More Like this

1. Observation of $\text{γ}\text{γ}\to \text{τ}\text{τ}$ in proton–proton collisions and limits on the anomalous electromagnetic moments of the τ lepton

   https://doi.org/10.1088/1361-6633/ad6fcb  

   CMS_Collaboration, The (September 2024, Reports on Progress in Physics)

   Abstract The production of a pair of τ leptons via photon–photon fusion, $\text{γ}\text{γ}\to \text{τ}\text{τ}$, is observed for the first time in proton–proton collisions, with a significance of 5.3 standard deviations. This observation is based on a data set recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb⁻¹. Events with a pair of τ leptons produced via photon–photon fusion are selected by requiring them to be back-to-back in the azimuthal direction and to have a minimum number of charged hadrons associated with their production vertex. The τ leptons are reconstructed in their leptonic and hadronic decay modes. The measured fiducial cross section of $\text{γ}\text{γ}\to \text{τ}\text{τ}$is ${\sigma }_{\text{obs}}^{\text{fid}}={12.4}_{-3.1}^{+3.8}\text{fb}$. Constraints are set on the contributions to the anomalous magnetic moment ( $a_{\text{τ}}$) and electric dipole moments ( $d_{\text{τ}}$) of the τ lepton originating from potential effects of new physics on the $\text{γ}\text{τ}\text{τ}$vertex: $a_{\text{τ}}={0.0009}_{-0.0031}^{+0.0032}$and $|d_{\text{τ}}|<2.9\times {10}^{-17}e\text{cm}$(95% confidence level), consistent with the standard model. 

   more » « less
2. Experimental investigation of circumnutation-inspired penetration in sand

   https://doi.org/10.1088/1748-3190/ad8c89  

   Anilkumar, Riya; Martinez, Alejandro (November 2024, Bioinspiration & Biomimetics)

   Probes that penetrate soil are used in fields such as geotechnical engineering, agriculture, and ecology to classify soils and characterize their propertiesin situ. Conventional tools such as the Cone Penetration Test (CPT) often face challenges due to the lack of reaction force needed to penetrate stiff or dense soil layers, necessitating the use of large drill rigs. This paper investigates more efficient means of penetrating soil by taking inspiration from a plant-root motion known as circumnutation. Experimental penetration tests on sands are performed with circumnutation-inspired (CI) probes that advance at a constant vertical velocity ( $v$) while simultaneously rotating at a constant angular velocity ( $\omega$). These probes have bent tips with a given bent angle ( $\alpha$) and bent length ( $L_1$). The variation of the mobilized vertical force ( $F_z$), torque ( $T_z$.), and the mechanical work components with the ratio of tangential to vertical velocity (ωR/ν, whereRis the distance of the tip of the probe from the vertical axis of rotation) is investigated along with the effects of probe geometry, vertical velocity, and soil relative density ( $D_R$). The results show that the soil penetration resistance does not vary with $v$, but it increases as $\alpha$, $L_1$, and $D_R$are increased. $F_z$decays exponentially with increasing $\omega R/v$, $T_z$initially increases and then plateaus, while total work ( $W_T$) shows little magnitude changes initially but later increases monotonically. The mechanisms leading to these trends are identified as the changes in the probe projected areas and mobilized normal stresses due to differences in probe geometry and the effects of $\omega R/v$on the resultant force direction and soil disturbance. The results show that CI penetration within a specific range of $\omega R/v$leads to small increases in $W_T$(i.e., $\text{⩽}$25%), yet mobilizes $F_z$magnitudes that are 50%–80% lower than that mobilized during non-rotational penetration (i.e., CPT). This indicates that CI penetration can be adopted forin situcharacterization or sensor placement with smaller vertical forces, allowing for use of lighter rigs. 

   more » « less
3. Observation of quantum entanglement in top quark pair production in proton–proton collisions at $\sqrt{s}=13$  TeV

   https://doi.org/10.1088/1361-6633/ad7e4d  

   CMS_Collaboration, The (October 2024, Reports on Progress in Physics)

   Abstract Entanglement is an intrinsic property of quantum mechanics and is predicted to be exhibited in the particles produced at the Large Hadron Collider. A measurement of the extent of entanglement in top quark-antiquark ( $\mathrm{t}\overline{\mathrm{t}}$) events produced in proton–proton collisions at a center-of-mass energy of 13 TeV is performed with the data recorded by the CMS experiment at the CERN LHC in 2016, and corresponding to an integrated luminosity of 36.3 fb⁻¹. The events are selected based on the presence of two leptons with opposite charges and high transverse momentum. An entanglement-sensitive observableDis derived from the top quark spin-dependent parts of the $\mathrm{t}\overline{\mathrm{t}}$production density matrix and measured in the region of the $\mathrm{t}\overline{\mathrm{t}}$production threshold. Values of $D<-1/3$are evidence of entanglement andDis observed (expected) to be $-{0.480}_{-0.029}^{+0.026}$( $-{0.467}_{-0.029}^{+0.026}$) at the parton level. With an observed significance of 5.1 standard deviations with respect to the non-entangled hypothesis, this provides observation of quantum mechanical entanglement within $\mathrm{t}\overline{\mathrm{t}}$pairs in this phase space. This measurement provides a new probe of quantum mechanics at the highest energies ever produced. 

   more » « less
4. No-boundary state for Klein space

   https://doi.org/10.1088/1751-8121/adc882  

   Melton, Walker; Sharma, Atul; Strominger, Andrew; Wang, Tianli (April 2025, Journal of Physics A: Mathematical and Theoretical)

   Abstract Analytic continuation from (3, 1) signature Minkowski to (2, 2) signature Klein space has emerged as a useful tool for the understanding of scattering amplitudes and flat space holography. Under this continuation, past and future null infinity merge into a single boundary ( $J$) which is the product of a null line with a (1, 1) signature torus. The Minkowskian $S$-matrix continues to a Kleinian $S$-vector which in turn may be represented by a Poincaré-invariant vacuum state $|C⟩$in the Hilbert space built on $J$. $|C⟩$contains all information about $S$in a novel, repackaged form. We give an explicit construction of $|C⟩$in a Lorentz/conformal basis for a free massless scalar. $J$separates into two halves $J_{\pm }$which are the asymptotic null boundaries of the regions timelike and spacelike separated from the origin. $|C⟩$is shown to be a maximally entangled state in the product of the $J_{\pm }$Hilbert spaces. 

   more » « less
5. Machine learning-powered data cleaning for LEGEND: a semi-supervised approach using affinity propagation and support vector machines

   https://doi.org/10.1088/2632-2153/adbb37  

   León, E; Li, A; Bahena_Schott, M A; Bos, B; Busch, M; Chapman, J R; Duran, G L; Gruszko, J; Henning, R; Martin, E L; et al (March 2025, Machine Learning: Science and Technology)

   Abstract Neutrinoless double-beta decay ( $0\nu \beta \beta$) is a rare nuclear process that, if observed, will provide insight into the nature of neutrinos and help explain the matter-antimatter asymmetry in the Universe. The large enriched germanium experiment for neutrinoless double-beta decay (LEGEND) will operate in two phases to search for $0\nu \beta \beta$. The first (second) stage will employ 200 (1000) kg of High-Purity Germanium (HPGe) enriched in⁷⁶Ge to achieve a half-life sensitivity of 10²⁷(10²⁸) years. In this study, we present a semi-supervised data-driven approach to remove non-physical events captured by HPGe detectors powered by a novel artificial intelligence model. We utilize affinity propagation to cluster waveform signals based on their shape and a support vector machine to classify them into different categories. We train, optimize, and test our model on data taken from a natural abundance HPGe detector installed in the Full Chain Test experimental stand at the University of North Carolina at Chapel Hill. We demonstrate that our model yields a maximum sacrifice of physics events of ${0.024}_{-0.003}^{+0.004}\mathrm{\%}$after data cleaning. Our model is being used to accelerate data cleaning development for LEGEND-200 and will serve to improve data cleaning procedures for LEGEND-1000. 

   more » « less