Publications

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• Tau identification in CMS during LHC run 2

  Mohammad Hassan Hassanshahi

  SciPost Phys. Proc. 16, 018 (2025) · published 15 July 2025 | Toggle abstract · pdf

  The LHC Run 2 data-taking period was characterized by an increase in instantaneous luminosity and center-of-mass energy. Several techniques have been deployed in the CMS experiment to reconstruct and identify tau leptons in this environment. The DeepTau identification algorithm is used to identify hadronically decaying tau leptons from quark and gluon induced jets, electrons, and muons. Compared to previously used MVA identification algorithms, the use of deep-learning techniques brought a noticeable improvement in the tau identification and rejection of contaminating sources. Low transverse momentum topologies were addressed separately with a dedicated identification algorithm, while machine learning techniques were implemented to improve the identification of the tau hadronic decay channels. These algorithms have been already used for several published physics analyses in CMS. The algorithms are presented together with their measured performances.

• Latest results concerning short range correlations obtained in the dp elastic and dp breakup processes at Nuclotron, JINR

  Marian Janek, Vladimir P. Ladygin, Alexander V. Averyanov, Eugene V. Chernykh, Dan D. Enache, Yuri V. Gurchin, Alexandr Yu. Isupov, Julia-Tatiana Karachuk, Anatoly N. Khrenov, Dimitry O. Krivenkov, Pavel K. Kurilkin, Nadezhda B. Ladygina, Alexei N. Livanov, Olena Mezhenska, Semen M. Piyadin, Sergei G. Reznikov, Yaroslav T. Skhomenko, Arkady A. Terekhin, Alexei V. Tishevsky, Tomohiro Uesaka

  SciPost Phys. Proc. 3, 011 (2020) · published 24 February 2020 | Toggle abstract · pdf

  Deuteron spin structure program is aimed on extraction of two and three nucleon forces information, including their spin dependent parts, from dp elastic and dp breakup processes investigated at intermediate energies. The dp elastic data were obtained at Internal Target Station of Nuclotron (JINR) in the energy range 400-1800 MeV using polarized deuteron beam. Strong sensitivity to the short range spin structure of the isoscalar nucleon-nucleon correlations is observed in deuteron analyzing powers. Preliminary results of the the cross section for the dp breakup reaction have been obtained at 400 MeV of deuteron energy.

• Necklace Ansatz for strongly repulsive spin mixtures on a ring

  Gianni Aupetit-Diallo, Giovanni Pecci, Artem Volosniev, Mathias Albert, Anna Minguzzi, Patrizia Vignolo

  SciPost Phys. Core 8, 022 (2025) · published 14 February 2025 | Toggle abstract · pdf

  We propose an alternative to the Bethe Ansatz method for repulsive strongly-interacting fermionic (or bosonic) mixtures on a ring. Starting from the knowledge of the solution for single-component non-interacting fermions (or strongly-interacting bosons), we explicitly impose periodic condition on the amplitudes of the spin configurations. This reduces drastically the number of independent complex amplitudes that we determine by constrained diagonalization of an effective Hamiltonian. This procedure allows us to obtain a complete basis for the exact low-energy many-body solutions for mixtures with a large number of particles, both for $SU(\kappa)$ and symmetry-breaking systems.

• Recent results from LHCb for astroparticle physics

  Hans Dembinski on behalf of the LHCb collaboration

  SciPost Phys. Proc. 13, 016 (2023) · published 28 September 2023 | Toggle abstract · pdf

  The LHCb experiment is a general-purpose forward spectrometer designed for the study of heavy flavour physics at the LHC. The acceptance in the pseudorapidity range $2 < \eta < 5$ with full tracking and particle identification capabilities down to very small transverse momentum make LHCb also ideal to study hadron production in the forward region. Measuring and modelling these processes is essential for the simulation of interactions of high-energy cosmic rays with matter, like Earth's atmosphere or the interstellar medium. We present recently published analyses from the LHCb collaboration relevant for this application.

• Status and prospects for $\tau$ property measurements at Belle II

  Michel Hernández Villanueva

  SciPost Phys. Proc. 16, 015 (2025) · published 14 July 2025 | Toggle abstract · pdf

  Belle II is a major upgrade of the Belle detector, operating at the SuperKEKB asymmetric-energy $e^+e^-$ collider with a design luminosity of 8×$10^{35}$ cm$^{-2}$s$^{-1}$. To date, the detector has recorded over 200 fb$^{-1}$ of data and aims to collect 50 ab$^{-1}$, a factor of 50 more than its predecessor. Belle II has a broad $\tau$ physics program, from high-precision measurements of Standard Model parameters to searches of new non-Standard-Model interactions. In this work, we review the status of the Belle II experiment and the prospects for the measurement of the $\tau$ lepton mass and lifetime, which are fundamental inputs in tests of LFU violation.

• Inclusive decays of heavy quark hybrids

  Abhishek Mohapatra

  SciPost Phys. Proc. 6, 008 (2022) · published 31 May 2022 | Toggle abstract · pdf

  In order to understand the nature of the XYZ particles, theoretical predictions of the various XYZ decay modes are essential. In this work, we focus on the semi-inclusive decays of heavy quarkonium hybrids into traditional quarkonium in the EFT framework. We begin with weakly coupled potential NRQCD effective theory that describes systems with two heavy quarks and incorporates multipole expansions and use it to develop a Born-Oppenheimer effective theory (BOEFT) to describe the hybrids and compute the semi-inclusive decay rates. We compute both the spin-conserving and spin-flipping decay rates and find that our numerical results of the decay rates are different from the previous studies. We also develop a systematic framework in which the theoretical uncertainty can be systematically improved.

• Implications of new physics in $\Lambda_b \to \Lambda_c \ell \nu_{\ell}$ decay processes

  Aishwarya Bhatta, Rukmani Mohanta

  SciPost Phys. Proc. 16, 012 (2025) · published 14 July 2025 | Toggle abstract · pdf

  Several indications of lepton non universality ratios, $R{(D^*)}$, $R{(J/\Psi)}$ and the measurements on hadronic and $\tau$ longitudinal polarizations in $b \to c \ell \bar{\nu_{\tau}}$ processes have attracted a lot of attentions. By considering the most general effective Lagrangian, we carry out a model independent analysis of the semileptonic $\Lambda_b$ decays, to inspect the nature of new physics. We constraint the new physics parameter space by using the chi square fitting. We study the implications of constrained new couplings on the observable such as branching fractions, forward-backward asymmetries, lepton non universality parameter and $\Lambda_c$ and lepton longitudinal polarization fractions of the decay modes.

• Breaking Standard Model global symmetries with the tau lepton

  Jorge Portolés

  SciPost Phys. Proc. 16, 010 (2025) · published 14 July 2025 | Toggle abstract · pdf

  Properties of the dynamics of the Standard Model processes such as lepton flavour preservation and lepton, or baryon, number conservation, are usually taken for granted. The only reason is that it seems that these non-gauge accidental symmetries of the Standard Model seem to be conserved in Nature with great accuracy. In addition, the coupling of lepton doublets to the electroweak gauge bosons is universal and does not depend on the flavour. The discovery of the non-zero mass of the neutrinos and, maybe, the hints coming from the B-anomalies at LHCb, point out to a different scenario. I will briefly summarize some aspects of these contingent symmetries as seen from tau lepton processes.

• Magnetic, electronic, and structural investigation of the strongly correlated Y$_{1-x}$Sm$_{x}$Co$_5$ system

  F. Passos, D. Cornejo, G. J. Nilsen, V. Martelli, J. Larrea Jiménez

  SciPost Phys. Proc. 11, 021 (2023) · published 6 June 2023 | Toggle abstract · pdf

  SmCo$_5$ and YCo$_5$ are isostructural compounds both showing large magnetocrystalline anisotropy, where the former originates mainly from the crystal-electric field and magnetic interactions. We investigate the contribution of both interactions by partially substituting Y by Sm in as-cast polycrystalline Y$_{1-x}$Sm$_{x}$Co$_5$ (with $x$=0.00, 0.12, 0.18, 0.31, and 0.40) and measuring their structural, magnetic, and electrical properties through X-ray diffraction, magnetization, and electrical transport measurements. Our results suggest an interplay between microstructure strain in as-cast samples and the electronic and magnetic interactions.

• Influence of the Pauli principle on two-cluster potential energy

  Yuliya A. Lashko, Victor S. Vasilevsky, Gennady F. Filippov

  SciPost Phys. Proc. 3, 021 (2020) · published 25 February 2020 | Toggle abstract · pdf

  We study effects of the Pauli principle on the potential energy of two-cluster systems. The object of the investigation is the lightest nuclei of p-shell with a dominant $\alpha$-cluster channel. For this aim we construct matrix elements of two-cluster potential energy between cluster oscillator functions with and without full antisymmetrization. Eigenvalues and eigenfunctions of the potential energy matrix are studied in detail. Eigenfunctions of the potential energy operator are presented in oscillator, coordinate and momentum spaces. We demonstrate that the Pauli principle affects more strongly the eigenfunctions than the eigenvalues of the matrix and leads to the formation of resonance and trapped states.