Following the quark-hadron duality concept, we show that the number of hadrons generated in the deconfinement matter is entirely determined by the exact non-equilibrium Green's functions of partons in the medium and the vertex function governing the probability of the confinement-deconfinement phase transition. In such an approach, compactifying the standard (3+1) chromodynamics into $ QCD_{xy} + QCD_{zt}$, the rate of the hadrons produced in particle collisions is derived in the explicit form provided that the hadronization is the first order phase transition. The pion production is found to be in good agreement to the experimental results on the pion yield in pp collisions.
Hadron structure from basis light-front quantization

Chandan Mondal, Jiangshan Lan, Kaiyu Fu, Siqi Xu, Zhi Hu, Xingbo Zhao, James P. Vary

SciPost Phys. Proc. 10, 036 (2022) · published 11 August 2022 | · pdf

We present our recent progress in applying basis light-front quantization approach to investigate the structure of the light mesons and the nucleon.

2 citations

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