Publications

Order by: publication date number of citations

• NLO inclusive $J/ψ$ photoproduction at large $P_T$ at HERA and the EIC

  Carlo Flore, Jean-Philippe Lansberg, Hua-Sheng Shao, Yelyzaveta Yedelkina

  SciPost Phys. Proc. 8, 011 (2022) · published 11 July 2022 | Toggle abstract · pdf

  We study inclusive $J/\psi$ photoproduction at NLO at large $P_T$ at HERA and the EIC. Our computation includes NLO QCD leading-$P_T$ corrections, QED contributions via an off-shell photon as well as those from $J/\psi$+charm channels. For the latter, we employ the variable-flavour-number scheme. Our results are found to agree with the latest HERA data by H1 and provide, for the first time, a reliable estimate of the EIC reach for such a measurement. Finally, we demonstrate the observability of $J/\psi$+charm production and the sensitivy to probe the non-perturbative charm content of the proton at high $x$, also known as intrinsic charm, at the EIC.

• Studying hadronization at LHCb

  Sookhyun Lee

  SciPost Phys. Proc. 8, 075 (2022) · published 12 July 2022 | Toggle abstract · pdf

  LHCb is a fully instrumented forward spectrometer with particle identification and muon reconstruction covering the pseudorapidity ($eta$) range from 2 to 5. Its full jet reconstruc- tion capability makes the LHCb experiment a suitable venue to explore jet substructure observables, particularly formation of hadrons and heavy quarkonia resonances inside jets. This contribution presents a brief overview of ongoing research program and dis- cusses recent results on non-identified charged hadron distributions in Z-tagged jets and charmonium distributions within jets. Future works towards furthering the knowledge of hadronizion are also discussed.

• Spin Density Matrix Elements for Exclusive $\rho^{0}$ Meson Muoproduction at COMPASS

  W.~Augustyniak

  SciPost Phys. Proc. 8, 073 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Spin density matrix elements were extracted from COMPASS data for exclusive $\rho^{0}$ meson muoproduction on a liquid hydrogen target. The measurement cover the kinematic range of 1.0 (GeV/$c$)$^2$ $< Q^{2} <$ 10.0 (GeV/$c$)$^2$, 5.0 GeV/$c^2$ $< W <$ 17.0 GeV/$c^2$ and 0.01 (GeV/$c$)$^2$ $<p^{2}_{T} < $ 0.5 (GeV/$c$)$^2$. Here, $W$ denotes the mass of the final hadronic system, $Q^{2}$ the virtuality of the exchanged photon and $p_{T}$ the transverse momentum of the $\rho^{0}$ meson with respect to the virtual-photon direction. We observe a violation of s-channel helicity conservation for the transition $\gamma^{*}_{T} \to \rho^{0}_{L}$. Additionally, we find a dominant contribution of the natural-parity-exchange transitions.

• Quantum Monte Carlo simulation of the 3D Ising transition on the fuzzy sphere

  Johannes Stephan Hofmann, Florian Goth, Wei Zhu, Yin-Chen He, Emilie Huffman

  SciPost Phys. Core 7, 028 (2024) · published 9 May 2024 | Toggle abstract · pdf

  We present a numerical quantum Monte Carlo (QMC) method for simulating the 3D phase transition on the recently proposed fuzzy sphere [Phys. Rev. X 13, 021009 (2023)]. By introducing an additional SU(2) layer degree of freedom, we reformulate the model into a form suitable for sign-problem-free QMC simulation. From the finite-size-scaling, we show that this QMC-friendly model undergoes a quantum phase transition belonging to the 3D Ising universality class, and at the critical point we compute the scaling dimensions from the state-operator correspondence, which largely agrees with the prediction from the conformal field theory. These results pave the way to construct sign-problem-free models for QMC simulations on the fuzzy sphere, which could advance the future study on more sophisticated criticalities.

• Stochastic field dynamics in models of spontaneous unitarity violation

  Lotte Mertens, Matthijs Wesseling, Jasper van Wezel

  SciPost Phys. Core 7, 012 (2024) · published 13 March 2024 | Toggle abstract · pdf

  Objective collapse theories propose a solution to the quantum measurement problem by predicting deviations from Schrödinger's equation that can be tested experimentally. A class of objective theories based on spontaneous unitarity violation was recently introduced, in which the stochastic field required for obtaining Born's rule does not depend on the state of the system being measured. Here, we classify possible models for the stochastic field dynamics in theories of spontaneous unitarity violation. We show that for correlated stochastic dynamics, the field must be defined on a closed manifold. In two or more dimensions, it is then always possible to find stochastic dynamics yielding Born's rule, independent of the state being measured or the correlation time of the stochastic field. We show that the models defined this way are all isomorphic to the definition on a two-sphere, which we propose to be a minimal physical model for the stochastic field in models of spontaneous unitarity violation.

• Exact effective action for the O(N) vector model in the large N limit

  Han Ma, Sung-Sik Lee

  SciPost Phys. 15, 111 (2023) · published 22 September 2023 | Toggle abstract · pdf

  We present the Wilsonian effective action as a solution of the exact RG equation for the critical $O(N)$ vector model in the large $N$ limit. Below four dimensions, the exact effective action can be expressed in a closed form as a transcendental function of two leading scaling operators with infinitely many derivatives. From the exact solution that describes the RG flow from a UV theory to the fixed point theory in the IR, we obtain the mapping between UV operators and IR scaling operators. It is shown that IR scaling operators are given by sums of infinitely many UV operators with infinitely many derivatives.

• Thermodynamic Bethe Ansatz and generalised hydrodynamics in the sine-Gordon model

  Botond C. Nagy, Gábor Takács, Márton Kormos

  SciPost Phys. 16, 145 (2024) · published 4 June 2024 | Toggle abstract · pdf

  We set up a hydrodynamic description of the non-equilibrium dynamics of sine-Gordon quantum field theory for generic coupling. It is built upon an explicit form of the Bethe Ansatz description of general thermodynamic states, with the structure of the resulting coupled integral equations encoded in terms of graphical diagrams. The resulting framework is applied to derive results for the Drude weights of charge and energy. Quantities associated with the charge universally have fractal dependence on the coupling, which is notably absent from those associated with energy, a feature explained by the different roles played by reflective scattering in transporting these quantities. We then present far-from-equilibrium results, including explicit time evolution starting from bipartite initial states and dynamical correlation functions. Our framework can be applied to explore numerous other aspects of non-equilibrium dynamics, which opens the way to a wide array of theoretical studies and potential novel experimental predictions.

• Physics from Photons at the LHC

  Lucian Harland-Lang

  SciPost Phys. Proc. 8, 072 (2022) · published 12 July 2022 | Toggle abstract · pdf

  LHC collisions can act as a source of photons in the initial state. This mechanism plays an important role in the production of particles with electroweak couplings, and a precise account of photon-initiated (PI) production at the LHC is a key ingredient in the LHC precision physics programme. I will discuss the possibility of modelling PI processes directly via the structure function approach. This can provide percent level precision in the production cross sections, and is therefore well positioned to account for LHC precision requirements. This formalism in addition allows one to make use of another useful feature of photons, namely that they are colour-singlet and can often be emitted elastically (or quasi-elastically) from the proton. I will discuss recent work on applications of the structure function approach to precision calculations of PI production in the inclusive mode, and to `exclusive' processes with rapidity gaps, which can provide a unique probe of the Standard Model and physics beyond it.

• What do DVCS data tell us about TCS observables?

  O. Grocholski, H. Moutarde, B. Pire, P. Sznajder, J. Wagner

  SciPost Phys. Proc. 8, 070 (2022) · published 12 July 2022 | Toggle abstract · pdf

  Deeply virtual Compton scattering (DVCS) and timelike Compton scattering (TCS) leading twist amplitudes are intimately related thanks to their analytic properties as a function of $Q^2$. We exploit this feature to use Compton form factors previously extracted from available DVCS data and derive data-driven predictions for TCS observables to be measured in near future experiments. Our results quantitatively illustrate the complementarity of DVCS and TCS experiments.

• Pion electronic decay and lepton universality

  D. Počanić

  SciPost Phys. Proc. 5, 025 (2021) · published 6 September 2021 | Toggle abstract · pdf

  In common with a number of simple processes involving elementary particles, charged pion decays are profoundly shaped by applicable Standard Model (SM) symmetries and properties. Given the highly precise SM theoretical description, pion decays are used as selective probes of SM parameters, and of possible SM extensions. The PEN experiment at PSI is studying the π + → e + ν e (γ), or π_ e2(γ) decay. The primary goal is to reach the relative precision of 5 × 10 ^{−4} in Re/μ^π, the branching ratio for π_ e2(γ) decay. We review the PEN research program, its present status, and prospects.