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Physics High Energy Physics (Experiment)

hep-ex Watch High Energy Physics (Experiment)

Saturday 3 October

High Energy Physics (Experiment) · Cross-listed from cs.AR

Alkaid: A Compiler Framework for Ultra-Low-Latency Kernels on Hardware

Chang Sun, Zhiqiang Que, Dimitrios Danopoulos et al. (+3 more)

Ultra-low-latency machine learning and data processing pipelines operating on the sub-microsecond level often contain static dataflow kernels that require fine-grained bitwidth control, arithmetic optimization, and fast hardware performance estimation. This works introduce Alkaid, a free and open source domain specific compiler that translates sub-microsecond latency dataflow kernels into platform agnostic Register Transfer Level (RTL) or High-Level Synthesis (HLS)-ready code in seconds. Alkaid targets ultra-low-latency ML pipelines, especially those addressed by existing ML-to-hardware flows such as hls4ml, while also supporting the surrounding pre-processing, post-processing, and control logic. At its core, Alkaid uses an arithmetic centric intermediate representation, Alkaid Low-level IR (ALIR), to preserve fixed-point semantics, heterogeneous bitwidths, and operation level structure for optimization and code generation. Alkaid further provides comprehensive hardware-aware optimization passes and an interpretable white-box analytical performance model for rapid design space exploration without synthesis in the loop. Across representative ML workloads, including MLPs, GNNs, and transformers, Alkaid achieves 20-30% lower LUT usage than the best prior flows for bit-exact equivalent designs, with up to 40% lower latency in some cases. Beyond typical neural networks, Alkaid achieves comparable performance to the state-of-the-art method for synthesizing boosted decision trees, while also enabling the implementation and integration of non-ML kernels such as sorting networks and histograms.
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All authors Chang Sun, Zhiqiang Que, Dimitrios Danopoulos, Maurizio Pierini, Wayne Luk, Maria Spiropulu

High Energy Physics (Experiment)

Search for Higgs boson compositeness effects in high-mass dilepton final states in proton-proton collisions at $\sqrt{s}$ = 13 and 13.6 TeV

CMS Collaboration

A search for beyond the standard model effects in high-mass dielectron and dimuon final states with the CMS detector is performed, with a specific focus on Higgs boson compositeness. The search uses data collected at the LHC at 13 and 13.6 TeV center-of-mass energies, corresponding to a total integrated luminosity of 207 fb$^{-1}$. Compositeness would manifest as distortions in the observed dilepton mass spectrum and the presence of bound states, such as the Higgs boson and new massive vector boson resonances. Assuming the existence of new boson states with masses well above the TeV scale, an effective field theory approach provides stringent bounds on the oblique parameters $\mathcal{W}$ and $\mathcal{Y}$, which are zero in the standard model. One-dimensional fits, in which only one of the oblique parameters is allowed to deviate from zero, provide the following limits: $-$3.9 $\times$ 10$^{-4}$$\lt$ $\mathcal{Y}$ $\lt$ 3.5 $\times$ 10$^{-4}$ and $-$2.1 $\times$ 10$^{-4}$ $\lt$ $\mathcal{W}$ $\lt$ 1.6 $\times$ 10$^{-4}$ at 95% confidence level. More stringent compositeness limits at the TeV scale are set in several new physics scenarios under the assumption that a new Z' resonance is physically present within or slightly above the visible dilepton mass spectrum. In this context, cases with large resonance decay widths are explored for the first time.
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High Energy Physics (Experiment) · Cross-listed from astro-ph.IM

Vector field dark matter search with Sagnac interferometer

Yuki Inoue, Quynh Lan Nguyen and Ippei Obata

We present the first calculation showing that a material-asymmetric Sagnac speed meter can improve quantum-noise-limited sensitivity to $B-L$ vector dark matter by nearly two orders of magnitude over a Fabry–Perot Michelson position meter at the low-mass end of the band. We introduce material contrast into a dual-ring interferometer to probe composition-dependent $B-L$ forces and compare the two configurations at equal incident power, input-mirror transmissivity, and cavity round-trip length. For sapphire mirrors and a one-week benchmark, the quantum-noise-only median expected $95\%$ CL upper limit reaches $1.2\times10^{-27}$ at $m_A=4.1\times10^{-14}\,\mathrm{eV}/c^2$ ($10\,\mathrm{Hz}$), a factor-$57$ improvement. This band-edge forecast assumes negligible classical noise; sensitivity at $10\,\mathrm{Hz}$ is not established for a realizable suspension and isolation system. The material-induced displacement is essentially identical in both configurations, with the gain arising from reduced low-frequency quantum backaction. These results identify speed-meter readout as a promising route to lower-mass vector-dark-matter searches.
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High Energy Physics (Experiment)

Simultaneous measurement of the Higgs boson decay rates to WW and ZZ in fully hadronic final states at FCC-ee

Jan Eysermans, Mila Pandurovic, Christoph Paus et al. (+2 more)

The precise determination of the Higgs boson couplings to electroweak gauge bosons is a key objective of the FCC-ee physics program. In particular, measurements of the Higgs boson couplings to W and Z bosons play a central role in the model-independent determination of its total decay width. This paper presents a study of Higgs boson decays to H -> WW and H -> ZZ in the Higgsstrahlung production process. The analysis focuses on events in which the associated Z boson and the vector bosons from the Higgs decay all decay hadronically, resulting in six-jet final states. The large H -> WW branching fraction leads to high signal statistics in the fully hadronic channel, while for H -> ZZ the much smaller Higgs branching fraction is partly compensated by the large hadronic branching fractions of the Z bosons. Due to the substantial kinematic overlap between the WW and ZZ decay modes, their signal strengths are extracted simultaneously. Jet-clustering and dedicated jet-pairing techniques are employed to optimize the reconstruction of the hadronically decaying gauge bosons and enhance the separation of the two signal components. Assuming a center-of-mass energy of 240 GeV and an integrated luminosity of 10.8 ab^-1, expected relative uncertainties of 1.48% and 8.20% are obtained on the production cross section times branching fraction, sigma(ZH) x BR, for the H -> WW and H -> ZZ decay modes, respectively.
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All authors Jan Eysermans, Mila Pandurovic, Christoph Paus, Michele Selvaggi, Aman Desai

High Energy Physics (Experiment) · Cross-listed from hep-ph

Angular Observables in the $\Lambda_{b}\to \Lambda \nu \bar{\nu}$ Decay

Wolfgang Altmannshofer and Shibasis Roy

We study the rare decay $\Lambda_b \rightarrow \Lambda(\rightarrow p\pi^-)\nu\bar{\nu}$ of polarized $\Lambda_b$ baryons produced at the $Z$ pole. We find that the differential decay distribution is characterized by five independent angular observables, four of which require initial $\Lambda_b$ polarization. While standard observables in mesonic $b \rightarrow s \nu \bar\nu$ decays ($B \rightarrow K^{(*)} \nu \bar{\nu}$, $B_s \rightarrow \phi \nu \bar{\nu}$) probe only two combinations of short-distance Wilson coefficients, $|C_L + C_R|$ and $|C_L - C_R|$, the angular observables in $\Lambda_b \rightarrow \Lambda(\rightarrow p\pi^-)\nu\bar{\nu}$ provide access to the orthogonal combinations $|C_R|^2 - |C_L|^2$ and $\text{Im}(C_L C_R^*)$. In particular, we identify a $T$-odd CP asymmetry, $A_5$, that directly probes CP-violating phases in the short-distance effective Hamiltonian. We present Standard Model predictions for the branching ratio and all angular observables using lattice QCD form factors, and evaluate the projected new physics sensitivity at the FCC-ee. Our results demonstrate that baryonic angular observables are essential for resolving parameter degeneracies and for completely characterizing the chiral and CP structure of possible new physics in $b \rightarrow s \nu \bar{\nu}$ transitions.
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Friday 2 October

High Energy Physics (Experiment) · Cross-listed from physics.ins-det

Application of sequence learning for predicting radiation damage of the CMS electromagnetic calorimeter

Mario Ivan Gallegos Torres, Leonid Serkin and Guy Paic

In this paper we use machine learning methods to predict radiation damage in the lead tungstate crystals of the CMS electromagnetic calorimeter at the Large Hadron Collider. We analyze LHC Open Data collected from 2016 to 2018 and study the time evolution of the crystal optical transparency. We apply deep neural network models to predict its behavior over different future time intervals, and find that encoder-decoder sequence-to-sequence architectures can effectively describe crystal aging.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

Reinterpreting ATLAS Dijet and Supersymmetry Searches in A Baryon-Number-Violating Heavy Scalar Framework

Tianyi Yang, Denis Rathjens, Alfredo Gurrola et al. (+1 more)

A reinterpretation of ATLAS searches targeting $b$-tagged dijet resonances and monotop-alike signatures at a center-of-mass energy of 13 TeV is presented using $pp$ collision data corresponding to integrated luminosities of 139 $\mathrm{fb}^{-1}$. These searches are used to constrain a baryon-number-violating new physics model that introduces two scalar mediators $X_{1}$ and $X_{2}$ to simultaneously address the baryon asymmetry of the universe and the dark matter relic abundance. By exploiting heavy-flavor signatures and allowing for jet-rich final states, this reinterpretation provides complementary sensitivity to the model relative to non-flavor-tagged inclusive dijet searches and conventional monotop reinterpretations. Assuming the mediators decay either into a pair of down-type quarks or into a top quark and a dark matter candidate, we translate the experimental upper limits into the model's parameter space. 95% confidence level exclusion limits are derived in the $\lambda_1$-$\lambda_2$ coupling plane for benchmark mediator masses of 1.5, 1.75, and 2.0 TeV. For all three benchmark masses, the $b$-tagged dijet reinterpretation excludes $\lambda_1 > 0.45$, while the bottom-squark reinterpretation excludes the region with $\lambda_1 > 0.3$ and $\lambda_2 > 0.6$, within the respective validated parameter domains.
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All authors Tianyi Yang, Denis Rathjens, Alfredo Gurrola, Francesco Romeo

High Energy Physics (Experiment) · Cross-listed from hep-ph

A Powheg generator for $t$- and $s$-channel single-top production and decay including non-resonant effects

Melissa van Beekveld, Robin van Bijleveld, Silvia Ferrario Ravasio et al. (+2 more)

We present a next-to-leading order + parton shower generator for $t$- and $s$-channel single-top production in hadron colliders, for a leptonically-decaying top, including off-shell and non-resonant effects. The generator, publicly available in the POWHEG BOX RES framework, describes the hadro-production of a $b$-jet and a leptonically decaying $W$-boson, accompanied by an additional jet, i.e. $pp\to \ell^{+} \nu_{\ell}\, j_b\, j $ and $pp\to \ell^{-} \bar{\nu}_{\ell}\, j_{\bar{b}}\, j $, where $j_b$ ($j_{\bar{b}}$) is a jet containing a bottom (anti)quark, and $j$ is a generic jet. We also provide an interface to the Pythia parton shower, suited to matching in the presence of decaying resonances such as the top quark. Our matching is designed to combine the advantages of a five-flavour calculation with the description of bottom quark mass effects in final-state jets. We perform a phenomenological study using fiducial cuts and discuss shower effects.
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All authors Melissa van Beekveld, Robin van Bijleveld, Silvia Ferrario Ravasio, Tomas Jezo, Tommaso Saracco

High Energy Physics (Experiment) · Cross-listed from hep-ph

An optimal observable for polarization measurements

Erik Bachmann and Mareen Hoppe

Vector-boson polarization provides a sensitive probe of new physics in the electroweak sector. Rare processes and suppressed longitudinal contributions make optimal polarization separation essential to exploit the available data. We show that parton-level differential polarization fractions define optimal observables and a fundamental sensitivity limit for polarized cross-section measurements. Their conditional expectations retain all experimentally accessible polarization information, yielding the best achievable sensitivity within the assumed model, and can be learned by neural networks for unbinned or binned inference. Measuring their distributions combines polarization sensitivity with the model independence of fiducial cross sections, probing deviations beyond constant rescalings of polarized contributions. We demonstrate the approach in inclusive ZZ production.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

Third-Order Logarithmic Resummation for Jet-Vetoed Higgs Production

Samuel Abreu, Jonathan R. Gaunt, Pier Francesco Monni et al. (+2 more)

Jet vetoes are central to precision measurements of Higgs-boson properties at the Large Hadron Collider, where they are used to suppress backgrounds containing hard QCD radiation. We present the first prediction for the Higgs jet-vetoed cross section at the third logarithmic order in QCD, consistently combining the next-to-next-to-next-to-leading order calculation with state-of-the-art next-to-next-to-next-to-leading logarithmic resummation. At phenomenologically relevant veto scales ($p_T^{\rm v}\sim30$ GeV) and jet radii ($R=0.4$), the resummation increases the fixed-order prediction by about $3\%$, and their combination leads to a residual perturbative uncertainty of approximately $3\%$. Our results mark a milestone in the precise description of jet-vetoed Higgs-production at hadron colliders, reaching the level of precision relevant for the high-luminosity phase of the LHC.
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All authors Samuel Abreu, Jonathan R. Gaunt, Pier Francesco Monni, Luca Rottoli, Robert Szafron

High Energy Physics (Experiment)

Search for pair-produced vector-like top quarks decaying into Lorentz-boosted top quarks and scalar bosons in proton-proton collisions at $\sqrt{s}$ = 13 TeV

CMS Collaboration

A search for pair-produced vector-like top quarks, T, decaying into a new scalar boson $\phi$ and a standard model (SM) top quark is presented. The search targets events containing a photon pair originating from the decay of one of the scalar bosons, accompanied by all-hadronic decays of the SM top quark pair. The analysis is optimized for boosted top quark signatures in which the decay products of the top quarks are reconstructed as large-radius jets. The search is based on proton-proton collision data at $\sqrt{s}$ = 13 TeV, collected by the CMS experiment at the CERN LHC during 2016$-$2018, corresponding to an integrated luminosity of 138 fb$^{-1}$. The search is performed for an array of T and $\phi$ masses. No significant deviation from the predicted background is observed. The largest local excess has a significance of 2.7 standard deviations, reduced to 1.5 standard deviations after accounting for the look-elsewhere effect. Upper limits at 95% confidence level are set on the product of $\mathrm{T\bar{T}}$ production cross section and the branching fraction.
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High Energy Physics (Experiment)

Track fitting as a language translation problem

Deepak Samuel and Christy Elsa Koshy

Particle physics analysis depends on information retrieved from particle tracks in a detector. Traditionally, this involves collecting individual detector hits, recombining them to form tracks, and fitting them to a model function. Large Language Models (LLMs) have demonstrated remarkable proficiency in comprehending the grammar and semantics of languages. Our exploratory study leverages transformers to conceptualise particle tracking as a language translation problem, wherein the language of detectors is translated into the language of physics. A simple decoder-only architecture with a custom tokenizer was designed for this task, and the behaviour of the model in this atypical setting provided interesting insights. We evaluated the advantages of this formulation in terms of track-parameter accuracy, and the ease of representing multi-track events, and finally tested the model on real cosmic-muon data. On synthetic datasets, the model outperformed a simple regression technique by an order of magnitude in track-parameter accuracy while being on par with the random sample consensus (RANSAC) method. The model also identified multi-track events with an accuracy of 98%. The analysis of real cosmic-muon events showed an excellent agreement of the zenith angle distribution with expectations. Our results suggest that a compact language model shows competitive performance and a natural ability to represent multi-track events. Further studies with complex geometries are required to understand the full potential of this technique.
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High Energy Physics (Experiment)

First observation of electron antineutrinos from nuclear reactors at Super-Kamiokande

K. Abe, Y. Asaoka, M. Harada et al. (+246 more)

In 2020, Super-Kamiokande entered the SK-Gd phase, improving its sensitivity to low-energy electron antineutrinos through the detection of neutrons captured on gadolinium dissolved in the detector water. An analysis of reactor electron antineutrino data has been carried out using data from SK-Gd, with a total exposure of 411.52 live days. The observed prompt energy spectra and monthly event rates are consistent with the oscillated reactor antineutrino prediction after accounting for accidental, geoneutrino, and spallation backgrounds. The no-reactor hypothesis is disfavored with a reactor-antineutrino signal significance of approximately $6\sigma$. The oscillation parameters are measured to be $\sin^2\theta_{12} = 0.500\pm0.155$ and $\Delta m^2_{21} = (9.08_{-0.54}^{+0.55}) \times 10^{-5} \mathrm{eV}^2$. A comparison with Super-Kamiokande solar neutrino measurements shows a statistical compatibility between the two datasets at the $1.9\sigma$ level. A combined solar and reactor fit in Super-Kamiokande yields best-fit values of $\sin^2\theta_{12} = 0.332_{-0.026}^{+0.028}$ and $\Delta m^2_{21} = (8.94_{-0.47}^{+0.46}) \times 10^{-5} \mathrm{eV}^2$.
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All authors K. Abe, Y. Asaoka, M. Harada, Y. Hayato, K. Hiraide, T. H. Hung, K. Ieki, M. Ikeda, J. Kameda, Y. Kataoka, S. Mine, M. Miura, S. Moriyama, K. Nakagiri, M. Nakahata, S. Nakayama, Y. Noguchi, G. Pronost, K. Sato, H. Sekiya, R. Shinoda, M. Shiozawa, Y. Suzuki, A. Takeda, Y. Takemoto, H. Tanaka, S. Chen, Y. Itow, T. Kajita, R. Nishijima, K. Okumura, T. Tashiro, T. Tomiya, X. Wang, F. J. de Garay Arcones, P. Fernandez, L. Labarga, D. Samudio, C. Yanagisawa, B. Jargowsky, E. Kearns, J. Mirabito, L. Wan, T. Wester, B. W. Pointon, J. Bian, B. Cortez, N. J. Griskevich, Y. Jiang, M. B. Smy, H. W. Sobel, V. Takhistov, J. Hill, B. D. Xu, D. Jung, D. H. Moon, R. G. Park, B. S. Yang, K. Scholberg, C. W. Walter, O. Drapier, A. Ershova, M. Ferey, Z. Hu, E. Le Blévec, L. Leplumey, Th. A. Mueller, P. Paganini, C. Quach, R. Rogly, T. Nakamura, J. S. Jang, R. P. Litchfield, L. N. Machado, F. J. P. Soler, J. G. Learned, K. Choi, S. Cao, T. V. Ngoc, L. H. V. Anthony, N. W. Prouse, M. Scott, Y. Uchida, V. Berardi, N. F. Calabria, M. G. Catanesi, N. Ospina, E. Radicioni, A. Langella, G. De Rosa, G. T. Burton, G. Collazuol, M. Feltre, M. Mattiazzi, L. Ludovici, M. Gonin, L. Périssé, B. Quilain, M. Fukazawa, S. Horiuchi, A. Kawabata, Y. M. Liu, Y. Maekawa, Y. Nishimura, A. Oka, H. Tanigawa, Z. Utagawa, R. Akutsu, M. Friend, T. Hasegawa, Y. Hino, T. Ishida, T. Kobayashi, T. Matsubara, T. Nakadaira, Y. Oyama, A. Portocarrero Yrey, K. Sakashita, T. Sekiguchi, N. Bhuiyan, F. Di Lodovico, T. Katori, R. Kralik, N. Latham, R. M. Ramsden, V. Siccardi, S. Aoyama, H. Bambara, Y. Inaba, H. Ito, M. Nishigami, T. Sone, A. T. Suzuki, Y. Takeuchi, S. Wada, H. Zhong, J. Feng, L. Feng, N. Fujimoto, S. Han, J. Hikida, M. Kawaue, T. Kikawa, F. Nakanishi, T. Nakaya, R. A. Wendell, S. J. Jenkins, U. Limbu, N. McCauley, M. Fan, M. J. Wilking, Z. Xie, Y. Fukuda, H. Menjo, Y. Yoshioka, J. Lagoda, J. Zalipska, T. Yano, M. Mori, J. Jiang, Y. Asano, K. Hamaguchi, H. Ishino, Y. Koshio, S. Ohshita, T. Tada, T. Ishizuka, G. Barr, D. Barrow, D. Wark, A. Holin, F. Nova, M. Jo, S. Jung, J. Yoo, L. Kneale, T. Peacock, P. Stowell, H. Okazawa, S. M. Lakshmi, S. Hong, E. Kwon, M. W. Lee, J. W. Seo, I. Yu, Y. Ashida, A. K. Ichikawa, S. Kobayashi, K. D. Nakamura, S. Abe, W. Cai, Y. Endo, S. Goto, S. Kodama, Y. Kong, H. Hayasaki, Y. Masaki, Y. Mizuno, T. Muro, K. Nakagiri, Y. Nakajima, M. Sekiyama, N. Taniuchi, T. Yamazumi, M. Yokoyama, P. de Perio, S. Fujita, C. Jesús-Valls, K. Martens, Ll. Marti, A. D. Santos, K. M. Tsui, M. R. Vagins, S. Izumiyama, M. Kuze, R. Matsumoto, C. Ise, M. Ishitsuka, M. Sugo, M. Wako, K. Yamauchi, Y. Nakano, A. Yankelevich, F. Cormier, R. Gaur, M. Hartz, A. Konaka, X. Li, B. R. Smithers, S. Chen, Y. Wu, A. Q. Zhang, B. Zhang, H. Adhikary, M. Girgus, P. Govindaraj, M. Posiadala-Zezula, Y. S. Prabhu, S. B. Boyd, R. Edwards, D. Hadley, M. O'Flaherty, B. Richards, A. Ali, B. Jamieson, C. Bronner, D. Horiguchi, A. Minamino, Y. Sasaki

High Energy Physics (Experiment)

Entanglement-sensitive observables in $e^+e^- \to \tau^+\tau^-$ at STCF: a detector-level feasibility study

Chentao Bao, Xi Tao, Hai Chen et al. (+3 more)

Quantum entanglement in $\tau^+\tau^-$ production provides a direct probe of non-classical spin correlations in a relativistic quantum system, with the $\tau$ decay products serving as spin analyzers. We investigate the detector-level feasibility of such measurements in $e^+e^-\to\tau^+\tau^-$ at the Super Tau-Charm Facility (STCF) at $\sqrt{s}=7$ GeV, using the $\rho\rho$ and $\pi\rho$ decay channels. Signal and dominant background processes are simulated with the full STCF detector and reconstruction framework. Dedicated reconstruction and event-selection procedures yield overall signal efficiencies of approximately $4.5\%$ and $4.8\%$, with corresponding purities of about $87.6\%$ and $93.2\%$ for the $\rho\rho$ and $\pi\rho$ channels, respectively. From the reconstructed decay kinematics, the $\tau^+\tau^-$ spin-density matrix is inferred and the concurrence $C[\rho]$ together with the Bell-sensitive quantity $m_{12}[C]$ are evaluated in a selected fiducial region. For the benchmark requirement $|\cos\theta|<0.2$ and an integrated luminosity of $1~\mathrm{ab}^{-1}$, the projected relative precision on $C[\rho]$ is about $2.2\%$ in both channels, while that on $m_{12}[C]$ is approximately $1.4\%$ for $\rho\rho$ and $1.5\%$ for $\pi\rho$, including statistical and detector-resolution uncertainties. The reconstructed $m_{12}[C]$ shows a larger separation from its reference threshold in the $\rho\rho$ channel, making this topology particularly sensitive to Bell-type spin correlations. These results demonstrate the detector-level feasibility of probing quantum entanglement and non-classical spin correlations in hadronic $\tau$ decays at STCF.
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All authors Chentao Bao, Xi Tao, Hai Chen, Lailin Xu, Xiaorong Zhou, Mingyi Liu

High Energy Physics (Experiment)

First measurement of the low-momentum negative-muon beam for the muon-to-electron conversion experiment at J-PARC

The COMET Collaboration: K. Oishi, R. Abramishvili, G. Adamov et al. (+182 more)

The COMET Phase-$\alpha$ experiment, the initial beam-operation stage of the COMET muon-to-electron conversion programme at J-PARC, took place in 2023 and marked the first beam operation at the COMET facility. It served to commission the delivery of a bunched, slow-extracted 8 GeV proton beam and the muon beamline. Its objective was to demonstrate experimentally that low-momentum negative muons could be transported to the experimental area through the Transport Solenoid (TS). We report a measurement of the transported muon beam using the Range Counter, a dedicated detector that identifies stopped negative muons by detecting delayed electrons emitted after the muons stop in a copper absorber. From the measured decay-time spectra, we reconstruct the number of stopped muons, the corresponding momentum spectrum, and the transverse beam profile. The observation of the stopped-muon component demonstrates that slow negative muons were transported through the TS to the experimental area. The reconstructed momentum spectrum indicates that the transported beam is concentrated in the low-momentum region. The non-uniform transverse profile is qualitatively consistent with charge drift in the curved solenoidal magnetic field. A Geant4-based simulation reproduces the overall dependence on degrader thickness and detector position; the measured yields are systematically higher by roughly 30%. These results provide the first experimental benchmark of low-momentum negative-muon transport in COMET and establish the basis for future beam characterisation and production studies.
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All authors The COMET Collaboration: K. Oishi, R. Abramishvili, G. Adamov, J. C. Angelique, K. Aoki, M. Aoki, Y. Arimoto, A. N. B. Az, I. Bagaturia, D. Bauer, T. Bouillaud, L. Del Buono, C. Cârloganu, N. Chadeau, Y. Chen, P. Chetry, D. Chokheli, T. Clouvel, P. D. Dauncey, S. Dekkers, R. Derveni, G. Devidze, P. J. Dornan, M. T. Dubouchet, L. B. Epshteyn, I. Evtoukhovitch, P. Evtoukhovitch, G. Faure, S. Fayer, G. V. Fedotovich, Y. Fujii, Y. Fukao, E. George, E. L. Gillies, M. Gouzevitch, D. N. Grigoriev, E. Hamada, I. H. Hashim, S. Hashimoto, M. Higashide, Y. Higuchi, N. Hiroshima, Y. Igarashi, F. V. Ignatov, M. Iio, M. Ikeno, K. Ishibashi, T. Itahashi, A. Jansen, R. Jeena, O. Jeremy, X. Jiang, P. M. Jonsson, Y. Kageyama, V. Kalinnikov, E. Kaneva, F. Kapusta, K. Kawagoe, R. Kawashima, N. Kazak, A. Khvedelidze, Y. Kojima, A. N. Kozyrev, B. Krikler, Y. Kuno, S. Kuribayashi, Y. Kurochkin, N. Kurosawa, A. Kurup, K. Ladhams, P. Lebrun, M. J. Lee, H. Li, W. Li, R. P. Litchfield, D. Lomidze, I. Lomidze, G. Macharashvili, Y. Makida, S. Makimura, G. Matsumoto, S. Matsumoto, A. Melnik, H. Miao, S. Mihara, A. Miles, M. Miyataki, Y. Miyazaki, T. Mizuno, M. Moritsu, R. Muto, R. Nagai, H. Nagashima, Y. Nakai, T. Nakamoto, Y. Nakamura, Y. Nakatsugawa, Y. Nakazawa, J. Nash, M. A. S. Nasrullah, T. M. Nguyen, V. Niess, Y. S. Ning, H. Nishiguchi, M. Nishihara, K. Noguchi, N. H. M. Nor, N. Norjoharuddeen, T. Ogitsu, H. Ohata, N. Ohuchi, K. Okabe, T. Okamura, H. Okurano, M. Oonaka, J. Pasternak, A. Paulau, D. Pieters, V. Raspal, R. Razali, A. Razquin, W. Roth, B. Sabirov, T. Saito, H. Sakamoto, P. Sarin, K. I. Sasaki, R. Sasaki, A. Sato, J. Sato, H. Sendai, N. Shigyo, M. Shinjo, Z. Shioya, M. Shoji, Dz. Shoukavy, W. Da Silva, A. Simonenko, D. Stöckinger, N. Sumi, A. Sumimura, S. Sun, J. Suzuki, S. Takami, S. Tanaka, J. Tang, J. Tojo, M. Tomizawa, T. Toriashvili, N. Tran, Z. Tsamalaidze, N. Tsverava, T. Uchida, Y. Uchida, Y. Uchiyama, S. Ueda, K. Ueno, Y. Uesaka, D. Vasileuskaya, E. Velicheva, M. L. Wong, T. S. Wong, C. Wu, T. Xing, Y. Xu, C. Yamada, H. Yamaguchi, M. Yamanaka, Y. Yang, W. Yao, B. Yeo, H. Yoshida, M. Yoshida, M. Yoshii, D. Yoshikawa, T. Yoshioka, Y. Yuan, Yu. V. Yudin, N. Yussup, I. Yusuff, J. Zhang, Y. Zhang, Z. Zhang, Y. Zhou, K. Zuber

High Energy Physics (Experiment) · Cross-listed from cs.LG

Conditional Capacity and Routing in Mixture-of-Experts Particle Transformers

Kaushik Pendiyala, Haris Zia, Trevin Lee et al. (+8 more)

Mixture-of-Experts (MoE) models can increase parameter capacity without proportionally increasing active computation, but it is unclear how this trade-off behaves in particle-physics transformers. We study dense and MoE Particle Transformers on 188-class JetClass-II, varying expert count, routing capacity, top-K, and auxiliary loss. We find that, when token dropping is avoided, top-1 MoE models improve over the dense baseline at nearly unchanged nominal forward compute, while further increasing the number of stored experts produces little additional accuracy gain. Activating multiple experts per token yields additional predictive improvements at higher computational cost. Routing analyses show that expert assignments become more strongly associated with particle identity and kinematics in some configurations, but this structure does not increase monotonically with classification performance. These results highlight the need to distinguish stored parameter capacity, active computation, routing capacity, and routing organization when evaluating sparse expert models for jet classification. Code and experiment configurations are available at https://github.com/kpendiyala/MPT.
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All authors Kaushik Pendiyala, Haris Zia, Trevin Lee, Timothy Legge, Alejandro J. De Leon, Zihan Zhao, Aaron Wang, Abhijith Gandrakota, Jennifer Ngadiuba, Richard Cavanaugh, Javier Duarte

Thursday 1 October

High Energy Physics (Experiment) · Cross-listed from hep-ph

Precise QCD Predictions for Photon-Associated Hadron Production at the LHC

Gabriele Fiore, Aude Gehrmann-De Ridder, Alexander Huss et al. (+2 more)

Prompt-photon production with recoiling QCD radiation is crucial for new-physics searches, determinations of parton distribution and fragmentation functions, and jet-quenching studies in heavy-ion collisions. We present the first fully differential NNLO QCD predictions for photon-associated identified-hadron production at the LHC. We compare predictions obtained with different fragmentation function (FF) sets to ALICE and ATLAS data at $\sqrt{s}=5.02\,{\rm TeV}$. Our calculation provides an important theoretical ingredient for FF global fits and offers a precision proton–proton baseline for photon-tagged heavy-ion studies.
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All authors Gabriele Fiore, Aude Gehrmann-De Ridder, Alexander Huss, Francesco Merlotti, Giovanni Stagnitto

High Energy Physics (Experiment) · Cross-listed from hep-ph

How Quantum Is Bottomonium in the Quark-Gluon Plasma?

Nora Brambilla and Tom Magorsch

We study how much quantum structure bottomonium retains during its evolution in the quark-gluon plasma. Within the open quantum system framework, we simulate the Lindblad equation obtained from potential nonrelativistic QCD in the quantum Brownian regime. From the resulting real-time evolution of the bottomonium density matrix, we compute the Wigner transform and study its negativity as a measure of nonclassicality and a test of a key condition underlying classical Langevin-type approximations. We find that the medium suppresses the negativity, which nevertheless approaches a finite plateau close to that of the $1\mathrm{S}$ state. The overlaps with the excited $2\mathrm{S}$ and $3\mathrm{S}$ states arise from near-canceling positive and negative phase-space contributions, driven by negative regions in the Wigner transforms of the bound-state projectors, while the $1\mathrm{S}$ overlap is insensitive to such contributions. We further show that the position-space coherence is similarly suppressed and plateaus close to the 1S value. We trace the finite residual quantum structure to conditional purification: the medium preferentially dissolves weakly bound and unbound modes with large $\langle r^2\rangle$, driving the surviving singlet $\mathrm{S}$-wave ensemble toward the $1\mathrm{S}$ state. More broadly, these results reveal that classicalization is partial and observable dependent, a feature that is relevant across applications of open quantum system methods in fundamental physics.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

Drell-Yan lepton pair production from low to high transverse momentum

Benoît Assi, Enrico Bothmann, John Campbell et al. (+7 more)

We present a technique for computing Drell-Yan lepton pair production at particle-level that achieves N$^3$LO and approximate N$^4$LL$'$ accuracy at small to moderate transverse momentum, tree-level precision for $Z+4$, $5$, and $6$ jets, and approximate NLO EW precision at high transverse momentum. A crucial non-perturbative input, the Collins-Soper kernel, is obtained from continuum-limit lattice QCD results. High-precision theory results are recast into strictly positive event weights using an information-theoretic approach based on the maximum entropy principle.
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All authors Benoît Assi, Enrico Bothmann, John Campbell, Christian Gütschow, Stefan Höche, Wan-Li Ju, Max Knobbe, Marek Schönherr, Jesse Thaler, Michael L. Wagman

High Energy Physics (Experiment) · Cross-listed from hep-ph

The Scalar MSW Effect: Compact analytical formulas for neutrino oscillations with large matter effects, including $\mu -\mu$ and $\tau -\tau$ dominant matter potentials

Sandhya Choubey and Andreas Lund

Deriving simple and accurate three-flavor neutrino oscillation probability formulas in matter is critical for understanding the phenomenology of upcoming experiments. In this article, we extend the Jacobi diagonalization method for deriving effective parameter mappings for neutrino oscillations in matter. The key insight behind the extension is to purposefully parameterize the mixing matrix, $U_{\text{PMNS}}$, using particular arrangements of Euler rotations. This novel extension allows for deriving simple and accurate effective mixing parameter mappings for exotic types of matter potentials. First, we revisit the Jacobi diagonalization method for neutrino oscillations with standard matter effects and use this to demonstrate our generalization. Subsequently, we apply the Jacobi diagonalization method to scalar non-standard interactions (SNSI) and derive effective parameter mappings for all three single diagonal coupling cases. The resulting formulas reveal that all diagonal SNSI couplings could give rise to a scalar MSW (SMSW) effect, that is an energy independent resonant enhancement analogous to the MSW effect. Finally, we study the accuracy of the derived SNSI formulas for various contemporary and upcoming experiments. For $\delta m_{ee}$, the accuracy is excellent for all considered experiments. For $\delta m_{\mu\mu}$ and $\delta m_{\tau \tau}$ the accuracy is worse since $A_{CC}$ must be neglected, and first order perturbative corrections are applied to amend this.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

A consistent $\mathcal{O}(v^2)$ NRQCD description of decays and high-$P_T$ prompt production of charmonia

Valerio Bertone, Jean-Philippe Lansberg, Kate Lynch et al. (+1 more)

We present a global determination of the six long-distance matrix elements (LDMEs) within non-relativistic QCD (NRQCD) appearing in the production of prompt $J/\psi$ up to $\mathcal{O}(v^2)$ using high-$P_T$ LHC data for direct and feed-down contributions from $\chi_c$ and $\psi(2S)$. Using a leading-power fragmentation framework at NLO+NLL, we fit $\psi(2S)/J/\psi$ yield ratios from ATLAS and CMS and $\psi(2S)$ CMS polarization data at $\sqrt{s} = 13$ TeV, injecting one decay width per charmonium. The fit LDMEs provide excellent predictions of the CMS and ATLAS cross-section data up to $P_T=360$ GeV for the $J/\psi$, as well as the $J/\psi$ polarization data from CMS. The obtained excellent agreement with production and decay data demonstrates that $\mathcal{O}(v^2)$ NRQCD is sufficient to describe $J/\psi$, $\psi(2S)$, and $\chi_c$ hadroproduction at large $P_T$.
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All authors Valerio Bertone, Jean-Philippe Lansberg, Kate Lynch, Tanjona R. Rabemananjara

High Energy Physics (Experiment) · Cross-listed from hep-ph

Confronting $K^-d$ dynamics with kaonic atom measurements within a novel unitary framework

Albert Feijoo, Àngels Ramos and Juan Torres-Rincon

We study the low-energy interaction of negative kaons with deuterons using chiral $\bar{K}N$ interaction models (OR and BCN) as input. The three-body $K^-d$ amplitude is constructed within the Fixed-Center Approximation to the Faddeev equations, where the unitary constraints missing in the conventional approach are formally implemented with the incorporation of coherent multiple-scattering processes. The unitary procedure is extended to coupled channels including charge-exchange processes, as well as isospin-breaking effects through the use of physical particle masses. This provides a consistent description of the low-energy $K^-d$ amplitude and allows for the determination of the scattering length and the effective range. The resulting framework is then used to assess the compatibility of the BCN $\bar{K}N$ interaction model with the recent SIDDHARTA-2 measurements of kaonic hydrogen and kaonic deuterium through a bootstrap analysis. The procedure leads to a readjustment of the BCN parameterization which produces visible effects in several isospin-sensitive $\bar{K}N$ scattering observables, hence highlighting the additional information provided by the new kaonic-atom measurements to better constrain the poorly known isovector component of the ${\bar K}N$ interaction.
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High Energy Physics (Experiment) · Cross-listed from hep-ph

An optimal strategy for experimental searches in high-mass dilepton production at the LHC

J. Alcaraz Maestre and O. M. Carretero

We present an optimal method for studying new physics effects in high-mass dilepton production at the LHC. This method relies on a reweighting procedure that is precise to the next-to-leading order in quantum chromodynamics. The only computationally expensive input required is a standard model $\mathrm{pp\rightarrow V^{(*)}\rightarrow\ell^+\ell^-}$ sample, with $\mathrm{V=Z,\gamma^*}$, generated at the same level of precision and with sufficient statistical coverage of the phase space at high invariant masses. The proposed method is suitable for any $\mathrm{q\overline{q}\ell^+\ell^-}$ contact-interaction scenario, regardless of the assumed underlying structure and couplings. It is also ideal for searching for medium-to-large-width new neutral resonances produced in the s-channel, as changes to the input values for mass, coupling, or width can be easily implemented using the same initial generated samples.
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High Energy Physics (Experiment)

A-GHOST: High-rate streaming of trigger-level data to programmable GPU inference

I. Xiotidis, N. Clarke Hall, M. S. Larson et al. (+11 more)

A-GHOST (A Global Heterogeneous Online Scouting Trigger) is an R&D effort investigating high-rate streaming readout architectures for high-energy physics (HEP) experiments. The central idea is to convert the deterministic front-end and fixed-latency processing close to the detector from a decision-making platform to an aggregation and streaming source. Compact trigger-level data are streamed to a GPU-enabled backend, where substantially more complex algorithms can run beyond the resource and latency envelope of the hardware trigger. This paper presents a proof-of-concept backend using the NVIDIA IGX Thor development kit. A software rate-controlled transmitter sends data through a QSFP interface and external loopback cable to a second QSFP interface, allowing the network-to-GPU path to be studied before integration with FPGA sources. NVIDIA DAQIRI enables reception directly into GPU-accessible memory, while a custom CUDA kernel reassembles packet payloads into persistent, contiguous TensorRT input windows without data-type conversion, which is handled by the models. Using a HEP-derived event representation consisting of the ten leading calorimeter clusters, the backend scales from 40 to 100 Gbps while sustaining a constant input rate and an inference latency of 0.118 ms at the p95 interval. The system operates for multiple hours without drops or inference errors. Generative and temporally aware neural networks demonstrate workloads beyond those normally deployed in fixed-latency FPGA trigger systems. The result establishes A-GHOST as a basis for future FPGA-to-GPU streaming readout systems.
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All authors I. Xiotidis, N. Clarke Hall, M. S. Larson, R. Gurunathan, C. Burdick, T. Du, N. Konstantinidis, K. Kordas, D. Leshchev, D. W. Miller, V. A. Petrovic, D. Sampsonidou, A. Thompson, T. Wengler

High Energy Physics (Experiment) · Cross-listed from hep-ph

Mechanisms of $D \bar{D}$ pair production in $e^{+} e^{-} \to e^{+} e^{-} D \bar{D}$ and $AA \to AA D \bar{D}$ reactions and production of exotic charmonia

Antoni Szczurek, Izabela Babiarz, Piotr Lebiedowicz et al. (+1 more)

We discuss mechanisms of $D \bar{D}$ pair production in $e^+ e^-$ collisions. We consider the $D^0 {\bar D}^0$-continuum mechanism with the $t/u$-channel $D^*$ vector-meson exchanges, where the $D^* D \gamma$ coupling constants are derived from the $D^* \to D \gamma$ decays. For the $D^+ D^-$ channel, we consider mainly the $D^{\pm}$ exchanges. We find a relatively large continuum contribution for the $D^0 {\bar D}^0$ channel and a significantly smaller one for $D^+ D^-$, concluding that the broad bump at $M_{D^0 {\bar D}^0} = 3.8$ GeV observed by the Belle and BaBar Collaborations has a continuum origin rather than corresponding to the broad $\chi_{c0}(3860)$ resonance. We also investigate the resonant production of $D \bar{D}$ pairs, including $\chi_{c0}(3860)$ and $\chi_{c2}(3930)$. The $\chi_{c2}(3930)$ meson is a good candidate for the first excited $P$-wave charmonium $\chi_{c2}(2P)$ state. This resonance can decay into both $D \bar{D}$ channels; however, its branching fractions are not well known at present. Comparing our model result with $\Gamma(\chi_{c2}(2P) \to \gamma \gamma) = 0.544$ keV (corresponding to the Buchmüller-Tye potential) to the BaBar data, we find $B(\chi_{c2}(3930) \to D \bar{D}) = 0.58 \pm 0.13$. We present results for differential distributions in several variables for Belle II kinematics. Finally, we shortly mention predictions for the ultraperipheral heavy-ion reaction $Pb Pb \to Pb Pb D \bar{D}$ for low invariant mass ($M_{D \bar{D}} < 4.3$ GeV) at the LHC.
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All authors Antoni Szczurek, Izabela Babiarz, Piotr Lebiedowicz, Wolfgang Schäfer

High Energy Physics (Experiment) · Cross-listed from hep-ph

Probing an up-phobic Higgs at colliders: the role of $b$-associated production in the democratic 3HDM

Dipankar Das, Teesha Khandelwal and Ipsita Saha

We show that there exists a theoretically well-motivated Higgs sector in which the conventional heavy-Higgs production mechanisms are suppressed. In this limit, the $b$-associated production channel assumes the role of the primary production mechanism. We demonstrate that the democratic three Higgs-doublet model (3HDM) provides a viable beyond the SM (BSM) framework in which this limit can be realized. We further show that existing $b$-associated searches provide the most sensitive LHC probe of this 3HDM scenario in the up-phobic limit and derive the corresponding constraints on its parameter space. We also present projections for future collider searches, demonstrating their potential to probe further regions of the model's up-phobic parameter space.
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High Energy Physics (Experiment)

Search for charged-lepton-flavour violating $e\mu tq$ interactions at $\sqrt{s}=13$ TeV with the ATLAS detector

ATLAS Collaboration

A search for charged-lepton-flavour violation (cLFV) in top-quark production and decay is presented. The data analysed correspond to 140 fb$^{-1}$ of proton-proton collisions recorded at a centre-of-mass energy of $\sqrt{s}= 13$ TeV by the ATLAS detector at the Large Hadron Collider. The possible cLFV contribution is studied via two mechanisms. The first is via the production of a leptonically-decaying single-top quark in association with a pair of oppositely-charged different-flavour leptons. The second is the production of top-quark pairs, where one top quark decays into a pair of oppositely-charged different-flavour leptons and a $u$- or $c$-quark, while the other decays into a leptonically-decaying $W$ boson and a $b$-quark, according to the Standard Model. The signal processes contain three charged leptons, taken to be electrons or muons. No significant deviation from the Standard Model prediction is observed, and these results are interpreted within an Effective Field Theory framework. Upper limits are placed at 95% confidence level on six Wilson coefficients, ranging from $|C^{\mathrm{tensor}}_{e\mu tu}|/\Lambda^2 < 0.018$ TeV$^{-2}$ to $|C^{\mathrm{scalar}}_{e\mu tc}|/\Lambda^2 < 0.32$ TeV$^{-2}$ for the tensor $u$-quark and scalar $c$-quark couplings, respectively. These Wilson coefficient limits are translated into 95% confidence level upper limits on cLFV top-quark decay branching ratios, ranging from $B(t \to e\mu u) < 6 \cdot 10^{-9}$ to $B(t \to e\mu c) < 2.7 \cdot 10^{-7}$ for the scalar $u$-quark and tensor $c$-quark couplings, respectively.
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High Energy Physics (Experiment)

Full Event Interpretation at Belle II: Current Status and Recent Developments

R. Tiwary, M. Marfoli, V. Vobbilisetti et al. (+1 more)

The Full Event Interpretation (FEI) algorithm is a central component of the Belle II analysis framework, designed for the efficient reconstruction of exclusive B-meson decays. The FEI performs a hierarchical reconstruction of hadronic and semileptonic final states, using multivariate classification techniques to tag one of the two B mesons produced in electron-positron collisions. The FEI is particularly important for studies of signal-side decays involving missing energy. By reconstructing one B meson with the FEI, the kinematics of the other, signal-side B meson are tightly constrained, leading to improved background rejection. In this contribution, we present the design, implementation, and recent developments of the FEI. We outline the reconstruction strategy, candidate selection, and multistage multivariate training based on gradient boosted decision trees. Recent improvements to the FEI workflow, including improvements in the simulated data used for training, reconstruction of intermediate particles, and improved robustness of the multivariate inputs, are discussed in detail. Beyond algorithmic updates, we also discuss newly developed techniques for the calibration and performance evaluation of the FEI. These include refined procedures to calibrate the efficiency, check the performance across decay channels and data-taking conditions, and application of reweighting techniques to diagnose and mitigate discrepancies between simulation and data. Finally, we briefly discuss ongoing and future developments aimed at further improving reconstruction performance and computational efficiency.
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All authors R. Tiwary, M. Marfoli, V. Vobbilisetti, K. Trabelsi

High Energy Physics (Experiment)

Search for dark matter produced in association with a low-multiplicity jet in proton-proton collisions at $\sqrt{s}$ = 13 TeV

CMS Collaboration

A search for dark matter particles is presented using events with large missing transverse momentum and a single energetic jet containing few constituents. The analysis uses proton-proton collision data recorded by the CMS experiment at a center-of-mass energy of 13 TeV. This corresponds to an integrated luminosity of 138 fb$^{-1}$, recorded during the 2016$-$2018 LHC data-taking period. This is the first search at the LHC to employ the low-multiplicity jet signature. Supervised machine learning is used to maximize sensitivity to potential signals in this challenging final state. No excess of events over the standard model background prediction is observed. The results are used to set upper limits on the dark matter production cross section at 95% confidence level (CL) within simplified models featuring vector and axial-vector mediators. For a dark matter particle mass of approximately 150 (550) GeV, mediator masses up to 4250 (3500) GeV are excluded at 95% CL.
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Wednesday 30 September

High Energy Physics (Experiment) · Cross-listed from physics.data-an

Developing Multi-Dimensional, Sequential sWeighting Routines for Reaction Selection with Emphasis on Kaon Identification at CLAS12

A. Acar, M. Bashkanov, D.P. Watts et al. (+1 more)

In nuclear and particle physics experiments, event selection is often a multidimensional classification problem which involves several correlated observables. The widely used sWeight technique provides a statistically rigorous means of separating signal and background using discriminating variables, but its conventional formulation is generally applied to a single discriminating variable or a simultaneous multidimensional fit. In this paper we present a novel extension of the widely used sWeight technique, in which an arbitrary number of discriminating variables can be used to construct a multidimensional sequential framework. This method allows the extraction of signal distributions in controlled variables in a rigorous way. Particular attention is given to the treatment of signal and background correlations, as well as the propagation of statistical uncertainties through successive weighting stages. The method yields high-purity signal samples even in the presence of large and correlated backgrounds. As a benchmark application, the validity of this technique is demonstrated on kaon identification in a dataset collected with the CLAS12 detector at the Thomas Jefferson National Laboratory for cascade baryon searches. The final workflow is shown to be robust and consistent across different run periods and beam/detector conditions, demonstrating minimal systematical uncertainties associated with the method. Statistical uncertainties are proved to be evaluable using a bootstrap-based procedure. The method provides a general framework for multidimensional event weighting and is intended for application in complex analyses requiring robust signal selection in the presence of complex correlated backgrounds.
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All authors A. Acar, M. Bashkanov, D.P. Watts, M. Nicol