Hasil untuk "Elementary particle physics"

S. Glashow

The CMS collaboration, V. Chekhovsky, A. Hayrapetyan et al.

Abstract A search for nonresonant new physics phenomena in high-mass dilepton events produced in association with b-tagged jets is performed using proton-proton collision data collected in 2016–2018 by the CMS experiment at the CERN LHC, at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138 fb −1. The analysis considers two effective field theory models with dimension-six operators; involving four-fermion contact interactions between two leptons (ℓℓ, electrons or muons) and b or s quarks (bbℓℓ and bsℓℓ). Two lepton flavor combinations (ee and μμ) are required and events are classified as having 0, 1, or ≥2 b-tagged jets in the final state. No significant excess is observed over the standard model backgrounds. Upper limits are set on the production cross section of the new physics signals. These translate into lower limits on the energy scale Λ of 6.9 to 9.0 TeV in the bbℓℓ model, depending on model parameters, and on the ratio of energy scale and effective coupling, Λ/g *, of 2.0 to 2.6 TeV in the bsℓℓ model. Lepton flavor universality is also tested by comparing the dielectron (ee) and dimuon (μμ) mass spectra for different b-tagged jet multiplicities. No significant deviation from the standard model expectation of unity is observed.

Archana Dixit, Saurabh Verma, Anirudh Pradhan et al.

In this study, we explored the cosmological implications of the modified gravity framework <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>,</mo><msub><mi>L</mi><mi>m</mi></msub><mo>)</mo></mrow></semantics></math></inline-formula>, taking the specific form <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>f</mi><mrow><mo>(</mo><mi>R</mi><mo>,</mo><msub><mi>L</mi><mi>m</mi></msub><mo>)</mo></mrow><mo>=</mo><mstyle scriptlevel="0" displaystyle="false"><mfrac><mi>R</mi><mn>2</mn></mfrac></mstyle><mo>+</mo><msubsup><mi>L</mi><mi>m</mi><mi>n</mi></msubsup><mo>,</mo></mrow></semantics></math></inline-formula> where <i>n</i> denotes the model parameter. The analysis was carried out within a spatially flat FLRW background by adopting the Barboza–Alcaniz (BA) parametrization for the dark energy equation of state, expressed as <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>ω</mi><mrow><mo>(</mo><mi>z</mi><mo>)</mo></mrow><mo>=</mo><msub><mi>w</mi><mn>0</mn></msub><mo>+</mo><msub><mi>w</mi><mn>1</mn></msub><mstyle scriptlevel="0" displaystyle="false"><mfrac><mrow><mi>z</mi><mo>(</mo><mn>1</mn><mo>+</mo><mi>z</mi><mo>)</mo></mrow><mrow><mn>1</mn><mo>+</mo><msup><mi>z</mi><mn>2</mn></msup></mrow></mfrac></mstyle><mo>.</mo></mrow></semantics></math></inline-formula> Based on this setup, an expression for the Hubble parameter <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>H</mi><mo>(</mo><mi>z</mi><mo>)</mo></mrow></semantics></math></inline-formula> was derived. The parameters <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>(</mo><msub><mi>H</mi><mn>0</mn></msub><mo>,</mo><mi>n</mi><mo>,</mo><msub><mi>w</mi><mn>0</mn></msub><mo>,</mo><msub><mi>w</mi><mn>1</mn></msub><mo>)</mo></mrow></semantics></math></inline-formula> were estimated using a Bayesian Markov Chain Monte Carlo (MCMC) technique, implemented via the <i>emcee</i> package, with Cosmic Chronometers (CC), Pantheon Plus & SH0ES (PPS) and DESI BAO datasets. For the CC+PPS+DESI BAO combination, the best-fit Hubble constant was obtained as <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>H</mi><mn>0</mn></msub><mo>=</mo><msubsup><mn>72.08</mn><mrow><mo>−</mo><mn>0.24</mn></mrow><mrow><mo>+</mo><mn>0.30</mn></mrow></msubsup><mspace width="0.166667em"></mspace><mi>km</mi><mspace width="0.166667em"></mspace><msup><mi mathvariant="normal">s</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup><mspace width="0.166667em"></mspace><msup><mi>Mpc</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup><mo>,</mo></mrow></semantics></math></inline-formula> which shows better consistency with the local SH0ES measurement than with the Planck <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mo>Λ</mo></semantics></math></inline-formula>CDM result, thereby reducing the Hubble tension. Furthermore, the dynamical evolution of the equation of state parameter <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>ω</mi></semantics></math></inline-formula>, the deceleration parameter, the impact of various energy conditions, and the optimal model parameters were thoroughly examined. The study also investigated the behavior of the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>(</mo><msub><mi>O</mi><mi>m</mi></msub><mo>)</mo></mrow></semantics></math></inline-formula> diagnostic and determined the present age of the universe predicted by this model.

Martin Rivas

Matter has two physical properties: Inertia and interaction. If we define the center of mass of an elementary particle in relation to its inertia, and a center of interaction in relation to its interactive properties, there are only two possibilities to describe this elementary particle: that both points are the same or that they are different. If they are the same, what we describe is the point particle model, while if we consider them to be different, what we obtain is the description of an elementary spinning particle. If the center of interaction or center of charge is moving at the speed of light, completely determines also the dynamics of the center of mass, and when quantizing this model satisfies Dirac's equation. We obtain the classical description of the spinning Dirac particle. The general analysis of the interaction Lagrangian, suggests a modification of the minimal coupling Lagrangian, for a possible classical description of the strong and weak interaction.

Hao-Lin Li, Hao Sun, Ming-Lei Xiao et al.

In this review, the fundamental concepts of group theory and representation theory are introduced. Special emphasis is placed on the unitary irreducible representations of the $SU(N)$ Lie group, the Poincare group, Little Group, discrete group, and their applications in particle physics. Based on the principle of local gauge symmetry, the construction of gauge-invariant Lagrangians and their quantization procedure are discussed. To address gauge redundancy, the modern on-shell amplitude approach is applied to gauge theories, demonstrating both conceptual and computational advantages. From the perspective of symmetry, the Standard Model is presented through the identification of its gauge symmetry, its anomaly-free matter content, and its global symmetries, including flavor symmetry, custodial symmetry, and baryon and lepton number conservation, etc.

Shaoguang Guo, Tao An, Yuanqi Liu et al.

High-redshift active galactic nuclei (AGN) provide key insights into early supermassive black hole growth and cosmic evolution. This study investigates the parsec-scale properties of 86 radio-loud quasars at z ≥ 3 using very long baseline interferometry (VLBI) observations. Our results show predominantly compact core and core-jet morphologies, with 35% having unresolved cores, 59% with core–jet structures, and only 6% with core–double jet morphology. Brightness temperatures are generally lower than expected for highly radiative sources. The jets’ proper motions are surprisingly slow compared to those of lower-redshift samples. We observe a high fraction of young and/or confined peak-spectrum sources, providing insights into early AGN evolution in dense environments during early cosmic epochs. The observed trends may reflect genuine evolutionary changes in AGN structure over cosmic time, or selection effects favoring more compact sources at higher redshifts. These results stress the complexity of high-redshift radio-loud AGN populations and emphasize the need for multi-wavelength, high-resolution observations to fully characterize their properties and evolution through cosmic history.

Chaoxin Luo, Xin Xu, Changrong Du et al.

Utilizing the databases from the European Pulsar Network (EPN), the Australia Telescope National Facility (ATNF), and published literature data, a geometric method was used to investigate the multifrequency emission altitude of 104 pulsars. We found that the evolution of emission altitudes with frequency for the majority of pulsars can be fitted using a power-law function with a normalization constant. In this work, it is found that the frequency evolution of pulsar emission altitude can be divided into three groups according to their different frequency dependencies of emission altitude (emission altitude decreases with frequency (Group A, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>η</mi><mo>≤</mo><mo>−</mo><mn>0.1</mn></mrow></semantics></math></inline-formula>), keeps relatively constant with frequency (Group B, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo><mn>0.1</mn><mo><</mo><mi>η</mi><mo>≤</mo><mn>0.1</mn></mrow></semantics></math></inline-formula>), and increases with frequency (Group C, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>η</mi><mo>≥</mo><mn>0.1</mn></mrow></semantics></math></inline-formula>)), where <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>η</mi></semantics></math></inline-formula> is the emission altitude variation rate. We also computed the emission altitudes across multiple frequency bands for these pulsars, thereby estimating the approximate range of the pulsar emission regions. We found that most pulsar emissions occur at altitudes of tens to hundreds of kilometers above the polar cap, with differences in emission altitude between the three groups becoming more clear at lower frequencies.

Yasmine Amhis, Jeremy Andrea, Etienne Augé et al.

In view of the European Strategy for Particle Physics process, the French HEP community has organized a national process of collecting written contributions and has pursued a series of workshops culminating with a national symposium held in Paris on January 20-21, 2025 that involved over 280 scientists https://indico.in2p3.fr/event/34662/. The present document summarises the main conclusions of this bottom-up approach centred on the physics and technology motivations.

Markus Q. Huber

Functional methods like Dyson-Schwinger equations, the nPI effective action formalism, bound state equations and the functional renormalization group are versatile tools to study quantum field theories. They are exact, nonperturbative equations but have to be truncated for practical calculations. After a general introduction, I focus on their use in particle physics and discuss common truncations and solution techniques. The complete process from choosing a truncation to calculating observable quantities is exemplified by means of the glueball spectrum.

U. de Freitas Carneiro da Graça, G. Gil da Silveira, C. Jahnke et al.

The Brazilian High-Energy Physics (HEP) community has expanded remarkably since its first involvement at CERN and Fermilab in the 1980s. Its recent organization under the Brazilian Network for High-Energy Physics (RENAFAE), since 2008, has further strengthened its scientific and technological goals, particularly in detector instrumentation, computing, and industry partnerships. In 2024, Brazil became an Associate Member State of CERN, opening new opportunities for deeper engagement in accelerator and detector R&D. This input to the 2026 update of the European Strategy for Particle Physics highlights Brazil's current participation in LHC experiments as well as ongoing developments in detector and accelerator technology, and details the community's view towards future colliders. The potential for expanded scientific and industrial collaborations between Brazil and CERN is also discussed.

Stefan Diehl, Raphaël Dupré, Olga Evdokimov et al.

This document is submitted as input to the European Strategy for Particle Physics Update (ESPPU). The U.S.-based Electron-Ion Collider (EIC) aims at understanding how the complex dynamics of confined quarks and gluons makes up nucleons, nuclei and all visible matter, and determines their macroscopic properties. In April 2024, the EIC project received approval for critical-decision 3A (CD-3A) allowing for Long-Lead Procurement, bringing its realization another step closer. The ePIC Collaboration was established in July 2022 around the realization of a general purpose detector at the EIC. The EIC is based in U.S.A. but is characterized as a genuine international project. In fact, a large group of European scientists is already involved in the EIC community: currently, about a quarter of the EIC User Group (consisting of over 1500 scientists) and 29% of the ePIC Collaboration (consisting of $\sim$1000 members) is based in Europe. This European involvement is not only an important driver of the EIC, but can also be beneficial to a number of related ongoing and planned particle physics experiments at CERN. In this document, the connections between the scientific questions addressed at CERN and at the EIC are outlined. The aim is to highlight how the many synergies between the CERN Particle Physics research and the EIC project will foster progress at the forefront of collider physics.

F. Archilli, Sw. Banerjee, E. Ben-Haim et al.

Heavy-flavour physics is an essential component of the particle-physics programme, offering critical tests of the Standard Model and far-reaching sensitivity to physics beyond it. Experiments such as LHCb, Belle II, and BESIII drive progress in the field, along with contributions from ATLAS and CMS. The LHCb Upgrade II and upgraded Belle II experiments will provide unique and highly sensitive measurements for decades, playing a key role in the searches for new physics. Future facilities with significant heavy-flavour capabilities will further expand these opportunities. We advocate for a European Strategy that fully supports Upgrade II of LHCb and an upgrade of Belle II, along with their subsequent exploitation. Additionally, we support a long-term plan that fully integrates flavour physics in an $e^+e^-$ collider to run as a $Z$ factory.

PIONEER Collaboration, A. Adelmann, W. Altmannshofer et al.

PIONEER is a rapidly developing effort aimed to perform a pristine test of lepton flavour universality (LFU) and of the unitarity of the first row of the CKM matrix by significantly improving the measurements of rare decays of the charged pion. In Phase I, PIONEER aims to measure the charged-pion branching ratio to electrons vs.\ muons $R_{e/μ}$ to 1 part in $10^4$, improving the current experimental result $R_{e/μ}\,\text{(exp)} =1.2327(23)\times10^{-4}$ by a factor of 15. This precision on $R_{e/μ}$ will match the theoretical accuracy of the SM prediction allowing for a test of LFU at an unprecedented level, probing non-SM explanations of LFU violation through sensitivity to quantum effects of new particles up to the PeV mass scale. Phase II and III will aim to improve the experimental precision of the branching ratio of pion beta decay, $π^+\to π^0 e^+ ν(γ)$, currently at $1.036(6)\times10^{-8}$, by a factor of three and six, respectively. The improved measurements will be used to extract $V_{ud}$ in a theoretically pristine manner. The ultimate precision of $V_{ud}$ is expected to reach the 0.05\,\% level, allowing for a stringent test of CKM unitarity. The PIONEER experiment will also improve the experimental limits by an order of magnitude or more on a host of exotic decays that probe the effects of heavy neutrinos and dark sector physics. This input to the 2026 update of the European Strategy for Particle Physics Strategy describes the physics motivation and the conceptual design of the PIONEER experiment, and is prepared based on the PIONEER proposal submitted to and approved with high priority by the PSI program advisory committee (PAC). Using intense pion beams, and state-of-the-art instrumentation and computational resources, the PIONEER experiment is aiming to begin data taking by the end of this decade.

Guillermo A. Mena Marugán, Antonio Vicente-Becerril, Jesús Yébana Carrilero

We investigate the implications of different quantization approaches in Loop Quantum Cosmology for the primordial power spectrum of tensor modes. Specifically, we consider the hybrid and dressed metric approaches to derive the effective mass that governs the evolution of the tensor modes. Our study comprehensively examines the two resulting effective masses and how to estimate them in order to obtain approximated analytic solutions to the tensor perturbation equations. Since Loop Quantum Cosmology incorporates preinflationary effects in the dynamics of the perturbations, we do not have at our disposal a standard choice of privileged vacuum, like the Bunch–Davies state in quasi-de Sitter inflation. We then select the vacuum state by a recently proposed criterion which removes unwanted oscillations in the power spectrum and guarantees an asymptotic diagonalization of the Hamiltonian in the ultraviolet. This vacuum is usually called the NO-AHD (from the initials of Non-Oscillating with Asymptotic Hamiltonian Diagonalization) vacuum. Consequently, we compute the power spectrum by using our analytic approximations and by introducing a suitable numerical procedure, adopting in both cases an NO-AHD vacuum. With this information, we compare the different spectra obtained from the hybrid and the dressed metric approaches, as well as from the analytic and numerical procedures. In particular, this proves the remarkable accuracy of our approximations.

Da-Ming Chen, Lin Wang

The spin-torsion theory is a gauge theory approach to gravity that expands upon Einstein’s general relativity (GR) by incorporating the spin of microparticles. In this study, we further develop the spin-torsion theory to examine spherically symmetric and static gravitational systems that involve free-falling macroscopic particles. We posit that the quantum spin of macroscopic matter becomes noteworthy at cosmic scales. We further assume that the Dirac spinor and Dirac equation adequately capture all essential physical characteristics of the particles and their associated processes. A crucial aspect of our approach involves substituting the constant mass in the Dirac equation with a scale function, allowing us to establish a connection between quantum effects and the scale of gravitational systems. This mechanism ensures that the quantum effect of macroscopic matter is scale-dependent and diminishes locally, a phenomenon not observed in microparticles. For any given matter density distribution, our theory predicts an additional quantum term, the quantum potential energy (QPE), within the mass expression. The QPE induces time dilation and distance contraction, and thus mimics a gravitational well. When applied to cosmology, our theory yields a static cosmological model. The QPE serves as a counterpart to the cosmological constant introduced by Einstein to balance gravity in his static cosmological model. The QPE also offers a plausible explanation for the origin of Hubble redshift (traditionally attributed to the universe’s expansion). The predicted luminosity distance–redshift relation aligns remarkably well with SNe Ia data from the cosmological sample of SNe Ia. In the context of galaxies, the QPE functions as the equivalent of dark matter. The predicted circular velocities align well with rotation curve data from the SPARC (Spitzer Photometry and Accurate Rotation Curves database) sample. Importantly, our conclusions in this paper are reached through a conventional approach, with the sole assumption of the quantum effects of macroscopic matter at large scales, without the need for additional modifications or assumptions.

Nicolas Chamel

By compressing matter to densities up to several times the density of atomic nuclei, the catastrophic gravitational collapse of the core of stars with a mass <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>M</mi><mo>≳</mo><mn>8</mn><msub><mi>M</mi><mo>⊙</mo></msub></mrow></semantics></math></inline-formula> during supernova explosions and the neutron star left behind (see, e [...]

The CMS collaboration, A. Hayrapetyan, A. Tumasyan et al.

Abstract Measurements of inclusive and normalized differential cross sections of the associated production of top quark-antiquark and bottom quark-antiquark pairs, t t ¯ b b ¯ $$ \textrm{t}\overline{\textrm{t}}\textrm{b}\overline{\textrm{b}} $$ , are presented. The results are based on data from proton-proton collisions collected by the CMS detector at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb −1. The cross sections are measured in the lepton+jets decay channel of the top quark pair, using events containing exactly one isolated electron or muon and at least five jets. Measurements are made in four fiducial phase space regions, targeting different aspects of the t t ¯ b b ¯ $$ \textrm{t}\overline{\textrm{t}}\textrm{b}\overline{\textrm{b}} $$ process. Distributions are unfolded to the particle level through maximum likelihood fits, and compared with predictions from several event generators. The inclusive cross section measurements of this process in the fiducial phase space regions are the most precise to date. In most cases, the measured inclusive cross sections exceed the predictions with the chosen generator settings. The only exception is when using a particular choice of dynamic renormalization scale, μ R = 1 2 ∏ i = t , t ¯ , b , b ¯ m T , i 1 / 4 $$ {\mu}_{\textrm{R}}=\frac{1}{2}{\prod}_{i=\textrm{t},\overline{\textrm{t}},\textrm{b},\overline{\textrm{b}}}{m}_{\textrm{T},i}^{1/4} $$ , where m T , i 2 = m i 2 + p T , i 2 $$ {m}_{\textrm{T},i}^2={m}_i^2+{p}_{\textrm{T},i}^2 $$ are the transverse masses of top and bottom quarks. The differential cross sections show varying degrees of compatibility with the theoretical predictions, and none of the tested generators with the chosen settings simultaneously describe all the measured distributions.

Giuseppe Gaetano Luciano, Massimo Blasone

Among all the known particles in our Universe, neutrinos are definitely the most elusive and mysterious [...]

Cervelli Alberto

In the following a review of the present status of silicon tracking and vertexing systems and their future developments will be presented. We will show the modern detectors used in present day experiments both in nuclear and elementary particle physics, and their achieved performances. Later we present a review of the near-future systems which are now being designed, built, or commissioned together with an outlook on the future developments for next-generation silicon detectors.

Edward A. Rietman, Brandon Melcher, Alexey Bobrick et al.

We describe the construction of an optical-space, cylindrical black hole induced by high pressure in a dense fluid. Using an approximate analogy between curved spacetime and optics in moving dielectric media, we derive the mass of the black hole thus created. We describe the resulting optical-space using a Bessel beam profile and Snell’s law to understand how total internal reflection produces a cylindrical, optic black hole.